b_spencer28

Hi! I need some help if anyone can. My 1996 z28 starts and runs fine but every now and then, I’ll be driving and I lose all throttle and the car stops and the check engine light comes on. And also every now and then, if I’m at idle, the rpms jump up and down from about 500-2500 without me touching anything then the car dies. What could be going on? Anything helps, thanks!

Injuneer

Have you scanned it for codes?

b_spencer28

Not recently, but the last time I did, the main ones were MAF ones and a misfire. There were a couple others but I don’t remember. But I changed all of the spark plugs and wires and I installed a new MAF.

Injuneer

When you say “the car stops”, I'm assuming you mean the engine instantaneously shuts down. Is that correct? If not, provide a bit more detail in exactly what happens when “the car stops”.

It also appears that the SES (check engine) light was NOT on, but turned on at the same time the engine shut down. Is that correct?

Think about it..... the SES comes on when the PCM diagnostic system detects a fault, sets a code, and turns on the SES light. You need to scan it NOW, and pull the code(s). You can't rely on what codes were set “last time” in the past. It defies all logic. If you are going to a shop or having a friend pull the codes WRITE DOWN THE EXACT NUMERICAL CODES. There's more than one code for the MAF, and for misfires.

As far as the RPM jumping up at idle:

- what brand Optispark distributor are you running?

- does the car have a manual or automatic transmission.

b_spencer28

Yes, what I mean by the car stops is, if I’m driving, I spontaneously lose all throttle and the car just crawls to a halt. And when it happens the engine light turns on. And I tried to get it scanned by a family member at their work but he couldn’t and no where else around where I live will do it for free, or do it at all because of COVID. And for the rpm, it is a manual but I have no idea what kind of optispark it has. Only had the car for about 2 months and haven’t checked what brand.

Chimera96

OBD2 scan tools are very cheap with ones that read codes and offer most likely cause for about $100. Just a code reader is around $40. Get one

Injuneer

Most auto parts stores will scan OBD-2 for free. OBD-2 scanners and apps are inexpensive, although it's best to get on with GM "enhanced parameters" and they can be more expensive. The alternative is to start playing "parts replacement roulette", and the cost of that is usually much higher.

So.... the engine shuts off like someone switched the key off.... correct? These cars are getting old. That could be a faulty ignition switch.

After is shuts off, and you pull to the side of the road, how long does it take before you can restart the engine? Or do you need to let the engine cool down before it restarts? After the restart, how long does it typically run before it shuts off again? If it won't immediately restart, it would be a good time to see if the spark plugs are getting spark. Pull a plug wire off a spark plug, place it close to the engine block, and while someone turns the key to "start" and the starter is cranking the engine, is there a visible spark from the wire to the block? Do not hold the wire in your bare hand while doing this.

If it does NOT restart immediately after the engine shuts off, when you turn the key to "start", and the starter is cranking the engine, does the tachometer needle move upwards about 200 RPM? What is the numerical reading on the dash voltage gauge, with the key in the "run" position, and with the key in the "start" position?

Answers to the above may point us in the right direction. Some of the possibilities at this point include:

- intermittent fault in ignition switch

- heat soak causing intermittent failure of ignition control module (ICM). An auto parts store can test the module.

- heat soak causing intermittent fault in the cam position sensor in the Optispark distributor. A fault in the Opti can also be the cause of the tachometer jumping up to 2,500 RPM.

b_spencer28

Hey. Got some stuff checked and I have a question, is the ACCEL distributor a good choice? O’Reilly has one for about $80.

And for the codes that it read, the codes are: P0300 (Random misfire detected), P0100 (Mass or Volume Air Flow Circuit), P0101 (MAF Sensor Signal Range/Performance), P0103 (Mass or Volume Air Flow Circuit High Input), P0200 (Injector Circuit), P0601 (Internal Control Module Memory Check Sum Error), P1351 (IC Circuit High Voltage), P1361 (IC Circuit Low Voltage).

I did the check at autozone, and it also said for I guess the recommended fixes are a distributor cap and rotor.

Injuneer

Was the PCM cleared since the last time you had it scanned for codes? If not, those could be "stored" (history) codes, and not indicative of the current problem(s). For example, you replaced the MAF sensor, but still have the code. Was it history or active?

Given those codes, I wouldn't suspect the high voltage side (cap/rotor) of the Optispark. Could be contributing to the misfire, possibly. Sounds like you need to take the ICM to an auto parts store and have it tested. Make sure they get it good and hot while testing, because it may be an intermittent fault due to overheating.

The only reliable Optispark seems to be the one sold by Petris. :

https://petrisenterprises.com/collec...32075760992310

Accel is middle of the road, hit or miss. An $80 Opti is a piece of Chinese crap... destined to fail quickly, if not defective right out of the box.

One problem here.... I asked several questions in post #7, to get the information I need to help you. But you didn't answer them. Makes it difficult to help.

b_spencer28

Sorry. I thought I replied to answer some of those questions but I guess I didn’t.

After it shuts off, I usually give it a about 30 seconds to a minute then start it back up. And when I did start it, it starts immediately. After that it’s fine for about a day or so then it does it again. The Spark plugs and wires are brand new ACDELCO ones so those are fine. Also, I read somewhere that if the car kinda shakes and vibrates a bit, that it could be the ignition switch.

But here’s that distributor I was talking about. https://www.oreillyauto.com/detail/b...r/8136/2473779
It’s an ACCEL one, so I thought it might be ok, but not amazing. And especially for me right now, because I’m not really in search of a completely permanent fix, just for the next like year maybe. Or if you think that getting a better, more expensive will be better, that’s fine.

Hopefully that answers your questions, sorry about that. I was going to buy that distributor and a new MAF connector. But if you think I shouldn’t and should get something else that’s fine. And thank you for the help too and for coming back and answering my questions after I forgot to before.

Also, forgot to mention, those codes are pretty new. The last time they were cleared was probably about 1-2 weeks ago.

And one more thing, I looked up the part # for that distributor to see what other ones cost of the same one, and they cost about $350 at other stores. And the one at O’Reillys isn’t refurbished or remanufactured or whatever.

I found the difference between the one at O’Reillys and the others that I was looking at. The one at O’Reillys is a cap and rotor kit, and the others aren’t. What is the difference between them though?

ACE1252

P0601 is an unusual one. Don't think I've seen that one before. When it happens, the PCM kills the injectors for one cycle. That might be the sudden shutoff you are seeing depending on how long the PCM detects the code. The factory manual calls for a PCM replacement if that code is in memory. Factory manual diagnostic for P0601 attached.

multicar

Does it only happen when it rains or after a car wash? If so, the hood seal on top of the cowl is allowing water to drip on the rear spark plugs. I added some generic weather stripping there on mine.
If it doesn't happen when it gets wet, it could be the water pump leaking on the opti-spark(distributor). Haven't had to replace mine w/87k miles yet, but I've done one on a 94 Vette, where the AC accumulator
sits nearby to the distro and sweats alot.