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  #1  
Old March 6th, 2005, 19:22
XJZ XJZ is offline
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MAP Sensor Questions of the Month

1) Can a bad MAP sensor *sometimes* work again temporarily after a disconnect-reconnecting (like the CPS)?

2) Does a bad MAP sensor cause no spark at the coil?

TIA
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  #2  
Old March 6th, 2005, 19:43
rdx4me rdx4me is offline
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Re: MAP Sensor Questions of the Month

Funny thing about XJ's... Either the ignition switch gives out, requiring a horn-type button to be installed to get the engine to turn over and/or there is suddenly no spark at the coil regardless of replacing every "normal" item in the entire ignition system!

Mine would produce no spark for the past 3 months regardless of my replacing coil, ICM, rotor, cap, wires, etc..

So I found this vacum hose that was disconnected from the MAP sensor... Plugged it back in and it started right up! Now, 3-4 days later it lost it's spark again...

I am determined to kick this gremlins ass if I have to rip out the entire electrical system!

I'm going to find the CPS this week and check it out. Funny how many XJ's have these problems but amazingly no recall? I would be happy with an ignition system from the 60's & 70's...

RDX
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  #3  
Old March 6th, 2005, 20:11
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XJXJ XJXJ is offline
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Re: MAP Sensor Questions of the Month

Quote:
Originally Posted by rdx4me
Funny thing about XJ's... Either the ignition switch gives out, requiring a horn-type button to be installed to get the engine to turn over and/or there is suddenly no spark at the coil regardless of replacing every "normal" item in the entire ignition system!

Mine would produce no spark for the past 3 months regardless of my replacing coil, ICM, rotor, cap, wires, etc..

So I found this vacum hose that was disconnected from the MAP sensor... Plugged it back in and it started right up! Now, 3-4 days later it lost it's spark again...

I am determined to kick this gremlins ass if I have to rip out the entire electrical system!

I'm going to find the CPS this week and check it out. Funny how many XJ's have these problems but amazingly no recall? I would be happy with an ignition system from the 60's & 70's...

RDX
The industry makes quite a bit of money with these "problems" so don't hold your breath for a recall. Replacing CPS is one of the most over-rated and over-sold components in the crank, but no-start checklist. They do go bad if physically damaged but 98% of the CPS problems can be found in the wiring harness and/or connector. I haven't had a CPS failure in years since splicing the wiring to eliminate the connector on the stock CPS.

As far as the OP ??? Knowing the problems I've had with XJ connectors, I wouldn't be surprised if the MAP could be affected. Complete lack of MAP signal might disable spark but if it's providing some voltage signal , I doubt it would halt spark.
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  #4  
Old March 6th, 2005, 21:09
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5-90 5-90 is offline
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Re: MAP Sensor Questions of the Month

1) I don't see any reason why not. If you notice this, I suggest you clean the connections. A little terminal cleaner in the MAP connection, and if you spend a few bucks you can get a set of terminal tools for weatherpacks which will allow you to remove the harness terminals and clean them as well (they're nice to have for nearly everything...)

2) I see no reason why this should be so. The MAP sensor generates a signal used to meter fuel. If you have no spark at the coil, I'd start checking the CPS sensor (11:00 on the bellhousing, looking from the rear) since this is a fairly common failure. Failure of the CPS will cause both NO SPARK and NO FUEL - the CPS pulse also generates fuel injection timing signals as well...

5-90
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  #5  
Old March 6th, 2005, 21:32
XJZ XJZ is offline
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Re: MAP Sensor Questions of the Month

I've just replaced the CPS.

When the Jeep initially died on me, I tried the disconnect- reconnect with what I thought was the CPS, and it worked-it worked for a least a few more start-ups. So I purchased a new CPS and when replacing it. I then realized the connector I was tinkering with wasn't the CPS, it was the MAP's connector. So that's why I'm asking.

