Well after searching, changing out parts, and visits to 3 different repair shops, I finally got rid of my dreaded "EGR stumble" in my 94 EFI 4x4.

I've kinda' been a "lurker" here for about a year now and have to say "Thank You" to all who have posted or replied to any and all of the EGR stumble type questions.

I used bits and pieces from past posts and found my cure !!!

To make this short.....what I did and what I found.

1. Repaired the wiring harness going into the PCM. There is a ground wire under the "foil wrap" in the harness that "cuts" into the insulation of some of the ignition wires causing a "short" .

2. Cleaned ALL of the connectors I could find under the hood. I took ALL of the pins out of the connectors and cleaned and re-crimped them for a snug fit and conductivity. While I was at it, I cleaned and re-seated any and all grounds I could find---bare metal to bare metal.

3. Re-cleaned the connector on the O2 sensor to remove the dielectric grease from a previous install. ONLY use dielectric grease on connectors that have more than 4-5 volts running through them. Dielectric grease will act as a barrier preventing an O2 sensors low voltage from being read by the PCM.

4. Check your EGR valve for vacuum loss. I had a "brand new" aftermarket valve that leaked from day one. I found this by taking the valve off the truck then sucking on the intake manifold side of the EGR valve. There was a HUGE vacuum leak (AT IDLE) around the pintle area of the valve. I bit the bullet and purchased a Motorcraft EGR and sensor ($ 200.00 + sales tax). Also, I was informed by a mechanic that the aftermarket valve I had purchased was suppose to come with a little insert that restricts the amount of EGR going back into the intake......VERY similar to the "EGR restrictor plate" idea !!!

5. I installed an inline 1 to 3 second vacuum delay valve on the vacuum line that goes from the EGR regulator to the EGR valve. This delays the EGR action just enough till the engine RPMs can handle the extra flow.
NOTE: any longer delay than 1 to 3 seconds will cause the PCM to throw a code and CEL.

6. I had to replace the fuel tank selector switch !!! My truck started throwing a "172 System lean" code and I was getting a nastier than normal intermittant stumble and ASSUMED it was the EGR valve sticking open. In reality it was the tank selector switch failing. It finally died and so did my truck @ 10:00 at night on a very busy road. I should have known it was the TS switch because I've had to relpace or repair other "in the cab" switches---ignition sw, headlight sw, turn signal sw, etc.

It was real pleasure to drive drive my truck that I bought a year ago and have it FINALLY run without missing a beat.

Hope some of this helps other "EGR Stumble" sufferers out there.


Bob

 

right on..i will be going down that list to isolate which one of the problems are affecting me. thanks for posting your solutions.hopefully i'll be stumble free!

 

Just an upadate.........

I took my truck on a 250 mile trip yesterday and it ran perfect.
No stumble, miss, or hiccups !!

Problem solved !!!!

Bob

 

Truckin Bob- I think that you may have solved my problem. I have been having a problem with my truck and posted a thread. Do these sound like the symptoms your truck had?

https://www.ford-trucks.com/forums/s...d.php?t=353584

 

Well, to tell you the truth, I WAS fighting the "dreaded stumble" thing from day one after I bought the truck from a car lot.
It had so many problems (warped head, blown head gasket, toasted E4OD tranny, bad injectors,.......the list goes on and on...) I wasn't ever able to get a good feel for the I6 motor till just recently.
When I finally corrected/repaired all the bad stuff, the truck woke up and has and still is performing great.

Check your EGR valve for leak(s) / leaking and of course the throttle body gasket AND the upper to lower plenum gasket....all known common causes of vacuum leaks.

Sorry to cut this short, But I'm on a borrowed puter right now. Moved last weekend and my stuff is still packed away somewhere......
I'll check back here to see if you found your problem.

Good luck and look for Vacuum leaks FIRST !!!

Bob

 

Truckin Bob, this is the first time I looked into this forum, saw your subject, thanks it was a big help. Solved a problem I had for a long time.

 

Right on !!!

Enjoy your 6 !!

Bob

 

I'm still not convinced that this problem is caused by the EGR system. I know that's what seems to correct the problem, but my truck had the stumble even after the EGR was completely removed. It always had it until I installed the larger fuel injectors. The it stopped and has never done it again. I think the trucks lean out over time and develop the miss. Modifications to the EGR system cover up the lean condition.

 

Hummmmm..........

Well, you and I know that the PCM reads and adjusts the a/f mix via the O2 sensor, injectors, and some of the other junk under the hood......

It wouldn't suprise me a bit if the Ford engineers (programers) were a bit off in their "wear factor" in the PCM program..... i.e. "leaning out" over time.

I'm still a little amazed that Ford decided to use small injectors with high fuel pressure to run our sixes. Maybe I'm wrong, but it seems to me that the 14lb. injectors have to work pretty hard to feed those big cylinders.

I'm sure their reasoning was justified, somewhere, somehow, for some reason, but DANG, where was their "Better Idea"....or was that only a marketing ploy ???

Anyhow, I'm pleased that I have my "bone stock" engine running without missing or stumbling now.

Keep on posting Silver Streak.
I've read most, if not all of your posts for about a year now and you, sir, are a wealth of information we all can learn from.


Bob

 

A larger injector would have required reduced fuel pressure. When the fuel pressure is reduced the chances of vapor lock increase proportionately. With the exhaust manifold being only a few inches from the fuel rail I'm sure this was a significant concern. I'm glad your truck's fixed. When mine was stock and had the miss it drove me nuts. It NEVER did it until I cut the baffle off the intake tube in front of the core support. From that day on it had the miss until I put the bigger injectors in.