87 Cherokee Laredo 4WD Manual 4.0L cranks, but won't fire.

[grasshappa]

Howdy. I'll start with the history, some of which may be irrelevant for the issue at hand. Every once in a while, she'll idle at a ridiculous rate. If I just turn the ignition off, and when the engine finally stops, turn it back on, it'll usually idle fine. From what I've read lately, this may be the IAC or TPS? One other thing is that when it's running and still cold, the engine won't really respond to the gas pedal. Also points to TPS? Anyway, lately (last few days) it's been really really cold, and it's been taking a lot more cranks to start. I've also been doing some travelling on jolting terrain in the last couple days. So, after one of these hard starts, we get going and a couple minutes later, it stalled and I haven't been able to start it since. It'll crank and crank, but hasn't fired one cylinder even once. I changed the fuel filter before I really had time to think about what was wrong with it, but it needed a new one anyway. The fuel rail has fuel, according to the spurt at the scraeder valve, the exhaust has a nice gasoline smell after a few cranks, so I assume fuel pressure is not the issue, but I haven't yet tried starter fluid. I pulled a plug, and there was no sign of evil happenings inside the case, and moreover, the plug sparked. I tried disconnecting the battery terminals and touching them together for a few seconds. All the fuses seem fine. I disconnected/reconnected the MAP sensor. Oh, and I duct taped a large hole in the vapor line from air filter to engine case. This was caused by the hood release cable housing rubbing against it. Nothing has had any effect. So I'm thinking it may be that the timing is screwed up from a bad distributor, coil, CPS*(see note below), or timing belt. #1 candidate in my mind is CPS.

So, for all things CPS, this http://www.automotiveforums.com/vbul...d.php?t=579517 is very helpful, but I'm still a tool and haven't actually found my CPS yet. And while on the subject, this http://www.automotiveforums.com/vbul...d.php?t=687635 is very useful, and has pix, but confused me regarding the CPS. This thread mentions:
"cam position sensor in distributor"
"camshaft position sensor"
"crankshaft position sensor"
Are these all the same thing, the CPS?
Can a bad CPS actually make the plugs fire at the wrong time, or will it just cause a no spark situation?

If you have other ideas of how I can narrow down my problem with more tests, let me know. (I borrowed my neighbors electric tester thingy, too.) Or if there are other things that I haven't considered (of course there are lots), please let me know. This is a great, informative forum, and I promise to post the resolution here. Thanks in advance for your time and help! Cheers!

[citizen@large]

Well Done!!!
That's a fantastic exlain of your sit, but...

Any, and I mean any other changes made in the last year or more will help. That most certainly could be the CPS (yes, all those combos = CPS) [As you may read below, they apparently do not! (READ- CPS ALSO= CAMshaft POSITION SENSOR)] That thing is one serious PITA!!! It can cause any # of descriptions of issues by it's victims. It seems that everyone's descript is different, and seems as though it is several systems failing all at one time.

My advise is to start there, as you have not mentioned the CPS's replacement in 20+/- years. That's a looong tiiimee for a very notorious sensor to go unchecked.

I will also advise, that if you do go this route 1st, to notch the new CPS's holes so that you can simply slide the new one(s) back on/off again... I used a dremell tool, very handy little thing it is.

Now for the links:
Good ol' same ol'..
http://www.lunghd.com/Tech_Articles/...iagnostics.htm

My personal experience..
http://www.automotiveforums.com/vbul...nk%2A+position

Interesting little ideas to hold onto the blasted bolts from up there: 11o'clock on the trans bell-housing facing the engine from underneath...
http://www.naxja.org/forum/showthrea...nk%2A+position

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And, from Florida Jeepers- all the tricks:
http://www.floridajeepers.net/viewtopic.php?t=20947

Tally_XJ
FJOA Premium Member



Joined: 21 Jul 2004
Posts: 899
Location: Tallahassee
Posted: Sat Feb 11, 2006 12:26 am Post subject: Crank Position Sensor Replacement Made Easier If you have a Jeep with the 4.0 litre engine, then you have a crankshaft position sensor located on the upper left edge of the transmission bellhousing.

If you do not have a transfer case drop, and even if you do, this is one hell of a hard place to reach with your hand or tools. A transfer case drop will move the bellhousing down and away from the body just a little. Its enough though to make it a lot easier.

Its not a matter of IF the crank position sensor goes bad, but rather when the sensor WILL go bad.

