88 no-spark (was: CPS woes)

[tetrad]

I did some work on the Comanche (ground refreshing, full brake job including magic prop valve bleeding, plugs, wires, and distr-cap/rotor) and when I buttoned it all back up I had a no-spark condition.  I pulled the ignition coil and shined up the leads.  I have 12V to the yellow plug below the ignition coil.  I have roughly 36-38 PSI on the fuel rail.  While replacing plugs, I did a compression test and have 130+ on all cylinders.  I just upgraded to a gauge-cluster (haven't run it since then) and my RPM is nearly pegged to 0 -- it bounces a bit but I think that's just from the Jeep rocking from the starter.  Are the RPMs supposed to register during a crank?  And if so, it reads that off of the CPS?

 

I have an induction style spark indicator that you just lay on top of the wires.  I tested it on the XJ and it definitely lit up.  Nothing on the MJ on the IC to distr wire or any distr wire to plug.

 

It sounds like the most likely culprit is the CPS, so I went and got two from the parts store (Carquest, one was a store brand, one was a Wells).  They both are testing marginal out of the box (0.2 to 0.3 VAC measured with 1 analog and 2 digital multimeters).  The one I pulled off was pretty gunked up, so I cleaned it up and at some point here I'll try throwing it back on.  I didn't get a good reading on it before pulling it (somewhere above 0 but below 0.5 VAC).  Is it worth trying to slot or expand one of the mounting holes and get it closer to the flexplate?

 

Before I hit the parts store, I called the local Jeep dealer to try to get the CPS straight from them -- they said it's been discontinued, and gave me numbers for a few different Jeep dealers that were showing one in stock so I can try to have them ship it to me.  Can anyone else confirm that it's discontinued?  I'd like to get a good one in ASAP so I can either go get it smogged or keep troubleshooting the no spark.  I've heard that NAPA has good ones, but their online site didn't show a match.

 

--

 

Cruiser's Tips status:

#1 ground refreshing: I pulled the dipstick grounds and shined them up, tightened the stud.  My B- to dipstick cable is marginal, but I have a set of new cables from Kelley's WIP coming shortly.  When I put that on I will probably chop and re-crimp the sensor ground wires here, but I got a ~0 ohm reading from wires to battery post.  I also shined up the braided-cable at the firewall, but didn't pull the side on the head bolt.

#2 C101: I pulled it open and it doesn't look terrible.  I gave it a quick clean-up pass and threw it back together.  At some point I'll eliminate it.

#4 Coil/ICM contacts: done.

[tetrad]

I widened the mounting holes on the CPS bracket for the CPS that was originally on the truck.  I am now able to adjust it far enough that it scrapes when cranking, then back it off enough to get a cranking CPS voltage of 0.5 to 0.7 VAC.  Still no start.

 

CPS is reading 194 ohms at the connector, and 195 ohms at the ECU harness.  I tweaked all of the ECU harness female pins to grab better.

 

I verified that I have +12V to the ICM 3-conn "A" pin from the B-latch relay.  On the "B" pin, which should be ground, I have 0.3 ohms with the key OFF, and 3.2 ohms with the key ON.  Seems a bit odd.

 

I wonder if I might have lost a ground terminal when I refreshed the dipstick ground -- I am supposed to have 1 for the battery negative, and 2 others, right?  One of them has 2 wires coming out but they are crimped to the same ring terminal.

 

Also worth noting is that I bled the clutch right before this, and I spilled a decent amount of brake fluid below the master cylinder reservoir.  It looks like the wire harness below that goes to the fuse panel.  All the fuses checked good, but maybe it shorted something out?

[cruiser54]

Yep. Tip 8 has the simple procedure for increasing CPS output.

[tetrad]

Yep. Tip 8 has the simple procedure for increasing CPS output.

You're supposed to drill the hole on the bracket attached to the CPS, not the hole on the bellhousing, right?  I took a file to the bracket hole and expanded it enough to get the CPS closer, and now have 0.5 to 0.7 VAC while cranking -- still no start.  [i'm guessing you meant your Tip#7 not Tip#8].

 

I'm now looking at my ignition coil and module.  My coil has a secondary resistance of 2.198 kOhms, and a primary resistance of 0.4 to 0.5 ohms.  The secondary seems low.

 

I'm not sure that my ICM is getting a good timing input from the ECU (based on my guess of what a multimeter should show for a square wave).  I'll throw an oscilloscope on it within a couple days to verify.

[cruiser54]

I meant 7. 

 

Your 88 sends the CPS signal through the C101 connector if it's never had the TSB done.

 

See Tip 27 on how to deal with the C101.

 

Good time to do Tip 6 also.

[tetrad]

SHE LIVES!  :thumbsup:

 

I did the C101 delete (and sensor ground fix), still nothing.  So I pulled apart the C100 and cleaned it out, still nothing.  I pulled my ignition switch off the column and tested it - I was getting +12V at the starter line in start.  I pulled off the starter relay coil wires and the terminals were very corroded.  Cleaned em up and she started right up :)

 

My dipstick ground is pretty messed up at the moment, which probably took out just enough current to not engage the starter relay with the corrosion.  I've got a new full set of cables coming from Jon Kelley (http://www.kelleyswip.com/electric.html), so that shouldn't be an issue for much longer either.