Also have no spark at the coil so was wondering if this is due to the faulty MAP. or if I have other problems. I did a search but really didn't find an answer. One bummer about some of these searches is you go through the whole thread, but the solution doesn't get posted.

A friend has an XJ with the renix also (if that even matters, mine's a renix) and thought I'd have him come over and do a MAP sensor swap just to see if mine will fire up.

If not, what's next? Coil isolator? Coil?

Thanks for the input thus far.
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  #6  
Old March 6th, 2005, 21:57
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martin martin is offline
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Re: MAP Sensor Questions of the Month

I take it this is a 89 XJ, that what you have listed under your profile. I have a 88 XJ and from 2000-03 I replaced every sensor under the hood, figured they were over 10 years old and were at the end of their service life.

I recommend you don't test just replace the MAP, don't use your buddies used sensor, just get a new one. The MAP if it is the factory one is at the end of it's life or very close. The MAP is a piezo electrc device and after all those milllions of pressure changes over the life of the engine have take it toll on the MAP. Also make sure the port in the throttle body is not clogged up with carbon.

I take it you are connecting a timing light to a spark plug wire to see if you have fire or not. If you are pulling the wire off and trying to see if it sparks may not give you good results.

You might be money ahead to take the vehicle to a shop that knows renix and have them figure it out may be cheaper than throwing parts at the problem. A hook up to the test set will tell a lot, may zero it to the ignition module under the coil, a bad coil or something else. You need a tech who understands Renix.

To avoid problems like this I replaced every sensor. Every time I got paid I'd buy a new sensor and install it. After the MAP id change the temp sensor in the intake manifold. You will notice your XJ runs just a little bit better.

Then I'd change the TPS and get it calibarted correctly. All these items wear and if you plan to keep the XJ then replace the sensors. Since the Renix was used for a handful of years some parts may not be available. If you want to know more, I can go on in another post.
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  #7  
Old March 7th, 2005, 07:10
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XJXJ XJXJ is offline
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Re: MAP Sensor Questions of the Month

Download the FSM (factory service manual) and read. Renix is simple and there's no reason to "shotgun" troubleshoot anything.
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  #8  
Old March 9th, 2005, 12:30
rdx4me rdx4me is offline
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Re: MAP Sensor Questions of the Month

Is there a FSM download on this site? My Haynes manual didn't even show a CPS for a 1990 XJ 4.0
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  #9  
Old March 10th, 2005, 11:12
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ssnsltd ssnsltd is offline
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Re: MAP Sensor Questions of the Month

XJZ,

Did you figure out what the problem is/was?

I have an '88 with the exact same issues.

thanks,
David
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  #10  
Old March 10th, 2005, 12:11
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Re: MAP Sensor Questions of the Month

Other than the CPS causing start up issues for the jeep, what other issues can it cause if the jeep is starting up ??

pete
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  #11  
Old March 10th, 2005, 13:20
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Runnin'OnEmpty Runnin'OnEmpty is offline
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Re: MAP Sensor Questions of the Month

XJZ, there's a stator/cam position sensor inside the distributor, that tells the ECU which stroke the #1 cyl is on (compression or exhaust). The ECU uses this signal in conjunction with the CPS signal to determine spark and fuel injector timing. If either signal (CPS or stator) is lost, then the engine will not start. Since you've already replaced the CPS, the next step would be to test the stator signal.

There are three wires going to it; blue, black, and gray/white. Blue is 5v reference, black is ground, and gray/white is the signal wire. A quick test is to check for signal on the gray/white wire. Backprobe the wire with the postive probe on a voltmeter set on 15v scale. The other probe goes to ground. Crank the engine and watch the voltmeter for a pulsing voltage. It should pulse once for every 2 engine revolutions. If there are no pulses, then either the stator is bad/open, or there is an open in the wiring going to it.

