If You Had To Pull The Head.....

[Allen]

What else would you do to the engine or look at?

This isn't a planned rebuild, and there are no known mechanical issues.

Would you pull the pan and take a look at a few rod and main bearings?

I'll be pulling my 4.0L head soon to de-carbonize it, and the pistons.

It still detonates badly on anything less than 93 Octane.

Allen

[PK99TJ]

Pressure test it while its out.

Good article (talks quite about about 258 vs 232), but covers general head tune-up:

http://www.monsterslayer.com/jeep/40Head/40Head.htm

[derf]

As long as the head is off, you may as well take it to a machine shop for a complete cleaning and rebuild with a 3 angle valve job.

[mnjeeper]

Originally posted by derf
As long as the head is off, you may as well take it to a machine shop for a complete cleaning and rebuild with a 3 angle valve job.

I was going to say the same, but I wasn't going to mention a 3 angle valve job...since I don't know what that is

[Jerry Bransford]

Somehow I don't think you're going to find the combustion chamber all carboned up. You did the water trick and I'm betting it's clean as the proverbial whistle in there.

[Allen]

Originally posted by Jerry Bransford
Somehow I don't think you're going to find the combustion chamber all carboned up. You did the water trick and I'm betting it's clean as the proverbial whistle in there.

And the detonation then would be caused by?????

Jerry, you also realize that I ran my TJ with an engine operating temp of about 160*F, instead of the normal 210*F, for almost a year?

Allen

[Jerry Bransford]

Not sure what the 160 temp has to do with it (other than the factory recommends 195) but any number of things can cause pinging. Even the wrong model spark plug can cause it. Good luck with it, wow what a mysterious problem.

[Allen]

Plugs are correct.

Last set was carbon fouled.

Last year I did some cooling system mods to correct an overheating problem and got carried away. I figured cooler was better, and what I thought was good, was in fact bad.

Now we have deduced that the cooler temps may have tricked the computer into running rich, and the excess fuel combined with cool internal temps and a lot of highway driving led to incomplete combustion, increasing build up.

Thoughts?

Because if I pull the head, and everything looks good, I'll need some ideas on where to go next.

Allen

[Dan-H]

did you already try seafoam?

[Allen]

Originally posted by Dan-H
did you already try seafoam?

6 cans of Seafoam went through the TB.

I also fried 2 different TB sensors from all the fluid that went down the intake to clean out the carbon.

Allen

[Dukes69]

Originally posted by Allen
Now we have deduced that the cooler temps may have tricked the computer into running rich, and the excess fuel combined with cool internal temps and a lot of highway driving led to incomplete combustion, increasing build up.

I dont really know how the computer works, but its my understanding that rich is cool and lean is hot. So with that, I would think the computer (knowing the engine is running cool) would want to lean it out to get the temp up where it should be. A lean condition can cause detonation. In addition if there is a bad sensor (whichever one controls the timing), it could be telling the computer to give more timing advance, causing the detonation. What about a worn timing chain, which could change the valve timing?

[Jerry Bransford]

Originally posted by Dukes69
I dont really know how the computer works, but its my understanding that rich is cool and lean is hot. So with that, I would think the computer (knowing the engine is running cool) would want to lean it out to get the temp up where it should be. A lean condition can cause detonation. In addition if there is a bad sensor (whichever one controls the timing), it could be telling the computer to give more timing advance, causing the detonation. What about a worn timing chain, which could change the valve timing?

Good ideas. On the temp vs. fuel mixture thing, the TJ's computer gives a richer mixture when the engine is cold than when it's up to normal operating temperature. I think what Allen was saying was that with his 160 degree thermostat, the engine didn't always get all the way up to its normal operating temperature so the computer tended to send a richer fuel mixture more often than was good.

[mnjeeper]

Originally posted by Allen

Because if I pull the head, and everything looks good, I'll need some ideas on where to go next.

Allen

I would look into a new tank of 93 octane at that point and a nice trade-in. You've been chasing gremlins long enough. I put a pretty low value on my time vs money....and I know even at that I would be considering getting rid of it.

[Robert J. Yates]

What year is your Jeep again Allen?

