Hey gang,
Thanks for all the responses to my first post, that helps a lot and gives me more options to work with. Kudos!

Need help on one other issue that's been a bit of a mystery..
Since I've owned my 91 F150 XLT, Whenever I'm accelerating from a stop, (usually around 1000 - 2000 rpms / 10-25 mph) most often (But not 100% of the time) the truck will jerk or jump. It almost feels like the engine revs up ahead of the shifting and something is delayed or struggling to catch up in a hurry. On the highway or above 40 mph, no problems. Rarely it will take 20 - 30 seconds to shift to the next gear when I'm going uphill.
Some additional info:

-I'm running the straight 6
-Running the Automatic from that year.. Can't recall if it's 3 or 4 speed.
-Noticeable in 1st to 2nd gear - happens at random, but more often when it's been run for more then 10 minutes and happens most often in town.
-I Dropped the pan and performed a very much needed transmission fluid/filter change (Just fresh fluid, no flush or tranny treatment)
-The rear U-Joint was replaced and that fixed a different issue, but the jerky problem still remains
-Replaced the Fuel filter/Serp belt. No dice.
-Tested while driving each tank fueling the engine, still jerks
-Truck was not hauling anything (box or trailer)
-It has 147 k miles

I'm really hoping this isn't the early symptoms of a transmission on it's last leg, but I want to be sure and ask to see if anyone is familiar with this behavior and what it might indicate.

As always, any help or suggestions are very much appreciated!
-91HT

 

I have a 91 with the e4od trans, and it has had the same trouble. Have you checked for codes? That might give you an idea.

Some other things that might cause trans issues (or what feel like trans issues) without a code:
TPS (on bottom of throttle body)
VSS (on side of trans)
RABS (on top of rear diff)

I replaced all 3 of these on mine, and noticed a difference with each one. Still didn't cure the hard shift. Some people have recommended adjusting or replacing the MLPS - haven't tried that. I did replace the main ground cables off the battery with new/heavier guage wire. There is one going to the starter, one going to the core support, and I added one going to the throttle body. Since doing that, I haven't had a hard shift yet.

 

Maybe the truck got excited

 

And they say cell phones are a distraction!

 

Almost forgot all about this post.
That is until I shifted my focus from the Vacuum issue to the Transmission hard shifts.

I took Alien's advice and replaced both Positive and Negative cables with fresh, brand new ones, using Gauge 4 heavy cable (I wanted the heavier 2 but the store didn't have the length I needed so I improvised).

Hard shifts reduced about 85-90% just by installing fresh cable.

Next, I am planning to add cable to the Throttle Body, as well as replacing any other wires/cables in the hope that it will reduce the remaining hard shifts (Most often observed when going from a dead stop to about 15-20 mph, and sometimes on a start when the road is uneven)

Will report back with results as I get them.

Thanks as always for the advice and help!

91HT

 

Out of the frying pan and into the fire?

Yesterday I had the MLPS (Manual Position Lever Sensor) replaced on my F150's transmission. For a few miles it ran beautifully. No Jerks, jumps or pulls. I thought for sure this issue was resolved then.

However..

While driving to one of my favorite fishing spots yesterday I felt what seemed like a massive slip or something. Basically I was trying to accelerate with traffic. The RPMs went way up, speed did not.

It gradually got worse until finally when trying to get back home (driving on city streets in the next town over) I could only manage a maximum speed of 10-15 mph with RPMs as high as 2 or 3K.

I'm Triple A covered so I decided to tow it home rather then make it worse (Plus I couldn't drive it on the highway and those were the only routes available for me where I was)

I'm going to call the place that did the MLPS work and see what can be done.

Is this e4od shot or could it be a computer/component/etc issue?

Quick stats:
-e4od Automatic
-1991 F150 XLT 4.9l 300
Recent work: MLPS, Fuel pressure regulator replaced (within last month)

Thanks much,

-91HT

 

It's been awhile since I've updated this thread.

Here's the latest:
The truck still bucks under heavy Acceleration. The longer it's driven, the more the bucks are felt. At this time it only does this between 25-45 mph and each time it has to rev up to 3000 rpm before a shift. Speeds lower and higher then the afore mentioned range are fine for shifting.

The following work has been done to my F150 since my last post:
-TPS replaced
-Throttlebody cleaned
-TSS (located on rear of the Transmission) has been replaced
-Transmission rebuilt @ 151k miles.

