rough idle, no power
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rough idle, no power
Hey all, I'm new to the sight.
I bought a 99 f150 lariat 4x4 with the 5.4 from a guy who said that it needed an oil pump. He said it lost pressure coming into work, he turned it off and coasted in. I towed it home and replaced the battery and bought a new oil pressure sending unit just to be sure it wasn't that.
Those things are so hard to get to. Finally I got an oxygen sensor tool on it and it was only hand tight. Rather than take it off I just tightened it up and started the truck. The dash guage read normal but the truck was idling so badly. Steady at about 1000 rpm and tooth rattling. 1500 with the foot on the pedal it evens out but still rough. Not sure if this was a good idea but I took it around the block. No power under 2500 rpm. Barely moving even. Just felt like there was no throttle response at all and again very rough.
Got it home and parked it. Now I'm wondering what to do to fix the Idle and power problem. Any suggestions on where to start would be great. And input on the oil pressure sending unit too. I suppose I'll have to get under there and replace it at some point anyways. Thanks in advance.
I bought a 99 f150 lariat 4x4 with the 5.4 from a guy who said that it needed an oil pump. He said it lost pressure coming into work, he turned it off and coasted in. I towed it home and replaced the battery and bought a new oil pressure sending unit just to be sure it wasn't that.
Those things are so hard to get to. Finally I got an oxygen sensor tool on it and it was only hand tight. Rather than take it off I just tightened it up and started the truck. The dash guage read normal but the truck was idling so badly. Steady at about 1000 rpm and tooth rattling. 1500 with the foot on the pedal it evens out but still rough. Not sure if this was a good idea but I took it around the block. No power under 2500 rpm. Barely moving even. Just felt like there was no throttle response at all and again very rough.
Got it home and parked it. Now I'm wondering what to do to fix the Idle and power problem. Any suggestions on where to start would be great. And input on the oil pressure sending unit too. I suppose I'll have to get under there and replace it at some point anyways. Thanks in advance.
Hotshot
Joined: Jul 2005
Posts: 11,931
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I would check the oil level... maybe change the oil and filter and look at the old oil.
NEXT... you need a CODE.. you should have some light on the dash. A code reader will tell you where to look.. Could be vacuum leak, could be bad COP, could be several things.. YOU NEED A CODE.
NEXT... you need a CODE.. you should have some light on the dash. A code reader will tell you where to look.. Could be vacuum leak, could be bad COP, could be several things.. YOU NEED A CODE.
Fleet Mechanic
Joined: Aug 2008
Posts: 1,446
Likes: 9
From: NE Iowa JD Country
best thing is to confirm proper oil pressure....with a mechanical gauge. The one on the dash is just not accurate...requires only like 7 or 8 psi to activate. if the oil pressure is not there...then you're gonna have to dig deeper and until that is remedied...the rough idle is secondary
scan for tripped codes. if there is a misfire this also could account for the rough idle
(considering that it is relatively new to you) for the rough idle you could remove the throttle body housing and clean it... while it is off clean the IAC too, which is what controls the idle.
scan for tripped codes. if there is a misfire this also could account for the rough idle
(considering that it is relatively new to you) for the rough idle you could remove the throttle body housing and clean it... while it is off clean the IAC too, which is what controls the idle.
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OK, thanks for the input. I'm borrowing a code reader today to check codes. About driving it without verifying the oil pressure. I did not hook a mechanical pressure gauge up. I just tightened the oil pressure sending unit. The dash gauge/idiot gauge read normal oil pressure then. I know it's not an accurate pressure gauge. I know it only reads normal oil pressure at 7 or 8 psi. The symptoms of the problem the previous owner were that it lost oil pressure while driving into work. I took that to mean that the dash gauge fell to the bottom and he assumed it needed an oil pump. The pressure sending unit was obviously not changed so rather than changing the oil pump I decided to check the sending unit first. Once I tightened it and the gauge came back I did drive it around the block. Long answer for a simple and unneeded question. I'll verify the pressure when I change out the sending unit.
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update
There are no codes at all now but it seems like it is missing, real bad even. Like maybe only 4 cylinders. Idles for about 20 seconds and dies. Any pointers on where to start next?
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Lead Driver
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Bstaff, you interpreted the two codes wrong!
The 138 is Ox sensor bank 1 #2 open circuit.
The 158 is Ox sensor bank 2 #2 open circuit.
Neither code tells you to replace any parts.
Replacing the sensors does not repair an open or trouble with the harness.
These 2 sensor locations and specific fault will not affect idle or running.
They exist for a different specific purpose.
Inspect the wiring for grounds, opens or crosses and the plugs that attach to those rear sensors.
Inspect for the front sensors as well. They will affect how the engine runs.
I suspect there are other issues but you should look at the IAC for being dirty, an intake air leak etc.
This fault normally will set two codes 171/174.
If not, then you need to look at the live data with a Scanner to see signs of an issue with the fuel or air.
I would also check the fuel pressure with a gage off the injector rail near the regulator.
Understand what your doing and why before you do it. It saves money , parts and hassle.
Good luck.
The 138 is Ox sensor bank 1 #2 open circuit.
The 158 is Ox sensor bank 2 #2 open circuit.
Neither code tells you to replace any parts.
Replacing the sensors does not repair an open or trouble with the harness.
These 2 sensor locations and specific fault will not affect idle or running.
They exist for a different specific purpose.
Inspect the wiring for grounds, opens or crosses and the plugs that attach to those rear sensors.
Inspect for the front sensors as well. They will affect how the engine runs.
I suspect there are other issues but you should look at the IAC for being dirty, an intake air leak etc.
This fault normally will set two codes 171/174.
If not, then you need to look at the live data with a Scanner to see signs of an issue with the fuel or air.
I would also check the fuel pressure with a gage off the injector rail near the regulator.
Understand what your doing and why before you do it. It saves money , parts and hassle.
Good luck.
Postmaster
Joined: Jul 2003
Posts: 2,544
Likes: 2
From: okc
What he said. Too many people start throwing parts at vehicles because it has a code for that part. The codes are to alert a tech where to start his flowchart diagnostics. I think you need to do a fuel pressure test and compression test first. If those check out, then research the proper testing procedure for any code that shows up. If it has an intake leak, the most you will get are cylinder misfire codes or O2 out of range codes. Test, test, test, diagnose, THEN repair!!!!
New User
Joined: Oct 2015
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I am by no means a mechanic so I would go with the other suggestions first but I had the same problem with my 2001 f150 4.6l and it turned out to be the Camshaft sensor and/or the crankshaft senor I'm not sure which solved the problem because I changed them out together. I was also getting an intermittent no crank also. Don't know if I'm any help or not just throwing in my 2 cents.
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