Dealer claims carbon buildup

[WELSCHJ]

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.

[90Pioneer]

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.


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.

[WELSCHJ]

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.

[Matthew Currie]

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.

[W%JSCHJ]

Forgot to add that I do not belioeve tdre is
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[WELSCHJ]

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!

[Ron Hyslop]

Buy a can of Mopar cumbustion chamber and follow instructions on the can, about $10. My Jeep tech freind recommends it be used every 50000mi.

[sw_mi_xj]

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 )

[WELSCHJ]

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.

[Matthew Currie]

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.

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.

[01_XJ]

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.

[WELSCHJ]

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!

[majic_tech]

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!
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!

[WELSCHJ]

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!

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!

[dizzymac]

LOL

[carnuck]

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!

We always called it the "Mother in Law" at the Ford dealership I worked at.

[Matthew Currie]

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.

[WELSCHJ]

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!

[90Pioneer]

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?

[Matthew Currie]

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?

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.

[88XJSport]

to pay $89 for the diagnostics

Man, good thing you didnt let them do that valve job, if it costs 89 dollars to pull a check engine code, just imagine how much a valve job would be at the dealership!!!!!!

[WELSCHJ]

Yeah, it would have been an obscene number. As i mentioned, only wound up at the dealership because of some unusual circumstances. But the $40 or so dollars they wanted for the De Carb wasn't all that awful since i had to leave the car there anyway.
A few years ago, my son had the car out of state and got a code/light which turned out to be bad O2 sensor-the place he went to also charged around $80 or so for the diagnostics--so while a lot of money not that outrageous compared to others we have seen.

Anyway, appears that we are back in business for now!

[WELSCHJ]

Yeah, it would have been an obscene number. As i mentioned, only wound up at the dealership because of some unusual circumstances. But the $40 or so dollars they wanted for the De Carb wasn't all that awful since i had to leave the car there anyway.
A few years ago, my son had the car out of state and got a code/light which turned out to be bad O2 sensor-the place he went to also charged around $80 or so for the diagnostics--so while a lot of money not that outrageous compared to others we have seen.

Anyway, appears that we are back in business for now!

Before anyone gets carzy I meant to say vehicle/truck!!!!

[WELSCHJ]

Well, all good things must end, I suppose. After approx 6 weeks and about 3000 miles the Check Engine Light came back on today-my son was traveling on the highway when it came on---as in the past, no symptoms, engine running fine, Gas mileage quite decent, etc.

When pulling the codes with the key turn method again got 12 and good old 43. Actually, surprised that 12 would come up-the engine has probably gone through 3-500 start cycles without the battery being disconeected...but obviously that is not my main concern. So, assuming "carbon buildup" was only a temp fix (although it did last long) and have done rotor, plugs, wires, cap, CKS (the one on the trans housing)..any other thoughts??

[Fish'nCarz]

I do not know about your year, but my '01 needed a little piece of white, insulated, wire-loom like stuff on the #3 injector due to the hot restart issue, and the mechanic recommended I run the carbon cleaner (I used SeaFoam) through it as well. My back window and lift gate looked like I'd been burning garbage right behind the beast for a week, but it really flushed some sh*t out! Ran really great on that tank O'gas. I'm going to wait a while and run another can through the tank before winter. I suspect I may have some moisture or other crap in the gas tank that exacerbates misfires when I'm running on the last 1/4 tank. CEL hasn't shown up again.

Again, YMMV.

[hotrodXJ]

Can we all stop badmouthing dealers/technicians here please? If you knew what was wrong and how to fix it, you'd do it yourself.
If cleaning out carbon was the repair (and nothing else) quoted how much time do you think the technician spent with it?
The 96 will not need the insulator like the 01. The injectors and intake are different.
There are many things that can cause misfire codes. However, its hard enough to diagnose it with the vehicle in front of you and not through your computer screen.
-Aaron
BTW, each time I see "CEL" I can't remember you actually mean MIL.

[WELSCHJ]

Not sure I am "bashing" anyone...just looking for some help. And, no kidding, obviously if I knew how to fix the problem I would do it and be posting the answer, as opposed to asking for help???

If nothing can be solved via computer screen, then what is the purpose of this forum-insn't to attempt to excahnge possible solutions? And by the way, I said "check engine light" not "CEL" because to you and a few others on here that really is such a critical issue!

[MG_43]

Everytime I see "check engine light" it reminds me of a funny story. My wife bought a 1980 Monte Carlo when the computer stuff was pretty new on cars, the check engine light came on and she pulled over lifted the hood and said "yup, its there" what the hell am I suppose to do now.

[carnuck]

I worked for a dealer and most of them are shooting in the dark nowadays because everything is computer controlled and if the computer can't diagnose the vehicle, they have to rely on the fixes others have found (basically what everyone does here too)
12 error code means there is a high chance that something caused and extreme power drop (lights left on, jumps starting another very dead car, etc) may have triggered it, BUT it can also be loose or corroded connections (if you pull the cable off, and wipe your finger through the inside and get a grey pasty looking stuff on your finger, that is lead oxide which, unlike lead, is a VERY poor power conduction agent. Clean, dry, shiny metal to metal contact at the battery posts, and power cables that aren't going green inside from corrosion are important.
The main ground connection at the block is infamous for getting "silent" corrosion between it, the bolt and the block which will flex and disconnect while you are driving at certain torque points. I've also had the stock ground cable pull loose from the cable lug on the block and leave just the tiny battery to fender ground lead to do all the work. You would NOT believe how many people will replace their alternator and battery as well as other parts trying to cure a migrating problem without taking the time to diagnose. I have bought quite a few for cheap after offering to repair it for a reasonable fee {they passed, citing "professionals" that couldn't find the trouble, so how could I? 30 years as a mechanic is how} and fixed this minor issue then resold for a decent price.
Last, but certainly not least, a battery with broken internal plates will give this error as well as work sometimes, but not always.

[WELSCHJ]

Thanks Carnuck...
I will check this out..did replace battery and negative cable recently (6 months) no doubt some of these other suggestios should be checked. As I said the code 12 isn't as concerning to me as the 43, but sometimes one problem fixed gets you on the road to fixing another!

Agree, the computer databases (including this one) are very valuable!