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Anyone using a MSD ignition on RENIX 4.0?


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I'm getting ready to put a MSD Street Fire in my '88 4.0 Comanche. Years ago I put a MSD 6A in my '91 4.0 Cherokee and really liked it. Pretty straight forward install and didn't take very long to do. BUT that was a HO engine, totally different wiring than a RENIX. Has anyone put one in a RENIX with that weird ignition module under the coil? Any tips on how to wire it?

 

Coyote

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Found a pin out for the ignition module. Starting at the far left (closest to radiator) It's

 

connector No1

C(Tach)

B (Grounding-)

A (Ignition +)

 

connector No2

B (ECU Square wave input ignition coil interface)

A (Blank)

 

connector No3

C (Blank)

B (Blank)

A (Blank)

 

Going off my best guess according to the MSD Street Fire instructions I think the box should be hooked up like this:

 

Heavy Red (Battery -)

Heavy Black (Battery +)

Red (switched 12v+) - connector No1A

Orange (coil +) - connect to new coil

Black (coil -) - connect to new coil

Violet (magnetic + coil input) - connector No2B

Green (magnetic - coil input) - connector No1B

Gray (Tach) - connector No1C

 

Does that look correct? Or should I be using the points/amplifier (White) connection? 

 

 

 

 

 

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Your wiring appears to be correct, the only thing I would be worried about is that square wave signal - since it's coming from the ECU, I don't think you can be confident that it's the exact waveform that the MSD box is expecting, but if it just triggers on the positive edge, you're good.  And it's probably just the CPS signal, which should be perfect. I'm definitely no expert on either the Renix ECU or MSD ignition systems.  Anyways, I've heard of people using MSD boxes in Renix Cherokees before so I expect it works just fine.

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2 minutes ago, scaleless said:

Your wiring appears to be correct, the only thing I would be worried about is that square wave signal - since it's coming from the ECU, I don't think you can be confident that it's the exact waveform that the MSD box is expecting, but if it just triggers on the positive edge, you're good.  And it's probably just the CPS signal, which should be perfect. I'm definitely no expert on either the Renix ECU or MSD ignition systems.  Anyways, I've heard of people using MSD boxes in Renix Cherokees before so I expect it works just fine.

Thanks. I know the ignition module has to be bypassed, just wasn't exactly sure how to do it. I know I'm not the first person to put a MSD in a RENIX, but not having any luck finding writeups or pics. Lol

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No luck on getting the MSD box wired up. BTW I messed up the above diagram; heavy red to battery +, heavy black to battery -. I played with the wiring for about 6 hours. Tried disconnecting the ignition module and wiring from those plugs (violet/green and White; not both at the same time). Tried it from the distribution (with and without ECU connected). In desperation I tried it off of the - + coil connections in the ignition module. I was able to use a remote mount coil (the way I'll leave it configured for now), but wasn't able to get the MSD box to fire. Strange considering that's how I wired my '91 Cherokee 4.0. Basically just used the coil wires as magnet pick ups for the MSD box. At any rate I'll settle for a remote mount coil and use the MSD box on my '96 Cherokee. If anyone figures out how to wire a MSD box into a RENIX 4.0 please share the wealth.

 

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SUCCESS!!! The MSD Street Fire is connected to the RENIX 4.0 and operating as advertised. The factory tach still works, the MSD rev limiter works and it's getting multiple sparks per cylinder. Unfortunately there's not a way to completely bypass the ignition module as far as I can tell.  Many thanks to Grewsum 2Sum for his instructions.  For anyone else that wants to do it here's how to wire it up (all MSD boxes use the same wiring):

 

 

Heavy red - battery + 

Heavy black - battery -

White wire (points pick up) - the - side coil connection in ignition module 

Small red wire - the + side coil connection in ignition module (supposedly also works spliced to yellow plug wire too, but didn't try)

 

 

Pic to clarify. Ignore my crappy wiring job, just temp mounting to ops check it. I'm cleaning up the wiring and putting it in loom now. Haven't road tested it yet, but it starts up better, idles smoother, better throttle response and appears to have more power. Still finishing up installs on the closed to open cooling system and 97+ heater conversion. I'll check mpg and run some 0 to 60 times this weekend to see if there's any improvement.

 

 

 

 

 

 

 

 

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Forgot to add;

 

MSD box organge wire to new coil + and black wire to new coil -

Config box for 6 cylinder (cut the red loop)

 

All of the other wires (gray tach, violet & green mag pick up wires) are not used.

 

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Finished product. Ignition module relocated to passenger finder by fire wall (to make room for '96 style radiator overflow tank). MSD Street Fire and coil mounted on fire wall. New coil to distributor wire. All connections soldered, shrink wrapped and put in wire loom. 

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7 hours ago, Carbon River said:

That's pretty cool. Thanks for the write up.  Were you having issues with the stock ignition?  Does it make a big difference?

