Bog/Stumble/Hesitation on gear change

[NateDogg]

Hey all,

I have a '91 240sx with: custom 3" short ram intake, 2.5" exhaust, ASP pulley, JWT ECU, Walbro 190lph pump on stock injectors and a Nismo FPR at 34psi (stock). Timed at 20-22 degress BTDC. The engine idles ok at 750 or so. AIV completely removed and hole plugged.

When I shift into 2nd from 1st I sometimes get a stumble for about a second and then it picks up. Somtimes it won't do that if I drag the clutch into the gear. But if it's a perfect rev-matched gear change it hesitates. Engine seems to have decent pull. Also seems like it happens moreso when the engine is cold..

I have cleaned everything and there's no codes of course. All the sensors check out ok. I added a few engine grounds and that didn't help either.

I have a couple of suspects:

1) fuel pump is pulling too much current for stock wiring2) water in gas3) EGR vacuum leak (didnt replace gasket on intake mani removal -dumb)I pushed up on the diaphragm and the engine stalled. 4) O2 sensor: I read in a search i did about a guy with the same problem. BUT I get pretty good mileage. About 350-400 mi/tank

What do you think it could be?? Thanks.

[benemorius]

zerothread?id=113297

[slipnfall]

Also check your throttle position sensor, it's easy, and it fixed a lot of my hesitation/stumble problems:

With the car warmed up, engine off, key in the 'run' position, and the TPS sensor *plugged in*, push a needle into the back of the connector, along side the wire. Do this for the black and the white wire(three wires total). Read the DC voltage with a multi or voltage-meter. The voltage should be between 0.4-0.5V with the throttle completely closed. If not, you can adjust the sensor by loosening the two bolts holding it in place.(7mm wrench was the only way I could get to it).

HTH

[NateDogg]

thanks slipnfall. I found a couple dirty grounds so I cleaned 'em and that helped.