Stumble, Surge at around 3K RPM part throttle

[SOADweskey]

I ran a search and couldn't find a thread with a problem quite like this.

My car idles great and runs fine if I give it gas and let the turbo spool.

My problem is that when I'm just cruising down the street at around 3,000 RPMs applying part throttle my car will stumble and surge. It gets worse going up a grade when the car has extra load.

I have a 16G, EVO3 manifold and O2 housing, full exhaust with high flow cat, SSAC FMIC, 1G BOV, K&N FIPK, 190 Fuel Pump, Denso 720 injectors, DSMlink, and Zeitronix Wideband.

I ran a Boost leak test because the problem feels like when an NA car has a vac. leak but my system is pretty solid. It is leaking at the throttle body shaft seals but those are soon to be replaced with a freshly rebuilt 1G throttle body.

My spark plugs look good. They are a bit white because I'm using the narrow band switching point feature of the Zeitronix to have my car idle and cruise at 15.8 AFR instead of 14.7 AFR. (I get about 50 more miles per tank by doing this by the way) I'm not ruling this out as the problem but I have been running like that for about 8 months and this problem is new and I switched it back to 14.7 for the last 400 miles and the problem persisted.

Any one out there have ideas?

 

[laserspeeddemon]

Sounds like you are venting your BOV.

 

[SOADweskey]

Whoops, left that out of my list. Mo my BOV is recirculated just as it should be. And it holds to 18 psi during the boost leak test so I'm sure that isn't my problem since this occurs under low or no boost.

 

[Defiant]

Start with new plugs (BPR6ES at .028) and new wires.

 

[Talonman86096]

Replace the TB seals and boost leak test again. See if replacing them helps it sounds like a boost leak somewhere. Also as Defiant said replace the plugs and wires too.

 

[lespaul4146]

Sounds like my car man, i changed the plugs and everything, i believe that your wire could be faulty, or maybe it just needs some tuning? These cars, to me, become more and more dificult everyday.

 

[SOADweskey]

Thanks guys, this weekend I will change in my 1G TB with fresh seals and try out some new plugs and wires to if I can find some cash.

I don't think tuning will do anything for it because it is occurring in closed loop with the ECU trying to keep my AFR constant and not using my open loop fuel maps.

 

[lespaul4146]

word, i would say the wires man, tuning i think would be a reach but you never know, i did not know what setup you were running. let us know

 

[SOADweskey]

Thanks to everyone who put their two cents in here. I stopped by Road Race today and they were kind enough to go for a drive in my car and put in their thoughts. Turned out that even at part throttle the ECU was in open loop so simply adding 1 or 2 percent to the values on my fuel map between 2 and 3 thousand RPM smoothed things out.

It is nice to live so close to a great DSM shop. I'm still going to change my TB this weekend because I want to fix the leaks at the shaft and I want a bigger TB.

 

[gio_daredevil]

You should check Your MAF