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1994 crank-no-start after swapping clutch cylinders (master, slave, and line)

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1994 crank-no-start after swapping clutch cylinders (master, slave, and line)

 
Old 05-29-2019, 01:14 AM
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electromdc
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Default 1994 crank-no-start after swapping clutch cylinders (master, slave, and line)

1994 LT1 6 speed.
200k miles. daily driver.

My clutch master cylinder has been leaking for a while and getting worse. I finally decided to swap it and went with a new master, slave and line. After the swap, I started it up, and tested the clutch by shifting to 1st and reverse, moving just a few inches in each direction, then shut it off. It ran normally for the entire 15 seconds. Then I went to hop in it to go to work the next day and it would crank, but no spark. I sprayed some starting fluid in the intake, and it would start for 2 seconds and die promptly. Sounds like a fuel delivery problem. I knew I had removed the battery to do the master, so I removed it and put it back in again; assuming a loose connection. I also observed the wires and fuse blocks around the battery; nothing out of place. I checked the fuel pump fuse in the box behind the battery: not blown, and has 12V at both sides. I checked the dark green/white wire coming from out of the ECM and it gets +12V for 2 seconds when the key is on, and it gets +12V while cranking. I listened with the gas cap off while my wife turned the ignition on: no fuel pump hum. Also no hum while cranking. While cranking, I get 20 pounds of oil pressure, so I am assuming its not the oil pressure switch. I looked under the drivers dash where I had to connect the master cylinder push rod: nothing obviously out of place or disconnected.

So, I moved to the passenger side under the dash where I have read that the fuel pump relay is and found 5 relays. I pulled each one and tested the resistance on the primary: about 90ohms each.
For the next step, I figure I need to either pull more of the passenger dash apart to be able to meter the leads going to the FP relay, or pull the gas cap cover thing and meter at the fuel pump electrical connector. From the schematic I saw online I thing I am looking for a gray wire that should be +12 when that relay turns on. I am not sure how I would have harmed anything at either the relay or the fuel tank/pump by doing my clutch cyclinder work.

Any ideas? I am a bit stumped.
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Old 05-29-2019, 08:55 AM
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Kevova
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Fuel pump fuse possibly in ip fuse box. I don't have 94 manual to be sure. Fuel pump relay pump feed wire is red to fuel pump fuse and grey leaving.
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Old 05-31-2019, 12:27 PM
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electromdc
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Thanks. I will try to find the gray wire and red wire coming from the fuse box by the battery and check voltage. The passenger side interior fuse box has no fuel pump fuse, just injectors. Both of those fuses are good.
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Old 06-05-2019, 01:09 AM
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I bought the corvette shop manual and here is what i found:
There is a 20A fuse in the engine compartment, leading to the FP relay, leading to a 10A FP(fuel pump... I was wrong in my post saying that it didn't have one in the IP. I didn't know that FP was referring to the fuel pump.) fuse on the passenger side of the instrument panel (mine is the Vin P OHV), then on to the fuel pump.
I get 12V at the 20A fuse, 12V at the 10A fuse, and at the fuel pump wiring harness when it is unplugged. I haven't tried back-probing it. I did bring a car battery back there and direct-wired to the fuel pump wires (+ gray and - black) and I get no fuel pump noise and the battery voltage doesn't drop when trying to load it. I measured the resistance of the fuel pump motor: 1.3megohms. I don't have a new one to compare, but that sounds like a high resistance value. It is behaving like it is an open circuit (maybe it came unplugged? doesn't sound likely). I ordered a new fuel pump, strainer, gasket today.

Does anyone have any ideas other than a bad fuel pump? hopefully that is all it is.

Last edited by electromdc; 06-05-2019 at 01:11 AM.
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Old 06-11-2019, 11:48 AM
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Default Fixed***

I found the problem. The wires in the sending unit must have gotten hot. Some of the insulation was melted and brown. The plastic connector attached to the old pump had connector holes almost melted closed. I carved out the melted plastic and it worked! I ordered another cheap fuel pump that comes with a connector so I can do a better fix later. But for now, she runs.
(Note: I also swapped the fuel filter in that process. One oring stayed in the used filter, so I had to do it all over again. So my whole garage reeks of gas (not to mention the smell leaked into the house some.)
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