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Dealer claims carbon buildup

W

WELSCHJ

NAXJA Forum User
Location
Connecticut
Getting mulitplew misfire codes-replaced wires, cap, rotor, plugs-dealer says they want to do "chemical wash" and if that does not clear it up it will need "major valve/head work"-car runs fine, no surge, start or hesitation problems-but does keep throwing the code 43 for multiple and cylynder #4. Any thoguhts/ideas? I told them to go ahead and do the carbon wash but I am skepticval.
 
WELSCHJ said:
Getting mulitplew misfire codes-replaced wires, cap, rotor, plugs-dealer says they want to do "chemical wash" and if that does not clear it up it will need "major valve/head work"-car runs fine, no surge, start or hesitation problems-but does keep throwing the code 43 for multiple and cylynder #4. Any thoguhts/ideas? I told them to go ahead and do the carbon wash but I am skepticval.
Click to expand...


What year XJ? The dealer has a technical service bulletin out for light pinging, or "spark knock." The fix is to reflash the ecu and retard the timing a little bit.

Another thing to try would be a cooler temp range spark plug. This helped a lot for me.
 
Thanks for the reply- Sorry, forgot to advise it is a 96 4.0
The confusing thing is it "appears" to run fine-no noticable misfire, starts easy, good acceleration, etc. If the code did not get thrown I would never know. The "cartbon buildup" thing sounds a bit fishy but at least he offered it as a cheap alternative to dong valve work.
 
Do NOT sign on for some dealer's valve work without running a vacuum gauge on this thing. Maybe I should make that a big, red NOT.

If you have a valve problem, it will always show up in a vacuum reading. So, usually, will an ignition problem. But if you have a fuel injection or harness problem it likely will not. I've had pretty serious carbon buildup but it never threw a code. If you have steady vacuum you just plain flat do not need a valve job.

Do you have combustion knock? If you do, carbon is may be a problem, but if you do not, I would doubt carbon as a serious problem. If you have some carbon-induced knock you can try GM Top Engine Cleaner. It works pretty well if you follow directions. I guess looking at your original post the dealer is already doing something like this, but I would not let them do any more before doing some serious analysis. I think somebody at the shop needs to make a boat payment or something.
 
Rd: Daler claims carbon buildup

Forgot to add that I do not belioeve tdre is hy jnoc$situat`n, at dast nod`inf ma
`r .not(bable!
 
Art:
Thanks for the comments-my concern actually is more about the misfire (and the code 43) than the knock issue. Agrred that I am not going to have dealer do anything re valves etc..I am just looking for ways to get the misfire issue resolved-extra tough when the car seems to be operating fine!
 
one more vote for the mopar upper combustion chamber cleaner ,
does a great job but ,
follow instructions because that stuff is wicked evil and will try to hurt you ..( skull & crossbones on the label )
well ventilated area is a must , if you want to keep breathing !!!!

there was an issue with the valves not rotating the way they should on some 4.0 litres , until 3500 rpm .( cant remember the affected years )
 
Well the dealer DID the De Carb and obviously reset the codes. Will keep you posted-the valve thing is what the dealer was talking about but he indicated pulling the heads, etc. Assume that is the same TSB you are reffering to?

Thanks to all for your comments-I hope I can come back in a week or so to tell you the light did NOT reactiviate.
 
WELSCHJ said:
Well the dealer DID the De Carb and obviously reset the codes. Will keep you posted-the valve thing is what the dealer was talking about but he indicated pulling the heads, etc. Assume that is the same TSB you are reffering to?

Thanks to all for your comments-I hope I can come back in a week or so to tell you the light did NOT reactiviate.
Click to expand...

I had problems with a 93 which had a slightly resistive splice in the wiring harness to the injectors. I went through a lot of unnecessary component replacement trying to hunt it down. It caused a misfire and a code (in this case the misfire was noticeable), and occurred only after the engine heated up. When hot, the resistance lowered the voltage to one injector just enough to cause a misfire, but it was high enough to trigger the injector tester! I mention this because a good digital ohmmeter can save you a lot of money. So can a vacuum gauge. They're cheap, and they usually come with reasonably informative instructions.

And I repeat, just in case it didn't echo loud enough: do not pay for valve work on an engine that has a steady vacuum reading.
 
my stock '01 keeps throwing a code for the #1 cyl misfire. the CEL will come on and stay on for a few days, then go off. i just ignore it now, because it runs fine, and i've already replaced the plugs, so unless it starts to run worse, i'm not messing with it.
 
Mathew-message heard, lod & clear-thanks!!

