A while back I answered some questions here by wadehilts on his 505 GTI fuel injection. The upshot was that he decided to convert to Megasquirt and I've been giving him some help off the forum. A side effect of this has been to convince me to move both my cars to use a toothed wheel crank position sensor in place of the distributor sensor.
I've done the 505 now and it has dramatically improved some aspects of driving. The job wasn't easy though, so I thought I would write it up in case anyone else wants to go down the same path. Pretty sure Wade will be at any rate.
New parts were a 6 3/4" 36-1 toothed wheel and sensor from DIYAutotune. That's about AU$100 worth. The trick was getting them fitted. The 505 harmonic balancer has a triple channel pulley (power steering, water pump/fan/alternator and A/C) pressed around it. There's a chance (low) that this might slip, so I preferred to bolt the wheel to the inner balancer itself.
Not very easy. The rim of it is only 6mm wide, and it's recessed relative to the pulleys, and it's not exactly on-centre (or mine wasn't at any rate). So mounting the wheel required a spacer to make up for the recess, and (I opted for) 12 5mm tapped holes in the balancer. So here we are:
That wasn't hard for you, but several weekends' careful measuring and machining for me.
Now we come to mounting the sensor. Very few suitable mounting points sprang to eye. I played with the idea of mounting it direct to the cam belt cover, but it's a flimsy thing, rubber mounted and probably prone to cracking. I ended up making a bracket going from the M10 A/C adjustment bolt on one side across to the M7 cam belt cover stud below the water pump. Made it out of 1.6mm (1/16") steel that I had lying around and braced it up so it was pretty stiff.
I was a bit worried about only having two mounting points and had a backup plan of bringing the alternator pivot bolt into action if there was too much flex. So far it seems fine with just the two mounting points. One other thing that had to be carefully considered from the outset was where the great tangle of belts were going to run and what they might lash out at if they broke. I managed to avoid the first problem. Will let you know how it goes when a belt breaks. Here it is in one of my trial mounts:
And here are a couple of photos of it fully assembled after a few weeks running with it.
It's pretty busy above the pulley and the fan's pretty close too. Adjusting the air gap was no fun (ended up taking off fan and shroud). Replacing an aircon belt won't be fun either. It's also pretty hard to see the timing marks. I think, given my time over, I'd try mounting the sensor looking up up from below. A few suitable holes tapped in the A/C-power steering brace might well have done the trick.
But it's working now and, as I said, driving has been greatly improved in several areas. I fully expected it to improve under changing conditions (i.e. acceleration) and it is dramatically improved. Much smoother. The bulk of this is undoubtedly down to the more accurate spark timing, but not all of it. I drove around for a couple of weeks with wheel and sensor mounted but not used (just to be sure they weren't hitting). The extra flywheel mass of the 450g toothed wheel held the revs up during gear changes, which smoothed upshifts noticeably.
One place I didn't expect much change was in creeping along in traffic. It used to be inclined to get into bunny hop mode, with the occasional kangaroo getting in on the action. That's all gone and I can creep on nicely with all the other happy Sydney drivers. I'm sure this is entirely down to the more accurate timing.
I've skipped over any number of blind alleys and pratfalls here, but I think I've given the guts of the job. Having spent several years running a Megasquirt with distributor based tach input I have come to the conclusion that it wasn't a good idea. I should have run fuel-only with the old mechanical distributor until I was prepared to fit a decent crank position sensor.
Now I just have to summon the enthusiasm to do the same for the 604 (which, I'm glad to say, looks a good deal easier than this was).
Have fun,
Rob.
I've done the 505 now and it has dramatically improved some aspects of driving. The job wasn't easy though, so I thought I would write it up in case anyone else wants to go down the same path. Pretty sure Wade will be at any rate.
New parts were a 6 3/4" 36-1 toothed wheel and sensor from DIYAutotune. That's about AU$100 worth. The trick was getting them fitted. The 505 harmonic balancer has a triple channel pulley (power steering, water pump/fan/alternator and A/C) pressed around it. There's a chance (low) that this might slip, so I preferred to bolt the wheel to the inner balancer itself.
Not very easy. The rim of it is only 6mm wide, and it's recessed relative to the pulleys, and it's not exactly on-centre (or mine wasn't at any rate). So mounting the wheel required a spacer to make up for the recess, and (I opted for) 12 5mm tapped holes in the balancer. So here we are:
That wasn't hard for you, but several weekends' careful measuring and machining for me.
Now we come to mounting the sensor. Very few suitable mounting points sprang to eye. I played with the idea of mounting it direct to the cam belt cover, but it's a flimsy thing, rubber mounted and probably prone to cracking. I ended up making a bracket going from the M10 A/C adjustment bolt on one side across to the M7 cam belt cover stud below the water pump. Made it out of 1.6mm (1/16") steel that I had lying around and braced it up so it was pretty stiff.
I was a bit worried about only having two mounting points and had a backup plan of bringing the alternator pivot bolt into action if there was too much flex. So far it seems fine with just the two mounting points. One other thing that had to be carefully considered from the outset was where the great tangle of belts were going to run and what they might lash out at if they broke. I managed to avoid the first problem. Will let you know how it goes when a belt breaks. Here it is in one of my trial mounts:
And here are a couple of photos of it fully assembled after a few weeks running with it.
It's pretty busy above the pulley and the fan's pretty close too. Adjusting the air gap was no fun (ended up taking off fan and shroud). Replacing an aircon belt won't be fun either. It's also pretty hard to see the timing marks. I think, given my time over, I'd try mounting the sensor looking up up from below. A few suitable holes tapped in the A/C-power steering brace might well have done the trick.
But it's working now and, as I said, driving has been greatly improved in several areas. I fully expected it to improve under changing conditions (i.e. acceleration) and it is dramatically improved. Much smoother. The bulk of this is undoubtedly down to the more accurate spark timing, but not all of it. I drove around for a couple of weeks with wheel and sensor mounted but not used (just to be sure they weren't hitting). The extra flywheel mass of the 450g toothed wheel held the revs up during gear changes, which smoothed upshifts noticeably.
One place I didn't expect much change was in creeping along in traffic. It used to be inclined to get into bunny hop mode, with the occasional kangaroo getting in on the action. That's all gone and I can creep on nicely with all the other happy Sydney drivers. I'm sure this is entirely down to the more accurate timing.
I've skipped over any number of blind alleys and pratfalls here, but I think I've given the guts of the job. Having spent several years running a Megasquirt with distributor based tach input I have come to the conclusion that it wasn't a good idea. I should have run fuel-only with the old mechanical distributor until I was prepared to fit a decent crank position sensor.
Now I just have to summon the enthusiasm to do the same for the 604 (which, I'm glad to say, looks a good deal easier than this was).
Have fun,
Rob.