RENIX ECM Ground Question

Does the RENIX ECM make its ground through the metal case, or is there a wire in the harness that goes out to a ground point?

oldradiostuff said:

Does the RENIX ECM make its ground through the metal case, or is there a wire in the harness that goes out to a ground point?

Click to expand...

I'd have to check. However, the most common ground problem WRT the RENIX ECU isn't with the ECU proper, it's with the ground reference to the chassis. The only ground path for the chassis (from the factory) is that asinine open braid from the firewall to the cylinder head - adding a secondary ground from the battery directly to the chassis (bypassing the engine) tends to solve most RENIX ground troubles.

What are your symptoms?

Slightly wandering and slightly rough idle when cold (open loop). I get a very very slight oscillation in idle when warm (closed loop), but really maybe a 40-50 rpm up and down.

I've cleaned up the ground at the block and put in a new negative battery cable to that point. I have cleaned up the connection points on the braid. The braid is old and I think I will replace it soon.

I've been considering putting in one of these:

http://www.ronfrancis.com/images/part-pic138.jpg

And tying all the ground points together in a star ground configuration so I'm sure everything is at the same ground potential.

I think I may have a small vacuum leak contributing to the idle, but I'm not sure if it would manifest with the difference between open loop and closed loop modes, that points more to electrical to me, what do you think? I have gone over every vacuum connection and line several times, as well as the throttle body and intake gasket areas, and I can't find a vac leak.

Thanks.
Dave

oldradiostuff said:

Slightly wandering and slightly rough idle when cold (open loop). I get a very very slight oscillation in idle when warm (closed loop), but really maybe a 40-50 rpm up and down.

I've cleaned up the ground at the block and put in a new negative battery cable to that point. I have cleaned up the connection points on the braid. The braid is old and I think I will replace it soon.

I've been considering putting in one of these:

http://www.ronfrancis.com/images/part-pic138.jpg

And tying all the ground points together in a star ground configuration so I'm sure everything is at the same ground potential.

I think I may have a small vacuum leak contributing to the idle, but I'm not sure if it would manifest with the difference between open loop and closed loop modes, that points more to electrical to me, what do you think?

Thanks.
Dave

Click to expand...

You could have a small vacuum leak (very common on side-draft inline sixes like ours,) but that should go away by the time you get to closed loop operation. Check your manifold screws anyhow - I'm sure you'll find at least one of them has loosened...

I'd suggest that you add a ground directly to the chassis from your battery. Also, clean up the "contact patches" for the chassis grounds - strip a small patch down to bare metal (about the size of a postage stamp,) paint with some variety of corrosion inhibitor (I use and like - and sell! - Gardner-Bender Ox-Gard. Check the electrical section at your local hardware store - do not use "liquid electrical tape" or WD-40!) and reassemble. Grounding to a painted surface is silly, and is only done because large companies don't like to spend the money on labour or extra materials. Clean up the contact patch for the firewall ground as well - and I believe there are a couple of chassis grounds on the fender liners that could benefit from that sort of treatment as well. That would have a similar effect to your adding the ground Buss bar - without spending anywhere near as much money.

(You know, it's amazing just how many automotive electrical problems I've traced to shonky grounds...)

You'll still have your "star ground" - it will be an electrical star, not a physical star - once you clean up your grounds and attach/protect them properly. It's kinda like the difference between a "logical drive" and a "physical drive" - they're usually the same thing, but they are sometimes not (you can have several "logical drives" in one "physical drive" - I've set them up that way from time to time...)

The main reason I'm wondering about how the ECM module is grounded is ground continuity. If it is grounded through the case or near the mounting location under the dash, I thought it might be a good idea to run a ground wire out from this point to a chassis ground under the hood. I realize the braid and the ECm are both tied to the chassis, but I suspect there are sheet metal seams between the two, and after 18 years there is probably corrosion and dirt in those seams, which could potentially cause some high resistance ground pathways. I'm thinking I want to tie everything together with fresh connections.

Thanks for the input.
Dave

oldradiostuff said:

The main reason I'm wondering about how the ECM module is grounded is ground continuity. If it is grounded through the case or near the mounting location under the dash, I thought it might be a good idea to run a ground wire out from this point to a chassis ground under the hood. I realize the braid and the ECm are both tied to the chassis, but I suspect there are sheet metal seams between the two, and after 18 years there is probably corrosion and dirt in those seams, which could potentially cause some high resistance ground pathways. I'm thinking I want to tie everything together with fresh connections.

Thanks for the input.
Dave

Click to expand...

Gah. Now I'm going to have to remember where I put that RENIX ECU I've got that's had the case stripped off...