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#51982
I'm 100% sure the pump is shutting off, but agree that it's definitely not right for it to keep limping along (see my reply to neovin). The injectors are also a bit oversized compared to stock Miata, so if they are getting stuck open, I think there would be a wider-than-normal aperture. Maybe I've just accidentally replicated a semi-functional gravity-fed setup, like an old model T...
Chris Wolfson wrote:
Sun Jul 18, 2021 8:27 am
Your fuel pump does not shut off if you think it does. There is no way for an electric injector valve to run on the engines vacuum. For that you need a carburetor...
The usual fuel pressure range is 2-3.5 bar, with the regulator port open to atmosphere. Set it once, then do not change it any more, as the whole fuel tune depends on it. When the engine is running, this port has to be connected to manifold pressure, so the differential pressure is kept constant, independent of trottle position/ engine load.
I prefer the fuel pressure to be on the high side, as fuel atomization is a little better, but you have to have an eye on injector opening times at idle, so you do not get too rich.
By moonie223
#51983
I had a 1991 miata running MS2 and stock fuel injectors.

To upgrade the injectors I removed the fuel pump relay and started/ran the car till it died, except it never died. I also assumed the intake manifold was enough to siphon fuel from the rail and probably the tank too, even without the pump running.

Any throttle at all would kill it, and then it would start right back up and idle fine.

I spilled a little fuel when I pulled the rail, and if I didn't raise the fuel ends above the cowl a good bit it would start gravity siphoning from the tank. I guess it's also important to mention I modified the gas cap to not hold pressure after removing all the evap stuff.

Just my experience. My NB is different and doesn't run with no relay, but it's pretty different than a NA fuel setup.
#51984
Of course right after I posted I seem to have figured it out: it does indeed seem that I had the FI open time set too long (1ms? didn't sound that long...). When I cut it down to 0.3ms, the black exhaust stopped showing up and the engine now dies a few seconds after turning the pump off. So that's all good.

Of course, one of the injectors is now leaking, because every problem has to be replaced by another. But this one is a lot more straightforward!
moonie223 wrote:
Thu Jul 22, 2021 11:24 pm
I had a 1991 miata running MS2 and stock fuel injectors.

To upgrade the injectors I removed the fuel pump relay and started/ran the car till it died, except it never died. I also assumed the intake manifold was enough to siphon fuel from the rail and probably the tank too, even without the pump running.

Any throttle at all would kill it, and then it would start right back up and idle fine.

I spilled a little fuel when I pulled the rail, and if I didn't raise the fuel ends above the cowl a good bit it would start gravity siphoning from the tank.

Just my experience. My NB is different and doesn't run with no relay, but it's pretty different than a NA fuel setup.
User avatar
By PSIG
#51988
TomLippincott wrote:
Thu Jul 22, 2021 11:29 pm
Of course right after I posted I seem to have figured it out: it does indeed seem that I had the FI open time set too long (1ms? didn't sound that long...). When I cut it down to 0.3ms, the black exhaust stopped showing up
Don't confuse a tuning or mechanical issue with dead time. Dead time is specific for your injectors, voltage and fuel pressure. It is not a tuning or workaround tool, and can play havoc with your tune if still incorrect. While many ignore the settings, it is a major influence to your tune.
TomLippincott wrote:
Thu Jul 22, 2021 11:29 pm
… and the engine now dies a few seconds after turning the pump off.
This is my confusion — why is the fuel pump being switched off while the ECM and ignition are still trying to run the engine? What are you trying to do here, and why?
TomLippincott wrote:
Thu Jul 22, 2021 11:29 pm
Of course, one of the injectors is now leaking, because every problem has to be replaced by another. But this one is a lot more straightforward!
This explains a lot and is likely the root of your symptoms. Back to my question above. :?
By LPG2CV
#51994
Normal installation uses the FP pin on the ecu to connect to the ground of the FP relay. So the relay grounds back through speedy. This provides a safety FP cut off when the engine stops.

With regard to running on badly, when the ignition is turned off. Do you have an alternator charging light in your new wiring? Is the alternator bleeding voltage back into the ecu when the ignition is turned of via the charging warning light?
#52001
It didn't start leaking until I lowered the injection open-time, so I don't think it's the direct cause. Though it must be correlated in some way. It looks like the o-ring on the injector failed, so I'm replacing that now.

Regarding the fuel cut-off, because I was running all the fuel lines from scratch, I just wanted a bullet-proof way to mechanically shut off the pump, so I put a physical switch on the dashboard that opens the relay. A couple minutes for belt and suspenders.
PSIG wrote:
Fri Jul 23, 2021 4:35 pm
TomLippincott wrote:
Thu Jul 22, 2021 11:29 pm
Of course right after I posted I seem to have figured it out: it does indeed seem that I had the FI open time set too long (1ms? didn't sound that long...). When I cut it down to 0.3ms, the black exhaust stopped showing up
Don't confuse a tuning or mechanical issue with dead time. Dead time is specific for your injectors, voltage and fuel pressure. It is not a tuning or workaround tool, and can play havoc with your tune if still incorrect. While many ignore the settings, it is a major influence to your tune.
TomLippincott wrote:
Thu Jul 22, 2021 11:29 pm
… and the engine now dies a few seconds after turning the pump off.
This is my confusion — why is the fuel pump being switched off while the ECM and ignition are still trying to run the engine? What are you trying to do here, and why?
TomLippincott wrote:
Thu Jul 22, 2021 11:29 pm
Of course, one of the injectors is now leaking, because every problem has to be replaced by another. But this one is a lot more straightforward!
This explains a lot and is likely the root of your symptoms. Back to my question above. :?

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