If you have my luck, it will quit on you at a traffic light in 5 o'clock traffic or maybe worse, several miles into the woods on a trail.

Symptoms of a Bad Crank Position Sensor
- Engine will crank over when turning the key, but will not fire and run
- Engine may intermittently run bad, especially at idle
- Engine will just shut off as if you turned the key off and is hard to get it started again


A new sensor can be purchased at NAPA, CarQuest, or at Advance Discount Parts. It is also available from your Jeep dealership at not much more cost than from the aftermarket (or so I read). Since they are not that expensive, it is adviseable to always have a spare on hand for those moments when you really want to take your Jeep home with you.


What to do now to make it easier on you later

Purchase a new sensor. Either make the modification now and replace the sensor, or keep it in your Jeep for future use when your current sensor goes bad.

This time, when you change the sensor, it will be a little difficult, but making the following modification will make it much much easier next time.

Installation and tools

Installation is straightforward, but is a tight reach. The sensor is located at about the 11 o'clock position on the left upper edge of the bellhousing. If you look at the firewall just behind the valve cover and follow down to the bellhousing edge, you should see a black plastic thing there that is held in with two bolts. A wire lead comes up and into a weatherproof plug just in between the throttle body and valve cover. This is the sensor and its pigtail lead. On some models, Chrysler made a modification to the wire lead. It did not go into a plug end, but rather ran into and through the firewall directly to the ECU.

The special shouldered bolts that hold this sensor go in from the back side, not from above. Reaching them is the hard part of this process.
I have done this two ways. The first time, I got them loose using a 7/16" combination box end wrench from the top (hardest way). The next time, I used a 1/4" drive ratchet, very long extension, universal swivel (wobble) and a 7/16" or 11mm socket and went underneath the Jeep reaching up between the unibody tub and transmission. If you look up along the left side of the transmission where the shifter cable runs into the body tub, you should see the sensor there just behind the exhaust manifold. Using the ratchet and extension tools, unscrew the sensors two mounting bolts.
Take caution! DO NOT allow the bolts to fall into the hole where the sensor goes into the bellhousing! You might have to remove the transmission to get them out!

Once you have the bolts out, go back up into the engine bay and unplug the sensor lead and pull it out.

Now, go back under and put the bolts back into the holes and turn them in a few turns, but not tight just yet.

New Sensor modification
Looking at the photo below, it will show the modification you will need to make to the sensor mounting tab. I used a dremel type die grinder with a thin cutting wheel on it to cut the slots into the tab. A hand file might work but would take longer.



Use caution when doing this. You only need to open up the mount hole just enough to slip over the shoulder bolt. Dont make it deeper as the sensor could very possibly go too deep and contact the flywheel. This would instantly destroy your new sensor.

What you are doing here is making the sensor installation easier by preventing the necessity of completely removing the mounting bolts. After this mod, it will allow you to simply loosen the bolts a little, slide the sensor out from the top, and then install a new (modified spare) sensor and tighten the bolts. You wont lose the bolts, you wont drop them into the bellhousing, and you should be able to use an open end wrench from the top to loosen them.

NOTE: Keep a few zip ties handy so you can tie the wire lead back away from the exhaust manifold. The manifold can and will melt the wires if they touch and you will be replacing or repairing the sensor again!

Last edited by Tally_XJ on Wed Jan 24, 2007 10:09 pm; edited 5 times in total

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opcorn: I know. It's what I do...

~Good Luck!!

[grasshappa]

Thanks for your response, citizen@large! Those are some very useful tips and links. Tomorrow morning, I plan to abuse my neighbor's voltmeter doohickey to test the CPS, TPS, MAP Sensor, and Stator (aka Sync Pulse Generator, aka CAMshaft Position Sensor, but not-aka CPS) per the directions in that first link given.

As for additional history, I haven't done anything to it under the hood yet other than augment fluid levels. I am the second owner as of 2.5 years ago. Original owner didn't do anything to it herself, she'd always just "take it to the shop." So, the age of all the sensors (and all parts) is quite dubious. It could certainly use a new front driveside axle and a new clutch. If that silly CPS proves bad tomorrow, I may just have to "take it in to the shop" to have them do the clutch, which I think may be well beyond my tool/equipment capacity? So, I'll just hand them the CPS with modified mount, since that would be a much easier time to install it, I reckon. Or maybe I'll raid my neighbor's garage again to try to find a 3' socket extension (didn't even know anybody ever forged such a piece of metal ) and an 11mm wiggley socket, and forget about the clutch for awhile. I really'd like to fix her up tomorrow before the snowstorm rolls in, but it may just have to sit in my driveway for a while. At any rate, it'll be a white Christmas!

