df70 surge

[troy kidd]

Hi all I'm new to this forum and hope I can get some much needed info.
I have a used 1998 df70. Idles great in and out of the water it just surges when under load at 3500-4000. This is what I have done so far. Compression .190 +-2-3 ponds on all cyls. New high and low fillters new fuel lines primer bulb. Spark plugs. New vst tank. New low psi pump tested all sensors I could per repair manual. I have fuel injector rebuild kit on the way. The injector fillters are Brown colored. The reason I've done all this is because of water intrusion from previous owner and I kept getting trash stopping up the high psi pump. Any ideas to what may be the problem would greatly aprechated. Sorry for being long winded just trying to give all the info up front.

[18pontoon]

I too am a 1998 DF70 owner. Is 3500-4000 your max RPM? If not, how does it do under full load? Are you using a water separating filter?

[keakar]

my thoughts are two things,

one, its fuel related from a bad pressure relief valve or a vacuum lock issue so try running with the gas cap off of the tank to check for vacuum lock. also it could be a pressure relief valve issue allowing the fuel rail pressure to drop then rebuild over and over and pressure fluctuations will cause fuel supply fluctuations. not sure if its save to cap off the fuel return line from the relief valve though so im not sure how you would go about testing it.

two, its electrical so check, test, or replace the fuel mixture sensors and anything else that tells the ECM how much gas to supply the injectors.

good luck with it

[troy kidd]

Yes if I run the recommended 18" pitch prop per prop wizard for my 17 ft Carolina skiff hull and 70 hp four stroke. It will only turn 4000 rpm and surge between 3500 and 4000 rpm. Now if I put on a 13" pitch prop ill get the engine to turn 5100 rpm with a surge at 3500 to 4000 rpm as I go thru the load to plane off but no surge at 5100 rpm. Very strange problem I have here.

[troy kidd]

my thoughts are two things,

one, its fuel related from a bad pressure relief valve or a vacuum lock issue so try running with the gas cap off of the tank to check for vacuum lock. also it could be a pressure relief valve issue allowing the fuel rail pressure to drop then rebuild over and over and pressure fluctuations will cause fuel supply fluctuations. not sure if its save to cap off the fuel return line from the relief valve though so im not sure how you would go about testing it.

two, its electrical so check, test, or replace the fuel mixture sensors and anything else that tells the ECM how much gas to supply the injectors.

good luck with it

Thanks. I have tried running with out gas cap off. And the fuel psi regulator is new but I could block the return off and give it a try. I have tested every sensor to the best of my ability. But I won't hurt to go over it again. Thanks for the info

[prattvan]

troy kidd, what did you find out about your problem ??

[prattvan]

Sounds like it may be running in safe mode. Does it make a beep every 7 seconds ??