1800 Cars: Manifold Absolute Pressure (MAP) sensor repairer?

[ChasesDragons]

Just checked my MAP sensors vacuum response at 15inch Hg and it loses vacuum rapidly.

This is following my series of posts asking for help to start a 1971 P1800e (goldmine of info from knowledgeable sources).

Does anyone know who might be able to fix these things? I will look at other marque sites too, where DJets were used.

I don't think I will go to Bosch Classic. If it came to that, the car would go into storage until I get enough £ for a Megasquirt kits from Kurt Incledon or even an engine conversion.

BTW - would appreciate it if one you beedy-eyed ones could link me to a pressure vs H graph for the MAP model 0 280 100 010 see if I can swap over a W114 MAP sensor that is reading good resistance and vacuum readings. Desperate? YES!!! :"(
Warmest Regards
U

[Clan]

Originally Posted by ChasesDragons

Just checked my MAP sensors vacuum response at 15inch Hg and it loses vacuum rapidly.

This is following my series of posts asking for help to start a 1971 P1800e (goldmine of info from knowledgeable sources).

Does anyone know who might be able to fix these things? I will look at other marque sites too, where DJets were used.

I don't think I will go to Bosch Classic. If it came to that, the car would go into storage until I get enough £ for a Megasquirt kits from Kurt Incledon or even an engine conversion.

BTW - would appreciate it if one you beedy-eyed ones could link me to a pressure vs H graph for the MAP model 0 280 100 010 see if I can swap over a W114 MAP sensor that is reading good resistance and vacuum readings. Desperate? YES!!! :"(
Warmest Regards
U

What is wrong with it? They are a simple device with a vacuum capsule inside .. back in the 70's there was a mod to drill the sealed screwed plug in the centre to get to the fine adjuster inside ... to have some control of the mixture to overcome weak running issues . Over the years any number of Toms. Dicks or Harrys will have twiddled it and messed up the basic setting .

You probably have the Idea of getting it to match the Vacuum / Voltage factory graph

[c1800]

This is the only place I’ve seen these available.

http://irollmot.ipower.com/oscom/pro...oducts_id=1449

[LawsonJD]

Hi.
Just for info Bosch Classic in 2019 charged 370 Euros inc shipping to refurb mine, they were the only people I could find who could do the job and I wish I'd gone to them sooner instead of wasting money on 2 useless eBay ones.
Bosch 20% trade discount if you can convince them you're a workshop.
David.

[142 Guy]

First off, have you read this - particularly the section on testing the sensor?

https://jetronic.org/en/d-jetronic/55-mapsensor

Your 0.5 Bar (15 in Hg) test is the correct test value. The 'loses vacuum rapidly' would be the issue. According to Dr. D, if the pressure drops from 0.5 to 0.45 Bar in 10 seconds that would be a pass. If rapidly means it drops to 0 Bar in 10 seconds, then you likely have a Bosch paper weight. Dr. D has a good explanation of why repair of the sensor is significantly more complicated than just replacement of a leaking diaphragm.

I am not sure what you mean by a pressure versus H graph. There is a table of sensor part numbers and cross reference to vehicle at the end of the link. There is also a reference to additional information in the table which may facilitate cross referencing to a different part. However, I think you may have to be a forum member to access that. I leave that to you to explore.

A MAP sensor that fails the leak down test has failed and needs to be fixed / replaced. However, as a side note to your reference to starting problems. If your engine is completely failing to start I am not sure how big an effect the MAP sensor has on starting. The one side of the MAP sensor transformer winding is in the pulse shaping / timing circuit for the injectors. I think as long as the the MAP sensor is electrically intact that circuit should still work during cranking. However, its effect during cranking is less significant. The main injectors do fire during cranking; but, most of the fuel delivery for starting comes from the cold start injector. If your engine is failing to start then you likely have other problems in addition to a leaky MAP sensor. If the engine fires up and then dies then the MAP sensor could be contributing to that problem. The operation of the MAP sensor and the way that it alters the injector pulse widths is complicated so I am not going to step out on a limb and state whether the MAP sensor might be a contributor to failing to transition from starting to sustained running.

