power to fuel pump

[samakijoe]

All though I have many years in the world of Alfa Romeos I now find myself the owner of a 1975 124 spider which I am enjoying working on and getting up to top condition. (replaced the old carburetor with a new 32/36 DFEV. I'm also going to get rid of a lot of the wiring that is not used now that the "smog stuff" has been removed.) One of the issues I have come across is that the fuel pump does not get power until after the engine starts. This seems a Little strange to me and I can't believe that this is normal. Right now I am powering the pump (before starting) with a jumper to 12V dc off the Electric choke terminal. After it starts I remove the jumper and there is power to the pump as normally expected. I remember reading here some where someone jumping the fuel pump directionally to the ignition switch and getting in to some trouble. Any thoughts??
Joe D.

[zachmac]

There are two feeds to the fuel pump circuit. First the pump gets power through the cranking position of the ignition switch. Then once oil pressure is sensed a second feed keeps power to the pump in the running position. This is a safety feature designed to stop the pump if you are in a wreck that stops the engine but doesn't turn off the ignition so that a leak doesn't pump fuel out all over the wreck. Sounds like the second feed is not working. You'll need a good wiring diagram. Mirafiori has several posted but as I recall not 75. They did change year to year so try to fond a set for your car. The Mirafiori site has a good set for a 76 and those are probably close enough to trouble shoot. Brad Artigue has a single pager of the 75 posted on his site as well but it is hard to read (all one one sheet) and has no legend but I looked at it just now and the dual relays that the pump power passes through look to be just like the 76. BTW, credit to Brad who created most of those fabulous wiring diagrams posted on Mirafiori and elsewhere. Maybe he didn't do the 75 because the 76 is close enough?

[zachmac]

BTW, a simpler modern solution is to wire a separate switched wire from the fuse box back to the pump that doesn't rely on the relays and just install a Ford "inertia" cutoff switch in the trunk ground wire feed path. Search this site for a couple of posts on the Ford re-settable inertia cutout device, a cheap and easy retrofit.

See this post for example: http://www.fiatspider.com/f15/viewtopic ... rd#p269638

[RRoller123]

http://www.fiatspider.com/f15/viewtopic ... ff#p216052

Here's another thread with some pics of the Ford inertial switch wired in.

Pete

[samakijoe]

Thanks to all for the information on how Fiat saw fit to use two ways/paths to power the fuel pump instead of one as most car designers/builders do. (I would love to know their thinking in adding this second path to power the pump. Normally when working on a starting issue with a car of this vintage the first thing you do is turn on the ignition key and listen to hear if the fuel pump is clicking..) I did find the problem it was a stuck relay used during the "start" position of the ignition switch. I will be putting a momentary push button switch on the dash board to be used for just 5-6 seconds before I turn the key to start the engine. This would be a big help to anyone with a "lazy" relay in the Fiat that only gets to go out and play once every few weeks/months..

As to the use of one of those Inertia Shut Off Switch it might cause (and here is just my opinion on this ) a problem on a sportscar that, shall we say, does not have the ride "quality" of a Crown Vic. I could see it "going off" (turning off the pump) after hitting a few pot wholes or going over a Rail Road crossing out in the country in Alabama. Not a way to impress that cute little blond you just met a few days ago.
(Although I just heard on the radio that S. C. has the worst roads in the country..)

Anyway, thanks again for the heads up. I be asking more questions soon...

[RRoller123]

Just an FYI, there has never been a reported case here (that I am aware of in the last 6 years) of the inertial switch shutting off during normal driving, even over extreme potholes. I believe that it measures simultaneously in multiple axes, so the pothole has no effect. Now, if you hit at tree with a pothole right at its base, that might be another matter......

[baltobernie]

It's a ball bearing inside a plastic housing. Very crude, yes, but remarkably accurate and effective. Not only used on the Taurus and Crown Vic, but also on F150 pickemups. I'll bet you've seen some of these in SC with suspensions w-a-a-a-y-y-y stiffer than your Spider, eh?

[samakijoe]

baltobernie said:
"I'll bet you've seen some of these in SC with suspensions w-a-a-a-y-y-y stiffer than your Spider, eh?"

Well, no I have not. But then again I live in NC. I had planned on going down to SC a couple weeks ago to check on the situation with the problem (to my mind at least) with the use of these inertial switch on the rough roads down would/might cause. My plan was to find a really rough road with a lot of pot holes. Then jump out in front of pickup trucks (these are prime test subjects. Picking the correct subjects is always prime when doing scientific/social experiments ) thusly, stopping the truck and asking the driver if he has any problems with his inertial switch shutting down the engine. I checked with a friend who used to live in SC. He advise to me was to cancel the trip because I might not get to return home. (I have my suppositions as to his answer was based on the fact that I owe him a bit of money but I can't prove this at this time because I was hoping that he had forgotten about it by now....) So I decided to stay home and watch movies on NetFlix and work on the Fiat...

Yes, I know that I sometimes write long convoluted sentences...

[zachmac]

I am in SC and the roads are rotten and the Fiat purrs along no matter. Switch works as designed.