Focus non-start now fixed - was it really a bad earth?
Discussion
Yesterday evening our Mk1 Focus went from operating completely normally to totally refusing to start. All the electrics were operating fine and I could hear what I think is the fuel pump relay clicking, but the starter motor wasn't turning at all.
We got the car recovered home and today I did some investigating. I swapped some relays to see if that was the problem (nope), and then starting looking at the various earth connections. After I removed the large earth connection bolt on the starter motor and cleaned the contact surfaces, the car started completely normally, and continues to do so.
So my question is, was that corroded connection really causing a high enough resistance to prevent the starter motor from turning? It wasn't even clicking when the key was turned, it was completely dead.
(Obviously I'm pleased that I've got the car working without spending any money, but I don't want this to happen again...)
We got the car recovered home and today I did some investigating. I swapped some relays to see if that was the problem (nope), and then starting looking at the various earth connections. After I removed the large earth connection bolt on the starter motor and cleaned the contact surfaces, the car started completely normally, and continues to do so.
So my question is, was that corroded connection really causing a high enough resistance to prevent the starter motor from turning? It wasn't even clicking when the key was turned, it was completely dead.
(Obviously I'm pleased that I've got the car working without spending any money, but I don't want this to happen again...)
Absolutely possible.
Earth cable problems on older cars as the cable corrodes are very common - the plastic covered variety can corrode to nothing under the sheathing so whilst the ends look OK there's nothing in the middle.
Crops up frequently on Land Rover forums & I usually advise connecting a jump lead directly from the battery earth terminal to a good earth point on the engine block to see what happens.
With a defective earth lead/strap it's not unusual for the current to try & find an alternative route & the handbrake cable is often the one. Can cause the inner cable to weld itself to the outer & melt the sheathing, has been blamed for vehicle fires.
Recently had similar issue with my outboard. The battery was fully charged but whist the starter motor would turn it didn't have the oomph to throw the gear into engagement & turn the engine over. A wiggle of the main earth lead at the battery end showed it to be slightly loose in the terminal & tightening the screws restored normal service.
Earth cable problems on older cars as the cable corrodes are very common - the plastic covered variety can corrode to nothing under the sheathing so whilst the ends look OK there's nothing in the middle.
Crops up frequently on Land Rover forums & I usually advise connecting a jump lead directly from the battery earth terminal to a good earth point on the engine block to see what happens.
With a defective earth lead/strap it's not unusual for the current to try & find an alternative route & the handbrake cable is often the one. Can cause the inner cable to weld itself to the outer & melt the sheathing, has been blamed for vehicle fires.
Recently had similar issue with my outboard. The battery was fully charged but whist the starter motor would turn it didn't have the oomph to throw the gear into engagement & turn the engine over. A wiggle of the main earth lead at the battery end showed it to be slightly loose in the terminal & tightening the screws restored normal service.
Edited by paintman on Saturday 27th August 16:06
Thanks for the replies. 
Megaflow said:
Generally starters don't have an earth cable, they earth through the mounting bolts and engine block, through the engine earth strap. You might have cleaned the main B+ cable, which could have been the cause if it was heavily contaminated.
I'm not totally sure what B+ means - the positive lead from the battery? The connection that I cleaned up goes from the starter motor to the body of the car, via the negative terminal of the battery. (I also cleaned up the earths at the body end, but that wasn't what fixed it.)This is the problem you end up with when cleaning connections etc without first proving what the fault is
If you were to use a multimeter to check for volt drops to the starter motor before touching any connections you would have found a bad earth or supply if there was one
The only thing you can now do is use it and see how it goes
Anything else is guessing
If you were to use a multimeter to check for volt drops to the starter motor before touching any connections you would have found a bad earth or supply if there was one
The only thing you can now do is use it and see how it goes
Anything else is guessing
Sounds like the earthing strap referred to by Megaflow which would be on the negative current side. On the positive side the heavy current flows from the battery to a solenoid and then on to the connection on the starter motor. Not sure what B+ is either but possibly the solenoid > starter lead. There are very heavy currents flowing as mentioned so anything which hampers their flow affects the performance of the starter as you have found.
A dab of petroleum jelly on the contact faces doesn't come amiss when fettling these heavy duty leads.
A dab of petroleum jelly on the contact faces doesn't come amiss when fettling these heavy duty leads.
Penelope Stopit said:
This is the problem you end up with when cleaning connections etc without first proving what the fault is
If you were to use a multimeter to check for volt drops to the starter motor before touching any connections you would have found a bad earth or supply if there was one
The only thing you can now do is use it and see how it goes
Anything else is guessing
Well, I was testing it after trying each fix, so in that sense I wasn't guessing - I was being quite methodical. You're right, I should have checked for voltage drops. (I was only checking for continuity which I guess doesn't tell you a whole lot.)If you were to use a multimeter to check for volt drops to the starter motor before touching any connections you would have found a bad earth or supply if there was one
The only thing you can now do is use it and see how it goes
Anything else is guessing
I've discovered that Haynes manuals are great for telling you how something is wired, but not so great at explaining where the actual physical wiring and connections are located...
MajorMantra said:
Penelope Stopit said:
This is the problem you end up with when cleaning connections etc without first proving what the fault is
If you were to use a multimeter to check for volt drops to the starter motor before touching any connections you would have found a bad earth or supply if there was one
The only thing you can now do is use it and see how it goes
Anything else is guessing
Well, I was testing it after trying each fix, so in that sense I wasn't guessing - I was being quite methodical. You're right, I should have checked for voltage drops. (I was only checking for continuity which I guess doesn't tell you a whole lot.)If you were to use a multimeter to check for volt drops to the starter motor before touching any connections you would have found a bad earth or supply if there was one
The only thing you can now do is use it and see how it goes
Anything else is guessing
I've discovered that Haynes manuals are great for telling you how something is wired, but not so great at explaining where the actual physical wiring and connections are located...
Now that you say you were methodical in trying each fix......I am guessing that there is a 75% chance that you have fixed it, there is a 25% chance that you disturbed something else when trying a fix and that something else will come back in the not to distant future
Penelope Stopit said:
I didnt mean that you were guessing, I meant any opinions about whether you had fixed it or not would be guessing
Now that you say you were methodical in trying each fix......I am guessing that there is a 75% chance that you have fixed it, there is a 25% chance that you disturbed something else when trying a fix and that something else will come back in the not to distant future
This is a fair point. Now that you say you were methodical in trying each fix......I am guessing that there is a 75% chance that you have fixed it, there is a 25% chance that you disturbed something else when trying a fix and that something else will come back in the not to distant future
MajorMantra said:
Thanks for the replies.
Yes, I did mean battery positive. That is the earth you have cleaned, I have never seen a separate stater motor earth myself, but I am aware so do exsist.Megaflow said:
Generally starters don't have an earth cable, they earth through the mounting bolts and engine block, through the engine earth strap. You might have cleaned the main B+ cable, which could have been the cause if it was heavily contaminated.
I'm not totally sure what B+ means - the positive lead from the battery? The connection that I cleaned up goes from the starter motor to the body of the car, via the negative terminal of the battery. (I also cleaned up the earths at the body end, but that wasn't what fixed it.)Gassing Station | Home Mechanics | Top of Page | What's New | My Stuff