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Posted by: thatguywiththedatsun Mar 21 2014, 01:36 PM

I've been looking for a 914 for a few months now, but life has been in the way. I found one last month that seems to be a good starting point, but I'm having trouble getting it to stay running atm. Seems like it's probably the l-jet system being out of adjustment or leaky, faulty sensors, or some old corroded electrical connectors. The question is; where?

I'm getting a buzzing sound with the key turned to "on" which I initially thought was the seatbelt interlock buzzer everyone seems to be so fond of, but upon closer inspection... it's coming from the injectors..? If i unplug the noisy injector, another one starts buzzing. There's no noise from the fuel pump at this time with the key on. The fuel pump relay, and power supply relay on the board were nowhere to be found when I got the car. I went ahead and bought a few new ones to get it back to stock wiring, but I'm really having trouble deciphering the current flow diagrams. (You guys seems to have a reference system to the pins in every connector, or which specific relay you're referencing. Is there a diagram for this somewhere, or are the labels just buried under the grime in this car?) If i hot wire the double relay (86d, 88d?) to the + battery post, the fuel pump will run, but this doesn't change my "start, rumble rumble, die" situation at all. I have a feeling that there is an area in the wiring that has been altered which, if put back to stock, would rectify the problems I'm having... It's just a matter of finding it and fixing it. Any suggestions?

What I have done:
-compression test: 125,130,90,135 - hoping it will improve pending a valve adjustment?
-tested the coil and wires for spark - checks out fine... nice and strong
-tested fuel pressure - 43psi holding steady for several minutes after the test (p.o. said he'd recently had the fuel pump replaced, but didn't mention why )
-renewed all the l-jet vacuum hoses and put hose clamps on every connection
-taken care of a few obvious electrical bugs (missing/rusty relays, broken wires, etc)
-checked the head temp sensor spade connection, but where does the other end of that connection terminate on the relay board?
-checked afm resistance. - With key on, if I move the flap by hand, the fuel pump does run, but there is no 1.5 seconds of priming with the key on, just the annoying injector buzz.

Thanks in advance for the help! I'll be much better off if someone could just explain the 'pin 13/relay 74/etc. references to me.

Posted by: Chris H. Mar 21 2014, 01:47 PM

Timothy_nd28 is the man you need to speak to, and he is perusing your thread right now. Highly respected L-Jet authority, LED gaugemeister, nice guy.

Posted by: timothy_nd28 Mar 21 2014, 02:14 PM

The injector buzzing sound is very intriguing to me.
My first initial thought was your dual relay. When you turn the ignition switch to the "on" position, the fuel pump should NOT turn on, this is normal. Your fuel pump only activates with you turning the ignition key to the "start" position. At this position, the fuel pump receives power thru the dual relay. When you release the key from the start position, the air flow meter takes over and keeps the dual relay engaged. Since you applied power to pin 88d on the dual relay, you essentially bypassed the dual relay. This test confirmed that your engine is not dieing from lack of fuel.

With a Ljet setup, your relay board isn't all that necessary for it to run. The 2 fuses on that board are not required, along with any relays plugged into it. All the wires needed for a running state, runs thru the relay board. So at this point, I wouldn't worry about the relay board.

Your CHT sensor is not wired directly to the relay board. This wire should be part of the fuel injection wiring harness, that leads to the ECU. This needs to be connected for your car to run. Capn Krusty has supplied me and many others with a manual for trouble shooting Ljets. I can email you a copy if you wish. If you were to unplug the ECU connector and ohm out pin 13 to engine ground, you should have around 2k ohm of resistance (depending on ambient temperatures).

Your fuel pressure is way high. Do you have a fuel pressure regulator installed on the fuel loop?

Also, your compression test is somewhat concerning. You may want to double check the valve lash on the offending cylinder. The proper way to test compression is with the engine warm. So after we figure out what is wrong with the staying running problem, you may want to re-check the compressions.

Back to the buzzing injectors. Again, really odd problem. If you unplug the ECU connector, does this buzzing go away?

