Help! Deamon missfire issue!!!!

[aallen]

2003 Suzuki DF 140 with around 700 hours.

Possible relevant facts before I get to the gripe:

1. When I first bought the motor used, usually at least once in the day I would be at WOT and then the motor would drastically drop RPM and only go to around 3krpm. I would simply shut the motor off, turn back on .. and No problem.

2. AT ONE POINT A YEAR AGO MY BATTERY CABLES WERE HOOKED UP BACKWARDS and it did get a little bit smoky. (A**hole who owned before me didn't label cables) BUT MOTOR RAN FINE FOR QUITE SOME TIME THEREAFTER, AND IT SEEMED TO ONLY BURN UP MY BATTERY SWITCH. NOT SURE IF IT BACK FED TO THE MOTOR SOMEWHERE, AND IF SO, WHERE IT WOULD GO TO WITH THE KEY IN THE OFF POSITION. I WILL TOUCH ON THIS LATER . . .

3. I did have an issue w/ water in the gas, which was corrected. (FLUSHED TANK, USE REC GAS NOW and ran 3-4 long days until I came to the following gripe:

I began to notice that when I would start my motor, it would shake badly and not go past 3k rpm, (similar to when at WOT and the engine rpm would drop drastically) and I could turn off, turn back on, and it would correct itself. Now the problem has deteriorated and long story short I found it to be a miss-fire in cyl 2,3 ONLY, and really isn't an intermittent problem anymore (which hopefully is good news for troubleshooting) .

When I test cyl 2,3 for spark on timing light, it will fire for 1 or sometimes 2 signals, and then the ECM shuts down spark and fuel. On a hunch, I swapped the injector harnesses from 1,4 to 2,3 to see what the ECM would do, and surprisingly computer continued to deliver spark to all 4 cyl all the time while turning the engine over (obviously wouldn't start, lol.)

Here is what I did (former car mech, and aircraft electrician .. I know my way around)
1. Swapped cyl 2,3 coil with used coil, which corrected the issue for several starts in the yard, but when I drove to the boat ramp, the problem came back. I then purchased NEW coils and Injectors and NGK plugs. Same Issue

2. Purchased USED ECM . .same issue.(Both ECM have been confirmed to work)

3. Checked and confirmed I have battery voltage on ALL grey wires,(yes the fuel pump turns on when key turns on) and also performed continuity check to all grey wires and moved main harness wires around to check for intermittent open. Also did continuity check to all other wires going to all injectors and coils and confirmed ECM and START relays work.

4. Ran new battery cables and soldered connections everywhere.

What the SUZUKI DEALER DID

1. Swapped flywheel and TIMING coils from a running df140 and checked flywheel pin.
2. compression and leak down test . .good to go in specs.
3. computer diagnostic w/ no codes.
4. Swapped new ECM harness (not main harness which goes to injectors, coils, etc) This is the only thing they did not check in my opinion.... They also probed my existing ECM harness, no issues . .
5. Isolated my engine w/ shop battery and key ignition harness.

The shop called today and gave up. They even claimed to call suzuki and go through all the troubleshooting proceedures except for swapping main harness (easy for me to do, and I figured they did plenty for $230, but I was hoping for the computer diag to chase wires for me .. . didn't work)

To sum it up: New plugs, coils, injectors. Flywheel and ignition timing coils were swapped from running motor, as well as ALL Harnesses other than Main Harness. ECM shuts off spark/fuel after 1 or 2 signals. Cyl 2,3 ONLY

My question(s) are..
Shouldn't a computer diag detect if any sensors are not working properly (I thought it would be cam or crank sensor, or even MAP)

They did not probe the wires from the harness the TIMING COILS under flywheel go to. Is this on the Main wiring harness and possible the main harness is bad?

This is obviously an electrical issue, and I am going to pull the main harness myself and probe it to see what I find before dumping more money on something not properly diagnosed at this point. Suzuki manual does not give resistance specs or have the ignition timing coils or even have it in the schematic. How would I independently confirm timing coils work properly?

I have a feeling the main harness is where the problem is. Probably a burnt or corroded wire in the harness, but I want to isolate so I'm not buying tons of parts not needed. What else can i be doing? Should I just replace all harnesses? I'm guessing the suzuki shop only sells new stuff and has no master tech or nothing but basic diagnostics searching for codes. Any suggestions would be appreciated.

[redlowrey]

The first thing you want to do is change your mechanic, the df140 has not got timing pins under the fly wheel.
The only thing under the flywheel is the stator which is used to produce ac voltage and current, which is rectified by the voltage regulator, which should have fried when you had the battery back to front, and you must have been lucky and blew the sixty amp fuse.
The crank sensor and the camshaft sensor bolt to the side of the flywheel housing. Checking battery supply is only half the job you need to check all the grounds too, check and see if you fried the voltage regulator ground when you had the battery back to front.
It is possible that you have some stray ac voltage leaking into the system if the reg was damaged, that will upset the ecu, normally to shut down cyls you will have a problem with temperature, neutral switch, over revving, oil pressure, and you need to do voltage drop tests to check them.

