N882928

Newbie to Rennlist but long time owner with factory manuals. 82 928 Auto L-Jet (Columbus, OH). Situation: Car sat over winter, charged battery etc. Normal stuff. Went to start one day in late winter. Car cranks, fires, runs for two secs then dies. End of last season fuel pump was buzzing so I ASSumed it was the pump. Replaced with new pump and check valve. Fuel filter only 1 year old so did not do, less than 10,000 on it. Same situation. Started shooting problem. Tested for spark from coil. Spark good and blue. Checked resistance of resistors to coil. Seem OK. Check resistance of coil primary and secondary. Primary (between 1 and 15) was .8ohm. Manuals say should be .33-.46. Manual says replace coil. Coil along with plugs, wires, rotor and cap are about two years old. I struggle to believe coil is bad so I kept shooting(although it could be but the problem seems more like fuel delivery?). Started checking L-Jet: Swapped out AFC relay. No help. Didn't think it was cold start valve as I figured that is what fuel the car was running off of for 2 secs.(?) Removed "Flapper". Plate moves OK. cleanned it up. Started car w/o flapper. No change to condition. Started with flapper wired up but not connected to throttle body. No change. Did not look at Aux. air as I thought this last test would be the same result, more air etc. Temp. 2 is 2 years old and conections were OK. Checked injector wires on both banks with light probe. When cranked all lit. Checked for fuel in rails at both banks. Fuel was there. Check for vac. leaks in usual places and could not find.
Things not checked: Don't have adapter for fuel press. gage. Where can I get? Did not check fuel press. correctly although seemed to be enough in rails. Did not check ECU or Injection brain. What is meathod? Could not find in manual. Thought about ignition switch. Where is it located? Did not see in manual. Can you Gurus please help a brother out??

Rez

The 80 to 84 L-Jet have a cold start injector. The car cranking up but dying shortly thereafter probably means your not getting fuel to the injectors. You already know the fuel pump is OK. By the way, turning the key and not cranking, hearing the fuel pump buzz means it's working.

Go to this website and click on your model year.

https://www.928gt.com/default1.htm

I'd check the fuel injection relay. Might be an easy fix before you start tearing into the other stuff.

I'd get into fuel pressure if that relay pans out. Attach the fuel pressure gauge to the end of the fuel rail. With most gauges you'll need some type of adapter to attach the gauge. The more expensive fuel pressure gauge kits will include metric adapters. You can fabricated your own adapter using an old fuel rail end cap which is drilled and tapped to accept an adapter (Pipe thread to SAE thread) which would work with amercian fuel pressure gauges.

John V

N88,

I'm going from memory but I beleive on the L-jet, during cranking (key in the start position), the fuel pump runs to build fuel pressure. Once the car starts and the key is returned to the "on" position, the fuel pump looses power from the key swtich. At that point, there is another switch in the air flow meter (AFM) that takes over in providing fuel pump power(if the engine starts and is drawing in air). Thats what keeps the fuel pump running once the key goes to the run position. It sounds like that circuit is faulty so when you release the key from the start position, you lose fuel pressure.


I think this was a safety device so that in the event of an accident where the engine stalls but the key is left on, this switch opens (becuase the engine stall stops drawing in air) and the fuel pump shuts down so you don't pump fuel all over the place if a line breaks

The easiest way to prove this is to jump the fuel pump relay so its always on (which isn't a problem to run this test). If the car starts and stays running, then I would suspect the AFM switch or wiring as the problem. I beleive you can also manually push the AFM air flap in (as if the car were running) and if the key is in the "run" position, you should hear the fuel pump running.

rjtw

I have had the exact same symptoms in my '83, and others have posted with the exact same symptoms with their L-jet cars. (Mine also stopped working after sitting for an extended period). The fuel injection relay is the main culprit, and a new one fixed my problem. (I'm not sure if this is the AFC relay you refer to). Try a new relay or jumper the fuel injection relay. A search of posts will provide further guidance if necessary. As indicated above, the car starts with a puff of gas from the cold start injector but that's the end of it.

Regarding the light probe test on the injectors, I am not sure if this shows what you need to know. The L-jet works by providing continuous 12v to the injectors and intermittently switching to ground to fire them in banks of 4. So, the test is not for the presence of 12v, but rather for the intermittent ground contact. If your light test measured this, fine, the fuel injection relay would not be the problem. If you are not getting switched ground, then the problem is likely with grounding attachments for the L-jet unit.

I also like John's theory about the switch in the AFM to keep the pump going! In my case, for what it's worth, after the engine died I could still hear the pump running for a moment or two. If the AFM switch circuit is faulty, then the pump would already be off when the engine dies. A careful listen after the engine stops could help you go down the right path.

