MPS Inductance Curves and Tuning, Is Fuel Injection Corp USA Selling Rebuilt MPSs with Bad Transformers? Options

[Cessnaporsche01]

So a lot of you will remember my thread from last year that ran for many many pages, trying to get my '74 2.0(56) running again after literal years of turmoil and confusion.

After much investigation and many suggestions, I was able to isolate the issue to the MPS, a rebuilt 0280100043 unit, remanufactured by Fuel Injection Corp USA and sold by Rich Bontempi's High Performance House back in 2020. Last fall, I was able to get the car running, idling great and driving spottily by simply using the Tangerine Racing MPS tuning kit to adjust the inner idle screw richer, but was never able to achieve full throttle. I ended up cranking the inner screw up to max, and was able to get about 60% throttle before the engine would die. Although idle became excessively rich, this made the car driveable enough to get it hot. Especially since nearing the cut-out point, it seemed to get very lean.

With the warmer weather back, I've been working on trying to tune the car in better, but have been met without much success. But I've dialed in with growing specificity toward what seems to be an MPS transformer problem.

I started by doing a full intake system rebuild/re-seal, just to be certain I wasn't fighting a vacuum leak. Slowly and carefully cleaning and re-seating all mating surfaces and using gasket dressing on gaskets. (I also 3D scanned and modeled the intake system, but that's a topic for another thread.) I'm now up to 100% confident that the car has no vacuum leaks, up from maybe 85-90% before.

Then I set about adjusting the tuning. I got a proper vacuum pump that could pull up to 25+ inHg and bench tested my MPS. Like last time, the 8-10 coil (secondary) curve came in FAR lower than both the graph value and chart values given on Brad Ander's MPS page, at least on the high-power end of the scale, with the primary coil being around 1/2 the secondary. [Graphs and chart shown below.]

With the inner screw maxed out, the 25inHg primary inductance secondary 0.67H and the primary 0.32H. At 0inHg, the secondary approaches .93H and the primary, .49H.

Now, I had posted this very low inductance curve in my last thread, and the community consensus was that the shape of the curve was more important than the actual values, but I question this, and wanted to test where the cutout point on my engine's throttle response was, so I hooked a vacuum gauge up to a long hose, plugged it into the manifold port where the decel valve usually goes, and went for a drive.

After letting the engine get hot, I did a few pulls, where I gradually increased my throttle position and watched the vacuum.

Sure enough, the engine would cut out each time the manifold vacuum fell below about 7-8inHg on the gauge, which is just past the intercept point between my MPS's secondary curve, and the 043 curve Brad has posted on his site.

This aligned well enough with my suspicions that I was willing to spend the money to test out another unit. I went out looking, and settled on a 0280100037 unit from EBS Racing, since I couldn't find any verified '043s, and '037s are compatible with my car/ECU - considered to be an "upgrade" due to their higher stock mixture setting.

When this one arrived, I found it had also been remanufactured by Fuel Injection Corp. And upon testing its coils, while the curve's shape looked much healthier than my '043's, it was similarly very low. And sure enough, the car wouldn't start on it. What's more, I found that on this unit, the inner adjustment screw was nearly maxed out already, only about a quarter turn from its limit.

At this point, I'm scratching my head a bit. Could I really have gotten 2 bad rebuilds in a row? Does the inductance value really not matter, and there's something else wrong with my car? Why are my values both so different than the nominal ones Brad measured?

I checked that my LCR meter isn't bad with a 2.2H coil from DigiKey, and it read that more or less dead on. I also pulled the top off my '043 and checked to see that the transformer actuation is free and clear. Even with the core pulled to its limit, the secondary won't go much above 1.0H. The resistances in the coils are correct, so they're not shorted. All I can think is maybe the cores have been replaced with something non-suitable?

I know Jeff drove his car with my components last summer, which is further confusing, though I don't know if he tried full throttle or not, and I know my 2056 pulls a little less vacuum than an engine with a stock cam.

