Fuel Pressure/Rough Start

[BigOrange]

Hey guys - I've searched it a few times here and other places on the web with mixed suggestions or solutions, but I've developed a situation where my '06 2500 6.0L has a rough start/stumble for about 1-3 seconds once it has sat over a period of about 8hrs or more.  

 

It certainly seemed like a fuel issue, so after some testing I was getting over 60 on my initial key turn - then erratic spikes and drops for a quick couple seconds on first start up/roll over while it stumbled and then level at around 55 psi or so and ran flawless/purred like a kitten after that.  When shut off it would bleed down to 50 after about 5 minutes, 48 after 20 minutes, 35 after about 45 minutes and so forth until a few hours it would be dead 0 psi.  I've read (or assumed) that the system (unless there is a leak) should maintain some pressure regardless of being sitting for hours.  Knowing that a lot of these quirky issues are caused by failures in the pump I went ahead and changed it out and it since it had 270K on it anyway.  

The results were - - - very similar.  If I come out to test the truck after sitting an extended period I have 0 psi and not even a little squirt of fuel when I go to install my gauge on the schrader valve which right off the bat leads me to believe I've got bleed down somewhere.  When I turn the key and can hear the pump clearly turn on, pressure up to 61 or so...then drop to 55 after it quits that first 1-3 second cycle period....try to roll over and get a stumble/erratic fuel pressure till it fired and levels off flat at 55psi and purrs after that initial couple seconds.  Steady after that/no hesitation/etc.  

 

- So does my next suspect sound like a sticky injector that's allowing fuel to bleed off and possibly get a little bit of air or hesitation in fueling initially creating the stumble or is there somewhere else I should be looking first??  I don't think it is an air or intake gasket leak since they've been changed and the fact that it only lasts a few seconds even when dead cold.  I've cleaned the throttle body/MAF previously (within the last 3-4000km) but could try that again however I don't think that's my issue here. 

 

If it is a suspect injector - is there any way to test for the one(s) that may be causing the problem specifically by getting someone with a more detailed scanner tool? 

 

[Jglew82]

Sounds kind of like an injector to me. Can you pull the plugs and see if one is wet? other than that, You can read the scanner and see if there is a rich condition on startup, but that will point you only to one bank which is still helpful. If you have one leaking, unplugging one at a time won't really tell you anything unless the leak is really bad, so best way is to pull the injectors and pressure test them. 

[BigOrange]

That'll definitely help Jg - The wet plug thing could work...but unless that particular cylinder happened to be at TDC it probably wouldn't have leaked enough fuel into the cylinder to get the plug wet unless I try and start it for that 1-2 seconds and immediately shut it off to start checking plugs for a damp one....but that could work.  Plugs could likely use a change anyways TBH.  I did head gaskets and they of course looked fine so I cheaped out and left them which was a lazy approach.

 

But even finding out which bank could be a good start or at least eliminate some testing time to isolate that side vs doing them all.  I'm going to cheat a little bit with a little injector cleaner or MMO in the next couple tanks (not really expecting much though) of fuel, but not expecting much.  Then it'll be over to a buddy that's got the proper equipment to watch for a rich condition.  

 

[Jglew82]

Well, I say "wet" plug but more specifically meant that if you have a leaking injector, you should be able to identify that by a plug that looks as though it has been burning more rich than the others.

 

I don't have the link handy, but if you get on youtube and search "tire valve injector cleaner" you'll find a super easy way to check and clean them. I just did this on a buddy's Jag last week and it worked really well. 

[BigOrange]

I'll do that!  And yeah - I had wet in my head but your right that a plug that's darker or is notably different from the typical lighter brown/etc. would indicate that it's not firing up to speed at first due to excess fuel.

[riverbanks]

Still erratic spikes with new pump?and who's pump did you purchase?these days,it's a gamble,like,be prepared to do it again

[BigOrange]

I did gamble Riverbanks on an aftermarket - but had quite a number of high reviews with satisfied owners - but it could definitely be a possibility that it’s got its own faults built right in from new.

 

 But because it’s literally the identical pressure observations, stumble, etc. (and it does run at 61 psi not 55 as previously posted, my mistake) I’m still leaning toward something else playing a factor.  But I’ll have to keep plugging at it.  

 

- speaking of does anyone think plugs would play a factor?  In my own experiences on other machines/engines...... it seems like they cause more notable issues or stumble/hesitation when warm, or at low idle, or under a load.....and I’ve got none of that.  Just the start up stumble.  

[Formulabruce]

Hate to ask this far into your diagnosis,  but did you remove the air box hose clamp and COMPLETELY CLEAN the Throttle Body with Throttlebody cleaner, ( not carb cleaner) and both sides of the plate? This can cause stumbling and even a stall. It has to be spotless.

[riverbanks]

Did some research,found out there is .73 fl.oz of gas per ft. in a 3/8 line,how many ft. of fuel line on the truck,so even if half of that went in cylinder(s),you should find the wet plug(s)

[BigOrange]

Still haven't had a chance to pull plugs to check on it yet - but hoping to get a chance this week when I can run the truck then let it sit for 12-15hrs or so...but will also do the throttle body clean trick again as well and report back and start going from there.  

 

- Does anyone know what pressure it should likely hold in the system after sitting for a period of time?