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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: burzaa on April 02, 2016, 10:30:06 PM

Title: Turns over, have spark, fuel pump works, no injection
Post by: burzaa on April 02, 2016, 10:30:06 PM

Hey everyone,

New to the forums here, just bought my first '90 K75c about 2 weeks ago. Got her stripped down for painting and putting back together.

SO I have a problem with the starting. When I bought the bike it started fine, no problems. Was able to start it multiple times and get it to the workshop. Issue is that after I took everything off for paint and put back together, it just won't start now.

Kill switch is off, key in ignition, lights come on. Engine turns over and cranks, but to start.

I've checked the following:

-New spark plugs, and do get spark when starting
-Fuel pump works fine, tested into a bucket when starting
-Fuel pressure regulator works.
-Battery at >12V, when starting voltage at some starter relay pins reads 10ish volts
-Tried disconnecting and reconnecting motronic, no  luck
- Tried starting with TPS unplugged, no luck
- Tried charging battery
-Injector internal resistance is 16 ohms

I think it's the fuel injectors not putting any fuel into cylinders. The spark plugs are bone dry after trying to start multiple times.


I've taken a look at the popular diagnosis diagram but can't really seem to pinpoint the problem. Any suggestions that could maybe point me in the right direction?


Thanks,
Burzaa

Title: Re: Turns over, have spark, fuel pump works, no injection
Post by: rbm on April 03, 2016, 11:34:35 AM

Did you hook up the fuel lines to the correct spigots on the tank?  Fuel delivery is the rear-most one; fuel return in the the front-most.

Title: Re: Turns over, have spark, fuel pump works, no injection
Post by: burzaa on April 03, 2016, 01:31:11 PM

Yep. Fuel lines hooked up correctly. I think we narrowed down the problem down to a fried ECU. Looked like something exploded inside. Gonna try and find a used ECU somewhere in the bay area and see if it solves the problem.

Title: Re: Turns over, have spark, fuel pump works, no injection
Post by: Laitch on April 03, 2016, 02:01:15 PM

Looks like mold. Maybe you should store it in air conditioning.

That's tough luck and unusual to boot, burzaa. Did you follow Bert Vogel's diagnostic chart (http://hrsbstaff.ednet.ns.ca/bvogel/K100/download/bike-wont-start1.htm) to get where you are now?

Title: Re: Turns over, have spark, fuel pump works, no injection
Post by: rbm on April 03, 2016, 02:03:24 PM

Nasty.  Are you able to identify a component on the circuit card that failed?  With that type of deposit, the failure would be very evident.

Title: Re: Turns over, have spark, fuel pump works, no injection
Post by: burzaa on April 03, 2016, 02:04:59 PM

Quote from: rbm on April 03, 2016, 02:03:24 PM

Nasty.  Are you able to identify a component on the circuit card that failed?  With that type of deposit, the failure would be very evident.b

Yeah. There were black marks of exploded solder on the leads that connect to Pin 9. The one that provides power to the injectors.

And yes. Checked the entire flow chart diagnostic. Tested the entire jetronic harness at the pins and everything checked out as it should.

Title: Re: Turns over, have spark, fuel pump works, no injection
Post by: burzaa on April 04, 2016, 02:14:27 AM

SOLVED.

As suspected, it was the ECU. Bought a used one not too far away from a gentleman. Got back to the shop, plugged in new one, and fired up right away.

Survived a nice long drive from the workshop to the house (the longest I've gotten to ride it as to date) - And wow, great bikes. New filters and plugs all around made a great difference!

Title: Re: Turns over, have spark, fuel pump works, no injection
Post by: Martin on April 04, 2016, 02:59:27 AM

Burzaa good work well traced.
Regards Martin.