Strange random hesitation/acceleration issue
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Strange random hesitation/acceleration issue
Hey everyone,
I have a 1999 F-150 2WD 4.2L V6 with an interesting issue. The previous owner claimed they replaced the TPS, MAF, Fuel Pump, Air & Fuel filters, and the IAC.
What happens is, only after she's at a good operating temperature and has been driving a bit, it'll randomly not accelerate. If I press on the gas, like 40% or so, the RPMs will drop and the engine will act like it wants to stall. If I'm real easy on the gas, like 5% throttle, it'll slowly accelerate. When it happens the symptoms will only last about a minute and then it accelerates fine again. I did throw it in neutral once during an episode and try to rev the engine and it wouldn't rev, same symptom. No Check Engine light appears when it happens. Outside of that she idles beautifully, even during an episode, and has plenty of power most of the time. I also noticed if I were to keep the throttle down during an episode the engine will stall. I can also throw the truck in neutral, shut the engine off and restart it, put it back in drive and boom, I can accelerate fine again for a little while. If I'm stopped and in park during an episode and I try to go wide open throttle I do notice intake blow back occasionally.
So far when I first started diagnosing it we checked plug wires for any damage and if any were arcing or anything, nothing, all is well. No CEL has ever come on, I was able to get a P0113 code once for the IAT sensor, I went ahead and replaced it for good measure since it was an inexpensive replacement but that didn't resolve the issue and it hasn't thrown the code again since.
I went as far as replacing the PCM and when I did, PATS locked down the truck and rather than towing it to a dealer to do the keys I figured it was in my best interest at this point to invest in a good scanner so I picked up an Autel MK808 which is incredible by the way. I was able to clear the PATS and reprogram my keys and all was well there, but it didn't solve the random hesitation/acceleration/stalling issue.
I spent hours watching live data, during an episode and while it was running fine, nothing seemed a miss except one thing, the knock sensor. I almost missed it since it didn't have an expected value range listed. The Knock sensor reading sits at 1034 at idle, when I slowly apply throttle, let off the throttle, regardless of rpm. It just sits at 1034. If I punch the throttle it might change to like a 34 or a 50 for a split second but then go right back to 1034. I was curious and I plugged my scanner into my buddies 2001 4.6L F-150 and the knock sensor reading for his was at "8" at idle and slowly rose in value as he increased rpms, for example, his was reading around 50 at around 2500rpms, when he let off and it was idling, his was back to 8.
I'm feeling pretty confident that the knock sensor may be the issue but I was wondering if anyone on these forums had any thoughts on my matter. It's just odd with how random it is and how it clears up by shutting off and restarting the engine.
Thanks in advance!
I have a 1999 F-150 2WD 4.2L V6 with an interesting issue. The previous owner claimed they replaced the TPS, MAF, Fuel Pump, Air & Fuel filters, and the IAC.
What happens is, only after she's at a good operating temperature and has been driving a bit, it'll randomly not accelerate. If I press on the gas, like 40% or so, the RPMs will drop and the engine will act like it wants to stall. If I'm real easy on the gas, like 5% throttle, it'll slowly accelerate. When it happens the symptoms will only last about a minute and then it accelerates fine again. I did throw it in neutral once during an episode and try to rev the engine and it wouldn't rev, same symptom. No Check Engine light appears when it happens. Outside of that she idles beautifully, even during an episode, and has plenty of power most of the time. I also noticed if I were to keep the throttle down during an episode the engine will stall. I can also throw the truck in neutral, shut the engine off and restart it, put it back in drive and boom, I can accelerate fine again for a little while. If I'm stopped and in park during an episode and I try to go wide open throttle I do notice intake blow back occasionally.
So far when I first started diagnosing it we checked plug wires for any damage and if any were arcing or anything, nothing, all is well. No CEL has ever come on, I was able to get a P0113 code once for the IAT sensor, I went ahead and replaced it for good measure since it was an inexpensive replacement but that didn't resolve the issue and it hasn't thrown the code again since.
