Test your diagnostic skills here!
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Joined: Mar 2003
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From: Santa Barbara
Test your diagnostic skills here!
Howdy Everyone,
This is my first post but I have lurked around this website for years. Here is my dilemma. I have an 86 F150 2WD SWB with 302 EFI. It has been a good truck for me, with the only let down being a shredded timing gear (imagine that). Now I have another. I get a major hesitation when I step on the gas. If I ease into the go pedal it will accelerate without the hiccup, but this means I get to about 25 MPH in about 30 seconds. If I am even slightly aggressive gassing it, the motor falls flat on it's face. I am at the point now where I know when it is coming (the hesitation). As soon as it hesitates I stomp on the go pedal, which gets the engine past it's flat spot. If I keep the go pedal at the point where the hesitation occurs, the engine will lurch really bad. Bad like a sore neck. The other symptom is while driving on the freeway, the truck will only accelerate. It does not like to maintain any freeway speed. Now here is the list of what I have tried.
1. Replaced fuel filter
2. Replaced manifold gasket at top of intake
3. Performed vaccuum test
4. Swore extensively
5. Checked TPS
Thanks for your time and help.
This is my first post but I have lurked around this website for years. Here is my dilemma. I have an 86 F150 2WD SWB with 302 EFI. It has been a good truck for me, with the only let down being a shredded timing gear (imagine that). Now I have another. I get a major hesitation when I step on the gas. If I ease into the go pedal it will accelerate without the hiccup, but this means I get to about 25 MPH in about 30 seconds. If I am even slightly aggressive gassing it, the motor falls flat on it's face. I am at the point now where I know when it is coming (the hesitation). As soon as it hesitates I stomp on the go pedal, which gets the engine past it's flat spot. If I keep the go pedal at the point where the hesitation occurs, the engine will lurch really bad. Bad like a sore neck. The other symptom is while driving on the freeway, the truck will only accelerate. It does not like to maintain any freeway speed. Now here is the list of what I have tried.
1. Replaced fuel filter
2. Replaced manifold gasket at top of intake
3. Performed vaccuum test
4. Swore extensively
5. Checked TPS
Thanks for your time and help.
Senior User
Joined: Dec 2000
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May not be of much help here, i'm kind in the same boat with my '86 Bronco. 302 EFI, not haveing the hesitation problems but on the freeway this truck really stuggles to maintain 65, the cruise control works but is pointless because i'm putting my foot in it every mile just trying to maintain. I was trying to find a thread i found some time ago on this being the plenum gasket but have had to luck. Anyone have any other idea's? Or is the plenum gasket a good place to start?
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Joined: Oct 2001
Posts: 93
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From: montana
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When does the problem happen, under what conditions.
Have you checked any of the other sensors? Especially the ECT and MAP sensors, these two combined with the TPS have the biggest effect on fuel delivery before it goes into closed loop.
Have you checked the base timing, it should be set to 10 degrees advanced with the engine warm and the spout connecter disconnected.
Does the engine idle ok, if not you might have a vacuum leak that could contribute to your problem.
Have you checked any of the other sensors? Especially the ECT and MAP sensors, these two combined with the TPS have the biggest effect on fuel delivery before it goes into closed loop.
Have you checked the base timing, it should be set to 10 degrees advanced with the engine warm and the spout connecter disconnected.
Does the engine idle ok, if not you might have a vacuum leak that could contribute to your problem.
New User
Joined: Feb 2003
Posts: 18
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From: Portage, MI
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Being 86's, these motors are carbed. Try checkin the springs in the distributor, you can get heavier and lighter ones so that when ya stick the throttle, you can delay the timing advance. Also, make sure carb is clean, especially the venturis. Other than that, i'd say do a normal tune-up and see if that helps.
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Joined: Dec 2000
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Hey Hangtime, i just found that posting i was looking for earlier on the plenum gasket. Do a search in this forum for "plenum gasket" or go through and look for Topic: Annoying flat spot '86 Bronco posted by lumberguy. Sounds like the way to go on this, i'm gonna see if i can pick one up tomorrow.
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Joined: Mar 2003
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From: Santa Barbara
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Hey mikes66,
I appreciate the research. I replaced my plenum gasket, thinking along the same lines. My old one was completely fubar but the hesitation still exists. I have a nice smooth idle, but still a lurching problem when fuel is in demand.
