ace

Hello all,

I'm hoping that if I can solve this issue, this post will be helpful to all the readers of the forum. (I've looked at numerous posts today, and I haven't found a situation just like mine). So here it goes.

The backstory: '96 4.0 XJ has been running perfectly for a year or more. Drove home one night last week and parked it. Next morning tried to start it: she cranks forever, but will not start. (On the bright side, it was in my driveway).

Tested for spark that night and had none.

I've replaced:
(In the last 3 months):
distributor cap
rotor
spark plugs
spark plug wires

(In the last week):
ignition coil
CPS (crankshaft position sensor)
pickup coil

I know many of us have had no-start issues; has anyone with a similar problem found another solution? Thanks.

Larry's XJ

Do rotor and cap still look good? Did you use quality parts or cheapest available?
Pull coil wire from cap and check for spark from it.

ace

Both cap and rotor are in great shape. I used parts priced "in the middle" mostly. No spark from the coil.

Jds12

Had a '98 at work, would crank forever but no spark. We tried a few parts that commonly fail, tested parts etc, still zero spark.

Ended up buying a used ecm computer and it fired right up.

ace

Thanks, Jds12. I have a feeling it's the computer. Especially with how it was working great and then just wouldn't fire up the next morning.

Has anyone had luck reprogramming a computer?

tjwalker

ASD circuitry and ignition switch still in play as well as computer. First thing I would try is to swap the ASD relay in the PDC (black box under hood) with another non-critical relay. Good luck and keep us posted!
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Spark: 12 volts from ignition switch to the ASD relay; when the key is first turned on the PCM provides a ground to the ASD relay to energize it, then the ASD relay passes 12 volts to the coil primary side. If no crank sensor signal is generated after a couple of seconds the PCM cuts the ground to the ASD relay (and fuel pump relay too) and that cuts power to the coil (and fuel pump). Key to START and once again the PCM energizes the ASD relay. Now, a critical element is the crank sensor--no signal from the crank sensor and the PCM won't trigger the coil to provide spark.

ace

Update:
Swapped out the ASD relay with another one. No fix.

We're gonna solve this!

madmanmarty

are you sure it is a strong spark?
what brand of crank sensor?
others, does a bad cam sensor cause a no spark?

ace

There is no spark at all.

97grand4.0

cam and crank sensors both can cause no start. B+ to all your sensors? fried wire under hood? Ground to all sensors?

BillyBoy

My standby answer to no start once all grounds are cleaned and minor parts replaced is to start wiggling. Have someone crank it. Put on a leather glove. Beware of moving parts like fan blades...

While it's being cranked, start wiggling wires, harnesses, and especially connections. I replaced my coil and all the regular tune up stuff and it turned out being a worn wire at the coil. Held at the right angle, fired right up. Next time was the wiring harness that runs across the inside of the firewall at the top. Wiggle hard, all directions.

Good luck. (At least my way of trying get is also cheap.)

Radi

You should have +12V at the coil (+) terminal when the ASD relay is energized. (for at least a few seconds after starting to crank the engine) Check to see if you do.
(This is the two-wire connector to the coil, not the high voltage lead to the cap)

The other wire in that connector is the (-) and it's grounded by the PCM to trigger the spark.
You can probe with a test light to see if it strobes when the engine cranks. If not there's a problem with the ECU signal. Check the three connectors and ground connections before condemning it.

jawalter

Check the pcm fuse in the PDC under the hood. Mine kept blowing due to a short - took forever to find that the fuse was the issue, but same symptoms as you. chafed wire rubbing on the block sparked and shut it off...
JW

BillyBoy

May be a silly question, but how did you check the spark?

ace

I pulled the spark plug wire off cylinder 1, put a used plug in it (one that was still in pretty decent shape - no corrosion/charring), laid the plug across the valve cover, and had a friend crank it while I looked for spark. Tried this twice.

Here's my silly question: the valve cover is a ground source, right?