No Spark, No Fuel, and No Idea What to Do

[gottarollwithit]

So i just bought my first Jeep Cherokee. It's a 98' model so it has many of the last gen updates.

However, i bought this car semi broken - the prev owner got stuck in a pit and tore the downstream 02 sensor wiring off when getting out. It was enough to yank the wires apart at the harness and yank out the 2 prong male connector that plugs into the top of the transmission. Any idea what this connector is for? It has 2 wires, one is black/red and the other is some other kinda black. It has a green weatherseal on the inside of it as well.


More importantly, the engine isn't getting fuel or spark. I don't hear the fuel pump kick on when putting the key in pos 2. Additionally, i put my multimeter on the crank sensor and it reads open between the far left and middle terminals, if the tab is on top.

Any ideas?? Maybe a bad ECU? What else should i be looking for here? Anybody know what else is tied into the harness down where the downstream O2 sensor is?

 

[gottarollwithit]

Forgot to add. The car is able to crank with no problems, and the fuel and voltage gauges don't move.

I assume these are supposed to move when the key is in pos 2??

At the moment, i'm thinking that some wires down near the downstream O2 sensor got yanked and are grounding or shorting out, which is causing the computer to not power on, hence the no fuel pressure or spark. Thoughts?? Any idea how to test this?

 

[JaVeLiN]

Fuel is a great place to start. Here is a trick from North Dakota... Take out the fuel pump relay, and grab a paper clip. Look at the bottom of the relay, and figure out what it takes to jump #30 to #87. Then jump those with the paper clip, and see if the fuel pump starts to hum. If that works, your fuel pump is not the issue, and those wires are just fine.

 

[gottarollwithit]

Oh yea, i swapped relays. I had a few of the same relays from the JY and none of them made the fuel pump kick on.
I assume the fuel pump is supposed to prime in ign pos 2, right??

Supposedly all of this stuff crapped out at once. Isn't it kinda suspicious that i can't get spark or fuel??

 

[JaVeLiN]

Almost sounds like the ASD system and relay thinks the XJ was in a bad crash. In a bad wreck, the ASD is supposed to shut off fuel and spark. If you just try a new relay, that tells me nothing. If you try the paper clip trick, it may tell me the answer... If I go out to my 1995 XJ and jumper the 30 and 87 where the fuel pump relay plugs in, the fuel pump will spin. Does it work that way for you?

 

[gradon]

I've blown a PCM from the front o2 sensor harness melting to the Borla and the 12V heater feed short out the ASD every time I tried to start it(of course I tried a good CKP and coil before I tried another PCM). Try a known-good PCM(do your homework on what years are compatible). Solder in a cut o2 harness with the connector from a JY(or online search). At least verify that the ripped wires aren't touching for the time being.

 

[CharlesS]

Have you checked your fuses? The shorted O2 sensor may have blown a fuse.
Do you have 5VDC reference voltage on the CKPS and CPS?

This past weekend a friend with a '97 TJ couldn't get his Jeep started. He installed a new CKPS because he heard they are known to go bad. He was also going to replace the CPS, but I recommended testing them first.... Later in the day I stopped by his house and found the problem to be oxidized terminals on the ASD relay.

 

[Tim_MN]

The car is able to crank with no problems, and the fuel and voltage gauges don't move.

Test your CPS.



The most likely cause of it cranks and cranks but won't start up is the Crankshaft Position Sensor (CPS) located on the transmission bell housing. Often this part is also referred to as the CranKshaft Position Sensor (CKP). CPS/CKP failure is very common. The CPS/CKP can stop working with no warning or symptoms and the engine will not run or the engine may randomly stall for no apparent reason. Crank Position Sensors can have intermittent “thermal failure”. This means that the CPS/CKP fails when engine gets hot, but works again when it cools back down.

Symptoms-
- Starter cranks and cranks but engine won't start up
- Fuel gauge and voltage gauges may not work or display properly.
- You sometimes will have No Bus on the odometer after 30-60 seconds.
- A failed CPS/CKP may or may not throw a CEL trouble code.
- No spark at the spark plugs.
- Fuel pump should run and prime for 3-5 seconds.

If the CPS/CKP is failed sometimes the OBD-II code reader cannot make a connection to the computer or cannot read Check Engine Light/MIL codes because the CPS/CKP has failed.

