Need some help with a shutoff problem

[95z28man]

I seem to be having a heat soak problem with my car causing it to shutoff while driving. No check engine light, check gauges pops up though. I had this issue last summer one day, randomly shut off while stopping, wouldn't restart til hours later. I replaced some easy cheap options this winter, ignition switch, coil and ICM. All OEM parts used. Now today, another hot day almost identical to what happened last year it shut off again. It did start back up after sitting 15 minutes. The car starts and runs excellent until driving it about 40 to 50 miles round trip mostly highway. Got lucky this time and it started to sputter coasting to stop sign in front of my house. Had to push it a few feet. As soon as i felt it dying, I tried gassing it to no avail. I'm a little stumped on this one and to make matters worse, my car will no longer communicate with either of my scan tools. They will power up when plugged in, but reading codes it will attempt to scan but won't be able to. The other one is my blue driver scanner and it also won't connect, but it works great in my suburban.

Any ideas on where to start with this thing? I've been going to my shop in recent years when I have problems these days but money is a little tight so I'm attempting this one myself like the old days.

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[Injuneer]

The optical cam position sensor in the Opti can heat soak. DTC 16 shuts down the fuel system. When it won't start, do you have spark at the plugs? Does the tach needle move up a couple hundred RPM when the starter is cranking the engine?

Heat soak can also affect the fuel pump, and in extreme cases cause vapor lock. Have you checked the fuel pressure when it won’t start?

Isn't Blue Driver an OBD-2 app? What type is the other scanner that won't connect?

[95z28man]

I wish I had known to watch the tach when it wasn't starting. Like I said I went out 15 minutes later and it fired up like nothing happened 2 times in a row so I parked it and left it go. So obviously I didn't check spark either. As far as the scanner goes I believe that I was mistaken, I was under the impression some of the 95s actually had OBD2, not just the 16 pin connector for it. So Ill have to try an OBD1 scanner and see how it works.

Just trying to get some ideas in the meantime since it seems like I will have to run the car hot for a while to replicate the problem


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[Injuneer]

ALL 1995 LT1's are OBD-1.

Consider a free download of Scan9495 software, pick up a 1995 16-pin cable, and you will have a scan/data logging program written specifically for 1994/1995 LT1's. The author, GaryDoug is here to help with install/setup problems, if any.

https://www.camaroz28.com/forums/computer-diagnostics-tuning-36/scan9495-free-obd1-scan-app-93-94-95-lt1-874306/

To use a 12-pin OBD-1 scanner on your 1995, you can use jumper wires:

http://shbox.com/1/xraycable.jpg

[95z28man]

I briefly read into that yesterday as I was looking for answers why it wasn't connecting. Thank you for the link, very simple and straightforward

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[LDM]

Check your grounds. I had a similar issues a few years back and it was annoying because it would only happen after the engine was hot. Turned out to be the ground cable to the engine had come loose and when it got warm it would lift off the ground bolt enough to sometimes kill the engine while driving and then refuse to start until the cable cooled down enough to make good contact with the ground bolt again. Took me a while to find too, especially since you don't want to start shoving your arm into the hot engine and exhaust to find loose connections. The ground cable on mine was on the passenger side near the starter.

[95z28man]

Thank you I will check that. This is the kind of thing I hope it turns out to be, something stupid and cheap or free to fix.

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[Uyepz28]

Im having the same issue . I havent replaced anything im going to check grounds and vacum leaks first hopefully its something along thoose lines.
Thank you I will check that. This is the kind of thing I hope it turns out to be, something stupid and cheap or free to fix.

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[Injuneer]

What year is the PCM?

You really need to scan for codes. For example - DTC 16 doesn't turn on the SES light.

[Uyepz28]

The pcm is a 95. Has obd 2 plug but is obd 1 . Hard to find what pins to jump to get the flash codes .

What year is the PCM?

You really need to scan for codes. For example - DTC 16 doesn't turn on the SES light.

[Injuneer]

You can’t flash the codes on a 95 by shorting the DLC pins. 1993 was the last year that worked. You need an OBD-1 scanner. Connect using the correct 12-pin —> 16-pin adapter, or jumper the pins from the DLC connector to the scanner connector:

http://shbox.com/1/xraycable.jpg

[Uyepz28]

You think this would work For the codes ? I dont wanna short something out though . .

https://youtu.be/iB87vdl0fH4

[Stormyweather]

GaryDoug' s. Scan9495 works great. No short pin.

[SSlowBoat]

The pcm is a 95. Has obd 2 plug but is obd 1 . Hard to find what pins to jump to get the flash codes .

