Compression Testing

thesameguy · **Joined:** Sat Oct 01, 2016 8:24 pm **Posts:** 652

Let me apologize in advance... I am sure this has been covered but my google-fu is apparently weak today. I can find nothing in the service manual.

I have an '05 CRD, and VM 1072 tool. I am going to do a compression & leak down test before pulling the engine, so I know what needs attention. Two questions:

1. Hoes does one prevent the fuel pump from spraying fuel everywhere when spinning the engine for a compression test?
2. What is intended to thread into the 1072? The elbow has threads that elude me... *none* of the 9 adapters for my compression tester thread properly. An M12 adapter is close, but it's not a reassuring fit.

Thoughts are much appreciated!

WolverineFW · **Posted:** Sat Sep 21, 2019 10:32 pm

How are you "spinning" the engine?

Sent from my SM-G965W using Tapatalk

thesameguy · **Joined:** Sat Oct 01, 2016 8:24 pm **Posts:** 652

With the starter... would there be another way?

WolverineFW · **Posted:** Sun Sep 22, 2019 12:00 am

You should be turning the engine by hand for a compression test. No fuel sprays with no key in the ignition.

Sent from my SM-G965W using Tapatalk

thesameguy · **Joined:** Sat Oct 01, 2016 8:24 pm **Posts:** 652

Are you maybe thinking of a leak down test? You can't do a compression test by hand turning an engine... an engine needs to be spinning at least a couple hundred RPM to get useful results. "Regular cranking speed" is typically what's recommended.

WolverineFW · **Posted:** Sun Sep 22, 2019 1:17 am

Maybe....but you should not have fuel spraying out.

Try these is instructions....

https://www.popularmechanics.com/cars/h ... -14912158/

Sent from my SM-G965W using Tapatalk

TKB4 · **Posted:** Sun Sep 22, 2019 7:42 am

Wolverine
Is your SEGR still in progress ? :roll:

but I also need to update my signature like many others.

Thesameguy
I have always done compression test with 5 turns of engine but either on small engine easy to hand rotate or large engine with starter easy to keep from starting. The CRD is pretty slow to turn over by hand 5 times and this may affect the readings. The engine cannot start without fuel injectors providing fuel so you can probably just unplug electrical connector to injectors . Guess you could also undo fuel line and let it run out of fuel. I am sure there may be other ways also. some ways may prevent ecm from allowing cranking but you may be able to jump pins in relays if necessary.

thesameguy · **Joined:** Sat Oct 01, 2016 8:24 pm **Posts:** 652

The adapter goes where the fuel injectors are, so I need to physically remove the fuel injectors. That leaves the feed from the rail wide open, and since the pump is mechanically driven as soon as the engine turns it's going to be sending pressurized fuel to the rail. I think I need to stop fuel from reaching the pump... maybe disconnect at the filter?

I started thinking "forget it, I'll do a leakdown test" but that poses a different problem... There is ZERO access to the crank pulley without removing the fan, and I don't have a viscous fan tool. I'm looking literally right now how to tackle that.

layback40 · **Posted:** Sun Sep 22, 2019 7:18 pm

thesameguy wrote:

The adapter goes where the fuel injectors are, so I need to physically remove the fuel injectors. That leaves the feed from the rail wide open, and since the pump is mechanically driven as soon as the engine turns it's going to be sending pressurized fuel to the rail. I think I need to stop fuel from reaching the pump... maybe disconnect at the filter?

I started thinking "forget it, I'll do a leakdown test" but that poses a different problem... There is ZERO access to the crank pulley without removing the fan, and I don't have a viscous fan tool. I'm looking literally right now how to tackle that.

If you disconnect the lead to the pump/injector the fuel will not flow.
You can use a socket on one of the hub bolts instead of the tool.

TKB4 · **Posted:** Sun Sep 22, 2019 9:35 pm

you will have to remove each injector one at a time anyway so all you would need to do is reattach injector that is removed at the time to the fuel line from rail up at a different angle and unplug but if unplugging cp3 will do it fine but about as easy to do above procedure.

You should be able to do this cranking or not. I guess will crank with cp3 unplugged, I know it will turn over with starter with injector unplugged.

Whatever you choose to do Good Luck !!

thesameguy · **Joined:** Sat Oct 01, 2016 8:24 pm **Posts:** 652

I clearly don't know what I am talking about, because I assumed the CP3 was mechanically driven and not electrically driven... LOL?

In any case, not having confidence in what I was doing I bailed on the compression test. I like to start with a compression test and then get specific with a leak down test if a cylinder is out of whack as compression tests are easier, but lacking confidence I just dug into the leak down test.

In case anyone doesn't know (I didn't!) the threads on the VM.1072 tool are 1/4" NPT, which shares nothing in common with common spark plug sockets. Both my compression and leak down tester have metric threads for spark plugs, so that was a problem. I ended up buying this:

https://www.lowes.com/pd/Kobalt-Compres ... 1000404921

And replacing the valve with a air tool quick disconnect which mated to my leak down tester. It was a pretty convenient solution.

I was able to remove the fan using a cam holding tool:

https://www.amazon.com/OTC-6613-Variabl ... NrPXRydWU=

and a very large crescent wrench. Fortunately the nut on the fan was not excessively tight... it came out with only a small fight.

The injectors themselves were also pretty easy to remove - I presoaked them in some Penetro (like Kroil) and was able to wiggle them out. There was a LOT of disgusting sludge around their bodies, probably from years of leaky valve cover or something. Nasty.

I let the engine idle for about 20 minutes prior to starting work. Coolant temp showed 150F (according to OBDII, anyway) which seemed like a good starting place.

