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View Full Version : need help with air fuel issue! (dyno pics and lots of info inside)


sr20dets13
02-21-2007, 07:25 PM
right now the motor has bad vacuum at about 10in/hg i know cams are sposto make your vac alil bad but ive had it running totaly fine with the cams, normal 18in/hg vac and everything.. well i had to send it back to the shop for them to fix a problem they made while rebuilding. when i took it back i decided to upgrade some things because i hatee just fixing.. soo i added titanium retainers and springs and a greddy intake mani.

to try and fix my ruff lopy idle and bad vacuum ive changed this stuff/fixed
cas.
maf.
ecu.
ignitor.
coils.
injectors.
had to fix cam timing.
timed the motor about 20 times.

after i did all that and nothing had really changed. the car runs realllllllly lopy at idle, and is kinda sputtery/ missfire/ maf issue? you know it runs but when your just crusing at low rps with your foot kinda on throttle, it gives a stumble sound, and when coming off from a dead stop i kinda gotta pop the throttle up before i let the clutch out, but when you wot the car theres no sputtering, IT GOES, but the top end richening is noticable. so all this said i took it to the dyno runing just how it is...
http://img.photobucket.com/albums/v294/sr20detb13/DSC01063.jpg

soon as i got back, i put a nismo fpr on, and a new tps sensor.. idle/vac/low rpm power, have not changed.. i turned the boost up to 11, but she spikes to 15, but let me tell you it feels mean, i can get a nice slide into 3rd.. but in honesty i think it was just the boost, i dont think the tps/fpr changed the fuel map issue.. im most likly going to go dyno again on high boost, like 14 or something... my t25 i rebuilt by hand and replaced it with a 360* bearing soo im going to beat her up to see how reliable it is to rebuild by hand..
soo with all the details said anyone have any light shine on this lol? whats up with my fuel pressure?

stock boost, stock det ecu, stock det inj, stock det maf, stock det turbo.
the motor has about 20mi on it.. and obviously i need some big big tuning help. what do you think is making my jump down into rich soo bad?

this was at stock boost 8-9 psi.
stock fpr.
walbro.
stock det ecu.
stock t25 turbo.
stock inj.
264 step 2 cams.
valve springs retainers.
greddy intake manifold.
tubular exauhst mani.
front mount.

boostin13b
02-21-2007, 08:11 PM
Do a compression test. It sounds like you have either a cam off a tooth, causing bad compression, or a bad valve job done, etc. causing your problems. You should never have vacume that low even with huge cams. Check for simple intake vacume leaks as well. It could be something as simple as a crack in your FPR vacume, or intake manifold gasket. So check for all vacume leaks after the throttle body and do a compression test to test the basics.

sr20dets13
02-21-2007, 08:28 PM
comp tested 150 across... and when i first got the motor back from them they installed the cams one tooth retarded.. i had to fix it, is it possible that im still off? my cas reads 15* with it in the middle of the adjustment, and the horsepower would be worse wouldnt it? a bad valve job is very very possible. do i need a leak down test to check that?

boostin13b
02-21-2007, 08:56 PM
comp tested 150 across... and when i first got the motor back from them they installed the cams one tooth retarded.. i had to fix it, is it possible that im still off? my cas reads 15* with it in the middle of the adjustment, and the horsepower would be worse wouldnt it? a bad valve job is very very possible. do i need a leak down test to check that?

Yes you would need to do a leak down test to test for that but the compression numbers sound good. It still is possible for you to be a tooth off. Make sure that when you set your crank pulley at TDC that both cam lobes are pointing away from eachother, then check the markings on the cam gears. They should both be pointing up and slightly away from eachother, not straight up or to the side.
If your timing is on they should be about equal on each side.

Sounds like you may just have a simple intake leak somewhere, possibly the IAC sticking open, or like I said before, a hose or manifold gasket. Throttle body gasket would fall under that as well.