ALDA, fuel delivery, air fuel ratio, and boost. - PeachParts Mercedes-Benz Forum

mrsaxman99 · #1 03-09-2009, 05:32 PM

So I'm learning more every day about how turbo diesel engines work...I know lots about gas turbo setups, but not much about the diesel side.

Put VERY simply, I was under the understanding that upping the amount of fuel will determine the max boost...but then I realized that these cars' turbos have set wastegates to limit boost. Okay, so you can install a manual boost controller to raise the boost...but without adding fuel (raising the max fuel delivery rate), won't the car run incredibly lean (more boost without more fuel)? I imagine if you just increase max fuel, the turbo won't boost any higher because the wastegate is still set to open at a certain psi.

I've also read that the ALDA does NOT increase MAX fuel, it just increases the curve (delivery based on boost) of fuel delivery. So (while keeping a close eye on EGT's) if I were to increase boost with a manual boost controller, would I want to find a way to raise the max fuel delivery rate?

I guess I'm just really confused with how the whole air-fuel ratio is maintained.

Thanks in advance for the clarification!

P.S. the reason I ask is because after just hooking up a boost gauge, I noticed my max boost is around 8psi. I realize that this may be due to a bunch of other things (bad turbo, clogged exhaust, etc.)...but it really got me thinking about how the whole boost pressure / fuel delivery / air-fuel ratio system operates together.

Brian Carlton · #2 03-09-2009, 05:38 PM

A diesel always runs on excess air. This benefits the diesel as it allows complete combustion of the fuel. Only in the case where absolute maximum power is desired, with no care of emissions or fuel economy, will a diesel be run with too much fuel.

That being said, the amount of boost should be sufficient for the available fuel. Increasing boost without increasing fuel is simply providing the engine with hotter air.

The ALDA is a fuel restrictive device. It prevents the driver from delivering more fuel than the engine can use. The IP is calibrated for maximum fuel under turbo boost conditions. When off boost, the IP would deliver too much fuel without some type of control. Hence the ALDA. It limits fuel based upon available boost. As the boost is increased, the ALDA allows more fuel.

You can do the same thing if you remove the ALDA and are careful with your right foot. Your foot controls the fuel...........the more you press down............the more fuel you get............you have no control over the air.

If you increase the boost from 8 psi to 12 psi, if the ALDA is still restricting fuel at 8 psi, it will then provide additional fuel when you provide more boost. However, if the ALDA is at the edge of the curve at 8 psi, increasing boost will only produce hotter air.

Yes, with an EGT gauge, you can increase boost and fuel............if you're very careful.

oldsinner111 · #3 03-09-2009, 06:33 PM

I'm wondering instead of injecting water methonal mix.Could you mist more fuel,lets say overide the weak pumps.Instead of buying a Euro pump.
I want to blacken the countryside if I want to.

cmbdiesel · #4 03-09-2009, 07:12 PM

Quote:

Originally Posted by Brian Carlton

The ALDA is a fuel restrictive device. It prevents the driver from delivering more fuel than the engine can use. The IP is calibrated for maximum fuel under turbo boost conditions. When off boost, the IP would deliver too much fuel without some type of control. Hence the ALDA. It limits fuel based upon available boost. As the boost is increased, the ALDA allows more fuel.

So as the ALDA gets old and needs adjustment, that adjustment is to remove some of its restrictive nature? My SD produces 9lbs of boost, if I were to put in a boost controller to achieve 12lbs, I may not see any increased performance because of an overly restrictive ALDA?
My plan is to have the overboost protection system functioning as designed, then install a boost controller, then make an ALDA adjustment. Does that seem like the proper sequence?

LUVMBDiesels · #5 03-09-2009, 07:18 PM

Lance tried methanol and I think he did not see any results from adding it. Do a search on Methanol Injection.

MrSaxman, I put a boost controller on my '81 300SD and raised the psi from 7 to 13. As the turbo ages, the spring in the waste-gate gets weaker. Add to that a very conservative original setting and you end up with boost that is way too low. The max boost cut off (the electrical overboost protection) activates at 1.1bar or around 16psi. When I upped my boost the power and responsivness of the engine increased and the EGTs stayed pretty low.
If I was going to push it to the limit, I would have added an intercooler and upped the fuel, as it was, I just turned up the ALDA 3/4 of a turn.

