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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; alright, Ive been trying to fix this annoyance on my car for almost 2 months. Heres the problem. Car runs ...

  1. #1
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    1999 TRANS AM WS6 M6

    car runs hesitates and misses at wot.

    alright, Ive been trying to fix this annoyance on my car for almost 2 months. Heres the problem. Car runs and drives perfect at idle and normal driving. anytime i give it 40% or more throttle at any gear the car misses and pops and stumbles. no steady pull. if i get off the throotle right after it drives normal. If i slowly ease the gas all the way to 3000 or higher rpm it doesn't miss or stumbles. only when its a sudden change in throttle the problem is there. I replaced all the plugs and wires and checked them. I replaced the map sensor. same problem. I got 3 new diffrent brand mafs and the all had the same result as the original. Now the funny part is when I unplug the maf it doesnt have the miss or hestitation at all when i get on it. I even replaced the harness part of the maf with a new pigtail. I checked the fuel pressure at idle and it was at 58 psi, sprayed carb cleaner to check for leaks around the hoses and there no signs of vacuum leaks. Only codes I ever got were p0172 p0175 that were pending but never illuminated the cl light. on the two older mafs. as of right now i got a new delphi maf thats on it and no codes thrown yet. I had the fuel system completely flushed at the shop. I have the hypertech power pac that reads everything that the car is doing and everthing seems within specs. any help or suggestions would be greatly appreciated. DONT WANT TO TAKE IT TO THE SHOP IF I DONT HAVE TO.

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    CAMARO not Maro asshead! HASTINGSRJ's Avatar
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    that was the first things i replaced. I put the ntk type sensors before the cats and bosch after the cats. car had long tube headers on it but i had to put stock manifolds back on. for smog of course. so the sensors are new also. car passed smog with flying colors.

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    Bone it like you own it FORD RECOVERY EXPERT's Avatar
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    Throttle Position sensor?

    When you unplug the MAF it puts the computer into open loop / speed density

    p0172 and p0175 are too rich, bank 1 & 2.... The o2's are seeing this and reporting it... THEREFORE they are not bad.

    you can test the TPS, should read Around .5 at idle and 4.65 at WOT. should be measuring across the top and middle wire I believe... (Blue & Black?)

    If the PCM thinks you are gassing it, and the IAC cant give it the air the PCM "thinks" you are, then its going to add fuel.... thus creating the rich condition indicated by the 2 codes...

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    Senior Member JayTA98's Avatar
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    1998 Trans Am

    is the MAF you got on now OEM brand new or used?

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    It is oem brand new delphi maf I have a grannatelli and ac delco used. the granatelli and ac delco seem to give it he worst missing and also are the only two sensors that gave me the trouble codes at that time. the delphi i put on about 30 miles so far so good no rich codes. . I plugged in my hypertech hyperpac to see what the tps was reading it gives me a display that i can watch as i press it down. it doesn't show the voltage but it shows it in percentage of throttle instead. the reading doesn't spike up or down and looks to be very smooth as i press the gas pedal down. I thought that was the problem also but its not jumping around on my scanner as i press down the gas pedal. I may replace it anyway since there only 30 bucks or so. I seem to be throwing away money a little at a time as i narrow down the actual problem.

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    alantic silver
    99 vt calais ls1

    wouldn,t belive it but i,ve got this problem check my thread

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    Moderator Cutlass's Avatar
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    1999 Formula WS6 M6-sold
    2001 Silverado Z71

    Is your car programmed with the hypertech? If so, have you tried going back to the stock tune?
    Any other mods we should know about?

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    I tried the programer on RFG mode, Non RFG mode, and stock tuning. it does the same hesitations on all the programs. as of right now i have it on stock tuning. all the things ive done was plugs, wires, stock exhaust manifolds and cats back on. stock y pipe, car use to have long tubes and off road y. professional ported throttle body, slp elbow, mti clear lid. cleaned K&N, lightly oiled. tried 3 diffrent mafs and maf cleaner. currently brand new delphi brand on it. 180 stat, coolant bypass, new map sensor and 4 oxygen sensors, cleaned iac sensor, and iat sensor. checked tps signal reads smooth. Pipes violator muffler. diamond subframe connectors. complete energy suspension busing kit. thats about all i could think of as of the mods. And honestly i dont remember when it started happening.. It was just there one day when i gave it gas at around 2000 rpm then floored it. then i noticed it missed and hesitated. I checked plugs and wires first and again. like i said before the car runs awesome normal driving and idle. Better then when i had the long tubes on it before.
    Last edited by mr.ws6; 06-30-2011 at 12:38 AM.

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    Moderator Cutlass's Avatar
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    1999 Formula WS6 M6-sold
    2001 Silverado Z71

    Can you drive around with the fuel pressure gauge attached and taped to the windshield so you can watch the presssure while this happens? If the pressure drops or spikes up, that could cause a problem.

