Poor running after warming up
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New User
Joined: Mar 2006
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Poor running after warming up
Good day to all,
I have a 91 F150 XLT Lariat 4x4 with a new 302 in it. Here is the problem I am having. When the truck is cold it runs great, instant responce at the throttle and plenty of power in all 5 gears. Once it reaches operating tempature the power goes to crap and it bogs down when you accelerate in all 5 gears. It runs great at a idle warm or cold, no misses or hesitations at all.
What could be causing this?
Replaced with new engine -
ECT sensor (the one with two wires)
Air temp sensor
oil pressure sender
all new gaskets and mostly new bolts.
all new hoses
all new injector o'rings
Again I only get this problem at operating tempatures.
Any help would be greatly appreciated.
I have a 91 F150 XLT Lariat 4x4 with a new 302 in it. Here is the problem I am having. When the truck is cold it runs great, instant responce at the throttle and plenty of power in all 5 gears. Once it reaches operating tempature the power goes to crap and it bogs down when you accelerate in all 5 gears. It runs great at a idle warm or cold, no misses or hesitations at all.
What could be causing this?
Replaced with new engine -
ECT sensor (the one with two wires)
Air temp sensor
oil pressure sender
all new gaskets and mostly new bolts.
all new hoses
all new injector o'rings
Again I only get this problem at operating tempatures.
Any help would be greatly appreciated.
Post Fiend
Joined: Mar 2002
Posts: 19,402
Likes: 38
From: Bonita Springs FL
Does it do it on both tanks? Sounds like it could be a dying fuel pump.
It could also be a clogged cat - did you drop a bolt down the exhaust manifold?
Also pull the codes if you haven't already.
It could also be a clogged cat - did you drop a bolt down the exhaust manifold?
Also pull the codes if you haven't already.
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New User
Joined: Mar 2006
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Andym,
Thanks for your reply.
It does the same thing running on both tanks.
I am pretty sure nothing dropped down the exhaust manifold or pipes. Made a mistake once on a engine by dropping the distributor cap bolt down the intake so I tape off all openings so it doesn't happen again.
I am getting no codes at all.
Some other things to add,
The fuel mileage is worse with the new engine than with the old worn out engine.
I have replaced most of the vacuum lines, it has new plugs and wires and also new cap and rotor.
I know the ECT sensor can cause this and I will run a test on it (even though its new) when I get time.
Other than that I am not sure what to test next if it checks out ok.
If anyone else has suggestions please let me know.
Thanks for your reply.
It does the same thing running on both tanks.
I am pretty sure nothing dropped down the exhaust manifold or pipes. Made a mistake once on a engine by dropping the distributor cap bolt down the intake so I tape off all openings so it doesn't happen again.
I am getting no codes at all.
Some other things to add,
The fuel mileage is worse with the new engine than with the old worn out engine.
I have replaced most of the vacuum lines, it has new plugs and wires and also new cap and rotor.
I know the ECT sensor can cause this and I will run a test on it (even though its new) when I get time.
Other than that I am not sure what to test next if it checks out ok.
If anyone else has suggestions please let me know.
New User
Joined: Jan 2004
Posts: 19
Likes: 0
From: Eastern Ky
I'm having this exact same problem, Have you found the fix yet, I also have a 91 F150, 5.0, 2wd, replaced engine with an 1989 engine that I had drove in the other truck and was fine. Replaced the eec from the 89 but still I have the same problem as stated.
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New User
Joined: Mar 2006
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Finally some codes tripped for me.
Code 21 ECT out of self test range 0.3 to 3.7 volts.
Code 24 ACT sensor out of self test range 0.3 to 3.7 volts.
I was kinda suspecting the ECT but was getting no codes at first.
Ran a resistance and voltage test on both. The ECT checks out for me, the ACT gives no readings at all. I went to the parts store and checked one off the shelf (ACT) and it to had no resistance to it. Not sure if the ACT could cause the fault with the ECT or not. Both are new sensors.
Going to do some more troubleshooting today to see what I can find out.
Code 21 ECT out of self test range 0.3 to 3.7 volts.
Code 24 ACT sensor out of self test range 0.3 to 3.7 volts.
I was kinda suspecting the ECT but was getting no codes at first.
Ran a resistance and voltage test on both. The ECT checks out for me, the ACT gives no readings at all. I went to the parts store and checked one off the shelf (ACT) and it to had no resistance to it. Not sure if the ACT could cause the fault with the ECT or not. Both are new sensors.
Going to do some more troubleshooting today to see what I can find out.
Laughing Gas
Joined: Oct 2005
Posts: 1,226
Likes: 42
From: The OC
I am sure your battery was disconnected when you replaced the motor, but before you commit to new parts, disconnect the negative battery cable again to clear your codes, drive it for a while and get to operating temp, then read your codes. Replace the sensors that are giving you bad readings.
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Well I did some more troubleshooting and researching and wanted to pass the findings on to others.
Pulled the radiator cap and coolant was a little low so I topped her off. I am thinking there may have been a little air still in the cooling system. I believe this may have given a bad ECT sensor reading due to the location of the sensor (near the top of the engine.
I pulled the connection on the ACT cleaned up the wiring harness and reconnected it.
Cleared codes and drove it no more codes 21 and 24. Then I got a code 33. That was my fault though because I forgot to reconnect the EGR vacuum line when checking things out.
Went back and rechecked the timing after clearing up all the other codes. It was out of time. Set the timing correct and took her for a drive. She does great at all temps now.
I hope this takes care of it, only time will tell. Thanks for all the replies and I hope this update will help someone else out.
Pulled the radiator cap and coolant was a little low so I topped her off. I am thinking there may have been a little air still in the cooling system. I believe this may have given a bad ECT sensor reading due to the location of the sensor (near the top of the engine.
I pulled the connection on the ACT cleaned up the wiring harness and reconnected it.
Cleared codes and drove it no more codes 21 and 24. Then I got a code 33. That was my fault though because I forgot to reconnect the EGR vacuum line when checking things out.
Went back and rechecked the timing after clearing up all the other codes. It was out of time. Set the timing correct and took her for a drive. She does great at all temps now.
I hope this takes care of it, only time will tell. Thanks for all the replies and I hope this update will help someone else out.
