My head hurts

[Rattlenbang]

Hey all, I got a 92 L300 being a pig. It blew a head gasket a while back, and so I bought a head and gasket kit online. Everything went well with the head swap, but after a couple of days, the gasket started leaking coolant. That was a major irritation. The gasket kit was one of those inexpensive ebay kits, and that's probably why it packed it in from the get-go. Hell and damnation, I pulled the head again and this time used a quality branded gasket that cost almost as much as the whole engine kit from ebay. I was very slow and careful about putting this thing back together yet again, as I didn't want any screwups. But now the engine is now running like *beep*, white diesel smoke, and tons of pressure in the crankcase, even at idle. Afraid that another gasket had somehow blown, I did a compression test and am getting just over 400PSI across all cylinders.

Ive checked and double checked timing - even went so far as pulling the crank pulley and lower timing cover making sure that the timing belt cog on the crank was where it should be, as well as the two upper cogs. Everything seems to be as it should be, but the smoke and running rough suggests otherwise, plus the sudden crankcase pressure.

What did I do wrong here? The crankcase pressure is not ring blowby. I was afraid the head gasket was now leaking into an oil port, but compression says otherwise. How can combustion gases get into the crankcase? White smoke says not enough pressure/heat to burn the fuel.

I'm stumped.

[Growlerbearnz]

I think you've got the right idea- white smoke plus crankcase pressure says that something is burning poorly/at the wrong time, and putting too much pressure on the piston rings. Your 400psi compressions suggest that valve timing is correct*, and since the engine starts it suggests that injection timing is also mostly good.

It sounds like one cylinder is firing at the wrong time. But now you have to find out if the head gasket failure was a symptom or a cause.

My initial thoughts are:
-One injector fires too early (or late), putting too much pressure on one cylinder, causing the head gasket to fail (though I think you'd notice the extra diesel clatter, roughness, and smoke).
or
-Head gasket fails from age, resulting overheat cracks head, oil or water from crack gets into one cylinder and causes a misfire.

I think the head has to come off again. I'd be looking for evidence of one cylinder firing differently to the others, and cleaning the head up to look for cracks. Maybe pull the injectors and see if the tip of one is different to the others.

Also, ugh. Stupid old vans.

*the woodruff key in the camshaft can shear, changing cam timing although the pulleys still line up, but that should also change your compression readings. Still, it might be a good idea to pull the cam timing pulley and check that all is well.

[Rattlenbang]

Of all the @%^&$#%! After much head banging, teeth gnashing, and 3AM angst, it turns out it's the friggin' EGR valve somehow. With the vacuum line connected to it, it pukes out heavy smoke, runs rough, pressurizes the crankcase and when you rev it, clatters like it's spun a rod bearing. Disconnect the vacuum line, and it runs fine. What the hell? Anyway, I'm glad it's not the new head!

[Growlerbearnz]

Damn. I never even considered a malfunctioning EGR (deleted mine long ago), but that would do it. I'm glad you investigated more before dismantling the engine!

The EGR is supposed to be switched on by the glow ECU only when the engine's hot enough and at high enough speed/correct conditions to handle it. Sounds like the ECU has gone haywire, or the vacuum solenoid is jammed open, or the vacuum lines are connected incorrectly.

Are you going to investigate the EGR system more, or just blank it off?

[Rattlenbang]

It seems fine just by disconnecting and plugging the vacuum line. But it does make me wonder if the vacuum lines are incorrectly routed because it kicks on as soon as you attach the line. i.e. it isnt on a switched vacuum line.