Bad Mprop?

Patrick Henry · **Posted:** Mon May 16, 2016 10:11 pm

At 200K +miles, after replacing all of my rockers, timing belt, and water pump and driving several hundred miles my jeep tractor was running fine. Then upon a short trip, I found the #1 fuel injector return line fitting had popped off, drenching the top works with fuel. I cleaned up the mess and re-inserted the return line fitting and all seemed well, until it popped off again 40 miles later. Then it happened again, this time throwing a p0087 code and refusing to start.

After reviewing other symptoms associated with p0087 codes, I suspect I have a failing Mprop or fuel quantity solenoid valve. If the valve is sticking or modulating erratically, this would explain surging flow in the fuel return line causing it to pop off. Thoughts?

flash7210 · **Posted:** Mon May 16, 2016 10:23 pm

First, check for air in fuel and replace the fuel filter if you havent yet.

If it still doesnt want to start, unplug the MPROP.
If the engine starts with the MPROP unplugged then replace the MPROP.

Mountainman · **Posted:** Tue May 17, 2016 12:01 am

hmm, usually the amount of return is an indicator of injector condition. I would think that the injector that is popping the return is your problem. If it's dumping fuel way too fast, maybe the Mprop code is getting thrown because that's where the system is seeing the problem?

Just a guess, Flash knows a lot more than I do.

Could a bad injector damage the Mprop is another thought?

good injectors on Ebay for around $200, they are a bit of a gamble, but I think it's worth it

dhenderz · **Joined:** Fri Dec 11, 2015 9:26 am **Posts:** 164

OK, maybe a silly question. But does the return connector have the (u-shaped) retainer spring? I wouldn't think it would be possible to pop off a return fitting (that has the retainer installed correctly) without damaging the plastic fitting. So if it did have the retainer, I would be suspect of whether the fitting is still intact.

Regardless, I don't believe an MPROP would cause excess fuel pressure in the rail thus leading to the failure you describe/suspect. A bad fuel pressure regulator (in the back of the rail) could cause excessive rail pressure by not bleeding excess fuel to the main return. Even then I doubt the scenario or failure described because that would be excess pressure in the rail, not in the top/return portion of the injector.

I agree with mountainman, I think you are more likely looking at a bad injector that is allowing injector/rail pressure to be seen/dumped to the injector return - which shouldn't be happening. I suppose the curious question would be why?

flash7210 · **Posted:** Tue May 17, 2016 5:59 am

P0087 is a Low Rail Pressure code.
You will want to be absolutely sure that the low pressure side of the fuel system, between tank and injection pump, is in good condition before you start replacing expensive parts on the high pressure side.

Are you using a tuner box?

Mountainman · **Posted:** Tue May 17, 2016 12:10 pm

flash7210 wrote:

P0087 is a Low Rail Pressure code.
You will want to be absolutely sure that the low pressure side of the fuel system, between tank and injection pump, is in good condition before you start replacing expensive parts on the high pressure side.

Are you using a tuner box?

Yeah, like Flash said initially, make sure that the fuel supply is perfect first, and always remember that many Lost members have replaced CP3's, and it was usually NOT BAD... Our CP3's are one of the toughest parts under the hood IMO. Look everywhere else first, but unplug that Mprop like Flash said because it's easy :2cents:

geordi · **Posted:** Tue May 17, 2016 4:32 pm

Should you decide to replace things anyway, I have several extra injectors and CP3 pumps now, but I would be curious to know the situation that caused this anyway. The return line should not be pressurized.

Patrick Henry · **Posted:** Fri May 20, 2016 12:43 am

No tuner box, just a GDE tune. Hopefully I can get the beastie towed to my place next week. In the meantime I had the shop check out the low pressure side. They tell me no problem in getting plenty of fuel but pulling the Mprop connector makes no difference when cranking. No other codes other than the P0087. I would think if I had a bad connector in the fuel system that I would see other codes. Anyway, I am out of ideas until I get it home to diagnose further.

flash7210 · **Posted:** Fri May 20, 2016 7:29 am

Good.
So the MPROP (on the CP3) is most likely not the problem,

Next, you need to check all your injector return lines and make sure the clip is holding them down on the injectors.
Also make sure that the rail pressure solenoid, at the back of the fuel rail, is firmly connected. If its disconnected or the connector is broken, pressure will not build in the rail and the engine will crank but not start.
I also recommend doing a injector return flow test.
I use this test kit: http://www.amazon.com/Generic-Diesel-Injector-Common-Adaptor/dp/B00N2JGZ2I/ref=sr_1_3?s=automotive&ie=UTF8&qid=1463743509&sr=1-3&keywords=diesel+injector+test+kit
But you can probably make your own with some tubing and little bottles.

Mountainman · **Posted:** Fri May 20, 2016 11:21 am

Since you suspect that the injector could actually be blasting the line off. For the return test I would just do what I do, and pull the return line off, and crank the engine. There should be tiny bits of diesel slowly accumulating, it will be obvious if one is shooting fuel by. I'd put a rag over each one separately so you can easily tell if one is shooting fuel, and it will keep a big mess from possibly happening. If you get more than a few ml's in 8 seconds of cranking a time or two, then you've probably found your problem. I guess you only need to test that one injector actually, or maybe the neighboring one for comparison.
I also agree that the line might just be bad, and is not staying snapped in, but that's just an extra problem on top of whatever is causing it to not run. The rail pressure sensors do fail once in a blue moon. If you end up thinking it might be bad, the best bet is to buy a complete rail from ebay, or junkyard, as the sensors are expensive, and a test rail is invaluable if you're going to keep the jeep long term. I can test the entire rail with my extra known good rail in a matter of minutes.

