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Discussion Starter #1
I recently purchased a 98 summit 670x with 1400 miles. I went over the entire sled and thought I had it ready for the winter. I found a wire connector disconnected so I connected it. After I did this the sled wouldn't go above 1/5 throttle without bogging. the more throttle I gave it the more it bogged. It would idle fine though.

So through some research I found that the wire connector is for the enrichment selenoid on the DPM rail. I then disconnected the wire again and the sled ran fairly well the other day. I rode 25 miles at 10-11,500' at 38 degrees F. I then pulled the hose from the air pump at the DPM rail. It is pumping gasoline as well as air. My guess is that when the enrichment selenoid is functioning (at cold temperatures during warm up) it is pushing more fuel into the carb and runing way too rich, thus causing the bog. I also tried unplugging the line from the air pump to the DPM rail and connecting the enrichment selenoid and it seemed to run fine. But I don't want to disconnect something that will cause a larger problem with the engine.

First: any idea why the air pump is pumping fuel?

Second: Can I leave the enrichment selenoid unplugged and still retain the good qualities of the compensation mode. I live and ride at 10,000' plus so I know it won't be running rich.

Third: could I disconnect the air pump hose from the DPM rail and run it like that or does it need to be a closed circuit?

thanks
Matt
 

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hi matt....learnin from my summit x.....you shouldnt have fuel comin out air pump hose.....my air pump was hooped too........the pump works off twin crank impulse hoses...chk those...any fuel there????......one impulse line tees off the fuel pump impulse....maybe chk fuel pump too!!!!....also.....there are 2 updates for your MPEM...(chk out my post......ThumbDoctor has them posted there)......i just got mine back from dealer...got new DESS tether and was told no updates were there......lookin forward to try mine again..after they reprogrammed mine!!!!!...hopefully ThumbDoctor catches this....he is truly the sled tech God....and hopefully he can give you more info....and make sure my recommendations are correct...good luck....let us know...and happy postin.........SUPPORT SW!!!!!!...............thanx Brian.
 

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I recently purchased a 98 summit 670x with 1400 miles. I went over the entire sled and thought I had it ready for the winter. I found a wire connector disconnected so I connected it. After I did this the sled wouldn't go above 1/5 throttle without bogging. the more throttle I gave it the more it bogged. It would idle fine though.

So through some research I found that the wire connector is for the enrichment selenoid on the DPM rail. I then disconnected the wire again and the sled ran fairly well the other day. I rode 25 miles at 10-11,500' at 38 degrees F. I then pulled the hose from the air pump at the DPM rail. It is pumping gasoline as well as air. My guess is that when the enrichment selenoid is functioning (at cold temperatures during warm up) it is pushing more fuel into the carb and runing way too rich, thus causing the bog. I also tried unplugging the line from the air pump to the DPM rail and connecting the enrichment selenoid and it seemed to run fine. But I don't want to disconnect something that will cause a larger problem with the engine.

First: any idea why the air pump is pumping fuel?

Second: Can I leave the enrichment selenoid unplugged and still retain the good qualities of the compensation mode. I live and ride at 10,000' plus so I know it won't be running rich.

Yes you can run the enrichment solenoid unplugged but the system will revet back to base jetting which will affect lower altitude and cold temperature operation. In a nutshell, you system works 2 ways.

1) At cold temps (cold engine) the combination of the coolant temperature sensor and the intake air sensor feed back to the ECM. The ECM commands duty cycle from the enrichment soleoid which allows pressurized air (keyword here is air) to be applied to the float bowls from the DMP manifold hence allowing the carb's venturi to pull more fuel than the vacuum signal could do on its own. This is the enrichment mode. The ECM is equipped with a pressure sensor (nipple barb on the box) or external HAC (High Altitde Compensator) which reads relative air pressure & RAD (relative Air Density). This also calls on the enrichment solenoid when you head down towards sea level. This also is enrichment mode.

2) Once the sled is warmed up (as indicated by the coolant sensor to the ECM) the ecm will stop signaling the enrichment solenoid and start the compensation solenoid's duty cycle and lean out the mixture according to temperature and altitude. As you climb, the compensator allows a slight vacuum signal to be applied to the float bowls making it harder for the carb's venturi to draw gasoline out of the float bowls hence leaning out the mixture. This is compensation mode When intake temperature warms, the compensation solenoid will do the same thing, vacuum is again applied to the float bowls. This is also compensation mode.


