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Carbon build up... my ass!

9

90Pioneer

NAXJA Forum User
Location
USA
I have a '96 4.0 AW4 Cherokee which recently (about a year ago) started pinging like a mother f*cker under load (hard acceleration). Stopped doing it when premium fuel is used.

I searched the boards, and have ran countless bottles of fuel injection cleaner, used GM Top End Cleaner, and even paid $100 having the injectors and fuel rail cleaned.

Took it to a mechanic and $300 later they told me it was carbon build up and could be fixed for only $800.

Months later I need a front U joint and take it to a different mechanic. I mentioned the pinging (actually sounds more like a rattling) problem to them. I guess the guy did some research for me and found a technical service bulletin Chrysler put out. Apparently my computer needs to be reflashed. The service bulletin said it affects the '96 and '97 model years.

I can get the bulletin # if anyone wants it to show the dealer.

Finally I will be able to stop running premium in the damn thing.
 
You know, whenever I suspect carbon deposits causing trouble, here's what works for me...

1) Disconnect catalytic converter at bolt flange (you don't want to clog the thing)

2) Remove air hose at throttle body (the one that goes to the airbox/filter. You need direct access for this.)

3) Start the engine and allow to idle to op temp.

4) With a pump/trigger sprayer on the finest mist you can manage, spray small bursts into the throttle valve. Watch for black clouds coming out from under the vehicle - that's the carbon that used to be built up.

5) Repeat until you don't get clouds anymore.

How it works -
The carbon, being porous, will soak up the water mist on the intake stroke. Since flash temperatures in the cylinder are well in excess of 1000*F, the water flashes to steam when the fuel is ignited. The sudden expansion of the water as it flashes into steam will literally blast the carbon deposits in the cylinder apart - and they are then blown out the tailpipe.

This won't do much for intake valve deposits - you'll have to use a deposit cleaner for that. However, intake valve deposits usually don't cause pinging.

5-90
 
I don't really think there are any (or very little) deposits to clean away. The engine is very clean. I just changed my oil with 4700 miles and you could still see through it. It doesnt even smoke anymore if I were to use a can of top end cleaner. I could eat off my throttle body, it's so clean.

I got the bulletin printed out.

Reference Number: 18-24-98 Date of Issue: 7/31/1998

LIGHT SPARK KNOCK TIMING RETARD FEATURE

Model(s):

1996-97 Jeep Cherokee

Also lists a bunch of other vehicles. Says it applies to vehicles equipped with a 2.5l, 4.0l, 3.9l, 5.2l, and 5.9l.

Symptom/Condition:

Some vehicles may exhibit LIGHT spark knock with a warm engine under load.

The PCM software update number is 04669020

Goes another 3 pages...

Says it should take them 1/2 hour, so even if they charge me, it wont be terrible.
 
Last edited:
Do bear in mind that there are no symptoms of carbon buildup that will show in the oil - but the still-clear oil does show that you don't have much of a blow-by problem (the contamination of engine oil by gasoline is what usually causes the darkening. I'd be willing to bet you can't smell much gasoline in your oil, either.)

Just some food for thought...

5-90
 
5-90 said:
You know, whenever I suspect carbon deposits causing trouble, here's what works for me...

1) Disconnect catalytic converter at bolt flange (you don't want to clog the thing)

2) Remove air hose at throttle body (the one that goes to the airbox/filter. You need direct access for this.)

3) Start the engine and allow to idle to op temp.

4) With a pump/trigger sprayer on the finest mist you can manage, spray small bursts into the throttle valve. Watch for black clouds coming out from under the vehicle - that's the carbon that used to be built up.

5) Repeat until you don't get clouds anymore.

How it works -
The carbon, being porous, will soak up the water mist on the intake stroke. Since flash temperatures in the cylinder are well in excess of 1000*F, the water flashes to steam when the fuel is ignited. The sudden expansion of the water as it flashes into steam will literally blast the carbon deposits in the cylinder apart - and they are then blown out the tailpipe.

This won't do much for intake valve deposits - you'll have to use a deposit cleaner for that. However, intake valve deposits usually don't cause pinging.

