Fuel pressure at RPM

[Joedirt]

Hi

I’m having a dilemma in figuring out wtf is going on with my 2012 cx7

Started misfiring and died one day

Plugs,intake gaskets,pcv valve etc etc are new

At startup it dies right away,only way to start it is to Disconnect MaF to get it idling but fluctuating 1000-750rpm untill hot then idles at 750rpm after that with maf connected

It passes the RV test ,At idle fuel pressure is around 1000psi at operating temps and initial start when cold

New O2 sensors but upstream is maxed at 25% at operating temps and open loop

Vac is 20 at idle,17 with ac on

Egr is clean

Car is undriveable, misfires and will not accelerate or even rev up

[Vansquish]

Originally Posted by Joedirt Hi I’m having a dilemma in figuring out wtf is going on with my 2012 cx7 Started misfiring and died one day Plugs,intake gaskets,pcv valve etc etc are new At startup it dies right away,only way to start it is to Disconnect MaF to get it idling but fluctuating 1000-750rpm untill hot then idles at 750rpm after that with maf connected It passes the RV test ,At idle fuel pressure is around 1000psi at operating temps and initial start when cold New O2 sensors but upstream is maxed at 25% at operating temps and open loop Vac is 20 at idle,17 with ac on Egr is clean Car is undriveable, misfires and will not accelerate or even rev up

I assume when you say that "upstream is maxed at 25%" that you're actually referring to fueling corrections.

What intake are you running? Does the new intake have a significantly larger-than-stock diameter MAF housing? Does it have an air-straightener?

Are all of the boost tubes, intercooler, and intake properly connected (no pinched, cut, or otherwise damaged or unsecured silicone tubes, etc.)

The reason I ask is that your symptoms sound like a classic massive vacuum leak.

[Joedirt]

All stock

It dose sound like it but not by the vacuum numbers on the scanner and i’ve Checked for leaks

What are the fuel psi numbers supposed to be at idle and then at 2000 rpm

Plugs are not lean but rich

[Vansquish]

Originally Posted by Joedirt All stock It dose sound like it but not by the vacuum numbers on the scanner and i’ve Checked for leaks What are the fuel psi numbers supposed to be at idle and then at 2000 rpm Plugs are not lean but rich

At idle, your fuel pressure should be in the 400-500 range, if memory serves. I couldn't tell you what it should be at 2000rpm, as it really depends on the driving conditions, calculated load, etc.. Under high load, your fuel pressure should be around 1600-1650psi.

[Jeff23spl]

have you checked engine compression, it will tell a lot about engine bloc and timing health just in case.
if i get it right, it die quickly if you start it with the maf connected but it can keep running for a while if you disconnect it. just in case your in tank fuel pump isn t receiving proper voltage thru the relay and resistor but i think it would die in both case....

it sound like a leak as stated above and your vacuum get irrelevant if it is between tb and maf....you would need to do a boost leak test to check it.

[Joedirt]

Done a pressure(boost) leak test on intake system

Fuel pressure is then very high if I’m 600psi above normal idle range

I’ve seen idle vids online at 1600-1660psi

In tank is fine 55-75psi prime pressure

[Vansquish]

Originally Posted by Joedirt Done a pressure(boost) leak test on intake system Fuel pressure is then very high if I’m 600psi above normal idle range I’ve seen idle vids online at 1600-1660psi In tank is fine 55-75psi prime pressure

Not necessarily. Even the idle fuel pressure depends on what you're doing to maintain the idle. If you're having to add throttle to keep the motor on, you may be inadvertently causing the car to increase fuel rail pressure.

The symptoms you've described really do sound like a massive vacuum leak. However, given that the car won't start at all with the MAF hooked up, and will only maintain idle after the car is already warmed up with the MAF sensor connected, you may have a bad MAF sensor.

I would suggest that you see if you can find someone near you who would be willing to swap MAF sensors to test that theory. If you need to buy a new MAF sensor ONLY an OEM MAF sensor will work. The aftermarket ones are not calibrated correctly, and this has been proven time after time on this forum and elsewhere.

[Joedirt]

MAF has been replaced and is reading good

This is not touching the throttle

[Vansquish]

What were you doing when the car starting to misfire and died?

If it is misfiring, you should be throwing some codes. What are they?

[Joedirt]

Car gas just being driven normally

No codes when it happens

The codes on it now are from disconnecting throttle body and replacing it,permanent codes that need to cycle off

Injectors have been replaced

It gets better when warm but no leak by injectors

[Vansquish]

If there are no codes, then it probably isn't misfiring. I know my car throws misfire codes within about 4 engine revolutions if something is amiss with one of the cylinders.

As to your comment about the injectors, why don't you give us a full run-down of what was done to the vehicle *prior* to the problem happening, and what you have done since then.

So far, you've given piecemeal information and have been adding variable after variable as a result. It's hard enough to try and remotely diagnose something without being given all of the background information.

Additionally, can you take a datalog of the car running and/or trying to run?

[Joedirt]

As the title states I’m looking for solid information on fuel pressure readings

All parts where replaced after problem started

No log possible at this time

[Vansquish]

Originally Posted by Joedirt As the title states I’m looking for solid information on fuel pressure readings All parts where replaced after problem started No log possible at this time

Well, you've been given that information (and you could've found it with about 5 minutes worth of searching of this very forum). Moreover, a comment that, "All parts where(sic) replaced after problem started" gives us nothing to go on at all. What parts were replaced? What is the full list of the parts that have been replaced? In any case, since you don't seem to want actual help with the diagnosis, I'll go ahead and bow out here and leave your questions to others with more time to burn on this than I have.

Good luck to you, sir.

[MSMS3]

Originally Posted by Joedirt MAF has been replaced and is reading good This is not touching the throttle

Did you use an OEM Mazdaspeed 3/6 MAF sensor? While many aftermarket parts work well, the MAF sensor is not one of them.

If you installed a new OEM MAF, then, obviously this points to something else. But, if you bought aftermarket, or bought the one for the standard Mazda 3, this could well be all or a part of your problem.