Died and will not start
Thread Starter
Instructor
Joined: Aug 2014
Posts: 173
Likes: 9
From: Denver Colorado
I wonder if you're probing the right wires in the ECM Connector.
How can 16 wires simultaneously short to ground? Well you'll notice in teh diagram I posted that there are really only two wires going to the ECM. IT's a "batch fire" system (your '91 is the same as that '93 schematic) so one wire (Dk BLU #467) is grounded in the ECM and all 4 injectors on one side fire, and the other wire (Dk Grn #468) is grounded in the ECM and the other 4 injectors fire.
All you need is for one of those wires to be grounded to 100% duty 4 injectors, or two of the wires for all 8 injectors. Have you inspected those wires in the harness visually?
If the ECM is unplugged, I don't see how those injector wires could "see" ground, unless there was a short in the harness to ground.
How can 16 wires simultaneously short to ground? Well you'll notice in teh diagram I posted that there are really only two wires going to the ECM. IT's a "batch fire" system (your '91 is the same as that '93 schematic) so one wire (Dk BLU #467) is grounded in the ECM and all 4 injectors on one side fire, and the other wire (Dk Grn #468) is grounded in the ECM and the other 4 injectors fire.
All you need is for one of those wires to be grounded to 100% duty 4 injectors, or two of the wires for all 8 injectors. Have you inspected those wires in the harness visually?
If the ECM is unplugged, I don't see how those injector wires could "see" ground, unless there was a short in the harness to ground.
I will also unplug the ECM and check for shorts to ground. If there is one then that's that.
I see your point that each bank ties into a single wire to the ECM, but even so getting 2 wires to short to ground seems kind of unlikely. I will look at the harness but when you think about how the car just died while loping along at 40 mph it would seem like the ECM just bit the dust.
A short could do the same thing but those kind of things usually happen due to a rub or an accident- I guess that could have happened.
I'll look at the wiring and run my tests and if I can't find anything then I guess that I'll have to throw a non-refundable, $125 ECM at it
If it doesn't fix the issue then I'll have another spare to add to my growing collection....
Last edited by Rik O'Shay; Sep 10, 2014 at 11:22 AM.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
getting 2 wires to short to ground seems kind of unlikely.... when you think about how the car just died while loping along at 40 mph it would seem like the ECM just bit the dust.
A short could do the same thing but those kind of things usually happen due to a rub or an accident
A short could do the same thing but those kind of things usually happen due to a rub or an accident
I think your testing plans going forward are good.
Thread Starter
Instructor
Joined: Aug 2014
Posts: 173
Likes: 9
From: Denver Colorado
Ok some results.
!st thing I did this morning was to pull the injection fuses so that I could clear the cylinders of any excess fuel I pulled the fuses and the engine STARTED.
Now it ran rough so I shut it off. I figured it was running on whatever was left over in the engine.
I replaced the injector fuses.
Next I removed the ECM, completely disconnected and disconnected all of the fuel injector connectors from their respective injector.
I then checked the resistance of the injector pins to ground-
Cyl 1, 3, 5, 7 - Pink/Black wire - 8 ohms, Blue wire- .5 ohms
Cyl 2, 4, 6, 8 - pink/Black wire - 8 ohms, Green wire - OPEN/ Infinity
I then removed the injector fuses to isolate the wiring between the fuse box & the ECM connector.
Cyl 1, 3, 5, 7 - Pink/Black wire - OPEN/ Infinity, Blue wire- .5 ohms
Cyl 2, 4, 6, 8 - pink/Black wire - OPEN/ Infinity, Green wire - OPEN/ Infinity
So it looks like I have a short on the blue injector wire, right?
How this makes the other cylinders flood is beyond me though. Maybe the short cooked the ECM, I don't know.
I have looked at the blue wiring and not found anything yet. I have to unwrap the harness to see what I can see.
!st thing I did this morning was to pull the injection fuses so that I could clear the cylinders of any excess fuel I pulled the fuses and the engine STARTED.
Now it ran rough so I shut it off. I figured it was running on whatever was left over in the engine.
I replaced the injector fuses.
Next I removed the ECM, completely disconnected and disconnected all of the fuel injector connectors from their respective injector.
I then checked the resistance of the injector pins to ground-
Cyl 1, 3, 5, 7 - Pink/Black wire - 8 ohms, Blue wire- .5 ohms
Cyl 2, 4, 6, 8 - pink/Black wire - 8 ohms, Green wire - OPEN/ Infinity
I then removed the injector fuses to isolate the wiring between the fuse box & the ECM connector.
Cyl 1, 3, 5, 7 - Pink/Black wire - OPEN/ Infinity, Blue wire- .5 ohms
Cyl 2, 4, 6, 8 - pink/Black wire - OPEN/ Infinity, Green wire - OPEN/ Infinity
So it looks like I have a short on the blue injector wire, right?
