Techie Help?!? Do I need a new MPEM?

[despower]

Looks like I posted this in the PWC forum by accident.

My sportster is giving me a Fault Code 5. According to my Shop manual, this points me to one of four possible sensor problems. I don't have the Vehicle Comms kit (bummer) so instead I went through all possible problems associated with code 5... these could be water (WTS), exhaust gas (EGTS), manifold actual pressure (MAPS) and throttle position sensors (TPS).

I checked resistance on WTS (within range) and the EGTS (within range) from the amps connector. I also checked the MAPS, and this seems OK (no dirt or obstruction, but I don't really know what the input impedances should be because the shop manual doesn't list them). Next I checked resistance on TPS (both the MAG and PTO side potentiometers). These all check out to within specifications.

And now for the problem...

On the TPS testing, the shop manual suggests to check the voltage coming from the Multi-purpose electronic module (MPEM) to the TPS potentiometers. The three TPS PTO side signals check out according to specs (5V, 0V and 0V), but the TPS MAG side signals should be (5V, 0V and 4-5-5V) and instead I am reading (3V, 0V and 0V). Since these signals originate from the MPEM, does this indicate that the MPEM is defective? If so, that would suck, big time. Replacing sensors are no big deal, but I suspect that the MPEM replacement is a big job that would have to be done in a shop with all proper equipment.

Advice would be most welcome at this point.

Des

 

[jords]

check where your throttle is when you tested it, at full throttle it should read 0, and will read 5 up to 80% throttle


I don't think its your mpem, its more likely your TPS, alot of people carry spares

 

[despower]

The throttle was at idle for all the tests.

Just to clarify my testing a bit, I tested the TPS pots resistances with the amps connector disconnected from the MPEM. With the TPS at idle, the resistances maps properly. Also, when I move the throttle through its full range, the resistances move smoothly (at least from what I can see on the multimeter). So, it doesn't appear to be a problem with the TPS pots, but I am not familiar enough with the TPS to know what else could be wrong.

The voltage problem that I mention is with the TPS disconnected from the MPEM, so that I can measure voltages coming from the MPEM to the TPS pots. I disconnected the PTO side pot first (voltages map correctly), then reconnected the PTO Pot and disconnected the mag side pot and measured voltages from there (voltages out of whack). So, I am assuming a problem with the MPEM because the improper voltages are coming direct from it and not the TPS.

I could try the voltage tests again and move the throttle through its entire range and see what that gives me, if you think that would help with the diagnosis.

I just checked price on MPEM... it is a (gasp) $1200 part. On the other hand, a new TPS is only $250. Believe me, I would rather it be the TPS.

Des

 

[jords]

yea they are pricey


hmmmm ......... ....seems it has been narrowed down to bad sensor or bad mpem. Going to have to take it to a dealer to hook it up to get more details. Hopefully the sensor is out

 

[despower]

Yes, that is what I figured. Big bummer since I can't get a service appointment until September after my vacation is finished.

It seems like a bit of a simple problem... improper volage supply on the MPEM, so I suspect it is a voltage resultator or some such thing on one of the boards. Anyone know of a shop manual for MPEM repair? I am comfortable working with electronics repair and have the gear to fix.

 

[despower]

Well, removing the MPEM to inspect it didn't help much. The %$#& thing is a potted unit rather than a box with cover and seal. But of course it would be. In any case, I would have to cut through the potting to get at the guts inside.

I guess if I have to replace the MPEM (heavy sigh), at least I can scrap the old one and maybe rebuild it. bye bye $$$$$

 

[despower]

I figured I would give an update to this saga... the shop managed to fit me in for a computer analysis today. Turns out that the problem was indeed a TPS and not the MPEM. I guess I jumped to the worst case conclusions. I get the Seadoo back on Friday (they didn't have a TPS in stock). A TPS replacement isn't something that I could do anyway since one needs the BRP software to reprogram the MPEM to the new TPS resistances. I think I am getting off cheap and I might be back in the water by the weekend. :cheers: :hurray: :cheers:

 

[despower]

Just thought I would close this one off.

As I had ]suspected, it was an MPEM failure as I had originally diagnosed. Looks like the dealership wasn't as diligent in performing the tests suggested in the shop manual and wrongly pointed to an ignition coil and TPS. Almost two weeks later (and I don't know how many pointless hours they are going to charge me), the realized it was a computer failure. I have a new one on order so maybe I'll be up and running soon.

 

[despower]

After an 8 week hiatus of dealer misdiagnosis and waiting for a new (Canadian made) MPEM to arrive from the US, I got the Sportster on the water yesterday. All is good (except for the two grand I had to shell out to swap the MPEM).