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Discussion Starter · #1 ·
I have a ‘99 MXZ 670 HO and have no idea if the DPM system is working. What I am wondering is if the system is not working, can it damage the engine? From what I have read on the system, I believe the machine should just run a little rich and basically not get the fuel economy it could if it worked properly. I just did a top end overhaul since the machine blew a piston thanks to the previous owner, so I want to ensure that it is good to go from that, before I spend money in confirming the system is functioning properly. Thanks.
 

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well, i guess start by making sure that the dpm isn't what caused the blow-up...i guess "thanks to the previous owner" is a bit vague....haha. i haven't had any problems with the DPM on my sled (same unit), but i have heard of problems with it.

good luck
nik
 

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froesen said:
well, i guess start by making sure that the dpm isn't what caused the blow-up...i guess "thanks to the previous owner" is a bit vague....haha. i haven't had any problems with the DPM on my sled (same unit), but i have heard of problems with it.

good luck
nik
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The sled blew up before because the motor was previously jetted down(dont ask me how i know). I was told by a reliable source that the DPM system was known to have problems, causing blown motors. Can anyone provide any insight?
 

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Discussion Starter · #4 ·
[quote name='froesen' date='Feb 7 2006, 02:49 AM']
well, i guess start by making sure that the dpm isn't what caused the blow-up...i guess "thanks to the previous owner" is a bit vague....haha.

To answer that Question....

I believe it was because it was jetted down 20 on both sides. a lean condition over heated the piston.
 

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I had a detonation on my 600 summit last year. Strangest thing was that it was in mid- range all day (half throttle). I rebuilt but never found the lean problem. I suspect one of three things.

1. Leaky carb flanges - I replaced them and bonded the new ones on with liquid gasket. They won't leak now.

2. Bad gas -always a possibility, doesn't take much to mess things up.

3. DPM failure- while it is true that the DPM will fail full rich. However, what if the sensors are mis reading. Say it is -10 C out but the sensor is reading + 10 C. Then the DPM may lean to compensate for the false warmer temp, bang your lean. I removed the DPM and unhooked all the wires. I have almost 200km on the re-build and my gas milage or performance has not suffered as much as I can tell. So I'm leaving it off.
This may not have caused the problem, but it's one less thing to worry about.

I hate rebuilds your on pins and needles for hundreds of miles after....
 

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The sensors are the same as your car. Granted what you say could happen it is highly unlikely. Failure modes are designed so that if the system hiccups it defaults to no compensation. The failure mode on those temp sensors is to fault to -40 or full cold. So it would remain in the no compensation mode. In almost 20 years of working on cars I cannot recall ever seeing a sensor fail with a warm reading - they fail with a cold reading. IE - dont worry about it.
To test the system you need to have:
1 -warm (+0 or 32) temps. I seem to recall the spec is 40F?
2- RPMs over 3200...

then check soleniod to here if it is dithering (rattling).
If so and all vac lines are connected correctly, no leaks, kinks etc.
then system is ok.
 

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Yellow Is Good said:
I have a '99 MXZ 670 HO and have no idea if the DPM system is working. What I am wondering is if the system is not working, can it damage the engine? From what I have read on the system, I believe the machine should just run a little rich and basically not get the fuel economy it could if it worked properly. I just did a top end overhaul since the machine blew a piston thanks to the previous owner, so I want to ensure that it is good to go from that, before I spend money in confirming the system is functioning properly. Thanks.
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i've seen one situation on a 2000 mxz 700 where the valve on the dpm module would not open, causing a major lean condition. two melted pistons and a new cylinder. the sled acted as if the float bowls were not vented,which is exactly what was happening.the valve seemed to work with an external power supply,so i'm thinking the problem may have been in the mpem. quick fix.... unhook the dpm,good as new. you also have to remove the brass airjet plugs in the carb bells and plug the external nipples.
 

