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Update: It runs! See post #31 for the current condition!
Update 2: It runs correctly! See end of post.
Hello all, picking up another C4 today. A 1989 L98 6-Speed Coupe.
Getting the service manuals and such on the way, but before I get these and start diagnosing, I figured I'd ask you all if you have any big ideas first.
The problem: Does not run. According to the previous owner, they drove it home, but it never started again after letting it cool off. No signal to injectors, no power to dash. DIC does illuminate and engine does crank. Engine will run off of starting fluid.
My idea is power to the ECM. Fuses, grounds, harnesses, connectors etc...
Feel free to tell me what you think. I will update you all frequently!
Last edited by OneRedVette; Jul 3, 2024 at 08:10 AM.
Check fuel pressure
check distributor pickup coil resistance @1kohm
check spark
ALDL con force fuel pump ( is it top right? Give it 12v)
air, spark, fuel it’s running!
my 87 sat 3 yrs cranked right up with good distributor signal
Alright finally got it in my hands and figured some things out.
When given power, the dash, radio, and HVAC controls do not have power. Like mentioned before, the DIC does have power. The fuel pump relay comes on for 2 seconds at key-on, however the relay does not come on every time. The car must sit for at least a minute before the relay will cycle again. Strange. Furthermore, the pump does not run at all even when the relay is active.
My money is on bad grounds. I'm only getting around 10 volts to the fuse panel and everything that does work (wipers, windows, mirrors, etc. is very slow)
Anyone have some other ideas?
Check the fusible links behind the battery, there is a terminal block back there that has many links located on one post, some of them power the computer and fuel pump. I have seen them go bad.
He already said the injectors don't pulse and it starts on fluid. Also poor voltage. Fusible links is a good start. Also, get jumper cables and clamp to the negative terminal with the battery fully connected then clamp to steel/aluminum somewhere on the engine to make a decent battery ground to see if that changes anything.
If your injectors aren't pulsing at all, unplug all of them and connect a noid light into either bank to see if it pulses. Motec injectors can short over time and if there's one short on both banks the ECU will not be able to drive them. The ECU controls the ground side of the electronics in these cars and not the hot side. Check your ground for the ECU as well.
I think cleaning up grounds is a good place to start.
Alright I made some progress last night. I cleaned several grounds, including the one by the battery. That revived several parts of the car. Radio, HVAC controls, anti-theft, interior lights, power antenna, and most importantly, the fuel pump.
Still no pulse to the injectors or power to the dash but getting closer.
I verified all fusible links at the tee were intact. Also, I noticed that tach signal wire had broken from the distributor, so I repaired that too.
Now, this TPI is something I'm unfamiliar with, but with key in the run position, all the injectors have +12v going to both the hot and ground side... +12v on the ground wire can't be correct, right????
Alright I made some progress last night. I cleaned several grounds, including the one by the battery. That revived several parts of the car. Radio, HVAC controls, anti-theft, interior lights, power antenna, and most importantly, the fuel pump.
Still no pulse to the injectors or power to the dash but getting closer.
I verified all fusible links at the tee were intact. Also, I noticed that tach signal wire had broken from the distributor, so I repaired that too.
Now, this TPI is something I'm unfamiliar with, but with key in the run position, all the injectors have +12v going to both the hot and ground side... +12v on the ground wire can't be correct, right????
I'm pretty confident a few of those injectors are trash multecs that are shorted. Unplug all of them and put a noid light in they are easy to build and see if you get a pulse.
If one is shorted on that bank they all are, it's batch fire and all the grounds are tied together, then the grounds are switched by the ecu
Now, this TPI is something I'm unfamiliar with, but with key in the run position, all the injectors have +12v going to both the hot and ground side... +12v on the ground wire can't be correct, right????
This is fine and is what you will see as long as the engine is not running. The ECM grounds the injectors to cause them to open so as long as the ECM is not commanding the injectors to open you will see 12 volts on the ground side. The 12V power will flow through the coil on each injector and show 12 volts on the ground side, until the ECM grounds the ground side of the injector harness.
I understand. I'm going to pick up a noid light and ohm out the injectors next. 12 to 16 ohms, correct?
I did attempt to test the injectors the other day... I just used jumper wires to fire them. 7 of the 8 gave a very faint click. One made no noise at all.
I did this same stuff on mine, just go ahead and order new injectors from FIC. Those early ones are junk and 35 years old now. Same with a fresh pump, I did the TI Automotive aka Walbro for mine and a new filter. Pump came from Summit so I know it was authentic and not a knock off Going to need new gaskets for the runners, do not forget to plug in that IAT sensor like me. New FPR diaphragm smart too as while in there.
Did the old fuel have any stabilizing agent in it? If not, I would pump it out as who knows actually how old it is in there.
Im out autocrossing my 89 6spd today. Will look to see that relay in a few minutes. Main Fan comes on around 228F/108C
I wonder if one injector was fully shorted, would it tak all the voltage and not allow the others to fire?
Im not sure if they work like that.
for giggles, disconnect the shorted injector from the injector harness — the one with very little resistance — and attempt to start the car a couple times.
These cars will run with an injector disconnected, i know that for sure. It will run with a misfire, the hood will have a good shake to it in the open position, but it will run and drive. I had an 85 that was running on 7cyl because the harness connector had a broken wire at the connector.
I'm going to disconnect the TPS I'm try again. I heard if the ecm thinks the car is at WOT, it won't send an injector pulse.
I'm also going to tape over the VATS chip to see if it's still cranks. Hopefully this will verify that the VATS is working correctly.
Do these cars have any roll-over circuits that need to be reset? I know some cars have tilt sensors that shut fuel if they've been tripped.
I'm pretty certain the ecm is getting the tach reference signal too since the fuel pump activates while cranking.
Now, back to the ECM codes. The only code present is code 12, even if I do some thing that should trip a code, like unplug the MAF... would this indicate the ECM is bad?
good idea on unplugging tps. u r correct. wot on crank is flood clear mode. worth a shot.
try disconnecting the esc electronic spark control single plug connector by the brake master.
here is a pic of it.
disconnect this. then start try to start it. it should throw a code. also if you shor a+b on the aldl, that triggers the ecm to turn on the fan. So if that doesn’t happen, something is up
New Project! Lets get it running
New FPR diaphragm smart too as while in there. 
