Skip to main content ↑ ↓
Topic: Inertia switch/fuel pump relay in '87 Continental (Read 4554 times) previous topic - next topic

Inertia switch/fuel pump relay in '87 Continental

Hello again!

I just got another Fox body car - 1987 Continental Givenchy. It has some issues, like rotted rear brake line, air suspension problems etc. I always wanted to have one like this and it looks like nice project.

I was wondering if I can ask one non T-bird/Cougar but still Fox-body question here?

I can't figure out what's wrong with the inertia switch and fuel pump relay in this car. Somebody grounded one of the wires going to inertia switch and the pump works all the time with key in ON position. If i remove the wire grounding the inertia switch wire and connect everything as it should be the pump doesn't work. When I ground that wire the relay clicks and pump works, what may be wrong here?

What does the grounding the inertia switch wire do? Is is a shot relay?

Thanks in advance for help!

Inertia switch/fuel pump relay in '87 Continental

Reply #1 –
sounds like you have a bad inertia switch  to me if you put power and a ground to the fuel pump relay and it clicks and the fuel pump turns on then the relay is good..

sounds like someone bypassed the inertia switch to get the fuel pump to come on..
Nick
Quote
there's only about a half a dozen man made objects that are herd by the human ear below 40Hz,a pipe organ,thunder,the space shuttle lifting off,a jet airplane taking off or landing,a large canon,an atomic bomb ignited in your back yard and the heat wave afterward oh wait you would be dead so you would'nt hear it scratch that!,and maybe beating your hear against a wall less then 40 times a second..rap music is'nt one of them!thats 40-60Hz@100+db the moving air is under 40Hz

Inertia switch/fuel pump relay in '87 Continental

Reply #2 –
But if I'd jump two wires going to inertia switch than the pump doesn't work either. It works only with one inertia switch wire grounded. I'll take a pic of this wierd setup tomorrow.

Inertia switch/fuel pump relay in '87 Continental

Reply #3 –
test the relay  it should have 4 wires the relay has two hot's "+" and one ground and one that is ran to the pump and the wire is hot only when the relay is powered if you find the hot's and you get power with the ignition on one wire is the ground and the other is dead till the relay is powered most likely the ground on the relay will be a small gauge wire i don't have the colors of the wires on hand.

find the ground and  ground it to the body quick with the ignition on and if it clicks and powers the pump the relay is good the the Inertia switch is most likely bad .. the reason why it won't work right when everything is hooked up factory is because the Inertia switch won't complete the circuit check it and let me know


Nick
Quote
there's only about a half a dozen man made objects that are herd by the human ear below 40Hz,a pipe organ,thunder,the space shuttle lifting off,a jet airplane taking off or landing,a large canon,an atomic bomb ignited in your back yard and the heat wave afterward oh wait you would be dead so you would'nt hear it scratch that!,and maybe beating your hear against a wall less then 40 times a second..rap music is'nt one of them!thats 40-60Hz@100+db the moving air is under 40Hz

Inertia switch/fuel pump relay in '87 Continental

Reply #5 –
Quote from: Blown306Cougar;340787
test the relay  it should have 4 wires the relay has two hot's "+" and one ground and one that is ran to the pump and the wire is hot only when the relay is powered if you find the hot's and you get power with the ignition on one wire is the ground and the other is dead till the relay is powered most likely the ground on the relay will be a small gauge wire i don't have the colors of the wires on hand.

find the ground and  ground it to the body quick with the ignition on and if it clicks and powers the pump the relay is good the the Inertia switch is most likely bad .. the reason why it won't work right when everything is hooked up factory is because the Inertia switch won't complete the circuit check it and let me know


Nick


Hi Nick!

I've done some reaserch today, I found one (+) wire always hot, one (+) hot with ignition ON and (-) which turns out to go thru inertia switch. I measured the voltage and found the problem. Both (+) have correct voltage while the ground is unstable. With ignition OFF I get 12.5V on that ground wire while with ingintion ON I get only 9.5V. That's why "external" ground is helping to get over 12V and power the relay.

What may be causing the ground voltage drop on the wire going to inertia switch? Where is the wire going to inertia switch connected? I found the end goes to the fuel pump realy.

Why the pump is working all the time with ignition ON, not only priming the system?

Thanks!
Mariusz...

Inertia switch/fuel pump relay in '87 Continental

Reply #6 –
Quote from: softtouch;340806
I can't make any sense out of your problem with the 87 T-Bird EVTM wiring diagrams.
There is an EVTM for your car for sale on ebay.
http://cgi.ebay.com/ebaymotors/1987-Ford-Lin-Continental-Mark-VII-EVTM-Diagrams-Manual-/190093186603?pt=Motors_Manuals_Literature&hash=item2c426fd62b


Thanks for the info! I've bought one.

Inertia switch/fuel pump relay in '87 Continental

Reply #7 –
Quote from: Shevretti;340952
Thanks for the info! I've bought one.

Can you scan and post the EVTM page with the fuel pump relay?

