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Discussion Starter #1
I'm currently running my MR2 on an ECUMaster Black. I have a Supra TT fuel pump and Aeromotive FPR. I've been having some issue with cold start (car would run lean on startup causing it to stall after cold starting). I think I narrowed that issue down to the ECU not priming enough fuel.

In the EMS pin 35 on oem ecu (FPR FUEL PUMP RELAY) is used for priming the FPR. So for testing instead of having it enable the pump for 3s I set it to run continuously. This seemed to have had the inadvertent effect of causing the car to run lean under boost.

My guess is that somehow this is causing the fuel pump to run in low speed mode. Setting the priming setting back to 3s fixes my lean issue.

I'm trying to understand from an electrical perspective how this is happening.
 

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...car would run lean on startup causing it to stall after cold starting...

...My guess is that somehow this is causing the fuel pump to run in low speed mode...
How do you know that you are lean on startup? The O2 sensor does not work until it is up to temperature.

Low speed is plenty for startup. High speed not necessary until you get into high loads.
 

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Discussion Starter #3
How do you know that you are lean on startup? The O2 sensor does not work until it is up to temperature.

Low speed is plenty for startup. High speed not necessary until you get into high loads.
I turned the fast heating setting on and waited 30s before starting the car. That should get the O2 sensor warm enough to get a decent reading.

And I agree low speed is fine for low load. I'm just trying to understand how the standalone ecu is able to control high and low speeds.
 

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The blue with red wire position 6 on the 22 pin connector is the control wire for the fuel pump relay. By default the relay bypasses the resistor, energizing the relay the resistor is used and as you know you get low pump speed.

How your EMS controls that I don't know, I know a lot of people just bypass the fuel pump resistor anyway.
 

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Discussion Starter #5
The blue with red wire position 6 on the 22 pin connector is the control wire for the fuel pump relay. By default the relay bypasses the resistor, energizing the relay the resistor is used and as you know you get low pump speed.

How your EMS controls that I don't know, I know a lot of people just bypass the fuel pump resistor anyway.
I'll verify the wiring.
 

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Discussion Starter #6
So probably a dumb question but if pin 22 controls the high/low speed what actually powers the pump?
 

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I'm currently running my MR2 on an ECUMaster Black. I have a Supra TT fuel pump and Aeromotive FPR. I've been having some issue with cold start (car would run lean on startup causing it to stall after cold starting). I think I narrowed that issue down to the ECU not priming enough fuel.

In the EMS pin 35 on oem ecu (FPR FUEL PUMP RELAY) is used for priming the FPR. So for testing instead of having it enable the pump for 3s I set it to run continuously. This seemed to have had the inadvertent effect of causing the car to run lean under boost.

My guess is that somehow this is causing the fuel pump to run in low speed mode. Setting the priming setting back to 3s fixes my lean issue.

I'm trying to understand from an electrical perspective how this is happening.
The OEM fuel system has no engine off prime system. It only runs the pump when the key is turned to START and when the engine is running.

I have covered how this system works a few timies. No boost and bogging after 10 to 15 minutes of driving
 

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How long does it run until it dies? If the motor kicks and starts then it sounds like your start extra fuel is close enough.

I believe that there is another fuel add setting that is active for the first 5 to 30 seconds after it starts. I cannot recall what it is called.

Are you sure the base fuel map is tuned correctly when the motor is at operating temp?

Are you sure that warm up enrichment is correct? When the coolant is 60F I’m only adding 2 or 3pct extra fuel.

Are you sure the air temp correction is setup correctly? I add zero fuel when air temp is around 110F and add 3 or 4pct when air temp is 60F.

I have disabled the low/high pressure functionality on my car.
 

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Discussion Starter #10
The OEM fuel system has no engine off prime system. It only runs the pump when the key is turned to START and when the engine is running.

I have covered how this system works a few timies. No boost and bogging after 10 to 15 minutes of driving
Okay this makes sense. I'm guessing what is happening when I inverted the fuel pump prime setting its setting the pump to run at low setting instead of always running at high.

How long does it run until it dies? If the motor kicks and starts then it sounds like your start extra fuel is close enough.

I believe that there is another fuel add setting that is active for the first 5 to 30 seconds after it starts. I cannot recall what it is called.

Are you sure the base fuel map is tuned correctly when the motor is at operating temp?

Are you sure that warm up enrichment is correct? When the coolant is 60F I’m only adding 2 or 3pct extra fuel.

Are you sure the air temp correction is setup correctly? I add zero fuel when air temp is around 110F and add 3 or 4pct when air temp is 60F.

I have disabled the low/high pressure functionality on my car.
The car doesn't always die. Most of the time the RPM just drops low and it's able to recover. The car always starts so cranking fuel is good. It after the start I have issues and only the first start after the car has been off for a while.

Base fuel map is good car runs great otherwise.

I've been messing around with the warmup enrichment but I'm already adding 20% fuel at 10C.

I'll have to check the air temp correction.

This only ever happens the first start when the car has been sitting for a long time like overnight. I can start the car, it'll struggle, shut off the car right away, start it again and it idles perfectly during warm up.

