Technical Questions and Discussions - Oil sending unit cooked fuel pump?

Print Page | Close Window

Oil sending unit cooked fuel pump?

Printed From: West Coast Fieros
Category: Technical Topics Forum
Forum Name: Technical Questions and Discussions
Forum Description: Got a technical question about your fiero? ask it here.
URL: http://www.westcoastfieros.com/forum/forum_posts.asp?TID=2105
Printed Date: 24 April 2025 at 6:27pm
Software Version: Web Wiz Forums 12.01 - http://www.webwizforums.com

Topic: Oil sending unit cooked fuel pump?

Posted By: Dawg
Subject: Oil sending unit cooked fuel pump?
Date 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

Replies:

Posted By: CFoss
Date 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

Posted By: Dawg
Date 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

Posted By: Dr.Fiero
Date 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!!!!)

Posted By: Dawg
Date 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

Posted By: CFoss
Date 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

Posted By: Dawg
Date 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