Fuel Screw
 

Hey peeps, having some difficulties turning up the fueling in my 85 d24t. I've bottomed out the screw on the collar, and adjusted the idle screw so it's about where it should be when idling. The problem is, when I start the car cold, the engine wants to rev really high, like to 3 or 4 thousand rpm, which is as you can imagine alarming and probably not good for the motor. I'm not very familiar with the pump design, but it looked to me that the cold start device is linked to the throttle linkage. I haven't seen this problem mentioned in the peformance sticky. Am I missing something? I've turned down the fuel so that it now stays at about 1500 until it's warm, but I'd like to be able to turn it up more. Maybe a problem with my cold start device?

Extremely bad for the motor and the transmission as well.

The cold start linkage uses a ball stud mounted on the advance arm, on the side of the pump facing the driver's side strut tower, that increases idle speed when cold. Adjusting the low idle stop for the pump to bring the warm idle back down after turning up the fuel quantity screw doesn't affect cold idle since the throttle lever stops on this ball stud when cold, instead of on the idle screw. As the engine warms up, the coolant that flows through the loop running to the IP warms up a wax motor that backs off the advance arm, and backs off the fast idle as a result.

You can reduce cold idle speed by moving the ball stud's position on the advance arm. 7 and 8mm wrench and you probably will want to back it all the way off to the far end of its adjustment. Look at where the throttle lever stops when the engine is cold and you'll see how this works. Back it off far enough so that the lever is almost touching the warm idle stop, to make sure you don't continue to race the engine when it starts cold. After that, if you want to increase it again for a little more idle bump when cold, you can do that but be cautious. Too slow is better than too fast.

Remember also when adjusting that fuel screw: too much fuel is bad for the engine. If you see any smoke at full throttle, you need to turn it back down. Once you see smoke, more fuel doesn't give you any more power, just creates massive exhaust temperatures, oil contamination and cylinder head heat. Not good for helping the engine last and you get no benefit from it. Usually you can't get away with turning it all the way in to the stop collar unless you have done other supporting changes, eg opened up exhaust, increased boost, intercooler, larger turbo, etc....

I thought I replied to this earlier, but thanks for the info. Hard to visualize what you mean, I'll have to print this out and take a look at the pump. It definitely smokes at full throttle.

Right now I have a larger cold side and upgraded turbine wheel from a ebay turbo. Could be I've gotten used to driving my s70 while this sat waiting for the turbo, but I swear it feels slower. I think the responsiveness of the smaller turbo meant I was getting into full boost before the governor started to de-fuel, but the odd thing is that the turbo seems to build boost more slowly. I can't remember if it did this before, is it more typical for diesels to build boost more gradually? In my gas car it's almost instantaneous.

edit: I experimented by disconnecting the WG and seeing how that might affect boost (ie weak spring opening too soon) but it's the same. Makes more boost, obviously, but still slow to build. Even at 15psi, still seems pretty sluggish.

Well, I reviewed the performance sticky and tried removing the blow off valve and capping it off with a 1 1/2 plug. Tight fit, but can be done. Definitely an improvement in power. Now it starts to build around 2500 and hits full boost a little after 3k. A properly adjusted boost controller will also help, with no WG I can only accelerate at half throttle or so to prevent boost from getting too high. Strange that it feels faster this way than full throttle.

Which screw is it better to adjust first, overall fueling or fuel under boost? I'm running a slightly larger than stock turbo.

There is only one screw that will adjust fuel if the pump is all ready seeing boost. That would be the max load/fuel screw. The set screw ontop of the LDA only adjust how far the fuel pin will go up to limit off boost fueling. Once the LDA has a few lbs of pressure that screw has no effect.

Okay, thanks for clarifying that. Is there any rule of thumb for adjusting it? I don't have an EGT gauge yet, but I am getting some smoke at idle and at high load. EGTs coming soon. I'm running about 15lbs max boost.

LDA is injection pump? I see it being used all the time but I'm not actually sure what it means :o

In my experience it seems that you have the main fuel screw turned up too much. You really shouldn't have mucch smoke at idle nor should you have a lot of smoke under full load in BOOST. Also if you can only do part throttle with no wastegate there's another sign to me from my experience that you have the fuel turned up too far and your EGT's are probably way too high also.

LDA translated is Manifold Pressure Compensator, the flying saucer appendage on top of the IP.

I like how this page explains how to tune it:
http://dodgeram.org/tech/dsl/more_power/Power_ve.htm

Nice description and cutaway:
http://vwdiesel.net/forum/index.php/topic,30340.0.html

More tuning tips, with helpful photos:
http://vwdiesel.net/forum/index.php/topic,645.0.html

I'll have to try playing around some more. I was able to get the cold idle to come down using v8volvo's info about the ball stud. EGT gauge will be helpful.