Suzuki DT115 cylinder 2 scored wall

[Marion Moore]

Model - ?96 Suzuki DT115STC (EFI)
Symptom ? Engine runs rough, idles poorly, and runs with reduced power.
Found - # 2 spark plug is fouled all others look normal.

I need your help in confirming the troubleshooting that I have done and determining if my results are correct. I believe the # 2 cylinder output from the Engine Control Unit is bad, here is why.

While running I removed the # 2 spark plug wire, no change in idle. I then removed the # 3 spark plug wire and the engine ran very rough. Same when removed # 4 spark plug wire. I removed # 2 again and no change.

I swapped the starter coil with # 2 and # 3. Same results as above, removing # 2 spark plug wire had no effect on the idle.

I swapped the spark plugs with # 2 and # 3. Same results as above, removing # 2 spark plug wire had no effect on the idle.

I attempted to do an ECU output test but I don?t have a CDI tester or a Stevens peak voltage tester model CD-77 requited by the shop manual. I used a Simpson 250 connected in line between the # 2 starter coil output from the ECU and starter coil. I was looking for greater than 104V but could get no meter deflection. I moved to the # 3 cylinder output for a reference but could not get any results either. I?m either doing something wrong or this is a shop test that needs special test equipment.

I did not have time to do a compression test last night. I have not done a spark test but could not find any other components that might cause the # 2 cylinder only to not fire. This is why I think the ECU is bad. If I am correct I will need to locate preferably a used ECU given the cost of a new ECU ($1750) is over half of the value of the engine and may not be worth replacing. Any help would greatly be appreciated.

 

[Marion Moore]

Re: Suzuki DT115 possible ECU failure

Re: Suzuki DT115 possible ECU failure

As usual I jumped the gun. I have spark. I made a rig with a # 6 copper wire grounded to the block. All starter coils fire just fine. Neighbor helped me do a compression check. Cylinders 1, 3, and 4 were 130 ? 135 but cylinder 2 was 75. I found the problem. I now have to determine what caused it and how extensive the damage might be. I doubt I?ll have time Wednesday to take the head off.

By the way, I replaced the head gasket last year while checking the water passages to make sure they were clear. I torqued everything by the manual and went back and re-torqued again after running the engine. That still doesn?t mean the gasket isn?t bad. I have not noticed any milky oil on the # 2 plug. It was black and wet. Any logical suggestions as to where to go next would be appreciated.

 

[James R]

Re: Suzuki DT115 possible ECU failure

Re: Suzuki DT115 possible ECU failure

It is unlikely that the ECU has failed but not impossible. You have individual carbs on this motor so lack of fuel supply is the probable cause. Before you do anything else a compression test is a must.

 

[Marion Moore]

Re: Suzuki DT115 cylinder 2 misfire (compression)

Re: Suzuki DT115 cylinder 2 misfire (compression)

Thanks James. See my compressions test above. All cylinders 130 except # 2 which was 75. I'm hoping for a stuck ring and a decarb to fix it but that is a long shot.

 

[James R]

Re: Suzuki DT115 cylinder 2 misfire (compression)

Re: Suzuki DT115 cylinder 2 misfire (compression)

75PSI is bad. Not likely to be a stuck ring. Failures like this on the Suzuki is probably due to bad maintenance of the carbs or the oiling system. Just a little dirt in the oil line check valve to that cylinder will do it. Not difficult to rebuild but you need some money.

 

[Marion Moore]

Re: Suzuki DT115 cylinder 2 misfire (compression)

Re: Suzuki DT115 cylinder 2 misfire (compression)

Yes, I'm worried about the cost of rebuilding given the engine would only bring around $3000 in perfect working condition. I'm going to try a decarb treatment just for the heck of it but don't really expect it to work.

 

[James R]

Re: Suzuki DT115 cylinder 2 misfire (compression)

Re: Suzuki DT115 cylinder 2 misfire (compression)

From your location I would guess that this motor has been used in salt water.
The motor, as is, is not worth much and taking it apart will result in sheared bolts. Lots of drilling out and tapping. You would be well advised to part it out. Hate to dump what is normally a great motor. We can talk more if you want. 704-219-2578.

 

[Marion Moore]

Re: Suzuki DT115 cylinder 2 misfire (compression)

Re: Suzuki DT115 cylinder 2 misfire (compression)

Salt water, oh yeah. I'll see what Saturday brings. I may be calling you in the end.

 

[Marion Moore]

Re: Suzuki DT115 cylinder 2 misfire (compression)

Re: Suzuki DT115 cylinder 2 misfire (compression)

Bad news? here is an update.

#2 cylinder is scored pretty bad. I have not gotten any farther than taking the head off and looking into the cylinder. I must find out what caused the failure or any repair would be a waste. I just have not had time to work on the engine. On the up side, I have a genius engine mechanic for a neighbor that can help me with a rebuild if that is what I decide to do so there would be no labor cost.

To rebuild or buy used, that is the question because there is NO WAY I could get a new engine. Best case I can spend about $500 on machining, seals, gaskets, rings, and one oversized piston IF that will work. The oversized piston will probably weigh more so it may need to be drilled to reduce weight if that is possible. Buying 4 new oversized pistons and paying to have all 4 cylinders machined would take the total cost to around $900. That?s a lot to put into a 12 year old engine (no hour meter) that might run another 5 or 10 years or may have some other big ticket item fail the next day. I can?t let myself forget it is an EFI engine which brings lots of special super expensive parts to the party. It?s a gamble.

Finding a reliable used engine (115 ? 150) will also be difficult and I could easily find myself in the same situation shortly after purchasing it or it may run without trouble for years.