Engine stumbles when throttle is opened fast

[drz71288]

I have a chevy 350 tbi, 65lb injectors converted from a quadrajet carb. The motor idles great and when you sit and rev it slow there is no issues. When i crack the throttle fast though the motor bogs down and will not rev til its past 2000rpm the same happens when i try and drive it after every shift. Once it gets past this point there is no issues and the motor runs good. It is msII fuel only no spark. Wondering if anyone could point me in the right direction. I have tried changing alot of parameters and nothing seems to be helping. Right when i crack the throttle the map is seeing 100 almost right away and running straight up the VE table in the 600 to 1100 rpm columns. I dont know if this is an issues or if it is normal.
Thanks

[msiddalingaiah]

What's your idle MAP?

[drz71288]

The idle map is about 30kPA

[Arrowhead]

Ya know, I have almost the same problem. Even though I have a supercharger, it acts very much like you describe. I've had this engine running on MS before, but this is a new ECU w/ updated software. I've played with all the parameters as well like the Accel enrichment, VE tables, etc. My engine would run up to 15 lbs of boost at 5000 RPM WOT max with the old ECU. Now it spikes up to 20 psi at 1/2 throttle at 3000 RPM and it breaks up and blows black smoke. I even went so far as to connect to my air compressor with a gauge to verify the MAP sensor was reading the correct air pressure.

I have noticed the TPS bar spikes with very little movement of the pedal even though the TPS has been calibrated correctly. A quick stab at the throttle and the MAP spikes on the VE table all the way to 180!!!

I'm starting to think there is a software problem or I made some kind of error when assembling the board.

[usagoal]

Sounds like a noisy TPS or noise being induced into that circuit. I get a choppy tps too, I have my threshold set at 90. I may try messing with the boat/MS again today.

[drz71288]

Im pretty sure its not noise on the tps signal. It always reads smoothly and there is not any spikes.

[usagoal]

Funny, I just solved my issue. Changed from 2 squirts to 4 on my TBI (with some accel tuning) and now it revs up nice. What's you're setup?

[drz71288]

Its a 350 tbi on a carb intake set to 4 squirts. Ive messed around with the accel enrichment. It seems like whenever i get it to not stumble when driving i lose speed in reving(itll rev real slow) but it wont stumble. But if I have it set that it stumbles when i open the throttle itll rev real fast and even after it first stumbles. Its a huge difference in power between the two. Im not too sure on what to all change on the accel enrichment. Some of it seems like it could be smoothed out there. If you could give me some pointers on what to change and how to that would be great. I cant seem to find much in the manual on accel enrichment.

[convertables_10]

Funny, I just solved my issue. Changed from 2 squirts to 4 on my TBI (with some accel tuning) and now it revs up nice. What's you're setup?

Thanks a million. That corrected a issue i had been having with mine as well. Now to retune the middle of my ve table.

[usagoal]

drz71288, do you have a msq and datalog you can post?

[drz71288]

No i do not have one. I cant get one right now because my computer freezes pretty quick whenever I run megatune with the motor running. I posted in a different thread trying to figure that out. I even loaded megatune onto a much newer laptop and get the same thing. Whenever the motor is running megatune freezes pretty quick. I can normally barely see if its rich or lean in a few bins before i have to start again to change the VE for a few more bins.

[drholl]

Here's how I solved my AE problem. I used the values from the build sequence (default). Boy that didn't work, but I know engines and it seemed to me there was too much AE. So I setup my AE for a TPS slider to 100% TPS, with "O"s in all the map bins. Then tried it again, bog city. Then put the slider to 50% still with "0"s in the map bins. Still too rich. I then moved the slider to 20%, oh yeah, that got me to where I knew about how much fuel it needed for AE. Then I read carefully and saw that the AE works on every squirt! Well my base fuel was 7ms per squirt, times 4 squirts = 28ms of fuel per engine cycle at WOT. The default was, I'm guessing here, 15ms, 10ms, 5ms and 2ms. but that was times 4! so a big stab was 60ms of AE fuel, plus my base at 100% (WOT) of 7ms times 4 per engine cycle. So I got 60ms AE plus 28ms of WOT fuel! 88ms of fuel. Three times as much fuel as the engine needed for WOT! And the AE only needs to last until the MAP kicks in and MAP takes over. Maybe 1 tenth of a second (0.1).
Oh yeah, that 88ms of fuel put the fire right out! My thinking is that the default is for 1 engine cycle on a 350 CI engine. And it needs to be divided by your number of squirts.

Holl