Mechanics

91 S10 4.3 TBI NIGHTMARE! PLEASE HELP.

1991 All Other Makes All Other Models

91 s10 4.3 186k miles. This thing is nuts! It's flooding it's self to death and I have exausted my resources.
It did this once before and the temp sensor front and center was bad, this time not.

I have a factory manual and best I can tell this thing should run. It sets no codes on ecm and the check engine light does not come on. When the aldl is jumpered it gives me code 12 only. Unless I induce a code by short/open temp sensor or unplug tps, or something like that, then it catches it and will display the proper code.

here are some statistics:

4.5v map sensor voltage output measured on pin at ecm

.5v tps reading at idle swings to about 4.8 smoothly while cycling to WOT measured on pin on ecm.

3.3 v across manifold temp sensor, measured on pin at ecm. Sensor reads about 3.5k ohms around 65 deg.

fuel pressure is 12 psi at TBI input.

plugged noid light to injector connectors and it pulses when cranked. Not on solid.

performed test on 4pin connector from distributer with test light to pulse the injectors / noid light and that worked fine.

I tried the ecm in a buddys 91 w/4.3 and my ecm ran his engine fine.

changed the ignition module because thats what gives the pulse to the ecm to fire the injectors. No help.

It has great spark and new tune-up

I did replace the distributer pickup coil with a junkyard unit not long before it started these shenanagans because the old one died and I had no spark. That fixed it and it ran fine for a couple of months after that.

It looks like you could take a shower under the injectors. I have seen the injectors operate properly making a nice cone shape of fine mist. They now are making almost a solid cone, Their really puttin it out!

Injectors do not leak a drop when unplugged from wiring harness.

Is it possible they can go bad and put out too much fuel but still switch on and off perfectly?

I am at wits end as my mom used to say. : Cry:
Avatar
K4ITF
March 23, 2007.




Check the injector wires at the TB, one or more may be shorting out on the TB, Or breather housing
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Tiny
Duder1
Mar 27, 2007.
Check this out as I don't have access to my manual until tomorrow to check this myself, but shouldn't the fuel pressure be 30-40 lbs.?

If the pressure is low, when was the last time the fuel filter was changed?

Tiny
Mcferrance
Mar 28, 2007.
I've checked the wiring to fuel injectors, its good and if I replace the injector (either one) with a noid light it blinks per the manual. And I can fire the injectors with a test light hooked to 12v on I think the purple/white wire (ref) on the 4 pin connector coming from the ignition module in the distributer. The manual says if I can do that the computer is good. I've went through the " enginecranks but will not run" in the factory manual, as for the fuel pressure, the manual says 12 is optimum. It seems to be flooding, kinda wishing the fuel pressure was lower ; -). I'm still poking at it though, I am going to buy another ecm, and maybe try a diffrent injector assembly from a junk truck my neighbor has.

Tiny
K4ITF
Mar 28, 2007.
This thing is still in my driveway and still broke! I put in another ecm and it does exactly the same. Is it possible for the fuel injectors to be bad even if they switch on and off great and don't leak? Their either on or off aren't they? Dosent the computer control the flow through them by pulsing them on and off at varying frequency? : Cry:

Tiny
K4ITF
Jun 29, 2007.
I know this is a old topic. Im just wondering if the user is still here and what did he find wrong with his blazer. I am having the same issues.

Tiny
Mrdonnie
Jan 28, 2010.

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