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jbell1981

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Ok, I have a '00 S-10 with a 4.3l v-tec.

Here is the problem: When I first start driving (after the engine has been off), between 10-20 mph the engine bogs down and will not go any faster. If I let off the gas pedal for a few seconds and then push it agian it seem to be fine and will not do it again until I shut the engine off and re-start it. It does not seem to matter whether the engine is hot or cold and it only does it when I first drive it after start up. The check engine light comes on from time to time but it does not go on immeadietly after this occurs and then it goes back out after a couple days.

I checked it with my trouble code reader and it came up with code P0174 (sytem to lean - bank 2) as the primary and P0171 (system to lean - bank 1) as the secondary.

So can anyone tell me what banks 1 & 2 are?

Before I used the code reader, my first inclination is that it has a bad o2 sensor. System to lean to me would mean that its not getting enough gas or its getting to much o2, right? So it could be the o2 sensor, but couldn't it also be a clogged fuel filter, air line leak, clogged air filter or something else along those lines? Or because it only does it on start-up would that mean that it would have to be the o2 sensor or something computer related and it adjusts it self after the first occurance?

I would appreaciate any input anyone can give me.

Ok, sorry for the long post but I wanted to give as much info as possible.

Thanks,

Josh

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I'd say bank 1 and bank 2 refer to the cylinder groups/banks on each side of the engine.

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Yeap, I was able to at least figure that much out. There are 2 seperate o2 sensors one for each side. I would doubt that both are bad so thats leading me to thinking the mass air flow sensor. I have had people tell me that it could be an intake gasket leak or vacuum line leak, but wouldn't I have problems everytime I accelerate then? Since it only has problems at start-up and then seems to correct itself I think it is something sensor/comp related.

Any comments/suggestions?

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Generally on GM vehicles bank 2 is the passenger side. On a vortec that would be cylinders 2, 4, and 6. When you initially start your truck the computer is in "open loop" on the computer. At this point the computer is running the vehicle on predetermined values, not through direct input from sensors. Once the engine warms up, the computer goes into closed loop, where input from sensors is processed and used to control fuel and ignion. This may also explain why its better after a few minutes of running. If you had a bad o2 sensor normally that code would show up rather than the lean code.

If you haven't replaced the fuel filter in a while I always like to first eliminate the things that should be done anyway, to avoid putting unnecessary parts on as a guess. My first though would be a possible vacuum leak or maybe a fuel pressure regulator in its early stage of failing. But these are just guesses at this point without more info.

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Let me know if I am understanding you correctly. You are basically saying that when I have the problems at start-up, it is because of some mechanical problem and then after a little bit the sensors take over and correct the problem?

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Correct it? Doubtful. Mask it? Maybe.

Fuel pressure regulator was one of the first things that came to mind for me too.

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Like Whoaru said, correct it? No! The computer is able (to a degree) to compensate for some conditions thereby masking the actual problem.

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Try unplugging the MAF sensor. It is located near the air box inline with the rubber air snorkel. It may or may not run funky. If it runs o.k. with it unplugged than I would be suspicious of that component. I have replaced several with simular symptoms already this summer.

The other thought is there is a vaccum leak large enough to cause both banks to go lean. Once the engine warms up the leak subsides or gets small enough not to affect engine management.

The next thought is the coolant temp sensor. It could be out of range but not enough to flag it as defective.

Just a couple of things for you to consider.

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Wow, it sounds like some mechanics post here who really know what they're talking about. I am having some trouble following them, so my advice is to bite the bullet and take it in before buying two new o2 sensors and a MAF sensor and who knows what else. Maybe the mechanic can't figure out anything new for you but its worth a try to get a professional's opinion.

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Airjer, I unplugged the M.A.F. sensor and that seemed to do the trick. It seems to run perfectly now, even seemed to cure a few things that I didn't think were related. My only question, is there any future problems that could arise from driving with it unplugged? I don't want to spend the $200 to replace it if I can just drive with out it.

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Two Words, FUEL ECONOMY!!

Hit a salvage yard. You could probably pick up four or five for $200. Find a low mileage one and you should be all set.

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Might it be a bit harder on the catalytic converter too (running without MAF)?

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