2003 Silvy 2500 Hd

[RJG183SA]

Iam having ongoing intermittent cold start issues w/ my 2003 Chevy 2500 HD, 6.0 auto. w/30k well maintained miles. It first started a week ago. I had run my fuel tank very low, to the point of activating the "Low Fuel Warning" on the DIC (not the first time I must admit). Went to my usual gas station and pumped in about 10 gals., returned home and parked the truck for the night. Overnight temps fell into the 20's. Heres when the fun begins.

 

While attempting to start the next morning, excessive cranking required to start, engine fires then stalls. After several attempts engine starts but throttle input is required to maintain idle. Engine continues to misfire and run roughly until temp comes up and gradually smooths out, running normally in closed loop. The truck runs and performs perfect under various engine loads and throttle inputs including WOT, with no apparent fuel starvation or hesitation during closed loop mode.

 

This scenario has repeated 3-4 days over the past week. Only on initial start up in the morningbut not consecutive mornings. Subsequent start ups throughout the day are normal. No DTC have set, with the exception of a flashing MIL (indication of misfire) that resets upon restart.

 

To date I have added 2 containers of "fuel line anti-freeze additive" (alcohol based) and changed the in-line fuel filter. No effect on start up issue.

 

My plan is to continue looking at the fuel delivery system, fuel pressure, pump, regulator, and injectors. Also the sensors that communicate w/PCM during open loop mode i.e. MAF, ECT, TPS.

 

Please chime in w/your tips and or advice. Thanks.

[RJG183SA]

Iam having ongoing intermittent cold start issues w/ my 2003 Chevy 2500 HD, 6.0 auto. w/30k well maintained miles. It first started a week ago. I had run my fuel tank very low, to the point of activating the "Low Fuel Warning" on the DIC (not the first time I must admit). Went to my usual gas station and pumped in about 10 gals., returned home and parked the truck for the night. Overnight temps fell into the 20's. Heres when the fun begins.

 

While attempting to start the next morning, excessive cranking required to start, engine fires then stalls. After several attempts engine starts but throttle input is required to maintain idle. Engine continues to misfire and run roughly until temp comes up and gradually smooths out, running normally in closed loop. The truck runs and performs perfect under various engine loads and throttle inputs including WOT, with no apparent fuel starvation or hesitation during closed loop mode.

 

This scenario has repeated 3-4 days over the past week. Only on initial start up in the morningbut not consecutive mornings. Subsequent start ups throughout the day are normal. No DTC have set, with the exception of a flashing MIL (indication of misfire) that resets upon restart.

 

To date I have added 2 containers of "fuel line anti-freeze additive" (alcohol based) and changed the in-line fuel filter. No effect on start up issue.

 

My plan is to continue looking at the fuel delivery system, fuel pressure, pump, regulator, and injectors. Also the sensors that communicate w/PCM during open loop mode i.e. MAF, ECT, TPS.

 

Please chime in w/your tips and or advice. Thanks.

 

UPDATE:

 

Today I ran a scan to establish some baseline data and obtained a static fuel pressure reading of 50 psi @ the fuel rail (ignition on, engine off). The spec is 55 - 62 psi.

 

Pressure bleed down, 2 psi after 10 mins., is within spec. (I did not isolate the fuel inlet/return lines).

 

I then started the engine. The rough idle / misfire still present and required throttle input to maintain idle. I used the scan tools “capture mode” to obtain additional data. Shut down the engine after apprx. 1-2 mins. run time.

 

So at this point I take about 20 mins. to compare baseline scan data to the capture scan data. While reviewing the throttle position reading of 20% (baseline 17%) I start to cycle the gas pedal, no input = 20%, pedal to the floor = 99%. Seems ok to me. I do this 4-5 times. I then crank the engine. It fires up and runs perfectly, no stumble, rough idle or misfire. Hmmm? TPS? I let the engine warm up and transition to closed loop mode then shut it down. What happened next seemed odd.

 

After shutting the engine off I recheck fuel press. Its 52 psi and increasing. It stops at 56 psi. Huh? Is this normal? Is the fuel system being pressurized by a cylinder through an open or defective fuel injector?

 

So I replace the fuel press. regulator with a new one. Static pressure is now within spec. (56psi).

 

My questions are:

 

Will a loss of 5 psi fuel pressure create a lean start up condition?

 

How can the fuel system be pressurized, engine stopped, key off?

 

Tomorrow morning I’ll try a cold start, see what happens.

[RJG183SA]

Fixed! Replaced faulty Fuel Pressure Regulator. Cold start issue resolved!

[Draenor]

Excellent!!

 

 

 

...Glad we could...uh ...help.....

 

 

It good that you were able to accomplish this on your own.

[RJG183SA]

Excellent!!

 

 

 

...Glad we could...uh ...help.....

 

 

It good that you were able to accomplish this on your own.

 

Thanks Draenor. I figured maybe someone may have had the same issue sometime and could have pointed me in the right direction. Just glad it was'nt the pump