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Discussion Starter · #1 ·
Hi. I've been getting CE codes on my 1998 Isuzu Tooper (70K miles). The codes are P1171, P0137, P0157. All of these codes have to do with engine running LEAN during hard acelleration. I've been chasing this problem for a few months now and was wondering if anyone has any advise on what to do next (besides bring it to a dealer). The trunk seems to run fine and gas mileage is normal.

Here is what I have done (in order)

1) replace fuel filter (twice)

2) cleaned EGR valve and pipes. Cleaned MAF. Repalced air filter.

3) repalce fuel pressure reg as pressure was reading 38 psi at idle.

4) Replaced Intake Manifold Gaskets and injector seals.

5) Replaced fuel pump and screen. Fuel Pressure still reading around 38 psi at idle (book says should be 44 to 48 psi). I've checked for any obstructions but cannot find any. Maybe the new pressure regulator is also bad? When I disconect the Pressure Regulator vacuum hose the psi goes up to 50.

Result - CE light will still come on at high speeds when I step hard on the gas.

Thanks in advance for your input.
 

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I had the exact same problem on my car. Unfortunately, replacing the O2 sensors was the fix for me. These are the post-Cat sensors that we are talking about.

Could the cats be fouled up therefore leading to consistently high oxygen levels? I highly doubt this, but I'm not sure how much of an impact these things could have on the O2 sensor readings as you've seemed to eliminate most of the other culprits.

I would check the MAF a little more closely with a voltmeter.
 

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MTB- Looks like you covered the usual causes. How does the truck run? any performance or economy issues? It's unusual to get low volt/lean codes from the after catalytic converter O2 sensors & not the pre cat sensors. Have you had any exhaust work done? are you 100% sure the EGR plumbing is totally clean with no air leaks? It's almost as if you are getting too much EGR on hard acceleration, or are aspirating air into the intake somewhere beyond the throttle plate. G/luck
Joel
 

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Discussion Starter · #6 ·
Thanks everyone for the inputs. I will check on the ERG unit again. Getting lean codes from the rear O2 sensors and not the front O2 sensors is a good observation. I haven't had any exhaust work done but will check for leaks. The truck performance is within the normal range although I notice that it runs better when it is cold and seems to lose some power after it has been well warmed up. Gas mileage is normal.

Again thanks.
 

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I read this on a web site: (they are talking about he wire in the MAF that gets heated to test for ambient temperature.)

One remark must be made: I hear very often that these heated wire MAF's are killed by using K&N filters. Jon Holdsworth about this issue:

"A well lubed K&N filter will deposit K&N oil on the MAF sensor wire and cause more of the wire to burn off at each shutdown, eventually destroying the sensor. Common consensus is to ditch the K&N and use the good ole paper filter."

And one last remark by me: do not try to clean the hot wire. It will break. Don't ask me how I know that.
Dont know how valid it is. Just FYI...
 
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