Fuel pressure....?

[azscott]

Upon reccomendation I tested the fuel pressure at the railllfor the hard start/rough idle...etc.

Pressure is 34 psi.....now it will hold that pressure for about 45 minutes before it starts to drop slowly...after an hour it was about 20 psi.

Oddly...or not addly...the pressure did not have anything to do with the rough idle. I let it sit for 10 minutes..started it...and it idled rough for about a minute or two. It revs up fine just idles very low and rough. Pressure on the rail was still at 34 PSI.

Let it sit for 45 minutes it had dropped to 20 PSI and is started fine.

Now it still idles low..changed the O2 today... still no help.

To me...it is running rich...if I had to guess. Which makes sense as I know the PO had changed the Cat a while back and this may be why. Driving me nuts..all the other sensors tested o.k....changed the IAS..no help. Adjusted the TPS no help. Fixed all the VAc leaks on the intake side..no help.

Hate to take it into the dealer...but not sure what else at this point. Of course it is 20 years old so..?

scott

[Eagle]

Compression readings? Uneven compression will cause rough idle and there's not a damned thing you can about it short of rebuilding the engine.

[azscott]

...hmmm...that was in the back of my mind too. I don't have anything to read compression at the moment. If that is the case...I would live with it. The PO did...he had a piece of metal glued to the throttle stop to adjust the idle...hah!. I hate jury rigging...but I may not have a choice.

I know I am getting some blow by as I am getting oil back out the CCV intake.

Well..heck..it runs good enough...I may just have to put that metal shim back in and move on..:-)

Been working on the Mj all weekend...time to take a break.....until next weekend.

Scott

[HOrnbrod]

Pull all your plugs, line them up in order, and read them. An easy test to do that will tell you a lot if you see major differences in color between cylinders.

[azscott]

I will take a look at that.

However I don't think the low idle/rough idle is related to the compression. I say that because it is intermittent. Sometimes the idle will be a little high...sometimes normal and alot of times low. It does not range over a wide range rather from 400 rpm-1100...which is wide I guess but not like it goes up to 200 or so. Usually it runs 500-800.

I think there is either sensor that is failing...or maybe faulty wiring...or? If it was compression it should be consistent and not come and go.

I do have to replace the knock sensor as it is physically broken. The plastic cover cracked in half and I had to glue the whole thing back on. Although on or off the truck did run any different....which could mean that sensor is not working at all..? I ordered one from Napa..which is a generic replacemnt it looks like but won't be here until Wednesday.

scott