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Hey guys, it's been a long time (probably close to 10 years) but I used to be pretty active on here back in the day. I have had my 96 Formula now since 2010, and it's been ripped apart since 2012. What started as a heads and cam swap was stalled by a marriage, kids, new house, etc. I held onto the car and accumulated parts over the years, and put together a pretty nice car.

383 LT1 M6

Ohio Crankshaft forged crank
Ohio Crankshaft 6" H-beams
SRP Flat Tops (Forged with 5cc valve reliefs)
LE2 heads/ported intake
237/249 cam
spec billet flywheel
spec 3+clutch
rebuilt T56
new fuel lines, tank, Walbro 255 fuel pump, sending unit, fuel pump wiring harness
ford 30lb injectors
95pcm swap with knock sensor and LT4 knock module

While the engine was out, I pulled the engine harness and front body harness completely out, relocated the fuel lines, had the hole professionally filled, had the engine bay painted black (white hardtop Formula - the engine bay was bad) and reinstalled the wiring harness. Got the shortblock back, put everything together and the car fired right up! (hold your applause, even though this was almost 9 years after I started taking the engine apart) Ran the car for about 90 seconds.

Shut the car off, put the hood, nose, lights, etc on. started the car again, backed it up a few feet and shut it off. Ran for maybe a minute. Plugged in the laptop and started a datalog, then drove the car around the block twice. Ran for 9 mins. Pulled the car in and noticed the heater bypass hose was leaking a bit. Jacked the car up, drained the coolant through the radiator, stacked rags around the opti and changed the hose. Liquid was minimal and I don't think the opti even got wet.

The car was idling at like 1700-1800 and the MAF was pinned at like 431 on EEhack on that first 9 minute drive. Tuner said before I started it again to unplug the MAF to rule out a vacuum leak. Unplugged MAF and went to start the car - it chugged once and then cut out. This was back in April. I have a GM service manual and have gone through the trouble trees, I have checked the following:

opti checked out - replaced it twice just to be sure this wasn't it. original unit was my old GM opti, I pulled it apart and it looks great still
ICM checked out, replaced it to be sure
MSD coil checked out, tried two others to be sure
spark at plugs
compression
fuel pressure is 45psi and holds while cranking
injectors are pulsing - verified with noid light and pulled and bench tested each injector

I even tried a harness from a friend's car but I think it was for a 94 (pcm wouldn't read and fuel pump never primed).
I had some tranny codes (95 auto PCM in 96 M6)
I had a MAF code, found a burnt wire on the pigtail and repaired it.

I tried my 96 PCM just to see if it would try to fire and nothing. I don't have the crank sensor or wheel on the car though, so I can't rule out the 95 PCM. I can still connect with EEHack and FlashHack, as well as my Actron scanner so I don't think it's the PCM. The car is not trying to fire at all, no pops or backfires through the intake either.

VATS is bypassed in the tune. The fuel pump relay under the drivers kickplate checked out too.
I checked the fuses and all check out. The only burnt wires I found were on the MAF and were repaired after the car chugged and died.

I've been all over Shoebox's site, my GM service manual and Haynes manual trying to figure out what is going on. I just want to drive this thing. I feel like it has to be something dumb but I'm too close to see it. Sorry for the book, any advice is appreciated!

Chrys
 

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So you replaced the opti. If you didn't buy a GM, Delco, or Delphi opti, this could be your trouble.

Invest in a $70 PC based oscilloscope. It's the only 100% way to check the low & high resolution pulses that opti sends out. Learn to use the scope, if you don't already know how.

The low & high res pulses from opti should be a nicely formed square wave. With no drop outs or waveform changes.

If you bought any opti besides the 3 I mentioned, it's likely to be dead right out of the box.
 

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Discussion Starter · #3 ·
So you replaced the opti. If you didn't buy a GM, Delco, or Delphi opti, this could be your trouble.

Invest in a $70 PC based oscilloscope. It's the only 100% way to check the low & high resolution pulses that opti sends out. Learn to use the scope, if you don't already know how.

The low & high res pulses from opti should be a nicely formed square wave. With no drop outs or waveform changes.

