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car runs hesitates and misses at wot.

This is a discussion on car runs hesitates and misses at wot. within the General Help forums, part of the LSx Technical Help Section category; OKAY IM GONNA TAKE OFF MY GAS CAP. THROW MY CAR AWAY. PULL ANOTHER ONE IN. PUT MY GAS CAP ...

  1. #21
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    1999 TRANS AM WS6 M6

    OKAY IM GONNA TAKE OFF MY GAS CAP. THROW MY CAR AWAY. PULL ANOTHER ONE IN. PUT MY GAS CAP BACK ON. AND HAVE A DRINK. LOL

    IM PROB GONNA TAKE THE CAR INTO THE DREADED DEALER. SEE WHAT THEY SAY.. THE CAR IS DEFINETLY RUNNING WAYYYY RICH. NO QUESTION.. PIPES TIPS ARE WAY BLACK AND SOOTY.. ALSO MY P0172 P0175 CODES CAME BACK AFTER ABOUT 100 MILES OF DRIVING AROUND TOWN. NO FREEWAY MILES. MY MPG AROUND TOWN SUCKS. THE CAR IS SIMPLY DUMPING IN TOOO MUCH FUEL WHEN I GIVE MORE THAN 40% THROTTLE. THAT IS THE THE CAUSE OF MY PROB.. DOES SEAFOAM WORK??

  2. #22
    Smiles for 9.5 Years cammed goat's Avatar
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    OK. Have you rechecked to see if the throttlebody is tight as well as the bellows? You could have a vacuum leak in that area. I haven't heard any negative stories about Delphi MAFs. I think Delphi remanufactures old MAFs and sells them. When you swapped out the MAF pigtail, did you use connectors or solder them to the existing wiring? I have used Seafoam and it worked for me. Try the Seafoam and let us know if anything has changed. The dealership is your LAST resort.

  3. #23
    ʢ ൧ ൨ ൩ ൪ ൫ ൬ ൭ ൮Ր Ց Ւ Փ Smittro's Avatar
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  4. #24
    Junior Member aggie897's Avatar
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    Pewter Metallic
    2000 Trans Am m6

    Any luck?

  5. #25
    Moderator 35th-ANV-SS's Avatar
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    Still think MAF, vacuum leak, or injector related.

  6. #26
    Junior Member jodibarber's Avatar
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    agree with Throttle Position sensor

  7. #27
    Smiles for 9.5 Years cammed goat's Avatar
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    Quote Originally Posted by aggie897 View Post
    Any luck?
    ^^what he said.


    extreme dimensions, driveshaft shop, harrop, hid(35watt/6k) lows, hurst, k&n, led fogs, maverick man, mishimoto, nitto, revshift, slp, stern st-1, smoked sidemarkers, whiteline poly radius rod bushings

  8. #28
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    1999 TRANS AM WS6 M6

    Its not the TPS. I changed it out. It didn't do anything different so i brought it back.. Also I notice if I WOT it in first gear then second then third. no hesitation whatsoever. it actually can burn out now. as long as i start in first. Its hesitates when i start pressing it from a roll to WOT in all gears except first.. weird.. also Im running really rich. when i give it gas and it hesitates then let go of the gas it kinda accelerates on its own for a brief second. Im gonna try to check the evap canister tomarrow and also a fuel return line. I heard if those are blocked. It could cause a rich condition.

  9. #29
    GM World Class Tech. vette&ws6's Avatar
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    x2 on the fuel return line, could be pinched or restricted somewhere. Has the fuel tank ever been out of the veh? This is where we normally see pinched fuel lines. Also x2 on checking the coolant temp sensor, disconnect it and check for corrosion or loose terminals. Make sure there are no exhaust leaks before the oxygen sensors. Also, make sure the oxygen sensors are plugged into the right connectors, have seen some customers that have done engine work and somehow mixed up the bank 1 and bank 2 electrical connectors...it will run filthy rich.

  10. #30
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    1999 TRANS AM WS6 M6

    what do i look for on a scanner. fuel trims, mass air readings, etc etc. I have a hyperpac that can display and record what the car does. I know what some of the sensors should be at. but like the injector pulse and a couple others. I have no idea what to look for.

    I check the fuel lines and return. everything seems ok with those.. still runs rich/ P0172 P0175. too much fuel being added when i part throttle it. so it cuts out, hesitates. I can smell the unburnt fuel after a few second giving it gas at part throttle. Im very close on taking it in and have gm check it out. I tried just about everything...

    why does the car not do this at all when I unplug the maf and drive it. no stumble, no part throttle hesitations. It runs fine.. but i do know that running it with the maf disconnected still makes it rich.. But my Part throttle and WOT problem goes away???

  11. #31
    Smiles for 9.5 Years cammed goat's Avatar
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    Possible defective MAF?

