'89 DT75 dropping a cyl at speed

[Flatsboy]

Great, took the rig out today, got all readings (within spec) again on the TPS, checked spark, counted secs, took videos. Will post results later today if I have time. It was way more than 10 secs though before it limped and when it did all 3 plugs were firing, no alarm.

[mphelle8vld]

Sounds like a good test plan, I'll knock the dust off of my old manuals.

[Flatsboy]

Protection/Limp/Fail Safe modes - Like to understand exactly how this works. I've read the OEM Service manual and the Seloc 1600 Repair Manual but I can't find a rundown on how the ECU processes the sensor inputs and how it reduces RPM. It drops a cyl (in the DT75) but how does it do this and which cyl? Does it block the fire signal from the ignition timing coil in the magneto or does it accept it and block the signal from the ECU to a particular ignition coil?

May get some test time in tomorrow and update. Going to install the 3 inline spark testers to see which cyl cuts out when misfiring and going into 3,000 rpm mode. Will also document how may secs after going above 3,400 mark it takes to misfire and drop into 3,000 limp mode. Will also get more exact readings on TPS.

The '88-'03 Seloc 1600 manual (as with Mercs) is more detailed in some areas than the OEM but is frustrating as it documents readings for most engines from 115HP and up, not much for the 3 cyl and below units.

[mphelle8vld]

It doesn't detect flow, only if the oil filter in the sensor is dirty. Let us know about the 10 sec, if you don't think the problem is limp mode related I'll defer to Solarman. 4700 sounds low for wot, overproped?

[Flatsboy]

I haven't timed it exactly but I seem to remember it's random, not exactly 10 secs. I'll get it on the lake and document. I noticed yesterday after warming it up idling about 5 minutes, I took off at full throttle (about 4,700 rpm) and it cut back well before it did when I ran it up from the same spot and took it to 3,800 or so several other times. That made me think it may be overheat related but I've replaced both heat sensors (puck and duckbill) with new.

I haven't used a Suzuki gauge. From what I see it warns of over-rev, temp and low oil, correct? Or does it also warn of oil flow? I can see where this might help direct a search but won't pinpoint failed components.

[mphelle8vld]

Sorry for butting in Solarman but the repeatable 10 sec caught my attention. I haven't got an answer yet but if it's exactly 10 sec, that's a unit used by the cdi for an over rev. Not that it's actually over revving but perhaps a short in the wiring is causing the limp mode. A clogged carb would give that symptom but it would take longer to drain the bowl at 3500 than at 5500, not the same 10 sec every time.

[mphelle8vld]

It's a gauge harness from a 91, the cables and meter changed through the years, if your cdi has a free six pin connector and a free pink/blue stripe, grey, and black wires in the vicinity it should work. Finding the correct gauge could be a challenge. One like this is a possibility...

Suzuki DT Gauge Oil Level Monitor Water Indicator 34701-92X50 Outboard | eBay

Is the interval exactly 10 sec or around 10, does your model have the 34250-87D11?

[Solarman]

I wouldn't just continue replacing parts, if the reeds are damaged, or have gaps (not sitting flat), then they may be bad, otherwise probably not.

When you tested TPS, was yours staged (throttle sensor changes voltage at certain positions), or smooth on voltage change between zero throttle and WOT?

Post back when able to let us know.

[Flatsboy]

Thanks for the offer, I'll check for the tach control and get back to you.

Is your harness the monitor gauge harness 36660-92e20 or the power harness 36630-92e00? Thanks again!

[Flatsboy]

Flats, if able, try another (known good) TPS for your motor, i don't believe it is going into safe mode.

When you had carbs off, did you visually inspect the reed valves?

Post back when able to let us know how it's going.

I don't have access now to another TPS, I did get the OEM test harness and mine checked out. I wouldn't blink at spending the $175 for a new TPS if I knew that was it but I've already replaced a lot of components. That's fine if I'm going to keep this motor, it gives me piece of mind for a 28 yr old unit but if the TPS isn't it I'm pretty much at a dead end again.

Yes, I did check the reeds carefully and they look fine. I've had reeds that look fine cause issues and that may be the next replacement. Removing/replacing these carbs takes twice as long as a Merc, Yamaha or OMC, not a job I look forward to. Don't mean to come off as negative towards all Suzi's but this one is definitely over-engineered and is a PITA ;-)

[Flatsboy]

I mailed my spare monitor gauge to a guy in Tasmania and never heard from him again, the cable is yours if you decide to get a gauge.

OEM SUZUKI KIT MONITOR GAUGE + HARNESS + POWER SUPPLY HARNESS NOS NIB | eBay

Is the 10 sec delay consistent (always 10 sec)? Does your model have the small plastic tach control unit (34250-87D11) next to the cdi?

Thanks for the offer, I'll check for the tach control and get back to you.

[Solarman]

Flats, if able, try another (known good) TPS for your motor, i don't believe it is going into safe mode.

When you had carbs off, did you visually inspect the reed valves?

Post back when able to let us know how it's going.

[mphelle8vld]

I mailed my spare monitor gauge to a guy in Tasmania and never heard from him again, the cable is yours if you decide to get a gauge.

http://www.ebay.com/itm/OEM-SUZUKI-K...1Zlfnm&vxp=mtr

Is the 10 sec delay consistent (always 10 sec)? Does your model have the small plastic tach control unit (34250-87D11) next to the cdi?

[Flatsboy]

I've been watching some on ebay and may go that route although I've gone far beyond what it could tell me at this point. I've heated thermostats, OHM'd and AC/DC metered every conceivable sensor, coil, wire, trigger, etc.

Have also put on new plug wires and sever sets of plugs.

Talked to the dlr at length today at his shop, service mgr and lead mechanic. They said that era small DT series was over-engineered and they've had these needle-haystack issues too. They didn't get that I wasn't getting an alarm when protection mode kicked in, the mgr suggested it could be a short in the main wire loom to the control box or the control box. Don't think so, it's too consistent and the alarm does work at start up.

Rebuilt carbs today and ran in the lake, re-checked TPS at .5v, same result. I'd like to think it's something basic I'm overlooking but I've triple check and replaced many components. Starting to think about another Merc or Yamaha, I know those well.

[mphelle8vld]

The Suzuki monitor gauge would tell you if it's in limp mode and cut your troubleshooting in half. If your friend with the cdi has one you can borrow or find a used one on ebay, it would be a useful tool. If your friend has a gauge but it's installed and doesn't want to remove it, I have an extra 18' cable, you could back down the ramp next to him and hook your motor to his gauge.