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    I can try that method, the only thing i feel its not pressure related is case the codes Ive ever got were rich codes and I can see my pipes in the back are a little more black than they normally are which tells me im no where near lean.. such as a bad fuel pump will cause. But i may be wrong. Also this morning I fired her up. let it warm up about 2 mins then got on it right away without the car ever reaching temperature. so 140ish temp. the car didnt hesitate or stumbled. However I can tell the timing was not there at wot cause it was a lil sluggish but then a rush of power after 3000 rpm. all my wot pulls i did where in second gear.. After i let the car warmed up. I did another second gear pull. It did hesitate slightly but not as bad. then the power kicked in after 3000 rpm.. Im thinking Maybe knock sensors or something temperature related as far as the missing/hesitation. Im not showing any codes as of 40 miles of driving or so.

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    Smiles for 9.5 Years cammed goat's Avatar
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    Did you spray soapy water or brakleen on the coils to see if they are arcing? You could have worn/damaged coils.

    Also, you posted about re-installing your factory manifolds to pass smog, so I assume you have the pump. Have you checked it for damage?

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    Moderator Cutlass's Avatar
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    Any damage to the coolant temp sensor when you we messing around with the exhaust headers/manifolds? That could cause a run rich. So could high fuel pressure, a bad MAF, leaking injectors, or another sensor giving bad info to the PCM.

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    still no cl codes after 50 plus miles. changed spark plugs again for the hell of it. had an extra set of ngk's laying around. no change. Definetly temperature related though. right after i put the plugs in the car i idled it for a minute then floored it in second gear and no miss or hesitation at all in the whole rpm range. just a steady powerful pull. hit 3rd also steady power and pull.. so now my question is what sensors would cause it to dump more fuel in after its warmed up. "closed loop I assume. may just change out the knock sensors and temp sensor for the heck of it also.

    also when i took out the plugs all of them looked pretty normal except number 7 cylinder. that plug was black as far as carbon. nothing to crazy like deposits or oil, but the insulator, tip, and strap where black. so maybe bad injector??? or weak coil????

    also wanted to thank everyone for there input. I really appreciate the advice and help you guys are giving me so thanks to all
    Last edited by mr.ws6; 06-30-2011 at 12:44 AM.

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    Smiles for 9.5 Years cammed goat's Avatar
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    You might have a weak coil or it's arcing...if not the wire. Check both coil and wire and get back to us.

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    Moderator Cutlass's Avatar
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    That rich, carboned up #7 plug is way more likely to be a bad injector, then spark related. You could try swapping that injector around to a different cylinder and see if the carboned up plug follows over.

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    Ive been reading and testing and cleaning and checking and replacing.. In the end I still think my MAF is still the culprit. Even though its my third one. And its brand spanking new.. I did a Run on my hyperpac to see what the sensors were doing and i recorded it. when I looked at the results. it looks like the maf had a slight hickup around 3000 rpm but then cleared itself out as it got higher around 4000 rpm. numbers were steadily increasing yet went to a low number for a spit second then went back to a higher number.. It showed no timing pulled through knock sensors it also shows what fuel trim numbers were doing but i dont know how to tell if its normal or not. tps looked good so was the iat sensor and map looked good as far as smooth number declining as rpm rised.
    I also notice that the new MAF had some redish lint on the screen which means my K&N may of been messing with the MAF. TO MUCH OIL Maybe??? I did cleaned it recently.

    After the weekend Im gonna spray the new MAF with MAF cleaner and then Maybe try an oil less filter.. What would Be a good brand Besides K&N that uses no oil.?

    Also I will definetly switch or replace that #7 fuel injector.. My mechanic friend told me the same thing on that one. so Thanks for all the info from all of you guys.

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    Moderator 35th-ANV-SS's Avatar
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    My guess with those codes and the hesitation is it is still the MAF.

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    Ok I know it has to be the MAF. I unpluged the MAF after the car was warm after driving for about an hour. There is no hesitation or stutering when I floor it. I put on a new TPS and did a new 7th injector and changed number 7 coil. nothing changed when I did those. Thats when I decided to unplug the MAF and drive it around. AGAIN this is a brand spankin new Maf with the screen still on. Could It be that I need a Cold Air tune on the MAF since I do have one of the slp ram air kits also installed under the airbox. I know when I unplug the Maf the MAP sensor provides all the info to the computer. So whats the deal with the new MAF giving the computer bad info when thers more than 40% throttle.??? I used a whole can of MAF cleaner on a new MAF. WASTE. I put a blue shop paper towel to soak up any oil left on my filter. Their was a lil on the Towel but not to much.. Should I just leave it without the MAF connected. ALSO my CL light does noy come on when I unplug the MAF. I have to scan It for it to show me the MAF code not PLUGGED in on the computer.???

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    Junior Member Ortiz11b's Avatar
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    2000 Camaro Z28

    maybe you already know this as well.. but 98-99-2000 used one mass air sensor.. and 2001-2002 used a different(internally)... i found out the hard way and got a SLP mass air sensor for my car to find out it wouldnt work because my car is a 2000 and the one i have is for a 2001-02 ls1... so just something to think about,,, dont know if the delcos or delphi are the same as the aftermarket maf...

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