5-90
Click to expand...


so your saying that water in the engine isnt always bad? damn...

i thought hydrolocking was a big deal... i guess thats why to took care to mention "fine mist"
 
Hey I got this symptom going on in my 94 XJ sport... whats the deal... I've checked the engine codes and it shows "55" which as far as I can assertain it indicates "normal" and end of check ?

This pinging/knocking is shitting me big time, any help please
 
browneee said:
Hey I got this symptom going on in my 94 XJ sport... whats the deal... I've checked the engine codes and it shows "55" which as far as I can assertain it indicates "normal" and end of check ?

This pinging/knocking is shitting me big time, any help please
Click to expand...
There's two suggestion in this thread, try them and report back. If is something that just started try the water misting.
 
browneee said:
"Apparently my computer needs to be reflashed" what is this ?
Click to expand...
If it has always had that problem then the computer needs the programing changed ("flashed" for flash memory) If its something that just started one day then it's bad fuel or carbon buildup.
Run a pint of Fosters through it, that stuff sure cleans me out.
drunk.gif
 
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well i've been becomming more aware of it... I think you may well be right, it could indeed be carbon build up... I dont think I'l use fosters as that stuff is shit, Only marginally better than your own millers :)

So correct me if I'm wrong, but if I disconnect the air intake, disconect the cat... converter and use a fine mist spray (gently) this should remove carbon deposits and not damage my engine ?
 
Depending on how fast the tech is is should be only a 15 min job.Had mine done in 98 shortly after I purchased my 96 XJ.
Of course knowing the mechanic and shop foreman helped $20 cash was the charge.
Wayne
 
Wayne Sihler said:
Depending on how fast the tech is is should be only a 15 min job.Had mine done in 98 shortly after I purchased my 96 XJ.
Of course knowing the mechanic and shop foreman helped $20 cash was the charge.
Wayne
Click to expand...

Sorry wayne... are you talking about the do it your self method or a professional carbon clean or the "re-flash"
 
browneee said:
Sorry wayne... are you talking about the do it your self method or a professional carbon clean or the "re-flash"
Click to expand...

This was the "Flash",the water clean/carbon removal thing has been around for decades.
Wayne
 
Just an FYI...

we had the same issue on the 1996 ZJ. They reflashed our computer ($120) and we still had some pinging, although not nearly as severe as pre-flash.

We have been running some 89 Octane for the last 3 or 4 tanks, and it seems to have completely taken care of the pinging...spark knock, I think they call it.

They also suggested the "decarbonization" of the system that we declined.

So...it is not just an XJ issue.
 
XJ_ranger said:
so your saying that water in the engine isnt always bad? damn...

i thought hydrolocking was a big deal... i guess thats why to took care to mention "fine mist"
Click to expand...

You, sir, are erect! Hydrolocking is very bad - but a fine mist won't clog anything up and is just fine. I used to run a water fog on my Bug all the time - which allowed me to really ramp up compression without having to run AvGas all the time (even tho, then, it cost less than 87 octane does now! Dammit!)

A fine mist will do exactly what I said it will - harmlessly blast the carbon out of the combustion chamber. You don't need a lot of water, and take your time doing it. That's exactly why I hit on that "finest mist possible" angle - not only does that keep you from getting too much water in the intake, but it also helps keep the water suspended until it gets to the chamber, and it will actually work better with the finer mist.

I've used this on a great many engines, and I've never damaged one. It's best to use distilled water for this, but it's not absolutely necessary (tap water works fine, but well water can be an issue.) This will work on pretty much anything - but you'll want to disconnect the exhaust if you have a catalytic converter.

5-90
 
They've got some really heavy-duty solvent or another that they use.

I can't lay claim to being a true environmentalist - I'm willing to use a more "natural" or "nature-friendly" means to get something done only if it works at least as well as the stuff I'm not supposed to use anymore. This works well.

Gawd, but I miss carbon tetrachloride! I used to use that to clean rifle brass, and nothing else has come close since! I used the same gallon can of the stuff for 15 years...

5-90
 
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