How this makes the other cylinders flood is beyond me though. Maybe the short cooked the ECM, I don't know.
I have looked at the blue wiring and not found anything yet. I have to unwrap the harness to see what I can see.
Thread Starter
Instructor
Joined: Aug 2014
Posts: 173
Likes: 9
From: Denver Colorado
just got back in.
I looked at the blue wiring and these nicks wer all that I found-
They were not in a place that would short to ground but I will apply a lttle RTV to them to insulate.
Now here is what is weird again-
I check the resistance again and now the blue wires are not shorting to ground.....
I looked at the blue wiring and these nicks wer all that I found-
They were not in a place that would short to ground but I will apply a lttle RTV to them to insulate.
Now here is what is weird again-
I check the resistance again and now the blue wires are not shorting to ground.....
Thread Starter
Instructor
Joined: Aug 2014
Posts: 173
Likes: 9
From: Denver Colorado
Because I didn't have a consistent short/failure I went back & started wiggling the wiring bundles while I was checking for continuity between the blue wire & ground.
I didn't see any changes until I removed the line between the plenum and the brake booster.
I checked again and low & behold the short returned.
By moving the wiring harness right below the tube (circled in the photo) I could duplicate the short to ground.
So I gotta remove the wrap, fix the short, reconnect everything and see if it starts later today.
Looks like I may have to remove athe rear runner to get in there.
I didn't see any changes until I removed the line between the plenum and the brake booster.
I checked again and low & behold the short returned.
By moving the wiring harness right below the tube (circled in the photo) I could duplicate the short to ground.
So I gotta remove the wrap, fix the short, reconnect everything and see if it starts later today.
Looks like I may have to remove athe rear runner to get in there.
Last edited by Rik O'Shay; Sep 10, 2014 at 01:53 PM.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
HOT DAMN!! That is sweet! Pic? 
EDIT; There it is! That is some excellent diagnositc work that you did. Well done! I admire your tenacity to stick w/it. Imagine the labor costs you've saved yourself AND what you've learned about your own car. I'm thrilled for you.
EDIT; There it is! That is some excellent diagnositc work that you did. Well done! I admire your tenacity to stick w/it. Imagine the labor costs you've saved yourself AND what you've learned about your own car. I'm thrilled for you.
Last edited by Tom400CFI; Sep 10, 2014 at 01:58 PM.
Thread Starter
Instructor
Joined: Aug 2014
Posts: 173
Likes: 9
From: Denver Colorado
This was an unsheilded metal splice that was wrapped in cloth electrical tape and then the entire bundle wrapped in vinyl tape.
I would bet that the splice was shorting through the tape to the brake booster steel line > plenum > ground.
Took a bunch of pics that I will post up later detailing the repair AS IT SHOULD HAVE BEEN DONE by whoever made the harness.
This is something that other C4 owners are sure to experience.
Last edited by Rik O'Shay; Sep 10, 2014 at 03:29 PM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Pro
Joined: Mar 2009
Posts: 702
Likes: 259
From: Middletown Delaware
I found that under the electrical tape was a splice of the blue injector wires- 4 wires to one as depicted in the diagram.
This was an unsheilded metal splice that was wrapped in cloth electrical tape and then the entire bundle wrapped in vinyl tape.
I would bet that the splice was shorting through the tape to the brake booster steel line > plenum > ground.
Took a bunch of pics that I will post up later detailing the repair AS IT SHOULD HAVE BEEN DONE by whoever made the harness.
This is something that other C4 owners are sure to experience.
This was an unsheilded metal splice that was wrapped in cloth electrical tape and then the entire bundle wrapped in vinyl tape.
I would bet that the splice was shorting through the tape to the brake booster steel line > plenum > ground.
Took a bunch of pics that I will post up later detailing the repair AS IT SHOULD HAVE BEEN DONE by whoever made the harness.
This is something that other C4 owners are sure to experience.
Thread Starter
Instructor
Joined: Aug 2014
Posts: 173
Likes: 9
From: Denver Colorado
Ok, here's what I found under the taped bundle- the crimp wrapped in cloth tape-
I removed the cloth tape and here you can see the steel crimp-
I found no evidence of the crimp cutting into any of the adjacent wires, but in order to ensure that this doesn't happen again I slid a slit piece of tubing over the crimp-
After that I wrapped the splice and the bundle with electrical tape and then slid a piece of 3/4" slit plastic loom over the harness to protect it from further damage-
After that I taped the end with electrical tape and reinstalled the brake booster line-
Then I buttoned everything up and low & behold it started. The engine ran like crap so I shut it down and pulled the plugs to blow out any residual excess fuel.
Then I ran out of daylight.
I hope to have it up & running tomorrow morning....
