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Discussion Starter #1
I’m stuck. We have a permanent P0402 (excessive EGR flow) code. Clear it and it comes back basically immediately. Troubleshot each part of the EGR. Unplugged the hose between the solenoid and valve. We got decent vacuum readings and got the insufficient EGR code. EGR valve is clean and working. Solenoid is working. Vacuum is good. Valve position sensor is good. All the inputs seem good!! I even tried a new MAF today in desperation. New O2 sensors (no CATS or post CAT sensors). No vacuum leaks (that I can find).

The reason I’m down this rabbit hole is because I have a lean condition on both banks. The result is that the short and long term fuel trims are WAY rich all the time and I can’t figure out how to fix it. The 0402 is just another thing that might be playing into the main issue of the lean condition. I’m really stuck. Any ideas?


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A crack in the air hose from AFM to intake can cause a persistent or recurrent lean code that can be hard to figure out, especially if the crack is on bottom of the hose


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The 302 is from a 98 mountaineer and it’s the original ECM. AFM is a GM thing not on Fords. I’m going to seal up the intake, find a cigarette and see if I can be a human smoke machine.


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We sealed the intake with cling wrap and started blowing smoke into the brake booster vacuum hose. Found a couple of issue. My IAC was stuck open and there was a leak in the PCV valve / grommet. So we fixed both of those things and the EGR code disappeared! So the open IAC was causing the EGR excessive. I guess the computer didn't know where that air was coming from so it blamed the EGR for lack of better information.

But we STILL had the blasted LEAN codes on both banks. No other vacuum leaks. I was about to pull the intakes and start again when I remembered that the original MAF housing had a little screen in front of the sensor - 'to smooth the airflow'. For lack of anything else to try I found a piece of mosquito netting and stretched it over the join in front of the sensor. Eu-bloody-REKA!! Codes gone and trims immediately very close to zero. Unbelievable.
 

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But we STILL had the blasted LEAN codes on both banks. No other vacuum leaks. I was about to pull the intakes and start again when I remembered that the original MAF housing had a little screen in front of the sensor - 'to smooth the airflow'. For lack of anything else to try I found a piece of mosquito netting and stretched it over the join in front of the sensor. Eu-bloody-REKA!! Codes gone and trims immediately very close to zero. Unbelievable.
Good golly! Talk about an obscure issue. I'm a detail freak with OCD but that might be even beyond what I might have come up with., Good Job!

Good Luck, L.M.
 
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