Quote:
Originally Posted by secondchance
You are thinking primary fuel pump may be bad. Arn't you?
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More to rule something in/out before pointing fingers at any one root cause yet.
Below 176'ish (F) coolant temp both pumps run. Once above that only the primary runs unless the ECM commands the secondary to provide fuel as well.
So, if this is happening when the car is cold or at least well under that coolant temp, then either BOTH pumps aren't providing fuel as it'll idle on one easily, or there's something else going on.
I thought my primary pump had failed as it would die once over 176* when the secondary pump stopped. Long story short... the pump was fine and a harness connection inside the car had come loose where the primary pump gets its 12V from. I already had swapped both pumps out by the time I found it, so now I have a pair of perfectly good spare used pumps on a shelf.
The secondary pump can be forced to remain on >176* by depinning light green wire at C21 of the ECM as this wire is the signal from the ECM is used to turn the pump off. Removing that wire makes it so the ECM can never turn it off. Marc has this buried in an article about converting to a single pump.
https://www.zr1specialist.com/HAT%20...l%20system.pdf
There is a fuel pump test lead near the ECM, which looks like someone forgot to plug something into a harness. I think 90s had this lead lower in the engine bay. If you put 12V to that lead with the ignition key in the off position and measure the amperage going through the wire you're using to provide the voltage, then you can tell if one or two pumps are running. I think it's about 5A if one pump is running and 10A if both are running. It can help rule some things in/out.