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2003 SSS Fuel Pressure Spec


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Sorry if I am asking something that appears somewhere in the site, but I have searched and searched for the stock pressure for a 2003 SS and only seem to find data for people who have put in an aftermarket pump. Does anyone know where I find it or can definitively tell me what it is? I see way too many people on the internet (not here) who state fuel pressure for the various GM trucks from memory or ignorance that is often wrong. I am really struggling with a very intermittent misfire issue when tipping into the throttle mostly at speed. I have changed nearly everything on the truck after following various forum threads and their info for troubleshooting. Still no luck. I have been focusing on fuel pressure lately as a last resort. Here are some reading from today's runs with pressure gauge on windshield as I drive.

 

Idle with pressure regulator vacuum line on - 45 psi off - 53 psi

Driving without p/r vacuum line on - Nearly constant pressure of 53 psi at all power and speed settings

Driving with p/r line on - Idle 45 psi in drive. As I tip into throttle, the pressure spikes to 54 psi until I let out of the gas and then drops to 40 psi until it stabilizes at 43 psi once again. The pressure is very throttle position sensitive. It has the "return" style fuel system.

 

During these tests, the misfire would come and go, with no seen correlation to fuel pressure.

 

This is what I have changed the last two months chasing this. New GM long block was installed in February after only 3 months of ownership, Truck had 61k miles. No misfire issue with new engine. Old engine broke two rods and pistons within 5 miles of first sound that really sounded like alternator bearing, but unfortunately was not. Engine blew at 25mph on off ramp limping home. I have blown engine before and this sounded nothing like normal rod knock. Suspect known GM oil pressure high pressure relief valve stuck issue, but could not prove it. Engine had broken block and starter housing where rods pushed block out into it. All seemed fine after engine change. Changed muffler to and Dynomax Ultra Flo X and developed issue shortly thereafter. Extra airflow seemed to throw off tune, so engine was tuned with great improvement, but intermittent misfire as described continued Hence started the massive parts and troubleshooting effort. Here are the parts.

 

MAF - After a MAF code.

All O2 sensors - After 2 codes.

New plugs and wires.

Switched out coils with my 75 K5 Blazer 6.0 swap.

MAP sensor.

Pressure regulator.

Used set of stock injectors.

New set of 8.1 liter GM injectors.

New air filter.

New CAI (Spectre unit)

It has been tuned several times during this.

It had the stock muffler and tail pipe replaced with Dynomax Ultra Flo X Muffler (3 inch dual in and out into turndowns right after muffler, but before axle).

Remanufactured ECU installed,

Used throttle body (old Blazer one installed) and then new until also stole from Blazer. No change to Blazer performance.

MAF flow rate test for Cats okay.

Cat temps are the same as exhaust pipe before and after cat.

Fuel mileage at 10 mpg city/13 or less highway.

 

ECU change gave me 3 days of trouble free driving and then it came back. Please ask questions and I will try to provide more info. I am at a loss. Early check of fuel pump showed 50 psi most everywhere, but this latest check seems to be different and thus my post. Thanks for any help anyone can provide. PS. This has me about to sell this thing and buy a G8, but this is a really really nice SS and I don't want to sell it. I just don't need the stress due to health issues in my life at the current time. Thanks again!

 

Jim Reynolds

 

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Base fuel pressure should be 58psi. You have a vacuum referenced fpr. So your final FP will be 58-vacuum. It sounds like you have normal operation.

 

Has a cam position relearn completes on the truck after the engine install. It's important once a cam or engine is installed. Symptoms are just as describes.

 

Sent from my HTC6545LVW using Tapatalk

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So I am clear on the pressure spec, you are saying it should be 58 psi for the return style fuel system, like installed on the 2003 version and I am operating normally? With the regulated pressure of 45 psi and an unregulated of 53 psi, I would be concerned that it is low compared to the 58 psi? I know my Blazer is right on 58 psi, but it is a 2004 Denali LQ4 with the returnless style system with an in-tank Aeromotive Phantom 200 fuel pump installed. That has been my concern, as I have seen both 50 and 58 on the internet as the correct pressure. Sorry for all the questions, but I want to be sure I am on the same page. Thanks for your input. I cannot say for sure if the cam position relearn was performed. This was a dealer installed GM rebuilt LQ9 long block and I am was not there for that phase of the install. I will check the invoice, but doubt it will show that, but it should unless an part of the install. Is the cam position relearn something that is easily accomplished? I will do some checking for the details of the procedure in the meantime and perform it if possible. These things that either the dealer or myself has overlooked are just what I hope to determine, so I have my truck back to normal.

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while your pressures are a little low, they are also with in spec. Have you calibrated your gauge to verify that its reading correctly??? I don't know if the dealer will perform the Crank Relearn Procedure, but it can be done by anyone with descent scanning software/hardware. I.E. EfIlive, HPtuners, Snap on solaris, Tech 2 and so on. it only takes a few minutes to complete. Id start there.

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  • 2 weeks later...

Thanks for the additional input. I did find that the new fuel pressure regulator I had put in early in the troubleshooting process was bad out of stock. I put the old one back in and have 50 psi regulated and 60 unregulated, which should be normal for a return style setup like our 2003 models have. At least that is what I have been told. It would be different for the 2004 models with the return-less, which is what my 75 K5 Blazer has (2004 Denali engine). It ran great for a few days and the problem returned. It seems to be less often with the old regulator on, but it does happen. STFT's still seem a bit high and erratic, especially when compared to the Blazer. I am going to put the fuel pressure gauge back on and do some test runs to see if I can find anything. I have seen that it might be a weak pump flow rate wise, but just in the range for pressure. Not sure if that would be valid, especially since it seems fine at WOT. Does anyone know what the fuel flow rate should be at idle and if that is a valid test to attempt and possibly the actual test procedure. I hate to take it in to the dealer or local repair shop unless I have a good idea what it is or that I feel like it would be reasonably quick to troubleshoot. I hate to take it in and get slammed with a bunch of troubleshooting bills, but walk out with no answer. Being intermittent makes it hard, especially with no codes. The crank relearn is still on my list of possibilities too. My tuning guy uses HPTuners, so he might be able to do it. I have not had time to call the dealer to see if they did it as part of the engine change, but I would think it would be a standard thing. We will see. Thanks in advance if anyone has flow rate spec and test procedure!

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