Hey guys,

Troubleshooting my way through my 1.7L Djet one component at a time and I think it's time for a rebuild on my MPS.

Part # 0 280 100 003 (VW 022 906 051) which after much digging seems to be the right part for an early 1970 Djet (which mine is).

I followed the Paul Anders AMAZING diagnosis guide. The vacuum tests passed surprisingly well!

But then I used my LCR meter to check the calibration. And while I used a different meter than Paul, the numbers were significantly less. (I did correct his data down to sea level)

@PBanders Sea Level Numbers for 0"/4"/15" - 1.40/1.20/.74 @20H
My MPS --------------------------- 0"/4"/15" - .95/.84/.63 @20H

Even given a difference in LCR Meters my numbers seem significantly low.

Add to this, a PO had drilled out the center of the large adjustment screw so I could adjust the inner screw. Using Paul's method adjusting the inner screw made no changes at all on the LCR meter, nor in the car engine running.

If I read his site correctly my diagnosis is that one or both aneroid cells has failed.

Am I on the right track?

Not sure if your aneroid cells are fried or not. Are you using the inductance meter correctly (there is a hold feature on a lot of those meters, make sure that is not on).

FWIW, with a handful of MPS's, including one stock unmolested 043, my cheap-azz inductance meter would never come CLOSE to Anders' numbers. As an example, here are my 043 numbers vs Anders':

Anders 043: 1.39/1.18/.71 at 0/4/15 psi.
My 043: 1.18/1.03/.7 at 0/4/15 psi.

I could completely take the full stop screw out of one of my other 043's and I would not even come close to 1.39 (I'd get to maybe 1.25). If I tried to get part load (4 psi) close to his number I would end up backing the screw out so far I'd lose vacuum. So, what's my point? I dunno

Or maybe it's: take Anders' numbers with a grain of salt without a WaveTek, get Racer Chris' tuning tools, and use an AFR wideband to tune. Then, tune it to what seems to make your engine happiest.

Believe me, I spent HOURS doing this. I created spreadsheets in Excel to map slope of the curve and compared 4 different units. Also, if you do this, I'd recommend taking a tip I got from Frank S (I believe) off this site: when testing, use a "Y" branch vacuum hose so you can (with a long hose), put a vacuum gauge where you can see it as you drive. You'll get a better understanding of what is considered "load," particularly "part load" as you're looking at AFR numbers.

But again, not sure why you're not seeing your numbers move on the meter

Hopefully @Bleyseng or @Frank S or other D-Jet gurus can chime in as well.

I would add here that the meters will read different. The meter Brad used is not easily available. He did mention is his posting that different meters would read different from what he measured. I also went through this and my numbers were way off from what was posted. I did have luck comparing and adjusting 2 MPS units. I used the numbers from a working one that I had and used those numbers to adjust the one I was rebuilding. It was pretty close

https://www.globaltestsupply.com/product/am...mponent-testers

That is the same device Brad used, Wavetek Meterman was bought out and folded into Amprobe.

I wouldn't recommend setting to pre-recorded numbers though as location and environmental factors can change the readings. Best way is to calibrate it against a known good reference unit.

That's effectively what I ended up doing once I got my hands on a working, unmolested 043.

Yikes...Well, first of all, thanks for the input guys, I really appreciate it.

@BeatNavy I just went out and re-tested with my meter to assure I didn't have the hold switch on, it wasn't. The numbers matched my earlier test.
https://www.amazon.com/gp/product/B07CYSV5L...e=UTF8&th=1 This is the meter I have

I 100% agree with you guys that his numbers may not be the numbers for me and my meter, but the inner screw adjustment clockwise and counterclockwise making no change whatsoever has me perplexed.
[i]

I do not have access to another known good 1.7L MPS.

Option A: From a financial aspect it seems the most cost effective solution is to send the unit to @JeffBowlsby for a rebuild and tune.

Option B: Spending $400 between the other meter mentioned above and a Tangerine Rebuild kit but possibly end up shit creek and still need to get it professionally dialed in (JB site says he won't tune what he doesn't rebuild which I totally understand).

I tend toward option B in life as I don't like being defeated, Lol! However pissing money away is a quick way to be defeated too!

Still trying to wrap my mind around why the numbers aren't changing and/or you're not seeing any changes to how the engine is running. I can think of two possibilities:

1. You're at the end of adjustment on the inner screw. Have you tried bringing it back the other direction? For example, when I would back out the full load stop screw (the big one on the outside), at some point it would just stop resulting in changes as the diaphragm was already at the end of its travel.

2. You're turning the inner and outer screw together. If you don't have the right tools (or technique) it's easy to turn both the inner and outer screw together when using a flat tip screw driver. When you do that there's no change to part or full load mixture.

This didn't make sense to me until I had the adjustment tools. I just want to make sure you realize there are three components that can be adjusted:

1. The inner screw, which is the thing in the exact center inside the MPS. It has a slot for a flat tip screw driver.

2. The outer screw, which is what the inner screw sits in inside the MPS. To turn either the inner or outer screw by itself you have to have something to hold the other on in place.

