[SOLVED] Possible Fuel Pressure Problem

J

Joseph Conley

Greenie N00B Member
A little history since I am new around here. I just bought my first Mazdaspeed 3. I am totally new to Mazda. I was looking for a fun little car, that wasn't to low to the ground and easier to get in and out of. I found the car I bought down in Atlanta and seems to be rust free, and in decent shape, but didn't run. It was a 1 owner car with 191,000 miles that had been traded into a dealer and I was told it had been running when the dealer drove it home 1 night and was parked in his garage and never started again.

I bought it and trailered it back to Indiana. I charged the battery and started doing some basic troubleshooting. Through some sensor testing, I determined the crankshaft position sensor was bad. I replaced it and the car started right up, but was running rough. I scanned for codes and it had a fuel pressure to high code. Fuel pressure was reported at 2281PSI, and never changed even when the engine was shut off. I unplugged the fuel pressure sensor and tested signal on the wires and they were good, and then checked the sensor and it seemed good as well. I don't have a digital o-scope to really test to much,but it had resistance and was putting out a signal. I noticed the wire had been back probed and slightly damaged. I plugged it back in and suddenly the engine smoothed out and ran well.

I took it for a test drive and noticed every time I accelerated very hard the engine would cut out and go almost into what I am going to call a limp mode. It would stay running but with no power. If I pressed on the brake very suddenly it would start running well again. I accerated all the way close to redline very slowly winding the engine up, and it ran great, but any sudden hard acceleration would cause it to cut out most each time, but not every single time. I downloaded a free app I found mentioned on this site and ran it on my laptop and monitored the fuel pressure on the next test drive. Fuel pressure was around 400psi at idle, and then go up over 1000 while running it. I noticed each time it cut out, the fuel pressure would be at 1760psi.

The dealer asked me to give him a call and tell him what the problem was if I got it running. I called the dealer and gave him an update and he told me he had replaced the fuel pressure sensor trying to get it fixed to no avail. I decided he might had damaged the wires and thought maybe the wires were being pulled on when under heavy acceleration. So I ordered a new wire plug and replaced the bad section, but it didn't fix the problem. I ordered a new Bosch fuel pressure sensor as I am not certain of the brand he installed. I am waiting for it to come in, but thought I would ask for your thoughts of other things to check while waiting on the new sensor to come in.
 
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When you accelerate it hard, how high of psi do you get to?

Does the car have any "performance parts" on it?
 
I don't know history of the car, but it appears to be all stock engine wise. The car has been lowered, with larger wheels, but that is all I see. Today I got a new fuel pressure sensor in the mail a day ahead of schedule and I installed it, and now the car will not stay running. I am back to the 2281 PSI all the time like the sensor is not reading at all. I am sort of back to thinking this is still a wiring issue, just in a spot other than right next to the sensor. I am not getting 5 volts on the wire now after unplugging it and plugging it into the new sensor. It got dark before I could check fuses and such. Does anyone have a good wiring diagram for this car? I have the one from the service manual, but it isn't very good in my opinion.
The max PSI it reported when falling on it's face was 1759psi.
 
These cars run very high fuel pressure. They have a "High Pressure Fuel Pump" that runs off of a camshaft lobe. It runs up the fuel pressure with RPM's to achieve high fuel pressure like a diesel engine. Since they both run direct injection, instead of port injection.

Idle fuel pressure is pretty normal at 400, and at wide open throttle it should be between 1600 to 1850 depending on whether the previous owner upgraded it for more flow. The max it should be at even with upgraded internals is 1850-1900. If your fuel pressure is higher than that at any point, then your Fuel Pressure Relief Valve is probably sticking.

The relief valve is on the opposite end of the fuel rail than the pressure sensor. The relief valve prevents damage to the fueling system by venting pressure back to the low pressure side of the fuel system, if it ever reaches over 1850.

Stop messing with the fuel pressure sensor, and check fuel pressure at its max. Otherwise you are just wasting money.

If you warm up the car to full operating temperature, go for a short drive, turn the engine off but keep watching fuel pressure.... it should steadily rise up to 1850 and then vent to a slightly lower pressure.
 
