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Old 09-04-2007, 09:37 AM   #1
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lean burn

could it work? An EFIE is supposed to lean out the fuel by manipulating the O2 sensor correct? Just recently I had my truck checked and the mechanic found that I was running 25% lean on both banks of my V8, later to find out I had a vacuum leak. Could an induced vacuum leak via a valve on the PCV hose (my former vacuum leak) be used to do the same thing as an EFIE?
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Old 09-04-2007, 09:49 AM   #2
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Did it actually lean out, or did the mechanic just discover that each bank's fuel trim value was shifted 25% lean to maintain stoich while compensating for the vacuum leak?

I thought the only way you can actually lean the mixture in an unmodified OBD2 system is if fuel trim maxes out while trying to compensate for some other problem (ie. if the vacuum leak is more than the computer can handle).
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Old 09-04-2007, 03:56 PM   #3
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Quote:
Originally Posted by MetroMPG View Post
Did it actually lean out, or did the mechanic just discover that each bank's fuel trim value was shifted 25% lean to maintain stoich while compensating for the vacuum leak?

I thought the only way you can actually lean the mixture in an unmodified OBD2 system is if fuel trim maxes out while trying to compensate for some other problem (ie. if the vacuum leak is more than the computer can handle).
From what I've seen from messing with my car and others,

OBD2 cars have a long term fuel trim and a short term fuel trim, so there's two trims that need to max out before the ecu reaches the end of the trim range. When that happens it'll flag an error code, stop using the trims and switch to internal preset fuel tables so the car can still run. These tables are usually set on the safe side, which means they're rich.

If there's no error code, then you're just looking at trim compensation.
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Old 09-05-2007, 08:20 AM   #4
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no more lean

he did mention long term and short term, that is was running lean and the computer was dumping fuel to compensate. According to Autozone it was showing codes for MAF sensor and O2 sensors. The leak was at my condendator. Itook it off and reset the computer so far no idiot light. I have built a new condendater using lighter weight materials ( hard plastic bottle instead of glass and silica gel from cat litter instead of BBs) I will reinstall the condensater when I refill the tank.

So the imposed vacuum leak will not work and I would need to go with an EFIE?
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Old 09-05-2007, 10:12 AM   #5
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So the imposed vacuum leak will not work and I would need to go with an EFIE?
Vacuum leaks usually don't work, the ecu is programed to handle them. The ecu is built that way so the car will still run well as the miles pile up, sensors wear out, and rubber intake hoses crack and leak.
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