supertex

I just put TPI on my 93 chevy truck. My wiring harness guy informed me that it would be best in my case to use my stock computer rather than to swap for the "7730" (90-92 camaro). The reason behind it was that I could keep my 4L60E, rather than having to annie up the cash for a 700R4. I was told that the chip programmer had the proper program to make my computer run the TPI.

Unfortunately, there seem to be issues that accompany this combo. For one, it bucks (off and on) on deceleration. This isn't really too bad on the highway, but in residential areas, it is quite another story. Next, and my guess is that this is related....is the fact that it has a terrible surge at idle and low speed. I cant do 40 mph without contending with a nerve-racking, relentless surge that bounces between 500-1200 rpm, at about a 1 second hi-to-low oscilation. It is simply undriveable "in-town".

I originally put #30 injectors in the TPI (and the stock Z-28/Trans Am fuel pump), because I was told that they would run fine as long as the chip programmer was aware of the change, and also because I was advised that they would easily handle any future mods that I might make. Now I get told one place that the injectors are the root of my evil, yet the programmer tells me the aren't.

The only other mods that I have made was the insertion of the ZZ4 cam in place of the stocker, and L98 iron heads with 2.05 undercut valves. Originally I had used the SLP 51010, which I was advised was way too big. I was told that the ZZ4 was the best choice of shaft for TPI. I am really disappointed in the power that the machine makes. I don't really think that it runs as good as a stock 92 Z-28 or Trans Am. And I think with the cam and heads it should run at least that good. I wasn't anticipating a top-end screamer, but definitely a tire-fryer. It has neither.

I have to find answers for this. I replaced the distributor, and bought #21 injectors. I have yet to put the injectors in place because of the mixed signals I am getting reguarding their impact on the truck's condition. I have adjusted the IAC and TPS until I am blue in the face. Has ANYONE ever done this, heard of a problem like this, or know anyone who has? Is there a better forum to place this in?

I sure could use some expertise on this.

slyforrest

i trier it in my 88 chevy truck it is all a wast of time know alls i am useing is my tbi

Repo_agent

Use the original tpi computer. 700r4 can be found at a good price.

sub006

Anytime you mess with GM stock equipment combos, you will usually have problems.

I dropped a 383 stroker with Crane RV cam, Edelbrock intake and headers, etc. into my '90 Suburban. Kept the TBI but the computer couldn't deal with the extra displacement, World heads, etc.

My experienced and talented shade-tree installer got it to run ok with a Jet chip, but there was only a small increase in power over the tired 350 and gas mileage was bad. I drove it like this for a few thousand miles to break it in.

On the advice of my Corvette guru Dick Guldstrand I took the truck to Van Gordon and Scott, a performace specialty shop in Claremont, California that does NASCAR and street rod consulting.

Over the course of two days and 1/4 tank of gas, they pulled the Jet chip and wiped all the engine management computers clean. Then they ran it on a dyno, noting what fuel, air, etc. settings yielded maximum efficiency at each 500-rpm interval. After entering the settings, they road-tested it, fined tuned further, back to the dyno, more road testing, more dyno, etc. until it was as good as possible. They also corrected numerous small things like an air cleaner hot-air valve that would not close, a distributor that gave full advance 1000 rpm too late, etc.

$650 later I have the truck of my dreams. It burns rubber in drive and gets about four additional miles per gallon. As much as I drive the tuning will pay for itself in a little over a year.

Sounds like you're in Texas. Find someone local with the GM software and a dyno who can dial in your vehicle.