Another 72-2 wheel...

[Redbird]

Guess it's about time I posted my build. I started this months ago but finally got everything together and made some progress.
I have a 91 Pontiac Firebird with a fuel injected 350, freshly rebuilt, and built for boost. I started this project with a big Paxton Novi 2000 blower, all the extra pulleys and plumbing off the crank and front of the engine made it tough to mount a trigger wheel on the front of the engine so I decided to use the distributor and a 72 tooth wheel. Recently plans changed and I wound up changing things around to a T-70 turbo, freeing up the front of the engine. I'm still going to go with the 72 tooth setup cause I already bought all the darn parts This was going to be step one towards a full megasquirt setup so in the future I can always add the crank trigger wheel and modify the distributor for cam sync for sequential injection. Now on with the show.....


The wheel is a spur gear, thank you Dean, drilled out and hand filed for a press fit on the end of the distributor shaft in place of the rotor. Threw the shaft in the freezer and the gear in the oven and carefully pressed the gear onto the shaft, first time it went on crooked and had to beat the gear off the shaft. A little forethought and a few thick washers notched for later removal made the second attempt go on straight as an arrow, lined up even with the factory pickup magnets.



I decided to keep the factory ignition module in place to keep the stock computer happy, providing an expected signal to fire the fuel injectors and tach signal.

I also hacked an older large base distributor to provide for a cover to protect the wheel and sensor. Gonna attach it to the smaller base and use the larger distributor cap which should cover everything with minor modification. All that remains is fab up a mount for the vr sensor out of an RX7, again thanks to Dean and others for already being the test mule on the 72 tooth setups.

[dr.occa]

that's great to see another 72-2 setup materialize.

i don't see why this wouldn't also work for the 4AGE using the factory distributor and performing a similar modification but using the vr/magnetic pickup already housed in it.

[NITROPIXIE]

How heavy is that 72-2 setup, does it not require more effort by the engine to turn it, ie like having a heavier flywheel. Or is it not really noticeable????

[Redbird]

Definitely heavier than the stock rotor would be, but on the cam it's spinning half crank speed and the inertia wouldn't be very much compared to a heavier flywheel since it's such a small diameter. All in all I dont see it as a much of a problem, of course I haven't run it yet either. Finished most of it off last night, all that really remains is to mount the sensor. Borrowed an oscillioscope from a friend at work to verify I have a good signal then it's going in the car. Still waiting on some other parts and need to fab up the downpipe for the turbo but she's getting there, hopefully early next month it'll be running.

[NITROPIXIE]

All the best for that first start coming up and fingers crossed.

Have you thought about timing chain/belt maintenance? Surely that would have to be more frequent due to the added weight and constant heavy acceleration and deceleration could stretch them causing the timing to go out abit. And increased wear in the camshaft to dizzy spindle gears.

Could be interesting to see if it affects them at all. Maybe would be a good idea to make a note/measurement of parameters before you start her up.

[Redbird]

Only thing I'm worried about is the distributor and cam gear wear, that is something I'll be keeping an eye on, I'll also be modding the distributor to see the gears get a little extra oil which a common small block chevy trick. Otherwise I dont see it adding much in way of wear and tear on anything else. I'd guess a huge lift cam and high spring pressures would put more of a strain on timing chains than a little extra weight on the distributor. I'll be keeping a close eye on everything though. She'll be getting alot more attention than the average daily driver and the little things will certainly be noticed.

[Redbird]

Looks like it about done. Sensor is mounted and tested, at least a basic test. Hooked it up to the scope last night and spun it up by hand. Signal looked pretty good, could see the missing tooth passing in the wave clearly. Need to rig up something to spin it up steady to do a proper test, old but good scope. I think I can justify a cheap USB scope for automotive work, be nice to spin it by hand a bit and review the output on screen.



Using the base cut out of a large base distributor and modified cap for a cover. The top extends up just a bit too high on the gear so I need to rig some kind of an extension and a top. Just waiting on a new distributor gear and give it a thorough cleaning and final assembly and I can start installing the electronics.

[Redbird]

Real close to firing this thing up now, minus turbo till I can get it to my welder to finish up. I'm finding the best place to mount the pair of coils is directly above the distributor. Would there be any issues with noise from the coils affecting the vr sensor in the distributor? We're only talking a matter of inches above the sensor. If so any ideas to isolate the sensor? The wires themselves will be shielded, just need a way to shield the sensor if necessary before I finalize the layout, and make the ignition wires.

[NITROPIXIE]

Fingers crossed for the initial start up, keep us posted.

No you shouldn't have any problems with interferance from the coil packs, just keep the wires shielded and you should be fine. I've only twisted my wires together without a shield and i don't have a problem with it.

[Redbird]

Well first attempt at startup is a wash. Got everything together for a first fire and started with a dead battery. Went to the store just before close to get a new battery, got home cranked it over and just spins. No spark, and no fuel, two separate systems both dead.

Got the system apart now going over everything, dont have the scope anymore so I can only assume I'm still getting a good signal from the wheel, and I did try reversing the polarity. Got to get the EDIS module tested today. On the fuel side I may have a bad pickup coil, which will supply signal to fire the injectors. I'll pour through the wiring and make sure all is well.

[Redbird]

Just poured through the schematics and realized I dont have pin 7 on the edis hooked up to anything, just the main ground on 10. Is this necessary? I have the shields grounded on the other end. Is pin 7 connected internally to pin 10 or is this maybe my missing link?

[Redbird]

Well I went to every parts store in the area and no one can test an EDIS8. After a bit of searching I stumbled across a page with instructions to simulate a vr signal with a headphone jack and wave file so I guess thats the way I'm going. If I cant get any spark or at least communication via PIP/SAW I'll ebay another module and go from there.

[NITROPIXIE]

Did you say you had it working before?? It could be you have all the pins the wrong way round, possibly?? I don't think i have my pin 7 connected (will double check tomorrow) on EDIS 4 and I have no problems, as i don't have any shielding.

Have you done continuity and insulation checks on each bit of wiring with all units disconnected just too treble check for any shorts or breaks?? I think the EDIS units are pretty robust. Could try without megajolt and try to achieve the basic 10 degrees advance using EDIS, VR sensor and coil pack. Leave the spark plugs out of the engine to watch for any spark and reduce strain on starter motor. Check your wiring again making sure you do use the EDIS 8 diagram and hopefully at will become apparent.

Best of luck and keep patient.

[Redbird]

Never had it working before. Double checked all the connections, continuity tests all good. Tried the simulated vr input and still got no spark and no rpm reading on the MJLJ. I've tried everything I can think of short of replacing the EDIS. I've got another EDIS coming soon, hopefully that will yield results, wont know anything else untill it arrives.

[Redbird]

Well one step closer, got the injectors firing. Didn't have 12v going to the ignition module to provide reference pulse to the ECU. Lol stood out in a downpour this morning after I had the brainstorm that I forgot that wire to test it. Still just waiting on the 2nd EDIS module now.