I went as far as replacing the PCM and when I did, PATS locked down the truck and rather than towing it to a dealer to do the keys I figured it was in my best interest at this point to invest in a good scanner so I picked up an Autel MK808 which is incredible by the way. I was able to clear the PATS and reprogram my keys and all was well there, but it didn't solve the random hesitation/acceleration/stalling issue.
I spent hours watching live data, during an episode and while it was running fine, nothing seemed a miss except one thing, the knock sensor. I almost missed it since it didn't have an expected value range listed. The Knock sensor reading sits at 1034 at idle, when I slowly apply throttle, let off the throttle, regardless of rpm. It just sits at 1034. If I punch the throttle it might change to like a 34 or a 50 for a split second but then go right back to 1034. I was curious and I plugged my scanner into my buddies 2001 4.6L F-150 and the knock sensor reading for his was at "8" at idle and slowly rose in value as he increased rpms, for example, his was reading around 50 at around 2500rpms, when he let off and it was idling, his was back to 8.
I'm feeling pretty confident that the knock sensor may be the issue but I was wondering if anyone on these forums had any thoughts on my matter. It's just odd with how random it is and how it clears up by shutting off and restarting the engine.
Thanks in advance!
New User
Joined: Apr 2020
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That sounds like my issue, but i was getting a CEL, 1071, 1074 ....fuel is lean right bank, fuel is lean left bank,.....and originally IMRC stuck (forget that code, it only showed one time)
Cleared the code after replacing fuel filter, and continued with random hesitations, loss of power, shut off engine and immediately starts and runs fine, except hard to start sometimes.
Fuel pressure check showed good pressure while runnuing, immediately dropping when turned off. Came to the conclusion was either fuel regulator or pump, and when replacing regulator found the plastic keepers on both IMRC shafts were broke and/or missing, although the rods were presently still in place to open the butterflies I am sure one had popped out and found it's way back in when I recieved the code.
Just replaced keepers and fuel regulator, and hoping my pump will prove to be good or that will be my next job....
Cleared the code after replacing fuel filter, and continued with random hesitations, loss of power, shut off engine and immediately starts and runs fine, except hard to start sometimes.
Fuel pressure check showed good pressure while runnuing, immediately dropping when turned off. Came to the conclusion was either fuel regulator or pump, and when replacing regulator found the plastic keepers on both IMRC shafts were broke and/or missing, although the rods were presently still in place to open the butterflies I am sure one had popped out and found it's way back in when I recieved the code.
Just replaced keepers and fuel regulator, and hoping my pump will prove to be good or that will be my next job....
1st Gear
Joined: Apr 2023
Posts: 1
Likes: 0
Follow up
Hey everyone,
I have a 1999 F-150 2WD 4.2L V6 with an interesting issue. The previous owner claimed they replaced the TPS, MAF, Fuel Pump, Air & Fuel filters, and the IAC.
What happens is, only after she's at a good operating temperature and has been driving a bit, it'll randomly not accelerate. If I press on the gas, like 40% or so, the RPMs will drop and the engine will act like it wants to stall. If I'm real easy on the gas, like 5% throttle, it'll slowly accelerate. When it happens the symptoms will only last about a minute and then it accelerates fine again. I did throw it in neutral once during an episode and try to rev the engine and it wouldn't rev, same symptom. No Check Engine light appears when it happens. Outside of that she idles beautifully, even during an episode, and has plenty of power most of the time. I also noticed if I were to keep the throttle down during an episode the engine will stall. I can also throw the truck in neutral, shut the engine off and restart it, put it back in drive and boom, I can accelerate fine again for a little while. If I'm stopped and in park during an episode and I try to go wide open throttle I do notice intake blow back occasionally.
So far when I first started diagnosing it we checked plug wires for any damage and if any were arcing or anything, nothing, all is well. No CEL has ever come on, I was able to get a P0113 code once for the IAT sensor, I went ahead and replaced it for good measure since it was an inexpensive replacement but that didn't resolve the issue and it hasn't thrown the code again since.