You cant flash codes on an obd1 lt1 to my knowledge

[LDM]

The pcm is a 95. Has obd 2 plug but is obd 1 . Hard to find what pins to jump to get the flash codes .

You cannot jump pins on your car to flash codes. It does not work on the LT1 PCM. You either have to use a scanner that can read OBD1 with the OBD2 style port or software like Scan9495 on a laptop (with an ALDL interface cable).

[Stormyweather]

But you can program your key fob.[emoji16]

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[95z28man]

Sorry for the late reply, wasn't able to acces the site for some reason. I haven't been able to say for sure if its fixed, however, I did go under it and repaired 2 ground wires. Small one from the starter looked almost as if a squirrel had nibbled on it a little. The large wire from either the battery or alternator to the block was fraying a bit so I replaced it. No issues since, but I haven't had it on a long enough trip to be 100% sure yet.

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[Uyepz28]

Nice I havent had much time to work on it but will definitely start there . I ended up buying the Bosch 1300 scanner. Just havent been able to diagnose while the problem happens . But i do have a Quad Driver 2 Bad that shows up from startup to shutdown any ideas what this does?

[Injuneer]

Is the code DTC 27? That was the Quad Driver #2 code up until 1993. After that, it's for the EGR vacuum solenoid.

[Uyepz28]

Could that be the cause for my shutoff problem.? I also noticed that the voltage starts dropping as the car gets to normL temp once the voltage drops to a little under half thats when it starts acting up .

[Injuneer]

MAYBE a faulty EGR vacuum solenoid COULD shut down the engine. The code indicates the solenoid may be burned out, the harness could be damaged/shorted, or not connected. That causes the voltage at the PCM to not match what it is expected. The code by itself doesn’t shut things down. But the code could indicate a short that ultimately causes a stall. See last paragraph.

Do you even have the EGR system intact, or has it been deleted?

If the solenoid stuck open (mechanically or electrically) causing the EGR valve to remain open at all times, it could stall the engine or make it run rough, particularly at idle. If the wiring harness’s gray wire shorted to ground, the solenoid could stay open..

[Uyepz28]

The Egr sytem is still in tact..

[Injuneer]

It’s normal for the voltage gauge to read higher right after you start the engine. The alternator is replacing the stored power that was used to start the engine. As the battery voltage recovers, the alternator voltage tapers off, and the system typically stabilizes in the range of 12.5-13.5 volts.

What are the numerical readings you are seeing? What numerical voltage is “a little under half"? The PCM will continue to function down to about 9 volts. If the system drops below that, a code(DTC 50) will set for low voltage.

[Uyepz28]

I would have to Hook it up nd do further diagnosing . Ill hook it up on saturday or sunday and let you know . Yo thanks for your input you're really helpful .

[Injuneer]

Just tell us what the dash voltage gauge is reading, when it is reading high on cold start, and what it drops to when you call it "a little under half". Don't need to hook anything up, unless your dash gauge is not working.

DTC 50 sets when the voltage drops below 8.0 volts. It turns on the SES light when it sets. The engine should still run, but the injectors and fuel pump will start to be affected. If the voltage drops below 5.5 volts, the PCM will start to lose serial data.

[Uyepz28]

So I Just had the the chance to try it out again after A TB coolant bypass A couple coolant hoses that had dry rot repair and a few vacum lines. I also changed both the collant temp sensor and coolant sending sensor. The voltage stays between 12 and 10 v starts at high 14 and drops. Has current draws when i hit the manual fan switch otherwise sits 11 12s. Noticed the fans dont come on by themselves

[Uyepz28]

Also The car still shuts off.

[meissen]

Injuneer - did this issue just start happening today? And I believe you're using the browser, not tapatalk, correct?

[meissen]

I have had the PHP version set to 7.1 for over a week now, but it looks like that all of the sudden started causing an issue today. I've changed it back to the very old and outdated PHP version that used to work before. Let's see if that fixes the issue.

Edit: And it seems to have fixed it. Injuneer - if you can confirm it's fixed for you now?

[Injuneer]

Test post

[Injuneer]

Let's make sure we understand what is happening. You tacked your question on to a thread that deals with an engine that shut off randomly and was hard to restart:


I seem to be having a heat soak problem with my car causing it to shutoff while driving. No check engine light, check gauges pops up though. I had this issue last summer one day, randomly shut off while stopping, wouldn't restart til hours later.

Is the problem the thread starter posted (quote above) the EXACT same problem you are having?

Does it ever shut down while idling?

Does the engine need to cool down before it will restart?

Is it hard to start after it has cooled down?

When the engine shuts down, and you retry to start it, but it won't start, does the tach move up 200-300 RPM when the starter is cranking the engine?

