Well I got the car to stop doing the bucking between vac&boost. Now its doing something else. As the w/g opens I can feel a fluttering/backfiring (not really the popping of backfiring) sensation through the pull. The best way I can describe it is that it sounds like a subaru with an exhaust. It has that same uneven pulsing noise. The car instantly looses power with he onset of the fluttering. If I go into the pull 50-75% throttle its not so bad, but straight WOT it does it almost instantly. I wonder if its possible to run too much fuel with my simple bolt ons? (12:1 FMU, 255Walbro, and OBX Fuel Rail) Will the car pull out Coil Voltage if it detects excessive fuel pres? It just doesnt feel like fuel cut, more like spark loss. Ive noticed that my idle fuel pres. is at 4bar which seems a little steep to me. Ive got my plugs gapped at .35 just as suggested. Please dont send me back to the archives... Ive read them til my eyes started to bleed. Im just looking for a check list of possible culprits.

Edit: Points for helpful tips.

what size injectors?

How much is 4 bar in regular psi, and what injector size do you have?


-------jezreel
1998 GS with hrc stage 2, sfmu, ml, prokits, egt, boost gauge, apexi tt, haydans tranny cooler, costum dp, dr. uber groundwires, dynotune fp gauge. gst muff, turbo spoiler
Boostin since Aug 03.

nothing like driving with the windows down and the music low: i love hearing the turbo spool, swwwhhhttt!!!!
thanks for www.kaptainmyke.com for the sig hosting :thumbsup

4bar is about 60psi, and I have stock 235cc injectors

60 at idle is a tad much but not the cause of your problem I wouldn't think.

Edit: double negative, I suck

Sounds like a high rpm missfire under boost..What boost pressure are you running? I had symtoms like that not too long ago..When i would hit 15 psi, i would get this misfire, kind of like a studdering of the motor..just not a smooth running sound i guess..Replaced my spark plug wires with high performace aftermarket wires, and problem was gone. Also, gap your plugs to a minium of .032 I personally think its an ignition issue..esp if you are running over 13 psi..the more boost you run, the harder it is(er more voltage it takes) for a spark to jump the plug gap..in my case, the wires helped to give that little needed jump in voltage from the coil..I suppose it could be that you are running way too rich also...what are your EGT's at the end of a pull, at the end of a gear?

Im running about 8psi, with EGT's at 1200 during most WOT pulls. I have a MSD Coil and Wires which I checked for resistance and theyre fine. I really think its something in the ignition, im gonna try gapping the plugs even tighter tmrw... may like .25 - .30. I dont know why my fuel pres. is so high. I cant wait to get a sfmu or at least a safc.

Originally posted by notagst
Im running about 8psi, with EGT's at 1200 during most WOT pulls. I have a MSD Coil and Wires which I checked for resistance and theyre fine. I really think its something in the ignition, im gonna try gapping the plugs even tighter tmrw... may like .25 - .30. I dont know why my fuel pres. is so high. I cant wait to get a sfmu or at least a safc.

1200 during a pull? are you serious? That is WAYYYY to much fuel...prob it right there..that is if your EGT probe is on the exhaust manifold, NOT after the turbo..What size injectors are you using? What is your fuel pressure at 8 psi? If you are running 60 at idle, and you are running a 12:1 rise rate, that means you have approx 156 psi of fuel at 8 psi boost!! haha..(although i doubt your pump will get that high, nor flow the fuel)

I had a problem like this, but it was the computer pulling timing at WOT. Never got to fix it though, as I pulled the motor.

Yea too much fuel...My car only backfires/bucks when I run avgas and am shifting at like 6500rpm at auto x.

I put the egt probe in the DP, right next to the turbine... yes I know it should be in the manifold. My fuel press. at 8psi is over 100psi, but certainly not 156psi. Well does any one know how to lower my fuel press. with what I have now.

gapped new colder plugs to .28, seems to be remedied.

id get rid of that 12:1 FMU and get a SFMU, WAY easier to tune with...both idle and static fuel pressure adjustable too