1995 Ford Cosworth ignition

ignition
ford

#1

Hello,



I have a problem with a 1995 Ford Scorpio with a 24V Cosworth engine. Every once in a while the car won’t start. It has no spark in any of the cylinders. I took it to the local Ford dealership in Spangdahlem, Germany, and they replaced the ignition module. The car started fine, but the next day would not. So, they then replaced the crankshaft sensor. The car started fine for a while after that, but then spontaneously would not create a spark. Weather (cold, rain) does not effect the problem. It may start 200 times in a row, then for some reason will not generate any electricity to the spark plugs. Now the mechanic says it’s time to look for a used PCM, which he apparently is having a hard time finding and says new PCMs are not being produced. I’m wondering how such a problem can be so sporadic. The mechanic also said it could be a wiring short, but can’t be sure until he has a new PCM. Why a new PCM is important I’m still not quite sure.



So, does anyone in your organization have any idea why, after a new crankshaft sensor and ignition module have been installed, this car would still have intermittent problems generating a spark? The car has never failed while running and may start for weeks just fine only to decide not to create any spark at all one day. Then it may start the next day just fine. Very strange…




#2

I doubt the problem is the PCM at all. You might consider the possibility of a failing ignition switch (the electrical part) as this can very easily cause the symptoms you describe.

One could probably verify this during a no-start condition by running a jumper wire from the battery positive terminal to the positive terminal on the ignition coil.
This is a test method only and is not intended as a permanent fix.


#3

Thanks, I thought the PCM was a shot in the dark. Somehow the dealership started the car with a jumper wire off the battery, but at the time I thought he was testing a faulty ground from the ignition module. When I go back I’ll take a look at the coil to see if I can find the positive terminal in the event I need to test your theory. Sounds more logical than a PCM for sure.

If your theory does work, do you have any idea where the ignition switch between the ignition module and coil would be located? I perused the diagram (see link below) and don’t see any reference to a switch between the ignition module and the coil.

http://www.fordscorpio.co.uk/24vlooms.htm

Thanks again for taking the time to respond to this problemm.


#4

The switch I’m referring to is the electrical part located inside the car on the steering column (part of the key and tumbler).

I’m not familiar with your car at all and have no wiring diagram as an aid in determining what color wire is what. (I do have one of those quirky German Merkur XR4s but it uses a different ignition system.

What is supposed to happen (and this is true of any car) is that power is supposed to be provided to the ignition coils when the key is in both the START and the RUN positions. When a switch starts to fail power may be provided in the START position but not the RUN position. This means it will start and die when the key is released.
Vice-versa, with a problem backwards to this it may have power provided to the coils but not when the engine is being cranked over by the starter. In this case the engine will crank over but spark will not be provided.

About all I can suggest is try to determine which wire at the coils is supposed to have 12 volts from the ignition switch and verify the problem with a test light the next time it refuses to start or either use a short jumper wire as a test method.

Granted, it’s always possible the PCM could be at fault but since a PCM could be very hard to find, and probably pretty darned expensive, I’d want to know with 99% certainty that is the problem rather than make an expensive guess.

Just curious. Have they checked for any codes present during all of this?

(As a footnote (and keep in mind I have no wiring diagram for reference) is that sometimes other items on a car can kill the ignition switch. Age and current draw can burn the contacts and/or distort the plastic housing which will then lead to faulty connections. Honda has an ign. switch recall and main relay problems which could be caused by failing fuel pumps and clogged fuel filters, VW used to have fuse block problems due to dragging fuel pumps, and one of my Fords went through 2 ignition switches due to a dragging cabin blower motor. When one gets high current draw electrical items like this that are routed through the ign. sw. rather than a relay then the switches are going to suffer as more current means more heat. An item on a new car that draws 5 amps may draw 10 amps when it’s aged and worn so you can see that increasing the current load is going to cause a problem. The same would apply in your house if you used items that drew too much current through a wall socke (burnt sockets, popped breakers, and even fires.)
Hope some of this helps. :slight_smile:


#5

Ok, now this makes sense. Add this that the guy I bought from said he had just had the ignition switch replaced because the “key got stuck”, and that makes the switch even more suspicious. When I originally called him he said he never had a problem with the car starting, but if he had just replaced the switch, it’s possible I inherited a faulty ignition switch. If I can get him back on the phone I’ll get more details, like whether or not the switch was used, who installed it, etc… and go from there. I’ll also make sure I know how to test for current at the coil when the switch is in the “start” position before I leave the garage so I know how to test it. Also I’ll inquire about any codes that may have come up during diagnostics. I’ll let you know what I figure out.

I just find it pretty suspicious the previous owner mentioned the switch had recently been replaced, yet he never had any problems starting the car. Hope he’s being honest with me and not sending me on a wild goose chase.

Thanks again!