[aallen]

The funny thing is when I shorted the battery out, it fried my battery switch. The fuse never blew, and both relays are intact . .crazy.

I found nothing in my service manual for the specs on what voltage drops need to be on anything really, which is the frustrating part.

I checked ground on all black wires on main harness, as well as continuity on anything I saw in the schematic that I could get to on the main harness without pulling flywheel myself. I was an aircraft electrician, so I am pretty good at troubleshooting, it is just a matter of exactly what to check and what it should indicate.

I initially thought about the voltage regulator, but it looked as if it's only job was to charge the battery so I kind of put that out of my mind but after what you are saying am I understanding that this could absolutely bleed voltage or leak AC somehow back to ECM? What tests should I do to test regulator and what should they read out at? Do you happen to know what the cam and crank sensors should ohm out at if that gets me nowhere? I'm totally with you on a bad ground somewhere or bleeding voltage, but simply am not familiar w/ suzuki and exactly what makes them tick? Da*n transistorized engines are beautiful until they arent!

Is this something that further diagnostics on a computer will help with and indicate quickly? How many different diag tests does suzuki have so I can confirm w/ a mech. if they have the proper equip . .OR is this just a grunt wire chasing job. Thank you so much for your time and help.

[aallen]

Also, it would be best to note that this was for a long time an intermittent problem. I went to transistor theory school in the Navy, and in my experience, I haven't really run into intermittent transistor or diode issues, but maybe the Navy just buys Shi**y parts that burn out completely, lol. The engine would run great, and had no temp issues or oil pressure issues that were apparent. Its almost as if when the boat goes down the road and hits different bumps it triggers something either on or off . .which I know on a car is usually a crank cam or map sensor. Obviously suzukis are more advanced! How exactly is the timing triggered to fire? I'm assuming the cam sensor picks up a signal which I assumed was produced by a timing coil that runs 2 cyl each? Does it just pick up the cam position and the computer tells it when to fire then, and I need not chase things under the flywheel? I just want to optimize my time and not chase a ghost, and get the best place to start checking this out. Much thanks again!

[redlowrey]

Mate there are no timing coils, on the bottom of the flywheel there are 34 reluctor bars spaced 10 degree's apart with a wider spacing between two, as the flywheel rotates the inductive crank sensor generates a voltage pulse as the reluctor bar passes it, and when it passes the wider gap spacing it produces a distorted voltage pulse.

On the end of the exhaust camshaft there are 4 pins spaced 120 degree's apart and as the pins rotate past the cam sensor, which is a hall sensor that produces an on off signal, or a square wave if looking at it with a scope. Between the two sensors the ecu will determine rpm, piston position for sequential injection and where number one is btdc.

Remember it is a waste spark ignition system meaning it fires two plugs at once, one on compression and one cyl on overlap, and the coils and injectors are ground side switched. Get your self a manual. I use an oscilloscope to check wave forms, a digital multimeter is not accurate enough.

[aallen]

Yes, I finally found the CORRECT service manual, which helps greatly. After going over the schematics, I'm going to try first getting a new regulator. It's likely back feeding ac as you said, and when I looked at the resistance values of the coils, 2-3 coil has slightly lower impedance value, which might very well explain why the gripe shows up on that coil. Also, I am going to look for the voltage on all the ground wires, as well as the signal wires (blue in this case) where the ECM is sending ground via pnp transistor.

As for the timing issue . .as I stated before, I used to work on cars long ago, which are much different than these engines! I simply took the mech. word that this is what was taking place. I have no idea why they would go through the trouble of swapping a flywheel (I know it could have damaged veins) before changing out the rectifier since it is a much quicker process). Now that I have all the values the sensors should read and troubleshooting procedures I feel a lot more confident that I can find the problem.

I still am wondering why when I swap the 2-3 injector harnesses to the 1-4 injectors, and vice versa why when I turn the engine over, I have spark at all times to both coils and cyls. A used rectifier is only $50 on ebay, so I can live with that price to see if that clears the issue up. Thank you again for your help.

[aallen]

It may also be worth noting that the temp sensor in the rectifier circuit has salt water corrosion . .not even sure if it could get a correct reading the way it is.

I also read that not all sensor faults trigger a code, and will go to fail safe operation which reads engine will run, but under predetermined conditions by INTERMITTENTLY controlling the fuel, spark, or BOTH. If I understand correctly, that if the rectifier doesn't fix the issue, than the problem could very well be one of the sensors listed in the fail safe operation, and I can just troubleshoot the sensors as per manual, and this would NOT cause a warning light?

[redlowrey]

When an engine goes into fail safe, the ecu substitutes a voltage for a sensor, not shut off injectors or spark, that will happen from what I previously told you

When the engine plays up again connect up a test light to ground, and probe the ground sides of the injectors, and the coils and see if it an ecu problem or something else. If the ecu shuts down injectors, when you connect the test light to the ground side of the plug it will light because there is no ground from the internal driver, if it is grounded the light will flicker.

It will be the same deal on the coils, you should be able to determine if is an ecu shut down or a mechanical problem causing the engine to miss.

[redlowrey]

I meant to add don't use a test light that will draw more than 500ma.