Lean gas codes 98 Ranger 4.0
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From: Tacoma, Wa
Lean gas codes 98 Ranger 4.0
I can’t figure out why I’m keep getting P171 and p174 codes saying bank 1 and 2 systems are getting lean gas. I’ve replaced 02 sensors, IAC valve, spark plugs, fuel filter, air filter and cleaned the MAF sensor. But I keep getting these codes. I hear the fuel pump working, I think it’s fine. Possibly the fuel pressure regulator? I know there’s a number of things it could be I’m just wondering if anyone has advice on what to check and how to test.
Yes +1 ^^^
Your fuel pressure regulator(FPR) is IN the gas tank on the fuel pump assembly
After engine is fully warmed up let it idle
Unplug the IAC Valves 2 wire connector, it will then close
Idle should drop down to 500rpms, barely running, or engine may even stall, either is GOOD, it means no vacuum leaks
If RPMs do not drop, you have a leak
1998 and up Rangers use 55psi fuel pressure, there is a test port on the engines fuel rail, looks like a tires air valve because it is, a schrader valve
You can rent a tester and then check pressure at idle and then raise RPMs to about 2,500 and hold it there and see if pressure is starting to drop
1997 and earlier Rangers used 30psi and FPR was on the engine, you have whats called a Returnless Fuel system, used starting in 1998 on Rangers
Also whats your MPG like?
Partially clogged exhaust will reduce power and MPG, and also set Lean codes on both banks
Run a can of Seafoam or similar injector cleaner in the gas tank once a year, it helps keep injector tips clean, dirty injectors can cause Lean codes
Your fuel pressure regulator(FPR) is IN the gas tank on the fuel pump assembly
After engine is fully warmed up let it idle
Unplug the IAC Valves 2 wire connector, it will then close
Idle should drop down to 500rpms, barely running, or engine may even stall, either is GOOD, it means no vacuum leaks
If RPMs do not drop, you have a leak
1998 and up Rangers use 55psi fuel pressure, there is a test port on the engines fuel rail, looks like a tires air valve because it is, a schrader valve
You can rent a tester and then check pressure at idle and then raise RPMs to about 2,500 and hold it there and see if pressure is starting to drop
1997 and earlier Rangers used 30psi and FPR was on the engine, you have whats called a Returnless Fuel system, used starting in 1998 on Rangers
Also whats your MPG like?
Partially clogged exhaust will reduce power and MPG, and also set Lean codes on both banks
Run a can of Seafoam or similar injector cleaner in the gas tank once a year, it helps keep injector tips clean, dirty injectors can cause Lean codes
Last edited by RonD; Feb 28, 2020 at 12:07 PM.
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Joined: Jan 2020
Posts: 107
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From: Lafayette, LA
I chased that demon on my '99 4.0. The only way I could find the vacuum leak is with a smoke test.
Turns out it was bad seals on the upper intake (plenum) to fuel rail.
Look up vacuum smoke test on you tube. There are many videos show how to do this yourself.
This is probably the only sure way to find a small leak. Don't waste time spraying carb cleaner all over
trying to find a leak. It didn't work for me, but I was able to find the gasket leak after about 5 minutes with the smoke.
Turns out it was bad seals on the upper intake (plenum) to fuel rail.
Look up vacuum smoke test on you tube. There are many videos show how to do this yourself.
This is probably the only sure way to find a small leak. Don't waste time spraying carb cleaner all over
trying to find a leak. It didn't work for me, but I was able to find the gasket leak after about 5 minutes with the smoke.
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Joined: Dec 2013
Posts: 127
Likes: 7
From: Maryland
Same thing happened to me. 171/174 and it was the upper intake gaskets.
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