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Intermittent Vac Leak


vivalavolvo

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Okay, so something is screwy with the load circuit (maf, tps, temp sender, trans ecu, etc.), when you change the load value the car dies, most likely starving for fuel. Hmmm, these can be challenging problems..... Still seems like decent odds it's the MAF.

I'd start with a different MAF, do yourself a favor and don't buy an aftermarket one, you'll be chasing problems for the rest of your ownership of the car. I'd suggest finding a used Bosch one, these are fairly hardy and can go for a long time without issue. My local pick-n-pull charges $10 for a MAF, I snag all the fresh looking OEM ones, I leave the aftermarket ones and old looking original ones! Call around to your local yards, I think even on the high side you are looking at $30 or so. There have got to be piles of them on ebay for cheap cheap.

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Alright, i got Volvo FCR kinda working and i managed to pull these codes, these did not trigger the CEL:

422 Atmosphearic pressure snesor signal

621 fuel tank pressure signal

251 Outside temp signal

522 Rear heated O2 sensor pre heating (i know about this one already)

From what i read in this codes are normal for a 4.3 to 4.4 conversion?

EDIT: I'm going to put the factory ECU back in after the engine is back to ambient temp and see what that does.

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Not sure when you received the 4.4 but the early ones had a coding problem. The car never enters closed loop and the purge valve doesn't activate. It didn't cause the exact problems you are experiencing (in my case), but perhaps it is playing a role in your problems.

I don't think this is a problem on all years but it was an issue on my '95. Of course it was fixed at no cost and no major inconvenience. Lucky is a fine gent to be in business with.....

Hope your problem gets sorted out...

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Alright. It has to be the 4.4 ECU. I went back to stock it runs like a dream. I guess ill be getting in contact with Lucky.

I think 4.3 and 4.4 just handle sensor readings differently .. I don't know the ins and outs of it by any means but I do know with a shot front o2 sensor in my 97 the car would run fine with a 4.3 (850 t5) ecu and then be all intermittently surgy with the stock 4.4 ecu back in .. eventually it started acting up a bit with the 4.3 ecu after a few weeks of driving and would want to stall once in awhile .. I had originally thought it was a vac leak also ... and I was pulling an IAC code with the 4.4 ecu in .. this was with crusty old original o2 sensors .. :blush:

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