Fuel screw and idle speed interdependence.

jetfiremuck · #1 01-31-2020, 04:53 AM

Q. Do all 2.4 turbo diesel emit some visible smoke at idle? I've replaced nozzles and pop tested injectors. Pump timing at .90. I'm running an inter cooler. Some puffing from oil fill but no major cap dance.

I rebuilt the injection pump as the tit on the fuel control plate was broken . Took measurements on fuel screw etc. From what I understand turning fuel screw out reduces fuel. Idle speed drops , so bumping up idle screw brings it back to spec. No difference in gray smoke at idle. If I snap the throttle it comes back to idle fairly quickly.

So. Any other ideas to reduce this smoke. I have a 03 and 98 tdi. Both have some blow by but no visible smoke. Is the 1.6 idi a smoker at idle.

ngoma · #2 01-31-2020, 10:02 AM

Your description of the fuel screw is correct. Small increments can have a large effect. Sometimes it can be hard to get it dialed in after opening up the cover, especially if the outside throttle arm plate was not replaced on the splined shaft in the exact same position.

Did it do similar before the IP rebuild? Or did this start after the IP rebuild?
What does it do off-idle, and at lower RPMs (< 2000 RPM)?

They all emit some visible smoke at all RPMs. One of mine more than the other as it is an oil-burner (~1 qt./700 mi.) We are dealing with essentially 1970s technology.

TDI technology is much newer, not a fair comparason.

What was broken in the IP, the sliding fuel collar way at the bottom?

jetfiremuck · #3 01-31-2020, 02:24 PM

Correct. The pin that moved the fuel collar was broken. The collar was seized on the shaft. I have a few pumps so replaced that part. Everything else in the pump was used, and not a mix of different pumps. It being an 84 does nog have an egr. Engine was a junk yard pull. Took engine and trans. Car had 160k and compression was around 400 on all cyls. I’m wondering if a diet of synthetic 15/40 over time might clear it up free oil control rings. with tdi technology v old idi.

So maybe some visible smoke is normal

v8volvo · #4 02-02-2020, 09:45 AM

I run 0W40 synthetic year round and have had pretty good luck with a few dirty engines improving in terms of compression and oil consumption and smoke. But it depends on what the condition of the engine is. If it's just sticky rings a diet of better oil over time can give great results. But if long term use of poor quality conventional oils, too long oil change intervals, habitual hard acceleration on a cold engine, etc has led to tapered bore wear and ring wear, then changing oil types unfortunately won't be able to reverse those effects.

If the engine starts quickly when partially warm and doesn't have too much visible blowby, then it's probably a pretty healthy starting point. I would at least give some thinner synthetic oil a shot and see what happens. Good oil and some good hard usage/Italian tune ups can definitely be beneficial for making these run more cleanly. Like any diesel, they like to work hard once they are warmed up, rather than loafing around. Just make sure every single part of your cooling system is in 100%, total perfect health before hammering on it and don't ever let it even come close to overheating. And of course make sure the timing belts are up to date. But if it's all good you could try just giving it a few hard workouts and see if it makes a difference.

jetfiremuck · #5 02-10-2020, 04:50 AM

Thanks for the advise v8 Volvo and ngoma. I'll try the low viscosity syn oil.

My observations on the injection pump fuel control screw and throttle lever.

If the fuel screw still has the sleeve still welded to the screw then it's straight forward. In my case I set the splined throttle plate to the furthest line marked on the plate. That is '/' on the pump shaft looking down from the top aligned / on the rt of the throttle plate. This setting gave an idle of 1400 and with the fuel screw turned in until the locknut contacted the lock sleeve. Turning the idle stop screw to 1000 rpm caused the revs to hang after a few snap throttles. Backed the fuel screw exactly 3/4 turn out , brought up idle stop screw which eliminated the hanging (and possible runaway). It doesn't take much adjustment from safe to runaway on fuel control screw. Be careful.