Calling Tom Lawrence

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Steve Lusardi - 06 Apr 2006 18:03 GMT

Tom,
I finally figured out the high speed miss on the Cummins. It was water in
the filter jar. This little exercise has taught me a few humbling lessons.
First, my schedule to dump fuel from the filter needs to be shorter than
every 6 refuelings. I understand this is dependent on the environment, but
there was no water in the bowl alert, which should have occurred.
I borrowed a DRB3 and ran all the tests in order to familarise myself with
them and a few tests created strange results. If you would, could you please
verify or interpret these readings.

Fuel water sensor voltage = 5.2 V (water in the bowl,. no error)
Boost pressure at Idle (750 rpm) = 100kpa (0 PSI on gauge)
Boost Pressure, Ignition on, engine stopped = 99 kpa (0 PSI on gauge)
Boost Pressure, WOT, max speed, 3200 rpm, (30 lbs on guage) = 260 kpa, (max
EGT 1100 F)

Thanks in advance,
Steve

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Tom Lawrence - 07 Apr 2006 01:38 GMT

> I finally figured out the high speed miss on the Cummins. It was water in
> the filter jar.

Really?? Hmmm... would have thought that would have it running like crap
all the time - not just at high RPMs.

> First, my schedule to dump fuel from the filter needs to be shorter than
> every 6 refuelings. I understand this is dependent on the environment, but
> there was no water in the bowl alert, which should have occurred.

I've found the stock WIF sensor to be practically worthless... mine goes
off from time to time, and there is ZERO water in there. I have another
water separator as part of my FASS system, and that's always clear, too.

> Fuel water sensor voltage = 5.2 V (water in the bowl,. no error)
> Boost pressure at Idle (750 rpm) = 100kpa (0 PSI on gauge)
> Boost Pressure, Ignition on, engine stopped = 99 kpa (0 PSI on gauge)
> Boost Pressure, WOT, max speed, 3200 rpm, (30 lbs on guage) = 260 kpa,
> (max EGT 1100 F)

The boost numbers are good... maybe a little low on the max number. If I
remember, you have a '600' engine, which should peak around 35psi or so
stock. However, if you did this test on a dyno (especially an inertial
dyno), the boost might not build as much...

As for the WIF sensor readings, you should be measuring resistance across
the sensor. With fuel in the bowl, the resistance should be off the chart
(ie. very high). With water in there, it should drop to around 30,000 ohms
or so.

I'd be more concerned about where the water is coming from. In my three
years of owning my truck, I've never had water in the bowl (I drain it every
filter change, and look closely... after the third fuel filter change, I
purposely added some water to see what it would look like... definately
never looked like that).

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Greg Surratt - 07 Apr 2006 09:38 GMT

>> I finally figured out the high speed miss on the Cummins. It was water in
>> the filter jar.
>
>Really?? Hmmm... would have thought that would have it running like crap
>all the time - not just at high RPMs.

I had the same experience. I was on a road trip and bought fuel about
600 miles from home. About an hour later, the engine started missing
at high RPM. Accelerating became almost painful. The further I went,
the lower the RPM where the miss occurred until when I got home, I had
the miss at cruising rpm for 65. Truck ran great at 55 though.

There was no water in fuel sensor indication at the time. Changed the
fuel filter and it was like I had bought a new truck. I'm just glad I
didn't have the trailer with me on that trip.

Greg

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