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914World.com _ 914World Garage _ Manifold pressure sensor calibration Bosch
Posted by: steuspeed Aug 30 2022, 08:14 PM
Does anyone know of a source for the MPS factory inductance settings. I have a 73 2.0 that was running on a tampered Volvo MPS. I picked up a 73 2.0 914 specific MPS with tamper plug in tact. Vacuum is good. The inductance readings are not matching up with pbanders numbers on rennlist.
https://members.rennlist.com/pbanders/manifold_pressure_sensor.htm#Diaphragm
I noticed his testing was done on a rebuilt unit.
Posted by: rjames Aug 30 2022, 09:34 PM
I think the consensus is to take his numbers primarily as a guide/starting point- even if you are using the exact same meter he used. (If you use a different model the numbers won’t match up anyway.)
If your car runs well with the MPS as is, I’d just run with it. If you really want to make sure it’s dialed in, it would be better to read your AFR numbers and then adjust it accordingly.
Posted by: JeffBowlsby Aug 30 2022, 09:36 PM
Does anyone know of a source for the MPS factory inductance settings. I have a 73 2.0 that was running on a Volvo MPS. I picked up a 73 914 specific MPS with tamper plug in tact. Vacuum is good. The inductance readings are not matching up with pbanders numbers on rennlist.
https://members.rennlist.com/pbanders/manifold_pressure_sensor.htm#Diaphragm
I noticed his testing was done on a rebuilt unit.
No factory source exists. Brad A used several NOS and good used/untampered with MPSs to develop his published values, using the same exact equipment he used, which in my experience have proven to be lean. They also depend on applying an altitude adjustment factor to them based on your location, not his. He describes that process on his site.
Another complication is that each engine is different due to its condition and wear which has implications to the optimum AFR needed. Best approach is to put the car on a dyno or EGA monitor to dial it in precisely. The meter/calbration values only get you in the ballpark fine tuning is neded with the corrct equipment to set AFR.
Posted by: brant Aug 30 2022, 09:56 PM
Todays fuel is very different from the fuel available when the cars were built. Your car will be lean on a factory tuned MPS You need to adjust the unit for todays fuel
Posted by: steuspeed Aug 30 2022, 10:09 PM
I think the consensus is to take his numbers primary as a guide/starting point- even if you are using the exact same meter he used. (If you use a different model the numbers won’t match up anyway.)
If your car runs well with the MPS as is, I’d just run with it. If you really want to make sure it’s dialed in, it would be better to read your AFR numbers and then adjust it accordingly.
Runs great on the volvo MPS, but lowest idle I can get is about 1200 rpm. With the proper MPS I'm getting low idle that hunts 700-1000 with the idle screw almost all the way out. Perhaps I need to play more with the volvo MPS since the tamper plug is out? I was just trying to hit the numbers on pbanders doc, which I could only get 1 of 3 to match.
Posted by: steuspeed Aug 30 2022, 11:53 PM
If this is true.
... low pressure in the MPS chamber at idle, they expand. As a result, the armature is driven out of the core, reducing the inductive coupling between the coils. The contact trigger pulse is minimally coupled to the output coil, causing the ECU to send a short injection pulse. However, at idle, the throttle position sensor turns on the idle circuit in the ECU, which lengthens the pulse and enriches the mixture independently of the MPS response.
Perhaps my idle problem is the Throttle position sensor. Must be an adjustment for that?
Posted by: emerygt350 Aug 31 2022, 05:06 AM
Your car shouldn't really be using the mps at idle. When the car goes into idle (according to the tps) the computer takes over and you use the dial on the ecu to set the mixture. That said, my car idles perfectly and changing the mps does affect idle performance.
I agree with the others. Get an afr and tune it yourself with Chris's kit from tangerine racing. I set it according to his directions and then fine tuned it in by running back and forth between two interstate off ramps. Do you have a head temp gauge? I wouldn't drive without one if you don't know what your mps is up to.
I also did some tuning on the dyno as well but found it much easier to do it myself on the road with Chris's awesome little tool. I also installed a vacuum gauge. Not necessary but very very helpful. And super cheap.
Posted by: BeatNavy Aug 31 2022, 05:33 AM
I also did some tuning on the dyno as well but found it much easier to do it myself on the road with Chris's awesome little tool. I also installed a vacuum gauge. Not necessary but very very helpful. And super cheap.
Yes, the vacuum gauge is very helpful to understanding what driving conditions constitute "part load," in particular. For example, light cruising on a flat road is NOT part load.
Based on my individual experiences, Anders' numbers were actually too rich for me for whatever reason.
You need to use all the "clues" to get to where you want to be, and Anders' numbers are a guide (the slope of the curve is useful). That unmolested MPS you picked up is very useful for calibrating your specific meter, but you still need to use: AFR readings, vacuum readings, performance/behavior from idle to WOT, head temps, exhaust smell, plug color, etc. etc.
Posted by: dr914@autoatlanta.com Aug 31 2022, 08:29 AM
fuel injection corp will have the factory original specs, but like the comments previously, each old engine is not different and factory specs may not make THAT engine run as well. I would also think that Chris at Tangerine should comment as he has made a diaphragm kit for the pressure sensor
Posted by: GregAmy Aug 31 2022, 09:18 AM
I wish I knew more about how that system worked; seems like it would not take a lot to create a digital-to-analog converter to mimic it from, say, a GM 1 bar MAP sensor...
Then again, for mostly-stock engines, Chris' diaphragm rebuild and tune pretty much covers it.
Posted by: JeffBowlsby Aug 31 2022, 09:46 AM
I wish I knew more about how that system worked; seems like it would not take a lot to create a digital-to-analog converter to mimic it from, say, a GM 1 bar MAP sensor...
