MAP sensor failure - causes?

[weasley]

On Friday I went for an annual mini-tour with a few friends, total of around 600 miles. It involved riding to a central meeting location where we stay for the weekend with a Saturday ride-out. Anyway, part-way into the outbound journey the FI light came on - the bike was still running so I kept going and found a safe place to pull over.

Once I had stopped and put it into neutral the FI light blinked its error code to me - code 9. This translates as "Manifold absolute pressure sensor cylinder 1 - input too high/low". Since the engine was still running I kept on going and completed the weekend with few issues - on first starting it would run a bit rough and occasionally stall until the ECU realised the sensor had failed and, I assume, defaulted to a fixed pressure value, after which it would run OK, if a little 'off'.

Anyway, this same sensor failed around 18 months ago and I replaced it with a genuine new KTM one. My question is, could there be an underlying cause of the sensor failing? Spiky voltage? Vibration (it is fixed on a rubber-damped mount)? Or is it just bad luck and/or poor quality parts?

There appears to be a global shortage of this particular sensor; as I was riding the rest of the way to the meet my wife phoned every KTM dealer in a 100 mile radius of my route to see if anyone had one - no luck and some saying back-ordered until November. I have found some used ones on eBay which I will try, pending the arrival of a new one from a KTM supplier. The good point (if there is one) is that I can change it in 30 seconds with no tools (which prompted me to wonder if I could swap it with any other LC8-engined KTMs or Husqvarnas I came across during the weekend... ).
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Yamaha XJ600 | Yamaha YZF600R Thundercat | KTM 990 SMT | BMW F900XR TE

[WD Forte]

Just because the ECU says fault doesn't necessarily mean the MAP sensor is actually faulty.
A lot of sensors run a on a 5v supply possibly less, so small variations can have a greater effect than a small signal variation in a 14V supply
( bike run at closer to 14v than 12V)

Bikes are an electrically 'noisy' environment so good connections cabling,grounding, shielding etc is important.
I'd be checking the above before shelling out any dosh

I fixed one on a scoot a while back that wasn't broken, it just had
a damaged cable
Nice easy fix for a change
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bikers smell of wee

[weasley]

Yeah, I did think about that. TBH I hope it’s the sensor because that’s an easy fix - tracing the wiring through the loom will be a right ball ache.

From the behaviour I observed it looks like it doesn’t log the error and keep it active - it resets for every start and then throws the error after running enough to determine it’s faulty. When I had the same error before a new sensor fixed it but I guess this could be additive on top of a wiring fault, or at least a changed resistance somewhere.

What I don’t know is if or how I can test the sensor itself; ideally I’d swap the #1 and #2 sensors over and see if the fault moves, but getting to the front cylinder sensor is another ball ache.
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Yamaha XJ600 | Yamaha YZF600R Thundercat | KTM 990 SMT | BMW F900XR TE

[WD Forte]

RE testing with only a meter not scope
I'd use the working sensor as reference and compare supply voltages
first
They should both have identical supply voltages
Next test ground resistance on both connectors, it should be identical again.

Output signals will be a wee bit more complex but I'd get a note pad to log results start with
Ignition on and engine not running
Tickover
3000 rpm
6000 rpm
and compare results

I often use small stiff-ish wires pushed into connectors and croc or spring clips on my meter leads
a paper clip might do
trying to do this by holding probes in place is fiddly and can skew results
I use an autoranging meter mostly but set a manual one to say 20VDC

Intake leaks will bugger up MAP pressure readings too
so worth checking pipework/tubes and fittings
____________________
bikers smell of wee

[MCN]

Wiggle Test.
Move the cables about and diddle with the connectors and see if the ecm changes it's mind.
WD-40 the harnesses. Unplug and WD-40 THE connectors too.
Is it possible to swap No. 1 sensor with No. 2 sort of thing?

Common failure on a common position might be 'environmental'. First to get wet, last to get dry, Hotter than other similar units.

Dealers, if you are lucky, sometimes tell about such things but they might also remain schtum about 'issues' unless you cross their palms with silver.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[Hong Kong Phooey]

This bike is running on canbus, so in theory it has a better tolerance to noise and voltage diffs, the signal is out of bounds for the expected value. The service manual for my RC8 states to check for open circuit, short circuit and voltage as per table below. Very likely the same part and values for your bike.

