Chevy TBI tuning help

[Truckedup]

So I bought the S10 with the 350 SBC...What we got is 1992 that had the 4.3 5 speed replaced with a 1995 350 from full size truck retaining the existing NV3500 gearbox.The swap was done nicely and looks like original equipment. No butchery to be seen...The seller said 350 was not modified ...So it's a 210 hp lump with small tube shortie headers and an adequate two into one Y pipe similar to stock ,2-1/2 single exhaust..The engine is mechanically quiet....good oil pressue. etc...
Problem...The engine starts quickly hot or cold but it runs rich at idle with the soft random misfires but does not loadup so bad it stalls. The seller did the work and claims the TBI unit and ECU/prom are the 4.3 items.......Looking up info it seems rich idle is a sure sign of using the 4.3 items instead of the correct 5.7 manual trans prom.......The 02 sensor may not be hooked up....
Supposedly the 90's TBI's can handle moderate tuning changes and there are custom chips available .This is no high performace engine but I want to work out the tuning...
But first I'll check compression, timing and be sure the cam is not worn......
I prefer to keep the TBI and not use a carb..........
So,what do you think?

[BOOT]

https://www.gmt400.com/

[rebelrouser]

If the prom is for a 4.3 V-6 why would you think it could even work right? The prom simply tells the computer what engine it has, so you now have two extra cylinders, and off the top of my head I don't know if the sensors have the same values, injectors the same resistance, and the idle speed motor is the same. The first biggest issue is the resistance of the injectors, the injector drivers in the computer are designed for a specific resistance, that has to be right. Next is to fire the injectors and ignition it looks at the cam and crank sensors, which is now getting 8 pulses instead of 6.
If I was going to try and do this cheap, I would hunt up a PCM and prom for a V-8 similar to what you have. But before that I would go to an information system like All-Data and pull up a connector view of the 6 cylinder computer, and of the V-8 computer and make sure all the wires and pins are the same. They sometimes change wire and pin locations by year, been there and done that. Bad thing is the prom can be flashed if you have the equipment, but not a lot of people still do that. And HP programmers only do 1996 and newer computers, which would make things much easier to deal with, you could go in and fix it in a couple hours.

[1980RS]

I have a 305 TBI truck right now and it's stock and like most of those old FI engines of their day run rich at idle, only way to fix it is to re-chip it. We had lots of "my car won't pass emissions" crap back in the day at our dealer and almost every time a chip from GM fixed it as there wasn't much to change. One thing that did make them run cleaner was adding more alcohol in the fuel mix (isopropyl) and that helped. Headers IMO do not play well with the old TBI system unless you are using a heated O2 sensor as the single wire sensor just will not heat up fast enough. One thing I like about this old 305 TBI truck, it gets great fuel mileage way better than my 350 TBI truck ever did.

[Truckedup]

If the prom is for a 4.3 V-6 why would you think it could even work right? The prom simply tells the computer what engine it has, so you now have two extra cylinders, and off the top of my head I don't know if the sensors have the same values, injectors the same resistance, and the idle speed motor is the same. The first biggest issue is the resistance of the injectors, the injector drivers in the computer are designed for a specific resistance, that has to be right. Next is to fire the injectors and ignition it looks at the cam and crank sensors, which is now getting 8 pulses instead of 6.
If I was going to try and do this cheap, I would hunt up a PCM and prom for a V-8 similar to what you have. But before that I would go to an information system like All-Data and pull up a connector view of the 6 cylinder computer, and of the V-8 computer and make sure all the wires and pins are the same. They sometimes change wire and pin locations by year, been there and done that. Bad thing is the prom can be flashed if you have the equipment, but not a lot of people still do that. And HP programmers only do 1996 and newer computers, which would make things much easier to deal with, you could go in and fix it in a couple hours.

I never thought it would function properly but it does run and can sorted out .....From what I can read about, the differences are not so much the injectors as having the correct prom...

[In-Tech]

Hiya Trucked,
I need pictures of ECM and connectors to determine which one you have. Is the TBI from the v6 or v8? I can do the eprom chip work to get you close, nothing like being there with my emulator to dial it in 100% though.

[Truckedup]

Hiya Trucked,
I need pictures of ECM and connectors to determine which one you have. Is the TBI from the v6 or v8? I can do the eprom chip work to get you close, nothing like being there with my emulator to dial it in 100% though.

I was told by the seller the ecm and TBI are from the 4.3 engine...I will be picking up truck this Wednesday so will take photo....Is the ECM under the dash ? I really appreciate you help...

[In-Tech]

Hiya,
As far as I know, the tbi v6 injectors will be too small for your v8. I look forward to seeing which ecm you have. The sticker on the ecm will give me a better clue and I should be able to research the eprom from there. I have not done a bunch of s-10 stuff. I think the ecm will be on passenger side behind the dash. You might want to start looking into that now so you will be ready.

[Truckedup]

Some guys use a availalable pump that increases fuel pressue to a steady 14-16 psi...A lot of conflicting info out there..

[In-Tech]

You will definitely need some eprom tuning and I will help all I can for you. We are hemi kindreds

Side note, I have always wanted to fish some trout from the finger lakes. Nothing like cooking up one on the fire at the shore

Here's some variants from Calif. https://wildlife.ca.gov/Fishing/Inland

Do you have a favorite there? We might have to do some trade

[Truckedup]

I'm not much of a fisherman...Generally at this time of year the lakes are ice covered with cycle ice racing...Snowmobiles roaring around...drag racing sleds with 1000 hp.....But no snow at all..Not the first time but it is unusual Yup, hemi heads, lol....

[mt-engines]

Could be your timing. Verify that first.

[dfarr67]

Your on the TBI fuel regulator can be modified to adjust PSI, but you need the proper in tank electric fuel pump.
Thirdgen.org and GearheadEFI have tons of TBI info, DynamicEFI has a few cheaper options for tuning. Both sites have a few venders that can make a tune for you.
If its truly 1995 TBI- I believe that one year before CPI had a high pressure TBI- so a TPI pump would work out.

[Truckedup]

Many specs online stating the 4.3, 5.0 and 5.7 have the same 42mm throttle bores....The injectors do have differerent parts numbers....Any here seen this as a fact....?

[rebelrouser]

I have found the specs on the internet, do a search of the part number on the injector to get the flow specs. You can check the resistance of the inject with a simple digital volt ohm meter. As long as the resistance is close it is OK. This website has some info.
https://www.enginelabs.com/engine-tech/ ... reference/