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TBI Trouble...Backfiring?

B_to_C

B_to_C

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My trucks engine is a 1990 5.7 liter serpentine setup TBI motor...

A couple of weeks ago I started noticing that while driving at a constant speed on the highway there would be a sudden jerk (like the truck died for a millisecond) but then everything would continue like nothing happened. I kept my eye on the tachometer and noticed minimal disturbance (not even 100rpm difference when the truck "jerked").

Over the last couple of weeks the problem has been getting progressively worse. As of today the engine sputters during acceleration (like if it was carbed I would say it was flooding on acceleration) and then "backfiring" while cruising at a constant speed.

-My "check engine" light has not come on

-My truck has 153,000 miles on it...could this be the time for new injectors?

In a possibly unrelated situation... a couple days ago as I started to drive the 4 minute drive to school I noticed a faint squeaking coming from the front end. By the time I got to school it was a LOUD squeaking...only on acceleration. I replaced the alternator and idler pulley today thinking that the bearings in one of those was probably the cause of the sound -to no avail. it doesn't do it everytime I get on the gas, but never does it while idling or "reving up" the engine while parked or while cruising at a constant speed down the road.


Couple random facts:
-My air cleaner is extremely dirty
-I replaced my fuel filter within the last year
-My exhaust has had a serious leak just after the O2 sensor for several months

My current guess is: a loose motor mount or some other loose bolt in or around the engine compartment that squeaks now because it loosened up a bit.
 
It sounds like it might be an ignition problem. When is the last time you gave this truck a tune-up?
 
sqeaking could be tranny tcase mount. as for the TBI Id grab some fuel injector cleaner, and run it through. Plugs wire etc. the normal stuff
 
last time mine did this, the injector was dying,,,EXACT same thinig,,,engine just sorta cuts out for a split second, to fast for you to really do anything about it.

then one day, it just wouldn't start.

then another day, it would,,,

then another day it would start


get my drift?:doah:
 
guess!...

Might be an ignition module or pick up coil failing ...loses spark momentarily,then it fires it off in the exhaust...I assume its backfiring out the exhaust,and not thru the intake??..

As for your squeal,I replaced a clutch trowout bearing in my moms old 1964 Ford "Custom" many years ago,because I thought the throwout bearing was seizing up..sounded like a combination of belts squealing,and a goose caught in the belts,but it would only do it once in a while,usually under acceleration!..I replaced everything,a suck job..went for a ride,and it was silent..UNTIL I GOT HOME!..as I pulled in the yard,it did it AGAIN!..only LOUDER!!..

I spent half a day under the hood with a rubber hose stuck in my ear for a stethascope..finally it made the noise again as I was racing and letting off the throttle..it was a intake manifold gasket!!..its manifold was warped,and it let the gasket vibrate at certain RPM's,like a kazoo,wax paper on a comb kind of sound!...no wonder the old clutch looked perfect,and the T.O. bearing felt fine when spun by hand!..:doah: ..

A vacuum leak might cause backfiring too....might be worth looking into,before blaming ignition or fuel..:crazy:
 
I assume its backfiring out the exhaust,and not thru the intake??..
Click to expand...

It was the mention of backfiring, which caused me to think the problem was ignition related too.
 
Thanks guys, all your replies are helpful. What do people think about the injectors going bad? Is there a way to test them?Napa wants $122 each :eek1: . But I figure if I could narrow it down to that I wouldn't have to go through the stages of a complete tune-up, fuel injector cleaner, searching for vacuum leaks etc. :dunno: Or should I start with the stuff that costs less and hope that fixes it?

:1zhelp:
 
Or you could take it in and see if it's flagging a code. Since I'm new to TBI I can only hypothesize. Look at your injectors while actuating the throttle, check for an even pattern. :dunno:
 
OH...Oh....I know....I know.
Your distributor is coming apart. The housing that contains the windings that are under the rotor is broken. It will slowly destroy itself untill it will no longer start. One of the last clues will be that the idle gets really high.

My 90 Burb did that. Still havent replaced the dist.
 
If you want to see your spray pattern of the tbi injectors,try shining a timing light at it.It shows a uneven pattern well this way as opposed to just looking at it while running.---A vacumn leak could cause lean misfire as well as the squeak stated before.A lean misfire would backfire out of the intake,generally when you hit the throttle hard.---The jerk when cruising,I would look at the ignition.Try misting water on the wires while running,you'll see the spark jump to ground if there leaking/bad.Look in the distributor cap for carbon tracking and arcing.
 
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