Cat Return Check Valve

Topic: Cat Return Check Valve (Read 3235 times) previous topic - next topic - Topic derived from I think my DD 8.2 is ...

Cat Return Check Valve

January 08, 2016, 04:34:52 pm

Quote from: mike leary – January 08, 2016, 03:44:18 pm

Great news! Most of us went to the dark side, at least now you know your top-end is in great shape. Is it just your engine, or do we ALL have "Fuel Check Valves"?

Mike,

Most diesels have a check valve to keep pressure at specs for the main injector pump. If faulty, it can cause the pressure to drop or if cracked (like ours), allow air to enter the fuel system. The check valve is usually located on the side of the Bosch injection pump or in our case with the 2 cycle Detroit, located where the fuel returns to the tank.

Low fuel pressure can damage the injection pump over an extended period. Very easy to check pressure. Low pressure can also be related to a faulty lift pump or clogged filters.

Working in a tight RV engine compartment, it's easy to see how a mechanic could cross thread or overtighten as was our case.

Check valves are relatively inexpensive. I shopped around and got ours for under $40.

As I recently found out, some CATs don't have a fuel return line.

Note the crack in the old valve in the photos below. Good time to "overhaul" the manual primer pump too (if you have one). Cost was $0.10 for two "O" rings plus about an hour of my time.

Pierce

Re: Cat Return Check Valve

Reply #1 – January 08, 2016, 04:41:16 pm

As Pierce said, most diesel DO have check valves. But, their location is different depending on fuel injection system used. Not familiar with the DD 8.2.

I know on many Caterpillar engines, it is on the back of the head with fuel return line connected to it. On a Caterpillar engine, taking longer to start is a symptom of bad check valve, as fuel pressure bleeds off and it takes a couple of additional seconds to build. On Cat engines with a manual primer pump, if you can pump it after the coach sits, the fuel is going SOMEWHERE as the pump is very difficult to push if fuel pressure is proper. Sure, there are other causes/places that fuel pressure can drop and other causes of slower than normal starting, but check valves are a pretty inexpensive place to begin your checking.

Re: Cat Return Check Valve

Reply #2 – January 08, 2016, 05:04:24 pm

Ya, don't know where the check valve is/how it affects starting on the 8.2 DD-- never worked on one.

The slow start, particularly after sitting is a very common symptom of bad check valve on Cat engines.

Re: Cat Return Check Valve

Reply #3 – January 08, 2016, 06:32:44 pm

Can't find anything in my manuals: anyone have a clue where our CAT return/check valve may be, or do we even have one?

Re: Cat Return Check Valve

Reply #4 – January 08, 2016, 07:39:35 pm

Mike,

On the Cat 3116 on the back of the head (toward front of motrhome, accessed easily by raising the bed): ~~~~~School Bus Mechanic: Cat 3116 Fuel System Schematic

Check valve #8 prevents bleed off of fuel from the head during engine shutdown. This could cause a hard start after engine shutdown overnight [depending on how bad the bleed off is].

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Cat Return Check Valve

January 08, 2016, 04:34:52 pm

Re: Cat Return Check Valve

Reply #1 – January 08, 2016, 04:41:16 pm

Re: Cat Return Check Valve

Reply #2 – January 08, 2016, 05:04:24 pm

Re: Cat Return Check Valve

Reply #3 – January 08, 2016, 06:32:44 pm

Re: Cat Return Check Valve

Reply #4 – January 08, 2016, 07:39:35 pm

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