HELP!! Lossing power?

[TurboGN871]

I have an 87 GN and it pulls strong until the middle of 3rd gear were it loses alittle power (almost like it flatlines) . The car does not brake up at all like weak valve springs but I did notice the O2s go back up some. There is no knock retard. The only mods are MAF Translator, Pit Bull chip, 36# injectors, Exuast.

Has anyone ever delt with this issue before?
I appreciate any help..

 

[suicide six]

Ace the chip,old technology.How much is O2 going up?Chip may be adding too much fuel or O2 acting up.Weak springs will make these cars flatline.

 

[TurboGN871]

The O2s dont go up much I just dont remember them ever going up in 3rd gear.
8.1 to 8.4 in witch would be good but its odd how loses alittle power the same time the O2s go up and only 16# of boost and 40# of F/P with line off.

 

[VadersV6]

Weak springs will cause the power curve to flatline depending on RPM, not what gear you're in. Maybe its just not as noticable in the lower gears cause of the torque multiplication? Best way to know is to stick it on a dyno and see whats happening. You may be experiencing some detonation that you're not picking up on the knock sensor. That would explain the power loss in 3rd gear, and not the other gears. Also, given the rpm's you're at while building boost on the brake, the valve springs shouldnt be a factor there, unless they're really really weak.
Also a really FAT A/F cause make it feel flat.
Dont depend on the O2 numbers on these cars. The factory O2 sensor is worthless. You can be anywhere from 11:1 to 15:1 on a 50 count spread with O2 millivolts. Its practically an on/off switch.

 

[suicide six]

Not sure what injector that pitbull requires but that may be it,cracked header will richen up wot values,what type o2 sensor?If its a bosch take it back.They use to have warranty,free exchange.

 

[VadersV6]

Gnttype seems to be down, so I had a hard time finding an 02 voltage graph. But here is a rough one. Look how totally useless the factory O2 sensor is for tuning:

This is why I would recommend pulling fuel just until you start getting a little KR, and then add a little to make it go away. Then write down that magic 02 number. Depending on exhaust leaks you cant see, quench differences in the chambers, plugs and a whole bunch of factors, 2 different guys may have the same 02 voltage but totally different air fuel ratios.

 

[TurboGN871]

Is it possible the MAF Translator might cause the car to lose top end?
The motor was rebuilt and has up graded valve springs but I cant be sure of that.

 

[WIKEDV6]

How good is your trans? In a stock tranny the third gear clutches are the first thing to go when you start making power.

HTH
Prasad

 

[TurboGN871]

Trans was done by Dynotech, Its been excellent.