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Posted by: boxster914 Apr 12 2022, 11:18 AM

Hi everyone

My perfectly running 71 914 1.7 D-jet has deteriorated rapidly this past week.

Early in the week I noticed what felt like a power drop out during a drive. It was very slight and only happened once and I wasn't sure I didn't cause it by unconciously lifting off the gas.

The next drive it happened a few times and was more pronounced. It was then that I knew this wasn't an imagined problem.

On the third drive it was like a bucking bronco, surging and stopping and the engine cut out a few times. It was undriveable.

Today it will start but won't run. The engine cuts out when I try to rev it and the red light comes on.

I've done some searching here but haven't been able to draw any conclusions or come up with an actionable strategy to diagnose the problem. I'm seeing people trace it to spark plug wires, air fuel ratios and bad distributors.

Is there a step-by-step process that you can recommend for me to get to the cause of this? (I'm a newb so I probably will need help with abbreviations like AFR, TPS, etc.)

Here is a video of it's rough idle yesterday when it was still running.

https://youtu.be/n61CP6O8UgM

Posted by: krazykonrad Apr 12 2022, 11:49 AM

I had a very similar issue. After much poking about, I think I have it down to two problems, 1) a worn out distributor and 2) a slightly bent pushrod.

Posted by: BillJ Apr 12 2022, 12:18 PM

Start with fuel filter? Sounds like a progressively clogging fuel issue to me

Posted by: Lockwodo Apr 12 2022, 12:32 PM

I can relate! I'm working through a similar intermittent issue with my '74 2.0 D-Jet. The 914 Tech Notebook is your friend. You might find this reference useful, see section "Procedure for Renewing and Testing the Fuel Injection:

chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/viewer.html?pdfurl=https%3A%2F%2Fbowlsby.net%2F914%2FClassic%2FzTN_Man06.pdf&clen=44162&chunk=true

I've replaced the fuel filter and checked and set the fuel pressure and verified it's stable when the missing issue happens, replaced the ignition wiring, disty cap, plugs, rotor, replaced the board on the TPS, cleaned the PCV valve, verified that the Cold Start Valve isn't leaking. The idle has improved. Now replacing all the vacuum tubing and testing the various sensor components like the AAR, manifold pressure sensor, CHT sensor etc. I think it's most likely a fuel/air issue so the injectors will be next. I also plan to have the idle mix set by a shop with a good CO meter. After that, if the problem persists, I'll be suspicious of the disty. It's a process of elimination but on the other hand, the car is 48 years old and I've little documentation on what's been done before.

Looking forward to any ideas/pointers that others have!

Posted by: ClayPerrine Apr 12 2022, 01:00 PM

"and the red light comes on."

Which red light? If it is the generator light, it may be a bad alternator causing the voltage to drop too low for the FI to function correctly.

Clay

Posted by: Root_Werks Apr 12 2022, 01:05 PM

Start with some basic maint items. If the 914 sits for long periods of time, not unreasonable to think crud could develop in the fuel tank.

Posted by: Lockwodo Apr 12 2022, 01:30 PM

Hmm, I hadn't thought about voltage drop off affecting the FI system. The battery on my car is on a trickle charger and seems fully charged when cranking the starter. No red alternator light in my case. Question: does the FI system run off the battery, in other words, if the battery is fully charged but the alternator is sub par, could the FI system be affected?

Posted by: mepstein Apr 12 2022, 01:49 PM

Also check all the grounds. Easy to do and while you are doing it, you may notice something else.

Posted by: Lockwodo Apr 12 2022, 01:53 PM

Thanks Mepstein, you're right and that's related to the potential voltage issue. My understanding is the most important ground points for the FI system are the negative battery cable to chassis connection, the connectors that are on the top rear of the engine under the air cleaner, and the transmission to chassis ground. I've taken care of the first two and the tranny to chassis ground point is on the list.

Posted by: 930cabman Apr 12 2022, 01:58 PM

+1, I would start with the basic and low $$ stuff

Posted by: BillJ Apr 12 2022, 02:51 PM

Everything he described could be due to a clogged fuel filter. The red light is always on prior to start.

Posted by: boxster914 Apr 12 2022, 03:48 PM

You guys are awesome!

My weekend of detective work is shaping up thanks to your help.

The red light I was referring to was the generator light.