Posted by: Cap'n Krusty Mar 21 2014, 02:28 PM

Unplug all of the injectors. Key on, plug them back in, one at a time. One shorted injector will cause them all to stay open, although they shouldn't "buzz".

Check the oil filler cap. There are 2 seals, one an o-ring, the other a flat gasket. They must both be there and intact. If they're not in good condition, the car won't stay running.

Take advantage of the offer of the troubleshooting guide.

The Cap'n

Posted by: thatguywiththedatsun Mar 21 2014, 02:30 PM

I'll be in the garage in the next few hours, and will report back. Thanks for the quick replies and the diagram! It does have a pressure regulator, but I really can't speak for it's integrity. The buzzing is there more often than not, but sometimes it just doesn't do it. If you turn the key to on and hear the buzzing from the injectors, if you turn on the headlights or hit the brakes or otherwise switch on a somewhat beefy load, it's like the buzzing toggles off/on alongside whatever else. It is bizarre.

Posted by: thatguywiththedatsun Mar 21 2014, 02:31 PM

Email address is xxxxxxxxxx@gmail.com. One chance to receive it, right? 0.0

Posted by: timothy_nd28 Mar 21 2014, 02:38 PM

2 manuals sent to your email address. I would re-edit your above email address so that you don't get tons of spam emails

Posted by: Dave_Darling Mar 21 2014, 04:17 PM

Here's a link to a diagram of the FI wiring harness, offered by Jeff Bowlsby: https://bowlsby.net/914/WiringHarnesses/HarnDia_FI_EC74-1.8.pdf

BTW, if you suspect your FI harness, go to https://bowlsby.net/914/WiringHarnesses/ and click the links to contact Jeff. It looks like he may now offer his "rebuild" service (the D-jet harness is 90%+ brand-new parts after he's done, so I'm not sure rebuild is the right word) for the L-jet stuff.

The L-jet fuel pump runs under 2 circumstances: 1- the key is turned to "start"; 2- the flap in the air-flow meter is open (and the key is "on"). You can check the pump by turning the key on and pushing the flap in the AFM open by hand.

There is a box with four resistors in it that also hangs off the battery tray; those are used to drop the power to the injectors. Make sure the one side of those has +12V when the key is on.

The injectors are really easy to remove from the manifold; one nut holds each one on. Remove both injectors from one side of the motor and stick them in jars. Crank the starter; look for squirts of fuel coming out of the injectors or at least look for fuel in the jars after cranking.

Note that there is a white wire in the FI harness that goes to the (-) terminal on the coil. That carries the signal from the points to the FI, telling it when to open the injectors. You won't get fuel without that hooked up, except possibly through the cold-start injector which dumps directly into the intake manifold.

--DD

Posted by: thatguywiththedatsun Mar 21 2014, 08:09 PM

Very useful tests! What I originally thought was the cht seems to be something else. Right behind the distributor, maybe an oil pressure sensor? Anyway, resistance from cht (right next to #3 plug wire, right?) to ground is 3.5K ohms, and from cht to pin 13 on ecu connector is a whopping 14.97M ohms. There's something that needs to be addressed. Am I correct in thinking that the cht is bad as well since it reads 3.5kohms to ground? On that note, while the ecu is disconnected, injectors do not buzz with key "on."

With the ecu plugged back in (ignition off, battery three feet away, just to be safe) and all injectors unplugged, they each buzz individually upon being plugged back in one at a time. It seems like only one (random) will buzz if they are all plugged in though. You got a picture handy of those oil seals? There doesn't seem to be anything special under there. There is one o-seal that seems like it would do it's job well enough, but I don't see a flat gasket..?

The pump does run with key "on" if I manually move the flapper, though I can't exactly hear the pump if I try to start it with the key. Even with the fuel pump hot wired to the battery, though, the problem persists. There is a white wire connected to the coil, poorly crimped, but it is there. There is 12v+ on one wire to the injector resistors with key "on," and fwiw, there's no buzzing with the resistor pack unplugged.

