rpm surge on start

[BrassBandit]

This is a copy paste from another forum but I figured I'd ask here as well. full disclosure I didn't end up checking glow plugs yet because fishing and whiskey got in the way.

So my truck wouldn't start this morning. it's smoking so I know it has fuel. wts light comes on. so I plug it in and five it 30 minutes then figure I'll go see if my relay is clicking. I turn the key controller sounds like it should single engage then hold. jump in the truck cycle it again and try to start it. this time it didn't even get a full revolution and the truck immediately fired up then it revved itself to 3500ish rpm for a split second then right down to a normal idle

I know how to test glow plugs and will be doing that later today after I run my errands but what the heck caused that rpm surge?

So does air intrusion cause am rpm surge? because that was the answer I got but this thing was dumping raw diesel out the tail pipe as soon as I started cranking

 

[IDIBRONCO]

Air intrusion will cause odd behavior, but I seriously doubt that it would ever cause your engine to rev up to the governor. I suppose that it could be possible that there was too much fuel in the cylinders and that caused it to rev high for a short bit. Since fuel was coming out of your tail pipe when you started cranking the engine over, this sounds possible. It's the only explanation that I could come up with. I'd say to not do this again. Fix your glow plug system first.

 

[Thewespaul]

Air intrusion into the pump will cause the pump to open the metering valve up to purge all of the air out of the housing, which effectively is like having the throttle at wot. This combined with a pump that may have an already sticking metering valve can cause it to “hang open” even for some time after the air has passed. From what it sounds like this is what happened to your truck.

Fix the air intrusion, and replace your fuel filter. Before you install the new filter, fill it with clean atf and start the truck. Once you hear the pitch of the engine change slightly, shut the truck off and allow it to sit overnight. At this point you will have the pump, injectors and lines full of diluted atf, which is a natural detergent and thicker than diesel. This works great at removing heavy buildup in the pump and injectors and has cured many sticking metering valve issues for many members on this forum.

 

[BrassBandit]

@IDIBRONCO glow plugs will be here Monday. I figured might as well swap them before it gets really cold here

@Thewespaul thank you for the explanation. I'll start looking for air intrusion and do that atf trick. the truck has 185000 km so I'm assuming the pump and injectors are most likely at the end of their service life