MysticBowtie

I want to start a thread of progress on the PCM conversion that I'm doing on my '94 Z28. I have been having huge drivability issues ever since I put my new setup together. Going into this, I currently have the following essentials:

- 383
- D1SC 15+psi (it pegs my 15 psi gauge)
- All interior accessories (A/C, large stereo system, etc)
- T56
- LTCC with LS1 coil per cylinder
- 85lb injectors
- speed density tune by Ed Wright
- huge front mounted intercooler
- all aluminum tubing after the blower
- a plethora of various other go fast parts

First, I would like to point out that Ed Wright is literally the nicest individual that I have ever met in the car world, and tuning-wise, the smartest that I have met. This man bent over backwards to get my car tuned, tuning it remotely through dyno logs that I emailed to him, and he would then email me a tune file that I uploaded to the car. Unfortunately, he had a '94 OBD1 PCM to work with. When he would tune the car (twice), the car would leave the dyno and run like a champ - until the weather changed. This is not normal on his tunes, but the factory PCM just can't keep up with all the boost on a very built motor. This change is in no way a negative reflection on his work!

The car last made 650rwhp in April of 2013. Three days after the tune, I had an event. The temperature outside (in Texas) rose 20 degrees in those 3 days to 90. I drove the car to the track in the morning. Once the heat of the day came, the motor would lean out under boost and fall on its face. I couldn't get past 3000 rpm. Currently, and all summer, the best I can do is drive out of boost, and it still has problems starting and will not idle with the A/C on (which it used to do). I finally have decided that my PCM is the problem. Due to the limits of it, it is very hard to diagnose problems, log good data without a dyno, etc.

Today I purchased all the stuff to make the car capable of an LS1 PCM to completely ditch the optispark. This includes a cam sensor, 24X reluctor ring, etc. Instead of the LS1 computer though, I have opted for the MegaSquirt MS3 Pro. From the info I have gathered, it has a faster processor, has the ability to update the tune manually while the engine is running, works with wideband O2 sensors, and is apparently slightly self-correcting. Once everything is done, it looks like I will be just under $3000 for the cost. This includes all the LS1 conversion stuff (I already have the coils and plug wires), a brand new engine wiring harness, 2 wideband O2 sensors, and the MS3 stuff. There are kits specific to the LT1 under $1000 that use the optispark for a cam signal, but allow for LS1 coils to be used. I however, want the newest technology I can get, and like everybody, hate the opti.

My current knowledge of computer tuning pretty much stops after the ability to read an air/fuel ratio gauge. I'm not being modest, I just never cared about tuning, and have relied on others to do it for me. I'm excited to see how smart this system makes me, or how dumb it makes me feel....

I'm pretty sure that this system will allow me to drive my car whenever I want (no matter the weather), easily troubleshoot problems, and possible gain me more power. I should have done a stand-alone engine management system much earlier, but I was being cheap (in obviously the wrong area). I am glad that I waited though otherwise I would have just done the LS computer swap instead of this much more advanced system.

I'm waiting for the mechanical pieces to come in the mail, and will install them ASAP. Unfortunately, with the way everything is shoved in my engine bay, the intercooler piping, blower, and a bunch of other stuff will have to come out, so it will be a chore. I'm going to update this thread as often as I can for other's education. Feel free to let me know of any advice if you have MegaSquirt experience.

Cheers

grim_reaper888

did you ever make any headway on this? Im currently doin the MS3 Pro on my lt1 for a turbo build. having trouble getting crank signal to register.

MysticBowtie

I'm having the exact same problem. I'm going to swap the crank sensor with a new one and see if that changes anything. If that doesn't work, then I'm going to add a 1k resistor. Aside from that, everything else seems to be communicating great. I just need some free time to get back under the car. Let me know if you figure anything out, and I'll post up my results when I get them.

grim_reaper888

i tried swapping to a new 96 camaro sensor( which looks different than the one included with the 24x kit) and nothing....

did you wire the ground side of the sensors to the CKP CMP - or to sensor ground?

this is what the 24x kit shows
A 20ga DARK BLUE/WHITE Sensor Signal
B 20ga YELLOW/BLACK Low ReferencePCM or ECM typically provides low reference
C 20ga LIGHT GREEN 12V ReferencePCM or ECM typically provides reference
voltage

But this is the stock lt1 crank sensor A and C are switched.
A 12volt ref pink
B Low ref Pink/black
C CKP sensor signal Yellow


im having issues getting my TPS to read too. this is how im wired

TPS

A - Gray = 5 volt reference WIRED TO 5 VOLT REF WIRE
B - Black = ground WIRED TO BLACK WITH WHITE STRIPE SENSOR GROUND
C - Dark Blue = Throttle Position Sensor signal WIRED TO TPS IN

grim_reaper888

finally got it to fire! the 1 k resistor seemed to do the trick


But this is the stock lt1 crank sensor A and C are switched compared to 24x diagram

A 12volt ref pink
B Low ref Pink/black 1 K resistor between A and C
C CKP sensor signal Yellow

MysticBowtie

Fantastic!! My new crank sensor is waiting for me to pick it up from the parts store. Hopefully I can get it in tonight and crank it.

Did you have to do any timing adjustments before the initial fire? That is all I have left to check.

The way I wired the MS3 was by cutting the wires at the original PCM harness and wiring them to new connectors.

For the TPS, connected pin 22 from the ECM's C plug to the MS3's White plug, pin #9 and had success.

grim_reaper888

My tps just had a bad connection in one of my solders. Got it working and calibrated.
Ahhhh I built an entire new harness from the ms3pro 8 foot harness.
I fired off of what it has basically preset. I don't have my turbo on right now so
I couldn't run it without oil lines hooked up

grim_reaper888

any luck?

MysticBowtie

Nope.

I can't get it to sync or show RPM's. The only thing I can think is that I don't have the fuel pump hooked up through the MS3, but that shouldn't affect the RPM reading - I wouldn't think.

I'm going to keep at it.

grim_reaper888

did you go with a oem camaro crank sensor or the one that came with the 24x kit?

MysticBowtie

OEM replacement. I have the resistor connected. I'm going to pull it off and see what happens.

grim_reaper888

thats my wiring

A 12volt ref pink to 12 volt source
B Low ref Pink/black to black with white stripe sensor ground
C CKP sensor signal Yellow to CKP positive wire(negative gets capped off)

resistor between A and C

MysticBowtie

That's exactly how I have it. I must have something else wrong elsewhere. I'm taking a break from it tonight, but everything else is connected, tested, and ready! Once or reads the rpm, I should be able to crank it up and get on the road. So close..... haha - there's always soothing that has to play dirty.

MysticBowtie

I finally got back into it tonight. I finally found the problem. I had an intermittent problem with my 12 volt constant. It would show good on my multimeter, but would fault under cranking.

Now that I have an RPM reading, I can test the timing and crank it. I'll probably get to that this weekend.

With the exception of my old wiring harness, this install has been easier than I anticipated. I want to get everything wired correctly, then I'm going to send the harness to painless wiring,and have them make me one that matches. I wanted all my cuts and solder joints to be on the original one.

grim_reaper888

nice!! ya i got mine up and driving, the self tuning is really nice, makes for a decent baseline to start with.