[emersonsc]

So after all the fun issues I've been dealing with between faulty 500 H.O. engines (crankcase vent blowing oil into the air box) and CFMoto changing the fix (were back to no fix at all, the latest service bulletin is no longer valid), to having now 4 800 engines blow (3 due to faulty air boxes, 1 to a cracked head which caused the motor to hydrolock and litteraly grenade the front piston and crankcase), to all of the 400s I've sold and have in stock having recalls on the decompression device (hard/no cold start issues), I now have a new fun issue. I'm hoping I can get a fresh set of brain cells to help me find something I'm missing.

I've got a ZForce 800. Rear cylinder is loading up with fuel. The header is full of fuel. The catalytic converter (the fat pipe attached to the back of the stock muffler) was glowing red after a few minutes of idleing. It has no power, and idles low.

I replaced the injector, the MAF, the o2 sensor, the plugs (several times because they were wet fouled), even the ECU. No change. The rear plug IS throwing a good healthy spark, BUT when we pull the plug boot there's ZERO change in the way the engine runs. We have 180psi of compression, so that's not an issue. We checked the timing, and it's dead nuts on.

Any ideas? What am I missing?

[NMKawierider]

I'm just going to toss this in there and see but the book says the compression should be 1000kpa which converts to 145.038psi. With 10.3:1 compression pistons and no comp. releases I would expect it to be something less then 150. You say it shows 185. The only time I ever saw something like that was on an engines that had a flat exhaust cam lobe. This caused the overlap to be reduced or non-existent at the bottom of the exhaust stroke increasing the volume being compressed...hence a higher number. It also causes that cylinder not to operate. So, I would check both sets of valves for operation. Heck might even be an issue with the rocker. Rollers might even be shot or damaged.

The front cylinder...is it operating OK? Anything strange with the plug? What's it's compression?

[emersonsc]

I'll check with another gauge just to be sure. 180 did seem high but I just moved on figured it was a funky gauge (used another techs).

Front cylinder runs perfect. Plug is dry and has the correct burn pattern. I didn't bother to check compression just due to the fact it runs and burns fine.

I even went as far as to rip the exhaust apart thinking there was a clog. But nothing there either.

Guess as you said, it's time to take the head apart and see what's going on.

My concern is there's a LOT of fuel. And it's building up quick. The manifolds were very wet, both intake and exhaust. It seems like something is telling cylinder 1 to run fat and heavy. But what and why is beyond me.

[locknload]

Have you put a noid light on the injector connector, should have stead blink if working properly. If stays on constantly with engine idling could have short to power or short to ground depending on how its triggered. Not sure how else you would get so much raw fuel in the exhaust unless the injector was wide open. Just a thought, good luck!

[NMKawierider]

Unless that injector was stuck but you replaced it..electrically it would have to get an extremely long pulse width, which comes from the ECU but you tried another one. What about crank position sensor(s) does it have one or two? Most just have one so if it was bad, the other cylinder would also have a problem. Fuel pressure OK...not too high? Some have regulators that go bad. Well, pop the valve cover and take a look at the valves and cam.

[Wheels]

Pull the injector and check the pulse duration.

[locknload]

You could compare compression with the front cylinder.

[locknload]

I have ran into similar situations in the auto industry, the ecu ground pulses the injector but if that wire is shorted to ground as soon as the ignition is turned on the injector is wide open. Fuel pressure test would also help, ignition on engine off see if it holds pressure.

[emersonsc]

Unless that injector was stuck but you replaced it..electrically it would have to get an extremely long pulse width, which comes from the ECU but you tried another one. What about crank position sensor(s) does it have one or two? Most just have one so if it was bad, the other cylinder would also have a problem. Fuel pressure OK...not too high? Some have regulators that go bad. Well, pop the valve cover and take a look at the valves and cam.

Cam and valves are good. We slowly turned it over to make sure they were opening properly and on time. Clearances are all good on the rocker arms.

These only have one crank sensor. Replaced it just in case, still no change. The very strange thing to me is everything worked perfect before the engine blew. Drop the new engine in, with all new sensors and all, and it does this.

Btw, this is the the 4th engine this unit has seen. First one blew due to airbox/filter failure, second was DOA from CFMoto (wouldn't build oil pressure), third one hyrdolocked and litteraly grenaded, and this one is pulling this crap.

I've got another 800 sitting in our shop waiting for its new motor to go in because it's airbox failed and took the engine out. I've been complaining about airbox failure since last summer, and we finally get the Chinese to come see the damage they cause and are told they'd look into it, but as far as I'm concerned the issue should have been addressed last year and we should already have seen some sort of production change or something.

[bezerk1]

What kind of airbox failure did the machines have?  Its a pretty straight forward setup.  The air filter is hose clamped to a tube that connects to the throttle body with clamps.  Even if you ran with the airbox cover off you would still be protected.

[NMKawierider]

Have you put a noid light on the injector connector, should have stead blink if working properly. If stays on constantly with engine idling could have short to power or short to ground depending on how its triggered. Not sure how else you would get so much raw fuel in the exhaust unless the injector was wide open. Just a thought, good luck!

How about this?

[Nighthawk]

The rear plug IS throwing a good healthy spark, BUT when we pull the plug boot there's ZERO change in the way the engine runs.

So you have not swapped or replaced coil to confirm proper operation??

[Wheels]

Remove injector cycle key and see if it pulses or just constantly sprays, pda can confirm this also.

[chuddly]

I agree...check the injector spray times against the front injector.  If you have spark and the cams are in time like you say they are (i believe you) then the only other thing it could be is a shorted wire to the injector its self which makes sense because when swapping an engine you can pinch, not ground, incorrectly ground or any number of other small things to 1 small wire and it will cause silly issues like this.  Im not familiar with these exact engines yet but is there any way to see inside the ecu with a laptop and see the injector pulse times? 

[NMKawierider]

This one is all stock right..no programmer or anything?