fuel pressure drops

S

sgian

Member
I've been getting a 0174 obd II code on my 2005 Tahoe gas 5.3. When I first tested the fuel pressure, it was low so I replaced the fuel pump with an AC Delco pump from RockAuto.com. It was fine for a couple of weeks, but today the code came back.

So I tested the fuel pressure again today and with the pump on it is about 59 psi, which I believe is fine. However, once the pump shuts off the pressure immediately drops to 45-50 psi. Then it very slowly loses pressure after that.

So I pulled the injector rails out and looked for any drips from the injectors while my son operated the key. No drips, but he accidentally started the Tahoe and it actually ran without the injectors in place until I got him to turn the key off. No fuel sprayed all over the engine, but I was also concentrating on getting my son to turn off the engine so I didn't pay attention. Now I'm just confused. No drips indicate the injectors are not leaking, and if anything no fuel mess indicates they might even be stuck closed. However there was enough fuel in the cylinders for the engine to run a few seconds.

Does anyone have an idea of what is going on and what I should do now?
 
if the injectors and the fuel rail were disconnected theres an excellent chance that the wire harness was not correctly plugged into all the injectors and the injectors were not properly grounded, the injectors only open when an electrical pulse caused the internal pindel solenoid to pop open.

ID suggest REPLACING YOUR FUEL FILTER and ADDING A CAN OF INJECTOR CLEANER to your next tank of fuel as a first step, and checking for loose injector O-rings and vacuum leaks once the injectors are re-installed,

http://garage.grumpysperformance.com/index.php?threads/locating-vacume-leaks.882/#post-45944
ID sure verify the OHMS resistance on EACH AND EVERY INJECTOR, and GET ANY CLEANED THAT WERE SIGNIFICANTLY
DIFFERENT READINGS
image_12926.jpg

http://wikicars.org/en/Fuel_injection

http://garage.grumpysperformance.com/index.php?threads/calculate-fuel-injector-size.1200/#post-31258

http://repairpal.com/OBD-II-Code-P0171-and-P0174

http://garage.grumpysperformance.com/index.php?threads/changing-fuel-injectors.3429/#post-9084

http://garage.grumpysperformance.com/index.php?threads/fuel-injector-resistance.607/#post-806
Injector3.gif
 
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Thank you for the help and explanation of why there was no fuel sprayed everywhere when my son started the engine with the injectors removed. I'll put the injectors back in and check for resistance and then clicking. Then I'll post back.

I had already added a can of Seafoam to the tank before all this trouble with the 0174 code started, I wonder if it is connected or just a coincidence.

I've already checked for and fixed any vacuum leaks that I could find due to an earlier problem with the MAF sensor, in which I replaced the intake manifold gaskets and rechecked for leaks.

The fuel filter is part of the fuel pump and not separately serviceable for this vehicle. (?!)
 
I took a picture of that area to show that there is no fuel filter, but I figured the Hayne's manual would be easier. I needed to doublecheck under the Tahoe anyway for fuel leaks.
201602%20tahoe%20man%20sm_zpsj63wn8zu.jpg

I think it is ridiculous that GM stopped having serviceable fuel filters, and it is just my luck that I have a Tahoe from 2005 which is the first year they put the filter in the fuel pump module. Anyways...

I checked all the injectors and they are all 11-12 ohms, which is within specs according to my Haynes manual. When I put a piece of rebar against each injector, I could hear it clicking. So I guess they are ok.

Is there anything else to check before taking the fuel pump module back out? Is that normal for fuel pressure to drop from 59 psi to about 47 psi as soon as the pump turns off?
 
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