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Anyone want to help start a C5?

 
Old 06-06-2019, 09:38 PM
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C5 Kirkland
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Default Anyone want to help start a C5?

1998 corvette ran great, so naturally, I wanted to add another 200+RWHP.
Stock LS1. Then I added a custom rear turbo from another forum member, bigger heads, cam, Lonnie's fuel pump, etc. No MAF, speed density 2 bar.
I also bought a used 2002 PCM and did the re-pin. Bought HP tuners, and installed (several different) tunes.

It will not start. It just turns over and over. I have checked and double-checked everything I can think of.
New battery, spark plugs, oil, coolant. I have 60psi fuel going through the lines, coils are working, battery has 12.6 volts.

If someone would like to come over and take a look, I can offer cash and decent company. I am just out of ideas, and I don't want to give up.
I live in Kirkland off of 100th and 136th (Juanita area).
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Old 06-06-2019, 10:55 PM
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NSFW
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PM coming in 3... 2... 1...
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Old 06-10-2019, 09:31 PM
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jdwtx85
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So your missing spark fire or inj squirt.
Have you checked either?
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Old 06-11-2019, 09:23 AM
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Turpid porpoise
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Try the BCM relearn procedure. Did you change the VIN in your tune to match your vehicle?
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Old 06-11-2019, 09:22 PM
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C5 Kirkland
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Originally Posted by Turpid porpoise View Post
Try the BCM relearn procedure. Did you change the VIN in your tune to match your vehicle?
Yes, the 30 minute version.
I don't have EFI live, so I can't change the VIN. I have a 2002 PCM, and that is what HP tuners is reading.
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Old 06-12-2019, 07:06 AM
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Turpid porpoise
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Is your tach moving while you crank or just sitting flat on zero?
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Old 06-12-2019, 09:05 AM
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Originally Posted by Turpid porpoise View Post
Is your tach moving while you crank or just sitting flat on zero?
Everything on the dash is flat/not on when I am cranking. Even the A-pillar gauges. As soon as I stop cranking, everything comes back on.
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Old 06-12-2019, 02:52 PM
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Turpid porpoise
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Do you smell fuel afterwards? If your tach isnt moving your car may not be seeing an rpm signal so the injectors and coils wont fire.

Check your crank/cam sensor plugs.

Last edited by Turpid porpoise; 06-12-2019 at 02:53 PM.
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Old 06-13-2019, 02:43 AM
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I came by to "help" today. The car still doesn't start, but I think we can rule out a few things.

What's weird is that every startup attempt begins with one loud pop that seems to indicate that fuel, air, and spark are all present... but then it just turns over quietly. I think that should be telling us something, but I don't know what.

We confirmed RPM, MAP and MAF readings using the data logger in HP Tuners.

RPM is around 250 while cranking - it fluctuates quite a bit but that seems reasonable given that it cranks with a chug-chug-chug rhythm to it. At least we know the PCM knows the engine is turning.

MAP was 15.2psi, which is higher than I'd expect but not unreasonable. We hooked a different MAP sensor to the wiring harness and confirmed that the signal varies when you blow in it, so that confirms that it's wired up correctly.

MAF is zero at rest and around 1.5 grams/second while cranking, which seems reasonable. It's using HPT's speed-density fueling upgrade, but since the PCM still reports a MAF reading, I'm guessing that the output from the SD math is used to calculate an equivalent MAF value that keeps the rest of the operating system happy. The fact that it goes nonzero during cranking seems to me like a good sign.

We tried smaller injector flow rates (slightly smaller and much smaller), on the theory that the flow rates might have been set too high, thus causing the PCM not open the injectors for a long enough period, thus causing too little fuel to get into the cylinders... That didn't make much difference. If I remember right, we didn't get the pop on the third try, which probably means the injector settings were way off at that point.

I guess we should have also tried a higher scaling (like 10% higher) just to see what happens.

We swapped in a different PCM, licensed it, applied HPT's 2-bar OS to it, copied the important tables to it (VE stuff, injector settings, some other odds & ends), and got the same results - pops then just cranks. So the PCM is apparently not the problem.

No security lights. Only one OBD2 fault code and it was for the gas cap.

it should start. But it doesn't.

