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The TPS adjustment thread

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On 3/29/2020 at 6:34 PM, SimsNT said:

350 and 450 XCFs are notorious hard hot starters- you can spend lots of time/ money and not fix it. 
If it doesn’t start, slow count to 30 and try again. I used think I was alone with my 350, then out on the trail I ran into a guy with a 450 & he called it the XCF 30 count. 
If there is a solution that doesn’t cost $$$ to implement, I’d love to know. I had to stop trying. 

Exactly what I experienced! Glad to hear I was/am not alone. 

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Posted (edited)
On 3/30/2020 at 6:46 PM, sirthumpalot said:

If you set the TPS to 0.40 with the plate closed, and you're now at 0.54 then you should be in the ballpark idle wise, probably not off by more than a few hundred RPM is my guess.  Some of the cheap hour meters on Amazon have a tach built in if you need one.  I don't know how accurate they are, but probably good enough to set the idle.  

...had to step away from this gremlin nightmare , pour over everything that has been done/not done.

Throttle body removed, cleaned without Map sensor, TPS,or Injector installed.  TPS kept giving lower and lower base settings every time throttle was opened fully and closed(slowly). Replaced TPS. TPS setting, .409v fully closed, redjusted .56v( closest to .54 I could get) bike will start and idle but idle is at 3300 RPM'S, turn down idle to 2300 -TPS now at .50v. Bike runs awesome run about 20 minutes. Shut down Restart hot immediately- nothing. Tried CHOKE just for the heck of it -Nope. Let sit 15 minutes-nope, 1/2hr.- nope ,3 hours- starts and runs awesome, but again won't start hot.

ALL electrical connectors disconnected, cleaned contact areas with electronics cleaner... NOTED NO CORROSION BROKEN OR BURNT WIRES, apply light amount of dielectric grease. ALL grounds resurfaced to bare metal -ALL grounds checked for continuity to source-ok.

All ignition components(coil, stator charge and pulse coils, plug cap) are all well within factory specs- new. NOTE: Stator , V/R, Plug cap and Kill switch were just replaced, had bad stator, so replaced VR as well. Plug cap replaced because of crack...if you own a ktm  4T you know why

Checked flywheel-ok, replaced flywheel key and torqued to spec.

TIP OVER sensor unplugged and plugged in with no change, even replaced with known good working sensor-no change

New fuel pump, pump relay,inline tank filter and mini inline filter. Original pump test was at 38psi , Factory spec 48-52psi. After replacement 50psi. 

New Injector (had 5 hours use) checked, poor spray patterned, professionally cleaned, still no good. Replaced injector( tested prior install -ok)

Engine top end rebuilt(38 hours), had defective/ broken comp. release so cam was replaced- which requires special set up to mount gear. New intake and exhaust valves , guide seals, timing chain ,cam chain adjuster and piston kit. Valves are currently in spec: Intake .13mm both L&R [ Spec: .10-.15mm], Exhaust .15mm both L&R [Spec: .13-.18mm]. Leak down test: 10%

 Swapped out ECU from a known running bike ,no change with hot starting

Fuel; 50/50 mix of 93 pump and Sunoco 110 new

 Battery: Scorpion, LiFePo4 219cca, 2 months old and motor cranks over fine,just like it has since bought

 NGK  LMAR9AI-8, New

 Despite all this , still an issue. The only possible nags could be 1) taking leak down test/compression test cold...."maybe' ring is sticking and loosing compression when hot- I have not tried to check this hot. 2) any one of the 3 sensors ,Air ambient temp. sensor, Water Temp. sensor or Map sensor could be causing an issue. There are no values given to check them in service manual. I could pull the water temp senors take a ohm reading cold then place in hot water to see if there is a change, but is that conclusive enough. The other 2 ?

Thanx for any responses... when this gets solved , I hope it will shed light and save others countless hours

Edited by guscycle

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It may sound silly, but if you haven't replaced the spark plug yet, try that.  I've seen some really odd issues from flaky spark plugs.  Also when it's hot and won't start, remove the air filter, open the throttle and shoot a little starting fluid down the throttle body.  Then try to start it.  Starting fluid is super flammable (might want to have an extinguisher handy just in case).  If it won't start with a shot of starting fluid, then it's almost surely an electrical issue.  Maybe that will help you narrow it down. 

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Well, after several dozen inspections and re-inspections of any possible components that could hinder hot start issues (after curing cold start and idle issues) retested a sensor that has been checked a least 6 times at different stages and found the water temperature sensor had crapped out. This part had originally been tested after the bike finally started and ran fine when first started but after several attempts failed to restart hot, sensor was pulled out and had measurements tested at different temp levels as per manual- and it worked/tested fine. Going through everything one last time after several failed attempts at restarting hot ,since then and trying to locate problem, decided, what the hell, let me do a quick test of temp sensor while it was still in bike--NOTHING-NADA!. took it back out and tested it different temp ranges as before...NOTHING! Bought a new sensor, monkeyed with TPS ,one more time, settled at 2100rpm's, TPS at .554v , starts cold and runs awesome "and" it actual would start hot!  Sometimes hesitant ,especially if you don't wait for relay to click- about 30+ seconds, but follow the rule and 90% it will fire off. No way is this ideal in a hare scrambles race ,due to the lack of a kick starter, but rideable.  Unfortunately, it will have to go...and back on my 'ol reliable '07 Husqvarna 2 stroke I go...

 

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Posted (edited)

At least you made some progress!  Now that the temp sensor is fixed, I wonder if you can dial the rest in to make it work properly now?  

Related side note; we had a 90's model Chevy truck with a 4.3L throttle body injected motor and the temperature sensor went bad.  The symptom was when you tried to start it, the injector became a gasoline fire hose and just flooded the motor, so whatever signal the sensor was sending caused the ECU to think it needed a ton of fuel.  Replaced the temp sensor and presto back to normal.  

Edited by sirthumpalot

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Posted (edited)

 

 

 

Edited by 2018KTM
Found info I was looking for

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