The possibility that the MAP sensor and the throttle switch might fail in a permanent manner were my primary reasons for switching from D jet to Megasquirt. Megasquirt can be configured in software to accept just about any solid state MAP sensor and any three terminal rheostat style TPS. If Volvo 850 TPS that I am currently using on my B20E ever become unavailable as replacements I will just have to find another TPS with the same diameter actuating shaft as a replacement.

[c1800]

“ There is also a reference to additional information in the table which may facilitate cross referencing to a different part. ”

I checked that table, there is no other compatible MAP for the 1800e listed.

A MAP that won’t hold vacuum i.e. senses no vacuum, will signal the ECU a WOT condition, which results in too much fuel for starting and idling.

[ChasesDragons]

Hi all,
Thanks again for your help in this ever deepening mire. Forgive me for not answering with poster names, I am using a little smartphone to message this! No luxury of reference.

For all who asked; H is the SI unit for inductance apparently.

Mine does seem to lose Vacuum in about 5 seconds. And as it has been mentioned by one of you, I have always thought a malfunctioning MAP would lead to a very rich mix. I thought this in itself might stop the engine firing up? I have installed another MAP from a Mercedes W114 250CE. There is no change in the car's behaviour.

I think there is £50 between IROLL's MAP and BOSCH's rebuild. Push to shove, I would go with Bosch just for the confidence in immediate aftersales support....but that is a LOT of money to just bet on.

There must be SOMEKIND of transducer out there which can be programmed to sense vacuum and fabricate the required inductance values to divert many of us from this mechanical mysery.

142 - did you build the MS system yourself or use Kurt's "Stealth System"? It might be the ultimate solution. But at about 300% of the rebuild cost.

Warmest Regards
U

[142 Guy]

Originally Posted by c1800

“ There is also a reference to additional information in the table which may facilitate cross referencing to a different part. ”

I checked that table, there is no other compatible MAP for the 1800e listed.

A MAP that won’t hold vacuum i.e. senses no vacuum, will signal the ECU a WOT condition, which results in too much fuel for starting and idling.

You are correct that the table that is visible does not provide any direct part number cross references between the early 1800E MAP sensor and other MAP sensors. But, Dr. D jet has mapped the response of a lot of the D jet sensors and if that information is available it might facilitate selection of a sensor with a similar response. I am assuming that information might be the reference to 'only registered users get more information'. Personally that is not a path I would take if Iroll is selling (and gaurantees) the correct sensor for the 1800E. If you have tried the registered user path and it yields nothing then that is the end of it.

You are likely correct that a leaking MAP sensor will cause the controller to extend the injector pulse width. Since Chase Dragons can still pull (but not hold) a vacuum of 0.5 Bar on the sensor the armature in the sensor is likely moving so it is not completely simulating a wide open throttle. However, the leaking sensor likely has no impact during the start / cranking phase.

During cranking the intake manifold pressure is essentially atmospheric. I have attached a data log of a cold engine start on my B20E showing RPM (white) and MAP (red). Atmospheric pressure at my altitude is typically 95 kPa and you can see the individual cylinder intake strokes during initial cranking. Pressure in the manifold does not start to drop until the engine speed rises above 300 RPM which is when my ECU switches to running mode. Even at 440 RPM the manifold pressure has only dropped from 96.5 kPa to 91 kPa So, under normal circumstances the D jet MAP sensor on a B20E would be reading close to atmospheric pressure during the starting phase. Hence my comment that if Chase Dragon can't get the engine to start it is not because of a problem with a MAP sensor leaky diaphragm causing it to read a high MAP. If the engine starts; but, will not continue to run that is a different kettle of cod!