Other symptoms observed recently:
-While accelerating slowly, vehicle struggles (and almost looses power) around 10 mph. Slower driving (10-15 mph) reveals a type of "RurrrrRurrRurrrRurrrrRurrr" noise and motion going down a city street.

Work up and coming:
-Planning to replace the RABS.
-(unrelated) Replacing both Exhaust manifolds (Truck is getting louder up front)
-Would like to replace the throttle cable, however need a new/updated housing clamp (secures to throttle body).

Starting to wonder if this mystery will ever get solved (or even worth it now?) or if I'm running a good transmission into the ground.

Thanks as always for any help.
-91HT

 

The Mystery continues.

Trying to keep a running documentation log on this. My searches continue to yeild repairs I've already tried or done but have no change in the end result. I now have an OBD 1 and 2 car scanner (Equus 3140 Innova Diagnostic Scanner) which pulled codes (See below).

Latest work:
-New Fuel Tank (Primary)
-New Fuel Sender and Pump (Ordered as a combo unit)
-New Fuel filter (Per warranty/personal choice, installed at time of new pump/sender and tank)
-New EGR position Sensor (Equus 3140 Innova Diagnostic Scanner codes 127 and 128. Ford technician said to replace this (EGR) sensor and these codes will go away. They did.)
-New TPS installed
-Throttlebody cleaned
-Spark plugs (motorcraft) checked. (They appear ok but show obvious signs of use)
-Ran Seafoam through the fuel system


Remaining Codes:
-Pass code 111 and error code 154 (152?) (secondary fuel pump circuit failure) Rear fuel pump is not being used at this time. That tank also needs replacement (Has a hole/is rusty) but cannot afford to do that at this time.
-Emission status: fail (According to the Equus scanner)

Work up and coming:
-Exhaust Manifold needs replacement (Truck is getting louder, Shop mechanic confirmed there's a hole in the existing manifold)
-Getting a quote to replace the Catalytic converter as well at time of Manifold replacement (Visual inspection reveals it to be very rusty, possibly the original)
-Considering having my timing reset/rechecked.

Symptoms remaining:
-Truck sluggish off the line. Continues to race up to 3,000 rpm before shifting when running warm and at lower street speeds. Sometimes it struggles in a headwind to maintain it's freeway speed or going up hills *even slight ones. Cannot surpass 50-55 MPH in this case.
-Truck continues to "Buck" or "Jump" under heavy acceleration, primarily between 35-50 mph. The RPMs also reach 3000 during jumps/bucks during shifting. (Keep in mind the Trans has been rebuilt as of November of this past year)

Suspect:
-Calling the trans shop guy to ask if the Torque Converter was fixed/replaced with the Trans. (I thought he said it was but need to double check to be sure)
-Catalytic Converter (I've been told this robs vehicle performance and kills gas mileage when replacement is needed)
-E-brake possibly stuck (?) (No light on dash indicating brake is engaged. Shop guys say it's fine, though I still can't engage it while parked. Rock hard to press down on, maybe I'm missing something, will consult manual. Cable is extremely rusty and so are the drums (brake).

Onward and upward. Sooner or later she's got to get better. Will post further progress & changes soon.

-91HT

 

One word: Relay.

The truck stopped turning over entirely last month. So I decided to let the local garage take care of that and the bad exhaust manifold. Upon it's return, was like night and day.

As it turns out, the green colored fuel relay may have been the culprit the whole time. After a solid week of driving it, it appears to not only shift on time, but accelerates normal and bucks far far less (Minor jumps at times around 45-55 mph and between 1500 - 2000 rpm around 35-45 mph, no where near as bad compared to 5 months ago)

That being said, I've decided to replace my EEC Power Relay as well. The truck will not start proper after 4 or 5 consecutive start-ups in a row (Meaning on average it will drive to point A, then B, then C, then D and not start again after that unless it's given an hour or so rest)

I suspect replacement of this will fix the random ignition issue, as well as some other electrical related (though minor) issues.

I will close this thread and declare this issue resolved once I'm satisfied with it's performance after replacing that EEC relay.

Hope this helps someone out there. Sometimes the littlest components cause the biggest headaches.

-91HT

 

thanks for posting back always nice to have a follow up