won't hurt to, you might want to know if you got problems elsewhere as well.

 

I have never done a compression test before.

Do I really need to let the engine heat up first?

Whats the best way to disable the fuel system?

I would search for these things, but the search function still doesnt seem to be working.

 

You can do a compression test on cool engine.
I would check all cylinders. #8 may be the worst, but you should check and see what going on in the other cyl as well. You have a serious problem there
Removing the fuel pump relay is the best way to disable the fuel system.

 

Yeah, got that figured out already, thanks.

About to give it a go.

 

Just tested my o2 sensor (bench test) and didnt get any readings at all.

Should I replace both of them?
Have not tested the downstream sensor, but the one in the converter seems to be bad.

NM, downstream seems to be functioning normally

 

OK, heres my results

1 197
2 170
3 197
4 172
5 188
6 200
7 181
8 165

All other spark plugs were perfectly fineand looked almost new.

I tried1 tsb ofoil in there to see if the readings changed, but they didnt, from what I can tell that means the engine valves or head gaskets may be leaking. (From what I read)

 

Those are interesting results. 200 psi is really high and 165 is actually in thenormal range.
I wonder if your engine is really carboned up and that's whats causing the high numbers.
If it was mine I would be tempted to toss in a new plug and run a couple of cans of combustion chamber cleaner through the engine and test it again.
I know you said you diagnosed a bad plenum gasket. How longago was that? Does your truck burn lots of oil?
I'm kinda thinking all this might be the long term effects of a really bad plenum leak. It would explain most of it including the bad O2 sensor

 

That IS interesting, I thought that the #8 cylinder was low, not that all the others were high.

I replaced all the plugs today with the Autolite 3923 coppers, I will try to get combustion chamber cleaner tomorrow. Is that process going to gum up my catalytic converter that was just replaced?

I just recently diagnosed the leaking plenum, but I think its been going on since the beginning of summer. Im not sure exactly how much oil it burns, but it is burning oil, I live very close to work so I dont put that many miles on the thing.

So do you think my heads are ok and can possibly just get cleaned out using the compression chamber cleaner?

I dont WANT to replace the heads, but if I have to I want to do it while I do the plenum gasket since I will already be all the way down there.

Thanks for you help.

 

Read some good things about Sea Foam, any experience with that?

Seems more comprehensive.

 

Well I don't want to get your hopes up but that sure wasn't the numbers I was expecting.
I can't find exact spec for compression but I know based on the 2001 service manual anything below 100 psi indicates a problem. I'm not sure what the normal range it. It's been a while since I've done a compression test on one of these engines but I think 145-165 is the normal range. (somebody chime in here if they know the exact #'s) 200 is really high. I only remember a few import engines with that high of a pressure. Now carbon buildup in the combustion chamber and piston top can increase compression but so can a worn cam shaft exhaust lobe. (lets hope not) 165 seems pretty good to me but you also want it to be even across all the cylinders.

Plugging up the cat? Hmmm..
Never seen it happen from decarbonising but I guess anything is possible. I doubt it though.
The only other way to get the carbon out is disassembly of the engine

I would try the combustion chamber cleaner/conditioner (not carb cleaner). You can get it at any good parts store in an aerosol can. The Dodge dealer sells it as do GM dealers (cleens) but I think It's all the same stuff. It it comes out white and kind of foamy thats the right stuff (insert crude joke here )

Get the engine nice and hot and at Idle spray a whole can down the IAC port on the throttle body.
Spray 1/2 the second can down around the throttle body plates. (I like to spray some into the pcv just to clean it out too)
Shut off the engine.
Spray the last 1/2 to 1/3 of the can down the intake and let it trickle down into the engine. (you can give the engine a few quick cranks to distribute the stuff but don't start the engine) now let it soak for a few hours (8 if you can or over night) In the morning (or whenever) it going to be hard to start so you might have to press the gas down 1/2 way. once you get it running rev it up a bit to clear things out. When it's running decent go for a 30 min drive. Try to keep the rpm's up so drive in 2nd gear or on the highway. Once the engine is warmed up give it some full throttle bursts. (you want to dislodge all this carbon and gunk)
BTW you are gonna get major smoke out the tail pipe and I mean major when you do this. don't worry

If you gonna replace the O2 sensors do this first.

Once it cools off check the compression again and see if it's more even.

Good luck