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Testing for possible leaking injector - physical inspection

Mossyoakglock

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Mossyoakglock Senior Enthusiast

Mossyoakglock

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I am having an issue when I first start my truck in the morning after sitting overnight (also does it when sitting all day at work as well). First off, the truck starts fine on the first crank and fires up strong and it's hard to start or take multiple starts. What happens is that when it first starts, the RPM’s shoot up to around 1,000 – 1,100 like normal and then all of a sudden it will drop to anywhere from 500 to 800 RPM’s, have a slight studder/stumble for about 2-3 seconds and then go back up to 1,000 and be completely normal. It then idles down to normal idle with no problems. The studder/stumble is not harsh but it’s one of those things you can feel since it’s your own vehicle. I took it to the dealer for this issue a few months ago and they attributed it to carbon build up but the most important thing is that they actually acknowledged the issue.

 

I tested the fuel pressure and Key On/Engine Off I got 60 PSI and at idle I got 45-46 PSI. I did get some pressure drop that was more than what the book says so I want to check the injectors. I want to pull the fuel rail as a whole and turn the truck on (NOT running but Key On/Engine Off) and see if there is any fuel leaking.

 

Is that the best way to physically tell they are leaking? Is that possible to do? It seems pretty straight forward in that I loosen the wiring harness and then unbolt the fuel rail, lift up and pull the injectors free. I was planning to put shop towels underneath each injector when I primed the pump to see if any fuel dripped. Also will replace o-rings before I reinstall the injectors.

 

How about to see if one is clogged? I don’t think they are since once the truck starts, it runs fine and have no codes, etc. I can stop and start the truck all day if driving around doing errands, etc and it never does it until it sits overnight.

 

I suspect that it might be the fuel pump and that the pressure is bleeding off somehow even though the truck runs fine. I even try turning the key and letting the pump prime for a few seconds but it still does the same thing. Sometimes just as bad as if I were to start it straight away but then sometimes not as bad but it will still do it. I figured I'd test as much stuff as I can and this is the next best thing since I don't want to throw any unnecessary parts at the truck.

Mossyoakglock Senior Enthusiast

Mossyoakglock

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2008 and 5.3 w/ AFM

 

Can I unplug the electrical connections from the injectors and still be able to prime the fuel pump and check for leaks?

Mossyoakglock Senior Enthusiast

Mossyoakglock

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yes

 

I thought you could since power will still be at the pump and force fuel into the rail.

 

I let the pump prime for the 2-3 seconds and tried starting and it did the stutter again. It started on the first key crank too. If it was a leaking injector, it would be hard to start and would maybe take multiple tries, correct?

hollywoodsle Enthusiast

hollywoodsle

Posted
Posted

it could, sometimes it takes a little while for it to leak down. you could pull the rail and put some paper towels under the injectors. let it sit over night . that will tell you for sure

Mossyoakglock Senior Enthusiast

Mossyoakglock

Posted
  • Author
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it could, sometimes it takes a little while for it to leak down. you could pull the rail and put some paper towels under the injectors. let it sit over night . that will tell you for sure

I didn't think about that. I'll probably do that Saturday night and check it Sunday morning. Then do Key On/Engine Off and prime the fuel pump and check.

 

When the truck shuts off, will there be a few drips from the injector or will it be bone dry? Something like when you turn off a water faucet and there might be a drip or two after you turn it off type drip?

 

I keep going back to it possibly being the fuel pump since I don't get a hard start or miss, just the stumble at first start after sitting for 8+ hours.

hollywoodsle Enthusiast

hollywoodsle

Posted
Posted

I didn't think about that. I'll probably do that Saturday night and check it Sunday morning. Then do Key On/Engine Off and prime the fuel pump and check.

 

When the truck shuts off, will there be a few drips from the injector or will it be bone dry? Something like when you turn off a water faucet and there might be a drip or two after you turn it off type drip?

 

I keep going back to it possibly being the fuel pump since I don't get a hard start or miss, just the stumble at first start after sitting for 8+ hours.

you might have to wipe a little gas off when you initially remove them. make sure you check the towel before you turn the key. you will definitely know without having to turn anything on.

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