[RealMcCoy]

And can anybody link me to where I can buy a proper data logging cable? I have looked everywhere and maybe its cause i dont know exactly what i am looking for or what not, but I cant seem to find one. any help would be much appreciated!

I am looking for a cable to go from the OBD1 Port to my laptop

Member Blackstealth on here can build you whatever you need.

I followed this procedure Stealth 316 - Fuel Pump Voltage Measurement so I hooked up the leads at the fuel pump beneath the hatch just as in this tutorial. Started motor, and read 12volts on the multimeter, but then the 12v goes to 0v and the engine shuts off.

When I ran an 8ga cable from the battery directly to the pump, for one I could hear the pump and when the engine started the car continued to run and did not stall.

This is the procedure I was wondering if this would fix my problem: Stealth 316 - Fuel Pump Re-Wire just to be specific. Would this procedure get my car running again, since i already tested it and it runs while directly hotwired so I just assumed that all I would need was the relay and switching circuit to turn it on and off. Or am I not undersanding something?

I am going to go out to the garage and preform the test on the MFi Relay you recommended, checking for power drop before the engine dies @ MFI relay on Black wire w/blue stripe...

That black wire with the blue stripe is the same wire I tested at the fuel pump and monitored it loosing power as the engine dies, would that be an equivalent measurement or should I check directly at the MFi itself on that black wire w/blue stripes?

Unplug your airflow sensor and start the car... I it doesn't die in limp mode, you know it's losing power when it switches to low speed. If that's the case, the relay bypass would in fact fix it, as would fixing the relay (probably full of water)

 

[RealMcCoy]

Yeah that would fix it, but the ECU wouldn't be able to turn pump off if engine quit unexpectedly. Like from busted fuel line or wreck, which if fire was involved pump would continue to feed it if you forget or not able to turn switch off.

Unless I'm missing something, I think he asked if the procedure he linked from Stealth316 would fix his car? That's just a basic pump hotwire that we all use often, and works as stock. (minus the low speed)

 

[RealMcCoy]

BUT….. If that wire is now dropping voltage as he says, it will still drop-out the added relay causing pump to stop. So nothing would be gained with that process, unless it’s simply open circuit on resistor side branch that’s causing the complete drop to 0 volts, instead of ~ 9 volts . Which if that's the case, the relay by-pass you mentioned in post #9 would be simplest cure.

You are correct on that, unless you follow his recommendation to bypass the resistor and relay: Stealth 316 - Fuel Pump Relay/Resistor Bypass

 

[RealMcCoy]

This strikes me as perfectly good logic, that's easy for me to agree with especially after reading the below quote from your post #16

I don't know why the ECU doesn't drop the ground with MAF unplugged (maybe @RealMcCoy does ), but it does seem apparent something is going wrong in ECU during some logic change. Pictures of ECU will only help if there's some obvious visual problems, unfortunately there can be problems with no visual evidence.

But it's obvious to me there's no need for added relays, jumpers, etc., until that ground being dropped by ECU is corrected.

The ECU switches fuel pump speed based on load.(Airflow) Default is high speed. Once you start the engine and it establishes low load, it switches to low speed. If it dies when attempting to make the switch, that tells you the ECU is trying to do it's job, but there is a break in the low speed circuit. As I already posted, the most common issue is the relay full of water, but simply forgetting to plug the resistor back in will do the same... Unplugging the airflow meter simply puts in into limp mode and deprives the ECU any means of establishing load, so it defaults to high speed and never tries to switch.

 

[RealMcCoy]

While this explains why/when ECU switches between low and high speed operation, it still doesn't explain why when ECU switches pump relay to low speed it also drops ground for MFI pump relay coil. That half of MFI needs to stay closed no matter which state the pump speed relay is in, that's what I'm trying to wrap my head around.

Are you indicating there's logic in ECU that can sense a load problem when it shifts to low speed circuit side and drops out MFI relay pump side because of some kind of imbalance, similar to how a ground fault circuit breaker works?

I missed the part where that was happening... I didn't read all responses, I was just addressing the way the system works, and some common issues I've seen in that system. If it is verified dropping the MPFI BEFORE the engine dies, (which needs to be very carefully verified, as normal operation turns off the fuel pump as the engine dies) that's a pretty clear cut and classic ECU failure.

 

[RealMcCoy]

Okay, so I should inspect my ECU? And attempt to narrow in on the problem circuit?

I am fairly proficient at replacing transistors, diodes, capacitors, etc.

Yes. Shutting off the fuel pump is a classic symptom of ECU failure.

 

[RealMcCoy]

I've seen this exact issue once before where the car stalled after a few seconds unless the MAF is unplugged.

On that car the issue was caused by the resistor for the low speed fuel pump operation was not plugged in by the air filter.

These cars always start with fuel pump in high speed mode and then after a few seconds they switch to the low speed mode unless the load is above a certain level or the MAF is unplugged.

That's the same road I sent him down. But it turns out it's turning off the fuel pump side of the MPFI. (which is likely an ECU issue)