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Discussion Starter #1 (Edited)
87 trx350 start/stall diag

Hey all been away for a while but I'm back working on my quad. I'll get right to it.

My bike had a multitude of back yard custom work done to it before I got it. Needless to say I have put everything back to factory best I can.

Situation is this...

Key on, kill switch on, choke, electric start. Fires up no problem. Idles nice, revs up nice. After about 30s to 1m oil light comes on, fan starts, engine dies and won't start again for several hours.

Has new battery and fuel pump. New ignition wiring harness as well.

I've read as much as I can here and although very helpful I'm a little confused as to where to go next. Oil sensor maybe?

Any help would be great.

Aube002
 

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Discussion Starter #3
I've read that those machines need to get to like 500 degrees to overheat. It doesn't run for more than a minute before it stops. I'm going to change the oil, filter and check the sensor tomorrow. See what that does.
 

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bad oil temp sensor ?, or bad fan control unit ?.
 

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I think shadetree is probably right about where to start. Only other things I can think of are the common things you would do for all electrical issues. Check the ground cable that comes out of the main wiring harness to verify its bolted down tight and free of corrosion. And check out the area and connections of the harness where the short oil sensor & neutral/reverse light switches harness plugs into. Those sometimes rub on the frame or pulled on and get bare/broken/unplugged etc. All that stuff can be accessed under the seat. I'd look for a mud-jam under the little sensor cover and clean up those connections too.
 

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Discussion Starter #7 (Edited)
Ok so from what I can tell sensor is good. Ground is good and wiring is good. Looking at the ownership turns out this is an 87. Doubt that makes a difference but anyway. I was always told it was an 86.
 

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Ok so from what I can tell sensor is good. Ground is good and wiring is good. Looking at the ownership turns out this is an 87. Doubt that makes a difference but anyway. I was always told it was an 86.
how did you test the oil temp sensor to determine it is good ?. most times, the oil temp sensors go out. other cases, the fan control/alarm unit goes bad. and yes, 1986 and 1987 ARE different, the wiring is NOT the same.
 

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Discussion Starter #9
I should have clarified. I checked the wiring to the sensor (as well as the neutral / reverse ) and found no shorts. Also checked the ground. Cleaned it up but wasn't really dirty.

Today it fired up as it usually does. Ran for about a minute then died. No fan or oil light. Started it back up 2 more times with the same result. Then it wouldn't start again. For the heck of it I checked all my fuel lines and carb again. Still good. Could I be having an intermittent spark failure? I'm running in circles here.
 

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Is your fuel pump working? Fuel filter not clogged? You can verify plenty of fuel by pulling the fuel hose where it goes into the carb after the motors quits... should be a couple pounds of pressure there, enough to squirt a bit of fuel out of the line.

So, this time the symptoms changed? First post you mentioned the fan started and temp light come on and then the motor quit. If so, it acts like your fan control unit may be shutting down the ignition due to it sensing a fault/seized fan motor. Dunno if 87 models had that shutdown feature yet though....? Could have been 88 and up? Shadetree knows...

Its probably time to put an ohm meter on everything. The service manual tells ya how and where. I think you can ground one of the wires connecting to the oil temp sensor and test your fan control unit too. Again maybe wait and see what shadetree thinks...
 

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Discussion Starter #11
Yes the symptoms changed. This beast is a real puzzle. I've had it for about 3 years and the previous owner gave it to me and said if you can figure it out nits yours haha. I guess I will pull out the ohms meter and get testing. I did check fuel delivery and it's fine. Plenty of fuel.
 

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I should have clarified. I checked the wiring to the sensor (as well as the neutral / reverse ) and found no shorts. Also checked the ground. Cleaned it up but wasn't really dirty.

Today it fired up as it usually does. Ran for about a minute then died. No fan or oil light. Started it back up 2 more times with the same result. Then it wouldn't start again. For the heck of it I checked all my fuel lines and carb again. Still good. Could I be having an intermittent spark failure? I'm running in circles here.
you can't tell a bad oil temp sensor just from the connections ?, it has to be ohmed or tested in a pan of hot oil. turn the key on ( this is a simple fast test ), touch the oil temp connection to the engine for a good ground, does the fan kick on ?, does it still run with the connection off the sensor ?. as I said, you either have a bad oil temp sensor ?, or the fan control unit is bad ?. and yes, all years/makes for these work the same way as far as the oil temp and fan control unit goes.
 
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Discussion Starter #14
So being short on time I decided to put a new plug in. Fired up right away no issue. Went on a couple short rides and no issue. I still don't trust it yet but it's a good start. I cleaned and greased ALL electrical connections front to back as well. Maybe that helped too. I've ordered a new oil sensor and cdi to have just in case. I plan on running it for a long time yet. Next job is to repair front brakes.
 

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Great! I also have a spare CDI, neutral and reverse switches, and oil temp sensor. I need to buy a fan switch and fuel relay
 

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Discussion Starter #17
Well here is another update. Went yesterday to fire it up again and nothing. No spark. So I've ordered a coil as well since it's only 8 dollars Canadian.
 

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Discussion Starter #19
87 trx350 start/stall diag

If you can believe it I am still having issues with this bike. I picked up an 89 for parts. Question today is... is the CDI for the 87 the same as the 89? I can't find OEM part numbers to check.
 

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If you can believe it I am still having issues with this bike. I picked up an 89 for parts. Question today is... is the CDI for the 87 the same as the 89? I can't find OEM part numbers to check.
I've been told NO, they must be from the same year ( I've been down this road many moons ago ). I do know for a fact, 1986 years will NOT work, cept in a 1986 year model. some claim from 1987 to 1989 all c.d.i's should work ?, but I know better..lol. go to partzilla.com, compare the part numbers in the wireing section, see if they match ?, if they do ?, then it should work. if not ?, then my answer stands..you must have a 1987 c.d.i.
 
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