1994 5.7 tbi stumbles and backfire

[travis mattson]

I have a 1994 sbrc 2wd 5.7 tbi 4l60e.
It stumbles and backfires when accelerating. Does not do it in park.
Does not do it with the timing wire un hooked under the dash when driving or parked.
I checked the timing and is spot on from when I put the motor in, I painted the marks.
I put in a new cap /rotor, Spark plugs today.
Wires and 2 years old ( 10k miles). I also put new fuel pressure regulator in and jnjectors today.
I only drive this in the summer months . It would slightly do it a few times when I parked it and then when I got it out last week it ran like crap. Starts fine no ext crank, fires righy up.
I put a new motor 3 years ago and have replace most every sensor besides map.
NON of the parts I put in today affected it. Just the timing wire thing.

 

[Ryno3]

Firing order correct? Ignition module ever been changed? Have you tested fuel pressure? Compression test? Could be ignition or fuel issue, burnt valve, etc.

 

[1997]

any codes?
94's (OBD1) can set codes without the check engine light coming on.

next question would be, have you got a scanner?
if not, sounds like you're going to need (borrow) one, better than firing the parts cannon.

 

[travis mattson]

I have a new fuel pump in it and it runs fine and pulls hard with timing wiring unplugged

 

[Ryno3]

I would question the timing marks being correct or if the damper has slipped, retard the timing a few degrees at a time and see how it runs

 

[Schurkey]

1. How old is the gasoline?

2. Connect a scan tool, check for "codes", but mostly look at the sensor inputs and computer outputs. How old is the O2 sensor? Does the spark advance WORK?

3. Verify fuel pressure. A "new" pump can still be defective, or connected to corroded wiring that doesn't supply proper voltage/amperage. A "new" pump, pushing through a plugged filter will not work well--and there's no mention of you changing the fuel filter.

 

[travis mattson]

Replaced fuel filter and runs good. Actually truck runs better than I can remember, I put a new fuel pressure regulator assembly in and doesn't load up and surge at stop lights anymore. I put 305 injectors in too. It used run rich as hell. So maybe ill get some MPG again

 

[Schurkey]

Hard to know what's wrong when you need undersized injectors to fix "rich" running.

You NEED a scan tool to verify those sensors and outputs.

 

[PlayingWithTBI]

Hard to know what's wrong when you need undersized injectors to fix "rich" running.

Yeah, unless OP's fuel pressure was too high before replacing the FPR. How do we know it was running rich? Was the O2 sensor feedback always high? Was it throwing a code 45?

I'd put the 5.7 Injectors back in and fix it the right way instead of masking the root cause