Low Compression- 198k. Rings? Carbon buildup?

srmitchell

NAXJA Member
NAXJA Member
Hey all.
Drove my xj out to a local river spot a few days back, about 40 miles from home. Lots of hills, 90 degree heat. Couldn't get out of its own way. Incredibly slow, hard to hold speed on hills, etc. Jeep has been well maintained for the 75k I've had it. Has 198k right now.

2001, 4.0, 4.56 gears, 33's and tons of armor.
Untitled by Sean Mitchell, on Flickr

Current engine mods- Otherwise stock internals.
-4 hole Grand Caravan Injectors
-Stock intake with front blocked off and rerouted to the cowl. (2.5 inch tubing- Shouldn't be that restrictive...Right?)
-DIY 60mm throttle body
-High flow cat and flowmaster 40 with custom pipe.

Cowl intake-
Untitled by Sean Mitchell, on Flickr

Did a compression check.
1- 85psi
2- 105psi
3- 95psi
4- 90psi
5- 95psi
6- 100psi

Retested 1 and 4, went from 85 to 95 and then 90 to 110 with oil in the cylinders.

So I was guessing rings. Doesn't burn much oil though. And no coolant loss. And I saw a TON of carbon in cylinder 1, which also had the lowest numbers. Is it common for carbon to stop valves from sealing well in the 4.0?

Thinking about doing a steam treatment. (slowly running water through intake.) Did the seafoam treatment a few weeks back too. Lots of smoke. My compression gauge was a rental from Oreillys so maybe I'll do the carbon treatment and then retest.

Advice?
 

RCP Phx

New member
There are way to many possibility's to say without tearing it down. Could even be your cam going flat. Run several tanks of fuel with the cleaner to see if that helps. Do you know what size (lbs/hr ) the injectors are? They could be washing your cylinders.
 

srmitchell

NAXJA Member
NAXJA Member
They are the factory flow rate, but 4 hole. Out of a 2005-06 Grand Caravan. Got them from precision auto injectors.com
 

CJR

New member
There are many new piston designs where the oil drain-back holes in the oil ring grooves are undersized. The oil "pools" in the oil groove and doesn't drain fast enough back to the crankcase. Over time, the rings stick/glue themselves in the grooves and oil blow-by past the rings occurs. Also, gasoline contains lacquers which are not soluble in gasoline. These lacquers tend to be deposited on the cylinder walls and eventually "glue" the oil control rings in the piston grooves so that the oil control rings stay in a "compressed state" in the piston. The fix I use periodically is simple and effective.
1. Get a couple cans of Gum-Out which dissolves lacquers.
2. Pull all the engine spark plugs.
3. Spray the Gum-Out into the spark plug holes and keep spraying until one or more of the Gum-Out cans are empty.
4. Let the engine set for awhile or overnight.
5. Replace the spark plugs and fire up.
6. You'll get some white exhaust smoke and then it will clear up.
7. Your oil rings will now be free and properly expanded against the cylinder walls.

Don't worry about any Gum-Out in the oil as it evaporates quickly. I've been doing this for many years and it works well.

Best regards,

CJR
 

Ivan

I Jeep, therefore, I am..
I too have 198k on my '98, which runs like a champ; so your symptoms puzzle me. Two things jump out....

What is the condition of your catalytic converter? If it''s failing/plugged, you could exhibit such symptoms.

How about your tranny? Slipping?

That's all I have...
 

RCP Phx

New member
They are the factory flow rate, but 4 hole. Out of a 2005-06 Grand Caravan. Got them from precision auto injectors.com
I've got a set of those, they are 0 280 156 007's w/ @ 22 lbs/hr . They worked great in my 2k before my stroker build!
 

srmitchell

NAXJA Member
NAXJA Member
I too have 198k on my '98, which runs like a champ; so your symptoms puzzle me. Two things jump out....

What is the condition of your catalytic converter? If it''s failing/plugged, you could exhibit such symptoms.

How about your tranny? Slipping?

That's all I have...
I have pre-cats, which are stock. But the downstream cat was just replaced with a full custom exhaust from Ray's Old Town in Eureka. Are you still around here Ivan? I'd love to compare my power to yours.
 