Enki said:
Start with the post right above yours.
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I don’t think it’s that though because I’m showing 2280 psi without the engine running. And HPFP sens volt is constant. I just put a new engine in mine and suddenly it has this issue. I traded everything fuel related on the new engine for stuff on the old engine that I know works and still have the issue
 
Joseph Conley said:
I don't know history of the car, but it appears to be all stock engine wise. The car has been lowered, with larger wheels, but that is all I see. Today I got a new fuel pressure sensor in the mail a day ahead of schedule and I installed it, and now the car will not stay running. I am back to the 2281 PSI all the time like the sensor is not reading at all. I am sort of back to thinking this is still a wiring issue, just in a spot other than right next to the sensor. I am not getting 5 volts on the wire now after unplugging it and plugging it into the new sensor. It got dark before I could check fuses and such. Does anyone have a good wiring diagram for this car? I have the one from the service manual, but it isn't very good in my opinion.
The max PSI it reported when falling on it's face was 1759psi.
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@Joseph Conley, you get it working?
 
Raider said:
@Joseph Conley, you get it working?
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OK so an update on the car. Sorry for the long delay, but this is a project for me. I have found the PCM to be faulty. I have sent it off for repair and it could not be repaired. I was getting a bad signal from the PCM on the circuit going to the fuel pressure sensor. The repair shop confirmed the problem, but said they were not able to repair it. I have ordered a new PCM and will update when it has come in and I get the PATS system reprogrammed.
 
Joseph Conley said:
OK so an update on the car. Sorry for the long delay, but this is a project for me. I have found the PCM to be faulty. I have sent it off for repair and it could not be repaired. I was getting a bad signal from the PCM on the circuit going to the fuel pressure sensor. The repair shop confirmed the problem, but said they were not able to repair it. I have ordered a new PCM and will update when it has come in and I get the PATS system reprogrammed.
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I am having the same issue and I was just about to tell the mechanic to replace my fuel rail sensor... Did replacing the PCM fix it?
 
Finally getting back to this project. I did replace the PCM and I had the dealer program it and the keys and I still have the same problems exactly. I still believe this has to be a faulty wire. I believe in the PCM plug. I have tested the wiring with the PCM disconnected and it checks out, but I don't have a good way to test the connector at the pcm. I pulled the high pressure fuel pump sensor wire from the pcm connector and found there was 5 volts on the PCM plug. This is why I replaced the PCM. The mazda service manual said this was a faulty PCM, and a PCM repair show said they saw the problem but could not repair it. I have not tested this since replacing the PCM. This is my next step.
 
I find the service manual diagnostics to describe general failures, I don't remember the last time those procedures solved a problem for me.

Going by the information you shared about the damaged wires, there may have been other damaged you aren't seeing, and that is concerning. I have seen expanded terminals on various connectors cause intermittent issues. This means that the female pin has been deformed/oversized to the point where it doesn't always make contact with the male pin. IF you have found proof of mis-handling, It could be possible that someone stuck a thick multi-meter probe in the pin and damaged it.

Check the condition of your throttle body connection as well, those tend to be a common issue with these cars, causing similar symptoms to what you described.

When it comes to electrical problems, modern day ECUs are incredibly robust, I don't see many failures with these ECUs. But to share some insight on the 5V you may have been seeing. Most sensors have a shared power and ground source that is supplied by the ECU. So if one sensor shorts something out, other sensors can be affected as they are part of the supply or ground circuit. Most automotive sensors operate on 5V.
 
Get a power probe or make a jumper wire circuit to apply power through the circuit with the PCM and HPFP disconnected. You'll need an extra headlamp bulb or high resistance test lamp on one end and then apply power through the other. This will verify that the circuit can carry a load.

You can test a circuit's resistance but if it has one good strand between each connector it can still show low resistance. However if that's the case and the circuit has a load applied then those lamps would either not illuminate or illuminate dim.

I also second the above post about disconnecting all other components that share the 5V reference circuit to see if the PCM reads differently.

If your PCM connector has damaged pins I have two spare connectors I keep in case I have to repin one. I dont mind taking one or two wires out to send to you if it helps remedy your problem just let me know if you need them and the size.
 