Hope this helps.
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  #12  
Old March 10th, 2005, 19:08
rdx4me rdx4me is offline
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Re: MAP Sensor Questions of the Month

Quote:
Originally Posted by Runnin'OnEmpty
XJZ, there's a stator/cam position sensor inside the distributor, that tells the ECU which stroke the #1 cyl is on (compression or exhaust). The ECU uses this signal in conjunction with the CPS signal to determine spark and fuel injector timing. If either signal (CPS or stator) is lost, then the engine will not start. Since you've already replaced the CPS, the next step would be to test the stator signal.

There are three wires going to it; blue, black, and gray/white. Blue is 5v reference, black is ground, and gray/white is the signal wire. A quick test is to check for signal on the gray/white wire. Backprobe the wire with the postive probe on a voltmeter set on 15v scale. The other probe goes to ground. Crank the engine and watch the voltmeter for a pulsing voltage. It should pulse once for every 2 engine revolutions. If there are no pulses, then either the stator is bad/open, or there is an open in the wiring going to it.

Hope this helps.
But what would prevent spark coming off the coil after replacing the coil, ICM, CPS, etc, etc...?
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  #13  
Old March 10th, 2005, 20:06
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Runnin'OnEmpty Runnin'OnEmpty is offline
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Re: MAP Sensor Questions of the Month

RDX, even though you've replaced those parts, the stator/cmp inside the distributor can still be bad. The engine won't start if either the stator or the CPS isn't sending a signal to the ECU. Even though your's started when you plugged in the MAP, it was probably a fluke. I don't think a bad MAP will cause a failure to start.

If you haven't changed the CPS, I'd suspect it first, or the wiring or plug going to it. The CPS plug-in is at the driver's side rear of the engine, on top of the intake, and easy to get to. Try un-plugging and re-plugging it, maybe put a dab of dielectric grease on it, and see if it starts.

You can also test it with a multimeter; I'll post the procedure if anyone needs it.
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  #14  
Old March 11th, 2005, 11:10
rdx4me rdx4me is offline
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Re: MAP Sensor Questions of the Month

I picked up a CPS at Advance Auto and will try and swap it out this weekend. I'm getting no spark out of the coil...

Thanks for the info!
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  #15  
Old December 9th, 2016, 04:08
purzner purzner is offline
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Re: MAP Sensor Questions of the Month

I am having the same issue, but my issue is intermittent but when it does decide not to start there is no spark coming from the coil.

Things i have done:
checked all ground wires
checked several of the connectors for the ignition system.
replaced the cps
replaced the distributor since the pickup coil is in the distributor and to change the pickup coil you have to pull the distributor anyways there was not a big price differnce in just the pickup coil and the distributor. and it comes with a brand new cap and rotor.
replaced the plugs and wires.
replaced the coil
tested the icm verified it is working properly.

my jeep is a 1990 with the renix fuel injection system and everything seems to be origional on it, with the exception of inside the interior someone decided to do some sort of custom wiring job with the radio and that type stuff. so some of this stuff even though they tested good was changed just due to the age.
I am still replacing random vacuum lines

It seems like the general consensus is that the Map sensor will not cause a no start or cause spark not to come from the coil.

My observations so far is when it decides not to start, i can take a screw driver and tap the map sensor while someone cranks it and it will start.

also when it does not start , the jeep get absolutely no fire so it doesnt even try to pop.
i can even unplug the map then the jeep will try to start and die almost immediately

From what i have read the MAP is supposed to help the computer adjust the fuel and timing depending on engine load which it recieves that information via vaccum and converts that into an electric signal and send it to the ecm.

So i would think just by the definition that it surely can not be the cause of a no start if it wont even pop or try to fire.
but from my observations it seems that the MAP is the likely culprit. I am just having some problems justifying it. Because it just doesn't make sense to me as to why this would cause the problem. But i am almost certain that the map is the problem.

Does anyone have any thoughts as to why or how this could be explained?
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