[Injuneer]

FAN PROBLEM:

If an auxiliary fan switch isn't wired into the system correctly, is can prevent the PCM from turning on the fans as programmed. Stock turns the fans on low at 226-degF, high at 235-degF. Do the fans turn on when you turn the A/C on?

[Uyepz28]

Injuneer it shuts off at Idle Only has done it at idle to me . After its warm. Sometimes itll start right back up at other times just crank and crank . . I let it sit for about 20 mins half an hour starts up and runs fine again it tends to do it when warm outside. When i first hot it woke up at 5 in the morning and it ran well over 2 hours . Same day around one started it up let it warm up and it shut off .

[Uyepz28]

And ac compressor is screwed up so its disconnect

[Injuneer]

Take the ICM to an auto parts store and have it tested. Make sure they get it good and hot.

After that, we'll work on the cam position module in the Opti.

[Uyepz28]

Will do i have a spare so i will take the spare then if they say is good ill slap it on there . And ill update you from there. Thank yo so much for your patience Nd knowledge Injuneer

[Uyepz28]

Couldnt find anyone to test the icm . .i switched it and it has the same problem. .

[Uyepz28]

I also changed the egr solenoid and it still shows quad driver 2 bad . I noticed when i changed the solenoid quad one went bad when unplugged as soon as i plugged it back in went back to ok .

[Injuneer]

There are no “quad drivers” on a 1995. I explained that to you in post #20.

You had DTC 27, which your scanner apparently indicated as “quad driver 2”. The correct definition is an EGR vacuum solenoid circuit.

Are you sure you replaced the correct solenoid? If your scanner displayed DTC 26 for “quad driver 1” when you unplugged the solenoid, you may have replaced the wrong solenoid. DTC 26 in a 95 indicates a fault in the EVAP Purge Solenoid electrical circuit.

Again, here is the correct code list for your car:

http://shbox.com/1/Dtcs.htm

The 94/95 codes are to the left. The 93 codes (which are different than 94/95) are in the column to the right.

[Uyepz28]

So I Replaced my ignitikn switch last night hooked up the scanner today Nd my quad driver 2 reads ok now on my 93 z . . Would that be a reason for my shutoff? There hasnt been a hot day so wont be able to tell if problem is gone yet.

[Uyepz28]

So I Replaced my ignitikn switch last night hooked up the scanner today Nd my quad driver 2 reads ok now on my 93 z . . Would that be a reason for my shutoff? There hasnt been a hot day so wont be able to tell if problem is gone yet.

[Injuneer]

Apparently you don’t believe me when I tell you there is no “quad driver”.

[Stormyweather]

So I Replaced my ignitikn switch last night hooked up the scanner today Nd my quad driver 2 reads ok now on my 93 z . . Would that be a reason for my shutoff? There hasnt been a hot day so wont be able to tell if problem is gone yet.What year is the car? A 93 Or a 95?

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[Injuneer]

The pcm is a 95. Has obd 2 plug but is obd 1 . Hard to find what pins to jump to get the flash codes .

^^^^^^^

[Stormyweather]

" Nd my quad driver 2 reads ok now on my 93 z " I'm confused. I now remember reading that. But. What is really going on? Maybe hes got a 95 z. I'll go back quiet.

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[Uyepz28]

Sorry about the confusion my mistake on the 93 95 thing was i was buying it when i was told it was a 95 . When i finally met the guy it turned out to be a 93 . So now i think im pretty close to solving the problem though.

The car stuttered on me today while coming to a stop . I didnt shut it off when i got to the driveway hooked up the obd one and low res code popped out. Now i have 2 codes to work on but quad driver 2 is ok now .

[Injuneer]

Sorry about the confusion my mistake on the 93 95 thing was i was buying it when i was told it was a 95 . When i finally met the guy it turned out to be a 93 . So now i think im pretty close to solving the problem though.

The car stuttered on me today while coming to a stop . I didnt shut it off when i got to the driveway hooked up the obd one and low res code popped out. Now i have 2 codes to work on but quad driver 2 is ok now .

Are you serious? The FIRST question I asked you, in response to your FIRST post was “What year is the PCM.” You said it was a 95 and went into the explanation about how it has an OBD-2 plug, but the PCM is OBD-1. And at no time over the 6 weeks I've been helping you, pointing out the differences between the 93 and the 94/95 computers, you never bothered to tell me you discovered it’s a 93? SMH

Good luck.....

[Uyepz28]

Sorry man. .my apologies. Ill try to figure it out myself now but you been a great help . Thank you . Happy holidays. And Ill still keep you guys updated as i throw parts into it untill the issue goes away.

[Uyepz28]

Cool So i think i figured it out was my opti and opti harness that were taking a shit. Thanks for all the help Guys.