91 F150 bucking
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91 F150 bucking
My dad has a 1991 F150 2wd, 5 spd, 4.9 I6, shortbed. Occasionally, it will take spells of missing and bucking bad on acceleration or crusing. The speed of the truck doesn't seem to be a factor, nor what gear the truck is in. It doesn't matter if it has rained, not rained, hot/cold, whatever. It's been to three different mechanics, and had more money thrown at it than the truck is worth. The first shop replaced at our request, the clutch plates and the clutch master and slave cylinders, and diagnosed the bucking as being in the injectors, all 6 were replaced. The second shop found a bad ignition pickup and modual, ended up replacing the distributor due to a bad bushing in it, changing spark plugs and wires. The third shop found a bad ignition modual (almost a year after the second shop replaced it), and a faulty coil. After all this, the problem keeps popping back up. My own code reader shows no defect codes stored in memory.
Can anyone give me any advice at all? This truck goes about 40 miles a day and the missing and bucking is really really annoying.
Can anyone give me any advice at all? This truck goes about 40 miles a day and the missing and bucking is really really annoying.
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From: Colorado, U.S.A!
Does your code reader give you the 1, 1 reading for the system checking good?
I guess you already replaced the fuel filter and PCV valve... Have you checked fuel pressure? I wonder if it might be an intermittent fuel pump problem? Saw a post here recently where a truck wouldn't start unless the gas tank was whacked. New fuel pump cured it.
That's all I can think of, good luck.
I guess you already replaced the fuel filter and PCV valve... Have you checked fuel pressure? I wonder if it might be an intermittent fuel pump problem? Saw a post here recently where a truck wouldn't start unless the gas tank was whacked. New fuel pump cured it.
That's all I can think of, good luck.
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Originally Posted by c96drumm
Does your code reader give you the 1, 1 reading for the system checking good?
I guess you already replaced the fuel filter and PCV valve... Have you checked fuel pressure? I wonder if it might be an intermittent fuel pump problem? Saw a post here recently where a truck wouldn't start unless the gas tank was whacked. New fuel pump cured it.
That's all I can think of, good luck.
I guess you already replaced the fuel filter and PCV valve... Have you checked fuel pressure? I wonder if it might be an intermittent fuel pump problem? Saw a post here recently where a truck wouldn't start unless the gas tank was whacked. New fuel pump cured it.
That's all I can think of, good luck.
Fordberg, thanks for the idea of putting the amp guage inline to the fuel pump, I happen to have a spare one here on my workbench, and may try that in the next few days.
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My 94 300-6 was doing something similar. It happened more just above an idle, but would happen in any gear. I replaced the IAC gasket, and the Throttle Body Gasket and the TPS and the problem is gone. I'm convinced the gaskets fixed it though, and not the sensor. The IAC on my truck was actually loose, and just tightening the bolts made a difference before I replaced the gasket.
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Check with your mechanic. There was a TSB (technical service bulletin) on the I6 engines that had you replace the computer and egr at the same time ( the old comuter maping was wrong)
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Ugh, before we go to the expense of replacing the computer and the egr, i think the truck will be retired. If the TSB applies to that particular engine in that year, three mechanics have failed to point it out. I still haven't had a chance to hook up an amp gauge inline to the fuel pump, but the funny thing is, it hasn't bucked once since I wrote that first post....Leads me to think that it's an intermittent problem somewhere, maybe a loose or corroded connection. I'll still look into that TSB about the I6, thanks for the tip.
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From: Ashland City, TN
Yea, i have a 302, thats a 91, and mine bucks every now and then too. Going along with the problem in my other threads.
does it in all the gears too.
mine feels like its in the dead zone of the transmission, when the truck dosn't want to supply adiquite power.
does it in all the gears too.
mine feels like its in the dead zone of the transmission, when the truck dosn't want to supply adiquite power.
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I too have a 302, my father has the I6, he told me about the T.S.B. but it only applies to the I6. One thing I did do the other day, I pulled the vacuume line off the egr (I plugged the line so I didn't have a leak) and took it for a drive. No engine light and no real noticeable jerking. I think I'll leave it for a few days to make sure.
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Your problem could be in the Throttle position sensor. The earlier ones would develop flat spots and cause conditions like you described. At idle, try revving slowly through the throttle range. See if the motor misfires slightly at certain throttle positions. This missing will be magnified when the engine is under a load. You can also test it with a voltmeter with the engine off - ignition on by moving the accellarator through its range. If the voltage drops, then you have found a flat spot. A TPS with flat spots wont set a trouble code.
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Thanks bigbadj's. I had the TPS checked at a local auto parts store, and it tested ok, but that was a few years ago, so it wouldn't hurt to check it again while I am under the hood of this truck....There is way too much electrical stuff on this thing.
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From: southern Indiana
My 91 F150, 5spd with I6 does the same thing. Really noiticeable when cruising at 45mph or better. I am going to replace the plugs/wires next(already did fuel filter and the other usuals). If that doesn't work, I will dig deeper.
If you find a cure, please post it.
Thanks,
Vince
If you find a cure, please post it.
Thanks,
Vince
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Redranger03
1983 - 2012 Ranger & B-Series
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Oct 7, 2005 11:33 AM
1990, 1991, 1994, 49, acceleration, bucking, bucks, engine, f150, hot, intermittent, missing, transmission, truck
