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Unread 09-04-2013, 11:37 AM   #1
Sykes
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Starter Relay Frame Sparks

I replaced a starter relay for a 87 XJ, and the steel frame that supports the Motorcraft style relay and the four module relays, sparked when I hooked up the negative cable. A good three inch spark at first, then less, until nothing. Has anyone seen a short like this? Last relay was gone. This Napa part had a loose power post which may be the design.

Starter turning over but no fuel; diagnosing the fuel system.

Also, I see no Fuel Pump Ballast Resistor on the driver's fender or a Fuel Pump fuse. We're these two items on the Renix engines or just the fusible link?

Thanks!

87 XJ Laredo S6 Auto 4.0L 4WD

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Unread 09-04-2013, 12:51 PM   #2
Sykes
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Still sparking every few times I hook up the negative cable; throwing a small click or inch spark towards the fire wall at the base of the relay steel frame connected to wheel well. It looks like it is coming off the steel frame to the steel wheel well.

I have diagnosed two other problems; possible dead pump and fuel relay not supplying electric to fuel pump.
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Unread 09-05-2013, 06:49 AM   #3
JWELK
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A spark by the firewall, would lead me to believe you have grounding issues. Specifically something is loose in that area. To verify that you don't have a large "short" you are going to need a large ammeter, or one of short circuit testers described elsewhere on this forum. CJ7 Tim linked to one, I've described how to make one several times. If you have a short you will have to find it and repair it. If a loose connection..... A short or fault will display a continuous heavy current draw. A loose connection will only spark when connecting or when a heavy load is present. A heavy load would be the starter or winch. After this is solved we can help you address any remaining issues.

Regards,

Jim W
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Unread 09-05-2013, 09:24 PM   #4
Sykes
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I will check for a large load short. It does look like a small short as it will sometimes throw a spark, then stops completely after reconnecting the negative battery cable. The relay frame has ground continuity and so does the firewall its attached to. After a few days of testing, I found the fuel relay is good on 87 (fuel pump +), 85 (fuel pump -), and 30 (red fusible link); its 86 that is the culprit, which I believe the ECU activates the ground to open the circuit. The line to the fuel pump is good. I believe the fuel pump is dead.

So as only the headlights, instrument panel, and starter works; I suspect a ground short is effecting the ECU, unless the ECU is dead. I am working cleaning all grounds and C101 connector (cruiser54 specs) with no changes yet. I am hesitating on putting in the new pump in case there is a large load short, as something finished the electric fuel pump; it was working a year ago when the car would not start and then died.

I did notice that five wires around the O2 exhaust area have no sheathing and look dark. I will take your advice below from a thread I reviewed and thanks!

"Do not power it up as you now must find the short. Place the black meter lead on black battery lead, and the red meter lead in the Pin 87 socket, disconnect the plug to the fuel pump module, if there is a short, it will read low resistance 2-3 Ohms. If it reads OL or infinity. Place the meter in the tone or buzzer position and wiggle the cable. Obvious places are where the cable crosses the exhaust pipe or is routed around bends."

I did give up looking for a fuel pump ballast resistor on this 87 XJ Renix (no fifth ballast pin on the starter relay either) and now consider the fuel pump relay 30 pin to red fusible link, the only fuse in the circuit. Battery cable and second cable are the main grounds to the engine block, which is where I believe the ECU is grounded. I have never confirmed where the fuel pump is grounded; that one cable may handle that too.
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Unread 09-06-2013, 10:08 AM   #5
Sykes
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Looks like early 87 XJs had no ballast resistor, system fusible links, and are prone to O2 sensors wires shorting at heat exhaust. The 5 blackened wires around the O2 I have been looking at could be a short point. Checking today.

Another thread said that the ballast resistor was put in late 87 to quiet the fuel pump. I had thought that it was to reduce voltage to maintain the pump life. Looks like I should expect a noise pump now if I can get this all going again.
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Unread 09-06-2013, 11:53 AM   #6
Sykes
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I am planning on cleaning the firewall electrical connector - fuse connection plugs through the firewall. Does anyone have a picture of this setup disconnected? Looks like two plugs into one large through the firewall plug, held
together by two large plastic C latches on each side. Is that right? Trying not to bust the setup right off. My C101 connector was tar hell.
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Unread 09-06-2013, 02:31 PM   #7
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I found an unidentified ground hanging out of the harness on its way to the C101 connector, above the dipstick on the firewall. This is a confirmed ground - continuity with engine block. It could be an accessory ground, but as I am dealing with a short, it would be good to ID. Attached is a shot of the wire and plug if anyone can identify. Early 87 XJ Renix
detached-ground.jpg  
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Unread 09-07-2013, 11:59 AM   #8
Sykes
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I may have solved the sparking problem with a new Napa 4 gauge grounding strap from engine to firewall; no spark at all anymore at relay steel frame. (Cruiser54 Renix specs with all metal abraised, cleaned of paint and coated with dilectric grease).

The unidentified plug with black wire ground seems to be coming from the heater wiring.

Fuel pump still not working so may pull that next.
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