Hi Guys,

Did a search on this but no luck as some ended with no solution or slightly different problem so any help will be GREATLY appreciated!

The car will crank, but will not start.
1992 stock Corvette automatic.

1. There is fuel verified to the rail @ 43psi.
2. Spark verified to coil and plugs. Car will start and run great for a second with a shot of starting fluid.
3. There is 12v to injector pink wires with KeyOn/EngineOff. No pulse to ground (green/blue wires) when cranking with test light to positive source, so the injectors are not firing it seems due to no pulsing ground.
4. All fuses are good and there are no trouble codes verified by grounding ALDL terminals A to G.

Anyone know of any diagnostics to figure if the computer could be the culprit of the no pulse condition?

Can the car still have strong spark but yet no ground injector signal from the opti?

Thanks in advance!

Can the car still have strong spark but yet no ground injector signal from the opti?
Anyone know of any diagnostics to figure if the computer could be the culprit of the no pulse condition?

Other than elec fault ( wiring / connection ) too high a TPS setting will shut the injectors down while cranking because it thinks your are trying to clear a flooded engine

The diagnostics are in the FSM ; the presence of the CCM makes '90+ a lot harder to troubleshoot than earlier cars

There were no codes in Module 4 the CCM module ?

CCM related faults or a fault in the ECM to CCM data link will prevent injector pulse

Other than elec fault ( wiring / connection ) too high a TPS setting will shut the injectors down while cranking because it thinks your are trying to clear a flooded engine

The diagnostics are in the FSM ; the presence of the CCM makes '90+ a lot harder to troubleshoot than earlier cars

That's a good idea, I didn't think about the TPS setting. I don't have a scan tool, is there any way to jump it and check the voltage w/a multi meter?

Thanks!

There were no codes in Module 4 the CCM module ?

CCM related faults or a fault in the ECM to CCM data link will prevent injector pulse

No codes the last time that I tried. I'll try cranking it again tonight and recheck those codes. I have been disconnecting the battery a lot, so I'll try leaving it connected for a while this time. I have a GM service manual and followed one section of tests down until it said replace ECM. The only problem is that I did have to skip one diagnostic due to no scan tool (tech 1). That step asked if it was reading RPMs while cranking, so I may assume that there was none and follow that diagnostic path tonight. I'm just praying that it's not the opti as it is a pain in the tail to replace, which leads me to another question: In replacing the opti, can it be done by removing the balancer (3 bolt part) and leaving the pressed hub on?

Thanks!

to check your tps you dont need scan tools besides a mulitmeter and three jumper wires

http://www.ecklers.com/product.asp?pf_id=41422&dept_id=1306


ok this is how you do it

1. turn the car off
2. unplug your tps plug
3. contect one wire to each prong to the correct prong on the plug.
4. turn the car power on
5. insert multimeter leads into the 2 outside prongs of the tps read the voltage.
6. if you havnt done so alrady i would recomnd and ajustable tps kit as i put the link above for you.
7 adjust it tot he correct voltage be carefull its tough.
8. take juper wires out and reconnect tps.
9. start her up.
10. send me money for the advice. lol

to check your tps you dont need scan tools besides a mulitmeter and three jumper wires




ok this is how you do it

1. turn the car off
2. unplug your tps plug
3. contect one wire to each prong to the correct prong on the plug.
4. turn the car power on
5. insert multimeter leads into the 2 outside prongs of the tps read the voltage.
6. if you havnt done so alrady i would recomnd and ajustable tps kit as i put the link above for you.
7 adjust it tot he correct voltage be carefull its tough.
8. take juper wires out and reconnect tps.
9. start her up.
10. send me money for the advice. lol

Sounds easy enough, I'll try that tonight. I had a turbo regal several years ago and was able to check the TPS on a laptop with a product called turbo scan, so I have adjusted one before but it's been a while. Also, just for giggles, I ordered a used GM ECM off Ebay today just in case for 90 bucks. Even if that's not it, I'm told that they (92-93 ECMs) are hard to find so I can just turn it if that's not it. If it's the TPS, checks in the mail, haha! ;>)

