k14 highway psi

[lilpig88]

Hi,
After reading this forum for years and scouring information on this topic for months, I've finally gotten around to my first post.  
I'm looking for, like everyone, the best combo of power and efficiency so after a recent re-ring job of my '86 1.6td I threw on a good k14 I had sitting around.  I figured the higher gearing of an ACN tranny with a k14  would be a good experiment for better mileage.  However, it doesn't really seem to have helped when compared to the lower geared tranny and t3 I had on it before.  So here is my question:
Is it normal to run 10 psi down the highway running 65-70 mph (again, 1.6td ACN and k14)?  If so, is there a way (besides going with no LDA) to avoid dumping more fuel than i have to with such high boost?  As far as efficiency goes, is there advantage to a large turbo running slightly lower boost at cruising speeds? Maybe most importantly, is there a way to get my cruising manifold pressure down?  Some folks say they run only 5 psi boost at 70 mph with a similar setup and I can't seem to get that to happen...would love some help.  I've had a recent alignment, newer wheel bearings, good tires with full air so the car rolls fine...
Any suggestions to try will be greatly appreciated.

Thanks!

[theman53]

I think your problem is tuning. The ACN isn't a lower geared trans it is a high geared trans so you shouldn't be turning the rpms. Take your star wheel and maybe make the spring stiffer so the boost fuel comes on later. I usually have 5psi at 70 on flat cruising, but I am intercooled. Also, when I intercooled I gained about 5mpg. I could stay into the fuel and not waste the heat I could use it.

[lilpig88]

Thanks! You're right about the ACN...I wrote it wrongly. 
I've put the start wheel almost all the way up so I have no LDA advantage (extra fuel) until more throttle.  However, I was thinking if I reach 10 psi then it seems the spring pressure won't matter as it'll still reach the full pin limit in the LDA it just won't be as soon.  Maybe I'm wrong on that one.   I've got a decent commute today so I'll try a few things. 
Thanks again!

[410]

The lda is basically a full throttle stop that acts directly on the governor lever.  It doesn't actually add fuel on its own.  Your right foot still determines the fuel being added.  The lda pin can be all the way down but if your foot isn't asking for more fuel you don't get more fuel.  On the turbo side of things, there is an adjustment on the turbo for the wastegate.  Someone before you might have played with this.  I usually back the adjustment off completely on the k14 and it will regulate the boost to about 10 psi max.  I found when this adjustment is cranked up for more boost it ends up limiting how far the wastegate valve can actually open which can translate to more exhaust back pressure that can really affect efficiency.  Something else that might be happening is the wastegate might be seized and not able to bypass exhaust gases by the turbine. 

[theman53]

I was thinking maybe it was being tuned to give fuel at less pedal input. If you adjust the starwheel down it can allow the boost to push down on the pin at 1psi. If you give it a little more tension and get it to come on around 5psi he could basically operate it like an NA until he really gets on it. I didn't think about a stuck wastegate, but that would do it too.

[vanbcguy]

What 410 is getting at is it doesn't really make any difference as to fuel usage - it's not like a gasser where the mixture can be "rich" or "lean" but the engine continues at the same speed.  With a diesel the engine spins at the maximum speed it can given the load on it for the amount of fuel being injected.  More fuel at same load, engine accelerates.  Less fuel, it slows down.

We're talking about steady state cruising here - the LDA can impact your fuel usage under acceleration, but only through altering how fast you can accelerate.  If you're cruising along the highway at a constant speed and you aren't ever putting the pedal to the floor, the LDA won't have any impact on your fuel usage whatsoever.  But if you frequently are mashing the go pedal and blowing smoke while you fly past someone cutting across 3 lanes, then yes you potentially can reduce your fuel usage by adjusting the LDA / max fuel screw.  You can also reduce your fuel usage by not doing that.

[ilikevwdiesel]

I have the same problem on my K14 AAZ rabbit pickup, have an FN trans, hits 10psi on the freeway just barely stepping on the gas. my mileage sucks (38 to 40 mpg)  too. should I back out the set screw on the waste gate and see what happens? it's all stock AAZ except for a 2.25 techtonics exhaust.

[R.O.R-2.0]

I have the same problem on my K14 AAZ rabbit pickup, have an FN trans, hits 10psi on the freeway just barely stepping on the gas. my mileage sucks (38 to 40 mpg)  too. should I back out the set screw on the waste gate and see what happens? it's all stock AAZ except for a 2.25 techtonics exhaust.

have you adjusted the wastegate with the set screw? you shouldnt move the wastegate set screw on K series turbos, a tiny bit of turn will make for a big change in my experiences..