Can you help me with the abbreviations from @http://www.914world.com/bbs2/index.php?showuser=26193 : PCV valve, AAR and CHT sensor?

If it ends up being the distributor is the 123 ignition replacement a good option to avoid future issues?

https://123ignitionusa.com/porsche-with-d-jet-912-914-356-vw-411e-412e-1600e-type-3-4-123ignition-distributor-switched-w-bosch-d-jetronic-includes-spacer/

Posted by: mgphoto Apr 12 2022, 03:49 PM

Clean and check the FI points in the base of the distributor.

Posted by: Lockwodo Apr 12 2022, 05:06 PM

PCV valve is positive crankcase ventilation. If you have one, there's a hose that connects to it right next to the oil filler. If the valve sticks closed or sticks open, it'll affect how the engine runs. AAR is the auxiliary air regulator. It allows air to be pulled into the intake for the first few minutes of startup but should close completely (internal heater element). CHT is the cylinder head temperature sensor. It sends a signal to the electronic control unit and affects gas/air mixture.

I've been thinking about the 123 disty also. I've heard it's great and also that it's difficult to dial in, and finally that the mechanical disty is better suited to the car and we best get the ones we have rebuilt. Seems to me that cleaning the mechanical distributor and making sure advance mechanism moves smoothly and points and dwell are correctly set (if you don't have a Pertronix electronic ignition or similar) and trigger points are OK is the first step.

Posted by: Ansbacher Apr 12 2022, 05:49 PM

Check all the wire connections to the coil. Make sure they are clean and TIGHT!

Ansbacher

Posted by: wonkipop Apr 12 2022, 06:41 PM

thanks for putting up that video.

its hunting as its trying to idle.
i'd go looking carefully over fuel first.
check the filter.
check the fuel pressure if you have a guage and can do it easily.

i've got a similar thing mine does when it gets warmer here.
and its sounds just like that.
i think in part is due to having a rhd car. took me a long time to work out what it was.
without going into detail too much what happens is my fuel overheats due to the very small volume of fuel in the circuit (the bulb at bottom of tank is way smaller in a rhd car).
combined with a new fuel pump in original position it can cause bubbling in the lines etc and fuel starvation. fill the tank up to halfway and its gone just like that. only in hot weather. but its exactly that kind of hunting.
so i would go there first. not saying your problem is that, but not getting adequate fuel through will do something very similar.

an air leak in a L jet will also give you that but tends to go up and down in revs a bit more than that. not really in the know about d jets and air leaks etc.

but that sure sounds like fuel issue from your vid.

it could be that its got clogged injectors, but the only way to know for sure is to pull them and get them tested. maybe leave that until a bit further along.

good luck with it.

stay methodical.

all other suggestions above are correct.
just go through everything one thing at a time.

Posted by: r_towle Apr 12 2022, 06:46 PM

https://members.rennlist.com/pbanders/DJetParts.htm

Welcome to Djet
Read the whole site

Posted by: emerygt350 Apr 12 2022, 07:09 PM

If it approached this point gradually, start with the filter. After that come back to us with an update. All kinds of good stuff mentioned above but a new fuel filter is a great start.

Posted by: Lockwodo Apr 12 2022, 07:24 PM

Hi wonkipop. My '74 2.0 with FI is having the same symptoms boxster914 and you have described. You're reminding me that I've observed very small bubbles in my fuel line. Here's what happened: I replaced the fuel filter which of course drained the line to the engine, so I wanted to purge the fuel line of trapped air. I separated the fuel line at the cold start valve and attached a clear tygon line which I put it into a clear jar, then bumped the fuel pump (by turning ignition on and off). I could see bubbles traveling through the tygon tubing, which I expected. Thing is, I repeatedly turned the fuel pump on and off and I continued to get very fine bubbles in the line.

I'm in California where the ambient temp is around 75. The car has a 2 port fuel pump installed below the fuel tank. The missing happens when the car is warming up so I don't think this is a fuel heating up issue. I'm wondering if I have some sort of leak in the fuel line, something that's letting air in but no fuel out as far as I can tell?

By the way, the tank is near full and I verified fuel pressure is correct and does not fluctuate when the missing occurs.

Posted by: boxster914 Apr 12 2022, 07:43 PM

Thank you @http://www.914world.com/bbs2/index.php?showuser=26193 for the definitions!

