L300 Fuel Screw

[jonsvibe]

Hey all! Been tinkering and reasonably confident in the cause but wanted to see if anyone else has some thoughts on this.

The head was replaced last week after a snapped balance belt, timing jump, and subsequent destroyed valves. Since then, I’ve done a couple 200 mile drives in addition to my work commute. Since the replacement, I’ve noticed a drop in power and more smoke. Cold starts have been near impossible at or below freezing. HEFTY black/white smoke on initial start at 0C which fades only after the engine runs for a couple minutes. The injection pump is advanced about 2mm.

So here’s the questions. With working glowplugs, would the the only other major factor on a cold start be fuel (Ex> Too much fuel)?
Air filter is free and recently replaced.

I’ve also noticed an increase in unburnt diesel on long climbs and the van can’t hold fourth gear on steep grades. Previously wasn’t an issue. EGT’s are averaging 100 degrees hotter than before the swap as well.

I’ve fiddled with the fuel load screw, but I’m probably gonna decrease it another half - full turn and shorten my throttle cable to maintain a 750 idle. However, I remember hearing that the fuel load screw should be used only to SET idle and the throttle stop and cable adjustment is just to fine tune. I’ll be doing this backwards by setting idle with the cable and decreasing base fuel. Any thoughts?

Otherwise, I still have yet to get a new compression/leak down test to see the piston ring health and current numbers on the new head. Oil level is holding. Coolant has also been fine. Very confident that it’s over-fueling but want to double check my logic and see if anyone has other ideas other than fuel load screw.

Currently living in Boulder, CO. Understand the altitude may factor in. Thanks all!

 

[13mclean]

Are you making sufficient boost?

 

[jonsvibe]

Are you making sufficient boost?

10 - 11psi max. I’m thinking of trying to up it soon but boost numbers are the same as before.

 

[13mclean]

I’d double check the timing marks

 

[13mclean]

Also valve clearances

 

[jonsvibe]

I’d double check the timing marks

Timing marks and clearances have been checked. I may tighten up the clearances a bit more but they’re in spec

 

[sk66]

I do think you need to tune the IP for altitude, but IDT the startup and acceleration/EGT issues are directly related.

In tuning the IP I would follow this guide: https://delicaforum.com/index.php?threads/tutorial-tuning-the-4d56-for-more-power.707/

 

[Growlerbearnz]

If you didn't touch the injection pump settings when replacing the head, then adjusting them now to compensate for the bad running might be masking a more fundamental problem.

If you've put a flush valve head on a protruding valve engine, you will have lost a bunch of compression which would explain the engine's symptoms. I'd get a compression test, you should have about 320-350psi if you're testing in Boulder, or 400+psi at sea level.

You said you've checked the timing marks but retarded timing (IP timing mark out by one tooth) could also explain the symptoms.

You mention adjusting the throttle cable to change the idle: that's not right, the idle should only be adjusted using the idle screw. The throttle cable adjuster is only to ensure the cable has some slack/free play at idle.

 

[jonsvibe]

You said you've checked the timing marks but retarded timing (IP timing mark out by one tooth) could also explain the symptoms. If your compression is good, try advancing the IP timing a little.

Understood, thank you. Compression test will be done soon but I did order a protruding head and double checked the part numbers with Coombs before ordering.

When you say advance the timing, do you mean by IP tilt or actually advancing the IP a tooth?

 

[Growlerbearnz]

Tilting the IP (though you say it's already advanced by about 2mm, which should be plenty). The timing marks should always line up.

 

[Scott]

The idle adjustment is the indicator with this. If you had to increase the idle adjustment just to maintain the previous idle speed. That tells me the injection pump timing is probably off.

Since the fuel is being injected at the wrong time, we have to add more fuel to just maintain low idle.

 

[jonsvibe]

Hey guys, thanks for the input. Here’s an update that may prompt more questions than answer.

This is something noticed by my friend, who is the mechanical guru performing the head swap

When swapping out the camshaft sprocket (another story) and subsequent re-tensioning of the timing, Crank position was a roughly four degrees off TDC.

- Installation of timing belt procedure and adjustment of timing belt procedure seems to yield different results.
Adjustment procedure specifically seems to cause the crank position to be slightly off with proper tension. I’ve noticed this in the past years when checking timing for valve adjustment and haven’t thought to mess with it as the van ran well.
I’m attaching a photo from 2022 (when I last checked) The crank position back then is exactly where it is now after just re-tensioning the belt.

Was this something intended by the manufacturer and simply not added to the manual as a disclaimer or something unexpected to watch out for?
With the crank at the 4 degrees off, the van seems to drive well. If anything, it just feels like it was before the head swap. Granted, still too much fuel going through the system based on excessive black smoke around town (I’ve been hauling ass and enjoying the van tho I will not lie).
Any thoughts?