Third: could I disconnect the air pump hose from the DPM rail and run it like that or does it need to be a closed circuit?

I would disconnect the fuel pump pulse line and see if the fuel is coming from a ruptured diaphram. If not check your float needles to make sure the are maintaining correct float level and not back flowing into the DPM manifold. If you need the suppliment on how to diagnose the system, PM me and I will get it to you. The system is pretty sound and doesn't give alot of trouble except in summer storage, bad things happen to rubber and fibre diaphrams & valves.thanks
Matt[/b]
 

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Discussion Starter #4
wow guys. You really know your stuff. I see that my sled isn't alone with this problem. We are getting 1-2' of snow here right now and I'm anxious. I'm going to pull the carbs and check the floats to make sure the needle/valve is sealing correctly. I will try to check the air pump, but it's burried under the engine and doesn't seem to easy to get to. Any suggestions, minus pulling the engine?

Are the lines from the crank to the air pump (and fuel pump) vacuum lines or pressure impulse lines? The reason I ask is because if they are pressure lines then the crank could be feeding the air pump fuel as well. This could possibly be coming from the faulty float valve seal in the carb, yes?

Thumb Doctor, it seems that you have so much information that you freely give. I wish I had a dealer who was like that. thanks again

Matt
 

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Discussion Starter #5
Update:

sorry it's taken me so long, but work has been crazy. So the air pump is not pumping fuel anymore. It doesn't seem to be pumping anything. I'm just going to bypass the enrichment part of the DPM.

Now, I tried testing the compensation selenoid by getting the air box at room temp and runing the engine above 3000 rpm's. I don't think the selenoid was pulsing, in fact I'm very sure. Is this selenoid activated by the switch built into the throttle cable? or does it run off the tachometer circuit. The reason I ask is that I pulled the connector that runs to the throttle cable housing (where the cable splits from 1 to 2 carbs and 1 oil pump) and used my digital meter to try to measure any difference given by the throttle. I couldn't get any change in readings in any wire combination with any throttle position. If the compensation circuit runs off of this switch on the throttle cable then I think I may have found my problem.

I'm pretty sure my sled isn't compensating for altitude. It bogs big time up at around 11,500' in the deep snow at 3/4 to full throttle. I'm going to find out if my sled has had the DPM MPEM re-programmed as per the recal in 1997 (as posted by thumb doctor-- thanks again). Maybe it's just a programming issue or maybe it's just that simple swtich on the throttle cable. That's where I'm starting anyway.

any comments or suggestions would be appreciated. also would jetting the carbs possibly help?

thanks
 

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Discussion Starter #6
Update:

This if for anybody searching this forum with a similar problem in the future.

The air pump is pumping only air now. What happened was before I bought the sled the previous owner pulled the handlebars off, so it would fit in the back of my truck with a cap. The throttle was squeezed open during this time and gas flowed freely through the carbs, I think. Anyway the point is that gas filled the crank case. maybe it was just bad floats. So from the crank being full of gas the air pump became full of gas, from the impulse lines from the crank that powered the air pump. Once the lines were cleared of gas, and the float problem fixed no more gas went to the air pump. The air pump now pumps air.

Anyway, to the problem that I was having with the enrichment selenoid. I found out that the cold start switch that is attached to the throttle cable isn't functioning properly. This switch is supposed to shut off the enrichment selenoid when it reaches 1/4 throttle or so. With the switch not functioning properly, as 1/4 throttle on up, the enrichment selenoid continues to pump and enriches the mixture so much that the engien bogs and almost dies. So I'm keeping the enrichment part unplugged and not worrying about that part. I am just letting the sled warm up properly.

The sled was also bogging and breaking up at high rpm's. I thought it was a jetting problem. It turns out it was the spark plug wires at the boots. they had vibrated loose and weren't making good contact, hence the missing.

so check your spark plug wires and boots. good luck if you had the same problem as I did.

My sled is running awesome....
 
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