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Not getting Spark or Fuel

7

79yj

NAXJA Forum User
Location
Troy, IL
I went out to start my 1998 XJ 4.0 today and it will crank fine but not start.
So I began the testing and determined there was no fuel coming to the rail.
So I unplugged the fuel pump and tested a few wires & no power back there. I double checked by running 2 wires to the pump and it will pump fuel with power from the battery and pump outa the rail connection. Tried to start it that way and no good so I continued testing & there was no spark.
No power is getting to the coil at all.
I checked all the fuses under and hood and under the dash. Changed one.
I did find 2 fuses under the hood that have no power on either side. They are in the cluster of teeny tiny fuses. (may be blanks?)
I also noticed that the gauges are not working. The nudge up when I turn the key but even the amp gauge doesnt come past the bottum. The oil pressure gauge doesnt move either & I feel like it should while I crank the motor over. The fuel gauge shows nothing so I added a few gallons with no change.
I switched the fuel pump & a/c relays just incase with no changes.
Where do I go from here ?
What to check or try next?
Thank you,
Eric
 
sounds like a bad CPS ( Crank Position Sensor)
no CPS signal means no spark...
sometimes if you disconnect the CPS connection (at the top of engine near back of block) and reconnect it, the motor will start again...
 
Not sure if I mentioned that I put a few gallons in the tank just to be sure it had fuel in the 1st place.

I did try the unplug the CPS trick but it didnt start.

Who has CPS for cheap maybe I will change it out just to see?

Thanks,
Eric
 
CPS not the easiest part to change...do a search on CRANK POSITION SENSOR and you will find many good threads about replacing it...what tools you need, and what to look out for...You will also get an idea for what other parts can cause this sympton...
ASD relay, PCM, or any of the sensors could be pulling down the 5 volt supply on the PCM...I would get a meter out, and start checking a few things before throwing parts at it...

The PCM monitors the crankshaft position sensor. If the PCM does not receive a crankshaft position sensor signal within 3 seconds of cranking the
engine, it will shut down the fuel injection system. The fuel pump is activated by the PCM through the fuel pump relay. Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then control the injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off.The PCM determines the proper ignition timing according to input received from the crankshaft position​
sensor.
 
Last edited:
it is the cps - you should get a no bus code on the dash, fuel pump wont turn on

trust me i know! it will take 75 for a new one and about an hour to change if u have never done it before
 
I changed out the CPS and the ASD relay today and it still will not start.

What to check next?

PCM ?

Thanks for all the responses. I need all the info I can get.

Eric
 
The 2 fuses that have no power on either side are in the cluster if tiny fuses under the hood directly before the relays.
I was thinking that they were blanks but it doesnt make sense that they have wires running to them from the bottum etc.

The lid of the box doesnt tell me what they do for the tiny fuses.

Anybody have a picture & know what they feed?

Thanks,
Eric
 
Just went through this a few weeks ago. I changed out the crank position sensor, cam position sensor, and still no go. Finally got a used PCM to try and she fired right up.

Before you spend the money on a new one, find a used one at a local yard and try it. I got a used one for $35.00 with a 90 day warranty and it still works great!! Search under my name and you will find some good info on all of this. HTH

Kim
 
I don't have an FSM for 1998...but I am looking at one for 1997, and if your rig is wired the same as this 1997 FSM, you have an electrical problem because there is only one unused fuse in that group of 12 small fuses. Which ones are out...which row, closest to relays, middle row, or row closest to bigger fuses? Which fuse in the row, 1st closest to fender, 2nd, 3rd, or 4th?
 
The fuses that are out are the row closest to the relays but not the one that is closest to the fender.

What can I do to resolve this other than splicing a wire into the bad fuses from a different one that does have power.....only to test the problem.

What do you think?
Eric
 
I only have 3 fuses in that row.
The one closest to the fender has power on both sides but the other 2 have no power at all.
 
looks like the first fuse, farthest from the fender, in that row of four, closest to the relays, is not used..
next two fuses in that row, F20(20Amp) & F23(15Amp) are fed power to them from the ASD relay closing...
last fuse in that row F26(10Amp) gets power from Fuse F9 and supplys power to the overhead module.
 
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turning key to Run/Start should power up thoses fuses until the PCM turns off the ASD relay ( if it is enabling the relay at all)...you can always try jumper wiring the ASD relay to check the power at those fuses...
...but since the guages don't seem to be working, I'm starting to think the PCM is hosed...check 5 volt output from PCM...if its not there, unplug all ther sensors that use +5 volts from the PCM one at a time to see if doing so makes the 5 volts come back, or changes your symptons...check your grounds, and power connection to PCM as well.
 
I have regained power at 2 spots on all relays and I get power to the 2 small fuses that control the fuel pump & coil power for a second or 2 anyway.
OK I put in a different computer & now I have power to the fuel pump...it primes when I turn the key. I also get power to the coil for a split second while the pump is priming. Then the coil looses power so it will not start. It did chug a lug a time or 2 from retrying it over & over & getting spark for just that split minute.
I feel like I can get power to the coil pretty easily & get it to start with a jumper wire from somewhere.....but I havent tried that just yet. If I do that maybe I can test to see if anything else doesnt work correctly....timing etc.

What could cause a lack of power to the coil? could the pick up coil inside the distributer shut down the coil ?

Thats what I get for mistreating my jeep and letting it sit unused for a few months.... its throwing a tantrum on me.

Let me know what & where to check next.

Thank you,
Eric
 
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