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PV, 120 (Amazon), 1800 General Forum for the Volvo PV, 120 and 1800 cars |
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Manifold Absolute Pressure (MAP) sensor repairer?Views : 2722 Replies : 34Users Viewing This Thread : |
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Mar 6th, 2021, 13:17 | #1 |
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Manifold Absolute Pressure (MAP) sensor repairer?
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 Last edited by ChasesDragons; Mar 6th, 2021 at 13:21. |
Mar 6th, 2021, 15:08 | #2 | |
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Quote:
You probably have the Idea of getting it to match the Vacuum / Voltage factory graph
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Mar 6th, 2021, 16:44 | #3 |
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This is the only place I’ve seen these available.
http://irollmot.ipower.com/oscom/pro...oducts_id=1449 |
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Mar 6th, 2021, 16:53 | #4 |
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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. |
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Mar 6th, 2021, 18:15 | #5 |
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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. Last edited by 142 Guy; Mar 6th, 2021 at 18:17. |
Mar 6th, 2021, 20:53 | #6 |
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“ 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. |
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Mar 6th, 2021, 22:04 | #7 |
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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 |
Mar 6th, 2021, 22:53 | #8 | |
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Quote:
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! Last edited by 142 Guy; Mar 6th, 2021 at 23:05. |
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