Hey all, I have started having a problem lately, and I was wondering if any of you had any ideas/tips for me. After I put in the TH400 in and got the car to the track again, I was noticing a stumble off the line. A pretty bad one at that. Looking at my datalogs from the runs, it seems that my car is running out of fuel for about .3 seconds or so after flooring it. When this is happening my wideband and the factory o2s all go lean (18/1 on the wideband) and the car seems like your off the throttle, then it picks up really well and goes.

A little info to go with this. My indash fuel pressure guage shows NO drop happening, infact, it shows the fuel pressure going up as manifold pressure goes up, even during the stumble. My datalogs show the IPWs coming up before and during the stumble also.

Its not just a track thing either. I drove the car around for the past couple weeks, and it does it at tip-in from a start, cruising, basically anytime. It also doesn't have to be on a WOT run. It does it when the TPS changes from say 5-10% up to 30+%. If I gradually roll on the throttle, there is NO problems at all.

Any help would be appreciated.

 

Mine did this when I went from my six speed to the t-400. I adjusted my Map enrichment (asynchronous injector pulse) to a more agressive curve and added about 8% more TPS enrichment. There was more of a MAP drop after the t-400 was installed due to the extra load of the less efficient trans - even with a 4000RPM stall.

Mine is a turboed 355 with DFI 7 with wide-band, but I am sure at lower RPM the MAP and TPS enrichment are close during tip-in operation.


Bryan

 

I have this exact same problem with my car. Let me know if you figure it out using TunerCAT/LT1Edit. My solution was to leave off idle - that way it lean-bogs before it even starts moving.

Mike

 

In my mind, the most logical thing would be the fuel pressure regulator. It seems that when the injectors first open dramatically, the regulator has to quickly close to keep the fuel pressure adequate. If this was delayed, all sensors would read as they should EXCEPT the o2s. That is exactly what my car does. Even the wideband shows very lean for a split second then goes to 12-1ish. The only reason I am not SURE thats my problem is my indash fuel pressure guage shows NO drop, but it may be possible that the response of the gauge isnt quite fast enough to pick up the pressure drop


As far as it being due to the TH400, I was wondering that myself. I dont think thats it though as it still does it in Park and Neutral, when the car wouldnt know what tranny was behind it.

As far as my fuel pressure regulator, I know it needs changed. With the intank 340m and the Boost-a-pump, it cannot keep the idle pressure below 48psi, as it cannot handle that much flow. Do you think it is possilbe that the regulator may be damaged from always being forced wide open at idle and still not keep the pressure low enough?

Thanks again.

 

I kinda' doubt it's the regulator. It should react just as quickly as for a stock motor.

My guess is not enough accelerator shot. In most computers, there is a table for additional fuel versus rate of TPS change, i.e. accelerator pump. However, I have not been able to find one in TunerCAT. Either the LT1 doesn't have that table, or the TunerCAT folks haven't found it yet. Then again, I could just try a new TPS sensor.

Mike

 

i fixed mine same as wingnut. didn't take much either. if that is the problem keep this tid bit also. after i got mine dialed in i noticed it came back one day turned out to be header gasket leaking produced the same result.

 

I happen to be fresh out of DFI 7's, though.

 

Heheh, damnit! I hate it when that happens...


I have a TH400 and don't have this problem.. I'd have to look through my LT1 Edit file though, I don't remember changing anything at all when I put the tranny in that would've caused/fixed this problem..

--Sean