Oooh, that brings me to another question...I recall reading somewhere about "high altitude CPS" or maybe "adjustable CPS." I live at 8000' and do ~95% of my driving between 7000-9000'. Is there a specialer CPS I should be shopping for?

Thanks again and cheers!

[citizen@large]

Originally Posted by grasshappa

Oooh, that brings me to another question...I recall reading somewhere about "high altitude CPS" or maybe "adjustable CPS." I live at 8000' and do ~95% of my driving between 7000-9000'. Is there a specialer CPS I should be shopping for?

Thanks again and cheers!

Well, I'm in VA and have no idea about any such deviation on the CPS's design parameters. *Read- Low Alt.

It's sure to be something that the local parts store should know though..

There's a difference!?!?!?!??? ?!?!??!? ?! ?! ? ??!? ?? ? ?? ???

Originally Posted by grasshappa

Stator (aka Sync Pulse Generator, aka CAMshaft Position Sensor, but not-aka CPS)

What/where is it!?!?? Got a pic?

[grasshappa]

Originally Posted by citizen@large

There's a difference!?!?!?!??? ?!?!??!? ?! ?! ? ??!? ?? ? ?? ???

What/where is it!?!?? Got a pic?

Here's the link with pix and instructions:
http://www.lunghd.com/Tech_Articles/...lse_Stator.htm

Now I'm going to sound like a loon again, but how do I know if I have a "Renix" or "HO" engine. Another stupid q - I see the abbreviation/acronym everywhere about XJ, CJ, MJ, etc, but I don't know what these mean. Does mine have one of those nice codes, or is it just Cherokee Laredo?

[grasshappa]

Ok, so here's my sensor results -

TPS seems perfectly fine - 5.0V supply and .85V output

MAP sensor supply is perfect 5.0V, but backprobe output is 3.5V (suggested cold range is 4-5V) How bad is this, if bad at all?

CPS seems borderline - resistance is 165ohm (should be 200 +/- 75), cranking voltage is .45VAC (should be .5-.8VAC) How bad is this, if bad at all? If you can't tell, I'm really hoping that this isn't the problem, so that I don't have to try to replace it. Perhaps I will try the "tonk the mount" procedure to get this in range. I know, I know, I should change it anyway...

Stator gave strange results, and I'm going to have to retest and make sure I am backprobing the correct wires. The blue B connection to engine block ground gave 7.25V (spec is 7.1V). The blue B to the black A ground gave 2.25V (should also be 7.1V, yeah?). The blue B to gray C gave 0V (should be 5V). <Implies sensor is bad! The DCV seemed to be fluctuating on the digital readout when cranked, so that seems to imply that the sensor is good! I will try to check these again soon, because now I'm not sure about those connections. 7.25V - 2.25V = 5.00V (proper B to C backprobe V) which is why I think I need to verify these numbers!

So, I guess the Stator seems like the biggest suspect now, but I suppose I haven't ruled out the CPS or the MAP. Like I said, I will test the stator again, and then do the continuity tests for the three wires involved.

So, if it turns out that all of these sensors seem acceptable, then I guess I'll have to see if I can borrow a vacuum tester? Any other idears?

[grasshappa]

Ok, here's the more accurate sync pulse generator results:
Blue (B) to Gray striped (C) = 2.23V
B to Engine block ground = 7.23V
B to Black (A, ground) = 7.23V
C to A = 5.00V

I cranked it a little and watched the B to C voltage change from what looked like 1 to 6 V on the digital readout. After a few tries, I was able to stop the engine in a position where the B to C read something other than 2.23V. This time it happened to read 6.99V. So I backprobed the rest of the connections and this was the result:
B to C = 6.99V
B to block = 7.00V
B to A = 7.00V
C to A = 0.01V

So, for what I can tell, the B to C voltage fluctuates from 2.23 to 7.00V, which I'm guessing is good. BUT maybe it's supposed to fluctuate from 5-7V, since the manual says 5V.