Posted by: boxster914 Apr 12 2022, 07:52 PM

I typically drive the car multiple times a week. It rarely sits undriven for more than a week.

Posted by: wonkipop Apr 12 2022, 07:52 PM

different problem. not sure how air bubbles would be forming in yours at ambient.
after the fuel pump? the original three port fuel pumps actually use the little sliding valve thats in the head of the pump to release air bubbles and send them off down the return line to the fuel tank (the return line being the line used to blow excess pressure out of the fuel pump). you need a diagram of the port assembly to understand it.
more modern in line type pumps should be releasing air bubbles back through the pressure side port into the fuel pump. if there is bubbles in the line after the pump the pump is not good. bubbles can be in the line before the pump and can be there for all sorts of reasons. heat etc. but should not be there after pressurization.

mine is related to actually running out in traffic. sitting at the lights, where the car, since its virtually original in all respects regarding engine etc, idles hotter. the L jets were/are known for idling hot due to retarded ignition for emissions at idle. so if its a hot day here, and by that i mean 90F + (in imperial) i think the fuel starts to boil in the line before the pump which is under the engine in original spot. (i have steel lines now which i think exaggerate the issue compared to original plastic lines). the reason it can boil is if the fuel volume gets smaller - enough of the fuel recirculating does not gain from a sufficient heat sink in the fuel tank itself. the bulb like area at the bottom of the fuel tank is reduced to half the size it is in a lhd car. soon as i increase the fuel volume by taking the tank to half full the problem goes away as the fuel volume decreases the fuel temp enough to keep it under the threshold in the line before the pump. it happens in my car if i get down to 1/4 of a tank on hot days. so mine is not so much bubbles after the pump but pressure drops due to interrupted supply flows.

i'm not saying this is boxter's problem. its just where i would start first with his car if i was him. just making sure he is getting fuel ok.

if boxster wants to solve his problem r_bowie's advice is very good.
go to the thread.
the other thing boxster needs to do is down load the factory work shop manual.
its got all the trouble shooting pages etc in it to methodically go through.
as soon as Van got hold of that manual he was off and running.
i think its the guy who has the 914/6 GT website. he has the manual there i believe.
i'd have to check again. you need a good manual if you are sitting at home trying to solve these things.

EDIT.
i don't have the problem of the car dying when i give it to it.
which is boxter's problem.
his was able to still idle but as soon as he gassed it, it died.
and now it won't go.
so i would be starting with fuel first and tick that off the list.
could be his fuel pump died.
usually they just go bang.
but a guy i know with a big citroen had his fuel pump go gradually.
and it did more or less what boxster is describing.
after he pulled it out, he tested it and it still ran but it just wasn't building pressure.
something had let go inside it in the pump section itself rather than the motor.
unlike me he never did the can opener trick to find out what it was.
just replaced his fuel pump and moved on.
with the original three port style fuel pumps that 914s had they just go bang.
cease operations. usually due to chewing up the brushes or something in the motor finally after 1 million miles. but a more modern fuel pump can fail gradually or give more warning its on the way out.

Posted by: wonkipop Apr 13 2022, 12:18 AM

@http://www.914world.com/bbs2/index.php?showuser=24700

not sure if you have factory manuals - if you don't and want them go here.

larry lee has them on his website. useful at times like this.

http://p914-6info.net/Manuals.htm

Posted by: Lockwodo Apr 13 2022, 08:03 AM

Thanks Boxster914, very helpful to have the manuals, it's an amazing resource and insomnia cure

Wonkipop: I've done some research and it seems there are two ways that air bubbles can get into the gas line. One is a leak in the suction side of the fuel system, i.e. in the fuel line before the fuel pump or in the fuel tank itself, such that air is getting pulled into the line by suction. The other way is a failed injector combustion seal that allows combustion gases to force their way into the injector nozzle.

Posted by: wonkipop Apr 13 2022, 08:51 AM

you are thinking of diesels. or direct injection. injectors in a 914 are in the intake outside the combustion chamber.

lets not digress from the man's problems.
he needs to check he is getting fuel through and its at pressure and tick that off the list.

Posted by: BillJ Apr 13 2022, 09:23 AM

This exact behavior happened twice in my 75. Went through two filters before simply changing out the tank. Never had another issue.
Changing just the filter may solve though.