[Allen]

Here's the full history in case anyone hasn't been paying attention to my previous postings, or may have forgotten the particulars.

It's a 2000 with just under 50,000 miles.

I doubt anything is that worn out, like a burnt valve or timing components.....but anything is possible given faulty OEM components.

Truth is, I haven't been chasing gremlins that much.

I've dumped a bunch of fluids down the throttle body to clean out the cumbustion chambers, but that hasn't solved anything except fubaring a few sensors. I've added a bunch of stuff to a nearly empty gas tanks and just flogged the crap out of it down the highway and back.

No dice.

So I've been running premium exclusively, because it won't detonate at all on 93.....

All this started with my faulty CSF radiator. My TJ overheated badly.

So I installed a lower temp fan cluth that locked up at a lower temp, and remained locked longer. I also added a 7 blade fan to move more air.

That didn't solve the problem, it still overheated.

So I returned the CSF, and installed an OEM radiator.

I left the "special" fan clutch and fan installed.

That was my big mistake.

My engine then never got hotter than about 160*F.

I thought that was a good thing. Cooler is better right?

After several thousand miles, the detonation started creeping up gradually.

So I gradually began increasing my octane rating on the gas I used and started with the cleaning process. That leads up to where I'm at now.

If I were to run a full tank of 87 right now, it would almost detonate just sitting there idiling. It starts right off of idle, regardless of throttle position, and continues.....

But running premium is getting old.....and what happens if it starts detonating on 93? A few times it's detonated on 87 so badly that I have some concerns about piston and bearing damage.....

It's time to look into this and see what I can find, then go from there.

I really wish the timing wasn't computer controlled, because that would give me some obvious things to check and set if necessary.

Kinda hard to look at a black box that runs on PFM and determine if it's the source of my problems.

It runs great on 93. Good power. No brown smoke out the tailpipe. Mileage is 14.5 to 16.5 depending.

I'm open to all suggestions.

And yes, the thought of dumping it has crossed my mind.....but I haven't crossed that line yet

Allen

[Tumbleweed]

Allen, any chance of checking to see if you have a plugged catalytic converter? I know this is reaching out there, and not sure since it runs well on higher octane. Short of plugging in another computer-seems you are chasing it well. Can you clear the computer memory or reset it to standard specs?

[Robert J. Yates]

I'm betting that its not combustion chamber related at all (most likely clean) and the radiator nonsense you have been chasing is simply coincidence. Have you actually had the PCM checked?

[Allen]

Originally posted by Tumbleweed
Allen, any chance of checking to see if you have a plugged catalytic converter? I know this is reaching out there, and not sure since it runs well on higher octane. Short of plugging in another computer-seems you are chasing it well. Can you clear the computer memory or reset it to standard specs?

Frank had the info on how to clear the computer so that it "relearns" itself for something like the first 50 starts. I'll see if I can find his info and do it again. MAybe someone has that bookmarked and can point me to the link?

I did it right after I installed the new OEM radiator.

Allen

[Allen]

Originally posted by Robert J. Yates
I'm betting that its not combustion chamber related at all (most likely clean) and the radiator nonsense you have been chasing is simply coincidence. Have you actually had the PCM checked?

Yep. It could be a coincidence.

But there'd have to be some sort of consequences for running the engine "cold" for such a long period of time. At least I would think there would be, anyway.

Never had the PCM checked. Where is it, and how do I go about having it checked?

If it's simply tapping into the OBD II with a scanner, I would think that the first time I fried the TB sensor from dumping fluid down the TB, the codes would have shown up then. I had it scanned to make sure it was the TPS before I replaced it.

Allen

[Tumbleweed]

Forced Flash

This very simple procedure will Erase the ?Adaptive Memory? stored inside the TJ PCM and allow a new ?Adaptive Memory? to be developed.

After performing this procedure the PCM will re-learn and store into Adaptive Memory your engines performance characteristics.



1.Disconnect the POSITIVE battery Terminal and touch it to ground for 30 seconds. (This is to discharge the PCM capacitors, which maintain the Adaptive Memory.)
2.Reconnect the Battery Cable
3.Turn Ignition Switch to the ?On? position but DO NOT start the engine
4.Turn Headlight ?On?
5.Turn Headlights ?Off?
6.Turn Ignition Key ?Off?


