OBD1 scanner/LT1 stalling issues

I have a 95 Z28 with an intermittent stalling issue that is beating the living shit out of me. I'm sick of throwing parts at it and I want to scan it to see if it's setting any DTC's. Does anyone around here have a scanner? Maybe one of the shops (LMT, WBD, etc)?

For the LT1 guys, here are the specifics:

It's a heads/cam stock cube LT1, short tube headers, catback, mail order tune. When I first bought it, it ran like shit in general and would occasionally stumble/stall and not restart until it cooled off. I replaced the ICM with a Delco part and it ran better, but then started having issues when I would launch it. On a hard launch, it stalls like someone flipped a switch. Doesn't lose power, no sputtering or stumbling, just an immediate shutdown. It fires right back up like nothing happened. Now tonight, it stalled on the freeway. I was cruising in 5th, then dropped tit into 4th and got on it, it died. I tried to restart it and got nothing, but then I put it in 3rd and popped the clutch, it fired right up and ran fine the rest of the way. The service engine light stayed on for about 20 seconds, then went out, so I'm hoping it has a stored code. It only seems to stall when I rev it up quickly under load, and even then is very intermittent. I've replaced the coil and ICM (both new Delco parts), battery and terminals, checked all grounds, played with all the ignition harnesses while running to see if something was loose, etc. I've been told it's the opti or fuel pump. It has a Walbro 255 with the Racetronix hotwire kit (previous owner installed), but if the pump were failing, it seems like it would happen more often, and not only under certain circumstances. Opti I can see, if it's the low res pulse that doesn't set the light. It feels kind of shitty over 3k, but I don't know if it's missing or if it's that's just what a cammed LT1 with a mail order tune feels like. I don't have a ton of seat time with the car yet, so it's all new to me. If somebody can scan it or tell me with some confidence that this is a bad opti, I'll rip it apart. It looks like a bitch though, so I don't want to do it just to rule it out if I don't have to. The opti that's in there is an MSD with maybe 4k on it, I have receipts for it. I think it was just the cap and rotor though, not the whole billet piece. The car sat for 6 months not running before I bought it, not sure if that might affect the opti or not.

I have datamaster for obd1 and the obd2 cable for 95 plus. right now for a 383 car I'm tuning at the moment. Crappy part about obd1, you gotta catch it right when it has the code in most cases, if the light goes out then the code is gone. Not as smart with storage like obd2. I thought you and Greg got the tuning/logging package from tuner car?

Haven't bought it yet and we weren't really in a big hurry. Any chance we can get together and scan this thing? I should be able to duplicate it.

Either way determining exactly if its simply an ignition shut down or if there is something of a fault in the harness somewhere that when you get it in it a wire connection opens up etc. did the the car have traction control option? Has it been disable in the PCM that you know of? Just wondering if something goofy is going on there

Yeah I'm just waiting for the authorization code for datamaster so I can fully use it. Should be today or tomorrow when I have that.

No traction control, not sure what's set in the PCM. It's a mail order tune from MadZ28. This thing has had issues since day 1 though. It would bog really bad on a hard launch and stumble, service engine light, then recover. Replaced the ICM and got the tune, replaced plugs and yanked all the MSD ignition parts, nitrous, etc. Now it's stalling under the same conditions. It feels shitty above 3k too, not sure if it's missing or not though since OBD1 doesn't have misfire detection. I've played with all the ignition harnesses, etc while it's running and I haven't been able to get it to stall. It won't stall unless it's under load, either. I can rev it in the driveway all day long and it doesn't miss a beat.

Send 95 TA The Beast a message, he's an LT1 guru and might tune it for you but you'd have to talk to him about it.
I had a MADZ28 tune in mine and the guy jacked up the tranny line pressure so much I am surprise it survived.

Did you replace the TPS, MAP sensor. It had a TPS sensor that would stall my car and jack around my idle until I put a new one in.

The thing idles like a beast... heard it this morning.

