How to confirm MPEM dead on 97 Challenger 1800

[steve on the water]

I am having trouble getting on the water this year. There is power to both starters and they will spin when trying to start the engines. There is no spark to either engine. I am hesitant to propose the same component failed on each engine. Looking at the wiring diagram, the only components I see in common for both engines are the battery and CPU Master within the MPEM. It is odd to me though since the starter commands also come through this component. I am starting to check all grounds and run through the MPEM Procedure in Section 7-06 of the manual but am concerned that I will not find an answer. The suggestion on the manual is replace questionable components to determine if they are bad. I do not expect that anyone has an extra MPEM laying around to swap it out to determine if that is the issue. I would be worried that if the MPEM was bad, and nothing was done to find the fault that killed it, you would risk killing a known good MPEM. How do I go about proving the MPEM is good or bad? The advanced diagnostic test causes the engine to try to start. The manual would make me think the MPEM is good. Is this a ground issue? Could a bad ground cause a drop in voltage to prevent a spark but still provide enough power to spin the starter? Maybe a bad battery? My wife is going to pull the plug and sink the boat. Help! Thanks

 

[BoLongo]

Steve, I’m going through a similar situation but my boat will start and will run but once it warms up I get intermittent ignition issues.

The charging system and ignition system are independent, The ignition is ran off the battery so the first thing I would do is test the battery, take it to your local auto part store and have them do a load test, if OK fully charge the battery.

You can disconnect both rectifiers because they have nothing to do with the ignition. The rectifiers charge the battery and provide stable voltage to the system; they have no effect on the ignition system when the battery is fully charged so you can start your boat without the rectifiers. So remove the rectifiers from your trouble shooting procedure for now.

Next I would use the wiring diagram to test grounds and power through the system. If you have power and ground throughout the system it will probably be the MPEM or both coils which seems unlikely.

Use some sort of spark tester to confirm you have a spark, never turn over the engine without a way for the electricity from the coil to find a ground.

What usually kills the MPEM is a bad rectifier that will allow too much voltage to short out the MPEM so with the rectifiers disconnected you can test a different MPEM without the worry of high voltage shorting out the new MPEM.

Once you have the ignition system working test the rectifiers before connecting them to the boats electrical system.

Good luck, I feel your pain!

 

[mobilefleet]

start with the simple stuff first, the grounds. There are 2 larger ones, each going to its respective engine block at the starter flange down low. There is also a smaller ground that connects the 2 engines that goes from mag cover to mag cover. If they are corroded or not connected there's the issue. Check all fuses in the mpem box too, and check for a cdi signal by using a test light (clip grounded to an unpainted bolt in the engine area) to probe the small white wire of each coil while a helper cranks each engine to see if it lights up. If no light suspect a bad pickup coil in the mag housing

 

[Hemidakota93]

Check voltage on bf1:f2 and bf1:f3 fuses. Should be same as battery. I have a twin 787 speedster with 3.2v on both of those fuses. When I apply battery voltage to those two fuses with my power probe I get strong spark. Soon I will figure out why it has low voltage on those two circuits. Just need a schematic.

 

[WHYMpem]

Yah I'm haveing same problem but I'm getting 12volts out of the F1 but 0 out of f2 and f3.

 

[Hemidakota93]

Yah I'm haveing same problem but I'm getting 12volts out of the F1 but 0 out of f2 and f3.

Do you have continuity from c101: pin 25 to f2/f3?

 

[WHYMpem]

Actually I think my mpem might be different then the 1997 I have a 99

 

[Hemidakota93]

Actually I think my mpem might be different then the 1997 I have a 99

Crap! I didn't realize this was for a 97. I've been giving wrong info like an idiot. My info is for the 98/99 models. Can anybody hook me up with a 97 mpem schematic so I can help decipher it?

 

[2x2smoke]

Crap! I didn't realize this was for a 97. I've been giving wrong info like an idiot. My info is for the 98/99 models. Can anybody hook me up with a 97 mpem schematic so I can help decipher it?

Did anyone get the 1997 schematic? Can someone with premium membership see if the service manual for the 1997 challenger 1800 is available in the private section? My impression is that the boat has one mpem with two separate CDI units embedded within.

Does your beeper function correctly? How are you checking for spark?

I have the same boat and I didn't get a test light to blink when probing the white a green wire to the coil as mentioned above. I do have spark to both engines, however. Maybe I'm probing wrong...

My mpem seems to be working fine, I'm investigating this stuff because I bought the boat with the seller exclaiming the the mpem was bad but the motors are good. I was pleasantly surprised to find spark at both engines then unpleasantly surprised to find one of the engines damaged internally.

 

[Didehcho]

I checked and they only have the 98 challenger / 1800

 

[steve on the water]

There is a single MPEM in the 97 Challenger 1800. The schematic shows the CPU Master, CPU Starboard and CPU Port. I have a 2 page scan of the wiring diagram but can't seem to attach it right now. There are separate RPM and Ignition circuits for Port and Starboard.

 

[Hemidakota93]

There is a single MPEM in the 97 Challenger 1800. The schematic shows the CPU Master, CPU Starboard and CPU Port. I have a 2 page scan of the wiring diagram but can't seem to attach it right now. There are separate RPM and Ignition circuits for Port and Starboard.

This is what I was thinking. The 98/99 speedster has one of the giant black integrated mpems that is sealed. Doesn't the 97 have separate circuits mounted inside a grey box?

 

[steve on the water]

 

[icecold1]

I have a 1998 Challenger 1800 and I ran into the same problem last year and it was the red wires I believe there's six of them coming off the positive side of the battery each one of them has a case with a fuse in them I took them apart and they were corroded cleaned it all back up was good to go