Another Back firing thru Intake

[North New Jersey]

Loosing my mind. I have been a tech and hotrodder for over 30 years.

I did search the forums before posting.

He is my problem. It literally looks like a jet car at the track when i lean into it. Whether in park or on the road trying to do a small climb up a hill. Sounds like it wants to blow the intake off the truck. Huge fire balls from the tbi.

1993 5.7 new heads, idle vacuum of 21 inches, fuel pressure 11 psi, TBI spray pattern looks ok with timing light, Timing dead on. , it will rev to 6000 rpm.Craziest ****.

Replaced new plugs, new wires, new coil, new coolant sensor, new map, new distributor ,new ecm, new tps, new timing chain, 4 new ground loops at the thermostat, new ground from thermostat to frame, new ground from abs module to chassis, new ground from battery to engine block, new ground from battery to fender. Spent plenty of money, im about to pull out the engine and junk it. Only thing i haven't replaced is TBI and knock sensor.

ARGGGGG

 

[PlayingWithTBI]

Put it on a scanner and see what's going on when it backfires or lean pops. Did you check fuel pressure when it happens? 11 PSI is OK, 13 is better.

 

[thinger2]

Loosing my mind. I have been a tech and hotrodder for over 30 years.

I did search the forums before posting.

He is my problem. It literally looks like a jet car at the track when i lean into it. Whether in park or on the road trying to do a small climb up a hill. Sounds like it wants to blow the intake off the truck. Huge fire balls from the tbi.

1993 5.7 new heads, idle vacuum of 21 inches, fuel pressure 11 psi, TBI spray pattern looks ok with timing light, Timing dead on. , it will rev to 6000 rpm.Craziest ****.

Replaced new plugs, new wires, new coil, new coolant sensor, new map, new distributor ,new ecm, new tps, new timing chain, 4 new ground loops at the thermostat, new ground from thermostat to frame, new ground from abs module to chassis, new ground from battery to engine block, new ground from battery to fender. Spent plenty of money, im about to pull out the engine and junk it. Only thing i haven't replaced is TBI and knock sensor.

ARGGGGG

That does sound like a timing problem.
But, if you replace a bunch of different TBI components they all need to be "reset" and they need to be reset in a certain order.
Remember, the gm ecm is pretty dumb.
You need to start with tripple checking the base timing.
Is it actually at tdc by checking the piston. not the timing mark.
One tooth off or a slipped balancer will screw you up.
Set timing at 0 with the dist reference wire unplugged while it is warm.
You may run into a open loop/ closed loop issue later but that is an easy fix.
Once you are absolutly sure beyond a doubt that the timing is right.
Then you need to look at ecm inputs
You can replace a whole bunch of parts on a tbi and end up with a situation where it just firehoses fuel down the intake.
TBI systems really like just one part and one reset at a time.
When you chuck parts at it. You are setting up a relearn parameter that the system isnt designed for and cant compensate for.
It can take a lot of screwing around to figure out that ecm logic chain.
And those old flow chart diagnosis manuals are getting rare.
If you are dead sure beyond any doubt that your timing and dist and cam and crank are valves are correct.
You have an ecm problem.
Wich is likely a series of problems due to sensors out of range/ uncalibrated etc..
That said, ive never seen anything shoot flames out the intake without it being a timing problem

 

[eran tomer]

if it's a standard engine it shouldn't reach 6000 rpm... maybe your tachometer is faulty, or the distributor gives false reading (maybe it's part of your problem).
could be valve timing fault. does it sound like this?
https://www.gmt400.com/threads/suburban-95-5-7-engine-is-gone.54672/

 

[Pinger]

I have a Vortec running on LPG (propane) and when I get inlet backfires it is because the mixture is too lean - and if/when they occur, it is always on initial application of the throttle.

Another member here had backfiring problems that traced to inlet valves not closing properly. You might have a sticky valve where there's enough time for the flame to get past it at low rpm but not at 6000rpm. A compression test would find it if the case.

 

[Schurkey]

I'd be looking at a leakdown test, and pull both valve covers, to find intake valves that are burnt or don't close/broken valve springs, or exhaust valves that don't open--wiped cam lobe/lifter, bent pushrod/failed rocker arm.