Out of ideas... need some help

Old 05-11-2019, 02:08 AM
calansvc is offline
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Out of ideas... need some help

1998 4.2L v6 RWD, 166K miles

Just got the truck back together after an intake gasket install, and now have a rough idle. Here's what's been done:

New coil, plugs, and wires
New fuel pump and fuel filter
New (refurbished) injectors
New fuel pressure regulator
New (updated) gaskets on IM and upper plenum, EGR, TB, ISC, etc.
New PCV valve
Replaced all vac lines
Cleaned IM, throttle body, and upper plenum, checked IMRC vanes and actuators (bench vac test), new bushings for IMRC rods
Cleaned fuel rail, checked for leaks before bolting up plenum, etc. Rail has pressure at key on (but not measured).
New t-stat, heater hose connectors at fire wall, water pump pipe
New EGR valve (pipe is still in decent condition)

This all started with hard starts (sometimes no start), maxed fuel trims, and rough I decided to replace the fuel system and vac lines...which led to injectors (which were horribly clogged). Figured while I was in that far I might as well pull the IM and clean everything and replace the gaskets. After putting it back together, it's now idling rough and hesitates on throttle stab, but has no CEL or codes. (MAF is clean and pulling the connection makes no difference). I've gone over everything and can't find anything I missed. Haven't measured vac, but I can feel it at the EGR line (and brake booster has good vac when I pull the hose). Did a smoke test on it and see no leaks anywhere (other than fog leaking back into the intake tube pre-throttle body from the CC vent as expected).

I've built a few cars, but I wasn't a Ford guy before getting this truck in a trade... and this has me stumped.

Any ideas greatly appreciated.


ST fuel trim on bank #1 is hovering around -11 to -13, and ST fuel trim on bank #2 is hovering around +11 to +13. They are almost mirror opposites of each other.


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