Do not forget that cyl 1 is the rear according to KTM!

There are specific requirements to do the test, and the dealer computer reads the voltage directly but you could piggy back the pins to take a reading.

Manifold absolute pressure sensor cylinder 1 - checking the voltage
Condition
The ignition is on.
The diagnostic tool is connected and running.
The engine is switched off.

Basically look for 3.42v to 3.78v depending on ambient pressure.

Manifold absolute pressure sensor cylinder 1, voltage "PM1AD"
at: 350 mbar (5.08 psi) 1.62… 1.68 V
at: 400 mbar (5.8 psi) 1.77… 1.83 V
at: 450 mbar (6.53 psi) 1.92… 1.98 V
at: 800 mbar (11.6 psi) 2.97… 3.03 V
at: 850 mbar (12.33 psi) 3.12… 3.18 V
at: 900 mbar (13.05 psi) 3.27… 3.33 V
at: 950 mbar (13.78 psi) 3.42… 3.48 V
at: 1,000 mbar (14.5 psi) 3.57… 3.63 V
at: 1,050 mbar (15.23 psi) 3.72… 3.78 V

If you already replaced the rear sensor then the connector and wiring could be the issue. So swapping them around is the logical next step. Don't neglect to check the vac hose condition and throttle bodies are properly connected.

AFAIK there is no general issue with these sensors.
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'81 CG125, '97 FZS600 : '99 CBR600F4, '09 KTM RC8

[to v or not to v]

probably no use to you. but in the past, ive had sensors go on my cars, and they were fixed by simply cleaning them.
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current bike Yamaha Thunderace.
its old and fat, but its a damned good ride. the bikes not bad either.

[weasley]

Great input, thanks! I hadn’t thought about air leaks - will bear that in mind. I’ll see if I can rig up a way to test voltages and I may have a vacuum pump somewhere that I could alter the pressure with. I don’t suppose the RC8 manual has the pinout for the sensor or loom? There are three wires there. [EDIT - don’t worry, found it on a wiring diagram].

I was aware that #1 is the rear cylinder - this is the easy one to get at. The other one is buried under the tank and airbox.
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Yamaha XJ600 | Yamaha YZF600R Thundercat | KTM 990 SMT | BMW F900XR TE

[weasley]

Not had a chance to test this out yet, but three MAP sensors off of a bike being broken have now arrived and one has been put in place. A new OEM sensor is en route from the Netherlands too, so probably expecting that some time next summer when it clears customs. I plan to carry a spare or two with me now, assuming at least one of the three used ones is good.

Hopefully I can give this used replacement a test run soon and see if that changes anything.
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Yamaha XJ600 | Yamaha YZF600R Thundercat | KTM 990 SMT | BMW F900XR TE

[WD Forte]

went down a google rabbit hole starting at Fowler parts to see what they looked like
part number 61041085100
£118 not in stock

then I did more gurgling and found this site
which offers the same part number for 30 euros
you may know of it already, they may not stock them, its a trap!! etc
but will bung the link here for your perusal

https://www.boonstraparts.com/de/teil/ktm-1290-super-duke-gt-2016-2018-luftdruck-sensor-2018-61041085100/000000524353
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bikers smell of wee

[weasley]

As it happens the one I ordered from motorcyclespareparts.eu turned up today. It was the only place I found with confirmed stock.
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Yamaha XJ600 | Yamaha YZF600R Thundercat | KTM 990 SMT | BMW F900XR TE

[weasley]

Fitting the used sensor has cured the issue, or at least it now runs as it did before and there’s no error light. As soon as I started it I knew it was sorted as it ran smoothly with no stumbling. A 2 hour ride confirmed no issues. The ride was to a bike dealer where I booked a test ride for Friday.
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Yamaha XJ600 | Yamaha YZF600R Thundercat | KTM 990 SMT | BMW F900XR TE

[Hong Kong Phooey]

Good result. Small enough to tape a spare to the airbox.
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'81 CG125, '97 FZS600 : '99 CBR600F4, '09 KTM RC8

[to v or not to v]

[weasley]

[weasley]