Diagnostic steps to confirm the CPS is the cause of your no-start

-You should be able to verify a bad cps, by unplugging it, and turning the ignition key to on. If the voltage gauge and/or the fuel gauge now displays correctly, replace the CPS.
-Unplugging and reconnecting the CPS sensor where it connect to the main harness near the back of the intake manifold usually resets the ECU and if the jeep fires right up after doing this you can bet that the CPS is faulty and needs to be replaced.
-Exchange the fuel pump relay and the ASD relay with one of the other similar ones in the PDC to eliminate the relays as the cause of the no-start Confirm that the fuel pump to runs for 3-5 seconds when you turn the ignition key to ON.
-Eliminate the NSS as a cause of no start. Wiggle the shift lever at the same time you try to start. Put the transmission in Neutral and do the same. Do the reverse lights come on when the shifter is in Reverse?
-Inspect the wires and wire connectors at the O2 sensors on the exhausts pipe. A short circuit from melted insulation or from broken O2 sensor wires can blow a fuse and the ECU/ECM will lose communication.

If you buy a new CPS, get a genuine Jeep CPS, or the premium one from NAPA. Cheap crappy “Lifetime Warranty” parts are often out of specification or even failed right out of the box. They usually also have a shorter service life than better quality parts. Buy good quality repair parts and genuine Jeep sensors for best results.

Begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables and replace as needed. Do the same for the grounding wires from the battery and engine to the Cherokee's frame/body. Jeeps do not tolerate low voltage or poor grounds and the ECM/ECU will behave oddly until you remedy this.

Crankshaft Position Sensor Connector (CPS/CKP)
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CPS Testing

TESTING PROCEDURE 1991 – 2001 4.0L H.O. engines
1. Near the rear of intake manifold, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals B and C (See Image). Ohmmeter should be set to the 10K-or-2OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.

TESTING PROCEDURE for 1987 – 1990 4.0 L engines
Test # 1 - Get a volt/ohm meter and set it to read 0 - 500 ohms. Unplug the CPS and measure across the CPS connector's A & B leads. Your meter should show a CPS resistance of between 125 - 275 ohms. If the CPS is out of that range by much, replace it.
Test # 2 - You'll need a helper for this one. Set the volt/ohm meter to read 0 - 5 AC volts or the closest AC Volts scale your meter has to this range. Measure across the CPS leads for voltage generated as your helper cranks the engine. (The engine can't fire up without the CPS connected but watch for moving parts just the same!) The meter should show .5 - .8 VAC when cranking. (That's between 1/2 and 1 volt AC.) If it's below .5vac, replace it.

The 2000 and 2001 will have the CPS in the same location on the bell housing, but the wire connector is on the passenger side, near or
on top of the Transfer case, not as shown in the diagram below. Simply follow the wire from the sensor to the connector.
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[gottarollwithit]

My initial diagnosis was a bad crank pos sensor b/c i saw that there was no spark, however there is also no fuel pressure.

Will a bad crank sensor cause no fuel pressure? The fuel pump does not kick on.

How do i jumper the ASD relay? Do i just paperclip whatever 2 terminals make voltage? I tried putting some JY relays in place of the ASD relay and it didn't do anything.


What is my PCM?? Is that my main computer?

Can anybody elaborate on how exactly the Automatic Shut Down (ASD) system works???
As i have neither fuel or spark, that seems plausible. Maybe the previous owner popped out of this rut and it made the ASD system kick on?? Any way to bypass it?

 

[x99j]

Will a bad crank sensor cause no fuel pressure?

yes it will.

unplug your crank senesor and see if the fuel and volt guages come back to life. if they do you found your problem. mike

 

[birchlakeXJ]

Agreed. The fact that the fuel and voltage gauges aren't working is a VERY common symptom of a bad crank sensor.

As x99j pointed out, a simple troubleshooting technique is simply to unplug the crank sensor at the connector under the hood. NOW check your fuel and voltage gauges. If they are working with the crank sensor out of circuit, replace your crank sensor (with a Mopar unit).

 

[gottarollwithit]

OK, update time now that i've done some testing.

-Still no fuel pressure at the rail or spark.
-There's no power at the coil.

-There's about 1.25v at the fuel pump, regardless of whether i jump the FP relay or use the relay itself.
-Obviously, the FP never spins up, even when i jump it from the relay.

-I get a solid 12v at the fuse box under the hood (based on the + wire under the second cover and grounding onto the block)
-At the fuse box under the hood, there is a solid 12v at each of the large fuse terminals.
-I measure 12v at the ASD and fuel pump relay terminals.

-I jumped the ASD relay from 30 to 87 and it did nothing

-I disconnected the crank sensor and my fuel and voltage gauges still don't work.
-I resistance tested the B and C terminals on the crank sensor and it reads open. Still a possibility?

-I tested the PCM computer by doing the diagnostic test of holding the odo reset button down and turn the key, and it seems to work just fine.

