Car hesitates under boost.

[zachdeagle16]

Ok i have a 91 gst, the car pulls hard untill it hits around 15 lbs of boost then it starts to hesitate vey hevaly almost like you took your foot off the gas. My only mods are act lightend flywheel, mbc, autometer boost gauge and rewired fuel pump. please help!

 

[tbTalonES94]

My car does the same thing! It will be pulling hard as hell then once it gets to about 4k or so it just dies off and its slow as hell? I have no idea what it is. I dont have any boost leaks either? Do you? I have change my coil, coolant temp sensor, plugs, wires, fuel filter....probably more! Mods are in profile. Please someone help us out?

 

[PaleDSM]

Probably knock causing the ecu to pull timing back to preserve the motor.

Boost leak test lately?

 

[tbTalonES94]

See heres the thing. My car will knock like crazy when i just take off in first gear (not flooring it or anything). im supposing this is phantom knock. But whenever i boost it does not knock. I will lose power and i can watch my timing and knock......knock stays at 0 and timing advances. I did a boost leak just a while ago and all I got is my TB seals. Could they be leaking THAT bad to make me lose almost all of my power at 4k. I mean the car is fast as hell untill it reaches about 4k or so. My boost doesnt drop or anything. 13 psi rock solid the whole time. Shoots up and sticks but once i reach about 4k it just bogs. I have richened up and leaned it out....nothing works. Fuel trims are 100% accross the board. 02 trims when cruising are around 50-80%....and while idling are usually slightly above 100%? What is the problem? My 02 sensor is brand new. My ground broke on my exhuast a while ago could that be causing this problem?

 

[zachdeagle16]

I dont have any boost leaks either, it pulls hard all the way to to like 4k or to 15 lbs then just quits trying, i replaced the spark plugs, lastnight and it helped it not hesitate so bad but the problem is definatley still there. i have also orderd a new fuel pump and fuel filter so maybe that will help.

 

[tbTalonES94]

Does yours boost and its crazy then all of a sudden it just stops at 4k and if you keep trying to go it just struggles very hard. It would seriously take me a LONG time to go through my first 3 gears. Somone help us out?? I have a brand new fuel pump, fuel filter, plugs, wires, coil, coolant temp sensor and FPR.

 

[zachdeagle16]

yeah my car does the exact same thing. please help.

 

[jjbrasil]

my car runs like crap also...i hooked a boost guage up to it and i had about 11-12 VAC in h.g which is bad..my last car was 16-17...and it hesitates like im not making the power i should be....tomorrow im going to be doing a boost leak test and if i figure anything out..ill let u guys know

 

[krazywhitboy]

sounds like a boost leak somewhere.....

 

[DSMatMSU]

sounds like a problem im having.... it just falls on its ass.... if you let off the throttle a little... say a 1/4 throttle... does it 'feel' like its picking back up again??
ive checked up on all my boost leak... and there none... even fixed the little ones on the TB... anyway, my logs show some annormal o2 readings, they flatline under throttle... and the LTFT shoot up to 200% when under throttle... but i have 0 knock, or very minimal... ive got an o2 sensor sitting here in front of me thats going in tomm... we shall see what happens...
plugs are brand new, the wires are fairly new, brand new fuel filter as well,

 

[tbTalonES94]

My condition does not change with throttle position. It just loses it at 4k. I dont have any boost leaks that i know of except the tiny leaks at the TB. I fixed the ones around my BOV last night and it didnt do anything. I also finally got my fuel pressure set at 38 psi with the line off and it didnt change a single thing. My 02 sensor is brand new? Could it have been fouled in some way? Before i got my new FPR i was running about 58 psi of fuel with the line on so i dont know if it fouled it. Maybe my brand new NGK's are fouled too? Anyone got any ideas? I am also getting very weird 02 readings. When i go WOT they will bounce between about .68 and .86 which is very lean. Ive tried to richen things up and it doesnt change a thing.

 

[zachdeagle16]

I changed my fuel filter and checked for boost leaks this morning and i had none the only difference it made is that instead getting the loss of power at 14lbs of boost now it starts up at like 17 lbs.

 

[tbTalonES94]

Could low coolant have an effect on how the car runs? I mean i bet thats why it has a hard time running the first few minutes when i start my car in the morning. I bet the Coolant Temp sensor isnt getting enough contact with the coolant to tell so the ECU just dumps fuel. Anyone??

 

[Generation1JeY]

i think i have the exact same problem as u guys do. This is whats going on: i have my boost at 15 psi. When i give it WOT its perfect, it spools up perfect and runs strong, then right around 4k maybe a little higher it just starts to make a terrible sound that sounds like fuel cut/misfire i cant explain what it sounds like but it just makes the sound really fast and my car doesnt accelerate anymore. My car never did this before, i used to pull 16 psi all the way to redline, but now somethings wrong. So i turned down my boost to about 11-12 psi and now it stays strong all the way to redline, but i'm just trying to think of what can be affected by just 3 or 4 pounds of boost?

I'm thinking maybe ignition, coil, mas airflow sensor, plug wires, Something along those lines, but i just dont understand it.

Anyone ever witnessed or heard of somethng like that?

 

[byebyev8]

Sounds like u either need to upgrade your plugs or wires thats what it was when my car did it

 

[tbTalonES94]

I replaced my TPS sensor and it did nothing. I fixed boost leaks and it did nothing. I tried to tune with my S-afc 2 but i just cant things go too wild. Ive got everything new on my car and nothing is happening. It will boost hard then when it hits about 4k my exhaust gets really loud and its just slow. My plugs are brand new NGK BPR7ES and i have brand new 10.3 mm wires. My coil is new. Could my injectors be bad and not carrying the needed fuel at high pressure?

 

[dmentdgst]

Has anyone fixed their car yet? Im having the same problem with my car, it starts to just buck while under boost in any gear, as if its choking or something even though everything checks out, the only boost leaks were around the throttle cable, maybe the o rings in the tb shaft?

 

[NvDiS]

Holy zombie thread batman

 

[Mellow23]

Holy zombie thread batman

Zombie thread maybe, but if anyone has fixed their problem it would be great to know what the problem was. seems like a lot of people have had it

 

[NvDiS]

Well the route this thread was going seem that could have been a few things ...such as a major boost leak..bad tps...maybe a MAF issue ...its hard to diagnose ..it would be nice if the OP chimed in

 

[Brentenorris]

mine does the same thing. im thinking its fuel cut on my car. bl test turns out good, i need more fuel. im going to try the fuel pump rewire and see if that helps

 

[DSMitsubishi]

it's most likely fuel cut. Check your MAF sensor, it's probably reading too much air flow. You could also try converting to speed density.

 

[Juanpa]

Have you done a boost leak check?

 

[Alex7747]

My car does the say!! But later on around 5.5k. Help

^^same

 

[dmentdgst]

The same with my car, it begins jerking around 5k rpms, and the only boost leak is from the throttle in the back off the tb