94' Jeep Grand Cherokee Limted 5.2L V8 - will not start to save my life


#1

So I had to replace my radiator early this week and after replacing that, the water pump, thermostat, and all the hoses I then filled the cooling system up. Cranked her up and let her run at idle for about 20 minutes. Got it up to operating temp. Burped the system of the air and got the radiator all topped off. Turned it off and then cleaned up the the puddles and hosed down the area underneath the car. Ran some water over the area of other radiator as well.

Came back out a while later that night and went to start the Jeep up, which has not had a single starting issue since I’ve had it, and it would crank over for days, but would not fire up at all. The relays click, there is pressure at the rail, just doesn’t seem to have any spark.

I have changed out the crank position sensor and cam position sensor on a hunch of best know problem areas. Changed out the distributor cap and rotor while I was there. Got someone over to look at the electrical, but they had only enough time to let me know that there is voltage to and from both the cam sensor and the fuel pump, but that there is voltage only getting to the crank position sensor, not back from it. I have learned that the PCM is a problem child as well.

However, out of curiosity I flipped the ignition to see if there were any OBD and for the first time I got more than just the two prior (12 and 55). This time I had ODB code 41 “alternator field switch” and the battery is basically dead. And the person that came out is thinking things a possible timing chain slip…

I’m descent with the mechanical. I will find someone for things outside of my comfort zone, like timing, transmission and the like. Electrical is okay, I just don’t have the right testing equipment yet. I have had my share of alternators go out, while I am driving. I have no clue if this is all related to one thing, not related at all, or just a calamity of errors.

If there is anyone that has had this history before, I’d love to get a little clarity on this before I start throwing more into it that may not be needed. I was just getting ready to go down the road of getting a PCM, but that is about as blind in action as the other items so far.


#2

" there is voltage only getting to the crank position sensor, not back from it."

The engine won’t start without a signal from the crank position sensor. If there’s voltage to it but no voltage out, it seems the sensor is bad. Replace it and see if you get spark.


#3

How often then is this a problem with a new sensor not working then? I just replaced it…granted the second time around will be a lot quicker to do.


#4

could something have gotten wet?


#5

i had thought about that, hence checking first then replacing for giggle the distributor cap and rotor. Even just the little bit of steam could have gotten up under the thing. Check all the fuses, and they checked out good. Did a continuity test with this little fuse tester I’ve had in the roadside kit for ages. Checked connectors, but its been almost a week now.


#6

I had a truck that the distributer cap would get wet if I parked it facing west on a foggy night.


#7

I like it when the most obvious problems are the ones you already know about from experience. For all the “issues” that older autos are maligned for, I’ll happily take those over all these computer/sensor/wiring issues any day. Though right now, I have to deal with this so I can later bang my head against a faulty carb or wet distributor cap…


#8

me too! I just bought a 1990 Cherokee afer driving 1975 ford trucks for about 15 yrs. just when I got carbs figured out I have fuel injection. luckily its not too modern.


#9

A 318 V-8 will usually throw a timing chain before reaching 200,000 miles. The most usual way that it is tossed is when cranking the engine. Old gear heads can often diagnose jumped time from the sound that the engine makes when cranking with little compression.


#10

my 75 ford truck did strip the timing gear when cranking a couple of years ago… :frowning:


#11

If I remember correctly, my rotor was not turning and that was how it was diagnosed


#12

Forgive me lack of knowledge, cause I have just thrown my hands up in the air at this point when the work “timing” comes into the conversation…I understand the working idea of the timing chain, but I had figured it would cause misfire or the like. Not a complete kill. Then were does the no voltage from the crank sensor come in and the no rotor spinning.

Sorry for all the questions. I should have paid more attention when my uncle was trying to teach me more of this when I was a kid.

BTW, if it is the timing chain, is that something that requires the whole engine to be removed, or could it be done in a driveway…


#13

in my truck, we did it in the driveway, it did not cost much, but the labor took awhile and entailed removing radiator, water pump and fan. I have no idea about your truck tho. definitely get a manual and an experienced friend to help you.


#14

Jasmed1’s right!!!

“The engine won’t start without a signal from the crank position sensor. If there’s voltage to it but no voltage out, it seems the sensor is bad. Replace it and see if you get spark.”

Yosemite


#15

yeah, don t assume the worst, but if you crank it and the rotor isn t spinning…


#16

If you replaced the water pump you were more than half way to the chain. If you have a compression gauge check compression. Compression below 90psi indicates the chain is likely jumped. If you remove the distributor cap and crank the engine over but the rotor doesn’t turn the chain has broken or the cam sprocket is stripped smooth.

I have replaced several Mopar timing chains and never ran across a bent valve, in case that question pops into your head, @kolbyjames.

Check the compression and post the results.


#17

yeah, my sprocket was stripped. it fired once and cut out then I cranked and cranked it with no result. my son finally noticed the rotor was not spinning the next day when we tried again


#18

How many miles on that old Chrysler 318?? If you are north of 130K miles, the plastic coated timing gear falls apart allowing the chain to slip and the timing to be grossly incorrect…

Remove the cap so you can see the rotor and rotate the engine with a breaker-bar on the crank pulley bolt…Rotate the crank back and forth as see if the rotor responds to this rotation. How far behind the crank is the rotor when you change directions…That will tell you how much slop is in the chain and gears…


#19

If the CPS sensor wasn’t working there should be a code 11 generated -“No crank reference signal detected during engine cranking. Intermittent loss of either camshaft or crankshaft position sensor. CKP sensor target windows have too much variation.”

In order to check the CPS output signal it may require a O-scope. The pulse duration may be too low and short for a basic voltmeter to pick up on. The trouble might be with the injector circuit. Perhaps something like the security system may be shutting that down. Try spaying some starter fluid into the intake to see if that gets the engine fired. If that doesn’t work then the ignition system, timing, and compression should be checked. If you feel the PCM is bad then you should be able to get a used one pretty cheap from a salvage yard.


#20

There was no code 11 at anytime. The rotor is spinning like it should with the crank. I’ll put the timing chain on the hit list for later this summer, just cause.

So I’m left with the feeling that it’s back to the PCM and the crankshaft sensor. Get a multimeter and a trip to the salvage yard to get some goodies it looks like.