Mysterious Engine Pause

[iloveandhatemyz]

i have a 1978 datsun 280z. I am experiencing what i can best describe as "engine pause". driving down the road and suddenly nothing for about 3 seconds, then all is well again. As the days went on, 1 pause became 2. then 3. then 4. then one day pause and died to a rolling stop aside the road. I pulled a spark plug and could see spark when i tried to restart. had it towed to the mechanic...started right up! replaced the fuel filter... next day, still paused. so, took it back to a mechanic and told him to drive the car for a while to replicate the problem. he did. for a week. nothing. so i brought it home...a week later...pause, dead. ugh. took it back to him. he drove it for a week and was finally able to get it to replicate and die. towed it back to his shop...then restarted before he could figure it out. ugh. you can nickname me "stumped z". fuel injected, fuel filter good, fuel pump good, has spark, full compression in all 6 cylinders. only thing i have not changed on this car is the good old cpu. thoughts? anyone? bueller?

[Zed Head]

Those are symptoms of ignition module failure, among other possibilities. Is it worse when the engine is warm? And does it happen more often after high RPM?

The symptoms seem to vary when they fail. I had one that was fine at low RPM, below ~3,000, but would start sputtering and misfiring after venturing up in to high RPM. Turn the engine off for a few seconds and restart and it was fine. Other modules just die completely, especially the later E12-80 modules (from the ZX engines).

I did also have an ECU go bad like yours. But it died, then only restarted about three times while I tried to get home, then it was completely dead. Elapsed time of about 5 minutes.

Edited August 15, 2012 by Zed Head

[Wade Nelson]

Ignition module failure, ignition SWITCH failure, sudden death while running is almost always electrical in nature. You're losing fire.

Confirm this by hitting it with some starting fluid next time it happens. If it won't start, it's definitely electrical. If it fires right back up it's probably fuel starvation.

[MotoManMike]

I too lean toward ignition module, ignition related issue, are all your wires nice and snug and clean on your connections the the coil? With the car running, jiggle connections just to see if you can find the troubled connection but this is a classic sympton of the ignition module.

[iloveandhatemyz]

Ignition module failure, ignition SWITCH failure, sudden death while running is almost always electrical in nature. You're losing fire.

Confirm this by hitting it with some starting fluid next time it happens. If it won't start, it's definitely electrical. If it fires right back up it's probably fuel starvation.

Not sure where to hit it with starter fluid since it is fuel injected.

[iloveandhatemyz]

I too lean toward ignition module, ignition related issue, are all your wires nice and snug and clean on your connections the the coil? With the car running, jiggle connections just to see if you can find the troubled connection but this is a classic sympton of the ignition module.

I did replace the coil recently and know that all the plug wires are nice and snug throughout. But...I haven't tried doing the wire jiggly dealio while it's running...hmmmmm. I'll give that a go! Interestingly enough though...it has never been an issue at idle. She purrs and purrs at idle. Only traveling down the road have I had this issue.

I did read on another post somewhere else on the WWW and found that someone had mentioned losing pressure in the fuel tank via a fuel cap issue? Anyone heard of this?

Like I mentioned in my first post...when it did die on me, I pulled 1 plug wire and could see spark when I tried to start it.

[Zed Head]

Like I mentioned in my first post...when it did die on me, I pulled 1 plug wire and could see spark when I tried to start it.

You might have been thinking it but you didn't write it. You said "has spark" but didn't really say when.

The followup question is "when you put the plug wire back did it start right up"? If so, that could still be an intermittent electrical problem. If you confirmed spark and it still wouldn't start, that could be an ECU or fuel problem.

It could just be a dying fuel pump. A fuel pressure measurement during the problem would tell you.

[iloveandhatemyz]

Sorry Zed Head...you're right..I didn't mention it. Yes, when I plugged the spark plug wire back in, it did not start. I then called a tow truck and had it towed to the mechanic. When we dropped it off at the mechanic...it started right up.

Currently the car is still experiencing this mysterious pause. I do plan to replace the ECU then will take it from there. If it were the fuel, would it be best to just go ahead and replace the pump?

Another interesting thing that I have noticed is that the headlights are very dim. I went to the fuse panel and matched it against the manual and noticed that some of the fuses are not the amps that are suggested. Some are higher and some are lower. Wondering if this improper use of the fuses could potentially cause the ECU to go fowl.

Thoughts?

[Wade Nelson]

Please, do NOT waste $$$ on a new ECU. Not until you have exhausted ALL other possibilities.

You just gave a major clue --- dim headlights typically indicate you have a poor ground. Check your main ground to your engine block and the littler one to the body. Make sure there isn't PAINT underneath them, if so, grind it off so it's bare metal to shiny bare metal.

Pull your battery terminals, inspect, clean, and re-install. I don't CARE if they look perfect, you can get white lead oxide between the terminal and the post that is INVISIBLE unless you remove them.

Your engine cutout is, in 99% probability, due to loss of nice, clean, 12V power to your ECU and other systems.

IF a fuse isn't blown, then it isn't your problem. But do replace them with the correct size.

[Wade Nelson]

i have a 1978 datsun 280z. I am experiencing what i can best describe as "engine pause". driving down the road and suddenly nothing for about 3 seconds, then all is well again. ?

How about some follow-up? Did you get this diagnosed / fixed? Please share so others can benefit.

[Jetaway]

Those are symptoms of ignition module failure, among other possibilities. Is it worse when the engine is warm? And does it happen more often after high RPM?

The symptoms seem to vary when they fail. I had one that was fine at low RPM, below ~3,000, but would start sputtering and misfiring after venturing up in to high RPM. Turn the engine off for a few seconds and restart and it was fine. Other modules just die completely, especially the later E12-80 modules (from the ZX engines).

I too am curious about the outcome of this thread, in the meantime, thought I would add this:

I have a ZX distributor in my '72 that came with the E12-80 module. A couple of summers ago, I thought I felt the engine cut out for just a fraction of a second, but couldn't rule out faulty sensory equipment (mine, not the cars;)). Then, couple of weeks later, engine stall at speed, maybe 1/2 second but since I have a manual, the engine refired without any actions on my part. Continuing into the summer, the stalls became engine stops, requiring cranking the starter, often for a several seconds before catching. Finally, engine kills that only a 20 -- 40 minute stop would "cure." Did a little rewiring and replaced the E12-80 module with a cheap GM HEI module. Cured the problem until this summer when again, thought I felt momentary cut-outs. Replaced the cheapie with a higher grade HEI module. No problems since.

So, my experience is that the E12-80s, maybe all ignition modules, won't necessarily fail without warning, but often/usually give advance, albeit sporadic and not reliably replicable symptoms before total death. Which, given what I know about electronic components, makes perfect sense.

Chris

[ZCurves]

Check the Fusible Links. Sounds link you have one that is going bad.