Low compression

MMADDOX

MEMBER
ISUZU

I have an '88 Isuzu 4x4 truck, 2.6 ltr engine, std transmission, with 200K miles. Compression is very low in cylinder 4 (about 1/2 of specs), slight loss of power and gas mileage, but generally starts and runs okay. I barely passed my last smog CA smog inspection (scooted by after replacing the catalytic converter). A mechanic squirted a little oil into the cylinder 4 and found that the compression remained the same, therefore suggesting a bad valve or possibly large valve deposits. A valve job was recommended, but that would cost more than the truck is worth. Is there a product that you could recommend that I could use to help clean the carbon off the valves or something that I could do to improve the compression without the cost of a valve job? Thanks!

3 Replies

MERLIN2021

MECHANIC
17,250 POSTS

If such a product exists, I havn't heard of it. Rings maybe, valves, no!

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Wednesday, September 19th, 2007 AT 6:20 PM

B.HUBS

MEMBER
17 POSTS

This is an old trick that sometimes works and sometimes doesn't. With the engine at operating temp. And the air cleaner off so you can look down the throttle bore. Way back when I was taught this it was a carb. With the engine running open the throttle to roughly 2000 rpm and very slowly pour cool water down the throttle bore. Not too much though, water does not compress and can bend things like connecting rods. Use very, very sparingly! Sometimes the cool water breaks up the hot carbon. There also was a product out there that was an upper engine cleaner. But for the life of me I can't remember the name. The EPA probably did away with it anyway. B. Hubs