return rates => bad injection pump?

[npauli]

Please check my diagnosis here and tell me if I'm on the right track or need to look at something else.

Symptoms:
fuel in oil (last test showed 6% at 3k miles). It's nothing catastrophic, but getting steadily worse
balance rates not too bad. #6 was 3.9, others within +/- 2
bit more diesel smell than I remember
no performance complaints

Tried today to test return flow as spelled out in the shop manual. I just got to the point where I'm measuring fuel from the main return quick disconnect with the injection pump return dumping into a bottle. The manual says I should get at least 35 mL after 15 sec, but I'm getting more like 10mL.

The cranking speed wasn't quite as high as its supposed to be though - they wanted 150 rpm and it fluctuated between 130 and 150.

At this point I'll probably do the following:

1) Try the test again tomorrow w/ some time charging the batteries and plugging in the oilpan heater to get the rpm's up.
2) If I get the same result, put the truck back together so I can drive to work monday. (i.e. I won't continue testing to find flow out of each head)
3) Borrow a Tech 2 to command 160 MPa and see what I get. If the actual pressure is low, would that confirm the pump is bad?


I'd love to have any advice you may have.

[DmaxMaverick]

With fuel in the oil, and your balance rates as they are, I'd suspect bad injectors. Could be one or more leaking return lines (under the valve cover), which won't effect performance if it's slight.

The injector balance rates are more than what they seem. One high rate does not indicate THAT injector is bad, but THAT injector is compensating for another. When you have one or several very high, and one very low, the likely suspect is the low one. The + or - rates are the departure from the baseline, and need to be deciphered to identify the actual individual injector performance.

[THEFERMANATOR]

When checking fuel return like you are, you want it to be a low amount. In a perfect world the injectors and popoff would return no fuel to the tank during cranking, so zero would be perfect. The test you did basically checked to see how much fuel all of the injectors and pop off valve are returning during cranking, and GM spec says that it should be 2 ounces or LESS to be within spec. Like stated, the one balance rate that differs greatly from the rest stands out to me as being a culprit here. And a weak CP3 isn't going to give you a strong diesel smell out the exhaust unless it can't build rail pressure above 25-30 MPA at an idle.

[npauli]

to clarify:

The 10mL/15 sec I measured includes all returns except the one from the pump that the manual told me to unplug and run into a separate container, so it includes the injectors.

So can this tell me anything about the health of the injectors, or only that something upstream of the injectors isn't returning as much fuel as it's supposed to?

[Kennedy]

If you truly believe that you have a problem brewing, I would start with the known common issue: Injectors

See what progresses from there. A weak pump isn't all that common, plus it will genereally show it's hand with performance related issues.

[THEFERMANATOR]

to clarify:

The 10mL/15 sec I measured includes all returns except the one from the pump that the manual told me to unplug and run into a separate container, so it includes the injectors.

So can this tell me anything about the health of the injectors, or only that something upstream of the injectors isn't returning as much fuel as it's supposed to?

In a perfect world the injectors shouldn't return ANY fuel while just cranking the engine over. They should ONLY return fuel when they are pulsed(triggerred open). Some fuel return is acceptable, and this is the 2 ounces or LESS for all 8 injectors and pop off valve with the pump disconnected so it cannot return fuel while doing the cranking test. Like said, I would be much more suspect of failed injectors than a failed CP3. And I have yet to hear of a failed CP3 that leaked fuel into the crankcase.