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Author Topic: Strange Intermittent Issue  (Read 110 times)

Offline MSA1R2K

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Strange Intermittent Issue
« on: 05:29:48 PM / 30-Nov-18 »
Hi all, this is my first post on Club S12 so i'll start with some background.

I bought an 85' CA20 auto hatch back in 2014, previous owner had put a ton of work (and dollars) into overhauling the engine as the car had sat in a shed for 20+ years. Only had 27,000 miles at the time of purchase.

Thing ran amazing for the last four years, almost no problems aside from the occasional battery or alternator replacement, but lately I've been encountering an issue that I can't pin down and has slowly become more frequent.  When I try and start the car the engine will fire once, then cease to fire and only crank.  If I wait a minute I can try again with the same results, the only fix I have found is to simply wait 10-20 minutes, try again, and usually it will kick off no problem.  Once in a fit of frustration I cranked the engine for 20ish seconds after which it slowly began to fire again until it started.

I encountered this problem once in the summer, around mid-July, but didn't think much of it and considered it an isolated incident.  Throughout the fall it started happening more frequently, about once a week in September to multiple times a day by November.  I recently replaced plugs/wires/distributor cap/rotor in a repair attempt (thought rotor might be the root of the problem cause points were pretty corroded) but the issue persists.  Pulling codes off the computer hasn't yielded much, it gives me "Fuel Pump" which I know can't be right cause I can hear the thing priming like normal whenever I turn the key.

The only modification I've done to the engine has been to replace the OEM alternator with a GM One-wire, which I did during a period of voltage loss that turned out to be a bad battery.  Still have the OEM alternator.

As you can imagine this has become an extremely frustrating issue, and hard to track down because of it's intermittent nature.  The car runs like normal every time it does start, and can idle indefinitely with no noticeable changes.  I'm sorry for the long post but I wanted to put all the info out there for anyone who might know what could be wrong, this has me real stumped.  I don't know if its a bad sensor or what, I live in Wisconsin so maybe it has something to do with the lowering temperature? Any help is appreciated.

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Offline kelso840

Re: Strange Intermittent Issue
« Reply #1 on: 07:49:59 PM / 30-Nov-18 »
Have you checked your ignition coil(s)? One or both may be one their way out.
Infrequently driving an s12.

Offline rednucleus

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Re: Strange Intermittent Issue
« Reply #2 on: 09:28:25 PM / 30-Nov-18 »
Once it runs does it continue to run well or does it ever die?
My 85 had a similar intermittent problem and it was due to failing solder joints in the ECU. Gave all the signs of a failing fuel pump. Once it's running, try wiggling the plugs on the ECU to see if it causes a problem.
IF you clear the codes does the fuel pump code recur?

Offline weitrhino

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Re: Strange Intermittent Issue
« Reply #3 on: 11:54:14 AM / 03-Dec-18 »
Check this temp sensor connection because it corrodes and the connector crumbles with age. This temp sensor coordinates with he ECU to determine the air/fuel mixture. If this connection is failing then the ECU thinks the engine is always cold and that will cause a warm engine to do exactly as you describe.


Offline MSA1R2K

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Re: Strange Intermittent Issue
« Reply #4 on: 01:38:10 PM / 03-Dec-18 »
Once it runs does it continue to run well or does it ever die?
My 85 had a similar intermittent problem and it was due to failing solder joints in the ECU. Gave all the signs of a failing fuel pump. Once it's running, try wiggling the plugs on the ECU to see if it causes a problem.
IF you clear the codes does the fuel pump code recur?

It runs fine every time it does start, never have to worry about it dying on me.  Fuel Pump code does seem to pop up every time I clear the ECU and have the starting issue.

I'll check the ECU connections and temp sensor in the coming days, car is currently sitting up at my parents place (heated garages go a long way during these cold December days) waiting for me to replace the ball joints.  Right ball joint broke in half the other day while I was doing 70 on the highway which was pretty terrifying, luckily I was able to temporarily wire it back together and putt to safety.

I think my coils are fine, I replaced the ignition coil probably about a year ago but I'll test them regardless.

Offline rednucleus

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Re: Strange Intermittent Issue
« Reply #5 on: 09:04:22 PM / 03-Dec-18 »
If once it starts it runs well w/o misses/skips/hesitations the ECU solder joints are probably ok.