(IMG:http://www.914world.com/bbs2/uploads_offsite/i.imgur.com-27426-1713200815.1.png)

Values:

Brad Ander's 043 (based on 2 rebuilt and 1 NOS unit)
0 inHg = 1.39H
4 inHg = 1.18H
15 inHg = 0.71H

My Rebuilt 043
0 inHg = 0.929H
4 inHg = 0.915H
15 inHg = 0.809H

Brad Ander's 037 (based on 1 rebuilt unit)
0 inHg = 1.44H
4 inHg = 1.26H
15 inHg = 0.72H

My Rebuilt 043
0 inHg = 0.943H
4 inHg = 0.883H
15 inHg = 0.601H

So I guess, I'd like to ask the forum a favor. Anyone who has an LCR meter and a WORKING D-Jetronic car, if you're willing, do me a favor and check the inductance across your 8-10 coil with no vacuum, and post it here. If you feel like graphing your response curve, all the better!

[rjames]

Just my $.02, from my experience: The LCR meter readings are interesting and good guidelines, but to set the MPS correctly, once the outer screw is in the correct ballpark, you really only need to be able to read the AFR for a given vacuum to adjust things further. Even with the exact LCR meter that Anders used, my car wouldn't run correctly when I mirrored his settings. You'll get different readings with different brand LCRs. Yet another reason relying solely on an LCR isn't recommended.

Also, you shouldn't be using the inner screw to dial in WOT. Use the full load stop screw for that.

My order of operations:
Get the outer screw set first on the bench. I do this by putting the MPS in a vice with the adjustment screws facing up, then insert the adjustment tool in the MPS and rest it upright in place. Then using a vacuum gauge start pulling a vacuum. Adjust the outer screw so you see the tool stop moving down somewhere at around 5-6 in Hg. (reflected in Anders curve you posted above).

Then install the MPS in your car and adjust the inner and full load stop screws (in that order) using an AFR wideband sensor to guide adjustments.

Just to make sure we're all on the same page regarding which screw is which- I'm using Anders definitions:

[Cessnaporsche01]

Just my $.02, from my experience: The LCR meter readings are interesting and good guidelines, but to set the MPS correctly, once the outer screw is in the correct ballpark, you really only need to be able to read the AFR for a given vacuum to adjust things further. Even with the exact LCR meter that Anders used, my car wouldn't run correctly when I mirrored his settings. You'll get different readings with different brand LCRs. Yet another reason relying solely on an LCR isn't recommended.

Also, you shouldn't be using the inner screw to dial in WOT. Use the full load stop crew for that.

My order of operations:
Get the outer screw set first on the bench, then adjust the inner and full load stop screw with the MPS installed in the car using an AFR wideband sensor to guide adjustments.

Yeah, what I really should do is take the thing to a dyno to at least get an AFR reading on it. But I'm disinclined to spend a bunch more money without checking off that I'm not overlooking something as simple as a bad unit.

You're also correct that the outer screw is the correct adjustment for WOT mixture, but at this point, I'm just running with it uninstalled. I backed it out 'til it was no longer doing anything, and for occasional test runs, it shouldn't hurt the diaphragm to stretch to its limit. The only reason the inner screw is maxed out is that it gives me enough useful throttle range to drive the car for testing. With the idle tuned more correctly that intercept falls well into the teens, and the moment I touch the throttle the car just shuts off.

How close were your numbers to Anders'? Were you off by a similar ~30%? I know his guide gives a tolerance of .01H!

[rjames]

Just my $.02, from my experience: The LCR meter readings are interesting and good guidelines, but to set the MPS correctly, once the outer screw is in the correct ballpark, you really only need to be able to read the AFR for a given vacuum to adjust things further. Even with the exact LCR meter that Anders used, my car wouldn't run correctly when I mirrored his settings. You'll get different readings with different brand LCRs. Yet another reason relying solely on an LCR isn't recommended.

Also, you shouldn't be using the inner screw to dial in WOT. Use the full load stop crew for that.

My order of operations:
Get the outer screw set first on the bench, then adjust the inner and full load stop screw with the MPS installed in the car using an AFR wideband sensor to guide adjustments.

Yeah, what I really should do is take the thing to a dyno to at least get an AFR reading on it. But I'm disinclined to spend a bunch more money without checking off that I'm not overlooking something as simple as a bad unit.

You're also correct that the outer screw is the correct adjustment for WOT mixture, but at this point, I'm just running with it uninstalled. I backed it out 'til it was no longer doing anything, and for occasional test runs, it shouldn't hurt the diaphragm to stretch to its limit. The only reason the inner screw is maxed out is that it gives me enough useful throttle range to drive the car for testing. With the idle tuned more correctly that intercept falls well into the teens, and the moment I touch the throttle the car just shuts off.