Don't really have time to pull the injectors tonight, but that fi harness rebuild may be a good option for me. It seems like half of the wires have cracked insulation from dry heat, or they're fraying at the crimped connectors.

I don't really feel great about making a jumper to the ecu connector boot. Seems like that's a somewhat sensitive area. Next chance I get, I'll get something rigged up and see if that fixes it I suppose.

Posted by: thatguywiththedatsun Mar 21 2014, 08:49 PM

Wait a minute.... You said pin 13 to ground. Lol, damnit. I'll try that one again tomorrow. Still doesn't sound good, though, does it? 15mohms between pin 13 and the cht, plus 3.5kohms for the cht itself to ground. :-/

Posted by: timothy_nd28 Mar 21 2014, 09:45 PM

Yep, pin 13 on the ECU plug to engine ground. The CHT is located next to the number 3 cylinder and depending what temperature your engine is, 3.5k ohms could be within spec. Go ahead and double check this at the ECU plug, it should read the same as you measuring right at the CHT to ground. If not, then Jeff Bowlsby may be in order for your harness

The oil pressure switch is located by the distributor, but this isn't required to be hooked up for the engine to be running right now.

Okay, next test. Remove all wires on the negative terminal on the ignition coil. We need to protect your points or pertronix module while doing these next tests. After this is done, remove the ECU plug and turn the ignition switch to the "on" position. With the meter set to DC volts, put one meter lead on the negative battery post and the other meter lead needs to probe pins 14,15,32 and 33. You should see 12 volts on every pin.

After this, turn the ignition switch to the off position. Measure pin 10 on the ECU connector, you should read 0 volts.

Posted by: thatguywiththedatsun Mar 21 2014, 09:57 PM

Man, you are good with this stuff. I'll try to get to the garage tomorrow. It's about 12 miles from home, and 5 miles from work, right in between the two. Not too bad, but still difficult to make time for on busy days.

Posted by: 69telecaster Mar 22 2014, 07:40 AM

While I don't really like Rivieras, that car looks pretty nice. And the cloth seats are interesting.
Sounds like you're getting some great help here, and it'll be on the road in no time.

Posted by: jim_hoyland Mar 22 2014, 12:21 PM

All the above info is very useful; I have on occasion had the same symptoms. Engine starts on key-start, then dies in key-on position Each time it was caused by one of the followiing:
1. Connector to AFM was not reinstalled

2. Loose wire at the dual relay

3. Brown dual relay wire ground not attached to engine

Posted by: thatguywiththedatsun Mar 22 2014, 06:57 PM

Interesting. I read 0V on 14 and 15, and I have no 32 or 33. Pin 10 reads 0V as well. Something is weird here. Confirmed 13.23M ohms from 13 to engine ground.



AFM connector is firmly plugged in. Like I said, the pump runs with key "on" if I move the flap by hand... The fact that I can jump 88d on the dual relay and have the pump run would suggest that it's grounded firmly. It does seem like the dual relay isn't getting the right signals, though. I bench tested the dual relay and it checks out fine by itself. Hmmmm...

Posted by: thatguywiththedatsun Mar 22 2014, 07:08 PM

I'm not crazy about the weird cloth seats myself. The wheels aren't my favorites either, but they're better than the stockers imho. It'll look a lot better out in the sun!

Posted by: Jeff Bowlsby Mar 22 2014, 08:53 PM

That's a standard 1974 1.8L FI harness. You can check the rest of the harness with this if you need to.

https://bowlsby.net/914/WiringHarnesses/HarnDia_FI_EC74-1.8.pdf

Posted by: thatguywiththedatsun Mar 22 2014, 11:00 PM

Man, I'm stupid. Okay, after testing the correct pins, everything thus far checks out fine.

Posted by: timothy_nd28 Mar 23 2014, 12:51 AM

Good, what was your reading from pin 13 to engine ground?