I went as far as replacing the PCM and when I did, PATS locked down the truck and rather than towing it to a dealer to do the keys I figured it was in my best interest at this point to invest in a good scanner so I picked up an Autel MK808 which is incredible by the way. I was able to clear the PATS and reprogram my keys and all was well there, but it didn't solve the random hesitation/acceleration/stalling issue.
I spent hours watching live data, during an episode and while it was running fine, nothing seemed a miss except one thing, the knock sensor. I almost missed it since it didn't have an expected value range listed. The Knock sensor reading sits at 1034 at idle, when I slowly apply throttle, let off the throttle, regardless of rpm. It just sits at 1034. If I punch the throttle it might change to like a 34 or a 50 for a split second but then go right back to 1034. I was curious and I plugged my scanner into my buddies 2001 4.6L F-150 and the knock sensor reading for his was at "8" at idle and slowly rose in value as he increased rpms, for example, his was reading around 50 at around 2500rpms, when he let off and it was idling, his was back to 8.
I'm feeling pretty confident that the knock sensor may be the issue but I was wondering if anyone on these forums had any thoughts on my matter. It's just odd with how random it is and how it clears up by shutting off and restarting the engine.
Thanks in advance!
I have a 1999 F-150 2WD 4.2L V6 with an interesting issue. The previous owner claimed they replaced the TPS, MAF, Fuel Pump, Air & Fuel filters, and the IAC.
What happens is, only after she's at a good operating temperature and has been driving a bit, it'll randomly not accelerate. If I press on the gas, like 40% or so, the RPMs will drop and the engine will act like it wants to stall. If I'm real easy on the gas, like 5% throttle, it'll slowly accelerate. When it happens the symptoms will only last about a minute and then it accelerates fine again. I did throw it in neutral once during an episode and try to rev the engine and it wouldn't rev, same symptom. No Check Engine light appears when it happens. Outside of that she idles beautifully, even during an episode, and has plenty of power most of the time. I also noticed if I were to keep the throttle down during an episode the engine will stall. I can also throw the truck in neutral, shut the engine off and restart it, put it back in drive and boom, I can accelerate fine again for a little while. If I'm stopped and in park during an episode and I try to go wide open throttle I do notice intake blow back occasionally.
So far when I first started diagnosing it we checked plug wires for any damage and if any were arcing or anything, nothing, all is well. No CEL has ever come on, I was able to get a P0113 code once for the IAT sensor, I went ahead and replaced it for good measure since it was an inexpensive replacement but that didn't resolve the issue and it hasn't thrown the code again since.
I went as far as replacing the PCM and when I did, PATS locked down the truck and rather than towing it to a dealer to do the keys I figured it was in my best interest at this point to invest in a good scanner so I picked up an Autel MK808 which is incredible by the way. I was able to clear the PATS and reprogram my keys and all was well there, but it didn't solve the random hesitation/acceleration/stalling issue.
I spent hours watching live data, during an episode and while it was running fine, nothing seemed a miss except one thing, the knock sensor. I almost missed it since it didn't have an expected value range listed. The Knock sensor reading sits at 1034 at idle, when I slowly apply throttle, let off the throttle, regardless of rpm. It just sits at 1034. If I punch the throttle it might change to like a 34 or a 50 for a split second but then go right back to 1034. I was curious and I plugged my scanner into my buddies 2001 4.6L F-150 and the knock sensor reading for his was at "8" at idle and slowly rose in value as he increased rpms, for example, his was reading around 50 at around 2500rpms, when he let off and it was idling, his was back to 8.
I'm feeling pretty confident that the knock sensor may be the issue but I was wondering if anyone on these forums had any thoughts on my matter. It's just odd with how random it is and how it clears up by shutting off and restarting the engine.
Thanks in advance!
I have the same issue, what about you did you find the root cause of the issue?
Thank you
Meher
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