I have a 1994 f150 5.o litre 4x4 that I have owned since it was new. For the past year I have had the check engine light come on after a few seconds after it is started and it rev's up about 4 to 5000 rpm's above the normal cold start rpm's and then when it is warmed up it goes to it's normal rpm's. I have had it checked out by 3 different mechanics and they can not find out what is going on. It dosn't leave a code a code. I had the computer changed along with the throttle control and all the sensors.

 

The fast idle you describe is much higher than it should be which makes me suspect a vacuum leak somewhere . Any other symptoms / driveability problems ?

 

What happens is when I start the truck it will start out with a normal fast idle for about 20 seconds or so then the light will flash three times and the idle kicks up about 4000rpms. The light goes out but it still idles fast for about 20 to 30 seconds more then idles down to it's normal fast idle until it's warmed up. Then it seems to drive normal. I did have a lot of popping that sounded like it was coming from around where the computer is on the fire wall when I would accelerate hard after it was warmed up. I generally always let the truck warm up to it's normal idle before I take off in it. After I had the ignition wires and rotor cap changed I didn't hear that for a long time, this has been about 2 months ago, I did hear it the other day only once. I do seem to have a problem with the transmission that has gotten worse lately. When I drive it it upshifts very hard most of the time. It down shifts good but when I accellerate it shifts hard. Sometimes it dosn't do that but not very often. Yesterday I was at a stop light and I made a turn onto a straight road and when I got straightened out I accellerated hard on it and it was like it went into neutral for a few seconds, I let off on it and it jerked into gear and took off. This truck never has seemed to have alot of power accellerating from a dead stop. I just always thought it was just the nature of the truck being a 4x4. It won't spin the tires from a dead stop. Not that I want it to but I always it should be able to accellerate when I needed it to in traffic. I am thinking of taking it to a transmission shop to have an inspection done because I was afraid it may have a problem with the clutch rings wearing but it only has 53,000 miles on it and it's all been highway miles. It's never been abused or used for towing.
Thank you for your interest and if you can help me or find out anything or anybody that could help me I would greatly appreciate it.

Ralph Scott

 

I also failed to mention that I did have a problem with the ac vacuum. The person that worked on found a leak there. The ac would go from the vents to the defrost vents back and forth. He originally thought the cannister was bad but it wasn't. I don't know if this helps or not I just thought I would mention it.

Thanks,

Ralph Scott

 

Ralph ,
One thing I did pick up on is when you first start the engine ( You said the check engine light blinks 3 times ) This usually occurs when you are doing the EEC IV Self Test . The initial blinks should be one half the number of clyinders ( IE: 6 cyl 3 blinks , 8 cyl 4 blinks ) This assuming that for some reason your truck is stuck in the self test mode . If it were , the timing would not advance & you would notice a lack of power on hills etc . Why was the computer changed ? Where did you purchase the one you have now ? One thing I would inspect is all the wiring to & from the computer & the self test connector .

 

Paul
The blinks occur 20 to 30 seconds or so after the engine is started. I hadn't had any luck finding out why it was doing that and why it was reving up like it does. I took it to a mechanic in florida where I used to live and he told me to wait until it came on and stayed on before he could tell what it was. Six months later it was still doing it and it was getting pretty annoying. The mechanic since then had retired and moved away so I had to take it to another guy who didn't beleive me when I told him it didn't leave a code. He started with ignition wires and rotor and cap. Then he changed sensors. After that he changed the computer and I'm still having the same problem I had to begin with. I have since moved from florida and not able to take it back to the same mechanic. I spent a thousand dollars doing all this work and nothing has changed. I just don't want to go through the same routine. So you think the wiring needs to be checked from the computer. And that the vacuum needs to be checked. I don't do my own work so what would I want to have checked first and then what would I continue with to try to resolve the problem.
Thank you for you interest.

Ralph

 

Ralph ,
My best advice is to let a tech that has the tools & the knowledge diagnose the problems with your truck since you dont do automotive work . Changing parts w/o cause is a waste of time & your money . Where ever you live now ask friends , co workers who they have do their automotive work . There is no reason why a competent tech cant find out whats wrong . Good Luck with it .

 

Paul,

Thanks a lot for your help I really do appreciate it. This at least gives me some ideas about what to have someone to look at.

Thanks

Ralph

 

Stateing that your trucks chech engine light blinks and the engine revs is indeed a sight that the computer is going through a diagnostic mode. There is most likely a short in the self test wire. Ther are 2 connector under the hood that hook up to the code readers. One is larger than the and has several wires connected to it. The other is a single wire. In order to retreve the codes teh self test wire is "shorted" to a wire in the other harness. If this wire is frayed and grounding out it could signal the computer to start the diagnostic routine as indicated by the check engine light flashing. A good tech can trace teh short by checking the resistance between the wire connections. These problems are usually simple in nature but time conuming to find.

 

Sorry about the spelling in that last reply. When I type, I get in a hurry and don't stop to check it.

 

did the mechanic show you where the leak in your vaccum line was. My a/c acts the same way and I'm sure myengine performance will suffer because of the leak. Iv' tried spraying starter fluid on all my lines under the hood and can't find the leak. This is driving me crazy so if you know which line it was I would appreciate some help here. Jim P.

 

Jimp,
Yes,it is the vacuum line that goes to the door control switch on top of the blower motor on the passenger side on the fire wall. Mine is a white hard plastic line coming from that door controll and comes out and makes a U turn back into a harness of wires with a plastic conduit over it. It was a small leak and was found by accident while he was just looking at it and happened to run his hand down that line. Mine goes back into that bundle of wires so you might have to trace it back into that. I hope this helps you to find it. It only happens when mine was on MAX AC. Let me know how it goes.

Ralph

 

Thanks Ralph. I was thinking that it had to be around that area. On Max the a/c always goes to the Def vents and on Norm only when there is a load on the engine. And when I went from Norm to Max there wasn't the normal vent change that used to happen. I'll look at it closer this weekend after my sons football game is over.
Jim

 

Nevermind about this weekend. I took a break at work and looked at it. When I touched the line it crumbled in my fingers. Did the Mech. replace the whole line or only a portion of it? Did he use regular old vac line or stock Ford parts? This is great. I can't thank you enough?

 

Jimp,

I'm glad you found it. I know it was nerve racking. The mechanic just used some flexible line that is pretty soft and just cut the bad piece out and slipped it over each end and it works fine. You might want to go back on your line to where it isn't so brittle and cut it off. He told me it breaks down because of the heat under the engine.

Ralph