Sounds like a "DEAD" spot in your TPS. The TPS is just a variable slide resistor. When your TPS resistor is being rubbed in the same place over a long period of time, you can develove a DEAD spot. Best way to check is to unplug the TPS put a DVM meter on the leads and check the resistance. You should read some type of resistance thru the entire throttle range. Resistance will read high to low as the trottle position moved from CLOSED to OPEN. If you read a dead short (0 Ω) anywhere in between CLOSED and OPEN, then you need a new TPS. The short tells the computer to not inject fuel. The BUCKING is caused by the throttle fluctuating back and forth over the short.

 

How do you come up with an answer like that? Firestone and Midas come up with.... bad fuel filter, bad catalytic converter, bad spark plugs, bad distributor cap.... and I know that all isn't true, it must be standard procedure. I'm not sure if your answer is common sense, but you sure as heck suprised me.

Thanks man I'll look into it and get back to you.

 

I've seen this issue numberous times over the years. I even had this issue with my 1983 Mid-Sized LTD (302), 1988 Ranger (2.9L) and 1994 Sable (3.8L). Engine would buck while trying to maintain a certain speed. No amount of dealership tools or troubleshooting ever came up with the TPS as the problem. Was always a HIGH $ guess. All 3 were a $35 TPS.

I was even at a Ford Dealership one day years ago and over heard a conversation with a Customer (about 75 yrs old) and the Service Manager. They were trying to convince the Customer that he needed an engine rebuild on his 1985 Crown Vic due to his PROBLEM. The problem was described as a BUCKING condition.

When I had the chance, I talked to the Customer and advised him of my thoughts. He bought a new TPS and I installed it for him in the parking lot. Problem solved and the Customer was very thankful to me and as PO's as a wet hornet at the Service Manager.

What happens is the dead spot is caused by running in the same position over a long period of time. In my case, the average driving speed in my area was 45 MPH. After time, the vehicles would start bucking when trying to maintain 45 MPH. Anything above or below was OK as the TPS was in a different position.

As the TPS passed the dead spot, the computer would stop fuel delivery, then as it went past it, fuel delivery would continue. Since you're trying to maintain a given speed the trottle fluctuates back and forth over the DEAD spot causing the fuel to be shut off and on, thus the bucking.

1. Fuel filter: Could only be dirty and would cause it to run like crap under any type of load.
2. Bad plugs: Basically would run like crap all the time.
3. Bad Dist Cap: Impossible, you have DIS.
4. Bad catalytic converter: Run like crap under any load.

Also, if not done for quite a while, it wouldn't hurt to replace the fuel filter, plugs and plug wires.

However, I could be going down the completely wrong road. BUT for a $35 TPS, I would check it first.

 

Bow down to the engine guys!

(bows)

wish I knew as much about engines as I did about transmissions....that's why I come here...

 

Hey man it was a better idea than I have heard in a while, but it definitely didn't change anything. Don't worry I didn't leave a scratch on the new part, so it can be returned. Any other suggestions?

 

I'm still pondering...But here are some other items...

Have you ever had the plugs and wires changed? It's possible that you have a high speed miss fire. Have you pulled any stored codes? Anothor thing that could cause the problem would be dirty injector(s) not being able to deliver enough fuel at that RPM. What happens if you try driving at 70-75 MPH with OD disengaged?

 

Well Common Sense,

This time it wasn't that common, after $350 bucks I found out it was the Camshaft Synchornizer. If I could have figured it out on my own, it would have only cost me $80, but of course the shop has to throw on their 450% overhead. I'm still not happy with them about it, but it purrs like it's supposed to, and at the end of the day that's about all you can ask, right? Thanks for the input I don't think I ever would have figured that one out. Nobody else even threw a diagnosis near that...... catalytic converter.... ha!!

 

Oh yeah, to plug a computer in your truck and read a black and green screen will cost you $99..... ???? You can try to reason that with me all day, and it still won't stick to the wall with me...... Overhead costs....

 

Well, Just back from a quick trip to Pheonix and Las Vegas. Was quite nice.

Anyways..."Camshaft Synchornizer"...Dang...I keep forgetting about those critters. Rockauto.com caries the OEM replacement for about $33 + alignment tool.

Tell me about the price...I'm out in the country and they charge $80/hr and move real slow. The only time they move fast is with the NY State inspection cause they don't make anything off of it...


At least I gave it a try. Glad you got it fixed.