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Unread 05-22-2012, 07:52 PM   #1
riverhippy
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1991 YJ Wrangler 
 
Join Date: Jul 2011
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no spark no fuel pump..... im getting ready to sell this pig.

Today, i fill up, pull out of the station and it dies. the fuel pump doesn't cycle and there is no spark.
there used to be a kill switch. i checked all of the old connections that i cut out and it all looks good.

what connection could be bad that allows it to turnover (the starter engages) , but not allow the fuel pump to cycle and kill the spark?

i wish they had a smiley face with a with a knife stabbing a jeep in the butt right now....



my jeep

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Unread 05-22-2012, 08:00 PM   #2
Desert_Rampage
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ECM could cause such an issue. Disturb any grounds lately??
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Unread 05-22-2012, 08:05 PM   #3
Jstout724
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Theres a few things I have learned recently that will affect this....

try your CPS... probably this, test it with a meter it should read infinity

also try the fuse in the 20a 'dome' slot. Its really an electrical feed to the PCM, I believe. I had this issue when I was checking what the F these fuses actually did.

If that doesnt work I got a few more ideas for ya

edit- check the fuse first cause it will take all of 5 seconds and might fix it
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Unread 05-22-2012, 08:06 PM   #4
riverhippy
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Quote:
Originally Posted by Desert_Rampage View Post
ECM could cause such an issue. Disturb any grounds lately??
ive actually got an extra....and nah...ive stayed away from those Indian burial grounds....haha
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Unread 05-22-2012, 08:09 PM   #5
riverhippy
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Quote:
Originally Posted by Jstout724 View Post
Theres a few things I have learned recently that will affect this....

try your CPS... probably this, test it with a meter it should read infinity

also try the fuse in the 20a 'dome' slot. Its really an electrical feed to the PCM, I believe. I had this issue when I was checking what the F these fuses actually did.

If that doesnt work I got a few more ideas for ya
brand new cps couple months ago...where would i put the probes to measure? all fuses are good.
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Unread 05-22-2012, 08:22 PM   #6
riverhippy
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where would one wire in a kill switch that can kill fuel pump and spark?
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Unread 05-22-2012, 08:33 PM   #7
Desert_Rampage
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Yea, really! I've been wanting to put one in... Just spark for me as I have the 4.2
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Unread 05-22-2012, 08:43 PM   #8
Jstout724
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I thought you were the one that cut it out.... you should know...

Are you familiar with using a multimeter and testing sensors?
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Unread 05-22-2012, 08:56 PM   #9
randomtrailhero
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ive had this happen to me on the trail once. it would crank but it would not start. clean/replace you distributor cap. see if that helps.
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Unread 05-22-2012, 08:56 PM   #10
riverhippy
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Quote:
Originally Posted by Jstout724 View Post
I thought you were the one that cut it out.... you should know...

Are you familiar with using a multimeter and testing sensors?
the location of where i cut it out looks good

yes, what sensors are you thinking? the cps? just one on each wire and it should show infinity?
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Unread 05-22-2012, 09:03 PM   #11
Jstout724
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You sure you checked all the fuses in the fuse box under the dash? Fuse #5, a 10 amp fuse, sometimes labeled 'dome' is a power lead to the PCM. Its kind of like a relay power for it. PCM wont work without this.

edit- sorry I just want you to be sure, this will save so much, also are you sure its gettin BOTH NO Fuel and NO spark, Again, sorry just making sure much quicker diagnosis then

Try checking it this way -
meter set on AC volts and probing both wires in the connector going to the CPS, have someone crank the engine over or remote start.
whats it read?

the way to check it at normal operating temparture to see if its dodgy
connect meter and set to ohms, put it on both the terminals and it should be 200 +- 75 ohms
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Unread 05-22-2012, 09:30 PM   #12
riverhippy
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Quote:
Originally Posted by Jstout724 View Post
You sure you checked all the fuses in the fuse box under the dash? Fuse #5, a 10 amp fuse, sometimes labeled 'dome' is a power lead to the PCM. Its kind of like a relay power for it. PCM wont work without this.

edit- sorry I just want you to be sure, this will save so much, also are you sure its gettin BOTH NO Fuel and NO spark, Again, sorry just making sure much quicker diagnosis then

al
ill double check to be positive......then repost
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Unread 05-22-2012, 09:31 PM   #13
Jstout724
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if its not totally disconnected or grounded out it should read infinity I believe

edit im learning alot right now, not a super pro like some of these guys - feel free to chime in if im wrong guys
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Unread 05-22-2012, 09:52 PM   #14
pete1991YJ
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Riverhippy: does your CEL come on when you turn the key? If so, do you get 12v at pins 3 and 9 in the ECU connector? If yes to all of the above, the ECU is good.

" CPS: You can check it's basic function but be aware that sometimes the darn things can be 'intermittant' but still read 'ok' when measured due to engine heat/temperature. Even so, these tests will show up a borderline CPS more often than not.

Check the connector first If you've just stalled out with same symptoms... unplug the CPS & plug it back in. If your motor fires back up you might get off easy, but don't count on it lasting forever. I dunno what doing this accomplishes other than cleaning the connector contacts enough to let additional voltage through to the computer. If unplugging & replugging worked then unplug the connector again and clean those contacts off. Then apply some OX-GARD, or other electrical contact cleaner & protectant (dielectric grease).

There is a distinct possibility that you're not getting a signal due to a faulty connector itself as well. Some people have cured their CPS problems by simply cutting the connector out of the harness and SOLDERING the wires together (Use heat shrink or electrical tape around the wire, of course!) Other's have replaced the connector with a newer, waterproof version from an electrical or automotive supply store.

Test#1 - Get a volt/ohm meter and set it to read 0 - 500 ohms. Unplug the cps and measure across the CPS connector's A & B leads. Your meter should show a CPS resistance of between 125 - 275 ohms. If it's out of that range by much; replace it. (* - Note: HO engines
are measured from the B & C connectors and should have near zero ohms.)

Test#2 - You'll need a friend to help ya with this one.
Set your volt/ohm meter to read 0 - 5 AC volts or the closest AC Volts scale your meter has to this range. Measure across the CPS leads for voltage generated as your friend cranks the engine. (The engine can't fire up without the CPS connected but watch for moving parts just the same!) The meter should show .5 - .8 VAC when cranking. (That's between 1/2 and 1 volt AC.) If it's below .5vac, replace it.

Desperate last ditch tip to get home or a few more miles from a failing CPS: - Other
than the unplug/replug trick... MJR passed on a trick of using a flat bar and a hammer to 'adjust' the CPS by smacking the CPS bracket and forcing a weak CPS just a tad closer to the flywheel. This lets a weak CPS get a stronger pulse and hopefully generate enough voltage to feed a good signal to the computer again. WARNING! - If ya smack it too hard... it'll go in too far and the flywheel will eat the CPS! Start walking.

Either way, if it fails ANY of the tests... you should replace it and save your self some major pain later. If not, at least carry a spare CPS but be aware that it's a royal pain in the *** to change on a cold motor and ya really don't wanna do it at night, on the trail and with a hot motor if ya can help it!"

http://www.lunghd.com/Tech_Articles/Engine/Bas...
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Unread 05-22-2012, 09:59 PM   #15
pete1991YJ
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http://www.lunghd.com/Tech_Articles/...iagnostics.htm
check this out - prolly your CPS tho.
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