88 5.7L backfiring through TBI

ericinga

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This started out as an intermittent SES light with the engine occasionally stumbling under acceleration. The only code was 12.

Now, the engine back fires though the TBI and has little to no power. Fuel pressure is good. Plug wires are fine. Cap and rotor look good.

Had a spare ignition module on the bench. Tried it and no improvement.

Could it be as simple as the pick up coil? How would I test it?

Eric
 

PlayingWithTBI

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I'd be checking timing first.

Yep, these engines like to be advanced for better performance. You can do it in the bin SA table or initial set up by disconnecting the wire coming out of the harness below the junction block on the passenger's side fire wall. OEM is TDC, try up to 8*BTDC.
 

Schurkey

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This started out as an intermittent SES light with the engine occasionally stumbling under acceleration. The only code was 12.
Never mind codes. What is the data stream telling you? Knock sensor active? What is the short- and long-term fuel trim numbers? What is the coolant temperature? Manifold pressure? O2 voltage and cross-counts?

Now, the engine back fires though the TBI and has little to no power. Fuel pressure is good. Plug wires are fine. Cap and rotor look good.

Had a spare ignition module on the bench. Tried it and no improvement.
Do all the exhaust valves open about the same amount?

Broken valve springs?

Exhaust valves that don't open, and intake valves that don't close will both result in popping in the intake manifold.

Mis-routed spark plug wires can also cause intake backfires, if the spark ignites the mixture when the intake valve is still open.

Lean fuel mixtures can cause intake pops, but typically only on acceleration.
Could it be as simple as the pick up coil? How would I test it?
I don't think that's likely...but I suppose it's possible.

There's no good tests for pickup coils that doesn't involve an oscilloscope. You can connect an ohmmeter to the leads. The ohmmeter can tell you that the pickup coil is bad. The ohmmeter can NOT tell you that the pickup coil is GOOD.
 
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