Weak spark, no start 1993 Corvette
06-27-2016, 04:56 PM
#1
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Weak spark, no start 1993 Corvette Got a 1993 Vette with weak spark and no start. I've checked all wires, good. Checked the opti, it was bad. Replaced it (MSD), still no start. Found ICM circuit open code, I put in the old ICM. Car ran great for about 10 minutes, then quit. ICM circuit open code came back. Got a new AC Delco ICM and coil, with heat compound installed. Still no start. Weak spark. Pulled Opti back out, opened it up to check the rotor, all was good.
So Opti is good. ICM is good. Injectors are pulsing. But still no start. It tries to, but just dies. I've tried to Data log it but can't get tuner pro RT to connect to the pcm, Damn CCM.
I'll need to check actual fuel pressure, the pump is priming and I can smell the fuel when trying to crank it. Maybe a leaking injector? Injectors are new, but the owner put in Accel injectors (this is before he brought me the car).
Any ideas?
So Opti is good. ICM is good. Injectors are pulsing. But still no start. It tries to, but just dies. I've tried to Data log it but can't get tuner pro RT to connect to the pcm, Damn CCM.
I'll need to check actual fuel pressure, the pump is priming and I can smell the fuel when trying to crank it. Maybe a leaking injector? Injectors are new, but the owner put in Accel injectors (this is before he brought me the car).
Any ideas?
06-27-2016, 05:35 PM
#2
well a FP check with gauge will rule in/out that quickly. Pump can still make a prime sound but be putting out next to no FP
You have gone through what would typically cause this issue....but, if you have not, check the wires that are all together at the coil/head mount on DS. A crack/break in one of those wires will cause a no run condition. Un-tape them and look carefully for any cracks/breaks in a wire.
Long shot but happened to me....the 4 pin connector that goes in opti. Remove it and carefully tug each wire at connector. My brown wire was never crimped when made and caused several sudden no start/run issues until I gave a small tug (read just touched it) and the brown wire just came out.
You will have to find your own needle in the haystack. Good luck
You have gone through what would typically cause this issue....but, if you have not, check the wires that are all together at the coil/head mount on DS. A crack/break in one of those wires will cause a no run condition. Un-tape them and look carefully for any cracks/breaks in a wire.
Long shot but happened to me....the 4 pin connector that goes in opti. Remove it and carefully tug each wire at connector. My brown wire was never crimped when made and caused several sudden no start/run issues until I gave a small tug (read just touched it) and the brown wire just came out.
You will have to find your own needle in the haystack. Good luck
06-27-2016, 06:08 PM
#3
What's the cars history? Low miles? Well taken care of? Stock? If higher miles and modified (especially MSD 6al, coil opti etc...) id check the wiring going to any of those aftermarket ignition components. Maybe the opti harness?? Check the FP first though, look around on Craigslist and pick n pulls for a set of stock injectors to see if that eliminates the problem. Maybe a loose ground, who knows. Like the above post mentioned, you'll find the needle in the haystack eventually. Hope it's sooner than later!
06-27-2016, 08:03 PM
#4
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I've checked all the wires already. The Opti harness is new. All the wires check out good with voltage, continuity, and ground as required. The only exception is the tach signal wire is exposed, but that only signals the tach IIRC on the IP so it should have no effect.
I'll have to get a new fuel pressure gauge as my adapter got lost in my last move. I'll have to find some time to get to a parts store and buy one, lol.
After that it'll be a compression check.
I'll have to get a new fuel pressure gauge as my adapter got lost in my last move. I'll have to find some time to get to a parts store and buy one, lol.
After that it'll be a compression check.
06-28-2016, 03:22 PM
#6
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Um, it's almost a spark. Barely visible. And you can't hear it at all. On my Camaro it's a loud crack with every spark, very loud and bright (I don't even need to see the color as the intensity of the noise is enough to call it good). With the Vette, you can barely see it and you can't hear it at all.
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06-28-2016, 10:54 PM
#8
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06-29-2016, 03:08 PM
#12
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Alright all, I got me a new fuel pressure gauge from Auto Zone. Hooked it up and primed to 5 psi..... 5. 5 freakin PSI. Not to be without question, I tested the gauge on my Camaro, 45 PSI during prime, holds 38 after prime. So the gauge isn't faulty, the Corvette has 5 PSI of fuel pressure.
So I found the reason for no start. This doesn't explain the weak spark, but MAYBE the spark is weak due to battery only and maybe the battery doesn't have enough juice to crank the motor AND give strong spark at the same time?? I did trickle charge the battery, but I've been doing all the tests on just battery and I didn't check for spark strength until I had tried to get it to start checking everything else I just installed first.
New question. I have my stock fuel pump (just the motor) from my Camaro sitting on the shelf in my garage. Does anyone know if the pump motors are the same between the Vette and F-Bodies??
Thanks everyone.
06-29-2016, 03:31 PM
#13
Since you have to pull the one from the Vette, compare it to the one you have from Camaro. If same physical size I would think it would work as both have the LT1 motor
and yeah a FP gauge is a must have in the tool box :-)
06-29-2016, 04:50 PM
#15
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in looking up 93 vette and 95 camaro the AC Delco part # is different on rockauto.com....with that said IDK difference.
Since you have to pull the one from the Vette, compare it to the one you have from Camaro. If same physical size I would think it would work as both have the LT1 motor
and yeah a FP gauge is a must have in the tool box :-)
Since you have to pull the one from the Vette, compare it to the one you have from Camaro. If same physical size I would think it would work as both have the LT1 motor
and yeah a FP gauge is a must have in the tool box :-)
06-29-2016, 06:17 PM
#16
yeah I run the Walbro 255. Put it in at least 10 years ago as a direct replacement of the OEM one in my B-body. I took the old pump out of the whole sending unit and swapped pump only.
assume you could do the same with the Y body.
assume you could do the same with the Y body.
07-05-2016, 06:04 AM
#17
To eliminate fuel, grab a can of starter fluid and spray while you crank and see if it runs on starter fluid.
If you have 5.5psi, fuel filter, then pull the tank and look at the pumps. You have to replace it anyways, even dangling the spare in there to fire it will eliminate that.
If you have 5.5psi, fuel filter, then pull the tank and look at the pumps. You have to replace it anyways, even dangling the spare in there to fire it will eliminate that.
07-05-2016, 12:51 PM
#18
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Don't need to drop the tank on a C4 to pull the fuel pump. Probably one of the easiest pumps I've ever done, seriously. Dear GM, please, for the love of all that's holy, please, I beg you, do ALL your fuel pumps like the C4 Corvette!
It is obvious this car sat around for a while though. Lots of surface rust on the pump sending unit. The sock was black too. Just got to put some fuel in her and give her a test run.
It is obvious this car sat around for a while though. Lots of surface rust on the pump sending unit. The sock was black too. Just got to put some fuel in her and give her a test run.