I appreciate the research. I replaced my plenum gasket, thinking along the same lines. My old one was completely fubar but the hesitation still exists. I have a nice smooth idle, but still a lurching problem when fuel is in demand.
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Joined: Oct 2001
Posts: 93
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From: montana
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Have you checked the fuel pressure?
If it is ok, then it sounds like one of the sensors.
How did you check the TPS?
Have you retrieved the codes, if any, from the computer?
If it is ok, then it sounds like one of the sensors.
How did you check the TPS?
Have you retrieved the codes, if any, from the computer?
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Hotshot
Joined: Oct 2002
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From: The Big, Oregon
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Does it stall when you pump the brake pedal? When was the last time you tuned it up, or cleaned the TB?
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New User
Joined: Mar 2003
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From: Santa Barbara
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Hmmm let's see,
The truck has tune up parts with less than 12k on them.
It does not stall when I pump the brake pedal.
I'm not sure how to check the fuel pressure, but I am thinking pressure regulator may be faulty.
I don't know how to check codes.
I checked the TPS by swapping one off another 86 F150.
Here is another symptom that may help with diagnosis. The truck has no hesitation while cold. Could this be the engine running rich (choke effect) thereby providing more gas and avoiding the hesitation?
Thanks again
The truck has tune up parts with less than 12k on them.
It does not stall when I pump the brake pedal.
I'm not sure how to check the fuel pressure, but I am thinking pressure regulator may be faulty.
I don't know how to check codes.
I checked the TPS by swapping one off another 86 F150.
Here is another symptom that may help with diagnosis. The truck has no hesitation while cold. Could this be the engine running rich (choke effect) thereby providing more gas and avoiding the hesitation?
Thanks again
Junior User
Joined: Oct 2001
Posts: 93
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From: montana
Test your diagnostic skills here!
Since the problem only happens after the engine warms up it would lead me to think the ECT (engine coolant temperature sensor) has a problem.
Do a search on this website for trouble codes and you should be able to find out how to retreive them without any special tools.
Do a search on this website for trouble codes and you should be able to find out how to retreive them without any special tools.
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From: montana
Test your diagnostic skills here!
Post Fiend
Joined: Nov 2002
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From: Memphis, TN
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Hangtime
You're not gonna want to do this, but make SURE your gears are still timed right - your symptoms can come from them being one tooth off.
Use the link 71 posted and be sure to clear the codes after you record them.
A Haynes manual (the best $12 you'll ever spend) tells how to pull, clear, & decode codes, AND how to test each sensor on the engine. You can get a fuel pressure gauge from Sears for ~$20, but the most common problem with the FPR is a fuel leak straight into the vacuum line.
You're not gonna want to do this, but make SURE your gears are still timed right - your symptoms can come from them being one tooth off.
Use the link 71 posted and be sure to clear the codes after you record them.
A Haynes manual (the best $12 you'll ever spend) tells how to pull, clear, & decode codes, AND how to test each sensor on the engine. You can get a fuel pressure gauge from Sears for ~$20, but the most common problem with the FPR is a fuel leak straight into the vacuum line.
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From: Santa Barbara
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Thanks Steve83 I will buy the haynes manual. I plan on having the truck for awhile so this probably won't be the last time I use it.
And 71mustang although a 71 Mustang really looks more like a Torino in my opinion I remember a 70 something fastback that had a stars and stripes and USA theme to it. It was white with red white and blue accent stripes. Do you know this car? I remember it from when I was a kid. My dad stripped it for the engine, I assume it was a 351C, and scrapped the body. There was nothing really wrong with the car, it was just in the wrong place at the wrong time. Thanks for your help as well.
And 71mustang although a 71 Mustang really looks more like a Torino in my opinion I remember a 70 something fastback that had a stars and stripes and USA theme to it. It was white with red white and blue accent stripes. Do you know this car? I remember it from when I was a kid. My dad stripped it for the engine, I assume it was a 351C, and scrapped the body. There was nothing really wrong with the car, it was just in the wrong place at the wrong time. Thanks for your help as well.
More Turbo
Joined: Nov 2002
Posts: 543
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From: Tulsa
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My '86 f250 used to have a similar prob. I washed the carb with some CRC carb cleaner and replace the cap and rotor with an MSD set. I also put in an Accel high performance coil and that seemed to really help a lot of things.
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