C4ProjectCar

Ever since I dropped a new engine into my '90, I've had a problem with the engine cutting out. I'll be driving along, could be in any conditions whatsoever, and the engine will just shut off like I turned the key off. Most of the time it will restart, but sometimes it dies completely.

My first thought was a bad wire, so I wiggled all the wires I could find with it running, but no dice. Also, it doesn't seem to happen more on bumpy road, which goes against the problem being a bad connection. My next thought was a bad ICM since it seems to be worse when the engine is hotter, but replacing that did nothing (it may have even made it worse). I also read that the distributor housing not grounding properly can cause this, so I threw a ground wire on it. Likewise, no improvement.
Other ideas I have are a bad coil (I've read bad things about the Accel coil on there now), bad ignition switch, or bad ECM, but I don't want to just start throwing parts at it. I also read that a short in the tach wire can ground the coil, causing the engine to quit, but there's no easy way to disconnect the tach without also disconnecting the battery wire.

Looking at datalogs I have, basically every running tally resets (knock count, O2 cross-counts, etc.) except engine running time.

I was planning on taking a short road trip tomorrow, so I'd love to get this fixed by then. Any ideas?

pcolt94

Before you go off into the electrical world of no spark I would eliminate a fuel problem first.

When it quits and if you can get to the side of the road see if you can still hear the pump for the 2 second prime. You might have to also attach a fuel gauge and tape it to the windshield and see if there is fuel pressure when it quits.

Cliff Harris

The tach wire is white and the battery (actually ignition switch) wire is pink. They just unplug individually, so it should be very easy to isolate the tach wire by just unplugging it.

C4ProjectCar

I don't think fueling is the issue. The fuel pump is relatively new, and it both quits and restarts very suddenly--not the sputtering I'd expect with a bad FP--right?

The clips were broken so they kept coming off, and when I replaced them the only pigtail I could find had the two connectors as a single unit, unfortunately. (Edit: I was able to get the tach wire out of the connector, but the problem persisted.)



Just finished replacing the ignition switch, which took much longer than I expected (of course). Didn't fix the problem, so I guess coil is next.

pcolt94

Seems like lack of fuel symptoms are different between old school carbonator engines that use a few pounds of pressure and a fuel bowl to draw from, and injected engines that need 35 or 40 psi to push thru the injectors. A little bit of fuel in a fuel bowel can give you sputtering as you said. Just saying - know what you mean.

Fuel just easy to check to get a variable out of the way where electrical you would be spending some time on from what you have indicated.

VikingTrad3r

how often does this happen? Like if you were to go over a 1 Hour Dr., how many times would it happen?

C4ProjectCar

I noticed the coil was missing the ground strap (unless that Accel unit grounds it differently?), which can apparently cause coils to go bad which in turn can eat ICMs. So I figured it had to be the coil.

Just replaced the coil, had my (new) ICM tested to make sure it was still good, and double-checked all the ECM grounds in a last-ditch effort to get it roadworthy by today, but no dice. So new coil, new ICM, new ignition switch, new(ish) fuel pump, new fuel pressure regulator diaphragm, and verified grounds. My only remaining ideas are a bad wire inside the distributor, maybe something wrong with the distributor cap, a bad ignition lock cylinder, or a bad ECM.

What would you check first, and how?

It varies pretty drastically, and seems to get significantly worse the longer I drive. I go on a 25min loop to datalog for tuning, and I'd say on a cool night, it happens somewhere around 4-5 times, but on a hot day the worst I've seen is 8-10 times.

pcolt94

Since it sounds like you don’t have a fuel pressure gauge currently so at least this;

When it quits you can at least listen to see if you hear the 2 second prime when you turn your key to on. You should know what it sounds like when things are OK like first thing when you get in the car.

VikingTrad3r

go borrow/rent a fuel pressure tester.


you cant do anything without obtaining some of these tools.

pcolt94

You are 110% correct.

I try not to get on a soap box, but try the help even when people can't help themselves. Not very often is a question asked and there is a silver bullet answer. The Forum gives suggestions to test or check and direction. But most of the help relies on the person having tools and some knowledge to perform these actions. You are going to need meters, gauges, tools and a FSM is not a bad idea. Or take you car to a mechanic to get fixed. Not everybody has every tool or meter. New jobs approached may require new tools and I go out and get things I need to be able to do it. But if you have a good base of tools and equipment, you're not buying things all the time. Backgrounds vary, some people are young and starting out, and some are older collecting tools and stuff for decades.

