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View Full Version : Truck back fires through TBI


adam90
12-01-2002, 09:20 PM
Hello, I have a 1989 chevy ton truck 4 x 4.(454,manual,tbi)
It starts great, Idles great, and usually runs great.
The problem I have is when you hard accellerate it will back fire through the tbi. I took the air cleaner off and the tbi was black,real black!!! I replaced the fuel filter which was clogged bad. Also I replaced the fuel pump and spark plugs earlier this year. If you drive the truck easy it's ok? I checked the injectors, they both had 1.6 ohms (for 90lb. injectors) Is that good or bad?There is no check engine lights on. I think injectors or computer are bad?How do you check the computer? The truck has 160,000 miles on it. Need advice or hints on What to do? Thanks

82_camaro_owner
12-01-2002, 09:24 PM
i hope you cleaned it after noticing it was dirty

timing could be retarded to the point it does that

exhaust could be clogged, egr could be be messed its so manythings can you be more specific?

fotw
12-01-2002, 09:34 PM
Still new to the game, what is a TBI?

Trader Ray
12-01-2002, 09:38 PM
Throttle Body Injection

fotw
12-01-2002, 09:41 PM
thanks, might as well ask. Like I saw I dont know much about new cars what is the differance between TBI and regular fuel Injection. What is the pros and cons of it?

Trader Ray
12-01-2002, 09:42 PM
the computer can be scanned by using a key that is free at places like auto zone, advance auto, it comes with a free book also,
check the codes for the oxegen sensor

adam90
12-01-2002, 09:46 PM
The truck idles great, you could stick a glass of water on the air cleaner and it hardly shakes. Also the truck has power under load. It pops sometimes not always, I will check egr valve. Does 1.6 ohms sounds right for the injectors? Thanks for the advice.

thecarguy
12-02-2002, 01:47 AM
Originally posted by fotw
thanks, might as well ask. Like I saw I dont know much about new cars what is the differance between TBI and regular fuel Injection. What is the pros and cons of it?

i consider TBI to be poor mans fuel injection. Its almost like a carburator. With other form like TPI (tuned port injection) or MPI (multi port injection) there is an individual injector for each cylender. TBI just has one injector at the top of the manifold.

danny
12-02-2002, 10:30 AM
pull off the valve covers(only one at a time) and make sure that all of the rocker arms are moving the same distance when running. it is possible that you have a valve sticking or not opening very much allowing for the compression to escape under acceleration through the intake valve.

adam90
12-02-2002, 01:19 PM
Just got done checking the EGR system it checked fine also the solenoid valve checked is in good condition. The pvc valve is new. I double checked timing (0 degree) with the EST plug back in its running at (12 degree) the truck has 160,000 miles on it and injectors have to seen better days? My 1990 corvette need new injectors at 80,000 miles. Wow what a difference that made.
I'll have to find specs on timing to make sure there right. I'll pull the valve covers off if I can't find anything else wrong. I like to do the easy stuff first!!! Thanks.....

justen
12-02-2002, 10:55 PM
TBIs can make a backfire sound through the carb from fuel filter getting plugged, a dirty injector, and also timing, And it can also backfire if the lobes on the cam are wore off, but my guess is try a new fuel filter, usually your only get a backfire through the tbi under hard acceleration or you'll notice it in overdrive. Start out cheap and replace those parts, then work your way up to figure it out.

adam90
12-02-2002, 11:21 PM
I put a new fuel filter in this week, I could not blow through the old fuel filter at all. Really surprised it ran at all? Took the truck for a drive and it really help but she pop once on me again but not as much as it did before. Tomorow I am going to pull injectors. The computer is fine had it checked out. If I had a stuck valve the engine would have to run, bad real bad and pop all the time. Thanks for all your replys!!!

Trader Ray
12-02-2002, 11:32 PM
I believe the fuel line pressure is at 90 lbs, you would not /should not be able to blow through it, even a new one.

adam90
12-02-2002, 11:35 PM
The new one I could blow throught it very easy.