Good luck!

Brian Carlton · #6 03-09-2009, 07:26 PM

Quote:

Originally Posted by cmbdiesel

So as the ALDA gets old and needs adjustment, that adjustment is to remove some of its restrictive nature? My SD produces 9lbs of boost, if I were to put in a boost controller to achieve 12lbs, I may not see any increased performance because of an overly restrictive ALDA?
My plan is to have the overboost protection system functioning as designed, then install a boost controller, then make an ALDA adjustment. Does that seem like the proper sequence?

You can adjust the ALDA to shift the curve toward more fuel. If the wastegate is adjusted or a boost controller is added, the 12 psi would certainly ensure that the ALDA is at the limit and is not restricting any fuel at that point.

At 9 psi, it's probably still restricting fuel slightly, even from the factory. Most of the diesels will test at less than 12 psi. Some folks believe that the factory shipped them in that condition.

mrsaxman99 · #7 03-09-2009, 07:55 PM

Quote:

Originally Posted by Brian Carlton

You can adjust the ALDA to shift the curve toward more fuel. If the wastegate is adjusted or a boost controller is added, the 12 psi would certainly ensure that the ALDA is at the limit and is not restricting any fuel at that point.

Brian, you re-affirmed my understanding of the ALDA...thank you. Let's pretend for a second that the ALDA doesn't exist (so you have ultimate control of fuel with your foot)...would it be correct in saying that the IP is designed/mapped/tuned for ~12psi max...meaning turning the boost up past 12psi would result in - as you said - just more hot air being blown through the engine with no real performance benefit?

Next - as I understand it, adding more fuel (again, forget the ALDA - I'm referring to adding more MAX fuel) at a given boost pressure - if it's enough fuel - will result in blowing black smoke out the exhaust (as you see tuned turbo diesels at the drag strip do). Am I correct in saying that if you found some way to raise the max fuel delivery rate (resulting in black smoke), and then slowly turned up the boost until the black smoke disappeared, you would have essentially found the best boost pressure for the given max fuel delivery rate, resulting in the best performance, and least amount of wasted/detrimental heat?

Brian Carlton · #8 03-09-2009, 08:02 PM

Quote:

Originally Posted by mrsaxman99

Brian, you re-affirmed my understanding of the ALDA...thank you. Let's pretend for a second that the ALDA doesn't exist (so you have ultimate control of fuel with your foot)...would it be correct in saying that the IP is designed/mapped/tuned for ~12psi max...meaning turning the boost up past 12psi would result in - as you said - just more hot air being blown through the engine with no real performance benefit?

Next - as I understand it, adding more fuel (again, forget the ALDA - I'm referring to adding more MAX fuel) at a given boost pressure - if it's enough fuel - will result in blowing black smoke out the exhaust (as you see tuned turbo diesels at the drag strip do). Am I correct in saying that if you found some way to raise the max fuel delivery rate (resulting in black smoke), and then slowly turned up the boost until the black smoke disappeared, you would have essentially found the best boost pressure for the given max fuel delivery rate, resulting in the best performance, and least amount of wasted/detrimental heat?

Correct

Correct again. You can raise the max fuel delivery rate via adjustments in the IP.........if you know exactly what you're doing.

Turning up the boost beyond 15 psi is considered somewhat risky by most of us. Other claim no issues..........YMMV.

mrsaxman99 · #9 03-09-2009, 08:17 PM

Quote:

Originally Posted by cmbdiesel

So as the ALDA gets old and needs adjustment, that adjustment is to remove some of its restrictive nature? My SD produces 9lbs of boost, if I were to put in a boost controller to achieve 12lbs, I may not see any increased performance because of an overly restrictive ALDA?
My plan is to have the overboost protection system functioning as designed, then install a boost controller, then make an ALDA adjustment. Does that seem like the proper sequence?

My understanding from my research, and what I have learned from Mr. Carlton - If you were to add a boost controller (to most likely compensate for a weakened wastegate spring) and up the boost from 9 to 12psi, the ALDA would notice this increase in boost, and add fuel as necessary. However when the ALDA hits its "ceiling" (or "edge of the curve", as Brian Carlton puts it), where it isn't restricting any fuel (and you have thusly hit your max fuel delivery rate possible for the stock settings), turning up the boost any further would not result in any performance increase, and in fact (because of heat generated) could cause engine performance to suffer (not to mention overall engine health).

