Misfire, heat related? Help... its getting worse!

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Ok, I have a misfire that starts up after the engine bay has gotten really hot after 10-15. It will drop a cylinder for a brief moment at idle or light throttle, which clears up with a little more throttle. It gets worse with time or heat to the point it will stall rather than idle, belches black smoke ect. the wide band pegs rich ect.

I found with the fan set to run constantly the misfire is much less frequent. I have also found going over seams in the road, or rough surfaces seeming help trigger it. Brand new coil packs. checked all the wires that I could think would be relevant.

So the question is, what in the engine bay could be heating up and possibly shock sensitive that could also cause a misfire.

maybe the CAS? i have no idea... any thoughts are appreciated.

 

[eurytopic]

How are the plug wires? Plug gap? You might also test your new coil. Heat tends to make coils less efficient, so that would make me think it's the coil even though it is new.

 

[BIRDCLAWTSi]

Take a spray bottle and spray all of the ignition parts, See if that will induce it. If not, Try the wiggle test, Wiggle wires and clips while engine is runnung, It sounds like it may be sensitive to bumps/ Vibrations. Do you have all the little injector clips that always disappear? Maybe a loose spark plug? Check your vacuum lines and intercooler pipes. Check for loose connections at the harness connectors. Did you wire anything into your computer harness? Maybe there is something coming loose.

 

[Eternalsolitude]

When I read your symptoms, my first thought was crank angle sensor, which you mentioned. Have you checked the readings on it?

Otherwise the only thing it could be is a spark related issue, since we know its not fuel or air as you mentioned your a/f meter reads rich when it's misfiring.

 

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Air:
I have deleted all vacuum lines, excluding the valve cover vents. I will do a boost leak test but this does not feel very much like a boost leak. What would be the MAF sensor's behave.

Fuel:
I have new injectors, maybe 2-3 months old. I suppose that a suck open injector could cause these system. I will check those injector clips and wires. i will also check dsm link for injector duty changes durning misfire though i am not sure if they would show up.

Spark:
the plugs are in good shape and are appropriate for the heat range. changed them with the last oil change. Wires are not a factor, nor should the problems be in the coils as I just changed to a COP set up and the symptoms did not change. i have been trouble shooting the wireing system, I will try the water trick.

I am starting to suspect the CAS, it would also be close enough to the fan to be affected by its use.




Thanks for all the ideas so far guys! ill give you another update tonight after i get under the hood again.

 

[zfanatics]

Have you check your ECU for leaky caps. I had the same thing happpened to me.

 

[And_44]

Some other things to look at. How old is the battery? The internal terminals could be cracked so when you have a rough ride the vibrations could cause a disconnect in voltage. The external terminals should get a looking at as well. But with the battery being at fault you may be loosing a ground and your ECU would turn off and on. Also, your alternator. Our Alternators have an internal voltage regulator. As the regulator goes out the alternator needs a higher load (rpm) to put out more voltage. A lack of voltage going to the plugs would cause no spark or a weak spark that'd get blowen out.

I personally had both the battery issue and alternator issue. But the one that sounds similar to yours is the voltage regulator going out. It's heat sensitive and the effects are felt more at lower loads and rpms. As you increase rpms it improves that's because the alternator is pumping out more voltage. If you were to take out the alternator and have it testes cold it would test fine, but as it heats up the contacts inside seperate.

 

[BIRDCLAWTSi]

Do a compression test, It may sound dumb, But it cant hurt.

 

[brassc2007]

just curious but do you have a stock cat if it is plugged it while cause the vehicle to spit and sputter when cold and worse warm but u can feather it u can test by taking out an o2 sensor and see if the vehicle still has the same issues taking the 02 out allows for exhaust that is backed up to be bypassed out the 02 hole

 

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Not running a cat the exhaust is 3in from turbo back so unless something crawled in and died it should be fine. Anti lag would have cleared out and carcase anyway

The motor was rebuilt about 10k miles ago, along with the head. I ran a compression test mid summer just to check health and my numbers were the same as 500 miles after the rebuild.


On the electrical side of things. The battery is an optima red top relocated to the trunk, less than a year old. The alternator is less than a month old, I seem to fry one every autox season. (Thank you life time warranty.) Generally before my alternator fails I get fluctuating voltage that is visible in the dash lights. Ill test it but its not very likely.

I will check all the connection points between the battery, kill switch, & main harness as well as the alternator. perhaps i will find something there. Also I will double check the power wires for the the coils all the way back into the harness.

I have not checked the ecu for bad caps. I will do that tomorrow if I can find no other answers tonight. also I will try to test the CAS and see whats up with that.

 

[Mph]

Do you have a 6-bolt swap?

 

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yes. 6 bolt block and head.

 

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went through and tested everything I could. The TPS function looks normal on dsmlink. I check and remade several splice connections done during the 6 bolt swap, all unions are now soldered.

I guess its down to a faulty CAS which I cant verify with the normal tests because its so sporadic. Or perhaps bad caps in the ecu, which i have not checked for.

anyone else have anythoughts before i go buying parts just to test.

 

[BIRDCLAWTSi]

went through and tested everything I could. The TPS function looks normal on dsmlink. I check and remade several splice connections done during the 6 bolt swap, all unions are now soldered.

I guess its down to a faulty CAS which I cant verify with the normal tests because its so sporadic. Or perhaps bad caps in the ecu, which i have not checked for.

anyone else have anythoughts before i go buying parts just to test.

Do you have access to a scope? I find it very nice to have when it comes to electrical issues. As long as you can read waveforms, It is a very simple diagnostic tool to troublshoot with. One more thing, I dont know why i didnt think of it sooner, I am not familliar with your C.O.P. set up, Do you still utilize the power transistor? This sounds like a classic ignitor issue.

 

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Regrettably I dont have access to a scope. I really should get one some time.

In any case I noticed this afternoon that shutting the car door with a reasonable amount a force would cause a short stumble. So The only logical course of action was to go around the engine bay banging on things with a hammer... obviously

the only thing affected by it was the fuse box. It would appear I have a loose connection on the underside of my fuse box. should be a simple fix.

 

[BIRDCLAWTSi]

Any luck with the fuse box?