HowTo: M56/Q70 5.6 (VK56VD) High Pressure Fuel Pump Lifter Bucket Replacement

[ohyunjin]

If you are getting all of these codes qx80 p0090 p0300 p0087 p219a, do you think the hpfp should be replaced as well as the lifter bucket?

[VStar650CL]

You can if you want to be safe, but all those codes would be caused by a bad bucket providing too little lift to the HPFP.

[ohyunjin]

Thanks. That makes sense. I don't think I can use this method on the QX80 without taking the manifold off. There isn't enough slack to pull it out. Unless someone else knows a method.

[VStar650CL]

There's no way to remove it without pulling the plenum on a gen2 Armada, and I'd presume your QX is the same.

[ohyunjin]

There's no way to remove it without pulling the plenum on a gen2 Armada, and I'd presume your QX is the same.

Got it out. Lifter was stuck and needed to use a puller for it. Replaced and everything is back. But I'm still seeing p0300 code. Any thoughts on that? Thanks.

[VStar650CL]

That's a multi-cylinder misfire. Did you clear the codes, or just let the ones for the HPFP go past? Misfire codes won't clear themselves immediately like some others, you need to clear them proactively. If you cleared it and it recurred, then maybe something else went south along with the fuel pressure. Low fuel pressure causes the engine to run way lean and the ECM has no way to compensate, so it can trash the spark plugs in an awful hurry.

[ohyunjin]

I cleared the codes, but the p0300 came back. The lifter didn't sit below the beveled part of cylinder. I don't know if that matters.

Maybe, I'll try replacing the spark plugs.

[ohyunjin]

I replaced the spark plugs. No CEL. Drove around for a little. Seems ok for now. Thanks for the help! Hopefully it runs fine for a while longer.

[VStar650CL]

[qwertylolman]

is there any maintenance for the pump itself? today i was looking for some traces of why my y62 has floating p0300, and I accidentally found that when p0300 occurred, the voltage on high fuel pressure was a bit low, as well as the pressure itself (2.5mPA and 905mV, when commanded pressure was 2.9mPa and minimum voltage should be 980mV)
the bucket and lever are fine, so may be there is an issue with the pump itself?

[VStar650CL]

In my experience the ECM's rarely exert tight control over the fuel pressure, as long as it's "in the ballpark" they don't move the PWM around much. However, they do usually err high and not low. There's no specific maintenance on the high pressure pump, but it's entirely possible you're actually seeing a secondary effect from low pressure or volume from the lift pump. Unfortunately there's no sensor for that (and trust me, we techs would kiss their arses to have one, it would make fuel system diag a whole lot easier).