cant start | new here looking for help

Hi guys I am new here and at my lowest with my mazda cx 7 with 2.3 mzr disi engine. From august i am trying to troubleshoot my car. Recently I found this forum which helped me understand more what is going on with my car and maybe I hope i will find some more info and knowledge here Also I am from Slovakia so sorry if my english is a bit off.

Year/Make/Model: Mazda CX-7 2.3 DISI TURBO
Mileage:161 000 miles (260 000 km)
Location: Slovakia
Concern: no start for over a month, HPFP cant build up pressure (i think)
DTC's: P0300
Modifications none
ECU/Tuning Software: none
Tuner: -
Is the concern intermittent? no
Can you duplicate the concern?
Recent Repairs: timing chain replacement in august 2024, new spark plugs
Correction:

So in august I changed the timing chain because of rattling sounds. Everything went with no problems. timing was good, crank position sensor good basically everything good. I got better fuel economy the car felt better. But after 100km (60 miles) car started stuttering, died and stopped on highway with code P0300. It wont start at all. After towing it home i thought i did something bad with timing chain but no. Checked the timing again and everything was good.

Then I changed sparkplugs but nothing at all. Spark was there i tested. Compression was also good. The car wont start at all. Also messured pressure from low pressure fuel pump and it was good. (i also have service manual for this car so i knew what the values should be).

After that i decided to clean the fuel injectors. Did that but no start at all.
After a week of no work i tried to start the car and it randomly started no problem. Checked for codes, nothing and everything looked good. It also run good.

Then after maybe 3 days i noticed the fuel consumption was higher and higher everyday (around 14l/100km which is 16.8mpg according to google). But then also after around 60 miles the car did the same thing on road. Stuttered and died no start. No code this time. After towing it home we called a mechanic with better diagnostic PC in hopes he will find something but NO. No codes at all.

I didnt know what to do next and the car was sitting outside for like a month. I was looking all over internet and found this forum. I discovered here that it is definetly a fuel problem so i started diagnosing again last week. Compression, sparkplugs, LPFP everything good again. Also tried staring with quick start spray but nothing. Not even slightest change.

Then I checked what pressure the HPFP is making when cranking the engine and it would not exceed 1500 kPa which is around 217 psi. Heard that this is too low to start the engine so i disassembled the HPFP and clenaed it. Nothing new at all. Then i also noticed that when engine stopped cranking the pressure will go down and stop at around 400kPa (60 psi). So after looking here today I read that it can be the fuel pressure relief valve. That it can be busted open and the fuel pressure in the rail cannot build up.
I removed the return hose that is attached to it goes back to HPFP. Blocked the return pipe on HPFP because it was spraying fuel.

Then I cranked the engine in hopes that I will see fuel coming out of the relief valve but nothing. I dont want to go ahead and change it because I dont even know if it is bad since no fuel was coming out but pressure was dropping. And it is impossible to find this relief valve here in Slovakia. Yes I can go buy it from mazda but it is over 200 euros for something I dont even know If it will solve my problem. Same thing with HPFP.

It is a long post but I am really at my lowest here. So thanks for every reply.

 

Here's a potential alternative to getting a valve from Mazda directly. Admittedly I don't know if this will be available in your part of the world, but it's half of the price from Mazda.
www.amazon.com/Genuine-Mazda-L3K9-13-2J0-Pressure-Valve/dp/B073C4T156


I actually used this on my speed3, so I can confirm this is a Mazda OEM part (even came with the OE tag and bag). I've also suggested this for others and they've had success as well with it.

As for testing, my personal favorite, disconnect the spill valve electrical connector. It should turn over. If it does, the likeliness of it being your relief valve is very high.

 

Thank you for reply. As for the spill valve I have already tried starting the engine with spill valve disconnected but no difference.
Looks like my only option now is to change every part related to this problem and see what helps.

 

You might also be able to get the relief valve from here:
https://www.amayama.com/en/part/mazda/l3k9132j0

But I don't know what the cause is of your problems so I wish you the best in that regard.

 

Thank you.

I have update on my problem. Today I noticed that the ground cable on HPFP was loose and bit rusty so I decided to clean all ground cables I could find.
I cleaned the one on HPFP, on the left next to the AC line, right side close to the suspension screws, one on the transmission and one under the air filter box.

After that the car would crank and also wants to start. It is hard to explain with words but when cranking a combustion happens for like a half a second every 2 seconds or so. And also the fuel pressure in fuel rail now builds up much higher around 8000kPa (1160 psi) but drops quite fast when I stop cranking the engine. No codes too.

After few times of trying, the battery was dead so I let it charge and I will try tomorrow.

If I find something else I will post here, maybe it will help someone in the future.

 

Do you have a set of jumper cables? If so just use the negative portion. Clamp one down to the block and the other to the negative battery post. See if that helps.

You said the ground was rusted at the HPFP. Bypassing the factory engine block ground could help identify if there are further grounding issues.

 

Yeah so I think this engine is cooked. Tried this morning with fully charged battery but nothing. Not even the small combustions like before.

I decided to go again and checked for sparks and fuel (good) but when doing the compression test it was 85 100 70 and 100 psi.