Does anybody out there have a better diagnostic of my situation? I have a spark of unknown quality and unknown timing (I see a spark when I pull a plug and crank.) I have some amount of fuel pressure (schraeder valve on fuel rail squirts stinky stuff.) Some amount of fuel is being injected into the cylinders at unknown timing (exhaust pipe smells like fuel after cranking.) I am assuming that there's still compression. TPS is working. Stator is working. MAP is functional/borderline. CPS is borderline...

Other ideas? Vacuum system. Poor spark from bad coil. Slipped timing belt? Oh, this has a timing chain, so it probably didn't slip.

Ok, it's time to conk the CPS...:

[grasshappa]

I was too timid to give the CPS bracket the tonk that it probably needed. But I checked the voltage after the 'procedure,' and it read .35VAC while cranking. Before it read .45VAC. This may be due to my battery being nearly dead now and the CPS supply V has probably dropped. Anyway, the new CPS is in the mail (for less than half the price of my local auto parts rip off shop.) It seems that a high altituded CPS just advances the timing a little, by advancing it's signal a little, by being a degree or two more toward the passenger side of bellhousing. This can be done pretty easily by modifying the bracket's screw holes, I guess. At any rate, hopefully I'll have my XJ running by Xmas...

[grasshappa]

I changed the CPS and voila! It still won't fire.

Any ideas?

[AlohaBra]

Originally Posted by grasshappa

I changed the CPS and voila! It still won't fire.

Any ideas?

Check for spark and then fuel.

[grasshappa]

Well, I had spark all along, but the quality of the spark was always suspect to me, as I didn't really understand how to test it. I wound up buying a new coil, guessing that that might be the problem. I had checked all of the ignition wires' resistance, and they all seemed fine, but upon replacing the coil, it seemed that the coil/dist wire was a little loose on the coil connection side. I pulled the boot back and kinda crimped it onto the new coil post, put the boot back, charged the battery with my new fangle dangle battery charger, and it fired right up! So, I'm not sure if it was the coil or the wire that caused the initial stall-and-never-fire-again symptom, but now it works and has been working fine for weeks.

Since I've got it running again, I've given it a little more love, and decided to change out a few things - ignition wires, spark plugs, air filter, rotor, cleaned dist cap inside connections again. Will change oil & oil filter tomorrow, and I'm even gonna fill up the windshield washer reservoir. I need to flush the radiator, too, but have to learn how to do that first. I guess I'll have to search this lovely site for tips on that...

Thanks to everyone for their help and guidance. I really appreciate it! Cheers to groundhog's day beers!

[citizen@large]

Originally Posted by grasshappa

and I'm even gonna fill up the windshield washer reservoir.

Dude! WTF!! LOLROFLMAOWWTDDBBQ!!! lolz...

There IS some kinda proceedure to flushing the coolant system.. but I'm still laughing too f'n hard to look it up!!!

BTW.. Punxsutawney Phil doesn't work on weekends! No forecast for you!! Aw hell, ORLY it's 6 more weeks..

^I had to look that up! hahah!! I am having a beer though!

[citizen@large]

On another note I'd like to say how 'pleased' I am @ everyone here for 'helping' this particular "case"...

From here on- I am announcing that I in no way, (cause I'm a noob..), have ANY and I mean ANY rights (dibs) to help anyone anymore, than any other member, for those that are seeking information from those of us that have been here for a while or with more/less available knowledge(s)...

ie- If you 'think' you can offer assistance, DO...

There are MANY things that are over my 'head'.. I have never been a mechanic in a shop.. (especially a Jeep Stealership shop) I am purely a research and dive-in type. Going to the 'shop' as a last resort.

Disclaimer~ If you, the recipient of any advice feel the need to get all kinds of 'weekend warrior' in your 'heep', YOU WILL IN NO WAY INFER RESPONSIBILITY TO ME- citzen@large (cause I suck @ this)

[dave92cherokee]

The way I flush the coolant system in my jeep every spring is drain all the old coolant and then remove the lower rad hose and flush water from the tap through it till it's clear. Then reconnect the hose and fill it up with water. Put the rad cap on and start it up and let it run for a while then shut it off and disconnect the heater hose from the tstat housing and remove the rad cap then start it up and let the water pour into the radiator alot will overflow so put a couple of buckets under the front if you're worried about the environement and animals getting into it. Then just let it run until the fluid coming out of the tstat housing is nice and clear. Then if you want to put coolant back in just pop off the lower rad hose and drain the water, then reconnect both hoses and fill up with 50/50. Personally mine used to run hot in the summer time so I used some water wetter and straight water during summer time and had no problems with it overheating anymore.