[142 Guy]

Originally Posted by ChasesDragons

Hi all,
For all who asked; H is the SI unit for inductance apparently.


I think there is £50 between IROLL's MAP and BOSCH's rebuild. Push to shove, I would go with Bosch just for the confidence in immediate aftersales support....but that is a LOT of money to just bet on.

There must be SOMEKIND of transducer out there which can be programmed to sense vacuum and fabricate the required inductance values to divert many of us from this mechanical mysery.

142 - did you build the MS system yourself or use Kurt's "Stealth System"? It might be the ultimate solution. But at about 300% of the rebuild cost.

Warmest Regards
U

OK, H is presumably Henries which is indeed the unit of inductance. However, it is the coupling between the two coils in the transformer inside the sensor that changes as the core of the transformer moves back and forth as the pressure changes that is the important factor. That is the 'response' that Dr Djet talks about mapping.

I saw prices a price range of 300 to 600 Euro for the Mercedes / Bosch rebuild service. If the cost is 300 Euro then perhaps its a wash. Scandcar lists them for sale on an exchange basis at a higher price.

https://classic-volvo.com/catalog/pr...nge-for-volvo/

The style of pressure sensor that Bosch used was quite common. The industrial practice when using this type of sensor was to apply a fixed AC exciting signal on the primary winding and then read the magnitude of the AC voltage on the secondary winding to determine pressure. The output signal changed as the diaphragm moved the core and changed the coupling between the primary and secondary winding. A modern low cost silicon chip MAP sensor coupled with a simple Arduino-like controller would easily emulate that type of voltage output device for less than 75 Euro. The problem is that Bosch got clever and instead of reading the output voltage they use the secondary winding to control current in a circuit which charges a capacitor which sets the pulse width of the injector pulse. That current control strategy is brilliant in execution, hard to understand how it operates; and it greatly simplifies the number of circuit components by eliminating the need to do an output voltage to charging current control conversion. It also precludes a relatively simple retrofit.

Winter here leaves me with idle time and I am cheap so I elected to build my own from a kit. My MS is now also heavily modified with sequential fuel and ignition control, E fan control, knock sensing and provision for meth injection (should I ever take leave of my senses) that a prebuilt system would be a waste.

If Kurt is still selling his system, he has put a lot of work into retaining the stock look. I believe he also provides a basic configuration which has value. You would likely be able to install it and then start and probably drive the car.
It took me two months of fiddling around before I was actually able to drive my car and about 2 years of tweaking before I eliminated the 'is it going to consistently start' under all conditions uncertainty. The one thing I would wonder about with his base configuration is cold starting. He is in Nevada so I expect that he has not spent a lot / any time configuring for cold starts below 0C. You might be on your own for cold weather starting. You do pay for the stock look and that initial configuration. If you are considering his system, I would find out what firmware he is running. I find that the MSExtra version of the firmware written by James Murray in the UK works much better than the original B&G firmware.

Note that MS2 is getting long in the tooth and rather expensive. When I built my first kit I think it cost around $200 - that ship has long sailed. There are some very good 4 cyl stand alone EFI controllers that are price competitive with MS2 - if you are inclined to do your own implementation and are prepared to go through the work of configuring and testing which is not insignificant.

[c1800]

“ I am assuming that information might be the reference to 'only registered users get more information'.”

142, I am a registered user on that website. There is no further information showing or available on that page or in the chart when I login. I can only guess that reference is to further information may be available by asking questions on that forum as a registered user.

To that end Dragon you might register and then inquire further on that forum. I have asked questions there and have been answered fairly quickly by Volker who is the author of the articles.

Dragon, wondering if you can start yours with some starting fluid (ether) ? Which might eliminate the MAP as the cause of your ‘starting’ problem. Your leaking MAP will still cause a ‘running’ problem. Possibly your leaking map and numerous starting attempts have fouled the plugs and the oil with gasoline?