Good luck, and let us know how it turns out!!
Rick

N882928

Update: First off thanks to Rez, John V, Rick for your suggestions. Here's where I'm at now:

Re. the fuel Inj. relay: In the manuals they refer to the L-Jet. relay as the AFC relay. I believe this is Air Flow Controlled Fuel Inj. As I see it it resides in the "XVI" spot on the master fuse/relay board. This location is one spot up and one spot to the left of the fuel pump relay in spot "XVII" I'm sure you guys know where this stuff is at. Anyway the AFC/F.Inj. relay was the first thing I replaced even before I posted. After replacement, still start then die..

AFM Switch: Next I bridged the fuel pump relay, terminals 30 and 87. Could hear an immediate hum of the pump. Tried to start, still died. I also tried another start with just the fuel pump relay back in. After the eng. died I could still hear the pump for 2-3 sec. By this rational I guess the AFM switch must be OK.(?)

Fuel Press.: I'm still working on finding/rigging an adapter. I'll post when I get this one as I have not correctly confirmed good Fuel Press.

Plugs: FYI...while I was in there I put new plugs in. I' didn't think this would help the current situation but what I did notice was on the pass. side bank the plugs were rich and the driver side bank the plugs seemed very lean. I thought maybe one of the fuel press. reg. may have kicked? Since I believe this problem is fuel delivery either related to electrical or mech this may be a clue? Any thoughts on this?

Sat. I am going to check grounds. The manual has a list of them so I'll go down that. However I still have not found any info. on the ignition switch and if it has any role itself in sending signals in the same way John spoke of the AFM.

Any more suggestion would be great as I need all the help I can get. Thanks again.

Rich9928p

My '83 had a similar problem. It turned out to be a vacuum leak. The A/T cars have a caps [item 24 & 27] on the side of the throttle housing to block off a connectors to a deceleration "vacuum limiter" [item 27] that is used for 5-speeds. If these caps breaks, there is a very large vacuum leak and the car will not start.

From the passenger side of the engine bay, look down between the intake spiders to the throttle housing. You should be able to see the cap and if it is cracked or has fallen off.

Good luck, let us know what you find.

Johnu33301

Hi all I new here to and I'm from Cincinnati, I checked everything possible . I did find that on pin 15 I do not have the full 12 volts going to injectors. Have not checked grround yet where are they located. I've been told that if no power at 15 then it has to be a wiring problem or ignition problem. They fuel pump runs fine and relays are good also brain has been check out by Porsche and it is fine. I do have an extra Brain forsale if someone needs it $100.... Anyways can anyone please help I dont know what else to do, I have changed the Regulators al three, Temp sensor, ICU, ECU, fuel pump, Filter, plugs, and relays.

Randy V

Dual personalities?

Daniel Dudley

When you test your coil, watch the spark as you keep turning the engine over. See if the spark diminishes over time, that is to say starts out fat and gets weaker over time. Also, check to see if the gap on the plugs is too wide. Just for grins, as you try to start the car, crack the throttle a little as it catches and see if that helps. Remember, a good coil will shoot a bolt almost a half an inch. Old school test for fuel delivery is to shoot starter fluid down the intake. If it runs, you know that it isn't ignition. Don't do this too long BTW, not super good for engine. Stale gas is also a possible cause, Although once it gets running it should keep running. Dry gas and fresh gas can't hurt.

Daniel Dudley

If you use starting fluid, KEEP YOUR FACE AWAY FROM THE INTAKE !!!!

Johnu33301

Where are the Grounds located behind the fuse panel?

N882928

Rich,
N8 here, not to be confused with Johnu33301. Thaks for that tip. I did replace those two caps to the throttle body you referenced however this did not change the start/die situation. But I'm sure that will save me down the road. An FYI to anyone who has not replaced these caps yet. NAPA stocks rubber bypass caps that work well for this fix and they were cheap. Did not have to mess with cutting hose,etc. I just popped them on. The sizes were 5/8" and 3/4" I believe.

Update: I'm still working on checking grounds and cleaning terminals right now but so far no luck...still start...die.

Dennis Wilson

It's possible you have a bad ballast resistor. To test it, measure the voltage at the 15 post of the coil when the ignition switch is ON (not crank). If less than 3 volts, the .4 ohm resistor is bad or needs the contacts cleaned.

Dennis

Mike LaBranche

Sadly, my 84 L-Jet has this symptom now also. It's only on cold start tho. I go thru the start,die cycle half a dozen times until it kinda runs... and as it heats up it starts to run better. As I drive it then, after a couple miles it gives me a sputter, sputter... BWAAHHHH. All better. I had the top end out to recondition the injectors thinking my hard starts were due to clogged squirters. Got it back together and the cold start issue is there. I'm thinking it's the temp II sensor or the aux air valve. First one figures it out wins. lol

Mike
84 S
78 OB

N882928

OK, Mike it's on. A race to the fix. Let me know if you figure yours out. Personally I miss that BWAAAHHH sound down the block so I must tell you I'm motivated. If you get time let me know if you have checked anything beyond what was in my list of possible causes. At least it's good to know I'm not the only one with this frustration. Our people are oppressed. Keep up the fight my brother.