Cold start backfire

[Morten]

Hi, I have a tahoe 96 with the vortec 5.7, when cold start (temperatur around 40f) it has started to what I believe is backfire in the intake manifold, it cranks for around 5 sec with a couple backfires and then starts and runs perfect.

I have an engine heater installed, if I use that to heat the engine to around 65f it starts right up.

any idears?

Regards Morten

 

[Schurkey]

1. Crossfire in the distributor cap; or among plug wires. Distributor cap problems seem common with Vortec 5.7s.

2. Lean fuel mix--low fuel pressure, leaky intake gaskets sucking air, etc. Seems less likely if the engine runs good otherwise.

3. Leaky intake valves. Seems less likely if the engine runs good otherwise.

I'd verify fuel pressure, and connect a scan tool to look at coolant temp, fuel trims, MAP sensor, and distributor offset.

 

[Morten]

1. Crossfire in the distributor cap; or among plug wires. Distributor cap problems seem common with Vortec 5.7s.

2. Lean fuel mix--low fuel pressure, leaky intake gaskets sucking air, etc. Seems less likely if the engine runs good otherwise.

3. Leaky intake valves. Seems less likely if the engine runs good otherwise.

I'd verify fuel pressure, and connect a scan tool to look at coolant temp, fuel trims, MAP sensor, and distributor offset.

Thanks, just removed distributor cap and it is worn out, cleaned it and the truck fired right up cold, I will order new.

Regards