Last edited by NSFW; 06-13-2019 at 02:46 AM.
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Old 06-13-2019, 07:23 AM
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Turpid porpoise
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Did you guys check the battery voltage with everything off? Is it on a tender?

Is the ground wire secured to the back of the drivers head?

Could try to pull one coil pack and plug out but leave them connected, crank the motor to make sure your getting spark. Obviously, disconnect the injector on that cylinder so you don't spray fuel everywhere.

Probably wouldn't hurt to go through all the fuses and make sure it's not something stupid like a blown fuse.

Completely irrelevant but I had an issue like this when I had Frost flash an OEM ECU for me and he failed to copy my VIN into the tune. I also had a similar loud pop without starting when I switched to the Haltech and messed up my crank trigger settings.
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Old 06-13-2019, 01:14 PM
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Battery reads 12.5 if I remember correctly. To rule that out we tried jump starting using my car with the engine idling. No change.

Plugs and wires are new but that's still a good test to try.

We talked about grounds a little, but since there are no trouble codes we didn't spend time checking them. Probably should anyway though.

It's a factory PCM with a 5.7L v8 tune so the crank trigger should be set up right... But would a bad cam sensor cause this kind of thing? There is no code for that but maybe the PCM just hasn't figured it out yet because it hasn't started yet? That seems like something that it should be able to detect during cranking though.
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Old 06-13-2019, 02:35 PM
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Turpid porpoise
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Originally Posted by NSFW View Post
It's a factory PCM with a 5.7L v8 tune so the crank trigger should be set up right... But would a bad cam sensor cause this kind of thing? There is no code for that but maybe the PCM just hasn't figured it out yet because it hasn't started yet? That seems like something that it should be able to detect during cranking though.
I'm not sure that the cam sensor would cause this but it wouldn't hurt to make sure the cam sensor and oil level plugs didn't get switched around at some point. If my memory serves me those two plugs look very similar and may be interchangeable.

I'm also not sure if the PCM would throw a cam sensor code if the engine isn't running, it's been so long since I've dealt with the OEM pcm.

We know that you need compression, fuel and spark to fire and it has fuel pressure and we're assuming it has good compression so we need to determine whether or not the engine is getting fuel and spark from the injectors/coils. Once we figure that out troubleshooting should be much quicker and easier.

Was anything changed on the coil pack harness during this rebuild process(relocation)? If so, they could be firing out of order.

Last edited by Turpid porpoise; 06-13-2019 at 02:36 PM.
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Old 06-13-2019, 03:11 PM
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Originally Posted by Turpid porpoise View Post
I'm not sure that the cam sensor would cause this but it wouldn't hurt to make sure the cam sensor and oil level plugs didn't get switched around at some point. If my memory serves me those two plugs look very similar and may be interchangeable.

I'm also not sure if the PCM would throw a cam sensor code if the engine isn't running, it's been so long since I've dealt with the OEM pcm.

We know that you need compression, fuel and spark to fire and it has fuel pressure and we're assuming it has good compression so we need to determine whether or not the engine is getting fuel and spark from the injectors/coils. Once we figure that out troubleshooting should be much quicker and easier.

Was anything changed on the coil pack harness during this rebuild process(relocation)? If so, they could be firing out of order.
Coils are stock, just using different brackets to attach to the valve covers.
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Old 06-13-2019, 11:30 PM
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I would guess you have a 12v signal requirement in the 2002pcm that you have pinned to a 5v source from the vette. A 5v source will look like 12v with a voltage check, but with crank will go down to 5v. Take all your 12v from pcm and run via fuse to battery terminal directly. It should fire at that point. I assume all good grounds in this scenario.
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Old 06-21-2019, 12:08 PM
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Originally Posted by merim123 View Post
I would guess you have a 12v signal requirement in the 2002pcm that you have pinned to a 5v source from the vette. A 5v source will look like 12v with a voltage check, but with crank will go down to 5v. Take all your 12v from pcm and run via fuse to battery terminal directly. It should fire at that point. I assume all good grounds in this scenario.
The only two 12v pins are 1867 and 631, and they are 12v for both pcm's.
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