89 F150 with 300, 5 speed manual, 3.08 axle,
127k miles.
HELP!!!!

My F150 developed a miss several years age that gradually has became worst. About 3 years ago
I put the truck in the shop at Dale Horn Ford in Malvern, AR to allow a personal friend and also one of the top award winning Ford mechanics in the mid-south area to check it out. He gave it
his best shot and made a big improvement but he
did say it wasn't 100%. What puzzled him the most
was that while test driving it with a portable
analyzer, or whatever it is he connects to the computer to monitor the engine, it would never generate a fault code whenever the engine missed.
The miss occurs most frequently when letting up
on the accelerator after getting up to speed. Usually while maintaining a steady speed it is ok.
It seems that when the engine is in a no or very low load situation something is confusing the computer. I have been living with this glitch for years and it is really starting to get on my
nerves. ANYBODY PLEASE HELP!!!!

 

My truck is the same as yours ....and has done exactly what yours has done since it was new . Like your friend at Ford , I have been thru every diagnostic routine Ford has as well as some Ive tried all to no avail . The miss is so random and unpredictable , I cant limit the cause to anyone thing or condition . What I have been meaning to try is replacing the actual ignition switch that mounts down on the lower steering column . Ford has had a recall on them for yrs and every yr I get a notice in the mail telling me to come have it replaced . Ive never been able to determine if the miss is ignition or fuel related ? Did your Ford Tech Friend narrow it down to either one ? I suspect its Ignition / Electrical and the cause may lie in a problem in the ignition switch . We arent the only ones with this problem . I have talked to several other owners of pretty much the same truck / engine combo we have that all relate the same symptoms . Since all the trucks are having the same symptoms , It has to be one component that is common to all these engines . The next time I have a day off , Im going to go let them install the new ignition switch and see how that does . Ive lived with it because the truck has never left me stranded in 161 K miles and its so sporadic . Hope this helps a little .
Paul

 

I did have the ignition switch replaced. A few
other characteristics it has developed in the past few years is an idle the varies from 600 to
700 rpm all the way down to around 300 and then
goes back up. Sometimes the engine will die when it dips down. It usually does this after the engine has reached operating temp and then I stop for about 30 minutes and then start it. After the restart I have to be careful about when I turn the AC on. The truck is horrible in stop and go slow city traffic where 1st gear take offs are common. Clutch and throttle position are very critical when trying to perform a smooth take off. There are times if I'm not applying enough throttle and engine will nearly fall flat and die. Usually I can respond quick enough to prevent the engine from dying but end up with a very annoying surge. Whenever I do manage to do the take off just right, slow, steady pressing of the accelerator in 1st gear results in an irritating surge or "Crow Hop" as my Ford mechanic friend calls it. Once the rpm is in the upper teens it starts to taper off. Once in second things are ok. Replacing the tps helped some but did not cure it. I'm going to experiment with the egr like opportunitech did. My hesitation/miss seems to occur when the engine is hot or cold. I read a response to opportunitech about somebody is going to change out the computer. Does the 89 300 computer have a chip(eeprom) that could be replaced with an after market one? A theory that my Ford friend has is that the engine is running on the ragged edge of being too lean and something pushes it over the edge every once in a while. Sounds like whoever wrote the program does not live in the real world and did everything based on theory and did not even consider giving it any fault tolerance. I'm wondering if a reprogrammed computer or chip could be installed with slightly richer mixture. Do such items exist? Thanks for your responses.

mxer201

 

Well, thank God I'm not the only one suffering with this. I have been going nuts trying to get mine to stop missing. Mine is most pronounced in 3rd gear, neither accelerating or decel, just at a raised rpm (around 1700). The thing will buck like a mule. I have access to a Snap-On diag. computer and it says nothing is wrong. The only code I ever got was a dirty ICS which I cleaned and it went away. One thing I did find that helped slightly is a gasket between the intake and throttle body that seem to have a tendency to leak air. Several mechanic friends confirmed this to be a problem with this model. The leak is usually small and sometimes whistles like a kid's toy at diffrent RPMS. I'm hoping for an answer just like you are. There is no sense in changing sensors as others have tried this approach and failed. I feel that this is a firmware discrepancy in the program and might be best addressed by an aftermarket chip. Has anyone tried this with any success??? We should start a support group for people like us who suffer quietly with this malady all these years with no answer in site. If I find anything out more, I will write back in, however, after years of research and no resolution to the problem, I have all but given up hope. I'll have to settle with 100% reliabilty............with a miss.

 

Mxer201 ,
To address the idle instability problem , When was the last time you cleaned the Throttle Body / Plates and Idle Air Bypass Valve ? Carbon buildup on these parts will drive the EEC nuts looking for the proper idle . Your Ford Tech friend may be on to something with the Lean Mixture Theory . What I did a few yrs ago (96) was replace the injectors with a revised Injector(s)...Ford Part Number F1ZZ 9F593 B that cured my rough idle . The new injectors have a better spray pattern and my instances of the Miss diminished but did not go away totally . It continues to idle so smooth that I often have to look at the tach to make sure its running . I think they gave the added fuel or at least a better saturation . I think the EEC leaning the fuel air mixture coupled with the further diluting that the Egr adds may be why we have all had pretty much the same problems ? In the next few days , Ill check if Ford offers a revised EEC IV for the 300 . I checked on an EEC IV for an F250 the other day and it was at least a revised part number . With Ford parts , its hard to tell if they just changed part numbers or if they actually changed the part ? The people that write the programs for these things may have realized that some aspect of the EEC IV for this engine may have been flawed ? Ask your Ford Tech friend if he thinks what I have posted seems to make any sense or is along what he believes may be what is causing this .
Paul