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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 29520
Experience:  GM Grand Master Technician 2007. 14 years experience.
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2000 Chevy express 3500 5.7. Starts great first thing in the

Customer Question

2000 Chevy express 3500 5.7. Starts great first thing in the morning. After it runs for about 20 minutes when i stop come to a stop the oil pressure gauge drops down and jumps and the van either runs rough like fuel is being restricted or it stalls. Then when i shut it down and try to start again after work it has a hard start. Delayed start. cranks for about 10 seconds then fires. And Process repeats.
Submitted: 1 year ago.
Category: Chevy
Expert:  GM Tech (Cam) replied 1 year ago.

Hi there, I am Cam. Can I get your name please? Can you tell me when you replaced the fuel filter last?

Customer: replied 1 year ago.
My name is ***** ***** filter was about 3k miles ago it was a fleet maintained van has 193k runs great with good oil pressure until you stop.
Expert:  GM Tech (Cam) replied 1 year ago.

Ok, what is the pressure doing when this happens?

Customer: replied 1 year ago.
have not checked pressure when this happens. takes about 20 mins for the problem to occur.
Customer: replied 1 year ago.
is it safe to drive with the dog house off and the gauge attatched?
Expert:  GM Tech (Cam) replied 1 year ago.

I am wondering if even though the filter is new, that there is a pump/pressure issue. At idle the pressure drops and causes this. We could also try now cleaning the throttle body and Mass Air Flow sensor (MAF) sensor with carb cleaner and then reset the system. Take the battery cables off the battery, hold the ends together for 10 seconds then attach them to the battery and see what happens. This will reset the whole vehicle.
If you have 2 batteries, then remove both and touch only one set.

If this does not then it may be that the fuel pressure regulator is failing/leaking. Yes you can drive with the dog house off for a bit. It will just be noisy.

Customer: replied 1 year ago.
Ok.i will go try that now and see what happens With the pressure.
Expert:  GM Tech (Cam) replied 1 year ago.

OK,. Also make note of idling pressure, pump only pressure and how long it holds with the key turned off.

Customer: replied 1 year ago.
ok be back soon.
Expert:  GM Tech (Cam) replied 1 year ago.

ok

Customer: replied 1 year ago.
ok so reading as follows.before start jumps to 62 and stays at 56.
at idle 54 psi
under load 56-60 psi
when it starts the madness gauge pulses quickly between 52-60 psi
takes about 18 mins to drop to 0.
Customer: replied 1 year ago.
to add when it does the drop it oil pressure and like it wants to stall it has hesitation going off the stop. not misfire wise but just lacks power.
Expert:  GM Tech (Cam) replied 1 year ago.

Ok, the only number that concerns me is it dropping to 0 that fast. It should hold and drop only 5 psi in 5 mins from the 53 psi. I am wondering if the regulator is leaking inside the intake or the map or mass air flow sensors are bad.

Customer: replied 1 year ago.
it shouldnt go any lower then a 5 psi drop?
Expert:  GM Tech (Cam) replied 1 year ago.

Right. When the pump stops, it should not drop more an 5 psi in the first 5 mins. If it does then the pump's check valve or fuel pressure regulator is leaking.

Customer: replied 1 year ago.
ok in 3 mins it dropped from the 54 psi down to 20.
Customer: replied 1 year ago.
about 10 psi per minute.
Expert:  GM Tech (Cam) replied 1 year ago.

So next we pinch the return line. If the pressure still drops, it's the fuel pump mid not then the fuel pressure regulator.

Customer: replied 1 year ago.
ok also forgot to mention. I got the other day a p0134 code and p0171/p0174 code.could this all be caused running lean due to either a fuel pump or regulator?
Expert:  GM Tech (Cam) replied 1 year ago.

those codes all point to low pressure so I think we have to look at the issue as being the pump or regulator.

Customer: replied 1 year ago.
ok pinched the return and it still dropped pretty quickly. more then 5 psi in less than 30 seconds
Expert:  GM Tech (Cam) replied 1 year ago.

Replace your fuel pump. It is failing internally.

Customer: replied 1 year ago.
even with the pressure reading being ok?other then its dropping down that fast.?
Expert:  GM Tech (Cam) replied 1 year ago.

, Yes, we need to chase what we see as bad, and that I am 100% positive is bad. And feel its 90% likely to fix your issue.

Customer: replied 1 year ago.
all those codes run to running lean. meaning not enough fuel right?
Expert:  GM Tech (Cam) replied 1 year ago.

Exactly. Many people think it means vacuum leak, and that is possible, but lean can and often is not enough fuel.

Customer: replied 1 year ago.
ok and that could also cause a hard start when warm?cold start is fine just hard to start after running and shut down.
Expert:  GM Tech (Cam) replied 1 year ago.

Possibly yes. That is the one part that does not fit as neatly into the mix. Hard start hot is usually leaking injectors or leaking fuel pressure regulator. Can you smell raw gas in the intake if you open the throttle plate and smell down in there?

Customer: replied 1 year ago.
have not tried that. but would a regulator make it so im dropping pressure that fast?
Expert:  GM Tech (Cam) replied 1 year ago.

Yes, the one test about pinching the return line does not rule out external leaks.

Customer: replied 1 year ago.
ok so either way its regulator or fuel pump what are the chances of replacing both and everything being fine?
Expert:  GM Tech (Cam) replied 1 year ago.

Unlikely. The more we talk, the more I think about it, I would take the upper intake off and reconnect the fuel lines, then simply power up the pump and see if fuel leaks from the regulator. This way you can tell with out replacing anything just yet.

Customer: replied 1 year ago.
if fuel leaks from the regulator then what?
Expert:  GM Tech (Cam) replied 1 year ago.

Replace the regulator.

If not then the fuel pump.

Customer: replied 1 year ago.
either way its the fuel pump or regulator?
Expert:  GM Tech (Cam) replied 1 year ago.

Yes, that’s what I believe it is.

Customer: replied 1 year ago.
ok ill get back with you when i do more.
Expert:  GM Tech (Cam) replied 1 year ago.

Sounds good. Please bookmark this page so you can easily navigate back to it so we can continue the discussion. This is done by pressing (CTRL D on PC and CMD D on Mac). You can reply at any time for follow up information regarding this issue, even after you rate the site and I will reply.