P0171 and 174
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Tuned
Joined: Mar 2007
Posts: 487
Likes: 6
From: Timmonsville
P0171 and 174
My son has 1998 f150. XL model 4.2 auto 4x4. Runs fine. Has CEL. Bank 1 and 2 lean. Sprayed around engine bay with ether while idling and found nothing. Pulled intake hose off air cleaner and blocked with rubber glove. Lit cigar and used small pump to blow smoke in brake booster line. Nothing. Forscan show both banks long term fuel trim at "25", whatever that means. They drop into teens while cruising highway. Opinions on next move?
Fwiw..also have P0133 and P0141.
Fwiw..also have P0133 and P0141.
5th Wheeling
Joined: Feb 2019
Posts: 47
Likes: 10
It can take a long time to fill an intake with enough cigar smoke to expose a leak. If the fuels trims are higher/compensating more at idle than with the throttle open it suggests vacuum leak but if the numbers are high when cruising on the highway like you said, then I would suspect a lack of fuel.
Thread Starter
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Tuned
Joined: Mar 2007
Posts: 487
Likes: 6
From: Timmonsville
The fuel trims are highest at 25 idling. Drop into teens cruising. Ill redo the cigar. Maybe burn more than one. I bought cheap ones. I forgot it also had p01120. I replaced the tps, cleared codes. After 50 miles or so the CEL came back....only code is p0141. Fuel trims are still up there.
Fleet Mechanic
Joined: Jun 2023
Posts: 1,402
Likes: 384
From: WA
The way to do the test is to watch trims while you spray. They'll drop then go back up. The IACV will compensate idle speed very quickly so you won't hear a change in dile speed.
And vacuum leaks are usually worse on a cold engine. The best time to test is before the engine gets up to temperature.
Even though you only have one code now you probably have pending codes. Check that. Also, freeze frame data will show you engine conditions when the code set. Cold, hot, RPM, etc.
And vacuum leaks are usually worse on a cold engine. The best time to test is before the engine gets up to temperature.
Even though you only have one code now you probably have pending codes. Check that. Also, freeze frame data will show you engine conditions when the code set. Cold, hot, RPM, etc.
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