Ivan

I Jeep, therefore, I am..
I have pre-cats, which are stock. But the downstream cat was just replaced with a full custom exhaust from Ray's Old Town in Eureka. Are you still around here Ivan? I'd love to compare my power to yours.
Yep, I'm still in Eureka, and now retired with all sorts of time on my hands.

Remember, my XJ is a 5 speed, but you are welcome to compare.
 

srmitchell

NAXJA Member
NAXJA Member
There are many new piston designs where the oil drain-back holes in the oil ring grooves are undersized. The oil "pools" in the oil groove and doesn't drain fast enough back to the crankcase. Over time, the rings stick/glue themselves in the grooves and oil blow-by past the rings occurs. Also, gasoline contains lacquers which are not soluble in gasoline. These lacquers tend to be deposited on the cylinder walls and eventually "glue" the oil control rings in the piston grooves so that the oil control rings stay in a "compressed state" in the piston. The fix I use periodically is simple and effective.
1. Get a couple cans of Gum-Out which dissolves lacquers.
2. Pull all the engine spark plugs.
3. Spray the Gum-Out into the spark plug holes and keep spraying until one or more of the Gum-Out cans are empty.
4. Let the engine set for awhile or overnight.
5. Replace the spark plugs and fire up.
6. You'll get some white exhaust smoke and then it will clear up.
7. Your oil rings will now be free and properly expanded against the cylinder walls.

Don't worry about any Gum-Out in the oil as it evaporates quickly. I've been doing this for many years and it works well.

Best regards,

CJR
Great advice. Thanks.

Worth noting, oil pressure in the motor is fantastic. Runs smooth, quiet and it's incredibly reliable. Just under powered.
 

md21722

NAXJA Member
NAXJA Member
Yes, carbon can cause low compression. I had this problem on my 2001 sometime around 150,000 miles. I did not try to clean the valves. The head was pulled and taken to the machine shop.

There is a TSB about what to look for, with some potential solutions such as using Mopar Throttle Body Cleaner. Here is a link to the TSB:

http://www.wjjeeps.com/tsb/tsb_wj_0900303.pdf
 

srmitchell

NAXJA Member
NAXJA Member
Yes, carbon can cause low compression. I had this problem on my 2001 sometime around 150,000 miles. I did not try to clean the valves. The head was pulled and taken to the machine shop.

There is a TSB about what to look for, with some potential solutions such as using Mopar Throttle Body Cleaner. Here is a link to the TSB:

http://www.wjjeeps.com/tsb/tsb_wj_0900303.pdf
Wow. Great info. Maybe I'll swing by the dealer and grab a can of that stuff. Obviously I don't have that tool so I can't do the first part yet.

Just another thing I am pondering- My timing chain almost certainly needs to be replaced. With enough slack, it too can cause low compression correct?

Also- I talked to a local engine re-builder. He said he has seen multiple 2000-2001 Cherokees, that have had cam failures where the lobes go flat on cylinder 1 and 4. Fully enough, those are the two I had with the lowest compression. Has anyone head of this? Perhaps I should pull the valve cover and measure the lift between 1+4 in comparison with the rest. And would replacement with a Mopar cam be good enough?

Only problem, is that cam/lifter replacement requires head removal. Cam/lifters, cloyes timing set and all gaskets is about $450 from Rock auto.
 

CJR

New member
I just read the hilarious TSB on carbon build-up. Give me a break! Valves not rotating because you're not above 3200RPM? Part of their solution is to rev to 4500RPM -yeah sure I solve all my engine problems by revving to 4500 RPM for 15 seconds! Or, how about "if the valves are rotating" - then look elsewhere. I love that definitive solution. This TSB is something I'd expect to be written by Chrysler Sales rather than their Engineering group. This kind of reminds me of the "zero valve clearance to piston" Mitsubishi engines, used in Chryslers, and their catastrophic failing automatic transmissions that almost put Chrysler out of business. But hey, the TSB was fun to read and made my day!

