92 Mercury Sable headache
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Joined: Oct 2002
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From: The Big, Oregon
92 Mercury Sable headache
I have been working on this car and it's a pain. It kept dropping the power to the fuel pump, sometimes stalling. Usually it would start cold ok, but would not restart hot. While cranking it would have spark but no power to the fuel pump.
When running, the ground for the fuel pump relay flickers until the relay can't hold closed anymore, then it dies.
So far, the CCRM has been replaced twice (previous mechanic did not understand diagnostics), the computer has been replaced, with no change as well.
I removed the fuel pump relay from the circuit and wired in a standard relay, now it runs a little longer since the relay has a bit more magnetic reserve, but isn't fixed.
Since the problem didn't change with the new computer, I have to rule that out. This pretty much leaves the inputs to the computer.
What does the computer look at to know when to run the fuel pump? Is it rpm based, or oil pressure, or something else?
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When running, the ground for the fuel pump relay flickers until the relay can't hold closed anymore, then it dies.
So far, the CCRM has been replaced twice (previous mechanic did not understand diagnostics), the computer has been replaced, with no change as well.
I removed the fuel pump relay from the circuit and wired in a standard relay, now it runs a little longer since the relay has a bit more magnetic reserve, but isn't fixed.
Since the problem didn't change with the new computer, I have to rule that out. This pretty much leaves the inputs to the computer.
What does the computer look at to know when to run the fuel pump? Is it rpm based, or oil pressure, or something else?
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Joined: Nov 2013
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Could be the EEC relay. If the EEC relay doesn't work or intermittently opens, the computer will turn off, causes the fuel pump relay's ground to flicker.
I had the EEC relay on my Explorer crap out. I replaced the fuel pump relay, replaced the computer, hacked up the wiring to the fuel pump relay before finally realizing it was the EEc relay. My only symptom though was intermittent no start. If it started up, it would run fine and wouldn't stall.
I had the EEC relay on my Explorer crap out. I replaced the fuel pump relay, replaced the computer, hacked up the wiring to the fuel pump relay before finally realizing it was the EEc relay. My only symptom though was intermittent no start. If it started up, it would run fine and wouldn't stall.
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Joined: Apr 2003
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From: Frequently frozen MN
I THINK that the computer uses the PIP to determine if the engine is running. It also gets the SPOUT, but I'm pretty sure that the engine will run without SPOUT because that's how you set the base timing.
The reason I think that is because, you CAN push start a manual tranny -- at least that's what I've read. If the computer senses rotation, it will turn on the fuel pump. Also, I don't recall oil pressure as an input.
I think that the EEC relay screws up more than just the fuel pump, but I'm not sure. I had an 89 F150 that had a bad ground to the EEC relay so it wouldn't close. That also killed power to the computer. But, replacing that relay is probably a good cheap test.
Maybe it is wiring between the computer and the fuel pump relay.
Just my .02
hj
The reason I think that is because, you CAN push start a manual tranny -- at least that's what I've read. If the computer senses rotation, it will turn on the fuel pump. Also, I don't recall oil pressure as an input.
I think that the EEC relay screws up more than just the fuel pump, but I'm not sure. I had an 89 F150 that had a bad ground to the EEC relay so it wouldn't close. That also killed power to the computer. But, replacing that relay is probably a good cheap test.
Maybe it is wiring between the computer and the fuel pump relay.
Just my .02
hj
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Joined: Oct 2002
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From: The Big, Oregon
Thanks for the pointers, I am going to try a new TFI module and see if that helps.
The car had a bad fuel pump, which burned out the CCRM (fuel, ecm, fan and a/c relays in one unit).
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The car had a bad fuel pump, which burned out the CCRM (fuel, ecm, fan and a/c relays in one unit).
Sent from my Brigadier using IB AutoGroup
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