Chasing down a no-start - fuel pump resistor CONNECTOR intermittent
12-29-12, 05:33 PM
#1
Chasing down a no-start - fuel pump resistor CONNECTOR intermittent
After a hard-run, as my engine RPM and speed came down, the car started to lose power, and then shut-down and wouldn't restart.
At first I thought I had blown an apex seal, but a compression test showed otherwise.
I knew I was getting spark, but I didn't hear the fuel-pump run, even when jumpered at the Diagnostic Connector.
Verified continuity and voltage on every circuit and connector, so I concentrated on the "low-speed" fuel-pump speed relay circuit.
Removed the fuel-pump resistor, measured the resistance, and it was out of spec at 0.80-ohms.
I cut the resistor out; jumpered the leads that went into the resistor, and did a test start, and it started.
Put everything back and it didn't start.
I jumpered the fuel-speed relay (FSR) (located near the front bumper), and it started.
Tested again the FSR (misnomer to be labelled "Fuel Pump Relay" on the box), and it was all good.
A bad assumption was that the FSR was "on" at start-up. WRONG.
The FSR is a HIGH-SPEED circuit.
That is, its function is to BYPASS the fuel-pump resistor circuit, so the fuel-pumps get FULL VOLTAGE at speed/boost.
Unfotunately, I made the wrong assumption so this lead me to test continuity between the FSR and ECU. It was fine.
Tested the real fuel-pump relay (GREEN) and adjacent to the battery, and it was good for continuity, coil, etc.
Perhaps my jumpered connector was bad- nope, good. Plugged it back in.
Divine intervention told me to jumper the Fuel-pump @ the Diagnostic Connector and pull at the fuel-pump resistor jumper.
The fuel-pump went intermittent.
Did more wiggling and it turned out that the "chassis-side" connector of the fuel-pump resistor was intermittant.
This connector is the same one used from the engine wiring harness to the transmission, but it uses thicker gauge wiring.
So which mechanically sound, it wasn't electrically sound.
This time I cut off the bad connector, soldered the two ends together, and double heat-shrunk the soldered end.
Everything back together and all is well.
Thanks to my buddy Jeff to bring over spare relays and even offerring to swap out PFC's. He also re-read from the manual when the FSR is active / "in the circuit" so I could concentrate on the low-speed / fuel-pump resistor circuit.
:-) neil
BTW: Also learned that even though all the grounds were connected at the PFC/ECU, the ECU bracket needs to be grounded too, otherwise weird sounds from the engine bay.
At first I thought I had blown an apex seal, but a compression test showed otherwise.
I knew I was getting spark, but I didn't hear the fuel-pump run, even when jumpered at the Diagnostic Connector.
Verified continuity and voltage on every circuit and connector, so I concentrated on the "low-speed" fuel-pump speed relay circuit.
Removed the fuel-pump resistor, measured the resistance, and it was out of spec at 0.80-ohms.
I cut the resistor out; jumpered the leads that went into the resistor, and did a test start, and it started.
Put everything back and it didn't start.
I jumpered the fuel-speed relay (FSR) (located near the front bumper), and it started.
Tested again the FSR (misnomer to be labelled "Fuel Pump Relay" on the box), and it was all good.
A bad assumption was that the FSR was "on" at start-up. WRONG.
The FSR is a HIGH-SPEED circuit.
That is, its function is to BYPASS the fuel-pump resistor circuit, so the fuel-pumps get FULL VOLTAGE at speed/boost.
Unfotunately, I made the wrong assumption so this lead me to test continuity between the FSR and ECU. It was fine.
Tested the real fuel-pump relay (GREEN) and adjacent to the battery, and it was good for continuity, coil, etc.
Perhaps my jumpered connector was bad- nope, good. Plugged it back in.
Divine intervention told me to jumper the Fuel-pump @ the Diagnostic Connector and pull at the fuel-pump resistor jumper.
The fuel-pump went intermittent.
Did more wiggling and it turned out that the "chassis-side" connector of the fuel-pump resistor was intermittant.
This connector is the same one used from the engine wiring harness to the transmission, but it uses thicker gauge wiring.
So which mechanically sound, it wasn't electrically sound.
This time I cut off the bad connector, soldered the two ends together, and double heat-shrunk the soldered end.
Everything back together and all is well.
Thanks to my buddy Jeff to bring over spare relays and even offerring to swap out PFC's. He also re-read from the manual when the FSR is active / "in the circuit" so I could concentrate on the low-speed / fuel-pump resistor circuit.
:-) neil
BTW: Also learned that even though all the grounds were connected at the PFC/ECU, the ECU bracket needs to be grounded too, otherwise weird sounds from the engine bay.
12-29-12, 06:19 PM
#2
RX-7 Bad Ass
iTrader: (55)
Awesome! Good find and good fix! I'm sure you were happy to solve that sucker!
Dale
Dale
Thread
Thread Starter
Forum
Replies
Last Post
trickster
2nd Generation Specific (1986-1992)
25
07-01-23 04:40 PM
ChrisRX8PR
Single Turbo RX-7's
21
10-18-15 04:01 PM
befarrer
Microtech
3
08-22-15 05:52 PM
