Mechanics

F150 STILL RUNS BAD...

1991 Ford F-150

Other Category problem
1991 Ford F150 V8 Two Wheel Drive Automatic 129000 miles

I have a 1991 Ford F-150 Supercab, 5.8 EFI V8, E40D Auto Trans, dual tanks, 129,000 miles. I posted a question before, but I am still having problems with my truck. I have replaced the rear fuel pump, totally bypassed the front tank, lines and all, replaced the fuel pressure regulator, fuel pump relay, another relay in same area as fuel pump relay, changed the transmission filter and fluid, and even had codes pulled, of which at first it pulled 12 codes, shop cleared those, and redrove and pulled 18 more codes. The shop said all my codes related to a bad ground somewhere. I have checked all the grounds that I could find under the hood and along the frame. Loosened them and cleaned them and retightened them. I'm still having problems with my truck not running properly. In drive it acts like it's cutting off and restarting itself, every so often the voltage will drop during this but not all the time. At idle, the truck just runs like it is misfiring/skipping. Now, if I drive the truck for more than 30-45 minutes there are strong exhaust fumes present and the truck won't restart for about 30 minutes if I cut it off. I'm to the point where I am thinking of starting to replace sensors one at a time, once a month, because I can't afford to do them all at once. That and the injectors. Fuel system is up to par on pressure. All my vaccuum lines are connected properly and none are leaking. Truck is costing me more to repair than to buy. Am I missing something simple?
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Blondewolf
February 4, 2008.



When was the last tune up done.

Tiny
98rangerxlt
Feb 4, 2008.
I did a tune up back in october. Its been less than 2000 miles since. My truck just keeps getting worse and worse. Tune up didn't help anything by the way, and when I did the tune up I replaced all spark plugs gapped to specs, wires, cap and rotor. It ran a little better after I changed the oil, but only for about 20 miles or so. Tune up was the first thing I suspected. I read another forum article and checked my MAP sensor, and I know its bad. Truck idles much smoother with MAP sensor vaccuum detached but I don't know whether I should really run without it connected or not. I know catalytic converter isn't helping matters as its poorly clogged, but that is another $130 I don't have right now. I just spent $130 replacing fuel pump with brand new with no improvement. As I said, front tank is completely bypassed so I didn't replace both, just the rear. I'm going to replace MAP sensor and coolant temp. Sensor in next 3 weeks and am hoping that helps some, but I still think i'm missing something simple.

Tiny
Blondewolf
Feb 5, 2008.
Well, guess what. All along it was something simple. I changed out my MAP sensor and now the truck idles just fine. Its amazing how something so simple can often be the last thing you check! I recommend that if anyone else is having similar ford issues like I was having, you check your MAP sensor first before spending more money than necessary. A MAP sensor runs about $50 for a truck like mine and takes about 5 minutes to change out.

Tiny
Blondewolf
Feb 9, 2008.
Good job! The shop didn't zero in on the disconnected MAP sensor and flag that as a possible issue?

Tiny
Indyuke
Feb 10, 2008.
Actually, there is still more wrong with it than just the MAP sensor, so now I am back to square one again. I plan on doing soething with the catalytic converter, and then valve cover gaskets and intake gasket. I'm planning on replacing most of my sensors after the catalytic converter is fixed. Hopefully by then I can figure out what is wrong with the poor thing. Besides the fact that its ford mind you. Actually it has its good days and its bad days. Today was a good day, tomorrow. Well we'll see.

Tiny
Blondewolf
Feb 11, 2008.
Only a ford! I'm offended! Ford's are the BOMB! : Wink: (their trucks at least)

Actually my real baby is a cherry (almost : roll: ) 1970 Chevy CST/10 pickup. That's a real truck. With still plenty of power at 130mph.

Tiny
Indyuke
Feb 13, 2008.
Actually i'll take a ford truck over any other truck. It's just this one particular truck has given me nothing but grief since I bought it. I've driven many ford trucks, most of them 450 or 550 diesel duallys, and all in excellent running condition. This one just has problems. But considering it is 17 years old and most everything in it is still factory stock, what can I expect. I just wish I could figure out what is wrong with the dang thing and get it fixed properly without having to spend more than what I paid for it. I finally took it to the shop for the exhaust system. I never realized that it had 2 catalytic converters and no muffler on it. Well, that is getting fixed as we speak. Once that is done, then I can concentrate on the valve cover gaskets and intake gaskets and idle air control valve, and go from there.

Tiny
Blondewolf
Feb 13, 2008.
My first vehicle was a ford truck. A '72. Since then i've owned more fords than any other make, and more ford trucks for that matter. I've never had anything really go wrong with any of them.

The OBD1 system is pretty good. I think the weak part of the whole system is the various sensors that seem pretty fragile to me. They need a lot of attention. That and the little plastic vacuum hoses that ford used at that time. Those are cheezy and they crack so easily.

Other than that the actual mechanical components are more or less tried and true, the wiring seems to be well routed and protected. Good vehicles.

Tiny
Indyuke
Feb 14, 2008.
Ok. So now i've gotten the exhaust fixed. My cats were fairly clogged, and my truck is running more consistent now. But it still has that irritating little loss of power hiccup that it has had since I got it. I changed out the idle air control valve, with no real noticeable change in performance. I'm still planning on doing the valve cover gaskets, but i'm beginning to wonder if there is a ground I have missed somewhere. Or if something else might be causing a power loss. When driving, you can watch the rpms drop and jump back up, and sometimes the voltage will drop also, but not all the time. So what's the simplist thing I can check that I haven't looked into already? Or did I just happen to get lucky in my unluckiness and get the one bad ford truck out of hundreds of good ones?

Tiny
Blondewolf
Feb 14, 2008.
That's interesting. I remember a 1991 f150 having rpm surges on the highway. It turns out that the torque converter was kicking in and out causing the rpms to go up and down. How often does your truck do this? Is it in high gear, or does it do this all the time. In park at idle too?

Tiny
Indyuke
Feb 14, 2008.
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