2000 C2500 stuck in closed loop.

[20GMC00]

I have an old body style 2000 C2500 with a 5.7. It has been getting harder to start. It has a new Delphi fuel pump and new battery. I need to crank it 4-5 times before it will start sometimes. Sometimes it won't start at all. I found out that if I put a 10 amp battery charger on it for just a few seconds, it fires right up. Also I have my live data scanner plugged in and it is staying in closed loop all the time and both rear O2 sensors are staying at 99%. It runs fine but it's just getting harder to start. Has anyone ever had this happen or have any ideas? Thanks!

[j cAT]

Originally Posted by 20GMC00

I have an old body style 2000 C2500 with a 5.7. It has been getting harder to start. It has a new Delphi fuel pump and new battery. I need to crank it 4-5 times before it will start sometimes. Sometimes it won't start at all. I found out that if I put a 10 amp battery charger on it for just a few seconds, it fires right up. Also I have my live data scanner plugged in and it is staying in closed loop all the time and both rear O2 sensors are staying at 99%. It runs fine but it's just getting harder to start. Has anyone ever had this happen or have any ideas? Thanks!

if the scan tool reports the wrong cold start temp then that is the problem

[20GMC00]

When should it go out of closed loop?

[20GMC00]

Looks like my fuel pump is taking a dump already. 50psi with key on and 60-62psi the second I put the battery charger on it.

[20GMC00]

I just took the filter off and the stuff that came out the inlet of the filter looked coffee.

[777stickman]

Originally Posted by 20GMC00

When should it go out of closed loop?

The system is in "open loop" when first started cold. The system generally goes into "closed loop" when 1) the o2 sensors get warmed up, 2) the ECT sensor reaches a specific temp, 3) after a specific amount of time from first start.

During normal operation the VCM will stay in closed loop and fuel is controlled by the o2 sensors.

[j cAT]

Originally Posted by 20GMC00

When should it go out of closed loop?

at about 160deg f plus.

[j cAT]

Originally Posted by 20GMC00

I just took the filter off and the stuff that came out the inlet of the filter looked coffee.

some one may have put crap in the tank. you will need to drop tank and wash it out. show picture .........

[20GMC00]

I will do that. Thanks.

[20GMC00]

It starts right up with the fuel return pinched off. Is the regulator replaceable or is it part of the spider? It's got 268,000 miles. I'd say it's about due.

[777stickman]

The regulator is replaceable on its own. It's under the upper manifold.

[j cAT]

Originally Posted by 20GMC00

It starts right up with the fuel return pinched off. Is the regulator replaceable or is it part of the spider? It's got 268,000 miles. I'd say it's about due.

probably returning too much fuel . driver side of the intake manifold.

[20GMC00]

Finally had time to drop the tank tonight and it is still spotless on the inside. I'm guessing the pump went to crap causing the filter to be full of the black stuff.

[harleyguy]

To me it sounds like your having a battery/electrical problem putting a charger should not boost your fuel psi.
As for your closed loop problem what are you showing for ect. As stated that is one thing that tells it when to run closed/open loop.
Check for 12.6v on your battery and also to your fuel pump

[20GMC00]

The voltage is good. I put the charger on 10 amp and it will start within 10 seconds after putting the charger on.