Fan & shroud out, injectors out, VM tool in... leak down test!

Cylinder 1:

Cylinder 2:

Cylinder 3:

Cylinder 4:

Basically 0% leak down, which is (IMHO) VERY impressive. Cylinder #3 shows a tiny amount in the photo, but after taking the picture I adjusted the crank position a couple degrees and got 0%.

This motor has 180k on it and a totally unknown service history.

The thing has basically been sitting for two years. It has a massive oil leak from some invisible place (search LostJeeps for my username.... ugh!), and I'm FINALLY pulling the motor. I am going to do the timing belt and head gasket while it's out, and I wanted to be sure I didn't need anything more invasive. With these great results, I think I can safely say I do not!

GordnadoCRD · **Posted:** Sun Sep 22, 2019 11:45 pm

In the power distribution center (next to the battery) there is both a fuse and a relay labeled for the fuel injectors.

Pulling either one or both will allow you to crank the engine either normally, or with a normally-open, momentary-closed to jump the starter relay, with NO FUEL sprayed from the injectors.

The same effect can be achieved by just unplugging the fuel injectors.

TKB4 · **Posted:** Mon Sep 23, 2019 10:41 am

The CP3 is driven mechanically by the timing belt but unplugging a sensor on it may well stop fuel flow to injectors via ecm or valve. I haven't tried it personally though.

thesameguy · **Joined:** Sat Oct 01, 2016 8:24 pm **Posts:** 652

GordnadoCRD wrote:

In the power distribution center (next to the battery) there is both a fuse and a relay labeled for the fuel injectors.

Pulling either one or both will allow you to crank the engine either normally, or with a normally-open, momentary-closed to jump the starter relay, with NO FUEL sprayed from the injectors.

The same effect can be achieved by just unplugging the fuel injectors.

I'm sorry if I'm being dense... but it's not just a matter of cranking with no fuel from the injectors, it's a matter of cranking with the injectors physically removed.

If the injectors aren't there, what stops diesel from spraying from the fuel rail? If the CP3 is timing belt driven, isn't it going to be pumping 2900psi of diesel out of the injector ports?

(The problem is in the past, but I'd still really like to understand the process!)

Diesel Dan · **Posted:** Mon Sep 23, 2019 1:20 pm

Don't they have an adapter for the glow plug location?

That's what I use on other GP equipped engines.

thesameguy · **Joined:** Sat Oct 01, 2016 8:24 pm **Posts:** 652

I'm not aware of one for the glow plug location... but yeah, that's what I've seen in the past. Maybe because the glow plugs are such a PITA on this vehicle... I changed mine out and DEFINITELY don't want to do that again!

The factory tool - the VM.1072 tool - goes in the injector hole. Removing the injectors is no fun, but not as nerve-wracking as removing glow plugs!

RDBUL · **Joined:** Thu May 09, 2019 9:25 am **Posts:** 5

thesameguy wrote:

I'm sorry if I'm being dense... but it's not just a matter of cranking with no fuel from the injectors, it's a matter of cranking with the injectors physically removed.

If the injectors aren't there, what stops diesel from spraying from the fuel rail? If the CP3 is timing belt driven, isn't it going to be pumping 2900psi of diesel out of the injector ports?

(The problem is in the past, but I'd still really like to understand the process!)

Remember, pressure is a byproduct of restricting the flow. With the system sealed (injectors connected), the de-energized injectors act as a "plug" in the system. When you crank on the engine, the fuel flows from the CP3 into the rail and "stops" when it gets to the injectors... thus allowing pressure to build. With the injectors hydraulically disconnected from the rail (like when your doing a compression test), the CP3 pump has no way to build pressure and fuel will barley dribble from the fuel rail connections.

As for disconnecting the regulator on the pump (aka: MPROP)... the regulator on the pump is a inlet volume control device that "springs" to the max volume position when de-energized (unplugged). So, unplugging it would would give you max volume/flow.

The regulator on the back of the rail (aka: DRV)... is a pressure control device that "springs" to the zero pressure position when de-energized (unplugged). So, unplugging it would "dump" any fuel in the rail back to the return circuit.

I hope this helps!

thesameguy · **Joined:** Sat Oct 01, 2016 8:24 pm **Posts:** 652

It does, immensely.... thank you!

I probably should not have thrown out that 2900psi value as it was loaded... it's understood without the injectors there pressure will be minimal.

It makes sense that at 250rpm and no injectors fuel from the injectors ports would be minimal... didn't wanna find out the hard way though.

Next step is pulling the motor, and then emptying my bank account on CRD parts.

TKB4 · **Posted:** Mon Sep 23, 2019 6:19 pm

if you remove an injector and turn it and retighten fuel fitting and unplug the injector electrical connector there also wont be any fuel released but yes sounds much easier to unplug the appropriate sensor.

Good Luck with the rest of the job!

thesameguy · **Joined:** Sat Oct 01, 2016 8:24 pm **Posts:** 652

I didn't want to risk damaging the small fuel pipes, and it's tight enough in there without adding an injector pointing out in a random direction. Getting them entirely out of the way was time well spent.

In restrospect I probably should have unplugged most of the wiring harness and gotten it out of the way, but I'm just not that familiar with things under the hood of the CRD at this point and changing too much at once seemed like a formula for disaster... I just didn't know if I was going to have to put it back together or not.

Looking at the FSM, pulling the motor doesn't seem like too much of a hassle... I'm less, um, confident in the head gasket and the timing belt. Seems a lot of the threads here that refer to alternative special tools (eg, cam holder) include dead links, etc. I'm sure I'll have a billion questions.

Compression Testing

Who is online