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Help please!
Hey guys ,hoping to get some help on a problem im having with my 99 tahoe. I bought it cheap for the winter but It has a P0300 and P0171 code. Which ive been messing with for a couple of days now. I cleaned out the MAF,replaced the IAT because it was cheap enough,cleaned out the Map sensor, and have already done a tuneup on it. Truck starts right up, i mean Right up with no hesitstion and runs perfect until it warms up. Once it hits closed loop,the idle drops real low,misfires like crazy,and the fuel trims go thru the roof sometimes 50% or more if you count the STFT. However, sometimes it kicks itself out of closed loop and back into open and runs fine again. I checked for vac leaks just for fun and didnt find any. I should mentionx after i cleaned the MAF ..it Seeemed to run fine for about 45 min . I shut it off. Turned it back on the next morning and it started doing it again. Also should mention the CAT is disconnected at the Apipe because the previous owner thought the cat was clogged and tried cleaning it out. But this problem was present then as well or so he said. Any ideas?
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see if this helps with troubleshooting.
http://troubleshootmyvehicle.com/gm/4.3L-5.0L-5.7L/how-to-test-a-lean-condition-1
http://www.ericthecarguy.com/faq/solving-automotive-performance-issues
Do you think this looks right? None of my O2s are much over .5v in closed loop. [IMG]http://images.tapatalk-cdn.com/15/11/03/7a9443f33a07375fc1891725830f5caa.jpg[/IMG]
[IMG]http://images.tapatalk-cdn.com/15/11/03/dffbdd0a09c725f4e00328ccad1b7627.jpg[/IMG]
I dont remember if this was before or after it kicked itself out of closed loop back into open loop. Or if it was at startup. What would cause it to be intermittent?
Both precat sensors stayed around .6v. Bank 2 sensor 2 actually came up to 1v but then shot back down. I took a video i wish i could post here but it seems too large
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It would appear it’s running lean from the LTFT PID. Have you sprayed around the intake to see if you get an RPM increase?. It’s possible you have a intake gasket leak. This would cause an enrichening of the mixture due to unmetered air.
I checked. 3 times for vac leaks. Listening and with carb spray at all points. Unless i missed some spot which is doubtful. I also dont think its a vac leak, i feel as if it would be present when its cold like right at startup. And it wouldnt be switching back and forth betweem open and closed loops. I feel as if a vac leak is or it isnt. Correct me if im wrong but ….
Again. From start up ,course of events is;
START UP
Open loop(cold engine) quiet motor,some bearing noise from the tensioner,no real vibration or miss.
Warms up,hits closed loop for about 3 minutes,runs like crap. Missing,bogging,black smoke. Then itll kick itself back into open loop.Fyi when i first bought it i had an hour drive home on the highway and the thing ran mint at highway speeds. Problem is really noticeable at idle only. Higher revs or speeds ,all i hear is exhaust leaks 🙂
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