 

Thanks. The stock ignition was ok, nothing major wrong. It was getting hard to start, idle was a little rough and acceleration didn't seem quite right. I'm pretty sure that was the original coil and it was on its last leg. I was converting from a closed cooling system to a 97+ open cooling system and needed to relocate the ignition module and coil so I could put a factory '96 XJ radiator overflow bottle there. Still not completely done with the conversion yet, so I've only cranked it up a few times, let it idle, played with the acceleration, ect. Should be all done and back on the road again by this weekend. I can give a more definitive answer on exact improvements then. In the meantime it does start much easier, idles smoother and the throttle response seems better. If you have to buy everything new, total cost for the MSD Street Fire, coil and extended coil wire is less than $250. I already had the MSD Street Fire from another project and was planning replacing the coil anyways so it was worth it to me. After I drive it for a bit I can post the 0-60 and mpg improvements (if any) so you can decide if it's worth it to you.

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Got to do some 0 to 60 testing on the truck today. Had a hard time keeping the tires from breaking loose and squealing which should say something about the improvement in power. If I had a perfectly straight, level, dry strip of road with good tires I'm sure it would do better. For now, it was a 1.5 second decrease in 0 - 60 times (previous best 7.77, current 6.27). Won't be able to tell if there's any mgp improvement until I get done messing with 0 - 60 tests. Lol I also replaced the clutch fan with electric fans and a high flow water pump (supposed to be less hp consumption) all at the same time. Not sure how much was due to that vs the MSD box and coil, but either way I'll gladly take a 19% improvement. It was definitely worth the time and money to me. 😁

PXL_20210409_163012888.jpg

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5 minutes ago, 89eliminator said:

thanks for the info on all this.  i've been looking at doing something similar for a while not but could never really find much info out there on whats been done to make it work. 

No problem, glad it helps. Once I got the wiring figured out the rest of the process was pretty easy. It only takes a little less than 2 hours to relocate the ignition module, mount the MSD box and coil, make a new coil wire and wire everything up/put it in looms and zip tie. The hardest part was soldering new leads to the ignition module coil contacts. I would have liked to completely by pass the ignition module, but I couldn't figure out a way to do it. The ECU uses the ignition module to control the timing advance functions and I don't think there's a way to get around that. Good luck and I hope the ignition upgrade works as well for you as it has for me.

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1 minute ago, Coyote said:

No problem, glad it helps. Once I got the wiring figured out the rest of the process was pretty easy. It only takes a little less than 2 hours to relocate the ignition module, mount the MSD box and coil, make a new coil wire and wire everything up/put it in looms and zip tie. The hardest part was soldering new leads to the ignition module coil contacts. I would have liked to completely by pass the ignition module, but I couldn't figure out a way to do it. The ECU uses the ignition module to control the timing advance functions and I don't think there's a way to get around that. Good luck and I hope the ignition upgrade works as well for you as it has for me.

 

what coil did you use?

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I don't remember the model number, but it's the Summit brand 55k volt one (about $50). You can do the MSD box with the stock coil if you want. Just have to flip the coil to the side and bolt it back into the ignition module, sort of hanging in the air off of the right side (towards fire wall). My coil was the factory orginal and questionable maintenance history so I just went ahead and replaced it. I have no idea how that thing managed to last this long, but they must of used some pretty decent quality parts at the factory. Lol BTW with the coil on the firewall the coil to distributor wire is too short. Checked the old plug wires and none of them are long enough. Ended up using a single universal speak plug wire from Advance Auto ($15 in stock in most stores). I would have liked a black one for a more subdued/factory look, but the red was all they had at the time.

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On 4/10/2021 at 9:55 AM, Coyote said:

I don't remember the model number, but it's the Summit brand 55k volt one (about $50). You can do the MSD box with the stock coil if you want. Just have to flip the coil to the side and bolt it back into the ignition module, sort of hanging in the air off of the right side (towards fire wall). My coil was the factory orginal and questionable maintenance history so I just went ahead and replaced it. I have no idea how that thing managed to last this long, but they must of used some pretty decent quality parts at the factory. Lol BTW with the coil on the firewall the coil to distributor wire is too short. Checked the old plug wires and none of them are long enough. Ended up using a single universal speak plug wire from Advance Auto ($15 in stock in most stores). I would have liked a black one for a more subdued/factory look, but the red was all they had at the time.

 

well you've convinced me enough that the parts for mine should be here on wednesday lol.  i'm wanting the rev limiter feature more than anything because i feel like i'm 1 over-rev away from blowing the motor.  

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1 hour ago, 89eliminator said:

 

well you've convinced me enough that the parts for mine should be here on wednesday lol.  i'm wanting the rev limiter feature more than anything because i feel like i'm 1 over-rev away from blowing the motor.  

Go for it, you won't be disappointed. 😁 It's pretty simple, but if you run into issues pm me and I can walk you through it. I set my rev limiter at 4800. Not sure if that's the ideal setting, but it seemed like a good compromise between red line (5k) and hitting the limiter all the time (4k). Maybe 4500 might be better? 🤷‍♂️ The rev limiter seems to be pretty accurate according to my REM. When the switches are set to 4800, it's 4800 dead on the nose.

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