How close were your numbers to Anders'? Were you off by a similar ~30%? I know his guide gives a tolerance of .01H!

I did not say the outer screw is for adjusting WOT. The full load stop screw is for that. Running the car without the full load stop screw will shorten the life of the diaphragm. Not a good idea and not necessary if you use the replacement full load stop screw that's provided with the kit since you can adjust the inner screw and outer screws with the full load stop crew in place.

You can't adjust the MPS correctly without a wideband AFR sensor.
Forget the LCR numbers. You're chasing your tail with those at this point. That said, a number of people, including myself, posted their numbers on an earlier thread. (The #s I posted in the thread aren't current anymore as I've made some adjustments since then).
MPS Tuning Analysis Thread

[Cessnaporsche01]

Yeah, apologies. I meant the full load stop when I said "outer screw". I've been referring to the 3 adjustments as inner, mid, and outer to myself.

Regardless, the full load stop is out, not stopping anything at any point. The outer adjustment on the diaphragm hasn't been touched.

I'll definitely be looking through that thread though.

[rjames]

Yeah, apologies. I meant the full load stop when I said "outer screw". I've been referring to the 3 adjustments as inner, mid, and outer to myself.

Regardless, the full load stop is out, not stopping anything at any point. The outer adjustment on the diaphragm hasn't been touched.

I'll definitely be looking through that thread though.

Getting the outer screw set correctly first is crucial (and easy to do using the steps I outlined above). I learned that the hard way. Good luck!

[Superhawk996]

My recollection from the original thread was that there were still basic assumptions that hadn’t been resolved such as low vacuum at idle and/or specific cam grind and potentially cam timing at assembly was an unknown.

Am I recalling that correctly?

D-jet just isn’t very tolerant of changes that would affect volumetric efficiency.

[Cessnaporsche01]

My recollection from the original thread was that there were still basic assumptions that hadn’t been resolved such as low vacuum at idle and/or specific cam grind and potentially cam timing at assembly was an unknown.

Am I recalling that correctly?

D-jet just isn’t very tolerant of changes that would affect volumetric efficiency.

After my little rebuild, it still idles at 15inHg at around 1100-1200rpm. Some people said that's low, but it fits comfortably in the idle zone from Brad's page. To quote, "At idle, the manifold vacuum is about 10 to 15 in. Hg".

I don't know what's happened to Mark DeBernardi, but I haven't been able to reach him about the cam spec - that said, and as I've said before - this car ran with this ECU and this cam/engine hardware for several years. Only new fuel control parts are the injectors and MPS, and I have bench tested the injectors to be almost exactly to spec and all identical. The fact that the MPS is very definitely not in spec is the only thing I've found that's off about this entire engine, and it happens to perfectly match the symptoms.





In other news, I know you guys are anti-induction-curve, but in that other thread, while there is variance, I don't see anybody with a full load data point below 1.15H, and most are in the 1.3-1.5H range. What's more, is where Not_A_Six was experimenting with the inner screw in that thread, it was translating his curve uniformly across the board, while mine stays within a couple dozen mH on the full load end, and only adjusts on the idle/overrun end.

Also, can't help but notice Chris Foley trash talking Fuel Injection Corp's refurb quality at the end, though he was disappointed with diaphragms rather than transformers.




Before posting this, I had an idea, so I actually just tried out popping the disassembled MPS into the car, with no cells or diaphragm, just the core extended out to its absolute limit, which is further than it probably should be, since this MPS seems to be missing the little tabs that engage the core stops.

The primary secondary coil reads 1.066H in this configuration. The car starts up immediately, pretty stinking rich but not too smoky, and responds very well to throttle input. But full throttle - even ~80% throttle - still kills it. Like, this MPS CANNOT PHYSICALLY provide any more pulse width, and it's still not enough fuel.

[emerygt350]

I agree with superhawk. My build actually produces more vacuum than the mps expects, which I believe was/is causing my cruise leanness (I think I finally have that fixed after my last trip to the Dyno). On my car there is a noticeable transition from 12inhg to 9inhg which matches nicely with dipping into the throttle from cruise. If d-jet is expecting a particular demand based on that you might be having that occur in the wrong place.

What does your car idle at for vacuum? What does it cruise at? Have you tried playing with the timing and watching the vacuum? The old way to time cars was max vacuum then bring it back a little. Maybe a degree. Getting the car in the ballpark vacuum can only help. As best you can with that cam.


