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Weird starting issue (plus gauges)

4K views 33 replies 3 participants last post by  rikkards 
#1 ·
Where to start.
Yesterday turned over fine but wouldn't start. All of a sudden it started and I was able to take it for a spin for about half an hour. Drove home and parked it.
Went today to take it out again and it did the spinning thing but no start.
The Relays are good as I swapped them around. I can hear a buzzing from the gas tank which I am pretty sure is the pump (Pump was replaced 3 years ago with a Bosch unit). Disconnected and reconnected the Camshaft Position Sensor and Oil Pressure Sensor (since I was there) and now it doesn't even spin without bypassing the starter relay.

Another symptom is the gas and power gauges stay at zero. Other lights work fine and the gauges work in the actuator test

I have mentioned before that I have had with rare intermittent issues with starting (I was able to work around it by putting it into run, and bypassing the Starter relay) and I am wondering if it has finally come to a head.
 
#2 ·
I am planning on pulling ignition apart, maybe it is a two parter where the switch pin just flaked out but it still doesn't explain why it doesn't start when the engine does turn over and why the fuel and voltage gauges are zero
 
#4 ·
When the gauges don't respond usually either you have no power to the PCM or power but no 5v from the 5v output at the PCM. Most, if not all I have seen are '97s but still check fuses 11 in the fuse block & 6 in the PDC with a meter. If good go to the black (C-2) connector at the PCM & check pins a-2 & a22 for 12v power & with it plugged in check pin a17 for 5v.

This does not address the no crank, so insert a fuse in slot 20 of the fuse block to bypass the clutch switch. If nothing, removing the ignition switch to check the actuator pin would be next & if good turn the switch with a screwdriver to see if it will engage the starter.
 
#5 ·
11 and 6 have continuity.
Ignition pin is good (I had already pulled it)
All off
Pin 2 0v
Pin 22 12v

Run
Pin 2 12v
Pin 22 12v

How do you check pin 17 for 5v if it is plugged In? Is there a different spot down the corresponding wire I can check based on?

Also wouldn't the actuator test negate this test?
 
#8 ·
You have to "back probe" it. Try getting a thin wire or the like to get between the connector plastic & the terminal. It is tight. You can also follow that wire to one of the sensors like the crank or cam sensors & check there (unplugged). You can penetrate the insulation on that wire but is not recommended as it allows corrosion to get in.

There is also a 5v supply in the white connector at pin b31 & so far every one that loses one loses both but can be checked the same way. You might be able to check that pin at the PCM with the connector unplugged & the black one plugged in but I'm not sure & don't want you chasing the wrong thing.

If turning the ignition switch with the fuse in slot 20 (manual trans) does not get it to engage the starter but jumping the relay does you may have a bad switch which can be tested if needed.
 
#9 ·
You have to "back probe" it. Try getting a thin wire or the like to get between the connector plastic & the terminal. It is tight. You can also follow that wire to one of the sensors like the crank or cam sensors & check there (unplugged). You can penetrate the insulation on that wire but is not recommended as it allows corrosion to get in.

There is also a 5v supply in the white connector at pin b31 & so far every one that loses one loses both but can be checked the same way. You might be able to check that pin at the PCM with the connector unplugged & the black one plugged in but I'm not sure & don't want you chasing the wrong thing.

If turning the ignition switch with the fuse in slot 20 (manual trans) does not get it to engage the starter but jumping the relay does you may have a bad switch which can be tested if needed.
Thanks will try it out!
 
#10 ·
Came across this thread
http://www.jeepforum.com/forum/f11/crank-position-sensor-problems-maybe-889010/

Symptoms -
- Starter cranks and cranks but engine won't start up and run.
- Fuel gauge and voltage gauge 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.


Could it be that simple?
 
#11 ·
It may be.

I skimmed through that link…

Missing in those tests appears to be the fact that you need 5v to the sensor as well as some other sensors. Start there. If you do have the full 5v you can move on to testing sensors, etc.


There are 4 basic problems that seem to happen most often with crank but no start. Fuse 11 gets blown or the ignition switch is not sending power to that fuse, the crank sensor goes bad, the PCM loses its 5v outputs or the PCM won't ground the ASD & FP relay coils. There can be other reasons (some also noted below) but I see these 4 most often. In the links below, badKrma lost the relay grounds from the PCM & the relays would not close so he was able to jump the relays to get it going. Ifixyawata was not getting 5v output from the PCM & added an external power source to get his going. Both are workarounds for bad PCMs. Obviously fuses & sensors are easier fixes.

