Autosport Labs

I've been running my V4 MJ for about six months now, no problems whatsoever until Sunday when my trigger wheel fell off just north of Bristol on the M5 when my welds failed

I know where it fell off because I heard it bounce of the underside of the car. My understanding is that once that happens the engine should stop working, have I got this right? I ask because the engine didn't stop until I pulled up at traffic lights 75 miles further up the road on the M42 off slip which is probably the first time the engine revs dropped below 3000 rpm.

Did I run all that way in some sort of limp-home mode? I'm running a MAP system on a 1330 A series.

Rich

I wouldn't of thought it could do that. Without a signal from the triggerwheel the ignition system wont know what position the engine is in and when to spark.

Did you have alot of missing, pinking or loss of power when this happened?

Could it not of been the welds snapping that you heard and it was rattling on the damper/crankshaft until finally it dropped off somewhere else.

Seems very strange.

Of course i/we weren't physically present but..... I would say that is quite impossible as the EDIS requires a continuous and accurate signal from the trigger wheel in order to accurately run the engine.

Perhaps your engine was turned into a zombie and became the the undead of internal combustion? "Megajolt of the Dead" would be the movie title?

I very distinctly heard something metallic twang off the floor of the car, the speed remained pretty constant between 65 and 70mph for a good hour afterwards. As I rolled up to the lights on the off slip it just died with no funny noises.

Weird!

If the wheel had gone there would have been no timing reference, so even if the EDIS module decided to just run in limp home it wouldn't know when to fire, even if it just kept firing at the same interval then after a couple of seconds it would slip out of sync and it would be firing on the wrong part of the cycle and the engine would die.

My suspicion is that some debris on the road clonked the wheel out of place but it was still just about located and resting on the now fractured welds. As the engine speed dropped that kicked off the interference fit of the fractures and the engine died.

This sounds more plausable. Go back and see if you can find your triggerwheel, then you would know, lol.

This time when you weld it give it a decent amount of heat (pre-heat the pulley if possible) and weld it on with some big stitches rather than "tacking" it in place as we have seen a number of people do. Here are our howto guides, look at the second link for a couple of pictures of what a decent bead of weld for a trigger wheel looks like.

http://trigger-wheels.com/store/contents/en-uk/d20.html
http://trigger-wheels.com/store/contents/en-uk/d21.html

Road Debris is a plausible explanation, if the pulley was exposed and not protected by other parts of a car, like an under-tray or whatnot.

Rich, do you have a picture of your trigger wheel, prior to destruction, so we can consider it's design?

We had a trigger wheel come off our our MR2 race car, at high RPMs- it was catastrophic and the engine died instantly. As it bounced around the underside of the car and engine bay, it struck a number of items- including oil hoses. Fortunately they were stainless braided- I saw the evidence of damage on the outer sheath. Had they not been protected, the wheel would've sliced through them like a knife through hot butter.

There are pics of the install in my earlier thread on the Midas http://www.autosportlabs.org/viewtopic.php?t=2494 the wheel isn't exposed under the car at all though I'm not currently running an undertray.

I was driving on a clean, reasonably quiet road and I would put money on there not being any debris of significant size in the road. I'm a blue light driver so I'm generally pretty much aware of what's around me at any given time. Thankfully my pipework runs through the car so there's nothing to damage underneath, you could actually hear the 'ring' of the wheel when it bounced. It just doesn't make sense to me at all.

Watch out people or the fuzz will be on our tail, lol. Better keep within the speed limits from now on, ha ha ha.

Seriously though it does't make much sense at all because like cng1 said, IF the edis module kept supplying sparks to the engine with no signal from the crank sensor then it wouldn't take many rpm's for the timing of the sparks to go out of phase with the engine position unless you could keep exactly at the correct rpm the edis is sparking at which would be near impossible.

I used to dj a few years ago and it only takes a fine amount of error to not be in sync, never mind sparking at 1000 - 6000 rpm x 2 (for 2 ignition events) without any position reference.

I have had a triggerwheel come loose before, but i had keyed it so it still ran in roughly the correct position.

NITROPIXIE wrote:Watch out people or the fuzz will be on our tail, lol. Better keep within the speed limits from now on, ha ha ha.

Seriously though it does't make much sense at all because like cng1 said, IF the edis module kept supplying sparks to the engine with no signal from the crank sensor then it wouldn't take many rpm's for the timing of the sparks to go out of phase with the engine position unless you could keep exactly at the correct rpm the edis is sparking at which would be near impossible.

I used to dj a few years ago and it only takes a fine amount of error to not be in sync, never mind sparking at 1000 - 6000 rpm x 2 (for 2 ignition events) without any position reference.

I have had a triggerwheel come loose before, but i had keyed it so it still ran in roughly the correct position.

No mate, paramedic.

The whole thing makes no sense to me at all, I know it shouldn't have run but it did. If the wheel had come off where I stopped I would have seen it, I was in the middle of a three lane off-slip and scoured the area looking for the wheel as I'm sure I could have lashed something up to get me home if I'd had the wheel.