Ideas to diagnose oil pressure cut out fault on Honda EX5500.

I should perhaps state at the outset that usually when the EX5500 oil pressure cut out operates  then 99% of the time it is due to failure of the nylon oil pump drive gear. However on this occasion the problem  only occurred once the machine was warm.

Description of the fault

Honda EX5500 cuts out due to oil alert button operating after 3 or four seconds running then when the machine is restarted is runs normally however if the machine is stopped and restarted once warm the problem is repeated

The machine had been suffering from overheating due to faulty fan motor which was resolved and then the oil and filter changed.

Possible causes

1)      faulty over pressure valve in oil filter allowing oil to drain out of oil filter very quickly thus presenting air to the oil pressure switch for a short while

2)      Faulty oil pressure switch

3)      Faulty oil pressure cut out in control panel

4)      Worn oil pump or oil pump drive

Procedure to diagnose

1)      Start the machine and then reduce the engine speed to see if the oil pressure cut out operates at low speeds. If this cut out does not operate at low engine speeds then that pretty much eliminates a worn oil pump or oil pump drive as well as the oil pressure switch. This is because one would expect oil pressure to vary with engine speed. Lowering the speed would lower the pressure. Reducing engine speed does induce a cut out then it points to either oil pump problem or oil pressure switch

2)      Stop the machine to create the conditions where the fault will occur and then test for continuity to earth of the oil pressure switch. Leave the meter connected and start the machine. When the machine cuts out one would expect the oil pressure switch to connect to earth at the same time as the spark is lost.if the cut out is due to low oil pressure. If it does not connect to earth until the machine has nearly stopped then it would point to a fault in the oil pressure cutout switch unit in the control panel.

3)      Replace the oil filter to eliminate a faulty valve in the filter.

Conclusion: 

It turned out that the nylon oil pump drive cog was slipping on its steel centre drive shaft. The oil pump drive must have been a very early version as it was unlike the later ones where this situation looks much less likely to occur. Once the machine was warm then I guess the expansion allowed the slipping to occur. Replace the oil pump drive with a later version and all was well. I’ve dealt with countless EX5500s and this is a first for me.

Advertisements