Posted by: rhodyguy Apr 13 2022, 09:46 AM

Could the tank well for the supply be filled with crud/rust? Have you drained the tank and looked inside of it with a flashlight? What is the condition strainer sock in the bottom of the tank? Kind of sucked flat?

Posted by: Root_Werks Apr 13 2022, 09:47 AM

Good point, don't forget there is a fuel strainer inside the tank that probably hasn't seen the light of day in almost 50 years.

Posted by: Jamie Apr 13 2022, 09:58 AM

When I moved the pump to the front I eliminated the troublesome sock filter in the tank, then a fuel filter before and after the pump. This allows easy access and inspection of any line junk that might come from the tank, which I had cleaned.

Posted by: Lockwodo Apr 13 2022, 11:16 AM

So I monitored the fuel pressure when the engine is running and the missing issue is happening. It's rock steady at 29 PSI. So doesn't that rule out the problem being related to a clogged fuel filter (which I replaced anyway) or crud in the fuel line/tank?

Posted by: DRPHIL914 Apr 13 2022, 11:56 AM

lots of good advice here already, if the fuel pressure is constant its probably not a blocked line or filter.
the hunting issue makes me think its running lean, but the missing makes me think more on the lines of intermittent short, like bad grounds or loose FI grounds, i had this happen 2x and now my ground wires for the FI are fastened securely to the spade connector thats on the back of the engine case bolt. check that. also - if its on acceleration the TPS could be an issue so you can unplug that to take it out of the equation, also take the cover off of it to chec the TPS board for wear, corrosion etc.
next item is the MPS- ihve had several fail we can go over that later. Go back to the distributor , there is a trigger points plate that fires the injector pulses and those need to be checked and cleaned , and inside your distributor the ground strap could be worn and shorting as well, so check these items and get back to us.
you can test each of these items so get your multi meter out. and vac test the MPS>


Phil -

Posted by: BillJ Apr 13 2022, 12:30 PM

Sounds like fuel delivery to the rail is fine. Good to eliminate that!

Posted by: emerygt350 Apr 13 2022, 02:48 PM

A quick thing to try that might tell us a little is have a buddy with some starter fluid or just a gas spritzer and see if you can rev it with that (or just rev it by hand in the engine bay while adding go juice). If it revs happy that points to injector issues (trigger, tps, mps, injectors), if not, ignition type stuff might be the issue (less likely).

Posted by: wonkipop Apr 13 2022, 03:32 PM

ok

fuels good.

ignition system next.

check the points first. are they clean.

then as above suggestions. go through the rest of the distributor and d jet stuff with the d jet guys.

Posted by: Lockwodo Apr 13 2022, 06:28 PM

Yes indeed.

Note to boxster914: I hope my car issues and the discussion in this thread are additive and helpful to you in resolving the issues your car is having. You started this thread and I didn't mean to hijack it

Note to everybody: you guys are great and your help/experience is much appreciated! I've checked and tested many of the things recommended and am working through the rest.

Posted by: boxster914 Apr 14 2022, 08:28 AM

Thank you all for your input (and @http://www.914world.com/bbs2/index.php?showuser=26193 I appreciated your contribution).

I am compiling a list of things to check which is exactly what I needed.

I will start work this weekend and be back in touch with my findings.

There may be some newb questions in the process. . .

Posted by: Dave_Darling Apr 14 2022, 01:31 PM

On a D-Jet car, the hesitation that happens when the throttle position switch is worn has been described as "trailer-hitching". This typically happens at steady-state cruise with a constant throttle position.

Unplug the throttle switch to see if the problem goes away. Don't worry that idle is a little funky, and that acceleration is slower than usual. Just check steady-state to see if the problem is there. If it is, then the throttle switch isn't the problem.

--DD

Posted by: Lockwodo Apr 14 2022, 06:27 PM

I recently replaced the TPS board and calibrated it. Disconnecting the electrical connector to the TPS doesn't affect the missing issue at all, so the missing isn't due to the TPS.

I did some tests on the MPS today and here is what I found: 95 ohms resistance between terminals 7 and 15, 340 ohms resistance between terminals 8 and 10, and no continuity between the coils and the case of the MPS. All good so far. Then I hooked a vacuum pump to the MPS sensing port and pulled 10 inches of vacuum. After one minute, the vacuum had dropped to 7 inches of mercury, then to 6 inches after a total of 2 minutes, then to 5 inches after a total of 9 minutes, where it seems to level off.

