SOOooo.... The story goes good things come to those who wait. The problem was...If you can believe this, PLUGS. TWO boxes of BOSCH plugs (7952) and we had FOUR bad plugs out of TWELVE. I believe they were from a bad lot, because when I got a box from another store......BINGO !!!!
I spent HOURS and hours tracing vacuum lines, making restrictors and all the related bologna...and stinking PLUGS turn out to be the problem. Checked every wire on the bench. Two distributor caps. ....AAARRRGGHH... Coil tests and every stinkin' sensor checked on the bench too....all to no avail.
But lemme tell you. She'll pull from a stop uphill at idle right now without touching the gas. SMOOTH as a new piece of blacktop. I measured my mileage with no tailgate and got 18.9 mpg with 31X10.50's and 89 octane. Engine is rebuilt with .40 over pistons and .10 under rods and mains. She's on her third oil change, about 9 thousand miles right now. I have noticed that she'll spark knock a little under a load, so I have been adding lucas fuel treatment to it and VIOLA....

SUPER SMOOTH 4.9 with no more spilled coffee.
clutch47

 

I simply disconnected the EGR Valve vacumm line, and magically the truck runs so beautiful now!!!

 

inst the spacer in egr, it improved the problem but did not cure it 100%, i will look at the idel controle next,my plugs ar new and if they wer the problem it would show on , or at lug. myn will pull like crazyand run fine when ever engine works????????? cliff

 

My friends 4.9 was cutting out, bucking under part throttle, especially in town. I unplugged EGR line and it runs PERFECT now. The mileage is much better too, it was about 10MPG before, its at least 15 now.

As for my own truck, I got it running today, it doesn't buck anymore but almost feels like it has a constant miss (just a slight one) I might replace the plug wires and see if it helps since I bumped one the other day when it was running and got shocked.

I'm going to make a restrictor for myself and one for my friend out of aluminum after I go back to school next week.

 

Interesting to read this older thread coming to life. Had a head-scratcher of my own about a year and a half ago, did some research here but it looks like I went in the wrong direction. At about 138k, my '91 would suddenly run roughly (truck normally ran like a clock), and just die. Always seemed to be at "operating temperature", so I replaced the thermostat and the ect. Truck ran a little smoother, and I noticed for the first time the idiot gauge on the dash reading something other than "C" all the time. Was starting to do the victory dance when the b!tch started to buck and stall, again just as the engine temp was starting to level off. Much hairpulling and Google-searching led me to replace the IAC sensor on the upper exhaust manifold, which also resulted in a smoother running but eventually bucking and stalling truck. Followed by profanity. From me, not the truck. Drove to work earlier the next day to take advantage of cooler temps, truck died as I reached the parking lot. I threw in the towel, and had it towed to a shop I have worked with in the past. They found good spark, fuel pressure within spec, and no codes at all registered with the computer; this resulted in three of standing around looking like idiots when the truck stalled for no reason, but at least I felt a little better that "experts" couldn't figure it out, either. After more Google-fu on my end, I replaced the ignition coil again(last one was four years old)based on evidence that sometimes intermittent stalling could be caused there, and that this module is almost always destroyed by heat. No love, still stalled. Fuel pressure at the rail indicated that the pumps were being *shut* off, so we came to the conclusion that it had to be the computer - it occurred to me later the symptoms were identical to using the inertia switch to shut the engine off when working on fuel systems, but not before the shop wired the fuel pumps directly to the ignition(after everything I replaced, plus tow and missing work I was too broke for the replacement computer). This cured the stalling problem, but I now have a rough idle when I never had one before when the engine is "hot", and have noticed the "hesitation" when cruising that I never noticed before. I am replacing the fuel pump relay this weekend, due to the pumps still running after the key is turned off - and I had read this could cause some rough running as well. One additional symptom - before this when I changed my engine oil the oil always looked good as new. Now, it's thick and dark and that scares me more than anything else.