One intresting thing-the Dealership mechanic indicated that Chrysler reccomends a de carb for engines throwing a misfire code when the usual suspects (cap, rotor, plugs, wires) don't fix it. Based on the various topics I've read here that seems pretty far fetched-was he just being lazy? He DID say if the CEL came back with the same code after a short while that the valves would need attention (No worries mathew, not gonna go that route) but I thought his analysis was wierd!

Anyway, 24 hours and all is well-but I think 3-5 days is my critical test time!
 
WELSCHJ said:
Mathew-message heard, lod & clear-thanks!!

One intresting thing-the Dealership mechanic indicated that Chrysler reccomends a de carb for engines throwing a misfire code when the usual suspects (cap, rotor, plugs, wires) don't fix it. Based on the various topics I've read here that seems pretty far fetched-was he just being lazy? He DID say if the CEL came back with the same code after a short while that the valves would need attention (No worries mathew, not gonna go that route) but I thought his analysis was wierd!

Anyway, 24 hours and all is well-but I think 3-5 days is my critical test time!
Click to expand...
I HATE THAT WHEN PEOPLE MAKE UP THIER OWN ACRONYMS!!!!! THERE IS NO SUCH THING AS A CEL!!!!!!!!!!!!!! the proper acronym is MIL and it means malfunction indicator lamp......damn idiots!
 
majic_tech said:
I HATE THAT WHEN PEOPLE MAKE UP THIER OWN ACRONYMS!!!!! THERE IS NO SUCH THING AS A CEL!!!!!!!!!!!!!! the proper acronym is MIL and it means malfunction indicator lamp......damn idiots!
Click to expand...

Well Rhodes Scholar, the owners manual refers to it as a Check Engine Light, not MIL. But the point is, people here are trying to help me, and not entirely sure what your problem is.
Here'a another achronym for you to figure out-Go F yrself!
 
majic_tech said:
I HATE THAT WHEN PEOPLE MAKE UP THIER OWN ACRONYMS!!!!! THERE IS NO SUCH THING AS A CEL!!!!!!!!!!!!!! the proper acronym is MIL and it means malfunction indicator lamp......damn idiots!
Click to expand...

We always called it the "Mother in Law" at the Ford dealership I worked at.
 
I emailed my son, who has a 96 FSM. code 43 is not listed in 95. According to him, it indicates misfiring, but it does so by monitoring the crank position sensor for slight variations in engine speed. In other words, it would appear that any number of misfire conditions might cause this, but it is definitely not directly sensing the firing within cylinders, or feedback from the ignition system. I would take this reading with a grain of salt under the circumstances. It could be anything - carbon buildup, coil, plugs, wires, injector harness, or perhaps even a weak CPS or wiring fault causing it to miss occasiona pulses.

ONe of the most valuable ways I've found to hunt down engine problems is a vacuum gauge with a long hose. You can snake the hose out through the edge of the hood and tape it to your side view mirror, and monitor it easily as you drive.
 
Update-has now been about 10 days of various around town and sustained highway driving and all appears well. Not sure even now I buy the Carbon buildup thing but no codes/lights and engine appears to be running fine as it has all along. Recap-got code 43 (misfire/multiple misfires) -replaced wires, plugs,rotor, cap-reset code and threw it again approx 2-3 days later. Dealer said to try de carb, i was skeptical, but let them do it & all appears okay. Perhaps as Mathew suggests, it is an intemitant problem of minor cause, but the de carb is certainly a somewaht cheap and easy fix attempt-and obviously there is no downside to it. So.....keep it in mind as a potential solution. Not sure what solvent Dealer used but I will find out!
Thanks to everyone for their help!
 
Doesnt anyone else worry about the chunks of carbon floating around the engine after the dealer is done decarbing? Possibly clogging oil passages or anything else?
 
Last edited:
90Pioneer said:
Doesnt anyone else worry about the chunks of carbon floating around the engine after the dealer is done decarbing? Possibly clogging oil passages or anything else?
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This is combustion chamber carbon they're dealing with, not sludge or carbon in the oil system. If they did it right, it will not be coming out in chunks, but dissolving and burning off and going out the exhaust as smoke.

I've done this a couple of times with my 95 using GM Top engine cleaner. You throw the stuff down the throttle body until it stalls (or almost stalls in the case of an XJ, which is virtually impossible to stall), then let it sit for a while. When you restart the carbon in the engine comes out the exhaust in the form of an awesome cloud of smoke. I worried about cat clogging, but it didn't happen.

In my case, the problem being addressed was combustion knock. Carbon cleaning worked for that quite well.
 
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