Inertia switch/fuel pump relay in '87 Continental

Reply #8 –
Here is the fuel pump setup for the 87 T-Bird. The inertia switch is in the voltage side of the relay coil circuit. In your case, it sounds like the inertia switch is in the ground side of the relay coil circuit.
The EEC is supposed to control the ground. Sounds like that is not happening.

Inertia switch/fuel pump relay in '87 Continental

Reply #9 –
I know exactly what happened here.

someone went poking around trying to jump past this and that with a paper clip or jumper wire to see if they could trouble shoot the problem.

someone jumped +12v directly to the fuel pump relay "coil ground" thinking they could get the relay to energize. 
Well,, what they didn't know is that the computer "finishes" supplying the ground to the relay to the component level on the circuit board.  Forward bias this , reverse bias that, diode here, bla bla bla,, all that boring stuff.

in short,, they screwed up your computer by injecting +12vdc directly up the ground lead going to your computer.
Simply said,, lay a screwdriver across your battery,, that's what happened to the circuit in your eec that makes the final ground path available.

The only fix is to locate the ground side of the coil of your relay as an example posted above which is the Tan / Light green wire.

Once you find your relay "coil" ground wire , splice it directly to chassis ground. 

The end results will be the symptoms you have now.
Turn on key and the fuel pump runs continuous.
turn off key and the fuel pump takes longer to shut off but eventually does,, like in 5 seconds.


At a glance you could argue that I am wrong,, but you have to understand that there are certain things that are suppose to happen well in advance of the fuel pump relay getting power under normal conditions.  The key goes in and gets turned forward, the eec relay powers up, the fuel pump relay coil gets its input power then next the ground based on certain conditions met at the board level of the eec.  In normal cirspoogestances and by design, there would be certain steps preceding already met to energize the fuel pump relay. 

However, by placing 12v directly on a wire that is "conditional" ground, totally hosed up your eec.
Its like telling your computer to bend over and take it.
You should see no adverse effects other than this small modification you need to do.


Softtouch- nice modification to the drawing,,, you bonded the inertia switch to the eec relay contacts which cant be found unless you posted the next page.

Inertia switch/fuel pump relay in '87 Continental

Reply #10 –
Hi jcassity!

That's the way it runs now, grounded to the bolt in the trunk. So, the correct fix is to replace the EEC?

The other computer related problem in this car is burnt one of the ground output from air suspension controller.

Is it possible that something else than idiot mechanic caused all these problems?

Thanks,
Mariusz...

Inertia switch/fuel pump relay in '87 Continental

Reply #11 –
im sure the mechanic tried the best he could,, its just to often shot gun troubleshooting gets you into more trouble than good.

I have no idea if the other issues are related but yes, an eec swap should fix the fuel pump problem,, im 99.9% positive.

if replacement of the eec fixes other problems then its just a bonus.

I am thinking the air ride has its own computer though,, hopefully the problems there are unrelated to the eec.

nice find!!!!

Inertia switch/fuel pump relay in '87 Continental

Reply #12 –
is the wire you have bonded to the bolt in the trunk a "tan/light green" wire?

if so,, it would be nice to know because my gut says the wiring diagram is very similair to the cougs/birds.

If so,, a coug or bird eec may work.

i would pull the eec out for a moment and snap a picture of the part number.

is this a v8 car?

Inertia switch/fuel pump relay in '87 Continental

Reply #13 –
It got a little warmer here (around 40F outside and 55F in the garage vs. 15-20F and 30F for last month) so I got back to work on the Continental.

I've replaced the air-suspension controller today and it fixed all the suspension problems (eg. one ground output gone), so I guess that good EEC will fix missing ground to the inertia switch.

Yup, the wire grouded in the trunk is tan/light green. I'll try to pull the EEC tomorrow and will post a pic here. I think you're right that T-bird or Cougar EEC may work.

All the Fox-Continentals were V8.

BTW. Is it possible that all these trouble are resut of welding something in the car with battery connected?

Inertia switch/fuel pump relay in '87 Continental

Reply #14 –
highly likely and because of one reason,, many circuits designed like the Tan / light green wire are eventual grounds but managed by a device the wire goes to. 

a welder doesnt have a filtered ground lead, and its likely the task of simply clamping a ground on to the car ended up "not" being a perfect ground at all but good enough to weld.  Having said that, a poor connection = high resistance which in turn equals a voltage drop. 
One could say that you injected a voltage up every ground conductor in the car but lucky for us, our cars are mostly relay and switch controlled. 

any grounds that are managed or switched on / off by ttl logic or whatever may suffer.

I would have did what the shop manual says, and as your gut probably said, unhook the battery before welding on a car. 
In my case, I would have known to unhook the EEC as well as a few other things.
simply unhooking the battery doesnt really isolate the equipment chassis grounds or transitor switched grounds.
I would have unhooked the battery, solenoid, alternator, eec and the options in the car that i wanted to protect.



In some cases, batteries have been damaged because of this and in many, electroics suffer as well.

double check all your high level electronics operation after you get really busy working on the car.
most people forget to think about the damage a welder can do , and many times nothing goes wrong.
I suspected originally that your fuel pump issue was someone jumpering the fuel pump relay and put low voltage up the tan/light green wire.