The Adaptive Memory has now been flashed, or erased from the PCM.

When you start the engine it will be running off a set of pre-programmed tables that come with the PCM from the factory.

When you get the engine up to operating temperature the PCM will start to collect data for the ?Adaptive Memory?.

The PCM will collect data for Adaptive Memory for the first 50 Warm-up Cycles.


Warm-up Cycle

A warm-up cycle happens when all of the following conditions exist.



1. Engine is running
2. A raise of 40F in engine temperature must occur ABOVE the engine temperature at start-up
3. Engine Coolant Temp must reach at least 160 F.



Once your engine has gone through 50 warm-up cycles in at least a 500-mile distance the PCM adaptive memory is set. It WILL NOT Change unless you flash it out and start all over again.

[Allen]

Originally posted by Tumbleweed
[B]1.Disconnect the POSITIVE battery Terminal and touch it to ground for 30 seconds.

Uh, ground where? To the negative terminal?

Allen

(And thanks for the info.....)

[Tumbleweed]

I just be the "cut and paste" guy. I would assume any ground, they are all connected-right? Frank had it under the supercharger post.

[Allen]

Originally posted by Tumbleweed
I just be the "cut and paste" guy. I would assume any ground, they are all connected-right? Frank had it under the supercharger post.

Done.

We'll see what it does.

Allen

[TJeeper]

Since you didn't mention it, you did change the thermostat back to a 195 (from the 160) when you put the OEM radiator back in right? Is it still running too cool with the 195 degree thermostat?

[Allen]

Originally posted by TJeeper
Since you didn't mention it, you did change the thermostat back to a 195 (from the 160) when you put the OEM radiator back in right? Is it still running too cool with the 195 degree thermostat?

That's just it.

The Jeep was running 160 with a 195 thermostat in place.

I never changed it out.

The 160 temp came from the superior cooling of the OEM radiator, special fan clutch, and 7 blade fan.

And yes.

I recently went and put a new OEM 195 thermostat it.

Allen

[TJeeper]

Originally posted by Allen
The Jeep was running 160 with a 195 thermostat in place.

I never changed it out.

The 160 temp came from the superior cooling of the OEM radiator, special fan clutch, and 7 blade fan.

It is unlikely the 160 temp came from the radiator, clutch and fan. It is more likely the 195 thermostat was stuck open, never allowing the engine to properly warm up. Think about it, if the thermostat was operating correctly, the engine temp will never go below 195 because the radiator is bypassed when the thermostat closes.

I have had this happen twice to my Jeep in the 6 years of owning it. This is the only vehicle I have owned that I have had repeated failures of stuck thermostats.

Hopefully resetting the computer will get you back to normal, and no damage was done.

[Jerry Bransford]

Originally posted by TJeeper
It is unlikely the 160 temp came from the radiator, clutch and fan. It is more likely the 195 thermostat was stuck open, never allowing the engine to properly warm up.

Unless you're driving in cold conditions, a thermostat that is stuck open (or if the thermostat has been removed) will never prevent an engine from fully warming up. Being stuck open just means the engine will take longer to warm up.

[TJeeper]

Wrong Jerry, I just had another theromstat stuck wide open last month. Lows were 50s, highs were 80s. My TJ was reading 160 around town, getting up to about 195 on the highway.

[kranky_kel]

My jeep and a Ford work truck I had never got close to operating temps when the thermostats got stuck open.

[truckjohn]

How about your O2 sensor(s)

I have had vehicles that would run *way* either lean or rich when the O2 sensor(s) went bad....

Like fouling out plugs, throwing off ignition, running cold, etc.... Some would even ping and complain.

I have also had vehicles that wouldn't show codes for bad O2 sensors even when they went nuts.....

I hate to say it but a trip to the Stealership service dept might be in order. Those computers are OBDII "compatible" but the factory does a *whole* lot more stuff than what the OBDII reader will ever read. The dealerships usually have the Factory magic diagnostic box which can do everything in the world.

Best regards

John