F250 surging

[sobriyah]

Just had the 200 hour service on a pair of 2007 F250's by the local Yamaha dealer. They were running fine prior to being serviced but immediately afterwards the low pressure pump failed on the stbd engine and now it has been replaced the motor surges above 4000rpm, by up to 800rpm Below 4000rpm it runs ok.

At first I thought it may be the prop cavitating or the rubber bush starting to fail, however the motor has a new Yamaha prop which was replaced along with the lower unit just 4 months ago (when someone stole the lower unit) and the dealer tells me he has never known a prop to fail so soon. There have been no external issues such as ropes around the prop.

The dealer thinks it could be an injector fault and is coming back to look at it next week as there have been issues with water in fuel, and 3 months ago I had to replace the low pressure pump on the other engine. At the previous service (100 hour service 8 months ago) a different tech fitted diesel racors. With diesel being more viscous than gas I expect the racor filters were coarser permitting more water to get past them.

If anyone has any suggestions I will be very grateful to hear from you.

Richard

[TownsendsFJR1300]

Re the water issue, with the ethonol (if your using ethonol) it attracts moisture and of course the water gathers in the bottom of the fuel tank casusing issues

I found and have been using a product (about 3.5 years) that keeps the water in suspension and it eventually burns it off with the fuel.

My boats a 1997, original built in 50 gallon tank, never been drained, removed, original filter inside. Since using this product and using NON-ethonol fuel, the fuel that I would drain out of my VST was VERY CLOUDY.

It took some time, but its spotless clear now, smells new, engine runs great! Its also a fuel stabilizer. I run Ringfree and K100 ONLY in my F150, nothing else, original VST filter, etc..

Demonstration Videos | Kinetic Fuel Treatment

Fuel Treatment, Fuel and Gas Additive | K-100 HOME

Re the filter, you want at least a 10 micron filter, preferably with a water separator.. You may want to (if not already) check your under cowl, Yamaha fuel filter.

[rodbolt17]

debris from the failing/failed pump can and will clog VST filters and the VST prefilter.
I would look there by testing fuel rail pressure at the failure RPM and load.

[sobriyah]

Many thanks for the suggestions. I will speak to the dealer about it.

Just using regular gas from the pumps as it's all that is available and is probably not very high octane.

Both low pressure pumps that 'failed' had blown a fuse. In each case after the fuse was replaced they ran again but the dealer recommended they be replaced, so they both have been now, along with the racors and the fuel filter assemblies under the engine cowls of both engines.

My main concern is how much damage a little water in the fuel is likely to have done downstream from the low pressure pumps and whether an expensive replacement of the injectors as the dealer is suggesting is absolutely necessary.

[rodbolt17]

long before I replaced an injector I would pull them and send them to Flagship marine in punta gorda Fl.
takes all of maybe 20 min an engine to pull them.
while they were out I would then clean the VST and replace/clean the filters as nessasary .