Equipment takes the guess work out enabling you to move forward in the right direction. You can't stare at the car and get answers. Gear up and get some basics and the help you get will go a long way much faster.

C4ProjectCar

Just got home from being out of town for the weekend, but tomorrow I'm resuming diagnosis. My plan is this: hook up a timing light and a FP gauge (I know one of the stores around me lends them out; I borrowed one a few years ago) and see what happens to spark and fuel when the car cuts out. I'm guessing the timing light will momentarily quit flashing, but who knows, maybe the gauge will dip for an instant as well.


Yep, it primes every time. Well acquainted with that sound from when I was tracking down a couple fuel problems the car had when I got it.

I do my best to follow people's suggestions; I just don't feel fueling is the problem, so going down that avenue wasn't high on my list. I've pulled the FP fuse and run it till it died to relieve fuel line pressure a couple times before, and the missing and stuttering the engine exhibited till it died then were far different from the instant light-switch type cut-out--with no loss of power immediately before or after--I'm experiencing now.

I have a FSM and used it to its full potential to get me this far, but it has its limits when dealing with uncommon problems such as the one I am experiencing. I've done hours of research, investigating every problem I came across that has ever caused similar symptoms, and I put in probably 14 hours replacing parts, checking grounds, etc. before I posted here.

pcolt94

There is always more than one way to approach a problem. A timing light is one of them. And any other method to check for spark off the coil will work. Collect as much solid data as you can. Know you have a bunch of time in it already but when you find what's missing when it cuts out, you're be on the right path.

C4ProjectCar

Alright, taped the gauge to the windshield and went for a spin. FP doesn't seem to do anything when the engine dies (although it's bleeding down I think faster than it should after the pump primes, maybe 5psi in 20sec; it varied a bit). Now to try the same with a timing light.

Stephenms

I had a similar issue in a 1991 Z28 Camaro. After about a 20-30 minute drive the car would just shut off while driving, then have no problems firing up again, then driving another few miles, then shutting off again so on so forth. Fuel pressure and spark were perfect even at the time of shut off. After weeks of racking my brain I took a crap shot and replaced the fuel pump. The problem subsided for a few weeks, then I defected that pump for another one. Three pumps later it came back worse than ever. It still cut off after the same time, but now the newest OE pump would make this high pitched squeal sound for a minute, followed by a grinding sound and then shut down. It turns out the fuel pump was getting extremely hot and shutting off. After looking into the tank with a scope, the entire top of the tank had flaking rust on it and the rest of the tank had some floaters in it. Not sure if there's a correlation but I ended up replacing the tank and the pump and never had an issue after that.

C4ProjectCar

Actually, decided there's no point to hooking up a timing light because if there's still fuel, the spark must be stopping for the engine to die.

I also checked injector resistance and injector plug voltage, and they all seemed okay (forgot to plug one side back in though, apparently my engine can run on 4 cylinders ).

I just made sure the chip emulator, stock memcal, and adapter had a good connection with one another, and now I'm going to check for bad wires in the distributor with a digital multimeter.

Anyone have ideas of what else to check? I'm running out of ideas here.

Man, that sounds frustrating. I don't think it's my problem though since my fuel pressure doesn't dip when it dies. Thanks, though!

(EDIT: Anyone else notice that on Chrome emojis get pushed to the end of the post no matter what?)

JimLentz

I'm thinking it might be one of these connections "I just made sure the chip emulator, stock memcal, and adapter had a good connection with one another, and now I'm going to check for bad wires in the distributor with a digital multimeter." What you mentioned in your first post about the datalog makes me suspect that or the ECM.

C4ProjectCar

I wiggled the heck out of those with the engine running but couldn't get it to quit.

Is it possible the ECM just automatically resets those counts when it detects the engine isn't firing?

aklim

After it dies and refuses to start, check for spark and injector pulse while cranking.

Injector resistance is a very vague test. That it seems good doesn't mean there isn't an issue which is why I never run those myself. It could short when hot which causes an issue but when testing, it doesn't show a thing. The pintle could be cut off and the coil is good and you would be given a false negative.

If you have a stock MEMCAL, why exactly do you have an emulator? Just because the connections are solid doesn't mean the electronic part cannot act up when hot.

aklim

I don't think the ECM is that sophisticated.

JimLentz

Is the engine modified? If not, how does it run with just the MEMCAL? I am not sure about that ECM and the counts.