Posted by: thatguywiththedatsun Mar 23 2014, 01:43 AM

3.5k ohms

Posted by: timothy_nd28 Mar 23 2014, 09:30 AM

Great, just wanted to verify that you weren't still in the meg ohm range. I'll assume that you were getting a solid 12volts on pins 14-15-32 and 33?

Never mind the dual relay at the moment. The fact that it turns on the fuel pump when you deflect the AFM flap tells me that it is wired correctly. Also your car does start briefly also says that you have fuel pressure when cranking.

Lets do a few more test. With the ECU plug pulled and the ignition switch at the "off" position, put one meter lead on the +12vdc battery post and the other meter lead on pins 5,16 and 17. The meter should read 12 volts on each pin.

After this, remove all fuel injectors from the manifold and insert into glass jars. Turn the ignition switch to the "on" position. Jump pin 88d to +12vdc on the battery post. Use one of your meter leads (detached from the multimeter) and find a way to ground one side of this cable to the negative side of the battery. With the pointy end of the meter lead, insert into pins 14,15,32 and 33. You should hear an audible click (no buzzing), you should also see one of the injectors spraying. Observe the spray pattern while the FI is engaged and be sure it fully shuts off when the meter lead is removed from its corresponding pin. Do this for all 4 injectors. Make sure only one injector is spraying when doing this test, that others are not simultaneously spraying.

Posted by: malcolm2 Mar 23 2014, 10:00 AM

QUOTE(thatguywiththedatsun @ Mar 23 2014, 12:00 AM)

Posted by: davesprinkle Mar 23 2014, 12:41 PM

Oh yeah, the old "leave the AFM disconnected" problem. I've done that...

Posted by: Chris H. Mar 23 2014, 12:46 PM

Yep met too. Runs terrible with that thing off doesn't it?

Posted by: davesprinkle Mar 23 2014, 03:02 PM

QUOTE(Chris H. @ Mar 23 2014, 11:46 AM)

Posted by: thatguywiththedatsun Mar 23 2014, 05:55 PM

QUOTE(malcolm2 @ Mar 23 2014, 08:00 AM)

QUOTE(thatguywiththedatsun @ Mar 23 2014, 12:00 AM)

Man, I'm stupid. Okay, after testing the correct pins, everything thus far checks out fine.

These guys are smart and they WILL figure this out for you. Let me throw in my 2 cents.

Admittedly, I have not read this entire post, so shoot me if this has been said or ruled out with your electrical checks. EDIT: post 14... but I added a picture.

But I recently had the air filter box off of my L-Jet and forgot to plug the connector into the AFM... My car did the same thing. Started then died.



the 2" wide connector on the bottom of this picture.

Posted by: thatguywiththedatsun Mar 23 2014, 06:55 PM

All injectors fire a nice even spray pattern with their corresponding pins. Nothing out of the ordinary aside from a leaky hose clamp connection. 5, 16, and 17 all show clean path to ground.

Posted by: timothy_nd28 Mar 23 2014, 11:16 PM

So far so good. Now with your multimeter set to ohms, measure between pins 6 and 9 on the ECU plug. Then measure between pins 7 and 8 at the ECU plug. Measure again pins 7 and 8, but move the AFM flap while staring at the meter. Do the numbers increase/decrease evenly when manually pushing the flap?

When you performed the injector spray test, did any of the injectors or adjacent injectors start to buzz? Are you still having the buzzing sound?

Posted by: jim_hoyland Mar 24 2014, 07:06 AM

As an aside: By grounding # 1 ( forward left spade ) on the 4 prong connector at the rear (left side) of the relay board you bypass the dual relays control of the fuel pump. Good for an emergency and testing but runs whenever the key is on. The power relay and fuel pump relay will have to be installed.

Posted by: malcolm2 Mar 24 2014, 08:32 AM

QUOTE(thatguywiththedatsun @ Mar 23 2014, 06:55 PM)

That's my problem... I don't have the factory optional afm box duct tape. Setting the tests up now. Feeling the love from this forum so far. You guys rock!