[ilikevwdiesel]

it maxes out at 12 but it gets to 10 pretty quickly. I'm going to start backing it out little by little and see what happens with it.

[vanbcguy]

I agree about the LDA not affecting the fueling under boost pressure unless he is pressing the pedal hard enough to get into the range where the LDAs motion would be in effect.  But, considering he is cruising at 10 psi, it is very likely that he is into the range where the LDA would be in effect and without it appropriately adding fuel according to boost he is hurting engine efficiency. 

I wouldn't suspect an issue with the wastegate as that is functioning or he would be spiking higher (stuck closed) or not reaching 10 psi (stuck open). 

Like I said, put the LDA back to functioning properly and fix all the other stuff that is affecting steady state cruise like timing, tires, alignment, brakes, etc, etc, etc.

Again, the LDA can't add fuel without causing the car to accelerate.  It is burning precisely the amount of fuel needed to sustain the RPM that he is running at, there is no "richness" or wasted fuel going on.  Regardless if the LDA is adjusted well, poorly or unplugged, he will be burning the same amount of fuel to keep the engine turning.  All you can alter with the LDA is how much fuel is added when accelerating, it has absolutely zero impact on steady state driving regardless of pedal position.  The LDA doesn't have any connection to the accelerator whatsoever inside the pump.

The LDA / max fuel screw set the upper limit of how much fuel can be added.  Period.  Steady state driving is not utilizing the maximum fuel output of your pump, unless you have it turned down so low that you need to keep the pedal to the floor just to maintain highway speeds; if you have it turned down that low, you will be crawling up hills well under the speed limit.

The only thing on the pump that will alter steady state fuel consumption is timing (both static and dynamic).  Internal pump pressure would be a very good place to start looking rather than worrying about the LDA, unless the problem is "massive smoke until the turbo spins up" or "not enough fuel to use all the boost"

[larry104]

My '92 Eco with a Giles-built LDA pump, intercooler, 2.25 in. exhaust, 3.67 R&P and .71 5th gear with the stock K14 runs 8 to 10 psi boost at 70-75 mph steady speed. I routinely get 46-48 mpg and have hit 50 mpg.

[vanbcguy]

I understand how diesels work and more specifically how the VE pump with LDA works.  If the LDA is tuned to a significantly reduced amount of on-boost fuel, then to meet the demand of the load, the pedal will need to be pushed further and the turbo will need to spool higher in order for the LDA pin to move down a bit more to add the additional fuel that's needed to reach equilibrium for that load at that rpm.  That added boost comes at the cost of increased back pressure and so a loss of efficiency.

A properly functioning LDA pump will have the LDA impacting the amount of fuel for a significant range of the pedal's movement.  Granted it is the upper *portion* of the pedal's movement, but it definitely affects a whole lot wider range than just totally floored.  Before the boost pin has moved, the upper portion (1/3-1/4?? depending on tune of the pump) of the pedal will not add any additional fuel.  When boost rises, that upper portion of the pedal is "opened up" proportional to the boost.  At a load/fuel setting that is generating 10 psi on a 1.6TD, the pump lever should be in the range where the LDA is adding more fuel.  If it is adjusted so it isn't, then it is adjusted inefficiently.  Period.

Simple test to the OP...

Please disconnect your LDA hose and try another test drive, and report back...

[ilikevwdiesel]

I understand how diesels work and more specifically how the VE pump with LDA works.  If the LDA is tuned to a significantly reduced amount of on-boost fuel, then to meet the demand of the load, the pedal will need to be pushed further and the turbo will need to spool higher in order for the LDA pin to move down a bit more to add the additional fuel that's needed to reach equilibrium for that load at that rpm.  That added boost comes at the cost of increased back pressure and so a loss of efficiency.

A properly functioning LDA pump will have the LDA impacting the amount of fuel for a significant range of the pedal's movement.  Granted it is the upper *portion* of the pedal's movement, but it definitely affects a whole lot wider range than just totally floored.  Before the boost pin has moved, the upper portion (1/3-1/4?? depending on tune of the pump) of the pedal will not add any additional fuel.  When boost rises, that upper portion of the pedal is "opened up" proportional to the boost.  At a load/fuel setting that is generating 10 psi on a 1.6TD, the pump lever should be in the range where the LDA is adding more fuel.  If it is adjusted so it isn't, then it is adjusted inefficiently.  Period.

Simple test to the OP...

Please disconnect your LDA hose and try another test drive, and report back...

you mean disconnect it from the pump and PLUG it before driving it so it won't bleed the boost right?

[vanbcguy]

you mean disconnect it from the pump and PLUG it before driving it so it won't bleed the boost right?

What he said!!

[vanbcguy]

Correct...