"Trailer-hitching" bucking problem, Rapid detrioration from running perfectly Options

[boxster914]

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

[krazykonrad]

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.

[BillJ]

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

[Lockwodo]

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

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!

[ClayPerrine]

"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

[Root_Werks]

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

(IMG:style_emoticons/default/agree.gif)

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.

[Lockwodo]

"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

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?

[mepstein]

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

[Lockwodo]

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

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.

[930cabman]

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

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

[BillJ]

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

[boxster914]

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 @lockwodo : 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-j...ncludes-spacer/

[mgphoto]

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

[Lockwodo]

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 @lockwodo : 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-j...ncludes-spacer/

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.

[Ansbacher]

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

Ansbacher

[wonkipop]

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.

[r_towle]

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

Welcome to Djet
Read the whole site

[emerygt350]

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.

[Lockwodo]

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.

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.

[boxster914]

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 @lockwodo : 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-j...ncludes-spacer/

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.

Thank you @lockwodo for the definitions!