Fires then dies. HELP

[Ozruss90]

This situation happened months ago after I removed the cam angle sensor to replace the Oring due to an oil leak. After the sensor was replaced, the engine would fire and then dies within a few seconds. At the time it was suggested to be the fuel pump at fault. So without confirming I ordered a new fuel pump/sender assembly.
Still have the Fire up and die within seconds scenario. Fuel pump is operating and pumping fuel as it should.
Need help as to where to look next. Unfortunately I don?t have an OBD1 scanner. I have read that the engine should run even without input from the cam angle sensor, so ruling that part of it out.
Very much a coincidence though that this start/stop situation happened immediately after I replaced the c/a sensor.
HELP from the brains trust on here appreciated.

Cheers, Russell. 🇦🇺 AUSTRALIA

[scorp508]

Does this happen even if the car is cold, or only if the coolant is warm and around 175* (F) or higher?

[secondchance]

Originally Posted by scorp508

Does this happen even if the car is cold, or only if the coolant is warm and around 175* (F) or higher?

You are thinking primary fuel pump may be bad. Arn't you? I was wondering the same. Car may be starting on pressure generated by the secondary pump but secondary pump shutting off and with primary pump not working resulting in fuel pressure drop.

[scorp508]

Originally Posted by secondchance

You are thinking primary fuel pump may be bad. Arn't you?

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.

[Ozruss90]

Originally Posted by secondchance

You are thinking primary fuel pump may be bad. Arn't you? I was wondering the same. Car may be starting on pressure generated by the secondary pump but secondary pump shutting off and with primary pump not working resulting in fuel pressure drop.

It now has a single pump conversion unit in it.

[Ozruss90]

Originally Posted by scorp508

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.

The fuel pump in there now is a new single pump unit, and the green wire at the ECM has been de pinned as per the instructions that came with the pump unit.
Power to the pump is fine and tested the pump running and pumping fuel with the sender unit / pump out of the tank ( submerged in fuel ) It is pumping fuel as it should, therefore I?m assuming the problem is elsewhere..

[secondchance]

Originally Posted by Ozruss90

The fuel pump in there now is a new single pump unit, and the green wire at the ECM has been de pinned as per the instructions that came with the pump unit.
Power to the pump is fine and tested the pump running and pumping fuel with the sender unit / pump out of the tank ( submerged in fuel ) It is pumping fuel as it should, therefore I?m assuming the problem is elsewhere..

I suggest that you check the fuel pressure at the fuel rail before the ignition key is turned and after the motor dies after starting. Fuel pump may be fine but the command it's getting from the ECM might be screwy with reconfiguration of electrical connector.
Just my 2 cents.

[scorp508]

Originally Posted by Ozruss90

Power to the pump is fine and tested the pump running and pumping fuel with the sender unit / pump out of the tank ( submerged in fuel ) It is pumping fuel as it should, therefore I?m assuming the problem is elsewhere..

Ok, so, just to confirm my curiosity... this happens if the car is COLD as well?

[Ozruss90]

Originally Posted by scorp508

Ok, so, just to confirm my curiosity... this happens if the car is COLD as well?

Yes, it can?t be anything other than cold because it doesn?t run. The car has not been running for 6 months because of this problem. It cranks as normal then starts and runs for only 2 or 3 seconds and dies.

[Ozruss90]

Originally Posted by secondchance

I suggest that you check the fuel pressure at the fuel rail before the ignition key is turned and after the motor dies after starting. Fuel pump may be fine but the command it's getting from the ECM might be screwy with reconfiguration of electrical connector.
Just my 2 cents.

I will try and borrow a fuel pressure gauge to test pressure at the rail, to see what?s going on there.
? reconfiguration of electrical connector ? are you referring to the de pinned plug at the ECM ?