And this is d-jet. Vacuum leaks don't matter.

[Cessnaporsche01]

I agree with superhawk. My build actually produces more vacuum than the mps expects, which I believe was/is causing my cruise leanness (I think I finally have that fixed after my last trip to the Dyno). On my car there is a noticeable transition from 12inhg to 9inhg which matches nicely with dipping into the throttle from cruise. If d-jet is expecting a particular demand based on that you might be having that occur in the wrong place.

What does your car idle at for vacuum? What does it cruise at? Have you tried playing with the timing and watching the vacuum? The old way to time cars was max vacuum then bring it back a little. Maybe a degree. Getting the car in the ballpark vacuum can only help. As best you can with that cam.


And this is d-jet. Vacuum leaks don't matter.

As stated above, idle is 15inHg on the dot. Right after startup it's a bit lower - like 10-13inHg - but stabilizes once the oil pressure and rpms are stable.

Agreed - other than the small trimming of pulsewidth by the TPS, the D-Jet system will just establish a higher idle if there's a leak. Heck, that's what the AAR does (and it's clamped off at the moment).

From the test drive I did, cruise is around in the 10-15 inHg range, light acceleration is like 8-12in Hg. I didn't see more than maybe 21-22inHg on overrun, but obviously I couldn't do a WOT pull. The MAP numbers seemed pretty reasonable for the car.

But again, it seems like I'm just not getting a steep enough EFI response curve. I set it super rich at idle, and it's leaned to death at WOT.

[Olympic 914]

(IMG:http://www.914world.com/bbs2/uploads_offsite/i.imgur.com-27426-1713200815.1.png)

Values:

Brad Ander's 043 (based on 2 rebuilt and 1 NOS unit)
0 inHg = 1.39H
4 inHg = 1.18H
15 inHg = 0.71H

My Rebuilt 043
0 inHg = 0.929H
4 inHg = 0.915H
15 inHg = 0.809H

Brad Ander's 037 (based on 1 rebuilt unit)
0 inHg = 1.44H
4 inHg = 1.26H
15 inHg = 0.72H

My Rebuilt 043
0 inHg = 0.943H
4 inHg = 0.883H
15 inHg = 0.601H

So I guess, I'd like to ask the forum a favor. Anyone who has an LCR meter and a WORKING D-Jetronic car, if you're willing, do me a favor and check the inductance across your 8-10 coil with no vacuum, and post it here. If you feel like graphing your response curve, all the better!

Just checked my spare 043 MPS with the Amprobe LCR set on 20

pins 8 and 10

This has been adjusted to the below


0 inHg -- 1.49

4 inHg -- 1.30

15 inHg -- 0.81


I am running a 2056 with a Raby 9590cam and a 037 ECU so my MPS is an 043 tuned to richer than 037 MPS specs.

This is my spare so you would be welcome to try it on your engine.




and just for reference sake here is a graph I posted in the above mentioned thread.



The numbers for the one on this graph were.

0 inHg - 1.52
4 inHg - 1.34
15 inHg - 0.83


But have been adjusted away from that, Graph just posted to give an idea of slope.


I know some people say you can't mix these parts but I have over 20k miles on this combo that says different.


PM sent.

[brant]

Innovate AFR up the tail pipe
No dyno needed
Drive down the road. Pull over. Slight tweek and test drive some more

Takes up to a dozen tests to get right
Then a drop of epoxy on the screws that nice you have it correct

[adolimpio]

It may be my simple mind, but it seems that something that is already relatively complicated is being over-complicated.

While it’s true that the curve is important, it seems to me that it is already predetermined by the design of the MPS - the design of the variable inductor and the aneroid cell. While we can set various points along the curve, I and not aware of any way to control the curve between those points.

I built a 2056 about 3 years ago and took great care to ensure that the MPS was functioning properly. Verified that the inductor core moved freely and that the aneroid cell was intact. I then adjusted it per Ander's spec for a 2.0 using a LCR 55a as a starting point.

I then installed an O2 and vacuum sensor so that I could read both while driving.

I drove it and noted that AFR at 15 inHg, 4 inHg and 0 inHg and adjusted the AFR targeting 12, but setting leaner toward high vacuum and richer toward lower vacuum resulting in:
15 inHg - 80h - 14.5 AFR (inner screw)
4 inHg - 128h - 13.5 AFR (outer screw)
0 inHg - 150h - 12.5 AFR (plug screw)

This was a long process:
1. Drive and monitor
2. Pull the MPS
3. Adjust
4. Repeat

What’s the curve – who knows?