So the resistance numbers are in spec, but is the vacuum loss over time acceptable? I understand that even if the vacuum loss is acceptable, the MPS can still have a defective aneroid cell. What do you think? Perhaps not worth testing it further at this time.

I'm working on the ground points and distributor next.

Posted by: boxster914 Apr 17 2022, 08:39 PM

OK so I have some results to report on.

I changed the fuel filter.

After the filter change the car had 3 instances of minor bucking (much less than the original problem) early on in a 20 minute drive and then it ran fine for the rest of the time with no bucking.

Although after I got home there was some idling dropouts as captured on this video:

https://youtu.be/u-ttZXnvmOk

Notice the drop out at 0:02 and 0:10.

I figured the problem was not solved so I moved on to thinking it is caused by a vacuum leak.

I consulted the excellent vacuum hose diagram at bowlsby.net

https://bowlsby.net/914/Classic/zTN_FI_Hose_Vac_1.7L_1970-71.jpg

I changed the 4mm line (yellow in the diagram) after the fuel filter change and took the car out for a 10 minite run and there was no bucking at all.

Here is a picture of the new line:

At the throttle body


At the vacuum can


I welcome your feedback.

What is the function of the 4mm vacuum line that I changed? I don't know what it does. Could this have been the problem?

Thank you for all of your help.

Posted by: wonkipop Apr 17 2022, 09:17 PM

if its anything like a L jet, its the vac retard line from the distributor to the throttle body.
not sure exactly how they work with D Jet but know in L jet its to retard the ignition at idle mostly. it retards timing when there is engine vac, in L jet its on the manifold plenum side of the throttle body so its functioning when the throttle plate is closed at idle. mostly there to assist with emissions on L jet.

D jet guys would be able to tell you exactly how it works on your car.

but aside from it possibly affecting the retard which i don't think is significant in terms of sitting there idling it would have been an air leak into the system.

combine that with your fuel pressure or fuel restriction problem and your mixture leaned right out. why it wouldn't idle, hard to start and was bucking.

you have probably been driving around the minor air leak (and it does look minor) for a while and not even noticing it. i think your main problem might have been fuel restriction. the air leak would have exaggerated it, perhaps not a lot.

good work solving it.



EDIT
ps
when i think about things back two years ago the problem i had was very similar.
even though i have L jet.
a combo of fuel and air leak.
i found the air leak first. it was the throttle body gasket had done hard.
as soon as the engine really warmed up thermal expansion difference between the throttle body and the plenum caused the leak. it wasn't much of a leak i thought but it was around probably 1./2 the perimeter of the throttle body. new throttle body gasket and the problem seemed to go away. a bit like yours subsided after the filter change. ....that was until i ran the gas down to a 1/4 of a tank.
see my posts earlier in this thread. i am glad your fuel problem was a little easier to solve. my own fault for "butchering" the car to convert it to rhd 30 years ago.

Posted by: wonkipop Apr 17 2022, 10:04 PM

i was just reading back through your thread @http://www.914world.com/bbs2/index.php?showuser=24700 .

and noticed that you did test the fuel pressure and it was right.
i'm guessing this was just fuel pump running and not engine (since it would not run anyway).

which makes me think of something interesting.
i remember mike, my mechanic saying to me when we recommissioned mine.
we had to test pressure and flow. two separate things.

sounds like despite the filter it built up pressure.
because it wasn't really circulating or using any fuel.
but you had restricted flow. it was a kind of a static pressure it built up?

classic fuel filter problem is the gunk floats off the filter after you switch off.
car will start often and run for a bit.
then the gunk gets sucked back up and jams it again.
you must have had a bit of that going on if it could build up pressure in the injector circuit.

throw a couple of spare fuel filters in your glove box.
might happen again. at least you can save yourself on the side of the road.
assuming you can get at the filter. i'd need to park mine up on a curb in an emergency to get under there.
others suggesting tank might be dirty could be good suggestions.

Posted by: emerygt350 Apr 18 2022, 05:04 AM

What year is it again? Is that an egr?