 

Cruiser, thanks to your mantra "RCBRC" I got the jeep running for the cost of some heat-shrink wrap.  And I was all excited to go drop a chunk of change on a new ignition switch or starter relay.   :yes:   I guess I did end up getting an ignition coil and ICM somewhere along the process, but for $20 I'm glad I did it now instead of later.

[cruiser54]

SHE LIVES!  :thumbsup:

 

I did the C101 delete (and sensor ground fix), still nothing.  So I pulled apart the C100 and cleaned it out, still nothing.  I pulled my ignition switch off the column and tested it - I was getting +12V at the starter line in start.  I pulled off the starter relay coil wires and the terminals were very corroded.  Cleaned em up and she started right up :)

 

My dipstick ground is pretty messed up at the moment, which probably took out just enough current to not engage the starter relay with the corrosion.  I've got a new full set of cables coming from Jon Kelley (http://www.kelleyswip.com/electric.html), so that shouldn't be an issue for much longer either.

 

Cruiser, thanks to your mantra "RCRBC" I got the jeep running for the cost of some heat-shrink wrap.  And I was all excited to go drop a chunk of change on a new ignition switch or starter relay.   :yes:   I guess I did end up getting an ignition coil and ICM somewhere along the process, but for $20 I'm glad I did it now instead of later.

Woohoo!. cool stuff right there.

[lunghd]

Chassis &  engine grounds are the #1 culprit in electrical gremlins on our XJ's & MJ's - glad you found part of your issue & got it fixed.

 

On a RENIX Jeep... clean EVERY connector. EVERY. CONNECTOR.

 

Let me say that again: EVERY. CONNECTOR.

 

Then add a jumper ground cable from the dipstick to the chassis... and one from the OEM location on the head to the firewall.

Then a jumper ground from the throttle body side of the TPS connector to the firewall connection.

 

If the ground connections are not good then supply voltage to a sensor does not matter... it won't sense the correct voltages from the sensor as the ground connection is not good and that adds resistance (and lowers voltage sensed) by the ECU. Affects damn near every system the ECU maintains...

 

Glad to see someone pimping the RENIX life! :banana:

[cruiser54]

Chassis &  engine grounds are the #1 culprit in electrical gremlins on our XJ's & MJ's - glad you found part of your issue & got it fixed.

 

On a RENIX Jeep... clean EVERY connector. EVERY. CONNECTOR.

 

Let me say that again: EVERY. CONNECTOR.

 

Then add a jumper ground cable from the dipstick to the chassis... and one from the OEM location on the head to the firewall.

Then a jumper ground from the throttle body side of the TPS connector to the firewall connection.

 

If the ground connections are not good then supply voltage to a sensor does not matter... it won't sense the correct voltages from the sensor as the ground connection is not good and that adds resistance (and lowers voltage sensed) by the ECU. Affects damn near every system the ECU maintains...

 

Glad to see someone pimping the RENIX life! :banana:

Glad to see you're here!!

 

Like this?

 

Renix Ground Refreshing

 

The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, failed emission tests, and wasted money replacing components unnecessarily.

 

 The components grounding at the dipstick tube stud are:

 

Distributor Sync Sensor, TCU main ground, TCU “Shift Point Logic”, Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal.  All extremely important stuff.

 

The factory was aware of the issues with this ground point and addressed it by suggesting the following:

 

Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.

 

Inspect the wire terminals.  Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.

 

While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely. 

 

Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.

 

 First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.

Remove the other end of the cable from the rear of the head using a 3’4” socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.

 

A suggestion regarding the braided cable:

I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18” long with a 3/8” lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.

 

A further improvement to the grounding system can be made using a #4 cable, about 10” long with 3/8” terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.

 

For those of us with Comanches, it’s very important to remove the driver’s side taillamp assembly to access the ground for the fuel pump. Remove the screw holding the black ground wire. Scrape the paint from the body and corrosion from the wire terminal. Reattach securely.

 

If you want to upgrade your grounds and battery cables in general, contact Jon at www.kelleyswip.com.  He makes an incredible cable upgrade for a very reasonable price.

 

 

Revised 03-04-2013

 

And this?

 

I suggest unplugging EVERY electrical  connection in the engine bay you can find, whether engine related or not, and  spraying it out with a good electronics cleaner, visually inspecting the terminals making sure they haven’t retracted into the plastic holder, and then plugging it back together. There’s a critical 10-pin connector for the front lighting system located in front of the air cleaner and behind the left headlight assembly. Don’t miss that one. Also be sure that the connectors to the ballast resistor mounted near the air cleaner housing are clean and tight.

 

ALL of the relays should be removed, the terminals wire-brushed until shiny, and the receptacles sprayed out with contact cleaner. Then plug them back in. I do this on every Renix Jeep I purchase or work on for someone else. 

 

Revised 07/23/2012