Occasional hickup DM run ADDED see post 37 FIXED post 40

[Don W.]

Re: Occasional hickup miss

Re: Occasional hickup miss

Oh ya. Been wiggling lots of wires everywhere. No luck yet. Heading to the shop now. I'm gonna pull the alarm box and check those wires. Gotta find the thing first... :lol:

I just wish I could find something definitive. As in wiggle this and it quits.

 

[DaveP]

Re: Occasional hickup miss

Re: Occasional hickup miss

Next time it quits, listen for the fuel pump to still be running until the oil press subsides. With warm oil it won't run long, but it won't be off either, when the engine dies. THEN, turn key on. does pump do the 2 second prime? If = yes, give it a very quick crank. Less than a second. Is the fuel pump running for a couple seconds?, if = no, the ECM didn't receive reference pulses. Look at the distributor, module, and pick up coil.

And just what IS the resistance of your pick-up coil? The one in the distributor, with the green and white wire. Check it after it dies. If it isn't the same as when it's cold, it's bad.


And let's try an out-of -the-box idea: what injectors are you running? Are they within resistance spec? We've had a few C4 Corvettes with delphi multec injectors have coil shorting issues because the ethanol in the gas attacks the insulation in the injector. The resistance gets very low, and thus the current through the ECM drivers then gets pretty high. The ECM gets so hot, it quits functioning. This was driving some C4 guys nuts until it became common knowledge.

Happy searching,
DaveP

 

[Don W.]

Re: Occasional hickup miss

Re: Occasional hickup miss

I have the alarm "CPU" out and it still runs. So much for that idea. It's a Cliffalert III (3) if that means anything to anyone. Acording the wireing diag. there is one splice in the ign sw line. I'll track that down and check it.

ECM is out from under dash with chip access panel removed. When it quits DM will show that it has lost contact with the ECM. It will flash the CEL (no code set), and it does the open/closed loop thing.

It does -seem- to be heat related. These 60# injs are from about April 2010. I will check resistance at both the PU coil and injs. Fuel pressure is not the issue. FP stays up the whole time.

You might be on to something in that it seems like an ECM failure but can it fail for that short of a period? Except for that one time when it did quit the motor doesn't die.

I think I will run a temporary hot lead direct to ECM from the bat and double check ECM ground.

 

[syclone32]

Re: Occasional hickup miss

Re: Occasional hickup miss

I had a similar problem for a year with my truck, Random misfires, random shuting off while driving or sitting. Tach would jump and indicator lights would flash. After it died it would start right back up again like nothing was wrong? I also had a clifford alarm and didn't think twice about it. I never used it. One day out of desperation, I cut all the wires leading from the alarm unit and realized it was wired into the factory ignition system as a start/ignition cut. After removing the alarm I haven't had a problem. Its been 2 flawless years now. May want to check that alarm out.

 

[Don W.]

Re: Occasional hickup miss

Re: Occasional hickup miss

I had a similar problem for a year with my truck, Random misfires, random shuting off while driving or sitting. Tach would jump and indicator lights would flash. After it died it would start right back up again like nothing was wrong? I also had a clifford alarm and didn't think twice about it. I never used it. One day out of desperation, I cut all the wires leading from the alarm unit and realized it was wired into the factory ignition system as a start/ignition cut. After removing the alarm I haven't had a problem. Its been 2 flawless years now. May want to check that alarm out.

Heading there now. Wiring diag in hand...

 

[wildphil]

Re: Occasional hickup miss

Re: Occasional hickup miss

I have also had a bad coil cause the engine to die when it got warm under the hood. Then the vehicle would start right up.

 

[Don W.]

Re: Occasional hickup miss

Re: Occasional hickup miss

No eureka moment yet. Alt is at a "real" shop for some load testing, heat soaking, whatever they can throw at it just to be sure the alt is not the issue. I may start it without the alt for a few minutes to see it the problem is still there.

 

[Don W.]

Re: Occasional hickup miss

Re: Occasional hickup miss

Minor update:

Completely removed the alarm. Although I ran a before-and-after test and it didn't seem to make any difference I did notice that when I removed the alarm harness from the "CPU" that it just fell out. IOW I didn't have to squeeze the plastic spring clips (similar to those on the ECM.) Hard to say if that was the issue or not. Next I'll remake the one main hot lead that was cut and spliced to the ign sw for the alarm. At that point I intend to start it and just let it idle for up to half an hour and just see what happens.

I've got the dash darn near completely disassembled to remove the alarm. I notice that the light for the glove box is not there? Anyone want to throw up a pic so I can see what I'm looking for...

I've also ordered some ECM connectors as I know a couple of those are a little beat up from excursions making changes to o2 connections etc. so will be checking those as well.

BTW the alternator passed without any problems so it wasn't that.

 

[Don W.]

Re: Occasional hickup miss

Re: Occasional hickup miss

Minor update. I start the truck and back out of the shop. Lots of stuff in the way so I'm watching the mirrors. Truck just dies at the door. CEL comes on but no code is set. The truck restarts like nothing happened. I'm running out of ideas. On a whim I change the ECM A fuse. Just put a different one in from the fuse panel. I drive the truck to and from the parts house for something else and it runs fine. Was gonna bring it home but nope, it's Halloween. Decide I'll just drive it more tomorrow.

What I've done so far:

Completely disconnect MSD, no help

Completely remove the alarm. This seems to cure the low voltage "alarm" from the inverter and had the side effect of somehow raising system voltage a bit.

Lost track of the number of times I checked various connections.