So if you want to achieve max performance, in theory you would want to turn up your boost until the ALDA hits its "ceiling", or the point where it is no longer limiting fuel delivery at all. Please note that adjusting the ALDA does not change its "ceiling" - only "how quickly" it stops limiting fuel (based on boost pressure), or put another way - how "sensitive" it is. Let me run off to microsoft paint and see if I can make a somewhat legible graph...brb

mrsaxman99 · #10 03-09-2009, 08:42 PM

Okay, I'm not proud of this graph...but I think it gets the point across.

You see when you turn up the ALDA, it results in the engine receiving more fuel at any given boost pressure until it hits 100%. This means that once you hit that 100% fuel delivery rate, turning up the boost any further will not result in any performance gains. Also, turning up the ALDA shouldn't give you any top horsepower gains (it would only help with off boost power and spool time).

I think the common misconception is that turning up the ALDA yields the dashed red line - where it will keep providing more fuel throughout the boost range. But the fact is, if the ALDA is reaching its max pressure (and thusly not limiting fuel at all) at whatever current boost boost you are running, turning up the ALDA won't really increase your max horsepower, and turning up your boost further also will not help increase power, and only result in more hot air.

Brian Carlton · #11 03-09-2009, 10:06 PM

Quote:

Originally Posted by mrsaxman99

Okay, I'm not proud of this graph...but I think it gets the point across.

You see when you turn up the ALDA, it results in the engine receiving more fuel at any given boost pressure until it hits 100%. This means that once you hit that 100% fuel delivery rate, turning up the boost any further will not result in any performance gains. Also, turning up the ALDA shouldn't give you any top horsepower gains (it would only help with off boost power and spool time).

I think the common misconception is that turning up the ALDA yields the dashed red line - where it will keep providing more fuel throughout the boost range. But the fact is, if the ALDA is reaching its max pressure (and thusly not limiting fuel at all) at whatever current boost boost you are running, turning up the ALDA won't really increase your max horsepower, and turning up your boost further also will not help increase power, and only result in more hot air.

Exactly.

#12 03-10-2009, 12:01 AM

Quote:

Originally Posted by mrsaxman99

would I want to find a way to raise the max fuel delivery rate?

IP Full Load Adjustment 617 Turbo

mrsaxman99 · #13 03-10-2009, 12:22 AM

Thank you, sir...that's a useful write-up.

So...in theory...just for fun...if I wanted to increase fuel and match it with the correct boost, I would slowly increase only the full load screw...or full load and torque control capsule (as this "reduces rack travel with increased rpms"...which sounds counter productive to the desired effect of increasing max fuel (max rack travel))?

Thanks to you, BC, and others for all input. I have learned a lot today!

#14 03-10-2009, 12:29 AM

Removing the rack limiter + 15psi boost = around 140hp at the crank. Thats all the HP the stock pump is capable of but you can adjust the torque capsule and high idle screw to change the fuel curve width.

mrsaxman99 · #15 03-10-2009, 01:14 PM

New couple of questions:

What should be the full open to closed travel on the ALDA adjustment screw? With the lock nut OFF, I can get only about 1.5 turns from lock to lock...is this normal?

Also, with the ALDA adjusted full ccw, I do notice a very nice bump in power in the off boost range...makes the car much more drivable. However, I am not seeing ANY smoke. I'll be at a full stop, mash the gas, (feel a good bit more power than before I adjusted the ALDA), but no smoke.

What could this mean? Clearly, I can't over-fuel the car off-boost, even with the ALDA adjusted all the way ccw. Could this be a sign that the IP is going bad? I would like to investigate the problem further by going ahead and removing the ALDA all together. However, I can't seem to find any pictures of removal on a 617 engine. I know there is a big hex nut underneath it...do I have to loosen that, and then the square ALDA fixture just unscrews?

Annnd finally, a quick boost question. Is the small line (~6") going from the turbo housing to the wastegate what I throw a check valve on to get my boost back up to stock levels? I don't know why, but I was expecting a pressure line running from the manifold to connect to the wastegate...guess I'm just used to my old 944Turbo.

Continued thanks!!!