Sounds easy enough, I'll try that tonight. I had a turbo regal several years ago and was able to check the TPS on a laptop with a product called turbo scan, so I have adjusted one before but it's been a while. Also, just for giggles, I ordered a used GM ECM off Ebay today just in case for 90 bucks. Even if that's not it, I'm told that they (92-93 ECMs) are hard to find so I can just turn it if that's not it. If it's the TPS, checks in the mail, haha! ;>)

OK, more info from tonight:
1. TPS voltage within the proper range
2. Checked ohm readings across all injectors, within spec at around12.5 for all 8.
3. Rechecked codes and did find one in the ECBM which is not related to the CCM or the ECM.

Any more thoughts? I don't know if it matters but the hood is off the car and that harness is unplugged but I'm not sure if that would matter.

Thanks guys, this heap is driving me crazy.

is your fuel pump comoing on

ok you have fuel no codes no nothing does the car start to crank over if so i have had the same issue beofre ok this is a pain in the butt to do but worth it take your driverside fender off and your battery take out the tray underneath the tray there is a bunch of wires there is a fusable link inside the wiring harness the link is orange and has a black plastic cover over a small secton of that check for continutiy between the two sides of the wire. if ther is then the fusable link is good if ther isnt replace the link do not go to a gm dealer to get the link just buy one at autozone all of your symptoms seem to point to this as it wont trhow a code but it will turn everything on and look like its working properly but infact it runs into your ecm and makes it a fault but not a code will pop up try this and tell me what you get man if any other issues call me at 6039570059

2. Checked ohm readings across all injectors, within spec at around12.5 for all 8.


Don't believe it is your problem but injectors should be closer to 17 ohm
However the ECM will shut the injector pulse down if it see the incorrect resistance in the injector circuits
What does your FSM say about checking injector loop.I onLy have books for L98

ok you have fuel no codes no nothing does the car start to crank over if so i have had the same issue beofre ok this is a pain in the butt to do but worth it take your driverside fender off and your battery take out the tray underneath the tray there is a bunch of wires there is a fusable link inside the wiring harness the link is orange and has a black plastic cover over a small secton of that check for continutiy between the two sides of the wire. if ther is then the fusable link is good if ther isnt replace the link do not go to a gm dealer to get the link just buy one at autozone all of your symptoms seem to point to this as it wont trhow a code but it will turn everything on and look like its working properly but infact it runs into your ecm and makes it a fault but not a code will pop up try this and tell me what you get man if any other issues call me at 6039570059

I'm willing to try anything at this point so I'll give it a try. What is the exact function of this wire? Thanks for the advice and phone number, that was very nice of you. Also, as an FYI, the car does have fuel and properly timed spark and will start with a squirt of starting fluid. It seems that the missing link is a timed injector ground, so there is no pulse thus no fuel entering the injector ports.
Thanks!

Don't believe it is your problem but injectors should be closer to 17 ohm
However the ECM will shut the injector pulse down if it see the incorrect resistance in the injector circuits
What does your FSM say about checking injector loop.I onLy have books for L98

From what I have read an injector will be considered shorted at around 6 OHMS and the loop will shut down. I did follow the injector loop by the service manual. 12 volts on all of the pink wires. Disconnected all injectors and followed the ground side to the ECM harness, it is one wire for each side, a dark green and a dark blue. The FSM says check this ground circuit for voltage (in case of a bare or shorted 12 volt source arcing) and it checked out fine. I hope that I'm not missing something simple and old timers kicking in, hehe. I do have another ECM on the way so that I can eliminate that as a possible failure. I'm still praying to the GM Gods that it's not an opti related failure. Many, many thanks!

It sounds very likely that the problem is in the ECM. Unfortunately the 92 ECMs are known to have problems and replacements are hard to find.

It sounds very likely that the problem is in the ECM. Unfortunately the 92 ECMs are known to have problems and replacements are hard to find.