Quote:

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Originally Posted by Firefighter Z

Send 95 TA The Beast a message, he's an LT1 guru and might tune it for you but you'd have to talk to him about it.
I had a MADZ28 tune in mine and the guy jacked up the tranny line pressure so much I am surprise it survived.

Did you replace the TPS, MAP sensor. It had a TPS sensor that would stall my car and jack around my idle until I put a new one in.

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I was actually referred to him by someone else as well, I'll touch base with him about looking at my tune.

With your bad TPS, what exactly was it doing? Did it throw a code?

If I remember correctly, it would idle like shit.
If you want, bring it over to my house and I could check it to see if its throwing a code. I have the freescan and a OBD1 cable.

I'm actually working on bleeding my brake system and it isn't work out to well for me. God I hate ABS...

Your stalling issue has all of the symptoms of a ICM but you replaced it. What about the crank sensor? Have you tested that? When you get it hooked up to a scan tool drive like you do when it shuts down while reading the data. Maybe you'll notice something out of spec. Those cars have MAF sensors right? Maybe clean it and test drive. Also sounds like a wiring issue, so how brittle does the harness feel?

Yeah, ICM has been replaced twice now, still stalling. Don't think these have a crank sensor, that was added in 96 for OBD2. I can definitely duplicate it, just need to get it warm and stab the throttle really quick. Haven't touched the MAF yet. Wiring harness is in good shape, but that doesn't mean there can't be a loose wire somewhere.

I reread your first post and I see that you have a tune but now that I think of it I believe that it's not tuned correctly. Since you said it's never ran right since you bought it. It sounds like when you apply a load its dumping fuel. Have you thought about getting it retuned?

That's what I thought it was initially. When I bought the car, it had BR7EF's and a nitrous tune. It ran like crap and would occasionally stall, so I replaced the ICM. It ran better, but then it started bogging on a hard launch, but wouldn't stall anymore. Then I got the new mail order tune, and the bogging turned into a stall on a hard launch. Replaced the plugs with TR55ix's and it ran great for a couple hours straight (which it had never done before), but then it stalled the first time I got on it hard on the freeway the other night. I've spoken to the tuner (MadZ28 in IL) and he swears there's nothing in the tune that would cause this. Since the old plugs I pulled out were soaked in fuel and totally fouled, I wasn't sure if it was just the plugs or a combination of overfueling AND the small gapped cold plugs. Since it doing it's now with the TR55's, I have no idea what to think anymore. I'd love to get somebody else to look at my tune and tell me if it's just pouring in too much fuel when I hit the throttle hard at low RPM's. I don't want to try to tune it with a potentially bad component causing it to stall though, either.

Ok, I think it finally got to a point where it should be able to be easily diagnosed. I took it around the block and got on it hard it 2nd gear. It backfired really bad and the RPM's dropped, but it didn't stall. I kept going and got on it hard again, it stalled as soon as I got close to 6k. Pulled over and tried to restart it, it would just crank. Waited a little bit and it started right up and I babied it home. When I got it back, I revved it to 6k in the driveway and it immediately stalled. Tried it again, same thing. No service engine light this time. So whatever it is, it's now failing consistently. Is this a bad opti?

Yeah sure sounds opti related!

I do agree with Tom that this sounds like a bad optispark. I had a similar issue with my 95 a couple of years ago. We tried everything under the sun and the car would still stall under load. Eventually i had the opti replaced and the car never misfired or stalled after that.

Andy I have a fully function data master scanner now and tuner cat if any changes need to be made. Let me know.

Thanks tom. I have a new opti coming this week, gonna swap it out and see if that solves this. If it does, I'm putting a wide band on it and seeing where the mail order tune has this thing. I think it's still stupid rich, so I'll probably need it tweaked a bit. I'll keep you posted.

New opti and harness installed today, appears to have fixed it. Runs smooth, revs to redline without missing or stalling. Fingers crossed that this is it.