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I've got a '99 HO too, but I'm sure the DPM is not working. Last season, my plugs were a nice tan, this year they are black. I also have a hard time if I stop the engine, and then try to re-start it right away. If it sits for 10 min., it starts just fine. I have not noticed any performance losses. All of the lines to the unit are in good condition, and are tight on the connections. All of the wiring looks good too. Are there any common problems which might cause these problems?
 

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thermopylae said:
I've got a '99 HO too, but I'm sure the DPM is not working. Last season, my plugs were a nice tan, this year they are black. I also have a hard time if I stop the engine, and then try to re-start it right away. If it sits for 10 min., it starts just fine. I have not noticed any performance losses. All of the lines to the unit are in good condition, and are tight on the connections. All of the wiring looks good too. Are there any common problems which might cause these problems?
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I would be more inclined to believe the carbs are dirty or air passages are blocked/restricted from sitting over the summer. Try having the carbs cleaned first. Disconnecting the flaot bowl lines to the DPM will tell. If unhooking them improves the performance they there is something wrong. If not its in the carbs.
Remember - DPM does nothing at idle or startup. It only will lean out the mix when at cruise speeds. It cannot enrichen the mix.

Only GTs got a variation that included the ability to fatten the mix and operated at idle/startup - these units required a vacuum pump to do that.
 

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zdooman said:
thermopylae said:
I've got a '99 HO too, but I'm sure the DPM is not working. Last season, my plugs were a nice tan, this year they are black. I also have a hard time if I stop the engine, and then try to re-start it right away. If it sits for 10 min., it starts just fine. I have not noticed any performance losses. All of the lines to the unit are in good condition, and are tight on the connections. All of the wiring looks good too. Are there any common problems which might cause these problems?
[snapback]713394[/snapback]​
I would be more inclined to believe the carbs are dirty or air passages are blocked/restricted from sitting over the summer. Try having the carbs cleaned first. Disconnecting the flaot bowl lines to the DPM will tell. If unhooking them improves the performance they there is something wrong. If not its in the carbs.
Remember - DPM does nothing at idle or startup. It only will lean out the mix when at cruise speeds. It cannot enrichen the mix.

Only GTs got a variation that included the ability to fatten the mix and operated at idle/startup - these units required a vacuum pump to do that.
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The 1999 670 HO and Summit X both have an enrichment mode that pressurizes the bowls of the carbs at start up based on coolant temp sensor readings as soon as the motor spins at 250RPM or above to richen the mixture, After warm up is achieved the system goes to a compensation mode where it looks at a number of factors and can either make the mixture richer [pressurize the bowls] or leaner [vacuum in the bowls] ,I cant speak for other years or models but that is right out of the factory manual for the HO and Summit X for 99..
 

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I am having a similar problem but mine is running too lean. I was told to test the dpm you unplug it so it will run full rich, the carbs are jetted for -20'C and the dpm will lean it out so if unpluged its suppose to run full rich, I am seeing no difference in plug colour weather its pluged in or not. Can the mpem cause a leaning problem?
 

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kaptiankent said:
I am having a similar problem but mine is running too lean. I was told to test the dpm you unplug it so it will run full rich, the carbs are jetted for -20'C and the dpm will lean it out so if unpluged its suppose to run full rich, I am seeing no difference in plug colour weather its pluged in or not. Can the mpem cause a leaning problem?
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If unplugging the vac lines yeilds no change then the DPM is not to blame.
 

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If unplugging the vac lines yeilds no change then the DPM is not to blame.
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[/quote]

What I did was unplug the wire connector from the mpem module. It is then suppose to run full rich, but its not. So what's my problem?
 

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kaptiankent said:
If unplugging the vac lines yeilds no change then the DPM is not to blame.
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What I did was unplug the wire connector from the mpem module. It is then suppose to run full rich, but its not. So what's my problem?
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OK -I am writing this for all - not just your response.

The DPM soleniod ONLY operates over around 3600 RPM when the air temp is over around 35 o F. (I am simplifying it for ease of understanding). What that means is that you cannot 'see' it work at idle.

It only leans out the sled (on most models). It does not enrichen the sled. So when the system is not operating or 'breaks' the sled will run as if it is not even there.
Therefore if you have an issue with fuel it is most likely not related to the DPM system. Unplugging the soleniod at idle will not help since it is not operating or effecting anything at that speed anyway.