I hope that you are right as it's a 1 minute switch as the old one is already hanging loose. Hopefully my "new" used one will show up this week and answer this question. Can anyone answer the optispark question? Can the opti be removed by simply unbolting the balancer and leaving the pressed hub on the crank snout?

Thanks!

I hope that you are right as it's a 1 minute switch as the old one is already hanging loose. Hopefully my "new" used one will show up this week and answer this question. Can anyone answer the optispark question? Can the opti be removed by simply unbolting the balancer and leaving the pressed hub on the crank snout?

Thanks!

Yes, that is actually the best way to do it. Soak it good with BP Blaster the day before and you might have to use a 2"x2" piece of wood and a BFH from underneath to get it to break loose from the hub.

Yes, that is actually the best way to do it. Soak it good with BP Blaster the day before and you might have to use a 2"x2" piece of wood and a BFH from underneath to get it to break loose from the hub.

That's a relief! I wasn't looking forward to trying to squeeze a puller in there and remove that hub if it came down to that, but I hope that it isn't the opti due to labor and part cost.

I know its been answered already but I just did mine not too long ago and after the 3 bolts come out it practically fell off. No hammer needed. Just a bf screwdriver.

I know its been answered already but I just did mine not too long ago and after the 3 bolts come out it practically fell off. No hammer needed. Just a bf screwdriver.

That does make me feel better and I do have a bf screwdriver AND a rbf hammer, hehe! If I don't get it straightened out soon anyone wanna see what a C4 looks like on fire and melting?
J/K!!!!

If you have to replace the opti this might help.
http://forums.corvetteforum.com/c4-tech-performance/2461779-replacement-optispark-and-water-pump-install-part-1-includes-pictures.html

If you have to replace the opti this might help.
http://forums.corvetteforum.com/c4-tech-performance/2461779-replacement-optispark-and-water-pump-install-part-1-includes-pictures.html

Wow, great write up. Thanks for the tip!

Wow, great write up. Thanks for the tip!

No problem. Just a quick note that you don't have to take the throttle body off.

Hi Guys,

Did a search on this but no luck as some ended with no solution or slightly different problem so any help will be GREATLY appreciated!

The car will crank, but will not start.
1992 stock Corvette automatic.

1. There is fuel verified to the rail @ 43psi.
2. Spark verified to coil and plugs. Car will start and run great for a second with a shot of starting fluid.
3. There is 12v to injector pink wires with KeyOn/EngineOff. No pulse to ground (green/blue wires) when cranking with test light to positive source, so the injectors are not firing it seems due to no pulsing ground.
4. All fuses are good and there are no trouble codes verified by grounding ALDL terminals A to G.

Anyone know of any diagnostics to figure if the computer could be the culprit of the no pulse condition?

Can the car still have strong spark but yet no ground injector signal from the opti?

Thanks in advance!

Well, finally got the new ECM installed and it's still not the problem. I've got the Opti off (thanks for the instruction video) and I'm trying to decide what kind to buy as I'm not planning on keeping this car much longer. I've heard too much bad about the Cardone, so that choice is out. Anyone had experience with the other brands out there such as Summit, Jegs, Richporter, etc? Thanks!

Other than elec fault ( wiring / connection ) too high a TPS setting will shut the injectors down while cranking because it thinks your are trying to clear a flooded engine

The diagnostics are in the FSM ; the presence of the CCM makes '90+ a lot harder to troubleshoot than earlier cars

The injectors only shut off at WOT during cranking. Don't think thats your problem. If your not getting the ground path required to fire the injectors it sounds like the ECM is bad:friday:

Well if it's not the ECM then start checking your grounds sorry didn't read your last post

I dont know if this is your problem or not. But several weeks ago I had a problem with my 93. At about 70 MPH it flat died. Tried to start several times but never did. After pulling the optispark out and looking at it and changing a couple rat chewed wires I decided the opti had to be good. I put it back in and replaced the ignition module. Still didnt fix it. Finall I tried a coil off my old 93 suburban and it cranked right up. The cheapest part of the whole ignition system was the problem. I dont know if it was getting fuel or not but I do know the plugs were never wet anytime I pulled one and I never got any sign of fire. Before you pull the opti you might want to try a $20 coil

Well if it's not the ECM then start checking your grounds sorry didn't read your last post

All of the grounds appear to be fine, but I'm at a loss to yet find a schematic that shows exactly which wire off of the ECM harness that it uses for the injector ground pulse. I have checked all of the ECM harness grounds that go directly to ground and they check out. Thanks!

