Hello everyone, new member here.
My best friend just sold me a 89 f150 2x4 with a 4.9 six. Over the last 2 years he has invested apx $2000.00 into the truck fuel and ignition system but it just gets worse and worse. All the repairs were done by the best reputable Ford mechanic within a 200 mile radius. The mechanic has replaced fuel pumps and multiple ignition components, maps sensors etc...
Upon the primary visit the engine would not idle and it was determined that the fuel pump needed replacing. It was replaced and the truck ran great for about two weeks then it failed. It was replaced as a factory defect and again it ran great of a week or two then slowly started running rough. The fuel pump checked out good and sensors tested bad, they were then replaced but the symptoms got worse and worse.
Now the truck starts up first click of the starter and runs great for about three or four hours then suddenly it loses about 50 percent of its power. From then on it becomes dangerous to drive because top speed is about 30, and it takes a long time to get there. The mechanic has repeatedly said along this journey that the biggest problem is the compression is low on all cylinders but particularly on #5 its 10 or 15 lbs lower ( I can't remember which), and the low vacuum cannot activate or energize the electronics correctly, so he recommends replacing the engine but I am not convinced.
The engine does not burn a drop of oil and runs strong when it runs. I am thinking I can resolve this problem by replacing the electrical and fuel injection with a carb and distributor system. This seems to be the most cost effective way to fix this as opposed to replacing every ignition component or the engine.
Does any one have a foolproof way of trouble shooting this or will I be better off installing a distributor and carb? If you agree which carb and distributor will fit this and off what year engine?

Sorry for the long story but I wanted to be as accurate as possible. Thanks for any advice you can give.

 

Take it to an independent mechanic. These dealers don't know what they're doing with the older motors

 

somethings not adding up here ... if the mechanic has said all along that compression was bad, why toss $2000 into non-compression related parts ?
10-15 lbs on one cylinder is no big deal, but i wonder what the compression readings are.

 

I do love these trucks and this is a great motor in my opinion(and many others) one of the best, I did also forget about this problem and to search for "rough idle" "random misfire" or anything of the sort is nothing short of frightening...
You quickly notice 2 things, it is a common issue, with no common solution...
I cant remember if its the 300 or 22r but I think the intake is different for carb vs efi and you'd have to buy a "conversion intake"?

 

I have used a haynes manual to test most other stuff, fuel pressure, egr valve, sensor, solenoid, tps, iac, etc. I replaced what tested bad and so far I am still with you, same running issue but more persistent now. I think this may be my culprit and before trying to swap to carb I would give it a shot.
https://www.ford-trucks.com/forums/1...s-pressed.html
and here is the relative link for vacuum lines
Replace Plastic Vacuum Hoses with Rubber - Ford Bronco Forum

 

First step is to pull the codes and see what the truck's computer is trying to tell you.

 

I can't believe an engine will run 4 or 5 hours just fine and then runs rough has bad compression. This sounds like it the PIP, or PCM might be over heating.

 

I agree, though, without the compression readings, we can't agree or disagree on if it needs a new engine, or internal engine work. However, I think any rough running situation due to low compression would be prevalent in a much shorter time span.

 

Thanks for the replies,
The mechanic is an independent. Both the previous owner and I have been told by many that he is the best Ford mech in the state. The Ford dealership mechanic could not figure out the fuel pump issue much less the other stuff. I bought a manual and I will get a code reader and see where that takes me first. If I remember correctly the compression was 90 psi on 5 cylinders and 80 on the #5. My friend is going to dig up the receipts with notes and description of the work that has been done. I will enter the info in the correct order when I get that.

Thanks again.

 

How many miles on this truck?

 

Double check those compression numbers with your own gauge. 80-90 PSI of compression would indeed mean that engine is about spent.

 

Thanks everyone,
I will get all the info together this weekend and post it. Thanks for your help and patience.

 

I would'run a compression test both dry and wet, if that shows up fine I'd check for vacuum leaks around the intake manifold. Check the simple stuff first. With a process of elimination it will come to light, just don't give up!

 

Agreed 100%. Compression issues don't show up after a 4 hour drive and then go away. Pull codes first, but then pull the PCM and open the case up. If it's original, I can almost guaranty you that you'll have leaking capacitors inside.

A failing PIP could also be the problem. I'd probably test it by swapping in a known-good distributor. I carry one as a spare, so it's an easy "test".

 

Mechanic probably has no clue, is throwing parts at it and using compression to cover his *** just in case it's an internal problem.


Pull codes, check the TFI, PIP, MAP, fuel relay and PCM if you can't figure it out by looking at codes. If it didn't actually have compression it would puff smoke, burn oil and have a hard time starting.