Acts like it wants to run but doesn't.

[exp500]

Do a compression test, pressure test cooling system, leakdown test if you can find/rent / borrow the tools.
What you can do now is swap a coil/ swap an injector and see if problem follows swap.
Slowly dropping fuel pressure- leaking relief valve, leaking pump check valve, leaking injector.

 

[NO4NSHIT]

Do a compression test, pressure test cooling system, leakdown test if you can find/rent / borrow the tools.
What you can do now is swap a coil/ swap an injector and see if problem follows swap.
Slowly dropping fuel pressure- leaking relief valve, leaking pump check valve, leaking injector.

My dad seems to think that it has a sticky valve. Yet the fuel pressure is at 46-48 and from what I've read it's supposed to be at 55-62? After replacing the fuel pump and the map sensor it backfired for probably about maybe four backfires and then quit back firing. Yet it still has a slight Miss to it it's not throwing up any codes but it still has a misfire. I'm going to try some seafoam in the gas tank and some mystery oil in the crankcase and try driving it tomorrow during the day and hope that it can help the situation I don't know what else to do. My dad watched a video on YouTube about how to diagnose sticky valves and what he found was by putting a piece of paper at the exhaust pipe if it pulls in and out that it'd be a sticky valve how do you go about fixing a sticky valve in a 5.3 LS?

 

[swathdiver]

It's a 2003 Yukon XL 5.3 l Vin Z. I've already replaced all the fuel injectors new plugs and wires, mass air flow sensor, O2 sensors. It will idle smooth for probably about 30 to 45 seconds then start to slightly miss, then it would start to backfire like every 10 seconds it would hit a backfire. It threw up a po300 and a po301 and then a po171. I just performed a fuel pressure test on it it went up to about 46 PSI and then slowly began to drop I was just curious that would that be a bad fuel pump I don't know how long it's supposed to hold and you can't trust everything you read on Google..

I don't have your exact specs but this troubleshooting is for mine which is similar. Key on, fuel pressure should go to 50-60 psi and not decrease more than 5 psi in one minute. With the engine idling it should be between 43 and 45 psi.

 

[NO4NSHIT]

I don't have your exact specs but this troubleshooting is for mine which is similar. Key on, fuel pressure should go to 50-60 psi and not decrease more than 5 psi in one minute. With the engine idling it should be between 43 and 45 psi.

I used my scanner and pulsed each injector and they all were 36-39psi. But fuel pressure goes to 52 and then slowly drops. Now I had a problem with the fuel filter line that goes from fuel filter to another regulator or whatever then another line from there to the motor. Well the line from the filter got damaged I ended up having to cut it and use a piece of 5/16 fuel hose to replace it not really wanting to spend $65+ on a hose when I made this work. Only thing is it's about 6 inches longer so it doesn't kink. Could that be part of the problem or is that ok??

 

[swathdiver]

I used my scanner and pulsed each injector and they all were 36-39psi. But fuel pressure goes to 52 and then slowly drops. Now I had a problem with the fuel filter line that goes from fuel filter to another regulator or whatever then another line from there to the motor. Well the line from the filter got damaged I ended up having to cut it and use a piece of 5/16 fuel hose to replace it not really wanting to spend $65+ on a hose when I made this work. Only thing is it's about 6 inches longer so it doesn't kink. Could that be part of the problem or is that ok??

No, I don't think that the bush fix is the problem, just make sure those clamps can take the constant pressure. I think it's time for a new flexfuel fuel pump.

 

[Fless]

I may have missed it but what were the results of the dry and wet compression tests?

 

[corvette744]

I may have missed it but what were the results of the dry and wet compression tests?

I dont see any results-if you keep saying sticky valves stop what your doing and verify internal engine parts are good.Stop guessing and do a compression test and leak down problem will be answered immediately.

 

[NO4NSHIT]

No, I don't think that the bush fix is the problem, just make sure those clamps can take the constant pressure. I think it's time for a new flexfuel fuel pump.

Actually just put a new fuel pump in it last night and well it started backfire about 2 or 3 times and then it stopped still has a slight Miss in it it sticks around 46-48 PSI when I turn the key on it goes to about 52 but then I mean I can't get to the fuel gauge fast enough to see how fast it drops to about like 44 46 area and then just slowly drops after that when that's with the key on.

 

[NO4NSHIT]

I may have missed it but what were the results of the dry and wet compression tests?

I'm still waiting for a compression tester it'll be here in a little bit.

 

[NO4NSHIT]

What is your fuel pressure and will it hold for 20 minutes? What code does it show? Can you see live data?

Key on it goes to 52 and then drops to 48 within 5 seconds