I dont know if this is your problem or not. But several weeks ago I had a problem with my 93. At about 70 MPH it flat died. Tried to start several times but never did. After pulling the optispark out and looking at it and changing a couple rat chewed wires I decided the opti had to be good. I put it back in and replaced the ignition module. Still didnt fix it. Finall I tried a coil off my old 93 suburban and it cranked right up. The cheapest part of the whole ignition system was the problem. I dont know if it was getting fuel or not but I do know the plugs were never wet anytime I pulled one and I never got any sign of fire. Before you pull the opti you might want to try a $20 coil

Have a spare coil/module assy and it was still the same with it connected. The opti is already off and I'm still trying to decide which one to buy, maybe something went wrong with the optical wheel inside? Sheesh, this is my first LT1 and it may be my last!! Thanks for the input, guys, all is appreciated!

Hi Guys,

Did a search on this but no luck as some ended with no solution or slightly different problem so any help will be GREATLY appreciated!

The car will crank, but will not start.
1992 stock Corvette automatic.

1. There is fuel verified to the rail @ 43psi.
2. Spark verified to coil and plugs. Car will start and run great for a second with a shot of starting fluid.
3. There is 12v to injector pink wires with KeyOn/EngineOff. No pulse to ground (green/blue wires) when cranking with test light to positive source, so the injectors are not firing it seems due to no pulsing ground.
4. All fuses are good and there are no trouble codes verified by grounding ALDL terminals A to G.

Anyone know of any diagnostics to figure if the computer could be the culprit of the no pulse condition?

Can the car still have strong spark but yet no ground injector signal from the opti?

Thanks in advance!


If it will run on a shot of starting fluid, then that means your ignition system is ok and your injectors aren't firing. Now you have to find out why..............

If it will run on a shot of starting fluid, then that means your ignition system is ok and your injectors aren't firing. Now you have to find out why..............

Good point. I agree.

Have a spare coil/module assy and it was still the same with it connected. The opti is already off and I'm still trying to decide which one to buy, maybe something went wrong with the optical wheel inside? Sheesh, this is my first LT1 and it may be my last!! Thanks for the input, guys, all is appreciated!

Worked on this rolling pile this weekend with no luck. I'm now trying to decide to either sell it or seek professional help. Would be willing to sell minus engine cheap so if anyone is looking for a prostreet/racecar project... Here is what has been diagnosed thus far.

Car will crank but will not start. Will start for a second or two with a shot of starting fluid.

1. Have good fuel pressure and spark. Ground circuit on both fuel injector banks are not pulsing to ground.
2. Tried a different ECM, same condition.
3. Tried another coil/module, same condition.
4. Installed a different opti, same result.
5. Pulled all 6 grounds from back of engine, inspected for breaks, cleaned, reinstalled, same result.
6. Checked all fuses and power to injectors, same result.
7. Checked CCM and ECM codes, none there.
8. Car now has no "security" or "sys" lights on any time at all, bad CCM perhaps? I do know that the CCM has to allow a signal called "feds" for the car to start.

Also forgot to add that TPS voltage was checked and was at .60 closed which is a tad high but should be a non factor.

Maybe this was mentioned before but check if your fuel tank breather is not blocked and maybe the fuel is contaminated??

Maybe this was mentioned before but check if your fuel tank breather is not blocked and maybe the fuel is contaminated??

I don't believe so. I've got about 44 psi at the rail and the injectors aren't pulsing. The tank was also empty and I put in 5 gallons of premium. Keep 'em coming guys, I'm desparate, hehe.

