Specs:
8746
454 TBI
388 Chevy Small Block

Problem:
On heavy acceleration from 0 mph, I get this loss of power and my O2 shows it get leaner also (approximatly 13.5:1). It will lose power from 4000 RPM to 4250 RPM, then from 4250 to 4500 full power, then 4500 to about 4750 loss of power, then 4750 on its full power.

-RPMs are approximations(although it pretty accurate at the 4000 rpms cause I am starring at it first).
-Adder fuel table is smooth, no crazy leaps.
-SA tables are all zeroed out and I am running a "mechanical" map in the main SA table.
-Eliminated slope by maxing it out (6375 RPM) and slope added is 0 degrees.
-Timing at 3600 rpms is 33 degrees. I am getting NO knock counts.
-Been adding more fuel, added about 15 VE since the problem started.
-Fuel pressure hangs out at 18 PSI and running 91 w/ booster (9:1 CR)

WTF I don't want to carb it, I hope it doesn't come to this. I have invested way to much into tuning.

 

Sounds like the injectors may be going static. Are they 454 injectors? Raise your fuel pressure up and tune the VE again I would say. I've heard of a few people encountering very similar fueling problems. I think RBob corrected this in his TBI code if I'm not mistaken. But anyway, what size injectors?

 

I am running the stock 454 injectors (err, the ones that came with unit when I got it, don't think they got switched out since I got it from the school lab brand new). Desktop dyno claims my engine should be making over well 300 horsepower. From the drag strip calculations, I am only making 280 at the flywheel, and I am sure this problem has to do with not making its potential. My VAFPR is almost maxed out, I can try to give it some more, but the lock nut is running out of threads. I am staring my carb down w/ an evil eye, help me!

 

Well, you can get a stiffer spring to run in there to give you a little more room to move. What fuel pump are you running? The injectors depend a lot on the year of the TBI unit, are there color codes still on the injectors? I would definitely try boosting your fuel pressure up a little ways and adjust your BPW constant accordingly, then see if the problem is at least lessened.

 

Do you have a WB? I had somthing very similar happen to me, except when I hooked up the WB it showed the AFR going rich while the NB showed lean....very confusing to tune around. Once you get your PW down to reasonable levels this will all go away. You need to take a look at this thread, https://www.thirdgen.org/techbb2/sho...hreadid=210908
there is some good info on how to get your PW to spit out your ALDL, it's also a good example of how a WB will save you a lot of time and headaches.

 

I am running a TPI pump with a Mallory VAFPR. The injecters appeared to have black as the color, but mostly no paint on it. I will bump the pressure up this week and try it out again. Thanks for the help!

It is also a problem cause I am running a NB O2. My A/F guage reads full green (.950 volts) and when it starts to cough it goes to yellow/green (.890 volts) and jumps back up when it gets its power back. I really do want a WB, it is definatly on the list (just got new job $3 raise), until then I have to rely on something not reliable to get me close.

I hope I can stick with this unit, I am upgrading my intake and cam to something a lot more aggressive (single plane race and big cam).

 

what year is the GM TB? 1995-1996 ran 45 lbs injs at high FP. post the injector part numbers.

not sure if anyone is running a VAFPR any longer. might be a chalange to tune. i tried one for a month before i went to tuning.

i would cease the heavy throttle action till you can confirm your not uber lean at WOT.

 

I actually have the computer tuned with everything acrossed the board having 125-128 BLMs with the VAFPR. Its just that WOT glitch in the system, I will get the part numbers for the injectors up ASAP, I am really hoping that is the problem.

 

when in PE the BLMs wont tell you anything. before i had a WB i ran dyno with WB and my 128 or so BLM's and commanded 12.5 PE turned out to be 12.0/1 WOT so in that respect getting the BLM's at 128 worked out for me in PE-WOT. there is a basis that underlying tables affect PE. however that was W/O the vafpr. there is no way of knowing what the A/F ratio is at WOT W/O WB log. i run a VAFPR(disconnected) and may hook it up just for kicks and read A/F but i chose to not to. i dont think i would have control of PE if i do. maybe someone can explain what circumstances are required to benefit from the vafpr. over 383 or 383 with larger cam?

 

Here are the numbers off the injectors:

GM17084304RPD 4162 GM --> Pass

GM17084304RPD 4212 GM --> Driver

Anyone know what they are?
Googles got nothing, but still searchin.

 

from diy-efi:

Blue/Black
Late big block pickup
80 lb/hr
GM 1708430 *RPD

 

those sound like winners to me. somewhere it was said the 80's are better quality(X2) over the 90's. two different manufacturers for GM?

 

This problem could be related to my head gasket being blown or cylinder wall cracked. My engine oil is green milk. Should be up and running in a couple weeks (probably a 305 for now).

 

Yeah, engines don't run very good on anti-freez. They also don't run good without oil pressure either, ask me how I know