I removed the cloth tape and here you can see the steel crimp-
I found no evidence of the crimp cutting into any of the adjacent wires, but in order to ensure that this doesn't happen again I slid a slit piece of tubing over the crimp-
After that I wrapped the splice and the bundle with electrical tape and then slid a piece of 3/4" slit plastic loom over the harness to protect it from further damage-
After that I taped the end with electrical tape and reinstalled the brake booster line-
Then I buttoned everything up and low & behold it started. The engine ran like crap so I shut it down and pulled the plugs to blow out any residual excess fuel.
Then I ran out of daylight.
I hope to have it up & running tomorrow morning....
Last edited by Rik O'Shay; Sep 11, 2014 at 12:00 AM.
Racer
Joined: May 2009
Posts: 261
Likes: 2
From: Boise Idaho
WOW! You are to be complemented on your perseverance!
Not only did you do yourself proud, and fix the problem....but now we all have a whole new trouble spot documented (I do not recall a thread about this before).
Good job!
Not only did you do yourself proud, and fix the problem....but now we all have a whole new trouble spot documented (I do not recall a thread about this before).
Good job!
Last edited by Black LS2; Sep 11, 2014 at 06:16 AM. Reason: Grammar
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Melting Slicks
Joined: Jan 2008
Posts: 2,054
Likes: 120
From: AZ
The larger lesson here, is that these 'new' cars rely on proper electrical flow and the FSM doesn't really address that, just as it doesn't address vacuum leaks. Either can severely affect operation as we have seen. Both are time-intensive yet require simple knowledge, inexpensive tools (and an FSM) but tons of patience! Any shop that will take this in will cost a fortune.
This is part of why I remarked that "I 'go' EMC failure as a last resort"; the real problem is simple as you said, but hard to find. I surmise that the holes in the wires at the injector wires indicate that someone was troubleshooting this before.
I am glad you shared your success and your lessons in good troubleshooting.
Last edited by whalepirot; Sep 11, 2014 at 11:27 AM.
Thread Starter
Instructor
Joined: Aug 2014
Posts: 173
Likes: 9
From: Denver Colorado
Thanks guys, but it still won't start...
I pulled the plugs again and they were all wet.
Also, I hooked up a new Innova 3120 OBD 1 & 2 scanner to the Vette and after inputting the info it required, it was unable to communicate with the computer.
On hold with Innova now....
Starting to think that the short took out the ECM.
I pulled the plugs again and they were all wet.
Also, I hooked up a new Innova 3120 OBD 1 & 2 scanner to the Vette and after inputting the info it required, it was unable to communicate with the computer.
On hold with Innova now....
Starting to think that the short took out the ECM.
Melting Slicks
Joined: Jan 2008
Posts: 2,054
Likes: 120
From: AZ
Okay, but I doubt that. It'd be grounding to ground.
Fuel and spark..... maybe something is disconnected. I have to stay slow and simple or my complicated mind gets lost!
I got a nice Innova, half price and like new, from a guy on CL. It reads many makes and OBD I and II, but has a learning curve and would not, initially, communicate with the '90 Camaro ECM, with custom chip, in my '84. It immediately 'read the '90 Mustang 5.0 GT ECM in our '55 Nash Rambler.
Actually, this is not weird, rather your prime indication that there was a wiring short. The injectors have a small coil inside, presenting around 14 ohms(?) to the circuit. If the ECM side of the injector wire is shorted, you'll see nearly zero ohms (short) as 4 injectors, wired in parallel on that bank, will normally indicate 1/4 that value; right around the DVOM's accuracy tolerance.
You'll get it. hang in.
Fuel and spark..... maybe something is disconnected. I have to stay slow and simple or my complicated mind gets lost!
I got a nice Innova, half price and like new, from a guy on CL. It reads many makes and OBD I and II, but has a learning curve and would not, initially, communicate with the '90 Camaro ECM, with custom chip, in my '84. It immediately 'read the '90 Mustang 5.0 GT ECM in our '55 Nash Rambler.
You'll get it. hang in.
Last edited by whalepirot; Sep 11, 2014 at 12:25 PM.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Thanks guys, but it still won't start...
I pulled the plugs again and they were all wet.
Also, I hooked up a new Innova 3120 OBD 1 & 2 scanner to the Vette and after inputting the info it required, it was unable to communicate with the computer.
On hold with Innova now....
Starting to think that the short took out the ECM.
I pulled the plugs again and they were all wet.
Also, I hooked up a new Innova 3120 OBD 1 & 2 scanner to the Vette and after inputting the info it required, it was unable to communicate with the computer.
On hold with Innova now....
Starting to think that the short took out the ECM.
Thread Starter
Instructor
Joined: Aug 2014
Posts: 173
Likes: 9
From: Denver Colorado
Okay, but I doubt that.
Fuel and spark..... maybe something is disconnected. I have to stay slow and simple or my complicated mind gets lost!