This is for the L98 maybe it will help??

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).

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”.

Engine "Catches":

When the engine

Worked on this rolling pile this weekend with no luck. I'm now trying to decide to either sell it or seek professional help. Would be willing to sell minus engine cheap so if anyone is looking for a prostreet/racecar project... Here is what has been diagnosed thus far.

Car will crank but will not start. Will start for a second or two with a shot of starting fluid.

1. Have good fuel pressure and spark. Ground circuit on both fuel injector banks are not pulsing to ground.
2. Tried a different ECM, same condition.
3. Tried another coil/module, same condition.
4. Installed a different opti, same result.
5. Pulled all 6 grounds from back of engine, inspected for breaks, cleaned, reinstalled, same result.
6. Checked all fuses and power to injectors, same result.
7. Checked CCM and ECM codes, none there.
8. Car now has no "security" or "sys" lights on any time at all, bad CCM perhaps? I do know that the CCM has to allow a signal called "feds" for the car to start.
OK try this only take an hour to do it
take out fuel rail and all fuel injector clean it. it very symple 4 bolt holding the fuel rail and 2 fuel line (a fuel line removed tool ) d/c fuel line
take it out ,take all injector out and use air compressor blow clean all injector and fuel rail use some gas or cab.to cleaner it.
you may need to get new O ring set Only $8.00
and put it back together It will fire right up
Hope that will help you to fix your car:friday:

It looks like you have done a thorough job of diagnosing the no start problem and are down to the fact the ECM is not sending the ground pulse to the injectors. Now the question is why no pulse? Once that is found it is probably easy to correct and you will be good to go. When you checked codes did you get a C12? Same with the second ECM? If the answer to both is yes then I would be suspicious of the VATS system. VATS does two things 1. Disable the starter (not a problem here) and 2. Disable the injectors by not letting the ECM send the ground pulses. Your not getting a security light might be a clue as well.

OK try this only take an hour to do it
take out fuel rail and all fuel injector clean it. it very symple 4 bolt holding the fuel rail and 2 fuel line (a fuel line removed tool ) d/c fuel line
take it out ,take all injector out and use air compressor blow clean all injector and fuel rail use some gas or cab.to cleaner it.
you may need to get new O ring set Only $8.00
and put it back together It will fire right up
Hope that will help you to fix your car:friday:

Did you try this fix? Did it work? I am having the same problem on an 86.

It looks like you have done a thorough job of diagnosing the no start problem and are down to the fact the ECM is not sending the ground pulse to the injectors. Now the question is why no pulse? Once that is found it is probably easy to correct and you will be good to go. When you checked codes did you get a C12? Same with the second ECM? If the answer to both is yes then I would be suspicious of the VATS system. VATS does two things 1. Disable the starter (not a problem here) and 2. Disable the injectors by not letting the ECM send the ground pulses. Your not getting a security light might be a clue as well.

Update! Two things here. One is that I was getting a vats message on a snap on scanner, not sure why as I'm getting pulse now. I also removed all of the plastic shielding from the injector wiring and I found some bare wires. I believe that my injector grounds were grounded to another ground thus not allowing the pulsing ground to function properly. It is running really crappy but I still have some loose sensor wires to reinstall. I'll keep you guys posted once I button everything up as it looks like someone "bubba'd" some of the wiring. Thanks for all the ideas, it was really appreciated!

Did you try this fix? Did it work? I am having the same problem on an 86.

I haven't tried this but may as it is running now but not well. Wouldn't you have to blow each end as it's not open all the way through unless it has voltage, correct?

Update! It is running really crappy but I still have some loose sensor wires to reinstall.
At least now you have it running so you know it is not a VATS / CCM problem.
If you look at the factory connections on the injector wires in the loom, the five wires are just crimped together and wrapped in black tape

My 93 was doing that after I blew-up my alternator (in pieces). That sent something to the computer. The computer thought someone was trying to steal the car and it would not start.
Could be a computer problem.