Non Turbo 6.5l surging

[tcpl123]

I have a non turbo 6.5 in a 70 series Landcruiser that suffers from surging.The engine was installed as a short replacement for a 6.2l that spun a a bottom end bearing and I re-used the old injector pump and injectors (which were tested and rated as ok) Initially the motor surged and would shudder and cut out and when I enquired about this with the supplier they advised replacing the injector pump. I installed a refurbished pump and this has fixed the shuddering/ cut out issue but the surging remains. Typically you will be driving along at 60km/hr and then it will accelerate to 70 or so and then wind back down to 60. Starting is fine. Any thoughts?

[Robyn]

First thing WELCOME TO TDP Mate :D:D


AIR IN THE SYSTEM COMES TO MIND RIGHT OFF


Connect a clear hose/tube to the fuel return line from the Injection pump (in series with regular line) and run it up by the windshield where you can see it.

Go for a drive and watch for streams of air bubbles heading back to the tank.

If bubbles appear and it happens at the same time as the surges, then you have found your gremlin.

Trace fuel line and repair source of air entering the fuel (Would be on suction side of lift pump normally)

What is the rated amount of fuel delivery from your lift pump (Electric or ???) free run into a container with the engine off and lift pump running ????

If the lift pump can't keep up, the transfer pump in the IP can in effect "Suck a hole" in the fuel and create an air pocket.

Seems your issue has followed the other changes.

Make sure you have plenty of fuel delivery capacity at about 5 psi (20 gallons and hour capacity on the lift pump is not excessive as all the extra goes back to the tank.

I assume you are running a DB2 iNJECTION PUMP ???


If no air is found then the governor in the IP is suspect.

You mentioned "Refurbished pump"

Was the IP rebuilt completely by a qualified Stanadyne repair/service shop, or simply cleaned and new seals installed ?????

What model pump is it ????

Get the numbers off the tag on the pump.

Something like a DB2-4911 or some other DB2-XXXX


Good luck

Keep us in the loop :):):)

[tcpl123]

Thanks for your reply. IP is a DB2 831-5209. It was rebuilt by Dewars Performance engines here in Australia. They import and sell these engines so I think they are on the ball. Thanks to your suggestions I found the lift pump had not been connected up and since then the surging has stopped in town driving but is still present on the highway.I suspect either the lift pump is not up to the task (although it worked ok on the 6.2 donk) or there is some sort of fuel blockage or restriction in the system. I will try the return line bubble test and see what results.

[Robyn]

Good deal...
At least we are on the right track.

Volume, volume, volume is the key word on fuel delivery.

Pressure will be fine at 5-6 psi

Another test you can do is put a temporary low pressure fuel gauge in the line from the filter to the IP

Get the test gauge out where you can see it while driving.

Watch the pressure when you open the throttle (Highway running)

The pressure needs to stay at least 1 or 2 pounds.

If the pressure drops to zero or actually draws a vacuum then your lift pump is not delivering enough volume.

The IP has a transfer pump inside and can pull a real strong vacuum if starved for fuel, which results in the surging.


Be sure the fuel tank cap is vented properly as well.

Fuel line size from the tank ???

Good luck