Mystery Ignition Failure

[480rider]

I'm baffled by an ongoing problem I'm having, and I'm hoping to get some ideas on how I might track down the culprit.

 

I have a 2002 Caterham with a Zetec and 5 speed. The car is set up for track only, so the only functioning lights are the brake lights. (It has no headlights or signals, no horn, no heater or defroster.)

 

Starting last season, the car would suddenly cough and sputter while on track, then cut out entirely. It started happening after a few sessions, usually later in the day. Over time, the problem has started to occur earlier and earlier, and with more dramatic results. That is to say, the car no longer gives any indication a problem is about to occur (no cough or sputter), but just cuts out entirely. The engine will turn over, but not fire. At first, no fuses would blow, and I could re-start the car after letting it sit for a short time.

 

More recently, though, the cut-out happens simultaneously with the blowing of a 20A fuse in the ignition circuit. (More on this below.)

 

So...I started last year searching for fuel delivery problems, and found all was in order. Now, of course, it's obviously an electrical problem, but I haven't managed to source it. I have found no bare or loose wires which could be causing an obvious short. I've replaced the coil pack. I've checked the O2 sensors, and they seem to be functioning fine. I've replaced the kill switch, ignition switch, and rewired the starter button.

 

The car will fire right away after I replace the fuse, and will run fine while sitting in the paddock. It ONLY cuts out while on track -- but today it took just one lap (in the first session, on a cool morning) to cut out and blow the fuse. I replaced the fuse, and ran it for about 40 minutes in the paddock with no issues.

 

I'm completely flummoxed by this! Ben and others have said it is very unlikely the ECU, but I'm wondering if I should replace that next. Any ideas? Is there a chance this type of "progressive" failure could be an ECU issue, or is there perhaps some other part of the ignition system (or related system) I could check?

 

Thanks for any and all help or suggestions.

[Guest speedcraft]

have you checked the starter itself? its a not uncommon problem with the magnetti units. suspect youre running the stock ford unit?

[480rider]

Thanks for the response.

 

I am running the stock motor with Ford starter. I will check on the starter and its wiring.

Edited April 16, 2011 by 480rider

[scannon]

Are you running the Ford Focus ignition coils? I've heard that they are infamous for things like this.

[480rider]

No. MSD. And a brand new coil pack at that. When it runs, the car runs strong and well. This seems to be some sort of progressive electrical failure (coil pack seemed like a good possibility), which has gone from relatively mild and intermittent, to quick and fatal.

 

I failed to mention in my first post that when this began, the car would stumble and cut out, then full power would quickly return (w/in a few seconds) and the car would generally run fine for the rest of the session. After a while of that (and sometimes with no problems at all), the cut-out duration got longer, happened sooner and sooner after starting out, then the fuses started blowing.

[scannon]

Next time it happens, put a hand on the coil pack and see if it is very hot. Also check the MSD box for heat.

[bsimon]

Make sure you are looking at the correct fuse. The fuel pump also uses a 20A. If it's the fuel pump packing it in, all the symptoms would be similar.

[Kitcat]

This is a long shot, but: Is there a chance that it is a mechanical problem caused by g-forces on the the track? In other words, something that looks normal in the pits but, under load, is distorted.

 

Classic example on my and other Cats was worn engine mounts allowing engine to rotate enough on the track to cause the air cleaner to carbs to make contact w/bonnet, cause air leak and screw w/A/F ratio and hence coughing, spluttering etc.

 

I know you don't have carbs but maybe something similar is occurring if engine is moving around?

[480rider]

Thanks for the replies -- I managed to solve it this morning, and the car ran great through the day. Kitcat wins for the right diagnosis.

 

While investigating the O2 sensors, I traced the wiring from the loom to the rear sensor. It was originally affixed to the top (underside) of the tunnel, but apparently a zip tie broke, and left the wires dangling down, where they had become lodged between the transmission housing and a frame rail. The rubbing resulted in the outer sheath being worn through, and one of the wires (the 12v heater feed, I believe) also being worn through. The wire was still intact, but with the outer coating worn through, it was able to contact the frame rail and short.

 

Now for the interesting part. Because it wasn't touching all the time, I was unable to cause the failure by gentle driving or just idling in place. And I realized the failures were occurring during high-G right turns. Aha! The forces and flexing allowed the transmission to move just enough to pinch the wires, thus causing the short and failure.

 

I'm a lot happier today than I was yesterday. I was getting very tired of this!

[super7guy]

Probably the MSD coil.

 

One of the guys here in town had his MSD coil go out during the National Tour. The dyno tune guy said that MSD is problematic and to stick with the Ford coils.

 

YMMV

 

Wayne

[1turbofocus]

If this is a track only car why are you running 2 o2 sensors , The rear o2 is for the CAT only and the front is nice to have for closed loop fueling (idle , cruise , part throttle ) but not used for Wide Open Throttle , you could take out the rear o2 altogether and just use the front or turn off the rear o2 with a tune

 

Tom

[480rider]

Thanks for the advice. The only answer I have for why I'm using two is that I didn't know any better! I realize each is typically used on different sides of a cat, but I assumed there was still a reason to have one downstream of the muffler.