Well......

Back in Janurary I purchased a 94 F150 EFI 4x4 with the intent of using it to pull a small boat <2000 lbs. and use it as my weekend fishing rig.
I knew it had some problems and figured a little tlc and some replaced parts and I'd have a winner.

The "truck from hell" has a pretty bad intermittant stumble @ around 1500 RPMs.

So far I've had nothing but headaches and a VERY large credit card bill to show for my efforts.

As it turns out, I've had done, and/or replaced.......

Head rebuilt & head gasket (warped from pervious "owner")
Transmission rebuilt--E4OD
Transfer case rebuilt
Radiator rodded and cored
New starter
New starter relay
New alternator
New OEM battery cables
New headlights
New upper and lower intake gaskets
New TBS gasket
New EGR valve and sensor
New O2 sensor
New TPS
New Idle Air Control Sensor
New MAP sensor
New injectors
New pressure regulator
New distributor
New plugs, wires, cap, and rotor
New exhaust manifold
New turbo muffler
New cat (rear only..front was hollowed out)
Checked and cleaned every ground I could find
(I may think of more before I end this post )

I recently had it in the "Best Shop in Town" ---they tried cleaning the (old) injectors, checked for vac leaks (found none), checked fuel pressure (at spec) and pulled a "running lean" code and said "everything else appears normal, we don't know what's wrong".
I still have the "somewhat intermittant" horrible stumble and miss @ about 1500 rpms.
It'll stumble in the driveway or while driving so "loading up the engine" doesn't matter.

I FINALLY got a "Check Engine" code last weekend so tonight I went out and purchased a code reader and did a little code pulling on my own.

What I got was......

Key On Engine Off-----
111 system passed

Continious memory -----
113 Intake air sensor above maximum voltage
118 Engine coolant temperature sensor above maximum voltage
126 Manifold absloute pressure (MAP) sensor above or below normal
172 HEGO (HO2S) sensor fault/lean
334 EGR closed valve voltage high

I haven't done the Key On Engine On yet...need a good helper or an extension cable for the code reader.

I've looked in my Haynes book (It's getting a good work out) at the wiring diagrams and it appears that all of the failed/out of spec sensors are linked in the same circuit. Hmmmm.......

Could it be a BAD ground that I've missed somewhere ???
Do I have an EEC going bad ????

Anyone got any ideas ??? Good guesses ??? Any been there done thats ???

I'd be VERY grateful for ANY help anyone might offer !!!!!

Thanks Guys,


Bob S.
Magalia, CA

 

MAPS rarely go bad. I'd say you're on the right track with either a bad ground or a bad PCM.

Also, you can pull the codes with just a paperclip. You jumper two wires under the hood, and watch the check engine light flash the codes to you in the cab.

 

I think I found it !!!!!!!!!

I did some testing of the EGR system last night and found that my EVP sensor (new) was leaking WAYYYYY more than the Haynes manual spec. ---their spec is for zero to 1 in-Hg drop in vacuum in 30 seconds---
I was bleeding off ALL vacuum in about 10 seconds.
I checked the EGR valve WITHOUT the EVP sensor and it held 100% vacuum.
My leak was in the EVP sensor assembly---the sensor on the end of the EGR valve.

My truck runs 99.99 % better now.

I'm guessing that the following was happening----any guru's out there please chime in if I'm off base here.

The vacuum leak caused the EVR (solenoid that applys vac to the EGR) valve to constantly try and "find" the correct metering by applying vacuum (only to have it bleed off through leakage) FASTER than the EEC could adjust to it. i.e. adjust the air/fuel mixture to a lean condition ???
Simply put....there was a vacuum leak that the EEC couldn't adjust to??

The repair was quite simple. I purchased some high temp gasket sealant and applied it to the EVR (where it mounts to the EGR valve) surface, the recess where the little rubber O ring seal is seated, on the O ring itself, a little around and in the screw mounting holes, and on the mating surface of the EGR valve.
I re-assembled everything and applied then vacuum. The guage held steady and only had a tiny (less than 1/2 in-HG drop in 3 minutes) bleed off. This is well within the Haynes spec !!!!!!
I re-installed the EGR assembly and took the truck out for about a 1/2 hour drive and it ran without the stumble !!!!!!
When I got back I popped the hood and moved the throttle by hand and did find a VERY SLIGHT miss just off of idle and by back probing the TPS confirmed there is a little voltage "spike" in the TPS just off idle. I already ordered a new Motorcraft one and was going to replace it Monday anyhow.


For What It's Worth......
ANYONE who's experiencing the "stumble" or "rough running" should give their EGR valve a COMPLETE and THOROUGH check. Check the system EXACTLY as your (in my case, Haynes) manual directs you and DON'T assume new parts are O.K., and don't do any shortcuts !!!!

Happy wrenchin' and hope this helps !!!!


Bob