Any input? Suggestions? It's been awhile that I've put up with this - I don't like the pumps bypassed like that so I'd like to return the wiring to normal, but I don't have the heart to go through all the stalling problems again. I am curious to try the EGR vacuum line test, but would that normally cause an issue with stalling and rough idle with a warm engine? Or contribute to the pumps being shut off? And what about the lack of codes? For the life of me I would say the truck acts like the timing was really, really off, but only sometimes....

 

sorry to bump an old thread, but i tried the EGR block with a tuna can lid, cut with some tin snips. i figure the steel from the can should be a little more durable than aluminum. just have to find out how long it lasts

 

Bought my '93 F150 about 4 months ago with 184k miles. It got 10mpgs and was a pig, esp with 3.08 ratios. After full tuneup, fuel system cleaner and performance air filter, I'm up to 17mpgs. I've had an an intermittent hesitation when cruising since i've had the truck, which is now at 194k miles. I'll be trying the egr restrictor plate tomorrow, and lowering ratios to 3.54:1 in the near future. I hope this works.

 

Before you do this restrictor plate thing I would simply unplug the small vacuum line to the egr. This will not allow the egr to open and if the bucking stops you will know its the egr. Read this thread from the beginning, there are explanations on how to do this. On my 91 the vacuum line was green.

 

I had the issue on my 94 and the 1/8" aluminun plate worked great. Just disconnecting the EGR caused a slight ping at cruise and I couldn't have a "Check Engine" light on for inspection. Emissions were actually slightly lower with the plate installed. Good thread.
YMMV
rikard

 

I have had mine disconnected for 4 years now, and no ping. I did plug the vacuum line so there where no leaks. We don't have emmisions testing here in KS. But when I lived in PA, I just plugged the egr line back in and went to the test and it passed. Then I would just unplug it again.

The check engine light did come on, but I knew it was from me, so I just unhooked that light. I would read the codes once every 6 months or so just to make sure nothing else was wrong. Never had any issues and yeah its been over 4 years now. But the permenent way to take care of this is to make that restrictor plate.

 

I made and installed the plate tonight. The truck definitely seems happier! Evidently GM had the same issue for a few years, and along with the plate, and according to a lifelong mechanic, there are a couple other solutions that are just as effective.

A drive-in freeze plug the same size as the opening of the EGR valve works nicely. just drill a small hole in the cup and use a new gasket.


Thanks for the help guys.

 

Just get a 5/8" freeze plug from any auto parts house. drill the middle of it 1/8" then just tap it in. you use only one gasket with less chance of leaks. no double gaskets or making a plate.

 

I heard about the freeze plug solution and would have done that but a machinist offered to make the plate for me if I paid for the beer. I was thirsty any way...Priceless!
regards
rikard

 

I signed up for this forum just to thank you guys for this potential fix. I too have been living with this problem for years (since '94). This morning I actually had to pull to the side of the road to let other cars pass me because I couldn't get up to 35mph ... just bucking and jerking unless i barely touch the accelerator. I have never seen it this bad. After a few miles it always goes away though (including today).

Hopefully this fix will help me too. Will let you know.

 

This probably isn't your problem at all. This bucking this thread is about is for very very light throttle.

Your problem sounds just like one I had. I would bet you its your Distributor Cap and Rotor inside of that. Mine did the same thing. I made the mistake of buying cheepo parts from Autozone, those only lasted 10K miles. and for 8k miles of that I had problems. Go to Ford and get motor craft of go to O'Riellys and get some parts that are made in the USA. Fixed my problem right up.

My problem sounds the same as yours. When I would first start it in the mornings, it would hesitate and buck and miss, especially under load, like trying to accelerate. Then It would go away after a few miles. I finally took of the Dist Cap to look inside and its no wonder why I was having troubles. Bought some good parts from O'Riellys, the dist cap and rotor, and problem solved! Also you may think of new plugs and wires while you are at it. Depending on when you replaced them last.

I would say that will fix your problem