3. The full load stop, which is the "plug" that threads into the outside of the MPS.

Based on the way you are describing it I feel like you MIGHT be just turning the inner and outer screw together.

Sorry if that's confusing, but does that help?

While rebuilding a customer's MPS recently, I discovered a secret method to calibrate the part stop screw without an inductance meter. It will remain my secret for the time being.
Best way to calibrate the inner screw is with an O2 sensor while operating the vehicle, although I have been able to find the operational sweet spot without an O2 sensor.
As Beatnavy says, you need a special tool to hold the part load screw while turning the inner screw.
I will also add that it is all too easy to adjust outside of useful parameters.

@BeatNavy Rob, if I ever meet you, dinner and a beer on me! You've more than earned it on this thread!

I did NOT realize there were 3 screws.

I have been adjusting the very center screw as you described. Click to view attachment

What you are saying is that inner screw is within another (which I can't see). THEN there is the larger flat blade screw/plug (Full Load Stop) under the yellow epoxy that holds everything in there?

The inner/outer screws must be moving together as you thought.

I'll get the Plug out and try this again!

Seriously, Thanks!!

Ok, can confirm the two screws were turning together.
Going to order that tangerine rebuild kit as well as the adjustment tools!
Have a little PB Blast to help these two move independently Click to view attachment

Out of curiosity, why would someone drill out so the inner screw can be adjusted but nothing else?

Yes, that makes no sense. Wow, that is a early MPS with the two little holes. See if you can find someone to loan you a O2 setup for the Best method of tuning the MPS to your car.
I have a Wavetek and can get the same numbers as Paul but it all depends on your own car's setup. Age and wear and maybe changes on the engine makes a big difference. VW's method of batch setting up the MPS's worked when all the parts were brand new and the engines were basically the same. Now, forget it.

I found the following method for adjusting the inner screw to work well for me:

Dial the idle screw on the throttle body almost all the way in.
Set the knob on the ECU (if your ECU has one) to the middle setting.
With the car warmed up (AAR valve closed) get engine idling steady using the idle screw on the TB for wherever is normal for your engine. On my mine it was 900rpm with the stock distributor, after installing a 123 distributor it’s now 1000rpm.
If idle is surging then adjust the ecu knob. Shouldn’t need more than 3 clicks or so clockwise. If the knob doesn’t change anything, you’ve got other issues (like a cracked MPS diaphragm).
Adjust MPS inner screw until AFR shows somewhere between 12.5-14.1.
Continue to adjust the inner screw so that the engine doesn’t bog down at all, even when barely giving it some gas. You’re near or at the right spot when the engine revs smoothly.

I can get the inner screw set correctly without an AFR meter using this method, but knowing the AFR is crucial for setting the full load mixture.

I can only guess they didn't know what they were doing

Do you have an O2 wideband? I've got a used one I could "loan" out indefinitely, but you still need to weld a bung somewhere in the exhaust.

Looking at the picture that MPS has been opened up so that could be the reason why the readings are so far off. Lots of MPS diaphragms have been "repaired" and are a problem.

Take it apart and see....maybe order the repair one from Chris

Order placed with Tangerine

What do you guys think about something like this?

AEM (30-4110) UEGO Air/Fuel Ratio Gauge https://www.amazon.com/dp/B00N3VGPYS/ref=cm...i_3ZuXEbX2B9RCN

Wouldn't permanently install the gauge, just use when tuning then plug the 02 Bung.

That one should work fine.

You can leave the sensor in and just disconnect it if you want (although eventually it will get fouled). They can be handy for troubleshooting and tuning, but they can also be TMI if you prefer less distractions or a more spartan look.

Do you have a mityvac hand vacuum pump?
If you do, gradually pull a vacuum and watch for diaphragm movement.
If it doesn't move at all, the outer diaphragm screw is in way too far.
In that case you can back out the two screws together with your small screwdriver until you see the diaphragm move just slightly as you start pumping. It should only go a small amount though, no matter how much vacuum is pulled. No need to go beyond 20", as that's close to the max that an intake manifold ever reaches.

Thanks @ChrisFoley and I got your email! I do have a handpump with gauge and will do as you posted.

I had another thread a few weeks back where I was looking for opinions on 02 Sensor Kits....

I think i'm going to go with the 14Point7 full kit $120 and good feedback from the members on here (Mark Henry recommendation)

Ok, slow and steady, still sitting in the pit, not gonna win the race, Lol!

I rebuilt the MPS with the Tangerine Kit. Huge thanks to @chrisfoley for going above and beyond helping me with my MPS housing.

I have also received and wired up my 14Point7 A/F kit, very cool stuff!

@Mark Henry Where did you weld in your exhaust bung? recommendations?

Got my 14point7 Kit built, 02 sensor installed and was able to do some tuning of the MPS last night. Really cool project and so cool to be able to dial in the A/F ratio. Kept the wires longs as I can use this on multiple applications. Got a bung plug so I can uninstall once I'm done tuning. Highly recommend this kit for anyone interested!

Click to view attachment Click to view attachment