Engine Quits Intermittently

[MichaelN]

'81 SC, 188K miles, no mods. Last Saturday took an extensive drive from Northern Calif. to Southern Calif on mostly back roads and returned Sunday via freeway (I-5). 800 miles total. On the drive down car was faultless with good power at all engine speeds and no problems. However on the drive back, shortly after getting on the freeway leaving L.A., the motor suddenly went completely dead for about 2-3 seconds and then back on again. Just like throwing a switch. No sputter, no gradually loosing power, just off...and then back on.

I continued on and it did the same thing about 10 minutes later. And then 30 min. after that, and about 45 min. after that, and so on through the afternoon and into the night all the way home. Sometimes it would go off for up to 5 seconds or so and I would start to move to the shoulder as the speed slowed, but it would always fire up again (I never took it out of gear when this would happen). Dash lights and gauges remained on and normal when this happened.

Everything looked normal on the engine when I stopped for lunch late in the afternoon, and the only thing I was able to do was make sure the leads on the coil and distributor were secure (did a complete tuneup around 5K miles ago) and swap in a spare fuel pump relay that I had in the glove compartment.

This morning I drove it a bit and everything was normal save for one peculiar symptom. The idle was, slow, rough, and irregular; barely above stall. But when I glanced at the tach it was showing 1,500 to 1,800 rpm. That was weird. Above idle the tach and engine return to normal.

I had previously gone through the receipts from the P.O. and found nothing that indicated that the fuel pump had ever replaced, so I bought a new pump and filter a couple weeks ago intending to change them last week. I got the filter in, but ran out of time to do the pump. So I'm going to start by putting in the new pump, but this idle/tach thing has me doubting that this will take care of it.

Any other ideas about what's going on here? I'm no CSI expert and I'm not that good with electrical troubleshooting either, so it's likely headed for the shop if the new pump doesn't do the trick, but I'm interested in any opinions.

[lsf911]

Could be your CDI box. Is it original?

When mine failed it would cut out like a switch turning off.

[john walker's workshop]

Get a cigar lighter digital voltmeter you can watch. Weird things happen with over charging. Unplug the over-rev relay up by the left front hood hinge. Check fuel pump fuse and wires for loose and crusty. Check the red wires on the + battery terminal for loose. Check the domelight fuse that powers the O2 relay, and the relay plug and relay under the pass seat. When that goes south, you get a low rough idle when it goes lean, but doesn't die.

[schoward]

At first glance, sounds like CDI box on the way out. They don't like heat when getting near death. Wonder if that is also whats giving the wacky Tach reading...

Agree with above items. My experience with a few

1. CDI - Intermittent shut down for no reason. Sometimes would start then finally no start. CDI boxes are about done after this age if original. Only time I ever needed a tow. I now keep a spare under the seat on long road trips.

2. The rev limiter relay cuts the fuel pump and can do odd things to your fuel pump power (by interrupting it) when they go bad. I have had TWO go bad (original and a used one) and they can cause behavior above (had the burbly idle one and fuel pump sounded like gravel was going through it). Simple test - unplug it; Its is the black box behind the fuel gauge with 'X' on it and white plug plugged into the bottom of it. If good again that is your issue. You can run without it you just wont have a rev limiter which is generally not an issue for normal driving.

3. O2 relay under passenger seat - unplug it and if no change that could be it (idle should go from bad to worse with that unplugged)

[smadsen]

Any competent shop will have a spare CDI box to swap out. If that solves the issue(s), then send your box our for fix, usually a couple hundred dollars inc. shipping.

When mine failed, it ran fine cold, but as it heated up it would start to splatter, then stop. I think the fix is just to re-solder all the circuit board connections.

[john walker's workshop]

CDs usually stay dead though.

[Mark Salvetti]

Those initial cutting out symptoms are consistent with a failing speed limiter relay, as John and Scott mentioned. Easy to disconnect it, and if the cutting out goes away, you've found the problem.

Here is a bulletin on the speed relay. I would definitely start there. The relay is a black rectangular box, just disconnect the white wiring harness connector from the bottom of the relay. I think access through the trunk is easier than pulling the fuel gauge:



Mark

[Ryce Stallings]

I’ve been chasing something similar for several months. Check the ground for the CDI.

[MichaelN]

Wow! Very gratifying that I could get so many thoughtful opinions on my problem in less than 24 hours. The people that participate on this board make it possible for someone like me to continue to own and maintain a 38 yr old car that I dearly enjoy. Grateful to you all for taking your time to share your knowledge.

Now I'll go to work.