Truck stalls+bad at high speed
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From: Germantown, MD
Truck stalls+bad at high speed
I have 2 problems that are most likely related, and seem to be regarding the engine performance. I just got an 86 F-150 with a 302 from my Uncle. It has done a lot of sitting for the last several years, but it has seen the road for about 90,000 miles. When I floor it, it will downshift, and accelerate, but then after a couple seconds it will wind down but stay in the lower gear. It will just pulse, accelerate and decelerate, when the pedal is at 3/4 +. It mostly does this at high speeds, 55mph+. The other problem is at idle sometimes it pulses. At night you can see the gauges dim as it pulses just idling in Park. This pulsing also accurs in Drive without any throttle applied. It hessitates at first, and often stalls. Even after a 10 minute drive home from work, I will pull in the drive way, accelerate from almost a stop to go up the curb, and it will sometimes stall out. But, then it is quick to fire up again. When I picked up the truck, my Uncle had not driven it for a week... I hit the key without any gas and it didn't hesitate to fire up on the first shot after maybe 3 seconds of cranking, which is pretty quick. Any help is appreciated, thnak you!
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From: Virginia
The high speed hesitation sounds like the fuel pump or the fuel filter. You can put a fuel pressure gauge on the fuel rail to check for a problem in this area.
The wandering idle sounds like the throttle body needs to be taken apart and cleaned. This includes the IAC motor and passages.
The wandering idle sounds like the throttle body needs to be taken apart and cleaned. This includes the IAC motor and passages.
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From: Germantown, MD
I can remove the throttle body and carb-clean the hell out of it in all the chambers and stuff. Is that what you mean? Where is the IAC motor located?
As for the high speed hesitation... The fuel pump was replaced last summer, so it should still be good. It probably needs a fuel filter. Where is that sucker located on an '86 F150 shortbed with a 302? Btw, would higher than standard 87 octane fuel do the truck some good? And, those fuel additives that are supposed to clean out the engine etc... is any of that stuff helpful, or is it kind of a scam?
As for the high speed hesitation... The fuel pump was replaced last summer, so it should still be good. It probably needs a fuel filter. Where is that sucker located on an '86 F150 shortbed with a 302? Btw, would higher than standard 87 octane fuel do the truck some good? And, those fuel additives that are supposed to clean out the engine etc... is any of that stuff helpful, or is it kind of a scam?
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From: Virginia
Yes, take the throttle body apart and clean around the throttle plate and the passages. One of the passages will lead to a black round thing mounted on the side of the throttle body, with wires going to it. That's the IAC(idle air control). It's a little motor that lets air go around the throttle plate to control the idle speed.
I believe on your model, the fuel filter is located underneath the truck by the fuel tank. Be careful when taking the lines off the filter, there is about 40psi of pressure on these lines, and they can squirt you with fuel.
Several tanks of new fuel would probably do wonders for the fuel system, but you can run some injector cleaner through it too.
I believe on your model, the fuel filter is located underneath the truck by the fuel tank. Be careful when taking the lines off the filter, there is about 40psi of pressure on these lines, and they can squirt you with fuel.
Several tanks of new fuel would probably do wonders for the fuel system, but you can run some injector cleaner through it too.
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Mine seams to do the pulses as it idles and almost always in gear and it will eventually kill itself. Last week one of my buddys thought that I put a huge cam in it because it was pulsing. It is seaming to get better as Im putting more miles on it. I have a tach on mine and the pulse will seam to range from 2000-200 rpms. Would carb cleaning the throttle body help or should I run some Marvil Mystery oil through it.
Thanks
Thanks
Last edited by kenworthfan; Jul 18, 2007 at 10:01 AM.
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From: Virginia
All fuel injected vehicles, no matter what make, have the gumming problem around the throttle body and the idle control. I just finished having to clean them up on my wife's honda.
When the engine is stopped, oil smoke wisps up out of the intake and over the years, builds up a black sticky gum around the throttle body components.
When the engine is stopped, oil smoke wisps up out of the intake and over the years, builds up a black sticky gum around the throttle body components.
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Would the Marvil Mystery oil help on cleaning that, and a few weeks ago I replaced the idle air control on my truck.
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From: Germantown, MD
OK. I got some fuel injector cleaner stuff from Advance Auto. It's this STP stuff that was buy one get one free! I put some high octane fuel in today to see if it would help, but it didn't seem to. I'll dump some STP in, and clean out the throttle body. I bet it needs a fuel filter too, so i'll get around to that as well. Thanks.
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From: Germantown, MD
Sure enough... I cleaned the TB and its passages. I also removed the IAC unit and sprayed it all throughout. I used carb cleaner and Brakleen, basically just sprayed everything, and then I blew it out with an air hose. I Put a wire brush on a drill and cleaned the intake manifold a little as well. It hasn't stalled on me yet, and the idle is steady and correct. Thank you all for the help!!! Now, if I could just get to the bottom of the acceleration issue.
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From: Virginia
You need to take it apart and do a good job at cleaning it. A lot of the gum ends up behind the throttle plate.
A certain amount of air goes by the throttle plate when it's shut, and the rest of the idle air goes through the IAC. When things get blocked, it throws the balance of the air from one to another off. That's what also happens if you try to adjust the throttle stop screw.
And the IAC area gets gummed up, and it sticks.
A certain amount of air goes by the throttle plate when it's shut, and the rest of the idle air goes through the IAC. When things get blocked, it throws the balance of the air from one to another off. That's what also happens if you try to adjust the throttle stop screw.
And the IAC area gets gummed up, and it sticks.
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From: Germantown, MD
I looked under the truck today, and there is a fuel filter up towards the engine on the left side next to the frame. It looked brand new unlike everything else on the truck, haha. But, I looked at the spark plug wires, and they were laying on the valve cover, and on the underside they looked really worn down. Obviously there is some arching going on there... Would that cause the problems I am having. It's actually more of an acceleration issue... Whenever I floor it, it will rev up, and accelerate, and then after a few seconds, it will slow down, and then pick up again, and so on. Then if I let off a little it will shift hard, and accelerate. But, when it is fully on the floor, it will downshift, rev up, and then it has difficulty. It seems this problem only occurs at high rpms... I will replace the spark plug wires because of their condidion, but do you think this will solve the acceleration issue?
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Indeed it will. DO NOT GET AUTOZONE WIRES. Get the $65 motorcraft wires from advance (parts america online), or the similarly priced napa or carquest wires. While you're at it get the most expensive cap and rotor, they'll be brass and won't corrode as fast. With the aluminum ones they only last a few months before they start to idle rough. Trust me, you might dump a LOT of money into it once every three years (about $100 to $120 if done with all high quality parts), or you can skimp on it and either get stranded or pay about $10 every month or so for a new cap and rotor... The choice is yours. I take the higher priced route so that I know it's done for a while.
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From: Virginia
If you want to test the wires, go out at night and run the truck and see if you have any sparking around the wires. You can even give them the acid test and spritz a little water on them at night and see if there is any sparking.
The difference between idling/cruising, and using the engine hard is fuel usage. That's why I suspect a fuel problem, and the fuel filter. If you have rusty tank problems(very common for these trucks) a new fuel filter may be clogged already. But a fuel pressure guage would verify if the fuel system was ok.
The difference between idling/cruising, and using the engine hard is fuel usage. That's why I suspect a fuel problem, and the fuel filter. If you have rusty tank problems(very common for these trucks) a new fuel filter may be clogged already. But a fuel pressure guage would verify if the fuel system was ok.