Massimo T-Boss 410 Died on the run and won't restart - FIXED

[Rocket]

2020 Massimo T-Boss 410 efi, UTV has approx. 600 miles on it. Traveling down a dirt road at 20 mph and slowed down to make a sharp turn, engine stuck in fast idle. Fast enough that the clutch would not disengage. Forced it into neutral and punched gas pedal trying to get the idle speed down to where it should be. Idle started to come down from the fast idle then in about four seconds the RPM dropped to zero and engine would not restart. Towed it back to the cabin. No one around here will work on Chinese UTVs so if I don’t fix it will be just another P.O.S.

Checked:

Spark plug sparks.

Fuel injector injects.

Rocker arms rock, cam turns

Will not run on a prime. (Prime, squirt gas in the spark plug hole, replace the spark plug and attempt starting the engine.) Ordered an OBD reader and the adapter for the Massimo /Delphi 6 pin connector. Down loaded fault codes from the;

Delphi MT05 # 28265491 ECU

P0311 Cylinder 11 misfire detected

P1800 Manufacture Control

P0711 Trans fluid temp sensor A

PIC Manufacture Control

None of these fault codes matched up with any published list of the Massimo/Delphi ECU and fault code reader would not reset codes. With all these nonsensical codes it must be a faulty ECU. After all how can you have a misfire on Cylinder 11 when it’s a single cylinder engine. Ordered and Install a new Delphi MT05 28265491 ECU. (Fig. 1) After attempting another unsuccessful start the new ECU showed P0311 Cylinder 11 misfire detected. Now I know what “P0311 Cylinder 11 misfire” means. It means the engine is not running and the ECU does not know why.

An engine needs three ingredients to run, Fuel, Compression, Ignition. Confirmed it has spark, fuel, and assume it has compression. After all it had enough compression to run moments ago. Ordered a compression gauge that fits that little spark plug hole used in the Massimo to get a real reading. Compression test, 35 psi. OK, now I know why it will not run.

Guess the cylinder head has to come off to find out why it has so little compression. EUREKA, FOUND IT! A small piece of metal stuck in the intake valve seat. (Fig. 2) Therefore the intake valve would not fully close. After further examination found a piece of aluminum mesh stuck in the intake port. (Fig. 3) Checked the cylinder bore for defects caused by the aluminum fragments. None were found. Removed the aluminum fragments from the head and reassembled the engine. (Fig 4) The valve timing was a challenge doing this in the field. After reassembly tested compression, 165 psi. Attempted another start. Started right up and ran as good as it did before. Shut it down right away to check for more aluminum mesh in the induction path. The air filter is where the aluminum mesh came from. (Fig 5)

Now that all the facts are in, this is what happened. The 352cc, Chinese made Linhai single-cylinder, 4-stroke, liquid-cooled, SOHC engine with Electronic Fuel Injection (EFI) and 25.5 horsepower is a very rough running engine with excessive vibration. It rattled and shook the air filter to the point where the screen on the inside of the filter fatigued and piece of screen broke off. The screen fragments traveled down the induction path and lodged in the throttle body jamming the throttle plate preventing the engine from returning to idle speed. When I punched the gas pedal the screen dislodged and traveled to the intake valve where the screen got stuck preventing the valve from closing. The engine died and would not restart. Now I know, change the air filter yearly whether it needs it or not.

Took 20 min. of running the UTV for check engine light to go out.

 

[Dale Halifax]

Wow.  Excellent detective work.  Great job.  And thank you for the detailed report on your sleuthing and very fine pictures of your findings.  Glad you were able to get it figured out and also glad there was no damages.

[Ridge Runner]

Good job Rocket!  Thanks for sharing this

[Joe Breaux]

Lucky