If you bought any opti besides the 3 I mentioned, it's likely to be dead right out of the box.
Thanks Coco, that's kind of why I replaced the opti a second time. I will pick up an oscilloscope. Any advice on which one to get? Checking out Amazon there are a few different ones.
 

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I use the Hantek model 6022BE It's a PC based scope. It has dual channels so you can test both low & high res signals at the same time.

If you've never used an oscilloscope, the hardest part is learning to get the signal into the middle of the screen.I would star with testing the output of a 5 to 10 volt DC wall, wort. Use the voltage & time knobs to learn how to get the signal on the screen so you can see it.

After you get that correct, testing the AC signals of opti should be easy. Be careful when setting the voltage. You don't want to use a lower voltage setting then the signal your testing.

It's been a wile since I tested an opti. If I remember correctly, the opti signal is around 5 volts. So you would set scope voltage to around 10 volts.

If you buy a set of 50K leads, you can use scope to check spark.

And don't forget to unplug opti wiring pigtail, with ignition off. Use your multimeter set to ohms- resistance to test each wire. Any reading above 1 ohms shows a wire or connector pin having a problem. Might be a good idea to order a new opti pigtail.

There's 2 different opti pigtails. 1 for 93-95 engines & one for 96-97 engines. Only difference is the connector on opti side of pigtail.
 

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Discussion Starter · #5 ·
I use the Hantek model 6022BE It's a PC based scope. It has dual channels so you can test both low & high res signals at the same time.

If you've never used an oscilloscope, the hardest part is learning to get the signal into the middle of the screen.I would star with testing the output of a 5 to 10 volt DC wall, wort. Use the voltage & time knobs to learn how to get the signal on the screen so you can see it.

After you get that correct, testing the AC signals of opti should be easy. Be careful when setting the voltage. You don't want to use a lower voltage setting then the signal your testing.

It's been a wile since I tested an opti. If I remember correctly, the opti signal is around 5 volts. So you would set scope voltage to around 10 volts.

If you buy a set of 50K leads, you can use scope to check spark.

And don't forget to unplug opti wiring pigtail, with ignition off. Use your multimeter set to ohms- resistance to test each wire. Any reading above 1 ohms shows a wire or connector pin having a problem. Might be a good idea to order a new opti pigtail.

There's 2 different opti pigtails. 1 for 93-95 engines & one for 96-97 engines. Only difference is the connector on opti side of pigtail.
Thanks for the recommendation on the scope. I ordered the same one. It will be here tomorrow. I got a new pigtail with the opti I got from autozone. Are you saying to unplug the opti wiring from the harness side or opti side?
 

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If your going to test the opti pigtail for excess resistance, you need to unplg both ends. One lead of multimer will go on pin at opti connector & one lead will go to corresponding pin at other end of pigtail.
 

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Discussion Starter · #7 ·
If your going to test the opti pigtail for excess resistance, you need to unplg both ends. One lead of multimer will go on pin at opti connector & one lead will go to corresponding pin at other end of pigtail.
Ah gotcha. Yes I've ohm'd out the opti harnesses I have and both are good.
 

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Discussion Starter · #8 ·
Ok, so after a little fiddling I was able to get the scope connected (had some issues with drivers on the computer at first). I also checked wiring again and found this under the dash. I can't see where it goes or if it's important. Any idea where it goes?

Also is there any sort of write up or video on what I need to do with this scope?
Automotive lighting Finger Thumb Nail Input device
Automotive lighting Gadget Finger Audio equipment Electrical wiring
 

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Don't know where wires go. It looks to me that 1 wire is black, & the other is black/white. If this is correct, GM always make ground wires black or black/white.

96 service manual will have all grounds shown in the wiring section. Maybe you can find the answer you need there.

Youtube has videos on how to use a scope. Even if the video shows a standard scope, rather than a pc based scope, the agjustments are the same for both types.

Once you,ve learned to set prope switch postion for the voltage being measured. Then turn voltage on scope to correct range, the only other major adjustment left is the time of signal.

Google serch will also have how to pages.
 
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