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this might be bad...I think

B

blue96jeep

NAXJA Forum User
Location
new jersey
I was doing a compression test on my Jeep that has 180K and my readings were 30 psi above the spec. I know the spec is 120-150 with 30 psi variance between cylinders. Cylinders 1-5 were 170 -175, cylinder 6 was at 135. did a wet test and it wet up to 150.

Now since my compression is high I am thinking that I have lots of carbon build up in the cylinders, or the gauge I was using is not calibrated.

so I am looking for fuel service treatment on the commercial/dealer level, to get rid of the carbon.

Thanks for the help.
 
Last edited:
Year? Type of engine? Did you have the throttle open all the way? Did you test twice?
 
blue96jeep said:
I never heard of doing the test twice.
Click to expand...
In case the battery gets a little weak, check valve problems, etc. I never did like the wet test, too inaccurate. If you could get a hold of a leak down tester it would help to narrow it down. Did you do the test with a warm engine? If not then I wouldn't worry about those numbers too much and try running some seafoam or professional removal as you suggested.
 
I know a leak down test should alway follow a compression test but when I saw the numbers i got I was a bit surprised. I was expecting low numbers. this is the reason why i want a professional grade carbon cleaner.
 
Sorry, I didn't read your original post very well, I was thinking that your question was about the compression and the test, when actually you were asking for which product to use, correct? I don't personally know of any commercial grade decarbonizer that doesn't use special equipment. Many on here have used sea foam with great results, I personally use 5-90's old fashioned method of using a spray bottle and water. If you do a search on here you can find all kinds of opinions and methods that pertain to what you want to do.
 
You don't ned to worry about too high compression unless you have engine pre-ignition. Up to the point of pre-ignition, high compression is nothing but good. Chances are your gage is no good anyway.
 
High compression is good but this is a totally stock motor that is not set up for high compression so I think I have lots of carbon build up which will lead to pre-ignition. but than again this is all going off a gauge is could be crap so before I go all crazy and fixing things that are not broken I will be testing this again with a good gauge.
 
Like I said though, the only bad effect of high compression is pre-ignition (AKA knocking). That means that you don't really have that high compression. Gage error!

When you accelerate lightly up a hill, or flat out, does it start tapping and lose power? If not, don't worry. On the old cars, we would turn the distributor to advance the timing until it started to ping (knock) a little. Usually uphill under light acceleration. Then we would back it off 1 degree or so.

The only variation on this would be on an early RENIX with the knock sensor, which retards the timing and could cut performance before you noticed the knock.
 
winterbeater said:
Like I said though, the only bad effect of high compression is pre-ignition (AKA knocking). That means that you don't really have that high compression. Gage error!

When you accelerate lightly up a hill, or flat out, does it start tapping and lose power? If not, don't worry. On the old cars, we would turn the distributor to advance the timing until it started to ping (knock) a little. Usually uphill under light acceleration. Then we would back it off 1 degree or so.

The only variation on this would be on an early RENIX with the knock sensor, which retards the timing and could cut performance before you noticed the knock.
Click to expand...

Winterbeater is right.

If you absolutely must have, for peace of mind, a product to remove carbon then head for the dealer--the Chryco product is as good as they come.
 
Another good product, which I've used a couple of times on my 95, is GM Top Engine Cleaner. Instructions on the can, but as I recall, you pour some in while running, shut down and let it sit a while, then restart, then run it and pour the rest in until the engine stalls. I may have that backwards, but at the end of the process, you get a huge cloud of smoke, and once it stops smoking, you're pretty well cleaned out. The only problem I had doing this was that I couldn't stall mine, so I just shut it off when it bogged down. For some reason, although it's never been a problem with the 99, the 95 likes a dose of this every few years to prevent knocking.
 
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