The result is a 914 that runs better than any 914 I’ve ever driven, and I’ve owned 3 and driven many. Smooth cruising, smooth acceleration, rock solid idle at 800 RPM and 31 MPG on the highway. (I also have cruise control that helps with the MPG) Note that a 123 dizzy also improved the build significantly.

I’ve helped many with their MPS and found that almost every MPS has problems. I’ve even seen one, brand new, purchased from a Porsche dealer that leaked and had a crack in the diaphragm that was almost impossible to see. I’ve also seen those that were run with a cracked diaphragm for some time, allowing moisture to corrode the inductor core so that it did not move freely.

I also built this web page to help with adjusting for altitude: https://mps.dolimpios.com/
Note that if your system has GPS capability, it will automatically determine your altitude.

[brant]

The meter gives you a curve. For a hypothetical motor

The AFR gives allows you to tune your actual motor. Even if it has some wear. Even if it’s fresh/tired/etc.

[r_towle]

I wonder what material was used for the diaphragm

[brant]

Beryllium copper
Lots of old threads about this
Doubt there will ever be new ones again beyond CFR

Fuel inject corp we’re ….. back in the day….. using a different allloy
Which also had different characteristics and did not work as well as original

[r_towle]

Exactly my point

[JamesM]

So I guess, I'd like to ask the forum a favor. Anyone who has an LCR meter and a WORKING D-Jetronic car, if you're willing, do me a favor and check the inductance across your 8-10 coil with no vacuum, and post it here. If you feel like graphing your response curve, all the better!

The values DO matter as well as the curve HOWEVER your values will most likely not match Brads as the readings are affected by altitude and atmospheric pressure. I would assume when anyone says the values dont matter that is only in the context of "I tested my stock MPS and it doesn't match Brads values, is it bad?" For tuning an MPS there is absolutely only one set of values that will be correct, but again, they wont match what anyone else posts.

I think I have at least one of every 914 MPS part number here, I could give you readings from any of them but it would do you no good.

The way I do it (in my opinion the only reliable way to bench tune a MPS) involves cloning the settings of a known good matching MPS side by side by way of a T'd vacuum setup and switch on the LCR meter between the two MPSs. This way you ensure the exact same vacuum reading produces the same inductance across the entire curve.

Unless you are using an identically calibrated vacuum gauge and the same LCR meter under absolutely identical atmospheric pressure, tuning from someone else readings will at best only get you in the ballpark, and often wont even do that.

There is also a secondary factory when dealing with the 914 2.0 MPS that have been rebuilt. There was an additional spacer ring around the diaphragm on the 2.0 units that was not used in the majority of d-jet MPS. If for some reason during the rebuild process that ring was omitted it could impact your ability to dial it in to the necessary settings. Then there is also the question already mentioned around the material and quality of the diaphragms FIC uses. I have a pretty large stash of MPSs, at least one of which is an FIC rebuild from an unknown date, and the diaphragm absolutely responds differently though the midrange.

[emerygt350]

Those vacuum numbers look good to me. I pull 20 at idle and 24 max on overrun but the rest are about right. I would definitely try the mps on offer.

The curve is modifiable, as in you can ruin it, and shift it with adjusting the inner and outer screws, but in my experience it was best to establish the curve as it is supposed to look on the bench (starting with Chris's tips on preset) and then make sure it responds/ ramps correctly. After that, in the car mess with the inner and full stop as you tune to taste with the AFR. At the Dyno I had to bring in the full load stop, I was too rich at wot across the board.

You did check your injectors and you did move to a 123ignition right?

[ChrisFoley]

I have examples of FIC diaphragms in my office. They are hand made from brass sheet, soldered to trimmed used hubs. They don't appear to have good flexural properties and also look like they are difficult to seal.
My diaphragms are precise reproductions of what Bosch used, but I have to be very careful pressing the hub onto the paper thin disc or I risk stretching the center, which changes how they respond to vacuum signals.
I recently ordered more hubs but I will need to order another batch of diaphragms later this year. It takes a long time to use up one order and sales so far this year is lagging previous years. It will probably be my final order of diaphragm pressings.