Posted by: thatguywiththedatsun Mar 24 2014, 06:48 PM

No buzzing from the injectors during the spray test. They all open and close as they should. Resistance between pins 6 and 9 is a steady 292 ohms regardless of where the flap is. With the flap fully closed, resistance between 7 and 8 is 135.6 ohms, if I deflect the flap it's really sort of erratic. Goes as high as 500-800 ohms briefly, but for the most part stays around 200-300 ohms. Wide open it shows 146 ohms. Doesn't seem as smooth as I thought it would be. Doesn't seem to be much correlation with the position of the flap...?

Posted by: timothy_nd28 Mar 24 2014, 06:57 PM

How far away do you live from Clark? It would be good to try a known good AFM with your setup. Everything else is checking out good with your Ljet, the only squirrely thing is your AFM

Posted by: thatguywiththedatsun Mar 24 2014, 07:23 PM

Not sure. I'm in Memphis. I did see a '74 412 at the junkyard the other day. Thought about grabbing the afm that was in the front seat. Don't recall if it was 6 or 7 pin though. Worth it?

Posted by: timothy_nd28 Mar 24 2014, 07:24 PM

If it can be had for under 5 bucks, maybe.

Posted by: malcolm2 Mar 24 2014, 07:53 PM

QUOTE(timothy_nd28 @ Mar 24 2014, 07:57 PM)

Posted by: timothy_nd28 Mar 24 2014, 09:32 PM

Pin 6 and 9 on the ECU plug show the total resistance on the AFM resistor plate, this number will not change (except with temperature, only slightly). This part of the test is good.

Pin 7 and 8 on the ECU plug is one half of the AFM's resistor plate. I expected to see 0 thru 200 ohms, or half the total resistance (pin 6 and 9) as you moved the AFM flap. Since you measured up to 800 ohms, (more than the total resistance of the resistor plate), suggests to me that the AFM wiper arm is not making good contact with the resistor plate. It could be dirty, or you could have worn carbon tracks on the plate.

Obtaining a known good AFM would be the easiest way to test. Or, you could clean the resistor plate with some good (hard to get) pot cleaner. If the carbon tracks are worn, the whole plate can move slightly if you were to loosen the screws and reposition the board. I'm not sure how in depth you wanna get with this.

Posted by: malcolm2 Mar 24 2014, 09:44 PM

Tim, did you give him the ITINERANT link?

http://www.itinerant-air-cooled.com/viewtopic.php?f=50&t=7761

only do stuff on here if Tim suggests it. ( or as a last resort, when Tim says you are ready for the last resort) There are a couple serious disclaimers in the document. READ and HEED.

Good Luck

Posted by: timothy_nd28 Mar 24 2014, 10:08 PM

Black22 found that link, all good stuff.

Posted by: thatguywiththedatsun Mar 25 2014, 12:54 PM

Oohlala. Definitely my cup of tea. I'll probably test the connector on the side of the box to rule out any problems in the harness between the ecu and afm and pop the black box open if I get the same readings. What have I got to lose, right? Anything else I should grab off this 412?

Posted by: thatguywiththedatsun Mar 28 2014, 05:16 PM

No dice, gentlemen. Got the afm responding reasonably well to the flapper arm location and the symptoms are the same. After a new cap and rotor (just cuz it's a new to me car) symptoms are still the same... Got wires, points, plugs, and condensor going in next time. Any more ideas?

I'm more and more leaning towards an electrical problem outside of the fi circuit. I've seen the injectors all fire a nice spray pattern, with adequate pressure in the lines as confirmed by a gauge. Checked for proper spark. Afm connector is securely plugged in, as is the cht which reads a nice steady 3.5k ohms. Even with the pump hot wired on all the time, it starts, revs to around 3000rpm, and dies within seconds. Makes me think that my nice strong spark is going away when the key goes back to "run" from "start." What am I missing here....?

