Map sensor testing?

[wayneg]

My system KME Diago g3 has started to play up and with no computer diagnostics to help I am looking to test the map for correct function. Can anyone help with a method using a basic multimeter.
As always the car changes over to gas after about 5 mins driving and then it will randomly switch back to petrol giving an alarm. some times if I switch the system off then back on it will go back to gas ok, other times it will not go back until the next day when it seems fine until the next drop out.
I understand the KME maps are suspect and dont like heat. Can I use one of the generic ones on ebay if I need one?

Map Sensor for LPG CNG Sequential Injection System on Gasoline Cars Black | eBay (http://www.ebay.com/itm/MAP-Sensor-for-lpg-cng-sequential-Injection-system-on-gasoline-cars-black-/181415606044?hash=item2a3d36771c&vxp=mtr)

[p38arover]

Which sensor do you have? I recently replaced my KME sensor with a new design unit. I got it from Germany as the local KME agent didn't respond to emails.

This is the one I'm running. http://www.ebay.com.au/itm/KME-MAP-Sensor-/261080071637

[wayneg]

I have the original, now obsolete unit. It is fitted into the airfilter box, external side of the filter. I dont want to randomly start changing parts if I can do some basic diagnostics. What are the symptoms of a Map going bad. The generic unit looks more like the one I have, gas connection is butted to map rather than straight through with the later model

[bee utey]

The output of the MAP I tested earlier is just a linear output voltage below the supply voltage to the sensor of 5V. You could simply run a pair of wires from the back of the MAP sensor plug (0V, sensor output) to the cabin and monitor the voltage with a multi meter. You can soon see which pin is the gas pressure output by the way it varies under full load. If it drops to zero and triggers your alarm you've got your culprit.

[wayneg]

I will have to find what each colour wires are for, are maps all 4 wire, poss neg and output from each of the 2 sensors? Is the Vac just on and off

[bee utey]

I will have to find what each colour wires are for, are maps all 4 wire, poss neg and output from each of the 2 sensors? Is the Vac just on and off
You don't have to "find out" anything. Basic learning: you have to test and identify each connector with the engine running and while varying the throttle. Absolute pressure is that which is above a full vacuum, eg sea level air pressure is around 100kPa. Manifold vacuum gives a quick rise in absolute pressure therefore voltage rise when you flip open the throttle. Gas pressure will drop at full load only and its voltage will normally be higher (typically 2-3x higher than the voltage at lowest vacuum) than the manifold absolute pressure (MAP) voltage output. I quote what I wrote below:


The output of the MAP I tested earlier is just a linear output voltage below the supply voltage to the sensor of 5V.

Nothing "on and off" about it. Use a thin wire probe and push it past the rubber seals on the connector. MIG welding wire or a small paper clip will do it.

[p38arover]

I have a KME Diego sequential system on my 4.6 litre P38A.

As mentioned earlier in this thread, a few months back I replaced the older style gas pressure/MAP sensor that had failed (again):

https://www.aulro.com/afvb/images/imported/2015/02/907.jpg

with the newer in-line design:

https://www.aulro.com/afvb/images/imported/2015/02/908.jpg

Recently, the system has started to shut off when driving and reverting to petrol. It seemed to happen on deceleration so did some playing around and I've found I can often get it to do this if I suddenly take my foot off the accelerator. Not always, but often enough.

I'm starting to think it's the new pressure/MAP sensor. I hope not. I had to get this one from Germany as the Australian KME supplier doesn't answer emails.

Are these sensors more reliable than the old ones? Am I looking in the wrong area?

I have the software and connector lead to look at the ECU - if I knew what to look for in this case. I suspect I'd be looking for a low gas pressure reading like I was seeing when the old sensor failed.

Any suggestions welcome,

Ron