Most recent driving tests seemed to indicate it was heat related because when it did hiccup it didn't do it until it was hot. Also it goes completely rich telling me it has lost ignition.

Counting the original MSD coil which had been there for a few years I'm on my third coil and back to the second module.

Next step will be to just drive it and see what it does.

 

[DaveP]

Re: Occasional hickup miss

Re: Occasional hickup miss

..... CEL comes on but no code is set.

When the engine is not running, the CEL comes on because there technically IS a code set. And when you pull it, it's code 12. Code 12= "no distributor reference pulses received". Makes sense, that if the engine stalls, the CEL comes on.

 

[WyoSyclone]

Re: Occasional hickup miss

Re: Occasional hickup miss

Wonder if it could be the ECM having a problem.... I didn't read back through to see if you'd tried a second.

 

[Don W.]

Re: Occasional hickup miss

Re: Occasional hickup miss

DaveP mentioned the ECM overheating but when it quit yesterday it had only been running for a minute or two. Sounds unlikely that it would be that. If it's a general failure of some sort in the ECM then yes, I suppose that's possible. And no, I have not tried another. I only have the one.

Code 12 sounds correct but DM did not show any code that's all I know.

I'll drive it more today and see what happens.

 

[wildphil]

Re: Occasional hickup miss

Re: Occasional hickup miss

If you are unable to borrow a ECM local. Let me know and I will ship you one that you can try.

 

[Don W.]

Re: Occasional hickup miss

Re: Occasional hickup miss

Thanks Phil, I'll let you know. Still in the dark but here's today's results. I drove the truck quite a bit today. Maybe 40-50 miles total but all local. Chased parts, home for lunch, that kind of stuff.

Anyway, it did stumble a very few times. Now when it does it it doesn't even act like I shut the key off. It will literally skip just a couple of cylinders. I feel it, the tach drops and returns very quickly and there's no CEL. Everything else is normal as best as I can tell. DM doesn't seem to pick it up but I could easily be missing something.

This after swapping the ECM A fuse. Very weird, I know.

Next step as far as I can tell is to disassemble the fuse panel and/or trace the entire ECM A circuit. Not looking forward to taking the fuse panel down but what the heck...

 

[DaveP]

Re: Occasional hickup miss

Re: Occasional hickup miss

If the tach is affected by the momentary hick-up, it almost has to be ignition. But what if it's the tach itself? Mike just had a tach-caused ignition problem.

Remove the engine wire harness connector from the coil. Remove the pin with the white wire from the connector shell and reinstall on the coil. This disconnects the tach from the ignition circuit. (You must still have the white wire to the distributor).

This test will eliminate/proof the tach and associated wiring.

 

[Don W.]

Re: Occasional hickup miss

Re: Occasional hickup miss

Hmmm, interesting. I will try that.

 

[Don W.]

Re: Occasional hickup miss

Re: Occasional hickup miss

Finally, here is the problem caught on DM. Check out record 1513-1514 where it switches from closed loop to open. Check the TPS% goes from 7 to 0. Then a little later at record 1549 ign volts drops from 14 to 12.7.

PLEASE look at any and everything you can think of.

I've had C100 (the fuse panel pass through) apart and cleaned everything. The only thing I gained (lost?) is now the oil pres ga pegs when I turn the key on. :roll: I have found no pinched wires.

Alarm is completely removed like I said. Today I disconnected the power to the gauges (one was on a fuse "tap") and disconnected power to the alky. All in an attempt to isolate and remove potential trouble spots. NO help, DM run was AFTER all this.

http://www.sonic.net/~donpris/AutoLog_227.uni

 

[Eric Sy GN]

Re: Occasional hickup DM run ADDED see post 37

Re: Occasional hickup DM run ADDED see post 37

Hi Don,
I see in the log that the baro resets, and runtime resets to zero. In the chip program, this happens if the ignition volts drops below 4.0 volts, even for a split second. Ignition volts is connected to the ECM at pin A6. Any connection that could drop the voltage at A6 will cause a problem. But it doesn't rule out an ECM problem.

Regards,
Eric

 

[Don W.]

Re: Occasional hickup DM run ADDED see post 37

Re: Occasional hickup DM run ADDED see post 37

Appreciate the info.

I had changed the ign switch a few years ago. I've jiggled the key countless times so I kinda doubt it's the switch. I don't mind changing it again but will continue to check wiring before I do.

 

[Don W.]

Re: Occasional hickup DM run ADDED see post 37

Re: Occasional hickup DM run ADDED see post 37

Well I think I may have fixed the problem. When removed the alarm there were two wires to the ignition sw that had been cut. One was the red ign wire and one was yellow. The yellow wire went to a relay that I just bypassed. The red wire had been cut then spliced back together but with a “tap” or second wire coming from the splice to the alarm. I just left that splice in place and cut the tap wire.

After checking uncountable connections and finding nothing I decided to lower the steering column and redo that splice. Thinking all the time how can it be bad since I’ve tugged and wiggled that splice many times already. Anyway, when I cut the wire at the splice I cut it at the end of the metal (not the end of the plastic insulator) just to conserve wire as there is not a lot of slack wire there to begin with.

Well I’ll be darned; I can now see where one end of the splice is crimped ON the wire insulation. Crap. All this work and trouble, all the good thoughts from you folks, and damn, it’s a crummy splice that someone else put in years ago and is just now causing trouble.

After making a CORRECT splice to both wires. A test run seems to confirm that the thing is fixed. There’s a bunch of wires to be tucked away yet then further driving to confirm the repair. So far I think I’ve got it.

Thanks again to all that posted their thought, ideas, and hints.