72456
 

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If it was fuel pressure, it doesn’t make sense that it would die on the first start and then run correctly on subsequent starts because the fuel pressure issue would exist on every start.

My ems has crank extra (only active while cranking). If your car kicks and exits cranking then this is fine.

Reading the log you posted, it looks like when rpm is 1,200 it goes lean, when it surges to 1,800 it has adequate fuel. This leads me to believe at low engine speeds enough fuel isn’t present (sticks to walls of cold engine instead of making it to combustion camber). At higher engine speeds the velocity of the incoming air makes better use of the fuel that is present.
I think your start extra needs additional fuel. This fuel modifier adds fuel for the first 5 to 30 seconds when the motor first starts.
 

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If it was fuel pressure, it doesn’t make sense that it would die on the first start and then run correctly on subsequent starts because the fuel pressure issue would exist on every start...
Maybe the check valve at the pump is leaky, and the fuel system drains overnight. Then the pump will need to run long enough to prime the system to get full pressure.

This can be tested by prepriming the system. Jump the crash interlock and turn the key on. The pump will then run and you can make sure that you have full pressure before starting.
 

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Discussion Starter #13
If it was fuel pressure, it doesn’t make sense that it would die on the first start and then run correctly on subsequent starts because the fuel pressure issue would exist on every start.

My ems has crank extra (only active while cranking). If your car kicks and exits cranking then this is fine.

Reading the log you posted, it looks like when rpm is 1,200 it goes lean, when it surges to 1,800 it has adequate fuel. This leads me to believe at low engine speeds enough fuel isn’t present (sticks to walls of cold engine instead of making it to combustion camber). At higher engine speeds the velocity of the incoming air makes better use of the fuel that is present.
I think your start extra needs additional fuel. This fuel modifier adds fuel for the first 5 to 30 seconds when the motor first starts.
I can add more after start enrichment fuel but 20% extra seems to be pretty standard across basemaps that I've looked at.

Maybe the check valve at the pump is leaky, and the fuel system drains overnight. Then the pump will need to run long enough to prime the system to get full pressure.

This can be tested by prepriming the system. Jump the crash interlock and turn the key on. The pump will then run and you can make sure that you have full pressure before starting.
I have a pressure gauge on the FPR(unfortunately I don't have a sensor that's connect to the ECU to properly datalog). I can see that I have 0 pressure after the car has been sitting overnight. This is why I was asking about priming the system. But it seems like its normal operation for the Aeromotive FPR to not hold pressure when off. Mine seems to drop from normal to about 25psi after the car is shut off then slowly goes down to 0. Fuel pressure drops instantly when car shuts off
 

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It is normal for the fuel pressure to go to zero when the pump is off. That has nothing to do with whether the system stays primed. If the system stays primed, then the fuel pressure will come back up as soon as the pump is on. However, if the system drains, then the pressure cannot come up until the fuel system refills. That is why the check valve at the pump is important. The regulator does not affect the priming, because it is at a high point and cannot drain the lines. The lines can only drain through the pump.
 

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Discussion Starter #15
It is normal for the fuel pressure to go to zero when the pump is off. That has nothing to do with whether the system stays primed. If the system stays primed, then the fuel pressure will come back up as soon as the pump is on. However, if the system drains, then the pressure cannot come up until the fuel system refills. That is why the check valve at the pump is important. The regulator does not affect the priming, because it is at a high point and cannot drain the lines. The lines can only drain through the pump.
Ah I see what you mean. I can try forcing the pump to run and see how quickly pressure builds. I'm also going to order a pressure sensor so it'll be easier to datalog the issue.
 

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It is normal for the fuel pressure to go to zero when the pump is off. That has nothing to do with whether the system stays primed. If the system stays primed, then the fuel pressure will come back up as soon as the pump is on. However, if the system drains, then the pressure cannot come up until the fuel system refills. That is why the check valve at the pump is important. The regulator does not affect the priming, because it is at a high point and cannot drain the lines. The lines can only drain through the pump.
The regulator should cause the system to hold pressure, for several hours to a day, maybe longer. You need the check valve at the pump as well of course.

I had an Aeromotive regulator that didn't hold pressure on my 2GR swap, and it caused some hot start issues (long cranking time). Replaced it with a regulator that does hold pressure and the problem went away.
 

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Maybe the check valve at the pump is leaky, and the fuel system drains overnight. Then the pump will need to run long enough to prime the system to get full pressure.

This can be tested by prepriming the system. Jump the crash interlock and turn the key on. The pump will then run and you can make sure that you have full pressure before starting.
I understand your angle now. It’s an easy test, as you have outlined, to verify if the check valve is functioning.
 

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Discussion Starter #18
So I did some checking on the car. I checked the voltage going to the fuel pump through the diagnostic port.

The pump is getting ~7V when the key is in the ON position but car is off. The pump gets ~12V when the engine is running.

Obviously the standalone is wired up differently than the stock ECU. But seems like my issue probably isn't with fuel pressure though I'm still gonna get a pressure sensor so I can monitor in the standalone.
 
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