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flywheel speed sensor?

XJ-Mayhem

NAXJA Member
NAXJA Member
Location
San Jose, CA
my 1990 4.0l cranks fine, but wont start. i'm pretty certain its the flywheel sensor (im pretty sure this is its correct name)

what im wondering is what your guy's experience is with replacing these, as i hear the fix used to be a patch wire from the sensor directly to the ecu, but i also hear they dont make these patch kits any more.

so can you guys please inform me of any detailed information you have about this issue?
once i get a hold of a ohm meter, i was told to test the plug of the sensor for 200ohm -+ 75ohm

i'm pretty sure i've located the sensor, on the transmission, driver side, slightly above and behind (towards gas tank) the linkage. i see a white connector, and can feel the two wires inside the loom, and also think i see another wire in the same area...but i cant really get my head up in there to see clearly.
any pictures would help, so i can visualize whats going on.
 
was hoping you'd chime in :cheers:


gonna start reading now


covered a lot of good stuff. my good friend told me all of this today, but i like having it in words because i learn better that way. one question though..how come once or twice the CPS was referred to being in the distributer? or is this talking about where this sensor feeds to, which is in the distributer?
going to do some testing tomorrow to see if i can confirm this is the problem

any one know what these sensors run as a replacement?
 
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there is a CAM position sensor in the dist......not CRANK position(which is on the bellhousing)

crank sensor will cost around $60 new at the dealer.
 
there is a CAM position sensor in the dist......not CRANK position(which is on the bellhousing)

crank sensor will cost around $60 new at the dealer.

x2. Part of the confusion over the years of production. Early XJ FSM refers to the engine speed sensor as CPS, later years it is the CKP.

CPS in later years cam position sensor, other non-jeep brands may refer to it as CMP and other terms.

That should make it clear as MUD! LOL!
 
thanks guys that makes sense.

i'm hoping i'll get really lucky and a good clean out of the connector will fix this (it was super muddy when i was touching it) but if not oh well.

would this have attributed to my slow start up prior to the no start issue? im talking its been for a few months prior. im talking a good 7-10 max seconds of crank time before a start up, and if i shift into drive to fast without touching the throttle itl stall (usually im quick enough on a throttle tap to keep that from happening, but a stutter none the less)
i know thats an off topic question, but just wondering.
 
I don't know whether it's still true (been out of the Renix era myself for some years), but last time I did a Renix CPS, it was available from the dealer in two versions. One was a kit that included a new piece of harness for the direct connection to the CPU, and for some reason it was cheaper than the CPS alone. If shopping at the dealer it might be worth asking after this if it still exists. You may not need the new piece of wire if your rig is a 90 with the later wiring harness, but check the price anyway.

The new kits also come with a plastic dust shield,. Make sure you use it, because it holds the sensor in place before you put in the bolts, and thus makes it much easier to install.
 
thanks guys that makes sense.

i'm hoping i'll get really lucky and a good clean out of the connector will fix this (it was super muddy when i was touching it) but if not oh well.

would this have attributed to my slow start up prior to the no start issue? im talking its been for a few months prior. im talking a good 7-10 max seconds of crank time before a start up, and if i shift into drive to fast without touching the throttle itl stall (usually im quick enough on a throttle tap to keep that from happening, but a stutter none the less)
i know thats an off topic question, but just wondering.

Renix is notoriously slow to fire. At least part of the problem is in the electronics design. The engine has to crank up to around 300 RPM before the CPS/CKP signal will trigger the ECU. A tired battery, poor cables, and a tired starter/solenoid will contribute to the cranking time.

Another problem can be loss of fuel pressure. When you turn the key to the ON position there is power to the fuel pump, bypassing the ballast resistor, for 3 seconds. Try cycling the key from OFF to ON, wait 3 seconds, and repeat two more times. If that seems to help reduce the crank time, then I would recommend you install a fuel line check valve back at the fuel filter. eBay seller jbass195 sells a 3/8" check valve for $14 + $2.50 s/h.
 
I don't know whether it's still true (been out of the Renix era myself for some years), but last time I did a Renix CPS, it was available from the dealer in two versions. One was a kit that included a new piece of harness for the direct connection to the CPU, and for some reason it was cheaper than the CPS alone. If shopping at the dealer it might be worth asking after this if it still exists. You may not need the new piece of wire if your rig is a 90 with the later wiring harness, but check the price anyway.

The new kits also come with a plastic dust shield,. Make sure you use it, because it holds the sensor in place before you put in the bolts, and thus makes it much easier to install.

Ok now I worried about this harness thing........is the oem cps harness on my 89 going to cause me problems without this other harness?
 
Don't sweat it. You could make your own "new" harness if you want to.

Sent you a PM.
 
here ya go. CPS is almost all the way at the bottom of the page.
http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

thank you for the link

I don't know whether it's still true (been out of the Renix era myself for some years), but last time I did a Renix CPS, it was available from the dealer in two versions. One was a kit that included a new piece of harness for the direct connection to the CPU, and for some reason it was cheaper than the CPS alone. If shopping at the dealer it might be worth asking after this if it still exists. You may not need the new piece of wire if your rig is a 90 with the later wiring harness, but check the price anyway.

The new kits also come with a plastic dust shield,. Make sure you use it, because it holds the sensor in place before you put in the bolts, and thus makes it much easier to install.

yes i know what kit your talking about, and according to my good friend who owns a gas station/shop and can order OEM parts from any dealership, and "used to replace these CPS/CKP sensors and the patch kit in his sleep" he says the patch kit is no longer available.

Renix is notoriously slow to fire. At least part of the problem is in the electronics design. The engine has to crank up to around 300 RPM before the CPS/CKP signal will trigger the ECU. A tired battery, poor cables, and a tired starter/solenoid will contribute to the cranking time.

Another problem can be loss of fuel pressure. When you turn the key to the ON position there is power to the fuel pump, bypassing the ballast resistor, for 3 seconds. Try cycling the key from OFF to ON, wait 3 seconds, and repeat two more times. If that seems to help reduce the crank time, then I would recommend you install a fuel line check valve back at the fuel filter. eBay seller jbass195 sells a 3/8" check valve for $14 + $2.50 s/h.

Thanks for the info, i have previously tried cycling the fuel pump twice before turning it on to see if it fixes it, but not 3 times. I dont remember it helping TOO much. But i'll address that once i get it running
 
Ok now I worried about this harness thing........is the oem cps harness on my 89 going to cause me problems without this other harness?
Probably not. Most problems as far as I know were with the original harness design, which had a big connector on the firewall. This was modified later (I think some time in mid 88 run), and my 89 had the later type.

Too bad the kit is no longer available. It was a good deal even if you didn't need the extra wire.
 
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