Posted by: rjames Apr 18 2022, 07:44 AM

The vacuum hose goes to the retard port of the throttle body and is used to retard the timing at idle. Shouldn’t have anything to do with the bucking problem. Disconnecting it would cause a high idle, or if the vacuum canister was bad it would cause idle surging.

Posted by: DRPHIL914 Apr 18 2022, 08:09 AM

@http://www.914world.com/bbs2/index.php?showuser=26193
to answer your question, yes, its possible a failed cell is possible. the leak is slow and should be addressed, you might as well order a rebuild kit from Chris Foley, it will have the o-ring and seals with the adjustment tool and new disc. i have a a couple old MPS that had cracked cases i took the aneriod cells out of that i have as spare, if you need one. not sure they fail very often but they can.

@http://www.914world.com/bbs2/index.php?showuser=24700
It looks like the O.P. has a fuel flow issue but still could be more than one thing, but keep it simple in your process of elimination of not changing out more than one thing at a time,

Posted by: emerygt350 Apr 18 2022, 01:22 PM

Now I see it, couldnt recognize the dizzy in that photo. What a tangle.

Posted by: ClayPerrine Apr 18 2022, 01:26 PM

Have you checked the little ground wire that is inside the distributor? It grounds the moving breaker plate to the body of the distributor. If it is broken, it can cause intermittent spark failure which may feel like the bucking you are experiencing.

The reason for it being intermittent is that the plate moves on ball bearings and grease whenever the vacuum can has vacuum. Sometimes the balls get enough grease between them and the bottom plate to make an open circuit to the ground side of the points.

Clay

Posted by: Garland Apr 18 2022, 04:05 PM

Posted by: wonkipop Apr 18 2022, 06:01 PM

different plenum and throttle body set up to your 2.0 as well emery.
kind of closer in resemblance to 1.8 would have looked strange to you.

interesting comments about dizzy malfunction in comments.
-----that it would raise idle in a D jet.
in a L jet it would probably not idle at all - would be pulling in extra air afm can't measure. interesting differences in D jet!
idle could probably come up in an Ljet if the retard didn't work on the distributor,
but would have to happen without letting air into the throttle body.

Posted by: Lockwodo Apr 18 2022, 06:41 PM

Clay: I'll check the ground wire in the disty. I'm going through the electrical connections and ground points and the ground in the disty is definitely an important one.

Dr. Phil: I checked the MPS today by pulling 15 inches of mercury on it then watching it drop. It dropped below 12 inches in less than 5-6 seconds, so I think it's toast. But ran the car today after replacing all the vacuum hoses and the idle is more consistent albeit the irregular miss is still there at idle and backfiring when I rev it. Could the failed MPS be responsible for those symptoms?

Posted by: boxster914 Apr 28 2022, 05:18 PM

I have more data to report on this issue.

The car has driven flawlessly up until yesterday when I started it cold and it ran rough and when I drove it it was bucking.

I drove for about 1/4 mile with lots of bucking and then turned it off.

About 30 minutes later I tried to start it and it was completely dead no click, no lights no nothing upon turning the key.

I opened the hood and manipulated the battery wires.

I've included a picture with yellow circles around the wires that I manipulated.



I turned the key and it started fine and no bucking.

This would suggest that this is an electrical issue, yes?

Is there a map on the web somewhere of the ground wires that I can check?

Any other suggestions?

Posted by: emerygt350 Apr 29 2022, 04:25 AM

Interesting! All kinds of badness can result from poor grounds. You have that one near the battery, you also have a big ground strap from the top of the transmission to the body.

One thing I did was took a multimeter and set it to resistance (ohms) and checked the resistance from places all over the engine to that negative terminal on the battery. The negative on the coil, the block, the fan shroud, the transmission etc. It should all be less than .8 ohms, lower the better.

Posted by: ChrisFoley Apr 29 2022, 04:43 AM

The clamp on the positive cable appears pretty tired, and could be a high resistance point.
Make sure the knob on the negative clamp is tight. That knob is your anti-theft device. When it's loosened the car isn't supposed to run.

Posted by: Lockwodo Apr 29 2022, 06:57 AM

Hi Boxster914. There is a schematic showing ground points here on the 914/4 Tech Notebook website:

https://bowlsby.net/914/Classic/zTN_Elect_GroundPoints.jpg

My understanding is the most important ones for FI functioning are the fuel injection harness spade connectors at the rear engine case bolt, the battery ground strap (as in your photo), and the transmission ground strap.

