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DIY Diagnostic system

87manche

NAXJA Forum User
Location
Ohio
So I had an idea the other day. Someone tell me if it's decent or if I'm off my rocker.
I have a DMM that has a serial port for data logging. I also have a laptop PC. If I were to tap into the sensors wiring harness, turn on the logging software and then log the voltages as I went for a drive would I get accurate readings. I could stash the DMM under the hood somewhere to keep the voltage taps short, then just run a serial connector to the firewall. I know that I could only monitor one sensor at a time, but I would have a nice realt time data dump saved that I could look at.
useful? Worth building? I've already got all the parts, it's just a matter of putting it together.
 
Sounds good to me. If it will work as planned, (does this ever REALLY happen) it would be GREAT to be able to start base lining the RENIX computer, and from there, MAYBE, just maybe, figure out how to re-program the thing. Please, let me, and others of course, know how this works out.
 
Potentially useful, yes, but what are you going to do with the logged data that you can't do right now with your dash gauges?

I have a similar setup for my '86 Camaro that uses a serial connection and taps right into the ALDL data connector under the dashboard. GM fuel injection systems have been hacked for a looong time now and there are quite a few free programs out there that do most of the grunt work for you. Not to mention simplified EPROM programming software that usually doesn't require using a hex editor anymore.

Personally, I think it'd be great if we could gain access to Jeep's fuel and timing calibration inside the onboard ECM, but I haven't seen any worthwhile efforts thus far. I guess DC didn't have as many "generous" engineers that GM did ;).

What sensors were you planning on logging? The only ones I could think of that may be worthwhile would be the oxygen sensor and the MAP sensor. I doubt the raw feed from the oxygen sensor would be of much use, however, since I'm fairly sure Jeep used a narrow-band sensor that doesn't tell the ECM precisely the air/fuel ratio (it only tells it how far away from an ideal ratio it is). Monitoring MAP voltage might be worthwhile if you could equate it to engine vacuum and measure the amount of fuel added versus the engine load. Unfortunately, these are all very coarse ways of doing something that might not have tuning value that's worth the hassle.

My friend and I are working on a Renix-based 4.0L for his YJ. We plan on stroking it to 4.7L and adding a few other goodies. Many have done this without any problems using the factory computer and calibration, but there's so much more to be gained if the system were truly tunable (or hackable, depending on how you look at it). My goal is to swap a GM ECM into his YJ, along with a custom wiring harness and GM sensors. Provided the calibration is tuned properly, it should work very well.
 
Hey Iroc, you answered your own q. about why. If nothing else, it is a place to start with figureing out the RENIX code, then later (hopefully), change it. As for the GM comp, are you planning on using the base programming for the 4.3 V-6?
 
I don't think data from a single sensor is going to be of much value unless you have an intermittant sensor that your trying to diagnose. Everyone want to reverse engineer the renix code but................................
 
ren said:
Hey Iroc, you answered your own q. about why. If nothing else, it is a place to start with figureing out the RENIX code, then later (hopefully), change it. As for the GM comp, are you planning on using the base programming for the 4.3 V-6?

Well, I suppose... but hacking the code would still be a major undertaking, something that would be quite difficult unless one had a thorough knowledge of assembly language programming. The GM enthusiasts have been doing this since their system came out in the mid-1980s; there's almost twenty years of DIY history with this thing. It might be a case of "too little, too late" with the Jeep stuff. Don't get me wrong, though; I think it would be awesome if somebody could reverse-engineer the onboard computer.

To be honest, I really wasn't sure what calibration I was going to start with. The 4.3 might work well, but I'm still leery about firing up a fresh engine without knowing what it's going to do. Until that oxygen sensor comes online you're working with hard-coded data, so I'll probably invest in an on-the-fly calibration system and an independent wideband oxygen sensor to start monitoring from the beginning. It might also be helpful to run some computerized analysis to get a rough idea of how a stroked six is going to differ from a vee motor.
 
well, it was more for diagnosing individual components than reverse engineering the system. I'd like to know real time what the map sensor voltage is, and equate that to engine vacuum. Things of that sort.
 
so, I've decided to buld this just for kicks.
Anyone know where I can get connectors that match the OEM ones. I'd like to build some connectors that go between the harness and sensor, so I can just plug in the DMM. I think that's the only way I could keep the probes on with all the vibes, inline connectors with bannana plugs on the proepr wires.
 
Most of the OEMR connectors on RENIX are "Delco Weatherpacks," you should be able to find them in the HELP! section or the electrical section of your local part house. Also, Googling "Weatherpack" will turn up distributors in bulk - I know MSD carried them, I think Mallory carries them, and I'm sure Summit Racing and Jeg's Performance will have them as well.

They're available in up to six poles, and are usually flat (poles arranged linearly.) The square ones can be a little more difficult to find, but stick to it - I've seen them out there!

I'd be interested in hearing what you come up with - either here, or posted to my RENIX projects (groups.yahoo.com/group/RENIXPower)

5-90
 
you sir are very helpful. I will buy a few in the coming days and fab up som inline "t" connectors. I will be sure to post my baseline values with engine running and at different throttle/load conditions. My DMM software does very nice timeline graphs. I was going to take my hacked CVS camcorder and put it so I can record the gauges. That way I can see what indicated RPM, Speed and oil pressure are at any given time during my data collection.
This project s more for kicks than anything useful. THe only real benefit will be my greater understanding of the RENIX engine system, and the ability to see the real-tie voltages for better component diag.
I found a place with all the pieces for the weatherpack connectors.
http://happyterminals.com/index.php?cPath=25
Seems they have all the inividual pieces also, might be useful for people with damaged pins. I had to hardwire my CPS because of damaged pins in the connector.
 
Don't forget - if you're going to "repair" a weatherpack terminal, you'll need the terminal removal tools as well - I know Motormite (HELP!) and Dorma both make them...

You're welcome - what do you expect from the guy that owns four RENIX XJ's (all I've got... 87, 88, & two 89's.) I've been wanting to redesign a few things for a while, just haven't gotten 'round to it yet.)

I'd still like to see your results, especially if you can correlate them with driving conditions and vehicle parameters. I've been kicking around the idea of getting a "data acquisition unit" and doing something similar myself - especially since most DAU's can be had with enough channels to have everything get "trapped" at once! Maybe when I restomod my 88 - I was going to build a new gage panel for it anyhow (using mostly aircraft gages.)

5-90
 
if someone can give me all the specs of what a DRB machine did then I might be able to come up with a cheap DIY unit. If it's just voltage and time monitoring then there's no reason a few fcpga units can't handle the math and collection. Electronics are by far cheaper and faster than when they first came out.
 
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