I just did a fuel volume test on my 98 Mazda 626 2L GF. According Tim Giles book Automotive Service:
Each injector is energized for 15 seconds... Variations of more than 5 ml calls for replacement of the injector.
In the 626 workshop manual, it simply says to energize the injector without specifying a time, and that the volume should be between 56-61 ml.
So I did the test by manually energizing the fuel pump, and grounding the injector ground pin while using some hose to route the fuel into a bottle:
I held each injector open about 15 seconds and I got the following results ( ml ):
Injector #1 #2 #3 #4 Try 1 58 61 66 61 Try 2 71 61 61 65
I'm pretty sure I was fairly consistent in my timing ( counting verbally 1-1 thousand, 2-1 thousand, etc... till 15-1 thousand ). Afterwards, I timed how long it takes me to say that and it was about 17 seconds. That's about 13% overtime potentially, which translates to about 7-8ml. But what seems more important is that only the #2 injector gave me a consistent reading.
The resistance on all the injectors is good at 15.5 ohms iirc and fuel pressure was fine at 35psi idle and 44psi with the fuel pressure regulator disconnected when I checked a few months ago. Also, fuel pressure dropped to 21psi after about 5 minutes. I do seem to have rough starts, but only intermittently, which is a bit confusing. Unfortunately, my fuel pressure gauge is broken at the moment, or I'd redo those tests.
Since I don't have a working fp gauge I did some other tests:
- The fuel pump drew 4.3 amps at idle
- The fuel pump drew 4.3 amps when activated manually ( engine off )
- I could clearly hear the sound of fuel flowing through the rail
- When I clamped the return line for a few seconds, the sound stopped and amps went up to 5.85
Now according to Tim Giles book Automotive Service, typical fuel pumps draw 1 amp for every ten PSI of pressure. Based on that I might expect to see about 3.5 amps being drawn during idle and about six to nine amps when manually activating the pump, since the WSM indicates expected readings of between 64 to 92 psi in that situation. The WSM also says that after the manual activation test the line should hold at least 50psi five minutes after turning off the pump. That makes it seem weird to me that pressure dropped from 36psi to 21 in my test a few months ago.
The reason I'm doing all these test is because I'm experiencing intermittent rough starts, and intermittent rough idle plus rough idle under load of varying intensity and I've eliminated just about every other cause I can think of. What I mean by "rough idle under load" is when I add a load at idle like the AC, electrical loads: turning on the fan + defroster + radio + headlights, or hold the break down with the car in gear, the idle gets rough. The roughness is inconsistent and is sometimes worse and sometimes better for the same action.
Based on my various results, I'm suspecting my injectors my be a bit sticky and need cleaning, and that there might be an intermittent problem with the check valve on either the pump or return line which is letting pressure bleed off too much sometimes.
Does there seem to be a fuel system problem here, or am I just chasing ghosts?
EDIT Jan. 1st, 2017 ----------------------------------------------------
So I redid the tests with a stopwatch ( 15 seconds ) and got these numbers:
Injector #1 #2 #3 #4 Try 1 60 61 62 61 Try 2 61 61 62 60 Try 3 60 61 61 61
Using the stopwatch made a big difference. Not any huge inconsistencies between the injectors, although #3 might be a bit borderline.
The car sat for 36 hours before I redid these tests, so I decided to check for any leaks before I did anything else. The #2 and #3 injectors were completely dry, but the #4 injector was noticeably wet, while the #1 was also a little wet:
Number Four Injector:
Number One Injector:
So I'm guessing I've got a bit of a leak from these two injectors, and as it happens these correspond to the spark plugs which had carbon fouling. I'm guessing this might be part of the reason I'm having rough starts after the car sits for a while. When I started the car after doing these tests it started up smoothly, which I'm assuming is due to the fact that fuel lines where properly pressurized as a result of these tests?
I also took some video of the spray patterns for each injector and here are some screen shots:
Injector Number One
Injector Number Two
Injector Number Three
Injector Number Four
The most I can say about the spray patterns is that they don't look identical to each other, which I would expect them to be. Now some that may be due to viewing angle, but it seems to me there is more variation in them than that can account for.
So, I posit my question again, do people see a problem here, or am I just chasing ghosts? I was thinking of running a few liters of homebrew seafoam through the tank at a 50% sf to gas ratio ( Seafoam's recommendation for cleaning injectors ) to see if that might help.