# Lean mixture correction needed.



## Glegor (Mar 31, 2008)

ok, so i have an 85 GTI, normal setup, nothing changed. it has a hole cut in the air box for a little colder intake charge. my problem rests in my fuel injection system tho i believe. it starts fairly well, idles pretty good, doesnt fluctuate too much. but, when you get on it, it pulls good till about 4000 rpms, then you can just feel it falling flat on its face. starts popping out the intake and misfiring, but sometimes its not quite as bad. sometimes it will pull clear to the red line with no problems, but other days it struggles to pull to 4000 before it starts popping. to me, it seems like a lean mixture condition, but CIS is not my specialty, i work on diesels, they only need air and fuel to run. way easier to keep them running good. anyway, i know lots about vw's, and cars in general, but i have never really messed with a CIS system with good results. any of you guys have any suggestions? oh yea, i replaced the air and fuel filters, neither fixed my problem, might have actually made it a little worse. but i know this car should have more power than it does, it will hardly burn out in first gear. my 1.5 diesel would own this thing for sure.


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## ps2375 (Aug 13, 2003)

*Re: Lean mixture correction needed. (Glegor)*

You need to find out what the actual AFR's are. I would suggest a wideband O2 sensor and maybe fuel system pressures to ensure it is working correctly. This car does have an O2 sensor on it, have you disconnected it to see if it runs any better?


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## ziddey (Apr 16, 2006)

*Re: Lean mixture correction needed. (ps2375)*

check for vacuum leaks. if you have access to a vacuum gauge, even better.
build a dpr test harness to see how the system is working. chances are, the idle mixture has been tampered, so at this point, might as well fix things up and set it again.
check that your idle switch is working properly.
the only sensors the car uses for fueling is the engine coolant temp sensor and the oxygen sensor.
check your grounds.


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## Glegor (Mar 31, 2008)

*Re: Lean mixture correction needed. (ziddey)*

grounds are good, i have a big stereo so i beefed up the power and ground wires from the battery. its grounded to the chassis and engine. it does have an O2 sensor. i do have access to a vacuum gauge. i do not have access to a DPR test harness, or even what they do. like i said, when it comes to gasser VWs, im completely retarded. ive owned 2 in my life, hated both. also, how do i test fuel pressure? figure out how to get a reading somewhere before the fuel dizzy?


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## wclark (Mar 28, 2001)

*Re: Lean mixture correction needed. (Glegor)*

Try unplugging the O2 sensor (single green wire) and see if the same thing happens or if it is different. Without the sensor in the loop the ECU controlling the mixture will fall back to the basic settings and depending on where you have the "CO adjustment" set it might not have a lot of power but by removing the O2 sensor temporarily from the control loop you can eliminate the effect of things like torque induced exhaust leaks before the sensor.
If for some reason the car runs and idles (more) poorly with the O2 sensor unplugged, you can put a DVM on the sensor output (still unplugged) and measuring between there and ground (the cam cover bolts are a good place) set the "CO adjustment" (the 3mm screw down in the little hole between the fuel distributor and the air flow sensor plate to .5-.7V from the sensor at warmed up idle. This gets you pretty close to the correct DPR current when the O2 sensor is reconnected.


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## Glegor (Mar 31, 2008)

*Re: Lean mixture correction needed. (wclark)*

is there any way that my catalytic converter could be causing problems? im pretty sure it doesnt function anymore tho. i was kinda gettin on it a while back, and i watched chunks fly out my tail pipe. and it gets continually louder the more i drive it. its been acting good now too, actually will pull clear to the red line without falling on its face at 4k. i still get a little pop in the higher rpms, but nothing like it was before. once in a while, i get a rattle coming from under the car, about where the cat would be. but its not steady. it rattles for a while, then it stops. when it rattles, it pops and doesnt pull hard. when it isnt rattling, it pulls good and runs as it should. all my exhaust gaskets are good, and there are no leaks. maybe it was my cat acting up the whole time? or something is just messed up and needs to be fixed.


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## wclark (Mar 28, 2001)

*Re: Lean mixture correction needed. (Glegor)*

If something is blocking your exhaust then it wont rev under load and may do things like you describe, especially if the blockage is on and off.
If a cat matrix has broken loose then it could do this. So could broken internal baffles in a muffler, though the smaller cat housing is more likely to keep the loose stuff in the way of exhaust gasses.


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## lilgreydentwagen (Sep 13, 2005)

*Re: Lean mixture correction needed. (wclark)*

don't mean to thread jack but does someone have a diagram how to make that test harness for the dpr? i thought i did it right but i cant geta reading in the ma range only voltage. it reads between 7.4 and 8.2 volts if that means anything


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## ziddey (Apr 16, 2006)

*Re: Lean mixture correction needed. (lilgreydentwagen)*

if it's not working right, you spliced into the wrong wire.
the ammeter goes inline. voltmeters go parallel.


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## Glegor (Mar 31, 2008)

*Re: Lean mixture correction needed. (wclark)*

the baffles in the muffler and resonator are fine. the muffler is a welded flowmaster 40 series. and the resonator is gone. even my dad commented on it getting louder a few days after i put the new muffler on. the day he commented on it being louder, i watched it shoot grey chunks (what looked like cat matrix to me) out my tail pipe. off and on it will rev out nicely, while other times it struggles to get to 4 grand. 
god i wish this car was a Turbo Diesel, i would not be going through this right now.


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## Glegor (Mar 31, 2008)

*Re: Lean mixture correction needed. (Glegor)*

so, it was spark plugs. high speed glazing. forgot VWs are picky with plugs.


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