I'm trying to test my fuel pressure and need some clarification.

On page F-97 the FSM says to put in line a fuel pressure gauge, jump GND to F/P, turn ignition to "on", and check that pressure is 36-38psi.

On page F-100 the FSM has the exact same test to check for hold pressure and it says it should be 71-106psi.

I'm confuseed because they are the exact same proceedure and set-up. So what is the correct psi I should see be seeing?

Thanks
Steve

 

If you look at page 101, you will see that "Fuel pump maximum pressure" as measured with the outlet tube from the gauge plugged should be 71-107 psi. That is the pump's capability. The test result on page 97 is correct for that setup, i.e. 36-38 psi. The test result on page 100 is incorrect and should be 36 - 38 psi for the illustration shown on that page.

On my '94, I usually read around 39 - 41 psi. Remember that the injectors are not active for this test; if they were (engine running) I would expect the pressure to drop slightly.

 

I figured as much. It would be nice if we had a sticky that was dedicated to FSM errors. So, when doing the maximum pressure test, how long should your pump hold 71-106psi when turned off after the test?

 

I don't think that's an error, that's just two different ways of testing the pump. Also, Mazda did revise the service manual over time, so there's fixes to some minor errors - putting out an errata sheet wouldn't work as it depends on what version of the manual you're looking at.

Dale

 

Dale,
It's an error. Pages F-97 and F-100 use the exact same diagrams and exact same set-up procedure for two different tests. I'm using the 93' FSM.

Steve

 

Dale,
Same error in my '94 FSM. The pressure spec on page F-100 is incorrect and contradicts the same test on page F-97, as the OP wrote above. The other test on page F-101 is written correctly and consistent with its illustration.

sbnrx7,
In the case where the output tube of the gauge is plugged (page F-101), I would expect pressure would hold up for a very long time. No injector leakage is possible for that case, only reverse leakage through the fuel pump. On my '94, I never ran that test, but for the F-97/F-100 test condition, IIRC pressure dropped very slowly, i.e. somewhere around 30 minutes for the first 10 psi.

 

Ok, so I performed the "Max fuel pump Pressure Test" and the max mine reached is 60psi and remained at 50psi when shut off for 10 minutes. The FSM says it should be between 71-107 which yields a mean of 89psi. So my pump is really off by 29psi. A new pump is on order. Also, from page F-96,when I performed the pressure test with the gauge in-line, it registered 38 psi but dropped to zero within 60 seconds of shutting off the fuel pump so I'm guessing my FPR is bad too.