Posted by: Valy Mar 28 2014, 05:37 PM

I bet it dies because the fuel is cut at the injectors. The spark should be working.
The FI cuts the fuel during deceleration so it thinks you have high RPM and the throttle is closed.
Something fools the FI to think that way so it's probably the AFM, throttle switch or cabling. The computer is very rarely at fault.

Posted by: timothy_nd28 Mar 28 2014, 07:42 PM

Okay, so some further tests you can do. On the (+) side of the ignition coil, you can jump straight to the positive side of the battery. Start the car and observe if the engine drops out. This tests your hypothesis with the ignition switch dropping out. I think this is unlikely, but its worth a shot. (if this test failed, remove the jumper wire)

Do you have a fuel pressure gauge installed, what is the fuel pressure right when the engine begins to quit?


Another test, for the throttle valve switch. Probe pins 18 and 3 on the ECU plug, what is the initial resistance. Now manually open the throttle plate all the way, what is the resistance between pins 18 and 3 now?

How did you remedy the AFM? What is your new numbers when rechecking? I'm still betting on the AFM being the issue here. The ECU could be faulty, however very unlikely. My money is on the AFM!

Do you happen to have the altitude compensator module installed on this car?

Posted by: timothy_nd28 Mar 28 2014, 08:03 PM

One last test, in addition to pin 88d being jumped to +12v on the battery, you can also jump pins 88a and 88b to +12volts on the battery. One half of this relay contrls the fuel pump, where the other half turns on the ECU. All these jumpers will essential bypass the dual relay, just another test we can do to rule things out.

Posted by: malcolm2 Apr 20 2014, 09:34 AM

so what ever happened here? Did you buy a new AFM? Is it running?

Posted by: thatguywiththedatsun May 2 2014, 02:24 PM

Once again, other stuff got in the way. I'm poking around as I'm able. Bought a $2 noid light from work. Really looks to me like an unreliable injector pulse. Maybe a bad coil? The light comes on and stays on *brightly* in conjunction with the buzzing that sometimes happens (and sometimes doesn't) with key on. When there's no buzz, there's no light. If I try to start it, it blinks a few times as it should, then turns off shortly before the car dies.

TL:DR; Haven't found a test afm yet, though I'm still trying.

Aside from a new afm, and the tests that I haven't got to yet... anyone have any other ideas?

Posted by: thatguywiththedatsun Mar 12 2015, 08:00 PM

Bought a rebuilt afm from fuel injection corp. Same results. Getting back to basics here....... The injectors are essentially just simple solenoids, which would buzz in a situation where they aren't getting adequate voltage. The starting has to be on the cold start injector alone. I have noticed that the buzzing goes away if the air flow meter is unplugged, and comes back if it's plugged back in.

Posted by: thatguywiththedatsun Feb 22 2017, 02:07 AM

Bringing a thread back from the dead here I know, but maybe someone else will benefit from my time spent troubleshooting this problem. I ended up reading a post somewhere that dealt with fiats I think... maybe volvos? Don't think volvos ever used l jet. My main source of confusion was the buzzing injectors, and this one was the only l jetronoc thread that I could find where a similar symptom presented. I eventually popped the ecu out, and open, and sure enough found burnt traces on the boards. I bought a reman unit from fuel injection Corp in Tracy, Ca and that was that. I never suspected the ecu because everything I read stated that they were pretty robust, but you really can't rule it out without testing it with one of those nifty Bosch testers, or an o-scope.

Posted by: Tjmrfe Feb 23 2017, 05:14 PM

QUOTE(thatguywiththedatsun @ Feb 22 2017, 12:07 AM)

Posted by: Root_Werks Feb 24 2017, 09:09 AM

ECU failure is uncommon....used to be. Maybe as they continue to age, it will become more common. I had one years back that was causing one injector to stay open. Fiddled with a number of things for too many days. One day a buddy showed up with an ECU just for giggles. Swapped it and ran perfect.

I'm not a supporter of blindly swapping parts to fix something. But if done one at a time, then swapped back if it didn't fix the issue is sometimes a quick path to correcting the issue.

Thanks for following up, this thread could save someone a lot of time.