96 Jeep XJ crank no start

[AJones96]

I have a 1996 Jeep Cherokee Country 4.0 with an auto transmission. I bought it for cheap because it has almost no rust but it came with a crank no start issue. The gentleman that I bought it from said that he was doing a tune up (plugs, wires, cap and rotor) and it would not start after he was done.



When I first got the Jeep, I cleaned all of the grounds, fixed 7 wires that were chewed on by a mouse, fixed the ignition timing ( it was 180 degrees out and the dustributor was very loosely bolted into place), and hooked up a ground that was disconnected between the cylinder head and the firewall. The 2 and 4 spark plug wires were also switched.



I verified spark.



The Jeep would run by pouring a little gas in the intake. I pulled the fuel rail and cranked it over with paper towels in front of the injectors and they were all spraying. I also cleaned all the injectors with throttle body cleaner and a homemade adapter and they all work on the bench and spray when 12v and ground is applied to the electrical connections.

I tested the camshaft position sensor with a multimeter and it tested out good with a constant 5v on one wire and an alternating 0v-5v on the other.



I thought it would be a fuel delivery issue since it would run when pouring gas down the intake so I thought maybe the fuel pressure was low. So I rented a fuel gauge and sure enough I had 5 psi at the fuel rail even after cycling the key a few times and hearing the pump run so I replaced the fuel pump and filter.



After doing that it seems to want to run more (1 or 2 seconds sometimes and sometimes a little longer when cranking when before it wasn’t even wanting to run) but still will not start.



I have verified a strong spark and I have read that with a bad crankshaft position sensor you will not get spark. The previous owner changed the crankshaft position sensor when he was trying to get it to run. I tested the cps using a procedure I found on a forum. My multimeter reads 1 when testing resistance between the “a” and “c” wires. The harness-side plug also reads just over 5 volts on both of those terminals. Is this correct?



I swapped the asd relay with the fuel pump relay which I know is working. The 86 pin on the ASD relay slot in the PDC also has ground with the key off and battery voltage with key-on-engine-off. Is this indicative of a short?



I also bypassed the fuel pump relay and cranked it that way with no luck.



It also backfires out the intake if you crank it too much (RIP to my eyebrows ). Not sure if this gives any clue to why it won’t start.

I’m no mechanic just a guy trying to learn in his driveway. I appreciate anybody that has any advice.

 

[AJones96]

I forgot to mention that there is no codes/check engine light

 

[Anak]

How old is the fuel? (Grasping at straws--you certainly seem to have hit all the majors)

Have you confirmed the fuel pressure with the new pump? (Yes, it is delivering more fuel, but is it at the correct 49 psi?)

If the above are both good then my guess is that your problem is on the spark side of the equation.

 

[AJones96]

How old is the fuel? (Grasping at straws--you certainly seem to have hit all the majors)

Have you confirmed the fuel pressure with the new pump? (Yes, it is delivering more fuel, but is it at the correct 49 psi?)

If the above are both good then my guess is that your problem is on the spark side of the equation.

The fuel was over a year old so I siphoned it out before dropping the tank to change the fuel pump. It has around 7 gallons of fresh gas in it.

I have not checked the fuel pressure since changing the pump. I’ll have to rent a gauge again. Thanks for your reply! I’ll let you know what I find out

 

[AJones96]

How old is the fuel? (Grasping at straws--you certainly seem to have hit all the majors)

Have you confirmed the fuel pressure with the new pump? (Yes, it is delivering more fuel, but is it at the correct 49 psi?)

If the above are both good then my guess is that your problem is on the spark side of the equation.

I rented a fuel gauge. It reads right at 49-50 psi. I guess I will start digging more into the spark side and double check the ignition timing

 

[Anak]

Consider the distributor itself (Particularly the "cam sensor" in the distributor).

Consider also the coil.

And consider the grounds. There are several at the dipstick as well as the battery cable that runs to the coil bracket.

Here was one of my experiences with some of those grounds: Intermittent stalling issue

 

[AJones96]

So I read your post and I looked at my grounds on the block by the dipstick and 2 of them looked good and the third was a little rough and actually broke when I spun the wire one revolution. I went ahead and replace all 3 ring terminals as the wires leading up to the loom seemed to be in good condition

I also found that the downstream 02 sensor (I assume that’s what it was. It was a group of wires back by the slip yoke on the transfer case) had been cut when aftermarket exhaust was put on and the wires were stripped back and resting on the shiny new muffler (possible short?) and the upstream 02 sensor (underneath the exhaust/intake manifold) had melted and all the insulation was melted off and they were all touching (somehow no blown fuses?). I fixed all that and still no luck.

I put the ol’ voltmeter on the fuel injectors and I have battery voltage on all 6 but when cranking I’m only getting about 2v+/-. The ground wires running to the pcm connector all read at right around 3 ohms. From what I can find this is within specs. Could this be a poor pcm ground or possibly a bad pcm? I can’t seem to find online where the pcm is grounded.

 

[AJones96]

*the wires to the upstream 02 sensor melted lol not the sensor

 

[Anak]

I know from experience grounded O2 wiring is a very effective kill switch. I am surprised fixing that did not fix the issue. I wonder if it is possible the PCM could have been damaged.

In what part of the country are you located?

 

[AJones96]

So I opened up the pcm and found the capacitors had spilled their guts all over the circuit board. I put new capacitors in the pcm and still no luck. I found a guy in my area parting out another 96 and bought his pcm and installed it and still crank no start. So I went through testing continuity to ground in the fuse box to see if I could find a possible short and found low resistance on the output wire of the fuel pump relay (which is tied to the fuse for the asd, engine controller and a myriad of other things). So I was like oh I found it another short! Tracked it down to the fuel pump and took the fuel pump out and everything (again) just to find out that dc motors (like on the fuel pump) have a low resistance between the + and - terminals. You learn something new every day. I saw a video on YouTube of a guy with a crank no start on a grand Cherokee and the cps was a tooth off on the timing and it was presenting a crank no start condition so I took another look at the distributor. I took a paint marker and marked the location of the #1 post on the base and took the cap off with the #1 cylinder at TDC on the compression stroke. The rotor was a little past my mark, maybe 1-4-1/2 in. I undid the bolt and set it to the right spot. Put it all back together and it fired right up. Probably the greatest feeling ever lol.

A lot of my issues getting it started was inexperience. Just with getting the ignition timing set (incorrectly at first) with the distributor and electronics and all that but I feel pretty confident now with understanding how the jeep runs after opening up all the loom and tracing wires and knowing how everything goes together.

I’m north of St. Louis, Mo.

 

[AJones96]

When I say the fuel pump relay output is tied to the fuse for asd, engine controller and a myriad of other things I mean when the relay is closed the input 12v power comes from that fuse

 

[Anak]

Congratulations on getting it licked.

And thank you for sharing what wound up fixing it.