Itsajeepthang99wj

I have a 1999 jeep grand Cherokee laredo 4.7 I need a little insight determining my problem please. So as of right now it's got a mind of its own as far as running and driving.it starts up fine (cold start) but if it's a hot day it tends to have hesitation at normal running temperature but when it gets to that point in temperature it feels like its running out of gas but it's got gas in it and sometimes just dies stalls out with no warning?? After the stall I go to start it and it just cranks and cranks no fire and all gauges don't move. But how ever if it sits for about a hour and unhooking the battery while waiting and rebook it up put key on the on position not start position the gates move and then fires up?? I'm puzzled but one of my friends said a bad cps? That sound right it's been happening on and of the past year more often when it's hot out then cold.just wanted to get some feed back from the jeep community thank you.

Noah911

The first thing I would do is verify the spark plugs are firing when they should. After it dies and you are cranking to no avail, you can pull a spark plug, ground the threaded portion of it to the engine, and check to see if the CPS could have died on you (when it cranks over not starting).. You would know by way of no spark happening when you test it.

Electricity problems in the CPS circuitry could cause it to not run well when it is starting. After running for awhile (maybe heat build-up causing CPS to fail right), it may die until cooled off. Test for spark when it is acting like it has died, to see.

If you see spark, but it is a weak spark happening, it could be something else like the ignition coil, the spark plugs themselves, distributor, etc...

No matter what, I would test the CPS with a DVOM.. To verify it is getting power supplied to it by the PCM, it has a ground supply being delivered to it, and that the CPS is delivering its on/off signal that it is supposed to create.

There is no test to do for resistance on a CPS, since the crankshaft position sensor is a Hall-Effect three wire CPS. What this means: it produces an On/Off DC voltage signal that can be easily measured with a multimeter. Resistance testing is non-applicable.

What I first said though.. if you are seeing appropriate spark happening when it should be, you probably do not have a CPS problem? Ultimately, it is possible it may be misbehaving electrically still, to cause issues though. A way to know is to test it with a DVOM.

The CPS is a little difficult to test though. You need to know how. It is easy to learn, but you have to know how. Test it to see if it is creating an on/off voltage.. the only way to correctly do this is by manually hand cranking your engine slowly to see if 5V comes and dissapears as it should...

Don't remove and replace the CPS sensor without keeping the 'air-gap' in mind. If you remove it, or install another CPS, you are supposed to set an air-gap here at the sensor for it to work right. You don't have to remove it to test.

You should be shutting off the fuel injectors too, while testing a CPS.

Itsajeepthang99wj

I will try these different test and narrow down my problem hopefully it's nothing major in terms of the problem it's self. It's very annoying and not to mention dangerous if be stalled while driving.thank you for your input. Will post with hopefully good news.

97grand4.0

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dave1123

crickets.