Hi all, I'm bringing this problem back up after a few weeks of not messing with it. A couple of you may remember the issues I've been having with my 1992 RS. I was driving home from work back in January and the car up and died on me out of nowhere. I had it towed home, and it hasn't started since (except for one time it ran briefly and poorly).
The root problem here is no spark from the coil. Injectors are not firing as a result of no spark condition.
Here's what I've done to the car and the order in which I did it:

1) Checked codes, got 12, 13, 15. None are related to my problem.
2) replaced pickup coil.
3) swapped on a "known good" spark module (the one under the cap).
4) replaced coil.
5) replaced ECM
6) replaced distributor with remanned unit
7) Checked all wiring from ECM to every sensor, module, injector, etc. with Multi-meter and visually. Found no faults.
8) tests on pickup coil, ignition coil, and two different spark modules all come up good.
9) all system grounds verified good, with multi meter and visual inspections
10) I cleaned the coil mounting brackets with a wire brush to ensure a solid ground

I've checked for spark with the distributor 4-wire connected, disconnected, with the tach lead disconnected, everything. The rotor is turning when I crank the engine. I have 12v at the coil with ignition on, and 42psi at the rail while cranking.
Here's where things get a little more interesting:
The one and only time I've managed to get fire in the last three months was for about 5 minutes a few weeks ago. I had it hooked up via jumper cables to my Duramax (you may know a diesel truck uses two batteries, so plenty of juice). It started, but ran poorly because it was out of time. By the time I went and got my timing light and it got all hooked up, the car wouldn't start again and hasn't since.
The reason I find this interesting is because even though I have 12v at the coil with ignition on, it drops to about 9.5-10.5 while cranking, this was tested last night, only this time the jumper cables were hooked up to my buddy's Mustang (would have had to move it to hook up to the DMax again). Also, back when the car was running, I was noticing an intermittent problem at night. Sometimes the lights (all of them, headlights, dash lights, everything) would dim, and battery gauge would drop well below 12v while stopped at light, or in a drive through or parking lot... anytime the engine was at idle with the headlights on. Placing the car in neutral and raising the engine speed would alleviate this, and again, the problem was intermittent. The day the car broke down for good, it was a cold, rainy, gloomy day, and I did have my headlights on.

If you're still with me, here's my question: Is 9.5-10.5v at the coil while cranking "good enough", or has issue been a power problem all along? Or have I apparently overlooked a bad wire somewhere?

Thanks for the help!
(I posted this in the Electronics section too for greater exposure)

Dave

 

I have a short attention span, but I think I read the whole thing LOL. Maybe your computer is bad. I have a couple of spares but there for TBI. But I don't think that would make your lights go dim. Hmmm

 

Yeah, sorry about the post being so long. I had two other threads going for the same problem, but each one is about 30 posts long. Figured a quick summary would easier to understand

I really don't think this is an ECM problem: a)I've replaced it, and b)I'm still getting code 12 indicating that its working, at least supposedly.
I really don't think its related to the ignition system either. I did get it start, only once, but that tells me the components there are good.

And I appreciate your offer, but a TBI ECM won't work, the car is converted to Tuned Port.

I just think I need to start looking in a different direction, but not sure exactly which.

Thanks!

Dave

 

The lights dimming at low rpm is a sign of alternator trouble (look for open diodes). Only if you have under drive pulleys would this be normal.

At 8 volts my car will start (at zero degrees).

I would look for a loose/corroded connection (high resistance short) between the battery and alternator (they pass by the starter solenoid stud). Check the grounds also.

 

His idea sounds better than mine. Sounds like somethings loose.

 

Yeah, about the lights dimming, I was also assuming I had some alternator troubles coming. I'll probably just replace the stupid thing. I'll check the wiring for it thoroughly too.

So it sounds like my 9.5-10.5v at the coil while cranking is sufficient to start the car. Could my alternator issues have anything to do with my no start condition?
For clarification, when I was driving the car daily, the battery always seemed to maintain a good charge. Never any slow cranking or what not. The battery is only a little weak now (requiring a jump to crank the engine) because of repeated attempts to start the car, plus its been sitting for a couple months now. The engine will crank just fine, just no spark off the coil.

