CPS modification help!

I have been searching for several hours no and I don't want to bore you with another CPS question, but I feel that I have no choice. So here we go: I have an 88 Renix 4.0 and I too am tired of the long cranking time normally associated w/ Renix, but I remember reading somewhere a while back about modifying the CPS to bring it closer to the flywheel to produce a stronger signal faster, thus faster start up time. Any help would be very appreciated.

I've never heard that one but would be interested to know what the experts think. You could PM Ecomike and 5-90 they seem to be the Renix experts on here.

Good Idea. I'll have to give that a try. Hope at least one of them knows what I am talking about. If not, at least we'll have a new topic.

If that's true, then maybe the hesco kit will help, if they make it for Renix

I thought about that, but I don't want to drop $289 to replace a sensor I just replaced (oem) and that's working fine. Maybe if it dies then I'll try.

I remember reading about it, but it was in relation to the hesco kit- if I remember right, there was an entire paragraph that stated something about the closeness of the sensor to the wheel made the signal superior to what a renix system produces-

there were some mods to move the sensor left/right to adjust- but Ive not seen any for depth to flywheel ring. I had played with an idea awhile back of adding a magnet to increase field, but never went further with it-

I've got a spare (used) OEM type, maybe I'll play around with it when I get bored. Then again, it's such a PITA that I don't know if I could get that bored. LOL

mikeforte said:

I've never heard that one but would be interested to know what the experts think. You could PM Ecomike and 5-90 they seem to be the Renix experts on here.

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So, please don't make it a PM, we could all benefit from that info.

I'd like to see a sticky (not saying it doesn't exist) that has a bona fide write up on the whole CPS process. I have 215K+ on the clock, I don't know if the PO ever changed the CPS, TPS, NSS (or BFD for that matter). But knowing how to change all that and test and adjust in language for the regular shade tree mechanic.

Stuff like this:

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

is invaluable to me. It just explains more stuff than 40 posts of guys saying "...well, I heard that...".

All I need is a stright answer I can understand, cuz I ain't too smart, but I can turn a wrench and read instructions.

Thanks:cheers:

What your looking to do is make the CPS adjustable. All you need to do is pull the CPS and oval out the mounting holes to be wider. That's it. This will allow you to slide the CPS up higher on the flywheel, thus closer and the end result being what you want. But 4.0 are notorious for their slow start up time. So really no matter what you do your still going to have some type of delay.


:wave: Good Luck with it.

ParadiseXJ said:

So, please don't make it a PM, we could all benefit from that info.

I'd like to see a sticky (not saying it doesn't exist) that has a bona fide write up on the whole CPS process. I have 215K+ on the clock, I don't know if the PO ever changed the CPS, TPS, NSS (or BFD for that matter). But knowing how to change all that and test and adjust in language for the regular shade tree mechanic.

Stuff like this:

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

is invaluable to me. It just explains more stuff than 40 posts of guys saying "...well, I heard that...".

All I need is a stright answer I can understand, cuz I ain't too smart, but I can turn a wrench and read instructions.

Thanks:cheers:

Click to expand...

My intent was to PM them to ask if they have ever heard of such a thing. If yes then have them post up how to do the modification. If they are as in the dark as me then by all means we need to know that it is a fantasy. I just wanted to ask him to contact the experts. They may be hanging around on another area and PMs pop up on my screen whenever I get one, so I figured it was the same for them. JMHO. One of them will chime in shortly "mark my words".

It's not really a matter of a needing a stronger signal, but rather that the engine rpm needs to be above a certain amount (200 rpm?) for a few revolutions before the Renix computer figures everything out. Anything that improves the crank speed should help. For example, cleaning up the battery contacts and replacing cables with heavier gauge will help.

There was a thread last year sometime, where we discussed adding a capacitor across the CPS to boost the signal. I did some measurements and found that it did boost the voltage, but adding too much would cause stumbling problems at higher rpms. It made no noticeable difference in cranking time.

Another quick thought , is it just the fuel that is delayed or is it spark also? The reason that I am asking is that I had a Volvo that had a cold start injector that was active when the starter was engaged. I wonder if something like that is plausible on Jeeps?

Long crank times are programmed into RENIX, and they get longer as your mains deterioriate (or your battery. Or you starter motor. Or...)

Essentially, the RENIX system doesn't start firing fuel injection or ignition until it reads 300rpm at the crankshaft position sensor and gets a valid SYNC signal from the camshaft position sensor. No reason for this is given, and it's possible for the RENIX setup to "guess" a firing order without a SYNC signal - I've experimented with this.

Typically, replacing the mains cables will shorten RENIX startup times - due to the clean connections. Also, replacing them with a rather larger cable (OEM is, as I recall, 6AWG) will help, since the larger cable can flow more current without any trouble.

Also, check the ground strap from the cylinder head to the firewall - this is informally known as "the RENIX killer" - it's the only ground from the chassis to the battery, by way of the engine block. This usually wants replacing after 10-12 years, as it soaks up just about everything. Adding a ground from the battery directly to the chassis can also help here, since you'll be improving the ground return for the various sensors and the ECU.

I'd be loath to "adjust" the CPS to ride closer to the flywheel/flexplate - that flying height is already fairly low, and it's rather easy to smack the thing on the teeth on the flywheel/flexplate anyhow. There was a TSB to correct a weak CPS signal some years ago - and a wiring kit - that ran the CPS directly into the ECU, instead of by way of the bulkhead connector. However, that was to correct a "weak" signal caused by wiring - and most of those have long since been ironed out.

You may also find it useful to remove the terminals from the harness connector (tools to do so are readily available at any local that carries the "HELP!" line) and clean them. Cheap toothpaste will work neatly for this, if you rinse thoroughly. Toothpaste (not gel!) is a very mild abrasive that works well for removing oxidation on electrical terminals.

There is a "high altitude" CPS available - but it doesn't adjust the flying height of the sensor, merely the location at which it reads (thus advancing the timing slightly, as I recall. I've not found a need for one - I've taken RENIX rigs pretty much everywhere without serious incident.)

Again, I would not "enlarge" the holes in the sensor bracket - it's too easy to smack the sensor tip into the flywheel. Even when I notch the sensor to make it easier to install and remove, I'll leave the "back" (outside) of the holes alone so it won't sit any closer or farther away from the flywheel.

I'll try the improved cables, sounds a hell of a lot easier and far more reasonable. Thanks for the info everyone.

I did what 5-90 recommends, a good battery, a good starter, clean grounds with a couple of extra added, clean sensor connectors and grounds. Bypassed the C-101 connector with my CPS wires and made the wire run for the CPS as short as practical.
My ignition system is in pretty good shape. Good plugs, wires, distributor cap and clean connections between the coil and module.
Mine started up in 30 degree weather after sitting for a couple of weeks, on the count of four, I'm a happy Renix owner. Now if it only lasts for awhile.

Shoot, Mine does that and didn't do any of those mods buddy. But hey anything you do will help prolong the life. Glad to here your satisfied.

Jeep on man!

MiNi Beast said:

Shoot, Mine does that and didn't do any of those mods buddy. But hey anything you do will help prolong the life. Glad to here your satisfied.

Jeep on man!

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Renix is a different beast. Mine used to take twice as long cranking to get it running; before the massage.