Hi everybody,

We left our 2016 CX-3 Mazda in the garage for a month without driving while we ere away. Now the engine is runnings very rough.

The check engine light is one and shows the following code:

P0087 - Fuel rail / System pressure too low
P0171 - System too lean Bank 1

My understanding is that P0087 is detected by the pressure regulator on the high pressure fuel pump and it detects the pressure into the fuel rail so it doesnt tell me if the high pressure fuel pump or the low pressure fuel pump (inside fuel tank) is the culprit.

Additionally, I believe P0171 indicates Bank 1 is too lean. And my understanding is there is only 1 Bank on this vehicle so the problem is not to do with a particular cylinder.

I do not exactly know what a mechanic could do next during this diaganosis but I would assume he/she would connect a gauge up to the low pressure line and the high pressure line with the car running to check if either is out of spec. What do you think? (I do not unfortunently have these spectialty gauges so I wont be able to conduct this test)

I went to the Mazda dealer parts store today expecting to be able to purchase a fuel filter for the low pressure pump, but unfortunenly after looking up my car in the system the pump doesnt have an easy to replace filter but instead it is built into the main pump. I believe the part number is "13-ZE0" and it costs $287.31

Any suggestions on what else I could try before I take it into the mechanic?

Edit: I've also added diagnostic data using ScanXL via OBDII

This diagnostic capture was taken while the car was idling. The 'fuel rail pressure absolute' value, sae.frp_abs, reads 500kpa which is 72.5PSI. From googling the idling fuel pressure at rail should be 450-500PSI

I've also tested with ignition on but engine not running and fuel rail pressure absolute is 460kPa which is 66.7PSI
And I should add when engine is running and I rev engine it bearly goes more than 500kPa. For 1 second it went to 600kPa (87PSI)

Digging a bit further into this, a reddit poster replied to a CX-3 owner who had a similar issue:

View attachment 26471

This seems to be a pretty good way to determine if the issue is the low pressure pump or high pressure pump. However there is no way I can determine the accuracy of the response. Can anyone back it up? If this is the case my low pressure fuel up is right on the threshold with ignition on (66PSI) so its very plausible the low pressure pump is ok.

It also doesn't tell me however if the rail pressure sensor itself is faulty though. Although it seems unlikely as its able to sense the 66PSI no problem. I also thought I read somewhere that the rail pressure sensor is inside of the high pressure pump. But it seems to be a different part. I must have read wrong?

Edit 2: It's become apparent to me that the HPFP is a mechanical device where the camshaft lobe compresses the spring to move piston to compress the fuel and force it though a small opening to create a high pressure high velocity spray. Based on this fact and that the sensor is reading a low pressure at the fuel rail Im fairly certain the HPFP is defective. I've ordered a new one. Its worth a shot

Do you normally allow the gas to get very low in the tank before refilling?, driving it until the low fuel light comes on?

 

Thread update: I fixed this issue by replacing the HPFP. Pressure with engine running ranges from 450-500PSI now. (before was 60PSI) Use this knowledge to fix it your self for future people with the same problem. Use ScanXL or Forscan (I believe the later is better but I dont have the cable in my intininary yet)

joseroig, no never have let thefuel become very low. Im not sure why it failed but the car has over 100KKM on odometer (62k miles)