Engine issue
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Mountain Pass
Joined: Sep 2004
Posts: 249
Likes: 2
From: AZ
Engine issue
Need help; I have a 93' F150 XLT extended cab, 2wd, 162,000 miles, very strong running 5.8 engine, E40D auto. It runs smooth most of time but between 1200 and 1500 rpm it lopes or bucks going down the road in no matter what gear, mostly annoying when in overdrive. It had 2 codes of O2 sensor and EGR valve so I replaced them both and throttle positioning sensor, plugs, wires, cap and rotor and it all did help a lot except for this issue; it did have a flat spot in the throttle but it was gone after I changed the TPS. I have no vacuum leaks after extensive searching. It did not do this with the old plugs in it and that is what I changed out first so I am wondering if I should try another set of plugs; I used the stock autolite ones (Copper not Platinum). Changed all of the other things after the plugs and didn't make any improvement except did run smoother and better gas mileage now, drivelinge is very tight and I changed the tranny fluid and filter, fuel filter, air filter. Very puzzling. Check engine light does come on after it is completely at operating temp and then it will go out while driving them come back on. We did clear them out after changing everything. Thanks for any help.
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Mountain Pass
Joined: Sep 2004
Posts: 249
Likes: 2
From: AZ
Yes it has the sensor on top; I will try that on my way home from work. I still have to put it on my friends Snap On code reader this weekend hopefully. The check engine only comes on when the engine is warmed up all the way. Thanks
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Mountain Pass
Joined: Sep 2004
Posts: 249
Likes: 2
From: AZ
Hey Thanks David7.3; I unplugged the positioning sensor from top of EGR and drove it home and it ran smooth with no hesitation or bucking at all. I don't know why it is this way and I guess I don't even care because it runs like it is suppose to. The check engine light is on but I will just drive it as long as it runs fine and gets decent gas mileage.
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Mountain Pass
Joined: Sep 2004
Posts: 249
Likes: 2
From: AZ
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Fleet Owner
Joined: Oct 2005
Posts: 20,783
Likes: 1,750
From: Kentucky
That sensor on top of the EGR valve (EGR Valve Position aka EVP) provides the feedback signal to the computer (PCM). You need to run the KOEO tests and CM code display with the EVP plugged back in. Since you already have a CEL on you know you triggered a code by removing the connector. You need to see if anything else pops up.
Since the truck appeared to run better with the EVP disconnected I suspect the sensor itself may be bad. On the other hand the computer may be running in "limp mode" so now it is running with default values instead of closed loop.
Check the codes and I also suggest checking the EVP output with a meter.
Since the truck appeared to run better with the EVP disconnected I suspect the sensor itself may be bad. On the other hand the computer may be running in "limp mode" so now it is running with default values instead of closed loop.
Check the codes and I also suggest checking the EVP output with a meter.
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Fleet Owner
Joined: Oct 2005
Posts: 20,783
Likes: 1,750
From: Kentucky
Just because it is new does not make it good. Forget the scanner, put a meter on it.
Fleet Mechanic
Joined: Feb 2007
Posts: 1,652
Likes: 79
From: Mooresville, NC
Sounds like the mix in this power regime (RPMs) is getting misguided either inside the EEC (bad electronic component -- a failing capacitor for example), or via faulty / erratic EGR inputs or a misbehaving O2.............the "temp" sensitive (and erratic) CEL is very telling.....
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