Newbie with rich running '99 748 Won't Idle - Ducati.ms - The Ultimate Ducati Forum
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post #1 of 26 (permalink) Old Aug 28th, 2019, 7:51 pm Thread Starter
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Newbie with rich running '99 748 Won't Idle

My 748 had been sitting for a couple of years. I sorted out some electrical issues with the fuel/ignition relay under the seat and replaced the fuel filter. Unplugged and plugged in all the electrical connectors. It was running fine but would occasionally hesitate low rpm and stall when coming to a stop. I would start it back up and ride along and all was ok. Then it wasn't. It's running rich -- black smoke out the exhaust with the smell of unburned gasoline, and now it won't idle. It'll start up with a little throttle and run rich up the rev range.

Last weekend, I replaced the spark plugs with NGK DCP9REs, stock ignition wires with a set of Magnecors, air filters, coolant temperature sensor, and swapped in a set of ExactFit belts. The old belt had loosened up but was still fine. When I pulled the tank the last time, I started it up with the little fuel left in the lines and it idled fine for a few seconds so I thought maybe the original fuel pressure regulator was stuck closed -- swapped in a new one but no change. I'll check the TPS tomorrow.

I'm befuddled. Please help.

Last edited by Subieho; Aug 28th, 2019 at 8:04 pm.
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post #2 of 26 (permalink) Old Aug 28th, 2019, 8:08 pm
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check all electrical connections especially grounds clean and lube them all--check the injector signal at the injectors & the spray pattern of the fuel out of the injectors-should be a nice fine mist --if not a fine mist could be sticking injectors

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post #3 of 26 (permalink) Old Aug 28th, 2019, 9:36 pm Thread Starter
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Thanks for the advice. I cleaned up the main ground while I had everything off for the t-belt replacement and the ground for the ECU. I think my TPS is fine because it was running fine and the issues were intermittent. I'll try pulling the injectors tomorrow.

Peaked inside the throttle bodies and noticed that the right side intake valves have more carbon buildup on both both cylinders. I wonder if this is due to sticky injectors leaking fuel onto the left side ones, thereby cleaning them when the bike is parked on the side stand.
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post #4 of 26 (permalink) Old Aug 29th, 2019, 2:04 pm Thread Starter
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TPS tested fine: throttle cable disconnected and idle stop screw backed off: 120mA and 4.76V with buttery fully shut and wide open, respectively.

Testing the injector spray pattern will have to wait, I just broke the fuel quick disconnect on the line feeding the front injector. I had to replace the other one a few years ago and went with a brass unit. Figured now that I have a little time, I also ordered the female ones as one them was leaking after I pulled the tank. If anyone is attempting to remove these old plastic ones, it helps to throw some heat on the aluminum thread bore from the other side (inside of tank) with a heat gun; otherwise the old plastic composite head will shear off. Just be careful not to melt the plastics and rubber in the fuel pump assembly.

The injectors, though, look good. The filter screen around the input ports was clean. As I cycled the solenoids with a tester and sprayed some cleaner through the tip what came out the input ports was clean as well. I don't have the means to test the injectors out of the bike so I'll check the TPS adjustment as I wait for the fuel line fittings to arrive.

Also attached is a photo of the rear intake valves on the rear cylinder. You'll notice there's more carbon buildup on the right side valve. This is true for the front cylinder as well.
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Last edited by Subieho; Aug 29th, 2019 at 3:53 pm.
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post #5 of 26 (permalink) Old Aug 29th, 2019, 4:09 pm
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if it's been sitting for a couple of years then the injectors probably need a clean.

reset the tps baseline, it'll help it when you do get it running.

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post #6 of 26 (permalink) Old Aug 29th, 2019, 6:04 pm
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Check the EPROM. You may want to go to stock if it's been replaced. A proper dyno diagnostic may also give you all the clues you need.

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post #7 of 26 (permalink) Old Aug 29th, 2019, 7:21 pm Thread Starter
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The bike is pretty much stock. Should have mentioned that it has just over 12K miles on the clock. In any case, I finally worked my way over to the left side of the engine as I was pulling the injectors and testing the TPS. Turns out I have a short in the crank sensor -- infinite resistance. Should have checked the easiest thing first -- just didn't feel like a bad crank sensor. I guess this is what safe mode looks like on a 748. Thanks for all your input.
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post #8 of 26 (permalink) Old Sep 17th, 2019, 5:43 pm Thread Starter
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Still searching for the problems with this thing. My old CPS was actually fine -- just needed to clean the terminals and resistance is right at spec.

I've been through every connection and tested for continuity in all the the leads for sensors, injectors, and coils to the ECU plug:
  • Cleaned all the male pins and spades & pulled out all the female terminals and tightened them all up a bit for better contact
  • Cleaned all the pins on the ecu connector
  • Tested the charging system
  • Coils tested good and getting good spark on both plugs

After I got things back together, I took it out for test ride, and it was running better but still a bit rough and would stall while idling. I had to increase the throttle stop screw to get it to idle. But it would fire right back up each time. Then I stalled out, and it did all sorts of crazy stuff, I'd start it up and the engine would wind up suddenly and die. This went on for a bit so I searched on my phone for possible causes. Then for no reason it ran the best it has so far, and I was able to ride it about 2 miles back home. Not sure if this was related to the previous incident but on the subsequent test ride, the throttle plate linkage was binding up at the rear pivot. I borrowed some WD-40 from the guys setting up for a 1/2 marathon here in Philly and was back on the road.

Next mornin', I start it up for another test run and the engine climbs to about 3K rpm and then back down -- seems normal for cold start. It dies 3 blocks from my house and won't start back up. The ECU relay under the seat would sometimes click on and off repeatedly when I cycled the ignition switch on. I could hear the fuel pump start and stop each time the ECU relay energized the fuel pump relay. I jumped the fuel pump which worked just fine. Then for no apparent reason, it started to click on and off normally, and the ECU & fuel pump relay sequence has worked every time, but it's running pig rich as before on both cylinders throughout the entire rpm range, hot or cold with the smell of gas from the exhaust and plugs & intake valves wet with fuel.

Only thing left, it seems, is the ECU.

Last edited by Subieho; Sep 18th, 2019 at 6:54 am. Reason: clarity
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post #9 of 26 (permalink) Old Sep 17th, 2019, 6:02 pm
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get a diagnostic tool - iawdiag is free - and cables from lonelec and find out what the ecu is seeing input wise. that is the info you need to work with.

have you checked the fuel pressure?

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post #10 of 26 (permalink) Old Sep 17th, 2019, 6:47 pm
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Originally Posted by belter View Post
get a diagnostic tool - iawdiag is free
Great tool, remember to donate to help keep development going.

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