Any help is appreciated.

My car will start but won't stay running longer than 5 seconds. If I unplug the Air Flow Meter the car with run at 3k RPM but is undrivable.

Recent upgrades.
New alternator
Replaced Air Flow Meter with good used unit (I did this after the problem 1st happened it did not fix the problem)
Fuel supply is excellent both when starting and when manually activating the AFM.
New Pertronix distributor and coil.

I know timing is correct and that the replacement AFM is good. I also checked the fuel pump wiring and relay, both are good.

Could the AFM red diode be bad? Is it possible to bypass for testing?

Thanks,
Adam

 

Red diode? I presume you mean the red diode pack on the firewall? It works on the fuel pump control circuit. If your fuel pressure is good while cranking and running then I don't think you have a problem with the diode pack.

But.....

Running for just a few seconds does sound like a fuel supply problem. I'd bypass the control circuit and see what happens:

Remove the fuel pump relay. In the relay socket/plug locate the terminals that go to the white/green wires. Use a jumper wire to apply 12v to the white/green wire(s)*. You should hear the fuel pump run, Now start the engine end see if anything changes.

Cheers
DD

You might have more than one white/green wire at the socket (long story). No worries. Just apply 12v to each until you hear the fuel pump run. You can't hurt anything

 

Hi DD, I actually did that last night. The pump kicked in but the car would only start for 5 seconds as before. Thanks for the help.

 

Move to ignition.


Perhaps, the coil and distributor get voltage in the crank position of the ignition switch, but not on the run position.


A favorite basic diagnostic procedure of mine is to jump battery 12v to the + on the coil. Try again. If it runs, trace the wires back to the ignition switch. if sound, the "open" may be in the switch itself.


AKA known as "hot wiring" !!!


Carl

 

Ok I did just that and no change.

 

Try checking the wiring from the AFM back to where it comes from. If you unplug and it runs to 3k then the wiring could be grounding somewhere.

Just a thought and hope it helps.

Jim

 

Hi Jim, I traced the AFM wiring loom back to the firewall. It appears to be in good condition. I also just cleaned the connections and sprayed with contact oel.

 

So I'm able to keep the car running if I push on the flap inside the AFM. I have removed the AFM plastic cover and the track looks to be in good condition. Any tips on what I should look for inside the AFM? Thanks Adam

It should be noted that I'm doing this while jumping where the two white wires enter the bottom of the red diode to engage the starter.

 

Removed the AFM and tubing connected to the throttle body. The throttle body is in spec then checked all hoses and tightened all clamps to ensure no air leaks. I even installed the front air filter canister. Still the same problem.

 

Today I cleaned all grounds in the engine bay. I also inspected all wiring and made sure I was getting good fuel pressure from the starter and the AFM. I checked each of the injectors with a 12v source and inspected all engine bay wiring.

Still the same problem when I go to start the car. It starts then dies. It will stay running with the AFM unplugged but as you can imagine it idles high. As soon as I plug the replacement AFM back in the car dies.

I have even removed the top of the AFM to look at the stip and contacts. It's in GREAT condition. Very little wear.

Could this be the L Jetronic ECU/5CU? Is there anyway to test this?

 

Pretty weird

As long as we're grasping .....

Are you getting a good constant voltage supply on the two brown/slate wires at the injector ballast? I can't think of any reason why the voltage would cut out specifically after 5 seconds but, what the heck, worth checking.

Cheers
DD

 

Never mind. If you're getting 12v at the injectors the injector ballast wiring must be OK


Cheers
DD

 

So I just had the car running without the AFM plugged in then I revved up the car and plugged in the AFM while wiggling the wiring harness at the back of the engine. The car started to sound better then a HUGE screeching sound came out of the back of the engine. I immediately killed power and the engine stopped running but kept Turing over as the starter had engaged. WTF.... Even with removing the key the starter wouldn't stop so I disconnected the battery -

This isn't very encouraging.

 

I suspect a wiring fault of some sort. The starter relay is probably being energized by a fault in the fuel pump circuit....most likely related to the red diode pack as that's where the two circuits cross. I think "+" voltage from the pump circuit is getting to the white/yellow wires

Do you have the S57 wiring book?

Cheers
DD

 

Hello DD

Yes I agree a wiring issue. I did get a color version from a member here. I'll look at it today.

 

Inside the AFM top box where the track is located is a pair of contacts that maintains engine running after you back off the ignition key when the car starts. They supply volts to the fuel pump relay and close when the flap moves open on engine start. These are notorious for not maintaining good contact after a few years, thus causing the engine to shut down due to lack of fuel. So check these out and clean them and also make sure they are making a good contact.
However, reading the thread, if you powered up the fuel pump directly, not via the fuel pump relay and the car still wouldn't run, then maybe these contacts are OK.

On my car I had the engine shut down whilst overtaking up a hill in traffic ! When I got to the side of the road and restarted it all appeared normal......until the next time ! Tweaking those contacts cured my problem, anyway.

Other thing is - are those injectors all ticking away nicely ? In my toolbox I have a special little light that plugs into a fuel injector plug, and enables one to check the pulse to the injector is there. The injectors rely on a good earth to work properly, but its too long ago for me to remember the location. On start-up, the cold start injector floods the engine with a load of fuel, so it will run for a few seconds on that.

 

Agreed. They work as the should. I'm picking up a new diode pack in the am. I'll post results ASAP.

 

I found this fantastic write up on adjusting the AFM and wanted to share with the community.

Itinerant Air-Cooled Forum ? View topic - AFM Adjustment

 

The car still won't stay running.

Timing is correct, the Pertronix distributor and coil are new. I've verified great fuel pressure before and on the fuel rail. Replaced the AFM and Red Diode. I ran a hot wire from the battery to the + on the coil to rule out the ignition switch. I cleaned all grounds and wiring connections, then treated them all with contact OEL. I removed all hoses and ensured they are tight and aren't leaking. The car will only run with the AFM disconnected or when I manually manipulate it while plugged in.

 

I've read that the Auxiliary air valve can prevent the car from idling if clogged/stuck. I sprayed it full of carb cleaner and I'm going to let it soak overnight. Maybe this will help....