THe only true test is to unplug the vacuum tubes from the DPM to the carbs. This 'opens' the float bowls in the carbs to normal air pressure. Now if a change occurrs its time to look at the DPM and its lines for a pinched or blocked vacuum line. (Maybe during summer storage something tried to make the open ports on the DPM a home... )

If after disconecting the line ther is no effect then the DPM is not to blame. Normal diagnotics for fuel issues need to be researched. For a rich running sled the most probably cause is a plugged or restricted air passage in the carb (allows more fuel to enter the engine).

Rich sled = carbs are getting too much fuel - air passages blocked
Lean sled = carbs not getting enough fuel - too much air - vacuum leaks, low fuel pressure, float bowls not vented or under a vacuum condition.
 

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when I tested the sled I drove in a open feild for 5 min at over 100km/h then checked plugs and tried unpluging the unit from the mpem unit and did the same run again, the plugs looked idenical weather pluged in or not. So what your saying is to take all the lines off teh dpm and try running it with the lines just hanging there? Let me know and I will try anything now. Cause itsnot the carbs, or the fuel system and the compression is ok and I did a leak-down test and it held 6psi for over 5min and never dropped at all untill i vented it.
 

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kaptiankent said:
when I tested the sled I drove in a open feild for 5 min at over 100km/h then checked plugs and tried unpluging the unit from the mpem unit and did the same run again, the plugs looked idenical weather pluged in or not. So what your saying is to take all the lines off teh dpm and try running it with the lines just hanging there? Let me know and I will try anything now. Cause itsnot the carbs, or the fuel system and the compression is ok and I did a leak-down test and it held 6psi for over 5min and never dropped at all untill i vented it.
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lets start over - your too lean? correct?

Why do u say that? (looking for background info)

(to read plugs u have to hit the red button at the rpm / speed you are trying to read them for, otherwise the change in load/rpm will effect the reading. in case you did not know this.)

When you did a leak down test, were you testing the whole engine with the carbs off and boots blocked?

For finding a vac leak take some silicone spray and spray around the carb boots, gaskets, seals and the carbs (just not in the air intakes or the DPM lines. Any significate change in RPM needs to be looked at for a possible leak.

The carbs should be set with the vac lines open - that is so they can get atmostpheric air pressure, by disconnecting them from the DPM will isolate the DPM from the system. There are 2 lines - vac supply which feeds vac signal to the DPM - that line needs to be plugged. This comes off the side of the carbs behind the throttle plates. It could be a source for leak as well so check it for a vac leak and seal off that line. The lines coming off the carbs in front (closest to the air box) are the float bowl vents and need to be left unplugged.

If you do this and all is still unchanged then the DPM is not to blame.
Do a vac leak check before and after disconnecting the DPM. If you do not find the issue then its not in the DPM and must be elsewhere. If you cannot find a leak at all then the carbs need to be adjusted for the lean mix (idle screws, polit rods, etc.) Remember main jets are primarily for WOT operation. Setting them for -20 does not address the idle and midrange.

Be systematic and go step by step only isolating 1 thing at a time. Once you get to the root verify its fixed and then reconnect the DPM.
 

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zdooman,
Yes im having a lean problem, not at idle but when driving at trail speeds or higher. When it was -10'c the plugs were white. At above 0'c temps the plugs are almost white or a very light tan. I have never had this problem before. they always looks good at every temp, even at -15'c which is cold nowdays. I do hit the kill switch at the test rpm around 5000-6000 or higher. On the leakdown test i did each cyclinder seprate with the reed/carb boot left on. Pluged the holes on the boot and on the exhaust port. The pressure never dropped for over 5min so I asumed it was great and no seal leakage. So I should try spraying some propellant around the carb area- I will try that. I will be leaving for this weeknd and will check back when I get back to let you know what happens. I will try the dpm test as you described to. Thanks for your help sofar, its better than the dealers advise of "keep driving it"
 

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