Best regards,

CJR
 

trippled

NAXJA Member
NAXJA Member
I just read the hilarious TSB on carbon build-up. Give me a break! Valves not rotating because you're not above 3200RPM? Part of their solution is to rev to 4500RPM -yeah sure I solve all my engine problems by revving to 4500 RPM for 15 seconds! Or, how about "if the valves are rotating" - then look elsewhere. I love that definitive solution. This TSB is something I'd expect to be written by Chrysler Sales rather than their Engineering group. This kind of reminds me of the "zero valve clearance to piston" Mitsubishi engines, used in Chryslers, and their catastrophic failing automatic transmissions that almost put Chrysler out of business. But hey, the TSB was fun to read and made my day!

Best regards,

CJR
It's actually more common than you think, and all manufacturers release bulletins such as this. Notice how the only labor lines are warranty times? Tsbs get released when a common problem is found to aid in repair. Most engines don't like be puttered around all the time.

And the Piston to valve clearance, almost everything now is an interference engine. Any engine now that goes out of time wil likely bend valves.
 

srmitchell

NAXJA Member
NAXJA Member
Minor update-
Did the steam cleaning. 12oz of water, ran terribly, but once it sat for a little bit and baked residual moisture off, its running well. Still burning through a can on seafoam.

Grabbed a factory air box lower to replace my snorkel setup. I actually don't use the snorkel as intended, ever anymore. We had one little beach spot locally with a stream crossing but too many people killed stock trucks and suv's there so its closed.

Seems to pull a little bit harder with the stock box. I used my Bosch scan tool to monitor air temps while driving, in order to compare my cowl snorkel versus stock.
Ambient air was about 65 degrees.
Snorkel IAT at 65mph- roughly 100 degrees.
at a stop light- highest temp 140 degrees.
I'll report back on the stock box.

Old versus new
Air box by Sean Mitchell, on Flickr

Its a decent sized tube but any reduction in restriction is good.
Air box by Sean Mitchell, on Flickr

Air box by Sean Mitchell, on Flickr

I tend to trust the jeep engineers more than the cold air companies- I just recently ditched my AFE intake in the WJ in favor for the stock box. I don't trust oiled filters anymore. They get dirty too quick, and I can see pinholes in the media. No thanks!
 

old_man

NAXJA Member
NAXJA Member
The best and safest thing to do first is run a can of BG44K through the fuel. It will clean the injectors and remove carbon. I have run a can in every vehicle I have every 10k miles for 40 years.

Once you have done that, do the basics that everybody refuses to do when diagnosing. Pull the plugs and evaluate their condition. If you are not skilled in reading plugs, post pix up here.

While all the plugs are out, do a compression test. Make sure your compression tester seals properly. Many won't fit down the sparkplug hole all the way due to the 4.0L head design and will yield very low and erratic readings.

Put it back together and do a intake manifold vacuum test.

These things will give a good and reliable idea of the health of the engine without tearing everything down.

In all my years, I have yet to see a timing chain cause any changes in performance other on a dyno.
 

srmitchell

NAXJA Member
NAXJA Member
Thanks for the info old_man!
BG44K is good stuff. Once I burn through the seafoam, I'll consider buying some. I can get it from my former job.

Plugs look good. And they're the correct NGK plugs for the 2001 coil rail motor.

I do intend on trying a different gauge. If it was even marginally out of calibration, this whole thing would be a wasted effort.

The only thing I intend on removing as of right now is the valve cover to inspect pushrod lift.
 

srmitchell

NAXJA Member
NAXJA Member
Pulled my rocker cover today, in order to measure valve movement.
Observations-
1) In the two suspect cylinders, (1+4) the valve movement/pushrod lift was identical to the other cylinders. Good news! It means my cam is fine.
2) My rocker arms/pushrods do not look like they have 200k. Even the cover is incredibly clean. Quite impressed. I change oil regularly, and I've been using synthetic for 75K miles. Currently running Rotella 5w40.
3) When turning the engine, I can feel the timing chain slack. Actually, I can hear it. Rotating the engine clockwise (facing the crank) I stopped a few times, and then gently went backwards, maybe 1/16th of a turn. When you turn it back clockwise, you can hear a clank and a rattle from the timing cover.

Time for a timing set.

Photos of the interior. I can't believe how clean the metal looks.
Rocker arms by Sean Mitchell, on Flickr

Rocker arms by Sean Mitchell, on Flickr
 
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