Dustin Ray

I have a 98 xj with a no start no fire problem. Ive tried a new Ecm, replaced coil, distributor pickup, wires, crank sensor and both O2 sensors. Wondering if the fuel presseure was low enough it would keep the coil from firing. Cant figure out what im missing with the auto shutdown. Help would be appreciated.

BillyBoy

My 98 had a similar issue. Replaced everything. Took it in. Paid to have them tell me it's the wiring harness across the top of the engine well. Grab it and pull or shake while someone turns it over. If it changes you found your issue. The wires wear in there.

Dustin Ray

Never wouldve thought that but anythings worth a try. Thanks. And whats this factory alarm stuff. Never knew it even had one.

BillyBoy

Look up your jeep at the dealership by vin number. Itll give u a printout of all options you have. Do this before u worry about factory alarms. I don't have one on my 98.

tjwalker

**Have you tried "swapping" the ASD relay with another one in the power distribution center? These relays are all of the same part number so swapping is not a problem. More on the route of spark below.

**Did you scan your old computer for any pending codes? Sometimes there are pending codes that can be very helpful in diagnosing a problem.
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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.

Dustin Ray

Ill look up the vin online. Dont think it has an alarm either. Had this for over 10yrs. Never heard of it. I have swapped relays and their is no codes in the Ecm. And live datalooks to be ok to me2. It is a new crank sensor but an aftermarket. Ive heard these were very picky about them.

tjwalker

Of course we can't say for sure if this is related, but this XJ forum and others are littered with threads of folks that have struggled with using aftermarket crank sensors in their efforts to repair no starts.

The only way to rule this out of course is to install a genuine Mopar crank sensor. I'd recommend doing just that.

Dustin Ray

Ive heard all about the after market cps being a little off. Still it shouldnt make that much of a difference. Replaced both o2 sensors and checked all the grounds on the block and engine compartment. Are there any more grounds i may have missed??

Dustin Ray

Ok so ive pulled the wiring harness apart and ohmed out the coil wires to the ecm. Test good with little resistance. Still cranks and flokds out. Would low fuel pressure have anything to do with the ecm not powering the coil??

jordan96xj

No. The PCM (computer) has no awareness of the fuel pressure or even whether the fuel pump is working. If everything was working correctly, the spark would still be present, even if no fuel was. If you have -no- spark, then that is your direction.

The ignition coil gets its postive voltage from the PDC via the ASD relay and fuse. If the coil is never being grounded, the problem is between the coil and the PCM. If the coil is never seeing positive voltage, the problem is typically between the ignition switch and coil (which includes the PDC ASD relay and fuse).

Common causes of no spark would be:
ignition switch
ASD relay or fuse
Coil
CPS
Cam Pickup Sensor (under distributor cap)

Dustin Ray

Voltage test at the relay is good. Constant power switch power and ground. Switched relays and no change.

jordan96xj

If your testing confirms that the positive side of the coil is present, and the ground is what is missing that leaves:

1. PCM not happy with startup conditions such as missing signal from CPS or Camshaft Pickup Sensor.
2. Bad coil or bad coil connector
3. Bad wiring between coil and PCM
4. Bad PCM (rare)

No spark can also be caused by low battery voltage during startup. When the available voltage is used to close the starter solenoid and the amperage begins flowing to the starter, it can momentarily drop the entire system voltage such that other relays (such as ASD) may not stay closed. Or when the battery/starter are not strong enough to achieve the minimum RPM required before the PCM will initiate ignition (by providing ground to the control side of the ASD relay). Most of this can be tested for by jump starting the vehicle, if everything starts and runs normally with jump start...it is a strong indication that battery/connections/alternator are in question.

Dustin Ray

So if the ECM has no knowledge or control of the fuel pump or fuel pressure, how could i have had a low fuel pressure code and misfire code pop up. It has an ECM controlled governor that cuts off the fuel at a certain speed which im assuming is part of the ASD controls.So the question is if the fuel pressure was low enough to run in limp mode and the CEL flashing before it died going down the road, is it possible the ECM killed the circuit for lack of pressure hence the prior low fuel pressure code that is nonexistant anymore in the ECM?? Not one single code can be pulled up with any regular scanner onvthe market, not even the miracle $5000 Snap-On scanner.