Oil sending unit cooked fuel pump?

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   Ok....I've been poking around with my test gear trying to figure out if my fuel pump is hooped and why.  It is practically new.

I think I found the problem.  Michelle drove the car home one night and shut it off.  Got up in the morning, battery was stone dead.  Brand new spiral wound battery I might add.  I told her to take the truck to work and I'd charge the battery up.  I figured she forgot to turn the radio off or something.

So spent the next afternoon charging the battery up.  It turns over but no go.  Was working fine the day before.  Hmmmm.  Determined it was fuel.  No pump noise at all.

Replaced the pump relay, no go.  So I started digging.

I noticed that there was 12 volts at the ALCL plug on the pin that goes to the starter.  All the time!  Unplug the relay, no difference.

So look at the wiring diagram and figure out that if the sending unit was to fuse it's conacts together it's possible that it could create the situation I was seeing.

Remove the plug from the sending unt and the voltage goes away.

So I'm thinking the pump kept running that night till the battery went dead.  Not good for the pump.....or the battery.

Pump must have over heated and died.

Bloody hell, what are the chances?

Anyone heard of this before?

The Dawg

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Dawg Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 15 August 2009 Location: Canada Status: Offline Points: 988	Post Options Post Reply Quote Dawg Report Post Quote Reply Topic: Oil sending unit cooked fuel pump? Posted: 26 September 2010 at 6:42pm
	Ok....I've been poking around with my test gear trying to figure out if my fuel pump is hooped and why. It is practically new. I think I found the problem. Michelle drove the car home one night and shut it off. Got up in the morning, battery was stone dead. Brand new spiral wound battery I might add. I told her to take the truck to work and I'd charge the battery up. I figured she forgot to turn the radio off or something. So spent the next afternoon charging the battery up. It turns over but no go. Was working fine the day before. Hmmmm. Determined it was fuel. No pump noise at all. Replaced the pump relay, no go. So I started digging. I noticed that there was 12 volts at the ALCL plug on the pin that goes to the starter. All the time! Unplug the relay, no difference. So look at the wiring diagram and figure out that if the sending unit was to fuse it's conacts together it's possible that it could create the situation I was seeing. Remove the plug from the sending unt and the voltage goes away. So I'm thinking the pump kept running that night till the battery went dead. Not good for the pump.....or the battery. Pump must have over heated and died. Bloody hell, what are the chances? Anyone heard of this before? The Dawg
	You dream it up....I'll make it

CFoss Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 13 February 2007 Location: Canada Status: Offline Points: 580	Post Options Post Reply Quote CFoss Report Post Quote Reply Posted: 26 September 2010 at 7:39pm
	It's a weird one. I think you've got it right though. Relay or oil pressure switch are the only 'hots'. Sucks that the pump died. I was trying to figure out how that could happen, 'cause it would be just like it was running...no bit deal.. Until the voltage got low enough that it couldn't run any more. Then the stalled motor would heat up due to the current flow. Chay
	86 SE 3.4

Dawg Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 15 August 2009 Location: Canada Status: Offline Points: 988	Post Options Post Reply Quote Dawg Report Post Quote Reply Posted: 26 September 2010 at 7:47pm
	What I'm trying to figure out is why the sending unit circuit is there at all. Why would you ever need to over ride the ECM signal? Lets assume the ECM shuts the pump off in error. Why in Gods name would you want the sending unit to keep it going? It's possible there are times where the ECM hesitates or gets confused for a short time and they needed a way to keep the power flowing. I'm stumped. The Dawg
	You dream it up....I'll make it

Dr.Fiero Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Post God Joined: 12 February 2007 Location: Canada Status: Offline Points: 1726	Post Options Post Reply Quote Dr.Fiero Report Post Quote Reply Posted: 26 September 2010 at 9:45pm
	The switch in the sender was put there so that if the FP relay went out - you could still start the car (after it cranked enough to build oil pressure). Mind you, the number of relays I've seen go bad over the years.... uhhhh... not many.... it's sort of a stupid redundancy thing. (AFAIK it's also the ONLY redundancy system in the whole car! They SHOULD HAVE put a redundant ignition module in!!!!)

Dawg Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 15 August 2009 Location: Canada Status: Offline Points: 988	Post Options Post Reply Quote Dawg Report Post Quote Reply Posted: 26 September 2010 at 10:08pm
	Makes sense I guess. And I second the ICM idea....:) I'm going to disconnect this sender "feature". Bloody hell, pulling the tank again..... The Dawg
	You dream it up....I'll make it

CFoss Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 13 February 2007 Location: Canada Status: Offline Points: 580	Post Options Post Reply Quote CFoss Report Post Quote Reply Posted: 27 September 2010 at 8:22am
	I think a bit of wire in the glovebox is good redundancy (You can always jumper at the aldl...great way to set your fuel pressure btw). Chay
	86 SE 3.4

Dawg Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 15 August 2009 Location: Canada Status: Offline Points: 988	Post Options Post Reply Quote Dawg Report Post Quote Reply Posted: 29 September 2010 at 1:05am
	Update: Pulled the tank today. Got the pump on the test bench and it's dead alright. Bought an 88 pump. Those pumps are over $200 retail now. Thank my fuzzy arse I get a discount.....geez. It's supposed to be nice again tomorrow so the car should be running by noon. The Dawg
	You dream it up....I'll make it