-Also, the Neutral safety switch seems to be having some issues now. When in Park, sometimes it'll crank, othertimes it doesn't. If i jiggle the selector, it usually will. In Neutral, it always cranks. It will not crank when in gear though. From what i understand, the NSS only controls the ability to crank, not spark or fuel.

Based on all of this, got any new thoughts??? Maybe the fuel pump wiring is on the same harness as the O2 sensor and the wiring got mangled under the corrugated sheathing, which lead to only having 1.25v??

Anybody know how to manually spin up the fuel pump using another car battery? There's a 4 pin connector and i dunno which pins to use...

I'm starting to think that i'm in a bit over my head. Anybody in the Bay Area interested in taking a look??

 

[Rush Power Systems]

The ECU (sorry Chrysler PCM) send gauge info via data bus lines, we have seen good self-checks and the ECU is still bad, I would go spend $100 at the dealer and find out if your ECU is toast, shorting the o2 lines can cause that. This assumes that all your fuses and fuse-able links are good. If your fuel pump was the issue you would still have spark. The problem I have with trying a new CPS is if you have a short in the ECU you can blow the CPS. You could also have shorted wires in the harness, so again I would start at the dealer, you may get lucky and it just needs a re-flash.

 

[Tim_MN]

It would be logical to assume you still issues with wiring. Perhaps a short to the bus that is overriding the 5 volt data signals from the sensors. Maybe you have a fuel pump issue, or a short/open circuit.

You have enough issues that you should be using a JEEP Factory Service Manual to diagnose/test systems and to figure out wire colors and functions.

In rare cases, a failed CPS will take out the ECU/PCM. (Not so sure if it happens in the other direction).

Start with the your obvious issue, getting 12 volts to the fuel pump. Why doesn't the pump run when the pump relay is jumpered ?

 

[Ecomike]

Have you tried an OBD-II scan yet for codes? I think the 98 O2 sensor gets its power from the PCM, so a bad short there is very likely to have fried part of the PCM or taken out a PCM fuse.

I recently had a no start OBD-II from jump starting a dead battery, that took out one of two PCM fuses (yes it had two ???), becayse the battery was shot, 0 volts, and cables were too small, and when I tried to run an OBD-II scan I got no signal, but the vehicle powered up and cranked, and we got no fuel or spark. So I dug and found a second fuse box, that had a PCM-B fuse that was blown. That fixed it!!! While it was not a jeep, it was OBD-II 2001, GM Saturn, so the 98 Jeep may be similar!!!

So check every damn fuse, no matter what it claims to control (my sons Ford 1996 had the AC control on an ABS brake fuse of all things, took me months to solve that damn AC clutch power problem even with the wiring schematics).

Next on my list would be to inspect the ignition switch and wiring!!!

 

[McQue]

- the prev owner got stuck in a pit and tore the downstream 02 sensor wiring off when getting out. It was enough to yank the wires apart at the harness and yank out the 2 prong male connector that plugs into the top of the transmission. Any idea what this connector is for? It has 2 wires, one is black/red and the other is some other kinda black. It has a green weatherseal on the inside of it as well.

These two wires and connector might be the 4WD switch connector.
The Black wire would be tied into the Z1 ground circuit, which is also the ground circuit for many other important circuits that must be properly grounded to start your Jeep. If this were my Jeep I would be checking out this harness that was damaged. Open the harness all the way from the downstream 02 sensor, up to where the Black wire is grounded near the starter. Or, use your meter to confirm all wire continuity point to point within this leg of the harness and check for shorts from wire to wire, and to ground on all the wiring in this section of the harness.

If this all checks out good, then next I would be trying to find out why I don't have voltage at the fuel pump.

 

[Rush Power Systems]

It would be logical to assume you still issues with wiring. Perhaps a short to the bus that is overriding the 5 volt data signals from the sensors. Maybe you have a fuel pump issue, or a short/open circuit.

You have enough issues that you should be using a JEEP Factory Service Manual to diagnose/test systems and to figure out wire colors and functions.

In rare cases, a failed CPS will take out the ECU/PCM. (Not so sure if it happens in the other direction).

Start with the your obvious issue, getting 12 volts to the fuel pump. Why doesn't the pump run when the pump relay is jumpered ?

That is a good point, bypassing the FP relay should give you a response from the FP but it does not explain no spark. If it was running when the damage happened, it could be shorted out ECU + wiring to and/or FP itself. It is a direct wire to the FP so if you run direct power at the FP relay you should get power. Still though I would take the guess work out of it and see the dealer, that way you know for sure if you ECU is ok.