Trader Ray
12-02-2002, 11:39 PM
was it a steel filter, and the lines bolted to it?

adam90
12-02-2002, 11:42 PM
Yes, you had to use a wrench to tighen or losein them up.

Trader Ray
12-02-2002, 11:49 PM
I figured with a high pressure fuel system that a person would not have the power to blow through. Learn something new every day.

Southtowns27
12-02-2002, 11:51 PM
I had a Blazer with a 2.8 V6 and TBI that used to do the exact same thing. It turned out that the heat riser tube from the exhaust manifold to the air cleaner was gone....literally. I replaced it and it was fine after that. It was a $4 fix. Double check the timing again and make sure none of the plug wires (especially 5 and 7) are crossfiring. Start it up in the dark and look at the wires to see if they are arcing onto each other or to ground. Also, pull the distributor cap off and check for signs of arcing and carbon tracking. It will look like someone drew a line with a pencil on the inside of the cap if it is arcing. Good luck

Trader Ray
12-02-2002, 11:59 PM
with the cap off, check the play in the timing chain by turning the crank pulley back and forth while watching the rotor, it should be a direct response movement, if you are getting a lot of play there the timing chain and gears may need help.

danny
12-03-2002, 12:00 AM
tbi is not high fuel pressure

Trader Ray
12-03-2002, 12:08 AM
I had only one or two vehicles with it, one was a 87 safari, I had a little trouble with a newer Cherokee though, it had a real high pressure system.

adam90
12-03-2002, 11:55 PM
Hello everyone, I pulled the tbi off and clean it up, pulled the injectors and rechecked with ohm meter both were the same. Reassembly everything, My heat riser tube was missing and I replaced it, didn't think it was important but its on now. Also change timing from (0 degree) to (4 degree) BTDC. The timing was off a little. Jumped in the truck today and the POP is gone!!! I guess it was a couple of things timing, plug fuel filter, heat riser tube, air cleaner, and dirty tbi. The truck ran great today, even in the snow in 4x4. I have to thank everyone who replied to my topic. You guys got me going in the right direction....and alot of ideas....Great place to come if you need help.... Thanks again hope to return the favor..

olds fan
12-04-2002, 12:28 AM
glad to hear it, I too have had some things addressed here and have learned a bundle.

lou
12-08-2002, 09:32 AM
fuel pressure should be 9 to 13 pounds on a GM tbi, popping from the tbi indicates a lean condition on the intake side possible vacume leak causing it to go into a lean condition , try takeing a propane touch NOT lit and open the valve move it around the intake and the base of the tbi , if rpm increases you found your leak

cvgrappler
12-08-2002, 01:29 PM
I'd have to disagree with whoever said that Throttle body injectors are the poor man's fuel injection. We have a suburban with a 454 in it and at first i though it was strange that it had a carb on it for such a newer vehicle... after some research i found that all GMs with 454's come with TBI stock... there may be some aftermarket fuel injection systems that aren't TBI ... but i haven't found one yet.

Daniel Wood
12-08-2002, 06:46 PM
Originally posted by adam90
Hello everyone, I pulled the tbi off and clean it up, pulled the injectors and rechecked with ohm meter both were the same. Reassembly everything, My heat riser tube was missing and I replaced it, didn't think it was important but its on now. Also change timing from (0 degree) to (4 degree) BTDC. The timing was off a little. Jumped in the truck today and the POP is gone!!! I guess it was a couple of things timing, plug fuel filter, heat riser tube, air cleaner, and dirty tbi. The truck ran great today, even in the snow in 4x4. I have to thank everyone who replied to my topic. You guys got me going in the right direction....and alot of ideas....Great place to come if you need help.... Thanks again hope to return the favor..

Even the people that work on vehicles all of the time picks up something here and there. You also need to check with BigBry and see why your post numbers aren't going up. Just a suggestion

fotw
12-08-2002, 06:50 PM
And if you are new to cars like me it is a great place to learn