Not sure if this is the right place to ask but I will try to be brief: My injectors are cutting out at WOT.... which is making drag racing very difficult. if I ease off the throttle the injectors start to fire again and if I gradually bring it to WOT they eventually stay firing, but this is really hurting my 1/4 mile times and making bracket racing this season troublesome. Starts just fine, idles just fine. In park it runs just fine, have even stabbed it to WOT and the injectors spray, part throttle is just fine. So now I am head scratching. any ideas??

Without some sort of data or better explanation it's going to VERY tough to explain whats going on.

Just an off the cuff guess is that your injectors are going static. What this means is that the ECM is asking the injectors to stay open longer than is physically possible. What happens is the injectors just go erratic and you loose all control of fueling. You said that it gets better if you let off the gas, this also further suggest what I'm saying as you will move to a leaner area of the fuel curve.

Try taking fuel out of the upper fuel table and see if it gets better. Of course if you really need all the fuel then you need to up the injectors size or fuel pressure so that you get your injector duy cycle back down close to 80%.

Can you give us a better explanation of your combo and what you have tried to do as far as tuning?? Do you have a WB? If so what are you seeing when this happens?

I don't think that's the problem, I have been using this set-up since 1999 years, trouble free and the fuel map was dialed-in years ago.

This issue appeared late last season.

I thought it was a bad/weak fuel pump,,,replaced it..but did not solve the matter. This started happening after I installed a 1" spacer, but I doubt that is the reason, all that could possibly do is cause a vacuum leak.

I would have to narrow it down to a bad TPS sensor or erratic tach signal.
What I need to do is get this thing off my trailer and put my street tires on then I can drive with my laptop and see what is going on in there.

After I find out what's wrong with it, I'll save the TBI system for a milder street project. I have been very happy with the system and almost broke into the 11s with it.

My next set-up will exceed the fuel capacity of the TBI system so it will be a simple carb with mechanical advance dist. and mech. fuel pump. Which is all an off road car needs.

Sounds like an interesting project, care to share the whole combo?

Is this projection setup a 2 or 4 barell? It wouldn't by chance have the black round caps on top of the injectors would it? Those chrysler style injectors were junk and would not take much more than stock fuel pressure.

It's the old 4Di system w/ 900 CFM TBI & (4) 85 # hr injectors.

I bought it a couple years before the Commander 950 came on the market.

This set up is good up to 600 horse and my current set up makes 465. (383 stroker, pump gas)

My new motor will be making around 750. (421 SBC, compression motor) I was thinking about upgrading to the Commander 950 and adding a 2nd TBI unit with injector driver but no one makes a dual quad intake for 18 degree heads..

I could switch to MPFI but by the time upgrade the ECM, modify the manifold, etc etc.. TO keep the budget down it's going to be a Carb.


I would not hesitate to use the 4Di on another project I am just exceeding it's capabilities. It would be nice to find the glitch so I can play around until the new motor is ready.