Thanks so far!

Dave

 

This isn't a vats sysem is it?

 

Yes, VATS is enabled. Its been suggested as a possible problem many times, but we've ruled out Vats so far becuase the car will crank all day long if you want. The way I understand Vats is that it disables the starter, however, I've looked a diagram that makes me wonder if it can cause a no-spark condition if the vats module was malfunctioning.

Dave

 

Do you have another spare key that you can try? My understanding is the chip is in the key. Possibly trying another one may tell you something. I don't know alot about them but there is more on the site if you do a search. Maybe the VATS disables the fuel and ignition.

Also do you know for sure that the car is getting fuel all the time? Can you hear the fuel pump running when the car is turning over? The reason I say this is you keep mentioning that you have voltage at the coil although low. With a fuel injected car if the fuel pump cuts off the engine starves for fuel immediately unlike a carb where it runs the fuel bowl out.

 

I've tried my spare key with no success.
I can't hear the fuel pump running when I turn the car on, but that's my fault. I don't hear well at all. I do have a fuel pressure gauge though and its reading 40-42 psi at the rail while cranking.
The coil is not providing spark, I've tested with my spark tester connected to the coil, not just one of the plugs. The injectors aren't firing either, but thats becuase of the no spark.

I'd like to test and make sure my spark module is getting the proper signals from the ecm, etc. Anyone know what readings I should be getting throught those terminals? I suspect the spark module isn't getting "turned on" or "activated" or whatever you'd call it, I'd like to verify and maybe figur eout why.

Dave

 

The pickup coil and the ignition module are the only things that are needed for a start. They also run the injectors. The dizzy supplies the pulses, that every fourth one fires the injectors (double fire) and every one fires the coil. Try disconnecting your est wire (like setting the base timing) should start and run. Est hooked up, and at 400 rpm, the ECM takes over and adds more timing advance.

 

Which distributor is in the car right now? Your old one or the one you swapped in that worked on another car.

 

It will not start and run that way. For some reason the distributor is not triggering the coil to spark, just can't figure out why.

The distributor is a new/reman unit I picked up from Autozone. I've tried the ignition module it came with, as well as a known good one I kept as a spare. Nothing helps.

Thanks for the replies. I'm open to any and all suggestions!

Dave

 

Tell Autozone their dizzy is defective. It wouldn't be the first time a new part from there was bad. They should even be able to check it themselves. I know they can check ignition modules.

 

sounds to me like u have a short in the battery sounds stupid but try replacing the battery. at 10.5 that tells me that u have a dead cell in batt

 

I really don't think the dist. is defective. Like I said in my initial post, I did get the car to start, once, briefly. That was with the new dist installed.

Bad battery? Intriguing. Would this have killed the car while driving? I was driving it home from work when it went t/u out of nowhere. The battery is less than six months old, I had just brought the car out of storage.

Dave

 

But if that's the case it still should start and run with jumper cables from another vehicle on it. Take the battery to Autozone and they'll check it for free.

 

The one time I got it to start and run for a few minutes, it was connected via jumper cables to the Duramax. The DMax carries two batteries, so I know for sure it was getting plenty of juice. Maybe I'll a battery out of it and see if it will start the Camaro.
I'm also gonna hit the junkyard tomorrow and pull every single ignition module I can find. I have two, one is new, the other known to be good, both tested good at Autozone... but I've heard of them testing good and being bad.

I'll keep you all posted. Thanks for the help so far.

Dave

 

Maybe this will help, I am not sure who wrote this.


L-98 Engine Start Sequence

When you start an L-98 engine Corvette, a series of events take place that causes the engine to run. Knowing the sequence will help you troubleshoot no start conditions.

Fuel Rail Pressurization:

When you first turn the key to the on position, the fuel pump will run for 2 seconds pressurizing the fuel rails. There is a Shraeder valve on the passenger side fuel rail near the rear of the engine and if you measure the pressure there after the pump runs, you should see between 40-42 pounds of pressure. The reading will go to 38-40 pounds nominal once the engine is running.

