Best replacement for D-jet AAR?, Looking for new, easy fit and cheap Options

[arne]

I have confirmed my auxiliary air regulator is toast. Shaft is sticky after cleaning, sometimes it works, some times it doesn't. After I determined it was bad, I even disassembled it for serious cleaning. (Figured it was already bad, what did I have to lose?) Even there, the valve portion is sticky, partially seized. Need to replace it.

I know the originals for the D-jet cars are NLA, but that others work just fine, most will need the addition of a ground wire for the heating element. No problem there.

But while I searched a bit, I haven't seen any recommendations of which ones work well and are affordable. Some references to parts for water cooled VWs, but no part numbers or year/model info. Does anyone have a recommendation of one that has worked well for them?

[arne]

After poking about some, there is no shortage of 2 wire AAR units still available new. Most are Bosch or designed to replace Bosch. I'm sure that the specs on amount of airflow and temp of closing differs some, but I suspect most any would work better than removing it entirely.

One big difference I've seen is that most of these for other injected European cars look to use a larger diameter hose, often 15mm instead of the 13mm on my '73 2.0. That shouldn't be too hard to adapt though.

[r_towle]

Look for an ljet Aar, that system evolved into lhjet which as used on many cars.

[boxsterfan]

Put up a WTB add in the classifieds.

[arne]

I thought about a WTB ad, but used ones are all 40+ years old. I'd prefer to figure out a new alternative.

[DRPHIL914]

back when I first got my car 7 years ago and I was working on sorting it out, I found a NOS one and that is what I have on the car now, although I have several others, one much used one that works one that doesn't, id say it would be cool to see someone come up with a more updated modern alternative. I live in warmer climate but some days in winter we do have the 30-40 degree morning but one could run with out it- not sure what someone would want for it but if you get a NOS one you are not going to need to re-invent the wheel, just use what the original car was designed to use. .

If you do come up with an affordable alternative im sure there are others that would be interested.

[McMark]

Look for an ljet Aar, that system evolved into lhjet which as used on many cars.

Both of the L-Jet AAR that I just played with close VERY fast. WAY faster than the D-Jet AAR.

The L-Jet AAR is wired to the ECU, so I think the 1.8 ECU actually controls the AAR based on CHT (I suspect).

[arne]

Both of the L-Jet AAR that I just played with close VERY fast. WAY faster than the D-Jet AAR.

The L-Jet AAR is wired to the ECU, so I think the 1.8 ECU actually controls the AAR based on CHT (I suspect).

Dang! That's discouraging. I've been trying to think of what other contemporary car with similar Bosch injection might have a part that is still available, haven't found any likely suspects. I figured the big differences might be in air flow, or temp, didn't think time to close would be a problem. But if even the 1.8 L-jet AAR was triggered by the ECU, the early ones that operate simply with a heating element (just like an old electric choke on a carb) may be unicorns.

[McMark]

I was just going through this with Vacca Rabite, but his car is MicroSquirt.

But one aspect I came up with that may help you, is that inserting a resistor inline with the L-Jet AAR would reduce the voltage to the heating element -- slowing the temperature rise. By using a potentiometer, you could adjust and fine-tune the open time. Once you found the 'sweet spot' you could measure the potentiometer and get a similar resistor to install permanently.

[Dave_Darling]

...I think the 1.8 ECU actually controls the AAR based on CHT (I suspect).

I'm pretty sure that's not the case. The L-jet system in the 914 was still pretty darned primitive--I'm pretty sure that level of sophistication was beyond what was practical to put into an analog computer of that time. Or rather, to put in one that needed to stay as cheap as possible for mass-production in an entry-level car.

It may not have been as simple as the D-jet's "when the fuel pump is on" control, but I doubt it's much more sophisticated than that.

--DD

[McMark]

...I think the 1.8 ECU actually controls the AAR based on CHT (I suspect).

