Confirmation of a dead MPEM on a 1994 GTS

[Dougsnash]

On my 'new to me' 1994 GTS, I have been experiencing intermittent hard to impossible starting. After an extensive cleanup, I am fairly confident in the test run capability of the fuel system and have verified with a spark tester that I am only intermittently getting spark to the spark plugs. I have trimmed both ends of the spark plug leads back and re-verified that I have a good ground path for the coil and MPEM. On a guess, I disconnected the MPEM from the coil so that the coil was being fed directly from the stator and verified I have good spark. The machine will start and idle with the MPEM disconnected from the ignition circuit and returns to very intermittent spark when the MPEM is reconnected. Thus, I am pretty sure the MPEM is in the process of failing. This is a 1992 vintage MPEM with external fuses and sockets with relays rather than the original 1994 vintage one supposed to be there. Another symptom of a failing MPEM is there is no voltage on the output to the buzzer/ overheat sensor.

Can someone with more knowledge on these machines confirm my suspicion that the MPEM is toast? Or, if I am wrong about a bad MPEM, point me in the correct direction. And if the MPEM is actually toast, where is a good place to find the proper replacement?

Thank you

Doug M

 

[GGuillot]

This is a 1992 vintage MPEM with external fuses and sockets with relays rather than the original 1994 vintage one supposed to be there.

Do you know if it ever ran with the 92' MPEM? If it's a 94' GTS, I'd verify if it's even compatible to be substituted with a MPEM from a 92' something model. May want to price the correct MPEM for it. You can contact https://www.westsidepowersports.com/ and see what he''s got. I dealt with a DESS recognition/no 2 beeps issue on my 96' GSX build and ended up getting another MPEM from Nick. Give him a call, reasonable and a quick turnaround.

 

[Dougsnash]

Do you know if it ever ran with 92' MPEM?

It seemed to run well when I made the deal on the machine. After I did a bunch of cosmetic cleanup on it, I put the machine in the water and gave it a short water test. Other than being very difficult to start, the engine ran well once it was running. After I pulled the machine from the water, however, it would not run at all, only occasionally farting. I cleaned up the wiring in the grey electrical box and shortened the plug wires a bit to get clean wire and the machine seemed to run great again that evening. The next day, however, it was back to its original intermittent spark issues. And again today, I could not get reliable spark with the MPEM plugged in.

The '92 MPEM wiring is slightly different than the '94 due to supposedly using external fuses and plug in relays. Once I looked at the '92 manual, I understood how the MPEM connects to the '94 machine. My MPEM does not have any external fuses installed which if it was going to work, would have been done before the machine was given regular use. The aftermarket 587 MPEMs listed on E-Bay and Amazon say they are good for 92-94.

Doug

 

[GGuillot]

It seemed to run well when I made the deal on the machine. After I did a bunch of cosmetic cleanup on it, I put the machine in the water and gave it a short water test. Other than being very difficult to start, the engine ran well once it was running. After I pulled the machine from the water, however, it would not run at all, only occasionally farting. I cleaned up the wiring in the grey electrical box and shortened the plug wires a bit to get clean wire and the machine seemed to run great again that evening. The next day, however, it was back to its original intermittent spark issues. And again today, I could not get reliable spark with the MPEM plugged in.

The '92 MPEM wiring is slightly different than the '94 due to supposedly using external fuses and plug in relays. Once I looked at the '92 manual, I understood how the MPEM connects to the '94 machine. My MPEM does not have any external fuses installed which if it was going to work, would have been done before the machine was given regular use. The aftermarket 587 MPEMs listed on E-Bay and Amazon say they are good for 92-94.

Doug

If you've done everything you can do, you only have yourself to convince if you should get another MPEM. Usually the MPEM is black or white, they either work or not. I'd double check all grounds, when that's not right, weird ignition run issues can occur.

 

[Dougsnash]

I'd double check all grounds, when that's not right, weird ignition run issues can occur.

I will double check the ground path back to the engine. I am pretty sure of the grounds internal to the electrical box but maybe the ground path back to the engine and thus the battery is a bit flaky

 

[Dougsnash]

I will double check the ground path back to the engine.

Ground checks good at 1 ohm from the coil ground through to the negative battery cable end (with the battery disconnected).

 

[POPPS]

Have you load tested the battery fully charged, (12.7 v)? Have you tested the trigger pickup? And of course have you checked the front electrical plug for corrosion

 

[Dougsnash]

Have you load tested the battery fully charged, (12.7 v)

Battery is brand new AGM battery and I have verified it is fully charged at or above 12.7 v

I have printed the resistance table from the shop manual and will ohm out the coil and trigger coils tonight after work. Given that the engine sparks and runs reliably when disconnected from the MPEM, and dies and has intermittent spark when connected to the MPEM, I am pretty sure the MPEM is defective. Definitely the MPEM unit I have in my machine is not the correct one so I have ordered a correct replacement.

Also, with the engine either running with the coil lead disconnected or turning over with the starter button pressed and the coil connected, I am not getting any output on the lead that is supposed to power both the buzzer/over-temp switch and the power output used for the instruments. This suggests to me that there is an internal failure in the MPEM. Once I have the new MPEM connected, I am going to cut this old one apart for curiosity sake. I cannot imagine that the internal circuitry is all that complicated so I will be interested to see how the box does what it does.

Thanks for your suggestions.

Doug

 

[Dougsnash]

A follow up to my spark issues. I purchased and aftermarket MPEM from Amazon and installed it in my '94 GTS tonight. Prior to replacing the MPEM, I had no spark. With the new MPEM, the engine fired up right away and seems to run well. I have not yet water tested the machine with the new MPEM so I am not calling things completely sorted yet but I am happy with the progress.

Doug