2009 Assault RMK 146 Starting Issue

[mobax]

Posted this on HCS but no reply, Hope for some info here...

Have a 2009 Assault RMK 146 with a start issue. Motor will usually not start unless power is input to fuel pump via fuel prime connector. When the fuel pump is running the motor starts every time, usually within two pulls if engine warm. Once the sled is running the sled operates normally under idle, part throttle and full throttle conditions.

On the (infrequent) occasion that the motor fires without running the fuel pump it can do one of three things. 1/ Start and run normally. 2/ Start and run only for a few seconds. 3/ Start and run with increasing RPM (perhaps it’s leaning out) then die.

Highest fuel pump pressure when recoil starting with ignition kill switch open (i.e., depressed) to ascertain highest pressure available using recoil with no ignition: 55 PSIG.

Lowest initial fuel pump pressure when successfully starting by recoil without powered fuel pump: 32 PSIG.

Fuel pump pressure when running: 58 PSIG steady.

Fuel pressure leakdown rate a few of pounds over 15 minutes.

Sled sat for over year without running after burning out the regulator and ECU. Got new aftermarket regulator and a 2010 Dragon 800 ECU. Fueled with 91 octane fresh fuel tempered with recommended ratio of Isopropyl alcohol, fuel selector set to 87 octane. Started OK for a while (idle only) while performing sled maintenance but then got progressively harder to start.

Ran extra grounds from ECU mounting plate to clutch shield and chassis and cleaned existing grounds. Replaced the stator with a spare even though the the original stator rang out OK. Stator AC voltage while running approximately 9-10 Volts, DC Voltage 14.34 Volts.

Pulled and checked reed valves (which were new two seasons ago and had minimal mileage) and were OK.

Checked the fuel filter (new last season of operation with only a few hundred miles on it) and it was OK.

Checked throttle body initial valve opening and OK.

Disconnected chassis power relay, ignition switch and all chassis connectors to isolate circuits with potential grounding issue except those necessary for engine operation and starting issue remained. (Throttle switch no-start function is not a factor with connector disconnected).

Replaced the Dragon 800 ECU with one from a 2009 Assault RMK 146 800 (same as my original).

Still no joy. Would appreciate any assistance.

 

[mobax]

Can't find an edit feature for my post above, so include here.

Edit: The issue is not related to the fuel pump, the engine is starting when power is applied via the fuel prime connector since that also supplies DC power to the regulator power splice. So it's power to that part of system that is enabling sled start.

 

[retiredpop]

So supplying DC voltage to the fuel pump prime connector enables it to start. What DC voltage do you read at that connector when you pull start or attempt to start the sled. You mentioned you disconnected the chassis power relay but I think it needs to be in the circuit in order for all DC voltage to only power the ECU and fuel pump. Do you have another relay you can put in? I am thinking the chassis power relay is faulty.
Chassis Relay: The chassis relay is activated by the
ECU at approximately 950 RPM. Below 950 RPM (700 rpm on the 900 cfi's), all
power supplied by the regulator / rectifier (RED circuit)
is used to power the ECU and fuel pump.

 

[mobax]

We read the DC voltage at pump prime today with recoil start and it was low, can't recall exact value, maybe 3 Volts, though my meter doesn't have a retain function for highest reading and the reading seen may not capture highest value. You have any idea what this value should be? Recall that I'm getting the same results with two different stators.

The relay is in system, removed it momentarily for check only and reinstalled. This is a new relay installed when start problem originated but made no difference from original relay.

 

[retiredpop]

I can check voltage on one of our sleds but it may be a couple of days before I get to it.

 

[retiredpop]

I get 11.7 volts DC at the pump prime plug when pulling it over with the recoil start.
This was using a digital voltmeter.
If I used my analog meter it peaks up to about 7 VDC but with the needle movement lag time I can easily understand that difference.

 

[mobax]

Tthanks retiredpop, will troubleshoot that variable.

 

[mobax]

Finally got around to checking the regulator voltage using the recoil starter with the fuel pump connector disconnected and immediately got 15 Volts measured at the harness. Once the fuel pump was reconnected Voltage dropped to 6 Volts.

So powered up the fuel pump separately with 12V battery at the fuel pump connector and the system ran perfectly at system 14+ Volts. Measured the fuel pump resistance and it was 0.5 Ohm: anyone know what the proper resistance is? Thinking the pump may be defective.

 

[mobax]

Swapped out the fuel pump with a known good pump and no change.

 

[retiredpop]

If your low speed injectors were a bit dirty or partially plugged I wonder if this could be the issue.