I got a nice Innova, half price and like new, from a guy on CL. It has a learning curve and would not, initially, communicate with the '90 Camaro ECM, with custom chip, in my '84.
Actually, this is not weird, rather your prime indication that there was a wiring short. The injectors have a small coil inside, presenting around 14 ohms(?) to the circuit. If the ECM side of the injector wire is shorted, you'll see nearly zero ohms (short) as 4 injectors, wired in parallel on that bank, will normally indicate 1/4 that value; right around the DVOM's accuracy tolerance.
Fuel and spark..... maybe something is disconnected. I have to stay slow and simple or my complicated mind gets lost!
I got a nice Innova, half price and like new, from a guy on CL. It has a learning curve and would not, initially, communicate with the '90 Camaro ECM, with custom chip, in my '84.
Actually, this is not weird, rather your prime indication that there was a wiring short. The injectors have a small coil inside, presenting around 14 ohms(?) to the circuit. If the ECM side of the injector wire is shorted, you'll see nearly zero ohms (short) as 4 injectors, wired in parallel on that bank, will normally indicate 1/4 that value; right around the DVOM's accuracy tolerance.
New ignition parts - AC Delco Rotor & Cap, B&D Ignition module, Petronix 50,000 volt coil, Moroso wires, AC Delco Iridium Plugs.
New Fuel pump, new Fuel Pressure Regulator too.
I just got done with the Innova Tech folks & we could not get the scanner to communicate with car, very frustrating. The only people that might be able to communicate with the car is a dealer and I really don't want to go there.
And everything is plugged in.
So I'm thinking ECM since it controls everything and there is no other reason for it not to start that I can think of. And since I had a verified short of the injector wire I think the computer might have got damaged.
At this point it's a new computer or a trip to the dealer.
Last edited by Rik O'Shay; Sep 11, 2014 at 01:05 PM.
Thread Starter
Instructor
Joined: Aug 2014
Posts: 173
Likes: 9
From: Denver Colorado
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
I'm with Whalepirot again; the short shouldn't have affected the ECM; IT's shorting a ground to ground...as far as the ECM is concerned.
Do you feel that this point, that the injectors are still flooding the engine? Or you don't know what is going on?
RE; testing the spark, if you can get the spark to jump a 1/2" gap or larger, that is a good enough spark. OR, if you install a plug in a cylinder, then have a wire jump a gap to the tip of that plug, that is proof that it is sparking in the cylinder, under compression; it HAS to jump the gap in the cylinder to get to ground. Either of those would fairly well prove that your have "enough spark".
I also agree with Whalepirot about the ECM. At this point, we haven't proven that it's bad...it's just a guess. You can spend the money, but I wouldn't make that recommendation at this point. Can you get the ECM to flash codes?
Do you feel that this point, that the injectors are still flooding the engine? Or you don't know what is going on?
RE; testing the spark, if you can get the spark to jump a 1/2" gap or larger, that is a good enough spark. OR, if you install a plug in a cylinder, then have a wire jump a gap to the tip of that plug, that is proof that it is sparking in the cylinder, under compression; it HAS to jump the gap in the cylinder to get to ground. Either of those would fairly well prove that your have "enough spark".
I also agree with Whalepirot about the ECM. At this point, we haven't proven that it's bad...it's just a guess. You can spend the money, but I wouldn't make that recommendation at this point. Can you get the ECM to flash codes?
Thread Starter
Instructor
Joined: Aug 2014
Posts: 173
Likes: 9
From: Denver Colorado
I'm with Whitewhale again; the short shouldn't have affected the ECM; IT's shorting a ground to ground...as far as the ECM is concerned.
Do you feel that this point, that the injectors are still flooding the engine? Or you don't know what is going on?
RE; testing the spark, if you can get the spark to jump a 1/2" gap or larger, that is a good enough spark. OR, if you install a plug in a cylinder, then have a wire jump a gap to the tip of that plug, that is proof that it is sparking in the cylinder, under compression; it HAS to jump the gap in the cylinder to get to ground. Either of those would fairly well prove that your have "enough spark".
Do you feel that this point, that the injectors are still flooding the engine? Or you don't know what is going on?
RE; testing the spark, if you can get the spark to jump a 1/2" gap or larger, that is a good enough spark. OR, if you install a plug in a cylinder, then have a wire jump a gap to the tip of that plug, that is proof that it is sparking in the cylinder, under compression; it HAS to jump the gap in the cylinder to get to ground. Either of those would fairly well prove that your have "enough spark".
Would the plugs be soaked if you cranked the engine with no ignition? Tons of fuel did not spill out of the cylinders (like before) now and all of the injectors continuity tests were good.
I am wondering if there is a bad part, maybe the new ignition module or the coil.
The spark is there but I can't tell if it is strong enough. I will strip an old wire back and see if it jumps the gap.