lopeing

[snd4mc]

Hi guys I have a 1990 4.0 that lopes from 500 to 1000 rpm i checked all the vacuum lines good i tried to clean the air bypass valve. new fuel filter, air filter, and pcv valve. when it's lopeing it's over fuelling you can smell the fuel. when your driving down the freeway and put to the wood it stumbles and blows black smoke, take your foot out and put it back in it goes like a bat outa hell. when your driving down the road you can feel the surgebut don't really see it in the tach. any help would be great thanks.

 

[almostclueless]

Wouldn't be surprised if the fuel pressure regulator needs replacement.

 

[Bruce]

May be ECT(engine coolant temperature) sensor which tells the computer what temp your enigine is running like hot or cold. The senor will go bad and tell the computer that the water temp is like 40 below 0 when its like 60 above 0 thus the computer will call for a richer fuel mixture.

My advice would get someone to put a scanner on it and check for codes or look at data stream(i think 90 had a data stream).

 

[snd4mc]

loping update

well i went to start my truck this morning and it wouldn't run had a bad miss like it was running on 3 cyl's. i check the rail, pressure key on 45 psi good
then started the truck and psi was normal for 3 sec's then went up to 75psi.
i think its a fuel pressure regulator. any advise out there? thanks