Hi all,

I've been troubleshooting my mom's 2015 CX-5 2.5L, following some of the advice in this thread: CX-3 Thread

I first replaced the fuel rail with sensor--no significant change. It was stalling at idle before, it may have stopped doing that now but still no power when you step on the throttle. Then I connected Forscan and read the sensors. With the key on engine off the fuel pressure sensor was around 1300kPa, falling slowly. When I turned the engine on, it immediately went to 430kPa. I disconnected the sensor and the reading stayed at 430kPa.

So now I'm thinking it's a bad ground and I will spend some time this weekend checking that theory. Before I freeze my fingers off though (windchill -40 today) I just wanted to check if anyone has some experience with a ground that shorts only when the engine is running. Is there a specific cable or grounding point I should focus on? Is it the ECU/PCM? Any ideas are welcome.

Thanks!

 

A simple test of the ground wiring with a multimeter will tell you if there's an issue with the sensor ground circuit.

My first suspect would be a bad HPFP, but unfortunately there's no conclusive way to test those pumps. The 'book' test is to compare sensor voltage to fuel pressure, but that of course becomes an invalid test of the pump whenever there's anything wrong with the sensor or associated wiring/connectors. However, you already replaced the sensor, so that makes the pump the prime candidate IMO.

 

Thanks for your thoughts.

Thinking it over last night I’m now inclined to agree with you. The sensor reading dropping to 0V (430 kPa) could just be that the HPFP is not turned on or is malfunctioning and the engine is using fuel faster than the low pressure pump can keep it at 430+ kPa.

I did hear a pump turn on when I jumped the fuel pump relay though following this procedure. So maybe that means it’s still working.

I will test the grounds today and then prepare to give my mom the expensive news if the wiring checks out okay. Maybe another backyard test would be to jump the HPFP as described in that link with the engine off and see if the fuel pressure reading changes. That would confirm wiring as the issue unless I misunderstand something.

I will update later as there’s nothing more frustrating than a forum post that describes your problem and not the solution!

 

What you're hearing is most likely the low pressure fuel pump, which is located inside the tank.

No idea what you read, but the HPFP is driven by the exhaust samshaft, and will therefore be doing nothing when the engine is not running.

I've participated in a number of forums over the years and my observation has been that threads don't get a final resolution posting from the OP somewhere around 99.9% of the time. It's just the way it is. Human nature I guess.

 

Or they join several forums and ask the same question on each of the forums .....
right? lol

 

Thanks for the info—are you saying the HPFP is powered by the exhaust camshaft? What is the electrical connector for? Out of curiosity.

I scanned the car again this afternoon as the idling performance was significantly worse than when I left it last. It’s now throwing P0192 - Fuel Pressure Sensor Low “Not present at time of request” and P0193 Fuel Pressure Sensor High “Intermittent at time of request”. It’s also saying P0171 System Too Lean and P0300 Random Misfire Detected. The latter three are new since installing the new fuel rail.

I’m thinking P0193 means the HPFP is probably fine and there’s a wiring issue to the pressure sensor somewhere.

I spent daylight hours catching my parents’ escaped horses and getting my vehicle up their icy driveway so I will get a multimeter on the CX-5 tomorrow hopefully. Am I on the right track? Thanks immensely for your help so far.

 

It's part of the circuitry for energizing the HPFP spill valve solenoid. And the spill valve BTW is a POSSIBLE reason for a low fuel pressure issue, if it's sticking or not energized/powered correctly. But please note that I'm not saying that is the problem with your vehicle, only that it is one of the possible suspects.

IMO that P0171 and the misfire code indicate a true low fuel pressure condition, not a bad reading from the fuel pressure sensor. In addition to the spill valve mentioned above, the HPFP, in tank low pressure pump, and the fuel lines are also possible reasons for the fuel delivery problem.

Based on the pressure values that you posted previously, it sounds like the low pressure pump is ok, but naturally I cannot be sure of that. The low pressure pump (and a good portion of the plumbing) is one thing that you can confirm with a pressure testing tool, after disconnecting the input low pressure fuel line from the HPFP. Unfortunately, you can't test the other stuff without taking it all apart first. And HPFPs show up frequently on the auto forums as the culprit in direct injected low fuel pressure problems (at least in my travels anyway). Some folks just replace the HPFP in your situation, and I can't criticize that part-throwing decision, given that there's no cost-effective way for a DIYer to test that pump. This whole thing is very annoying to me because I always prefer to diagnose via testing, instead of just throwing parts. Good luck to you, whichever way you decide to go on this.

 

I had another crack at it, looking for shorts and bad grounds. I am pretty sure the wiring is not the culprit.

After disconnecting the pressure sensor and the PCM and reconnecting everything, I cleared the code (only P0193 at this point), cycled the ignition, and the scan came back clear. The battery was not capable of turning the engine over so I boosted it with my car. The engine started and died about 5 seconds later. The MIL stayed on throughout. I tried rescanning the codes but I think my cheap wifi adapter succumbed to the cold and stopped allowing wifi connections.

As you mentioned, it seems the HPFP is the least reliable part here but that isn’t an obvious culprit for a high fuel pressure reading.

So at this point, I think it has to either be a fuel delivery issue or I need to do something else to convince the PCM that there are no active codes. I also don’t trust my scanner any more, and I’m not confident enough about anything to start buying more parts and playing with high pressure fuel connections outside in the snow and cold.

My mom is going to call CAA and have the car towed to a shop and fixed. I encouraged her not to let them change the PCM unless they were extremely confident, and I will update with their story and the fix.