does anyone know or have any suggestions as to what could be causing my car to hesitate or stumble for a split second under full throttle. when i nail this thing it hesitates and then takes off and runs fine throughout the rpm band. anyone?

 

Check the voltage setting on the TPS. Sometimes raising it to the range of .62/.65 will cure a stumble/bog that you described.

Jake

 

thanks jake.....its at .54 right now, so tomorrow ill adjust it up...i cant figure it out. it only does it when i mash the peddle to the floor. it almost acts like it dies and then comes to life......thanks for the reply.........

 

A stuck EGR can also cause a similar problem.

 

tko, thanks for replying. the car will throw code 42 if its 35* or colder outside, dont ask me why because i have no idea. ive checked vacuum to the egr, ( which checked out good ) put a new egr on the car and made sure it was working properly. it also throws code 32 at the same time under the same outside temp of 35* i just put a new holley afpr on it and ive still got the surging problem. ive checked my tps, iac, and everything else you can think of but i cant find it. ive got a guy thats gonna make my chip but i cant get the bugs worked out good enough for him to get good readings on it. this **** is driving me crazy........

 

Could be a transition enrichment problem. Which car are you having the problem with? The stocker, or the one that's been pretty heavily modified?

 

Code 42 is ESTC related, and the code 32 is EGR related according to my sources. It could still be an EGR solenoid problem, even if the valve is new, and the hoses are all good. Check the solenoid for continuity and measure its resistance.

Could also be distributor related, but i doubt it. It sounds more like a lean bog condition, which could be caused by the EGR, or a computer calibration problem.

 

its my formula 350.....it only has about 750 miles on everything...its all new. even sensors and everything that pertains to the motor or that has any effect on engine performance.....thanks

 

when you said it sounds like a lean bog condition you hit it on the head.......ive never been able to fatten this thing up even with fuel pressure set on 50-60 #s. does it still sound like an egr issue?

 

Did you already try upping the TPS voltage? I'd do that and see if it makes a difference. If it does then I think you definately have a lean bog condition. The guy that burns your chip should be able to correct this by increasing value for transition enrichment in the PROMs tables.

 

no i havent had time to set the tps yet. for some reason im thinking ive tried that before but i cant remember. my header temps were running at 600*-650* when we fired it up and my engine builder said it was running lean. so we tried everything to fatten it up but to no avail. would my egr system make it run lean like that?.....thanks

 

Upping the fuel pressure won't do anything at part throttle, or transition throttle settings. It only affect the A/F mixture at WOT. Under every other condition the ECM takes a reading off the O2 sensor and will adjust pulsewidth to get the ratio it wants.

Adjusting the TPS voltage will fool the ECM into thinking the car needs more fuel that it would normally want to give it at a given rate of change in TPS movement and TPS position.

 

ok, im gonna try it......thanks for the advice.....

 

No problem, post back if it doesn't work and we'll try something else.

 

I just spent about a week trying to help a guy on the CorvetteForum who was having a problem similar to yours.

He thought it was ignition, but turned out to be his fuel pump.

The way to eliminate the pump as a possible cause is to tape a fuel pressure guage to the windshield then accelerate the car in the same manner that has caused the problem before.

Watch the guage, or better yet, have someone ride with you so that you can keep your eyes on the road.

Make sure the pressure does not drop when you nail the throttle. In fact, when the vacuum drops off due to WOT, the fuel pressure should increase.

It would be great, too, if you could log the run using Diacom to see the 02 readings, commanded A/F ratio are and any knock (retard) counts.

Hope this helps.

Jake