Hello every one, thanks for reading this far, I need your help. a few months back i bought a 03 coupe with 30k miles and a salvaged title (i think it was a front end collision). the car was previously owned by someone who was misguided to say the least. it appears the fast and the furious played a large role in how he modeled himself and his car (stereo, custom subs, ugly fiberglass ebay body kit, cut springs, etc. thats why i got the car for cheap)

anyway my problem is that when i put load on the engine, the car stumbles or hesitates like its misfiring on a couple cylinders. when im driving just regualuarly there is no stumble and i dont really notice it when the car is cold but i definitely notice when the cars warmed up. the local stealership suggested replacing the MAF and i did, but no significant change. i scanned my obd recently and theres no misfires but it did say that my car is running on a closed loop when warm, using o2 sensors for fuel mix. the car does have a injen exhaust and aftermarket air filter.

what do you suspect would cause this problem (multiple answers preferred) what would you look for? what could i diagnose?

thank you for your help and i will update this with more details very soon, thank you

Edit- i only hqve a quivk second but i need to update with more info.

First off, i will send $20 to whoever answers first with the solution!

On my obd reader it says info is available for 4 o2 sensors, but i only get readings from two, on one side

I think my problem has something to do with air fuel mix. You can hear the car cut in qnd out when WOT.

Also this problem primarily occurs when wot, under load, between 2k and 3.5k rpms

 

I also have the same problem and I only have a pop charger as far as intake/exhaust. I have an 03 coupe as well. I haven't noticed anything unless I floor it passing someone or something like that. I am also interested in an answer.

 

$20 reward for first solution that solves problem

 

Fuel pump! They are made somewhat cheaply and I have seen several fail. Use a fuel pressure gauge inline while letting it go to WOT (obviously with wheels off the ground) under load and watch fuel pressure. I would have to double check with a service manual what stock fuel pressures are like but your best bet is to ELIMINATE different systems as a possibility. Sounds like it is fuel related to me though. Other thing I can think of is a big vacuum leak. Do you have a plenum spacer? Maybe a broken hose coupling or something letting in air after the mass air flow? Third thought is that if you have 1 whole side of o2 reading that usually causes huge runability issues, but as to why it is not reading could be anyones guess. Most likely a wiring issue especially if the wiring has ever been messed with. Hope this helps bud! The more info you have about the issue the better. Good luck!

 

wiring to ecu, fuel pump, spark plugs...etc...good luck fixing someone elses mess

 

Thank you for your ideas so far.... Though im suprised there hasnt been more responses bc of the $20 reward.

Anyway i think i may have found the culprit but wont know until i fix it...

Pre cat exhaust leak.. when i was looking at the live o 2 readings they were fluxuating too much, plus the car is lowered too much and has an injen exhaust thats definitely been hit and pulled on various objects and since o2 readings help determine how much fuel is injected it may be causing lag.... If it was the fuel pump or injectors themselves i think i would be getting lag throughout all rpms, especially higher....
But i wont know for sure until i get the exhaust fixed, ill be sure to let you guys know the outcome.

Also i still welcome all your thoughts, experiences and comments, if the exhaust leak isnt the culprit and one of you have posted the right answer, ill send $20 your way.

Mbweeks- is it possible or likely you have an exhaust leak?

 

^^exhaust leak is not ur problem ..ive ran the car with no cats before and its fine..ive ran the car with no o2's and it was fine....i still say fuel pump, or injectors,plugs or wiring issue to the ecu...

your acting like the car is breaking up bad and hesitating and sputtering like a misfire correct?

 

Sounds like a loose wiring harness. I had a similar situation with mine. No one had the answer cause it was such a weird effect.

 

Sounds like an electrical issue, and I bet it's your timing ... Could be the dtc solenoids for th cam shafts or the cam phase sensors


Are you getting any check engine lights when you are under full throttle?

Have you done the throttle body reset and idle relearn procedures? Do all the resets for car first ....follow this link

https://g35driver.com/forums/engine-...rocedures.html

 

Ummm..... how is he gonna put load on the car with the wheels off the ground???

 

Thx for the replys..
Issue found! I assumed that since there was no check engine light that there was no misfires... I was wrong. There were two coils failing under load. I replaced them and voila
Also i was wrong about the second bank of o2 sensors, i didnt know they had to warm up before i got a reading!

Thank you all for your participation, i love it when a forum comes together!

If you have any questions for me, email or im me, thank you