Hard Starting And Code P0300

[johnnyquick]

Guys, my truck had been progressively harder to cold start in the past couple weeks, and I was waiting to give her a tune up.

1998 K1500 with a 5.7 liter 208,000, owned since new.

So ran great yesterday all day other than the initial hard start when cold, parked last night and when started this AM it ran REALLY rough, and the Check engine light lit, stayed lit and when I drove a bit it started flashing then went back to staying lit.

Went back home hooked up code scanner and got the infamous P0300, random misfire code.

So went in my caddy and got Cap, rotor, plugs, air filter and fuel filter, installed it all and runs the same, searched on here and read a TON on info and went and tested my fuel pressure which is 56# when off and 52# when running, fuel pump is about 3 years old and all was running fine when i shut her down last night.

I don't want to run out and buy a fuel pressure regulator, then a fuel injection spider, etc...... I would like to properly diagnose the ONE issue and fix that with only the parts I need, according to my Mitchell, the pressure may be a bit low when running what do you guys use as a fuel pressure # for that engine?

Any great input for me Gentlemen?

Thanks

[rickmac]

bet its the fuel pump

[rodram]

... I have to suspect the fuel pump ... on the 96-99 Vortecs like this the fuel pressure needs to be 61 to 66 psi at all times for the poppet valve at the tip of each injector to function properly

... some will argue about where the cutoff is but as the fuel pressure starts to drop below 60 psi, the truck will get harder and harder to start ... and then one day you will just be stranded somewhere requiring a tow

 

... get a ACDelco (from a dealer) or a Delphi brand from a good parts house... the other brands of fuel pumps are far less reliable and for a fuel pump you don't want to be replacing a cheap pump again any time soon.

 

... replace the in-tank filter sock and the external wiring harness at the same time

[johnnyquick]

... I have to suspect the fuel pump ... on the 96-99 Vortecs like this the fuel pressure needs to be 61 to 66 psi at all times for the poppet valve at the tip of each injector to function properly

... some will argue about where the cutoff is but as the fuel pressure starts to drop below 60 psi, the truck will get harder and harder to start ... and then one day you will just be stranded somewhere requiring a tow

 

... get a ACDelco (from a dealer) or a Delphi brand from a good parts house... the other brands of fuel pumps are far less reliable and for a fuel pump you don't want to be replacing a cheap pump again any time soon.

 

... replace the in-tank filter sock and the external wiring harness at the same time

 

So, isn't the fuel pressure regulator suspect?

Been reading alot on Mitchell etc. and not wanting to throw parts.

Thanks

[rodram]

well John ... I can only relay my personal experience since I am not a trained mechanic..

 

.. I have heard of fuel pressure regulators going bad on 5.3L engines .. they can leak to the outside or they can allow a major bypass of fuel so that the required pressure never builds up.. I don't know what the required fuel pressure is on these newer engines ... like the 5.3L, 6L, 6.2L etc....

 

.. however, EVERY fading fuel pressure incident that I have heard of (including my own last year) on a 1996-1999 5.7L (or 5L or 4.3L) Vortec was resolved by replacing the fuel pump and associated parts at the tank. Now, fuel pumps can fail for other reasons (other failure modes) but your truck is exhibiting a classic symptom of a fuel pump that is near the end of its useful life.

[johnnyquick]

Okay, put on a new Delphi pump, just under 400 bucks with tax. AND pressure regulator, 4 hours and 60 bucks for that, truck starts right up and pressure after the pump reads a nice solid 62#.

Still runs like crap though and shows the P0300, the slow/ hard start was cured but NOT the driveability.

Where would you gents go from here?????

I am screwed as I need my truck to haul my work tools around and was scheduled to work Saturday as well at another location

To Rod R, thanks for the input thus far, the old punp definately was not getting the job done.

[wierdo124]

I'm thinking ignition coil. Not getting a good spark. Usually like $30 and 15minutes to install.

[johnnyquick]

I'm thinking ignition coil. Not getting a good spark. Usually like $30 and 15minutes to install.

 

Okay I did need the fuel pump as it starts right up now, but the culprit for the rough running was a bad coil wire, I tested it with my ohm meter and it was supposed to be 1k ohms per inch and it read .754 ohms, put in a new one and she runs PERECT again.

Damn what a hassle, and I thought I was doing everything right, I diagnosed through the Mitchell guide step by step etc...............

I should have done the wires with the rest of the tune up, but this way i REALLY isolated the issue, so hopefully someone else can benefit from this.

THANKS ALOT gents and cheers