Initial Crank Action:

If you then rotate the key to the start position (assuming the anti-theft system has not disabled the starter), the engine will rotate.

Once the oil pressure has reached 4 PSI, the oil pressure switch will close allowing the fuel pump to run. (Note that you should have a black oil pressure switch/sender. It is mounted behind the distributor on the driver's side and if it is not black, it is suspect due to a run of bad units that stayed in the GM parts pipeline for some time).

The distributor will send a string of pulses to the ECM (Engine Control Module) in response to the engine being rotated by the starter. These pulses continue as long as the engine turns (both starting and running) and if they are not present, the engine will not run.


ECM Reaction:

If the ECM sees oil pressure greater than 4 PSI and the reference pulses from the distributor, it will energize the injector drivers which will begin pulsing the injectors on for 4 ms (milliseconds) periods. (In the L98, all injectors on one side of the engine fire at the same time followed by all injectors on the other side firing at the same time. On the LT-1, the injectors are fired individually at the appropriate time). Correction: Note all of the injectors fire (spray) at the same time. HoJo

The ECM will also pull in the fuel pump relay in effect paralleling it electrically with the oil pressure switch. (If the fuel pump relay fails, you can still normally get the car to start and run unless you can't make at least 4 PSI oil pressure. This is a limp home mode feature put in place to allow for a fuel pump relay failure).

The ECM also monitors the TPS (Throttle Position Sensor mounted on the throttle body assembly) and wants to see .54 volts at this time. If it sees appreciably more than 0.54 volts, it will assume the engine is flooded and the driver has pressed the accelerator to the floor to clear the flooded condition and restrict the fuel flow as a result. (.54 volts during start and at idle from the TPS is very important to both starting and run performance.)

Assuming the ignition module is good (meaning there is a spark of sufficient intensity to ignite the fuel), the engine will catch.

HTH

 

There's my problem. No spark at all.
I just got went to the local boneyard and pulled an alternator (looks like it was recently rebuilt/new), and three ignition modules. I installed the alt, then I tried the modules. None of them worked. Granted, they all came from a junkayrd, but this is now five different modules I've tried on the car, none of them have worked.
Maybe the new distributor from Autozone is bad after all. I can't find my receipt. Hope they'll take it back or exchange it.

Dave

 

Maybe - My 86 Roc did the same thing. After a lot of troubleshooting, I found the little rotor button in the dizzy broken in half. Replaced it and good to go!

It might be worth checking next time you go near the dizzy.

 

Any update?

 

"L-98 Engine Start Sequence" (do a web search)

This is posted one the c4vettes web page of www. corvettebuyers.com:

www c4vettes.com

"This web site no longer exists at c4vettes.com
The previous web master was kind enough to pass on its content to me."
(www. corvettebuyers.com)
"My personal gratitude goes out to him for this generous act."

There is more L98 info listed under fact sheets.

 

Look at the bottom middle of this print. It shows the wire paths from the dizzy to the coil. One of the wires or parts is not working/connecting.

Start at the pickup coil (pulses), then to the Ignition module (amp SW B applies ground to spark coil, pin "C" ), tan wire to "B" tan/blk (est connector, open to set base timing), then on to the ignition coil, rotor, cap, plug wires, and spark plugs.

This wiring diagram is shown in the, est open position (SW A is unenergized and SW B will pulse the ground to the spark coil). Running SW B directly from the pickup coil.

It has to be something right there, along that path.

Check power and grounds.

Est wire (connected) 0 volts key on, 4.6 engine on (cranking).
PPL- WHT wire pin "R" ignition module, 0 volts key on, 1.5 engine on (cranking).
WHT wire pin "E" ignition module, 0 volts key on 1.3 volts engine on (cranking).
Tan wire pin "B" ignition module, 0 volts key on, 4.75 volts engine on (cranking).
BRN wire pin "C" ignition module, 0 volts key on, 4 volts engine on (cranking).
SW B is the electronic "points" (old school).