Posted by: wonkipop Apr 29 2022, 08:24 PM

when you say you were manipulating battery wires.
you mean just jiggling the wires but the clamps are still tight on the battery.
those clamps are not rotating when you jiggle them?

if the clamps are good and tight its saying that maybe one of the wires inside the outer coating isn't so good? or your connection of wire to clamp is not so good.

as mentioned above those screw down "anti theft" battery disconnectors as well as not being screwed down tight - can go bad, or even be bad from new.
the first one i fitted to my big citroen which has constant battery drain problems was a dud and gave me all sorts of problems even screwed down tight.
i threw it away and replaced it. no trouble afterwards.

worth cleaning up all your ground points while you are at it as suggested.
i gave that battery earth on a real good wire brush and sand paper clean on mine a couple of years ago and did the transmission one at the same time when i had the gearbox out for a clutch.
the trans one had never been done since new and it was real dirty.
a lot of road muck ends up on that one under the car. worth an inspection.

it does sound suspiciously like one of those battery cables is not good somehow.
or its that anti theft device?

Posted by: boxster914 Apr 30 2022, 04:01 PM

Yes @http://www.914world.com/bbs2/index.php?showuser=24231 the wires did seem tight to me. I just jiggled them, correct. Nothing rotated while I was jiggling them.

Posted by: Lockwodo Apr 30 2022, 05:41 PM

I've come to believe that battery cables should be replaced periodically, like after 10 years even if they look "OK" externally. They can degrade internally and become less conductive.

Posted by: wonkipop Apr 30 2022, 06:08 PM

if it happens again, don't jiggle them all.
just jiggle the negative. then try a start.
do that a few times before switching to jiggling the other one.

see if you can isolate it.
often times its the negative (earth) connection that gives you the trouble.

Posted by: boxster914 May 1 2022, 08:26 AM

Thank you all for your input.

Thank you @http://www.914world.com/bbs2/index.php?showuser=26193 for the bowlsby link.

I'm going to do two things:

1. I'm going to clean up the ground point connections listed in the Bowlsby diagram

2. I ordered and will install the heavy duty ground cable set from AA (http://www.autoatlanta.com/Porsche-914-Ground-Cable-Set-Parts-PN-BTG9141.html)

Posted by: Lockwodo May 1 2022, 09:36 AM

Thanks for the link. I checked it out and it looks like it will do the job for both battery to ground and tranny to ground.

Also, there is an alternator to ground strap that would be good to replace. You can find an example of that on the AA site.

Posted by: mgphoto May 1 2022, 10:06 AM

This takes 5 minutes to check, you will need to retime the distributor.
Those points are low power, oil and dirt will not burn off like regular ignition points.

Posted by: Lockwodo May 1 2022, 10:53 AM

I'm not seeing misses on two cylinders at once, but cleaning those trigger points and checking for disty shaft wobble and smooth advance action are all things I need to do. The disty has a Crane ignition module and stock coil, and I don't know how well it's working, but a weak spark will cause erratic missing.

Posted by: mgphoto May 1 2022, 02:02 PM

I would install the standard points and condenser for testing.
Your rotor shaft wobble could be a detached circlip which holds the rotor to the mechanical advance.
Injectors fire in pairs, 2 behind closed valves, 2 behind open valves, don’t remember off hand if it’s left and right or forward rearward injector pairs.
Low speed bucking is usually associated with an advance problem or TPS and a combination of the two. High speed is usually the injector pairs not firing at the correct time.

Posted by: ChrisFoley May 2 2022, 04:12 AM

I remember having trouble with old Crane optical systems. Much prefer Pertronix as a points replacement.

Posted by: Lockwodo May 24 2022, 07:17 AM

Right you are, mgphoto. My intermittent "bucking" problem was due to the distributor trigger points. Why do I always find what I'm looking for in the last place I look? I pulled the points and they were oily and cruddy which was causing intermittent problems. Cleaned up the points and re-installed and now it starts up, idles and revs up great. I have a distributor rebuild or 123 Ignition in my future, but for now,

Posted by: mgphoto May 24 2022, 04:30 PM

Glad it worked out.