  12. #32
    GM World Class Tech. vette&ws6's Avatar
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    Has the engine or trans ever been out of the car? If it has, make sure the oxygen sensors are plugged into the proper bank (as I stated in an earlier reply).
    Doesn't sound possible you say....I have seen it quite a few times. They always run really rich, and the computer doesn't have a clue how to control the fueling. If you have a scanner, unplug one of the pre-cat O2 sensors and see if it corresponds to the proper bank on the scanner. Also pull your plugs and see if one bank is running rich and the other is normal, this can be a good diagnostic tool.

  13. #33
    GM World Class Tech. vette&ws6's Avatar
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    To answer your question on why the car runs better with the MAF unplugged. It puts the pcm in "Speed Density mode." Basically the pcm uses predetermined tables based on coolant temp, throttle position, and MAP. A stock pcm definetely does not like to function off of "Speed Density" because it really doesn't have a good handle on real time fueling. The MAF determines how much airflow you are using to determine fueling events. The MAP only lets the pcm know how much load is on the engine. Probably not a MAF problem, this is just masking a deeper issue. Might be best off taking it to a dealer, If you get an experienced GM tech to look at it he should be able figure it out pretty quickly. He is going to know how to interpret the data and know where to look for the problem. Hard to diagnose an issue like this over the internet....

  14. #34
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    I really appreciate all the input. I will get under the car again and unplug a pre oxygen sensor see what happens on my scanner. I am not sure if the motor ever been moved. The guy i bought it from said he had a cam put in and ls6 this and ls6 that. But once I saw and heard the vehicle.. It was bone stock. heads intake throttle body all stock. guy was trying to make it sound better than it really was. But i showed him clearly that he was wrong. all the numbers on the heads and intake were stock. so he came way down in price. Plus I wanted a more stock vehicle so everything he said was just garbage. He even said he had the computer tuned but when i plugged it my scanner it didnt give me any problems. and showed everything with stock settings. It hooked up like a stock computer to my programmer. So I may take it in to the dealer tommarrow or the day after.

    also fuel injectors numbers came up stock. throttle body when i got the car stock. intake is not an ls6. it is an ls1. it even had possibly original plugs cause when i changed the plugs the first time the were old looking.. So i knew the guy was a bullshiter once he started talking about it. He even said he didnt know much about cars so i had to figure out everything before i decided to buy the car. MAF stock.
    Last edited by mr.ws6; 07-19-2011 at 10:10 PM.

  15. #35
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    That sucks the guy lied to you about the car. Thats alright, you can make it your own now. It's defienetely better to buy a stock firebird anyway, you see a lot of them that have been destroyed by people that didn't know what they were doing.

  16. #36
    Junior Member aggie897's Avatar
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    I had something similar happen with my Jeep. I changed the plugs first then the coils. Throwing money at it didn't solve my problem. I got frustrated and took it to the shop. Ended up an engine wiring harness had rubbed down and started to ground out. It only did it when the engine warmed up and the wires were more pliable. I would have gone crazy trying to figure that one out on my own. Maybe you have a harness that isn't getting a good connection after it warms up or is moving around. Just another thought to throw in the mix.

  17. #37
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    okay got the car back from the shop today. Here are the results from my paper.

    a scan test for a very rich running condition with hesitation on acceleration with no ses light on, customer has been changing a lot of parts to correct problem..

    Inspected for concern, verified rich run condition, checked data and found fuel trim at -15% long term, checked operation of MAF and MAP sensors, okay.
    performed fuel injector balance test, okay, called customer to learn of prior work, noted aftermarket programmer, (programmer removed by customer prior to diagnosis).
    checked ECM and found incorrect calibration in car.. reprogrammed ECM and cleared DTC'S stored, rechecked data and fuel trim is at 7%, test drove and detected no hesitation..

    So there you have it. It was the ecm all along. Guy I bought the car from probably fatten up the fuel trim when he had the headers put on. So when i put the stock exhaust back it. It was to much fuel. I dont Know how to read the fuel trim curves and what not so i couldnt tell on my scanner if it was good or not. Anyways Im happy the car is running great now. I cant believe how much more powerful it feels now when i get on it.. Dealer charged 200 bucks so it was worth it to me.. Thanks for all the info and input you guys gave me. Dealer tech told me I changed and checked all the right parts trying to diagnose it and since it was in the ecm. I had know way of knowing what parts worked or not. He was surprised how clean everything looked and how it ran after. Said IT WOKE up after the ecm update..

  18. #38
    Junior Member aggie897's Avatar
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    I hate to take my car to the dealer, but sometimes its the fastest way to get it fixed. Glad you're back up an running!

  19. #39
    Smiles for 9.5 Years cammed goat's Avatar
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    Very good. Let us know if any further issues arise.

  20. #40
    Senior Member JayTA98's Avatar
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    nice that you have back online.

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