Rough idle/black smoke/coolant burping

I think I already know what you're thinking and THANK GOD I'm asking for a friend, and not for myself (at least yet).

I helped a friend do some maintenance on his van the other night, he's getting ready to sell it and he did a fly/buy from the east coast (we're in CA) a few years ago, coming home with a rusty-ass hunk that didn't really run right (shame on him for hardly consulting me about it!).

Anyway, it's always had issues and the PO('s) effed this thing up in a few different directions. More to the point, it idles a little rough, blows black smoke like crazy, and he said it will periodically not go over 60mph.

I did a leak-off test, but all I had was 5/16"ID clear tubing, not 3/8"ID so using the 1 1/2" method was maybe not as reliable, and I didn't have a way to measure the volume. Just for information's sake though, #1 and #5 both had 1 1/2" of fuel. Reading another current thread here right now about pressure building up in the cooling system and it jogged my memory that while we were working on the thing for like 4 hours, the coolant cap would periodically squeak and burp, and I'm now realizing that he may have a much bigger issue than he can deal with on his hands.

Two bad injectors, and a head gasket? Does a periodically burping coolant cap hours after shutdown possibly mean anything else?

Sure, it could be a damaged cylinder head with an actual crack or hole in it...[emoji16]

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So I guess the next step is a compression test right? I've yet to check if there was oil/water cross contamination...

I would, but the better leak down kind.

In case its a crack.

Brings back memories of blowing the coolant back in the rad on my Dodge Ram Van with my mouth over the overflow bottle. Cut down on coolant usage with mouth to mouth, I could get 2 or 3 overheats before topping the rad up again


It's evil, but if that was me I'd sell it and feign innocence on the problems


Oh, and black smoke...i had an egr stick open and cause black smoke, loss of power. I shut the egr, jammed the shaft so it wouldn't turn and deleted it


(Just a shot in the dark)

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Rough idle usually means bad injectors or top end damage. The leakoff test will not identify a overfueling or sticking injector.

Midwestdrifter said:

Rough idle usually means bad injectors or top end damage. The leakoff test will not identify a overfueling or sticking injector.

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It's a little rough and smoothes out a bit when warm, but this is in CA in summer so I'm not suspecting glow plugs, especially coupled with the black smoke/other symptoms. What does a leak off test show then exactly? I thought it helped test for overfueling? And is the coolant burping pretty symptomatic of a bigger issue? My guess has been that since it's been running rough for years - even though he doesn't drive it much - an injector or two has been overfueling and is now causing possible cracks or hg damage...

The injector assembly has two major assemblies, the servo valve that the electronics trigger, and the needle valve that controls nozzle flow. The needle opens and closes in response to the movement of high pressure fuel, which is controlled by the servo valve position. The leak-off test measures the fuel that passes through these cavities during the movement of the injector’s servo and needle valves, not past the nozzle. If these wear and leak then this is its own problem, but while a worn needle valve may accompany the servo or piston wear, a low leak-off is not a guarantee that the nozzle’s needle valve is in good shape and still controlling the injection volume and timing accurately.

-dave

From a non grounded 737s view..

Zundfolge said:

More to the point, it idles a little rough, blows black smoke like crazy,

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I would guess an over fueling injector or two.. If it's really rough an injector could be stuck open.

Zundfolge said:

and he said it will periodically not go over 60mph.

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probably an unrelated boost code although the boost code could be related to the black smoke (is air filter clogged???)

Zundfolge said:

Does a periodically burping coolant cap hours after shutdown possibly mean anything else?

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Not entirely sure what you're trying to say here but it could be a faulty rad cap. To test for a HG leak, remove cap when cool, put plastic glove over cap, pinch overflow tube, increase rpm while in neutral.. Does the glove inflate at all. If yes, suspected HG leak.

I'm in the East Bay with a MBZ scan tool and lots of working knowledge in this area if you want to get to the bottom of it quickly. PM me.