I'm pretty sure that's not the case. The L-jet system in the 914 was still pretty darned primitive--I'm pretty sure that level of sophistication was beyond what was practical to put into an analog computer of that time. Or rather, to put in one that needed to stay as cheap as possible for mass-production in an entry-level car.

It may not have been as simple as the D-jet's "when the fuel pump is on" control, but I doubt it's much more sophisticated than that.

--DD

I'm basing my opinion on two facts:
1. The ground wire from the L-Jet AAR goes to the ECU.
2. The L-Jet AAR closes too quickly to be of any use when powered continuously.

So I conclude from those two pieces that the ECU must NOT power the AAR at key-on. Or it could simply have an internal resistor to ground. Or it could have a 'switch' that powers the AAR once CHT reaches a certain threshold. But somehow the ECU is involved in some rudimentary control of the AAR. It may be REALLY simple, but it's something.

But I can see how my comment sounded like I was implying something more sophisticated. (IMG:style_emoticons/default/wink.gif)

[arne]

This is great info, gents, thanks for chiming in.

So if the L-jet AAR closes quickly when powered, I suppose one could put some sort of timer or even a manual switch in the ground wire, to make it wait for a bit before closing.

Of course, since those early L-jet units aren't much more available or affordable than the originals, I may not be gaining much on that front. Might be just as easy to rig a manual hand throttle type of thing to accomplish this. But that kinda defeats the purpose of the start-it-and-drive function of fuel injection.

I may have to settle for a used original after all. But some day 914 owners are going to need to find a solution for this.

[McMark]

Did some testing for you.

At 10v supply (using a dying battery) it closed completely in around 1m.
At 4v supply (using a really bad battery) it had a tiny sliver still open at 15m.

So somewhere in between those. (IMG:style_emoticons/default/laugh.gif)

[arne]

Thanks, Mark. Good info. So 8-9v would probably put me in the right ball park. I'll give that some thought.

[ChrisFoley]

One reason we install my hand throttle kits in customer cars is because of the nla AAR.

[jcd914]

This is great info, gents, thanks for chiming in.

So if the L-jet AAR closes quickly when powered, I suppose one could put some sort of timer or even a manual switch in the ground wire, to make it wait for a bit before closing.

Of course, since those early L-jet units aren't much more available or affordable than the originals, I may not be gaining much on that front. Might be just as easy to rig a manual hand throttle type of thing to accomplish this. But that kinda defeats the purpose of the start-it-and-drive function of fuel injection.

I may have to settle for a used original after all. But some day 914 owners are going to need to find a solution for this.

The AAR used on the 1.8l L-jet is the same type as used on thousands of other european cars. The cut out in the shutter and how far the shutter opens varies for different models and engine sizes but you should be able to find one that is workable.
You might have to adjust the cold open position (yellow or red painted nut) of the shutter to keep the high idle down some and add resistance to slow the closing speed to suit the 914 but it is do-able.

You could also look up Arduino idle control, there are people programming Arduino's to control and idle stepper motor to provide idle control.

Jim

[arne]

A lot of info and food for thought here, folks. Thanks! Long term, a replacement package and/or process will need to be worked out and tested. But for me in the short term, I don't want to invest the effort and expense to do this until I'm certain that all the rest of the bits on my car are healthy. And since I have only had it running at all since mid-day yesterday, I am not close to that point. Will need to save this project for a later time.

[r_towle]

I took mine out a long time ago....in the cold you just need to warm it up for a few minutes attended and it's fine....at least mine was.

[Rand]

I'm a fan of the simplicity of removing the aar, csv, and decel valve. Depends on the climate somewhat, and how much you care about originality on the car. (I wouldn't remove them if everything is working flawlessly, but when you start chasing failures or vacuum leaks, good riddance to unimportant parts - KISS is good.)

[arne]

Part of me agrees with that thought, Rand. But another part of me recognizes that this simple sports car had fuel injection that was quite cutting edge for the early '70s, and I'd like to keep that intact if I can.