So I went out today and am fairly certain the problem is at the PCM wire connector harness. I had tested the old PCM and it was outputting 5 volts on a fuel pressure sensor wire where it should not have been and that was with no wire connected to the PCM pin. Manual said to replace the PCM. I sent it off for repair and they agreed it was faulty, but could not fix it. I ordered a new one and today I tested that same pin on the PCM without anything connected to it and it seems to be corrected now. In put some voltage in the 1.7 to 1.8 volt range and this made the engine smooth out and run well, where it was very rich running previously. So I do truly believe the PCM was bad previously. I had removed the fuel pressure sensor pin at the PCM and had tested and was getting good signal from the Fuel Pressure sensor with a varied voltage as the RPM went up and down in the 1.8 to 2.8 volt range. I inserted the pin at the PCM and suddenly the engine smoothed right out. I tried to recrimp that pin a little bit, but didn't feel I made much progress. I checked the fuel pressure reading from the PCM and it was in correct idle range now. I took it for a test drive and it was like a whole different car. It ran smoothly for about a block and then all the problems returned and the fuel pressure reading shot back up to the 2281 mark so I knew that pin was disconnected again. Matter a fact the engine even died on me. I wiggled the PCM connector 2 and got it going again and nursed it back home. I moved the PCM connector around several times and found the Fuel pressure reading would read correctly one moment and then not the next.

So in summary, I believe the prior "dealer" owner where it first broke down had probed wires trying to fix it and I believe in doing that they might have shorted something in the PCM and burned it up. I know the wire connector at the fuel pressure sensor was completely mutilated and the crankshaft position sensor was also shot when I bought the car (un-running) and I have replaced both with a new ones. This got the car running again, though poorly. Those sensors seems to be working well and making good contact now from what I can tell. I think at this point the only problem is with the PCM connector. I think it has some bad pins and also both of the white clips have been previously broken off or removed. They were both missing when I got the car. So I think I am going to look for new PCM connectors, so I can hopefully reinstall the clips if they are removeable, and replace some of the pins as well. I believe that should get things back to a stable point. I think I have only put 10 miles on the car in the little over a year I have owned it. Mainly driving to the dealership to have the new PCM programmed. But I think it will be close to being back on the road once I get that PCM connector sorted out, now that I am nearly certain that is where all the remaining problems are.
 
So this is a very slow project, but I went out today and replaced the PCM pins for the high pressure fuel pump and the car ran great after this. I also installed new Plastic PCM connector hold down cams. Previously mine were missing. I drove the car today and it ran great for about an hour and then the problem came back, and it was the same problem. However through side of the road troubleshooting, I found another bad spot in the wire harness. This is nearly a break in the high pressure fuel sensor wire way down as it going under the intake manifold. I can barely even touch the spot, but I can squeeze it and the problem will come and go with each press/squeeze. I have the car in the garage now. Cleaning the garage has been such a big project that I have not worked on the car. So tomorrow it is suppose to be raining. So I think I will go out there and turn on some heat and pull the factory inner cooler off and see how much access I can get to the wire harness down there. I will likely just run an whole new three wires from the pressure sensor to the PCM. I will post another update when I have this done.
 
Joseph,
Were you able to correct your problem?

I have had similar problems from a full rebuild and have not been able to identify the issue.

Thanks,

Mike
 
Morning. Have tried tuning rebuilt MS6 for months. Have constant issues with stumbling idle and stumbling/stalling performance when running - similar to Joseph Conley's situation. I have reflashed the ECU, it runs fine for 12 -15 minutes then starts stumbling again. I stop, reflash, same thing - runs for 12 -15 minutes then same problem. Thoughts?
 
Did Joseph get the problem sorted ? If so how ? As I am suffering the same fate. 2011 ms3

Meik said:
Morning. Have tried tuning rebuilt MS6 for months. Have constant issues with stumbling idle and stumbling/stalling performance when running - similar to Joseph Conley's situation. I have reflashed the ECU, it runs fine for 12 -15 minutes then starts stumbling again. I stop, reflash, same thing - runs for 12 -15 minutes then same problem. Thoughts?
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Hey bro did you end up getting your issue sorted. How? As I am suffering from the same issue
 
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