F150MACH3

Hi everyone. This is my first post here. Joined the forum after bringing my F150 to the shop 4x for the same problem, three of those times to 2 different Ford dealerships. I had other less important issues corrected too, but the following issue was always the priority and nobody seems to be able to fix this or even figure out what the problem is. Anyway, here we go with the problem ...

It's a 1994 Ford F150 Mach III Stepside with 5.7 liter V8 engine with 155K miles and automatic transmission. Dual tanks, captain seats, electric sliding window, extended cab but only 2 doors. BTW, my gasoline is usually the mid-grade unleaded. The truck drives perfectly fine with zero symptoms of any kind for about 15 minutes. Only when the engine is good and hot, usually after driving about 12 - 15 miles, does the following occur (this happens with or without the use of the cruise control).

First the engine light comes on. Absolutely NOTHING changes in driving performance while the light is on. After 15 - 30 seconds the light will turn off again by itself and within seconds after that the truck will lose about 200 - 300 rpm in power which also becomes noticeable as the truck begins to slow down. This power loss goes on for about 15 to 30 seconds at which point the engine catches itself again. There's a slight forward lurch, the rpms go back to normal and the speed is back to normal. With the cruise control on the highway the problem is bearable. But for city driving it's a royal pain in the rear, needing to keep both feet available at red lights to make sure the engine doesn't die when the idle drops from 600 to 650 down to only 400 rpm.

Once these symptoms begin, they don't stop. The light on, light off, power loss, power/speed back to normal, goes on endlessly. I had to drive 150 miles like that for a major medical appointment. On the way back, same thing ... Hours later the now cooler engine/truck performed normally for the first 10 minutes, and then the grief with the symptoms started all over. This has been going on for the past 14 months and nobody seems to be able to figure this out. I don't think this is related to the transmission because the tranny shifts just fine and it's never slipped to this day.

Here's what I've had done: We had it on computers for analyzing twice. The fist shop replaced some relays and told me further, more detailed analyzing would need to be done at the dealership. Brought the truck to a well established Ford dealership, started from scratch (didn't tell them about the first shop). Total computer diagnostics! They told me that some electronic "stuff" (I'm not a mechanic) needed replacing and I paid $1260 bucks for that as well as other things that I had done which were unrelated. The problem still persisted, no change at all.

Then I thought to myself that if they couldn't find the problem, perhaps it's something quirky that can be corrected with some common sense. Brought the truck back to the dealership, told them to change the transmission fluid, (tranny filter if it had one), and flush out the entire fuel system with a high pressure something or another that they offer to clean out everything fuel related. Well, this did improve the performance a little bit, but the main problem itself with the light and power loss still persisted.

Most recently the truck started behaving even worse, right about the same time that my AC compressor started going. I couldn't believe how bad it got almost overnight and never associated the worse symptoms with the AC, until I turned off the AC one day while still in the vehicle, at which point engine performance noticeably improved. Awesome, we finally knew what the problem was (or so I thought). Brought the truck back to the shop, had the AC compressor, lines, and other minor items replaced for almost $1000 bucks, drove the truck home (7 minutes) without any negative symptoms ... only to find out a couple of days later that the initial engine light/power loss problem was still there. The more serious, apparently AC compressor issues were gone, but the initial problem was still there, exactly as it was from 13 or 14 months ago.

I love this truck, I really do. But at this point in time I'm beginning to think that nobody will ever be able to correct this. What else can be causing this? Since the engine has to be good and hot before the symptoms occur, is it possible that there are broken baffles in the muffler/exhaust that could be causing some sort of delayed or intermittent restrictions? This is nuts !!! Please, does anyone have any idea what I can try next? I've already put as much money on the truck as it's book value, I can't keep on paying money that I don't have for problems that can't even be found ....
HELP ....

joshtowal

First thing you need to do is pull the codes. If the engine light came on, there is at least one code stored in the computer. Without knowing what the code was, you should check your O2 sensors. Off the cuff, it sounds like a sensor/computer/electrical problem.

F150MACH3

Thanks, but didn't you read what I said? It was on the analysis machine to pull the codes and some repairs were made. Then it was on the analysis machine at the dealership where every code was pulled that could be possibly be pulled. Cost me almost $150 bucks just for that, no repairs. You're not helping. This is some kind of really weird problem that nobody seems to be able to figure out ... which is why I'm starting to look in other directions, perhaps some things that may not even have anything to do with codes or sensors since the one and same problem can't be tracked down after 4 visits to the shop ....
Three different shops total ... I don't think that all of those techs were morons or their equipment faulty. This is a 1994 F150, there wasn't that much computer stuff on them back then to begin with. I'm hoping to stumble across someone here who's experienced the same issues so that he or she can point me in the right direction. Thanks anyway

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sylver91

Yes we read what you said, but WE need to know the codes so we know whats going on, its hard just guessing and codes eliminate allot of the guesswork.

