Karcher high pressure cleaner is pulsing when using at high pressure only

SOURCE: pulsing and lost pressure

depending on amount of use i have found failures of the piston spring and retainer which are located inside main housing of pump,these cause pulsing and no pressure,you need to remove pump head and face plate to get to them,hope this is of help

SOURCE: Karcher/Winner 11 - motor pulses when hose is not operating

Hi, I had the same problem, Replaced the O rings and the rubber seals and cups inside the pressure washer and eventually the hose itself burst. Turns out the hose was leaking, internally between the inner sheath and the outside plastic cover, for quite some time and this caused the pulse. New hose and pressure cleaner is as good as new.

SOURCE: I have karcher 620m pressure

Try this. While pushing the trigger of the gun, turn lance fully anticlockwise and then turn back fully clockwise.

SOURCE: My Karcher 2.99 starts and stops, (pulses) when th...

Is liquid leaking from the base, when the Pressure washer is on ?
I have the same Problem, the leak is from the seam of the Manifold housing. There is a small crack in the seam. A manufacturing defect.. A New Manifold Complete Replacement is $61.03, about the half the price what I paid for this pressure washer at Walmart... :( If under 1 year old, and you can find a receipt,Karcher will replace the whole Pressure washer under warranty.

SOURCE: My Karcher pulses when on standby,stops when i use

Is there a leak from the bottom ?
If so Problem, the leak is from the seam of the Manifold housing. There is a small crack in the seam. A design weakness.. A New Manifold Complete Replacement approx. $61.03.
If not you may replace the Pump Manifold Housing from Karcher, or locate a local Karcher Service Center.
If under 1 year old, and you can find a receipt,Karcher will replace the entire Pressure Washer under warranty.