so the other night i was out driving car was running great for once. Shut it off let it turbo time and went into my friends house. Came back out jumped into it and went to a job interview. Got on it a little and it was good then right around 3400-4000 it would just bog down an felt like it lost all power. So i was like wtf took it home afterword. Took my intake off looked at my secondaires to make sure the pulg wasnt loose. Was still good nothin loose checked to make sure all my vac lines were ok all 4 of them hahaha.

Put it back together jumped in it warmed it up got on it to boost a little an the same thing but now it would just happen then an kinda go away after 4000 but you can still feel it there. Like its loosing power after 4000. Unpluged my fcon thinking maybe it is that. Drove around no piggy back just stock ecu an still the same thing. Thought maybe it was a boost leak an checked went over all my IC piping an couldn't find anything tightened an check agian nothing. Put my fcon back on sence i couldnt find it still there. I unpluged my tps when it was running an the car just died. dont know if thats good or bad. could it be my o2 doing this to its kinda old not old old but about 2 years an i didnt drive it for a year cause it was blown up.

 

Sounds like you secondaries aren't fireing up right away. I would check the wireing... it often gets baked up there and becomes brittle. Peel back some of the loom and electrical tape and see if any of the wires are cracked and possibly shorting out.

P.S. I had this exact problem shortly after I bought my 7, and this was the issue.

 

what happens if you put the pedal to the floor when it does this?

 

it still does it but it seems to go away a littlew but i can still feel it there

 

sounds like a fuel issue, i would guess your secondaries are dirty. But it could be anything. If you have the tools i would check fuel pressure when it does this.

Also, i cant see the O2 causing a problem like that.

 

Yea definetly sounds like a fuel issue to me. I would change the fuel filter and then check the injectors and fuel pump.

 

is it just a hesitation or does it spit and sputter. and if it does spit and sputter you might want to check your water thermo sensor. I had similar symptoms

 

i think i have one off my NA motor i can throw on an see if it makes any difference on the motor. I dont think its cause i just rewired my pump after this started happening an still doing it...

 

yeah o2 didnt do anything im glad i changed it though now my air fuel reads faster an more efficent... i dont think its fuel though cause after this happened i rewired my fuel pump. an my afpr is saying im getting 38-40 on idle it might be something when the car has load maybe my afpr is going out

 

fuel pumps good i checked it the other day... my injectors are stock primarie an 720 secondaries an the the 720's are brands new like maybe a month old.. fuel filter is only 1000 miles old from when i did my rebuild

 

I've been having a similar issue....my car hesitates noticeably under load from about 3k-3800rpm (when the secondaries kick in).....I had my injectors cleaned and tested...Im still having the same problem..........There's like little hiccups in power during that part of the rev range....The rpms continue to climb and the hiccups eventually go way once i reach 3000rpm......I may look at the tps next

 

Well that is likely your issue right there!!! If you have bigger injectors in the secondaries than during staging you are likely going stupid rich, and probably running too rich after that as well. It may be leaning out toward the top end if you are still running the stock fuel pump, possibly bringing the AFR's back to where they should be. If you put bigger injectors in you need something to control them.

 

Likely the common 3800RPM hesitation. Usually traces back to a ground issue. Aaron Cake has a good writeup on his website about it.

 

yeah well i have a hks fcon to run my fuel computer. but even when i pulled it off the motor still had the hesitation. I was think it was the fcon but he stock ecu did it do. I havnt had a chance to look at gounds or anything cause colorado just got a crazy snow storm an my car is out side its lame lol... but fuel pump is upgraded walbro 255...

 

My problem ended up being the TPS. I adjusted it using a multimeter. The car runs alot better now. Also fixed my cold start idle. My idle used to bounce between 1k-1500rpm when cold. After the TPS adjustment, my cold idle hovers around 2k and it slowly drops as the engine warms up.....My problem wasn't the 3800 rpm hesitation. My car ran better once it hit 3800rpm and up. Try adjusting your TPS and see what that does

 

the stock ecu will do it if you're running 720 secondaries... when those come on it'll be way too rich. have you tried leaning it out with the fcon if you can when it stages? I don't really know how fcons work... maybe it got bumped and one of your settings is off.

also, are your primaries low impedence or are you running a resistor on the secondaries? if you're running a resistor it might have gone bad or something.

 

i dont think it my fcon cause it ran fine before like i had the fcon on with the 720s for about a month with no problem an my af is at 13.9 14 at idle an about 12.8 12.5 wot an when the cut happens the a/f dont change. the injectors are low like it said to run for a s4 s5's are high. so i thinking maybe a sensor or a plug is loose. i havnt had achance to go over anything cause colorado got sick snow storm an its gay now lol...

 

kk for sure i will try that how do you do it with the meter