It could be something as easy as a fuel filter.

F150MACH3

Hmmm, I think you're missing what I'm trying to get at ...
It's been analyzed, the codes have already been pulled ... more than once ... yet still the problem couldn't be detected by 3 different shops. Consequently I don't think it would make a difference what code you have since it never made a difference before either. At this point I don't think that this is a code related issue, I'm thinking that this is something else and I'm trying to figure out what I'll be looking into next. Again, the codes have been looked at more than once already and the pros in the shops couldn't fix it, which is why I joined the forum, to find unconventional methods of figuring out what might be going on ...

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sylver91

Alright then, but it will be much more difficult, because I have a hard time believing you paid to get 1200 of electronics fixed ( which is usually a rare case they fail) and your still having the same problems. Codes will give us a starting point where to start.

But anyways, fuel pressure needs to be checked, might be very simple like a fuel filter, then ignition system for bad wires, plugs, scored rotor cap or even a failing ignition module

F150MACH3

Thanks. Like I said, there were other things done too. The first shop found a minor relay or sensor ssue that was fixed. Based on their advice for a full diagnostic that only the dealership could provide the truck went in again. At that point I was told that this or that needed replacing but I don't recollect what exactly was replaced. When I posted here, I figured that the key to the problem would be my comment about the truck driving perfectly fine until it was good & hot about 12 - 15 miles down the road. I'd think that that would eliminate the fuel filter. I also thought that we could narrow down the rpm reduction to something more specific, but I'm not a mechanic which is why I'm looking for pointers. YES, timing system sounds like it could be related, but I'm again a little hesitant to go there because when I've had older vehicles in the past with timing issues ... it never took 15 minutes of driving for them to become evident. How about a defective or badly placed spark plug cables? Couldn't that be something that causes a delayed reaction, something that doesn't become noticeable right away? I'm thinking that that's the whole key to this puzzle ... the fact that the truck runs 100% perfectly for around 15 minutes day after day after day ... before the strange symptoms occur.

Or how about a fuel pump that's starting to go? I had a 1976 Chevy Blazer with 350 V8 where exactly that caused similar issues, the engine had to be good & hot before I'd experience hesitation and bogging down of the engine ... but I'm shying away from that on this Ford F150 of mine because of how well the truck runs while the cruise control is being used, even with the symptoms which kind 'a seems to eliminate the fuel pump after all.

On a 1980 Chevy Van with a 350 V8 we experienced idling and bogging down issues because one of the two mufflers had baffles that literally collapsed within the muffler itself. As soon as we replaced both mufflers, bamm, everything was fine ... which prompted me to cut one of them open (no kidding). Took us forever to figure that one out. That was all before the years of Internet & Forums though ... being the reason why I figured this time around we'd be able to pinpoint the culprit of this odd phenomenon a little faster. I don't know anything about Ford vehicles though.

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sylver91

Well misplaced wires are noticeable immediately, but plugs get old and weak, distributor gets hot and misses cause of shorting in the rotor and cap. To find out if your fuel pump is bad or not, you will need to test fuel pressure on the fuel rail with a gauge. You may also have a vacuum leak or your EGR valve may not be working either. Heck you may have a blocked catalytic converter thats restricting exhaust.

This is why we need the codes the shop pulled, cause you can't always trust every mechanic out there, it will help us narrow down allot of thing. You can pull codes yourself using this thread if you want.

https://www.f150forum.com/f10/how-re...es-obdi-10907/

f150cam

does the truck start doing this if you just leave it idling in the driveway? or MUST it be driven to do this? if it will do it in the driveway, park it and watch the engine, see if you see like the AC compressor turn on and the engine slows (i know it was replaced but it was an example).

DISCLAIMER: i couldn't bring myself to read your entire post but i read about 75% of it.

F150MACH3

Well, I found some more helpful info. Online, including error codes and other stuff. I'll post that here to help someone else and I'll get back later, after I find out more. The truck will have to go to the shop for my own error codes 'cuz me and wiring just don't get along. I read the first 5 pages about that error code post and I'm just not any good with flashing morse code, aside from being too paranoid about damaging something important. I did find 2 posts Online though where people had the same problem with dealership analysis i.e. the machines displaying no error codes at all, or error codes that didn't match the symptoms. Regardless, I'll be back ...

My Truck and the EPA:
http://www.fueleconomy.gov/feg/noframes/11232.shtml

7th post in this thread:
http://www.fordf150.net/forums/viewtopic.php?t=71346

Description of all error codes:
http://answers.yahoo.com/question/in...4080952AAOGji5

Ford EFI Fuel Injection site:
http://oldfuelinjection.com/

Picture, very similar to mine, but missing paint with Mach III
http://upload.wikimedia.org/wikipedi..._Flareside.JPG

Thank you for your help thus far. It's appreciated.

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