Then again, for mostly-stock engines, Chris' diaphragm rebuild and tune pretty much covers it.
Others have suggested this…no one has succeededed
Posted by: emerygt350 Aug 31 2022, 12:48 PM
I wish I knew more about how that system worked; seems like it would not take a lot to create a digital-to-analog converter to mimic it from, say, a GM 1 bar MAP sensor...
Then again, for mostly-stock engines, Chris' diaphragm rebuild and tune pretty much covers it.
Others have suggested this…no one has succeededed
Yeah, there is some dark magic going on in that thing. P banders describes all the interrelated actions pretty well. I tried just sketching out a little bit of what was doing what under different conditions and I gave up pretty quick and just used the vacuum, the afr, and my gut. You learn pretty quick about how each adjustment will affect the outcomes.
Posted by: ChrisFoley Aug 31 2022, 01:06 PM
Your car shouldn't really be using the mps at idle. When the car goes into idle (according to the tps) the computer takes over and you use the dial on the ecu to set the mixture.
That's not accurate. The brain still reads the inductance signal at idle. The knob on the ECU provides a narrow adjustment range - for idle only - which isn't useful unless the AF mixture is already close to optimal. It can't be used to correct a too lean or too rich mixture.
Posted by: ChrisFoley Aug 31 2022, 01:09 PM
Yeah, there is some dark magic going on in that thing.
...
Its a simple electro-mechanical device with limited adjustability. No need to create an electronic substitute if you understand how it operates.
Posted by: rjames Aug 31 2022, 01:18 PM
@http://www.914world.com/bbs2/index.php?showuser=17042 . What amount of vacuum are you using to set part load AFR? 4 in. Hg?
Posted by: ClayPerrine Aug 31 2022, 01:29 PM
I wish I knew more about how that system worked; seems like it would not take a lot to create a digital-to-analog converter to mimic it from, say, a GM 1 bar MAP sensor...
Then again, for mostly-stock engines, Chris' diaphragm rebuild and tune pretty much covers it.
Others have suggested this…no one has succeededed
If you are going to go to the extent of making a converter, you might as well go with a complete microsquirt system. It is probably easier to do.
Clay
Posted by: GregAmy Aug 31 2022, 01:52 PM
I still admire the D-Jet system. Ahead of its time, it's a natural predecessor to my Microsquirt design. Sadly, just not very tunable.
Posted by: emerygt350 Aug 31 2022, 03:56 PM
Your car shouldn't really be using the mps at idle. When the car goes into idle (according to the tps) the computer takes over and you use the dial on the ecu to set the mixture.
That's not accurate. The brain still reads the inductance signal at idle. The knob on the ECU provides a narrow adjustment range - for idle only - which isn't useful unless the AF mixture is already close to optimal. It can't be used to correct a too lean or too rich mixture.
Anders states that at idle the mps is taken out of the loop. As I said, I don't think that is the case since I noticed adjustment does alter idle. Just stating that anders wrote otherwise.
And as far as idle mixture goes, my ecu really moves the afr, 10.5 - over 15
Posted by: BeatNavy Aug 31 2022, 04:40 PM
@http://www.914world.com/bbs2/index.php?showuser=17042 . What amount of vacuum are you using to set part load AFR? 4 in. Hg?
Hey @http://www.914world.com/bbs2/index.php?showuser=4467 Robert, yes, 4 in Hg as per the Anders' baseline.
Posted by: rjames Aug 31 2022, 08:27 PM
@http://www.914world.com/bbs2/index.php?showuser=17042 . What amount of vacuum are you using to set part load AFR? 4 in. Hg?
Hey @http://www.914world.com/bbs2/index.php?showuser=4467 Robert, yes, 4 in Hg as per the Anders' baseline.
Thanks!
Posted by: mgphoto Sep 1 2022, 10:46 AM
@http://www.914world.com/bbs2/index.php?showuser=17042 . What amount of vacuum are you using to set part load AFR? 4 in. Hg?
Hey @http://www.914world.com/bbs2/index.php?showuser=4467 Robert, yes, 4 in Hg as per the Anders' baseline.
Thanks!
That number is based on a torr factor, that is the height above sea level where the measurements are made.
If you are tuning you must take into account the difference in altitude between your location and pbanders. Because of this you might not be playing in the same ballpark.
Posted by: rjames Sep 1 2022, 12:27 PM
Adjusting for sea level, I calibrated mine using Anders' #s and the the exact same Wavetek LCR55 meter he used, and the AFR was way off. It was a nice learning experience, but didn't really help me get to the correct settings for my car. All that was needed was the correct starting point for the outer screw and a wideband sensor as a tuning guide. YMMV.
Posted by: emerygt350 Sep 1 2022, 12:41 PM
Adjusting for sea level, I calibrated mine using Anders' #s and the the exact same Wavetek LCR55 meter he used, and the AFR was way off. It was a nice learning experience, but didn't really help me get to the correct settings for my car. All that was needed was the correct starting point for the outer screw and a wideband sensor as a tuning guide. YMMV.
Yep, same here. Although I didn't have the same meter.
Posted by: tjgalvin Oct 17 2022, 02:49 PM
Adjusting for sea level, I calibrated mine using Anders' #s and the the exact same Wavetek LCR55 meter he used, and the AFR was way off. It was a nice learning experience, but didn't really help me get to the correct settings for my car. All that was needed was the correct starting point for the outer screw and a wideband sensor as a tuning guide. YMMV.
Yep, same here. Although I didn't have the same meter.
My MPS won't hold vacuum. The O-ring is split. Is there a source for new gaskets for the MPS?
Thanks.
Posted by: emerygt350 Oct 17 2022, 04:16 PM
Tangerine racing has everything you need. Awesome kit and instructions. Make sure you get the tuning tools.
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