Patrick Henry · **Posted:** Sat May 21, 2016 1:42 am

When my Libby died on me, it was instantaneous, no rough running or mis-fire, just dead, rolled to a stop dead. Cranking it just turned the engine over with no hint of any combustion.Confirming the P0087 code tells me the rail pressure was low but with the CP3 still pumping leads me to believe all of the fuel was flowing into the injector return line. The increased flow into the return line, not pressure, was taking the path of least resistance back to the fuel tank. That shift of momentum puts a load onto the plastic connectors that are anchoring the return line. The #1 injector connector is an elbow whereas the others are tees, so the elbow takes most of the load and when it pops the load on the remaining tees is dissipated. The elbow was probably already worn, making it more susceptible anyway and needs to be replaced.

Anyhoo, the return line issue is just a symptom that the rail pressure is low and no flow was being injected into the cylinders. It seems logical to me that something failed and failed quickly to drop the rail pressure. Hopefully it is a connector or the rail pressure solenoid like flash indicated.

One other thing that has been bothering me is when the Libby was coasting to a stop I could hear a faint ringy tingy ticking sound coming from the engine, something I have never heard before. Of course the engine was rolling over but not firing. Maybe it was just the valve train?

geordi · **Posted:** Sat May 21, 2016 2:39 am

Jingly noises are possibly your turbo blades doing things they shouldn't be doing: Touching the walls. I'd have a good look inside the turbo mouth and see what you see.

Several people have asked this and now I am too - the return lines should not pop free of the injector unless the metal hair clip is not there? If you have an empty slot in the metal ring on the top of the injector, then you are missing the clip.

rankom · **Posted:** Sat May 21, 2016 8:55 am

1st perform compression test (CHECK VALVES) if still no start and injector is a suspect, you need to remove jumper tube to cap fuel port (rail side) check fuel rail pressure when cranking .

flash7210 · **Posted:** Sat May 21, 2016 8:03 pm

Quote:

One other thing that has been bothering me is when the Libby was coasting to a stop I could hear a faint ringy tingy ticking sound

That's the sound the front driveshaft makes when it has a bad joint.

rankom · **Posted:** Sun May 22, 2016 3:55 pm

lol , yeah i take drive line noise any day over VALVE TRAIN NOISE AND OR INJECTOR NOISE ,

Patrick Henry · **Posted:** Sun May 29, 2016 11:09 pm

Update. I went back into the low pressure side and replace the fuel filter and bleed all the air out. I took the return lines off the injectors and check for bypass flow differences from each injector. After extended cranking I got little to no bypass flow from any of the injectors. I then checked the pressure control valve on the rear of the rail to see it it was dumping return flow during cranking but it was not. However, I did have to plug the open return line to the tank securely as the CP3 was pumping a lot of flow back the tank. I removed the crank position sensor and checked with a hair dryer to see if it's resistance changed with temperature. It did not vary very much at all. On a gamble I replaced the mPROP, but it made no difference. After every crank I check for DTCs and clear them for the next crank. After some cranks I get not DTCs at all, some cranks I get P0093, Fuel Rail Positive Pressure Deviation.

Just in case, I have a new crank position sensor on order. If that doesn't do it, the Jeep is going to a shop for further diagnoses as I am to my limit on tools and instrumentation.

flash7210 · **Posted:** Mon May 30, 2016 6:13 am

So far, you have done all the right things as far as diagnosis goes.

Do you have a way of reading the pressure in the fuel rail?
There are some OBD tools/apps that can help with that.
If not, try unplugging the fuel rail pressure sensor and then starting the engine.
If still no start then that only leaves two possibilities:
A bad CP3 pump
Or one or more bad injectors

Given what you've done so far, the CP3 does not seem to be the problem.

dhenderz · **Joined:** Fri Dec 11, 2015 9:26 am **Posts:** 164

I suspect a broken injector tip. If it were me I would pull the injectors.

flash7210 · **Posted:** Mon May 30, 2016 6:44 am

A little bit of background about fuel system components based on my experience.

MPROP on CP3:
A fuel control solenoid that directs fuel either up to the rail or out the return. When OFF or unplugged, all fuel goes up to the rail.

Fuel rail pressure solenoid:
A fuel control solenoid at the back of the fuel rail. Controls pressure inside the rail. When OFF or unplugged, it cannot hold any pressure in the rail and will send all fuel out the return line.

Fuel rail pressure sensor:
Pressure sensor mid way on the rail. The only way for the ECM to know pressure in the rail. When faulty or unplugged, the ECM will force limp mode with limited power and acceleration. While in this state the ECM will force the rail pressure solenoid to be fully closed and hold at maximum pressure (~26,000 psi)

Patrick Henry · **Posted:** Mon May 30, 2016 9:01 am

I disconnected the fuel rail pressure sensor and cranked without success. The only DTC afterwards was the high/low pressure sensor voltage. I don't have any way to monitor rail pressure. After I get the new crank position sensor installed, it's off to the shop for further diagnosis.

I really appreciate the help the folks here have provided. I can now tell the shop in particular what to go after.

However, either replacing the CP3 or the injectors may be the tipping point on me keeping this 203K mile vehicle much longer.

Bad Mprop?

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