In the cases of the bad PCMs both started out with what seemed like the same problem but the process lead to differences which eventually identified the underlying issue. Both were bad PCMs but are now on the road.


badKrma
http://www.wranglerforum.com/f210/no-spark-in-97-wrangler-se-please-help-708666.html#post10742890

Ifixyawata
http://www.wranglerforum.com/f210/no-start-97-2-5l-705906-3.html#post11636018


Then there is this with low voltage at the 5v pins

5v supply to speed sensor shorted causing low voltage to all sensors. Not found until about post 35

http://www.jeepforum.com/forum/f9/need-help-03-rubicon-dead-4053786/index3.html#post38075434

There are also cases where the capacitors in the PCMs leak & some have replaced them & not had to replace the PCM. 2 cases here…

http://www.jeepforum.com/forum/f9/1997-jeep-wrangler-sport-not-starting-2901058/

Even this…

Corrosion at PCM connector

http://www.wranglerforum.com/f210/n...17-on-97-tj-2-5-pcm-1979666.html#post30002297

You see there can be several causes; it is just a process to finding the problem.
 
#12 ·
Sounds good. I am going to try to see if I get the +5V on the other connector first if I do then I might try to see about getting into the black connector and probing it but tight is an understatement you can't even see any of the wires going into the connector.
Will have some more reading material tonight I see.

That all said though, by doing the actuator test and the gauges jump wouldnt that confirm the +5V is working?
 
#15 ·
Progress!



Probably just the link above where the speed sensor (wiring) was shorted. The sensor or the wiring from it (sensor or ground wires) may be draining the 5v from the PCM causing none of the sensors to send data & the cluster gauges not to read. It may be a shorted sensor, easy to check, or one of the 2 wires other than the 5v one may be shorted to ground. Also easy to check. If it was in the 5v wire, disconnecting the sensor would not get the rest of the circuit working.

Did you get it to engage the starter with the key?
 
#16 ·
Yes and I suspect the not starting with the key is my existing issue that just decided to show up.
I measured the resistance from the signal pin to ground of the Crankshaft sensor and it was considered open. Isn't it supposed to be some kind of value?
 
#17 ·
I think as the engine (flywheel) turns & the sensor sees the notches the signal will go to 5v then to 0v, up & down. If you connect the sensor, still have 5v at a17, & crank the engine you should get 5v,0v,5v,0v etc. at a8 (crank signal). The signal wire being open may be OK, not sure. If grounded (no resistance) I would be more concerned, certainly if grounded with the PCM connector unplugged.


BTW, it seems a bit odd that you had 5v (post 13) but no gauges until you unplugged the crank sensor.

Any chance reconnecting everything the gauges will now work? If yes, try starting it.
 
#18 ·
Will have to check this afternoon after work if I have a chance. The one thing I noticed while looking into this is I am not the first to notice the disconnecting as I have come across a couple links where people said they did this to get the gauges to display and ultimately just replacing the sensor made everything work. I wonder if the sensor fails the PCU detects it and just shuts down power to the gas pump which disables that gauge. Not sure why power doesn't show up either though with it connected. But the interesting thing is that to get it to work I had to turn off then on until the third time all of a sudden they popped up. It might be that something is resetting??
 
#20 ·
From the 05 FSM:
ENGINE START-UP MODE
...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.

I realize yours is different, being on the other end of the TJ spectrum. However, I'm sure it works similarly.
 
#21 ·
That's what exactly what it says in mine as well which is why I am leaning to it being the sensor. The only thing that was confusing me was the lack of gauges and I can't find anything that says it would be caused by the sensor going bad although I have seen several links where people have had the fuel and voltage gauges being dead and unplugging it fixed it and subsequently replaced the sensor.
 
#23 ·
Looking at the wiring diagram all of the sensor grounds are based off the above splice which connects to pin A4 on the PCU. I wonder if internally the voltage gauge is also connected to pin A4 so if something is making it wonky in either the harness or one of the sensors it could make the gauges stay flat . But that is pulled out from where the moon don't shine
That all said I dont think the splice is my overall issue otherwise I would be having problems with a plethora of other things.
 
#27 ·
Not sure if that would necessarily be right though. Looking at 8W-70-3 in the FSM it shows the wiring for that splice and doesn't look like it connects to true chassis ground anywhere. Now the PCM may actually be internally connected on A4 to chassis ground but I don't know.
Kind of like with the turn signals up front. They aren't true ground
 
#28 ·
Ordered a new CPS and it arrived today.
Well there is definitely something different between my old and a new CPS I measured the resistance between the signal and ground and found that my old one was coming back with open resistance while the new one was under 10k.
The catch is although Rockauto has it as being compatible I think there were some models that had a slightly different connector so I have to send it back
 
#34 ·
Interestingly I am still getting the dead gauges if I let it sit, but if I immediately turn it off and back on it works. I think (not sure as I need to see if I can replicate it) that at one point I turned it on with dead gauges and a bit later (couple seconds but less than 10) the gauges kicked in
 
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