2000 C2500 stuck in closed loop.

[Schurkey]

You cannot diagnose fuel pump pressure problems until you know the voltage drop of the wiring that powers (and grounds) the pump. Under-sized wiring used by GM on some vehicles drops pump RPM significantly. If that's the case with your vehicle, it will be VERY intolerant of corroded connections, or corroded contacts in the pump relay and oil pressure switch.

If the pump has broken-up mechanically, so there is pump debris in the filter...fine, you need a new pump. You certainly need a new fuel filter. Diagnosing fuel pump pressure with a plugged filter is a waste of time, and leads to incorrect diagnosis.

"I" will not install a pump without looking at the pump voltage, (measurement taken as near the pump as practical) ground-side voltage drop, and pump amperage draw. Amperage draw is best looked-at using an amperage probe and an oscilloscope. With a digital oscilloscope, I can verify the amperage draw of each individual armature bar in the pump motor, and also determine the pump RPM.

[20GMC00]

Ok. I'm just telling you what's going on.

[20GMC00]

And I don't remember saying that I was trying to diagnose fuel pump pressure with a plugged filter. I change fuel filters more often than I need to.

[Schurkey]

Originally Posted by 20GMC00

And I don't remember saying that I was trying to diagnose fuel pump pressure with a plugged filter. I change fuel filters more often than I need to.

No problem. Let me remind you.

Originally Posted by 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.

Originally Posted by 20GMC00

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

Based on your own words, and the times that you posted, you were testing fuel pressure before you found the icky stuff in the fuel filter.

But that's ok. I can walk away from this. Unsubscribed.

[20GMC00]

Your right, I did check it that one time. A guy shouldn't have to worry about the filter being that dirty that quick. I got it fixed. Don't worry about it.

[maxwedge]

I believe this truck has heated o2 sensors, so coolant temps are not part of the parameters needed for closed loop, see if they have 4 wires.

[20GMC00]

You are correct. They have 4 wires.

[rhandwor]

Hold the volt meter on the battery. Have someone else try and start the car.. A battery can have proper voltage and when loaded drop way down.

[777stickman]

Concerning the questions of OPEN vs CLOSED Loop. This is from a '99 Old Body Style service manual. Yours is an '00 Old Body Style so I would think it would be the same? This manual also shows the 4 wire HO2S.

[j cAT]

Originally Posted by 20GMC00

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

what is important is the power at the pump. most times these trucks have new pumps installed this is then a wiring screw up when the repairer does not solder in the new connector to plug in to the NEW different pump assy.

then the frame rail ground needs cleaning or repair for a low resistance ground contact.

also engine goes into closed loop at 160 deg f . so if it never is in open loop the ect or ect wiring is shorted out. low resistance causes closed loop.

poor cold start can be this .. cold start PCM increases injector ON time [MORE FUEL] IN OPEN LOOP .

[20GMC00]

I did solder in the new connector. I wil look for that ground tonight. Thanks.

[20GMC00]

It has 270,000 miles. When does the fuel spider usually go bad?

[20GMC00]

I pulled the upper intake off and the back half of the lower intake is shiny so I guess that answers that question.

[20GMC00]

Now it starts right when the key is turned and I'm getting P0171 & P0174. Haven't found any vacuum leaks either. About had it with this thing.

[20GMC00]

Both LTFT are constantly at 25%. I'll be getting some for sale signs today. Thanks for the help.