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TBI Backfire

Old 02-10-2019, 03:40 AM
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Car: 92 RS CONV
Engine: v6 3.1
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TBI Backfire

Just picked up this 92 Rs 305 with TBI. My first v8 Camaro. Plans is to rebuild trans and eventually swap in a beefy 350 Trans is bad so I'm gonna rebuild it but I want to get the motor running good before I pull it. So it idles good and sounds good. I can give it gas steady and doesm't backfire but if I stab the throttle it backfires and shoots out fuel I think. I read that It could be a wiped cam lobe. If so I wanna swap the cam out while I have it out of the engine compartment. I might as well do it right? Even if it's not a wiped cam lobe. What do you guys think?

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Old 02-10-2019, 09:06 AM
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Re: TBI Backfire

First two items to check: fuel pressure and base distributor timing. For fuel pressure test attach the gauge near the TBI unit (need an adapter), Then do the same as you were whacking the throttle open. There must not be any drop in the pressure when doing this.

If the pressure drops, even a little, there is a fuel delivery issue. Note that the service pressure is 9 - 13 psi.

For the base timing, warm up the engine and open the EST/BYPASS connector (over by the HVAC unit, tan with black stripe). Stock timing is 0, can bump it to 2 BTDC.

Instead of just swapping the cam on a hunch, Do a compression test. If the engine is OEM stock, it is a roller cam so very doubtful there will be a wiped lobe.

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Old Yesterday, 01:20 PM
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Join Date: Sep 2014
Location: Los Angeles
Posts: 414
Car: 92 RS CONV
Engine: v6 3.1
Transmission: 700r4
Axle/Gears: Torsen Zexel 3.42
Re: TBI Backfire

I ordered me an adapter and fuel pressure gauge. Should be arriving soon. If it was a cam lobe would it make a clacking sound? It doesn't make any weird noises. Sounds very good. Anyways was snooping around and I noticed the ignition coil is loose, like its on its bracket but not bolted down completely. I'm pretty sure that could cause some some similar symptoms. Gonna be checking timing this weekend. So I'm gonna do full tune up and go from there. What CA legal headers would you recommend for this 305?
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Old Yesterday, 02:20 PM
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Re: TBI Backfire

ignition coil is grounded through the bracket so if its loose... definitely fix that.

Some simple things to check while you are waiting on your tools to arrive...
How old is the gas?
Do a visual inspection for any broken, cracked, missing vacuum tubes.
Spark plug condition, and gaps
Spark plug wires
Rotor button and distributor cap (especially the contacts on the inside of the cap)
PCV valve (take it off and see if it rattles, or just replace it as I would no matter what on a car that is unknown to me)
Fuel filter (again I do these on any used car I buy anyways)

Make sure both injectors in the TBI are spraying when you hit the throttle. And the spray pattern is a nice cone. Also spray some starter fluid or carb cleaner around the base of the TBI to make sure you don't have a leak there (the engine will surge when you hit it with the spray if there is a leak there or in one of the vacuum tubes.

The TBI doesn't have a fuel port to test the pressure you will need an adapter that goes on the fuel line for the test.

If it has been sitting for a while you could have a sticky lifter or sticky valve guide.
O2 sensors (or leaks around the 02 sensors)
The cat if original to the car is probably starting to fall apart inside and that also doesn't do good things.

With the cat off my old L03/TBI it would pop some on idle down if you floored it, not quite a back fire though, more like the popping in Ferrari and performance BMW's

I wouldn't try to put headers on the 305, save that money for the 350 swap if you are serious about that.
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