1998 TJ 2.5L MT Cranks but won't start. No spark. No fuel. Bad PCM? - Jeep Wrangler Forum
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Old 03-03-2014, 10:46 PM   #1
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Question 1998 TJ 2.5L MT Cranks but won't start. No spark. No fuel. Bad PCM?

Background:

1998 Jeep Wrangler SE 2.5L with manual transmission. Bone stock. 128,000 miles.

I bought a 2013 JK in December of 2012 and, since then, my 1998 TJ has been a little neglected. It has been run on and off since then but no regular driving. At the end of November 2013, I started it up and moved it to another location in my yard. At that time, the only issue I noticed was that the windshield wipers were not working. I assume the motor went but haven't had time to check it.

At the beginning of February 2014, I went to start it up to move it and prep it for sale. The battery was a little weak so I charged it for a few days and then tried to start it. It cranks and cranks but will not start.

Initially, I thought it may have been the crank position sensor (CPS) so I bought a "new" one at AutoZone. Upon initial inspection at the store, it looked like it had been used. I pointed this out but they only had one in stock so I decided to try it. I installed it and it would still not start. I removed it and took it back for a refund.

What I have found/done since then:
  • No fuel. A dribble of fuel comes out if I depress Schrader valve on fuel rail. I don't hear the fuel pump come on when I turn the key to the run position.
  • No spark. Screwdriver in boot method.
  • No "check engine" light when key is first turned to run position.
  • Gauges don't seem to be working.
  • Checked gauge cluster with key on/tripmeter reset button method. All lights work, gauges cycle, etc. including "check engine" light.
  • Checked all fuses in PDC and under dash with an ohmmeter. All are good.
  • Checked all relays in PDC, fuel pump and automatic shut down (ASD), by popping them into horn location and testing horn. All are good.
  • Starter relay is good since starter is cranking engine.
  • PCM connector pin A2 gets battery voltage when key is in run position.
  • PCM connector pin A22 gets battery voltage when key is on or off.
  • PCM connector pins A31 and A32 get continuity to ground when key is in off position.
  • ODBII code reader cannot establish connection to PCM. When I connect it, the reader powers up but errors out with a can't connect message. ODBII reader connects to JK with no issues.
  • I had read that a bad CPS will sometimes cause a code reader from connecting to the PCM so I followed the suggestion of disconnecting the CPS, disconnecting the battery ground, and shorting it to the positive battery cable for 15 seconds to "reset" the PCM. This had no effect.
  • Did the previous with the both the CPS and camshaft position sensor disconnected with no effect.
  • Tried disconnecting the pre-cat O2 sensor, in case there was a short, with no effect.
  • Everything else works. Radio., Heater blower. Lights. Turn signals, 4 ways. Etc.
  • I also pulled the PDC apart and checked underneath for corrosion and it is clean.
  • PCM connectors are also clean with no corrosion.
One interesting thing that I did find is that, if I remove fuse 6 from the PDC, both the fuel relay and ASD relay click on. I can also hear the fuel pump turn on. From what I understand, fuse 6 sends power to PDC connector pin A22 as well as the ASD relay. If I leave fuse 6 in and pull the ASD relay, nothing happens. The fuel pump relay does not click on.

Any thoughts?

Thanks in advance,
SpecMan



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Old 03-04-2014, 01:03 AM   #2
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See if you are getting power to the ASD relay socket terminal 30 (from fuse 6). Then jump from terminal 30 to 87 & see that you get power to the c12 (gray connector) wire (dark green/pink) at the PCM. If not lift the PCM & check the wires there for damage or corrosion at the terminal crimps. If good, with the jumper in place see if it starts or at least if the fuel pump pumps.

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Old 03-04-2014, 06:38 PM   #3
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Quote:
Originally Posted by RUBI 4 MY MRS View Post
See if you are getting power to the ASD relay socket terminal 30 (from fuse 6). Then jump from terminal 30 to 87 & see that you get power to the c12 (gray connector) wire (dark green/pink) at the PCM. If not lift the PCM & check the wires there for damage or corrosion at the terminal crimps. If good, with the jumper in place see if it starts or at least if the fuel pump pumps.
Thanks for the reply.
  • Getting battery voltage at terminal 30 of the ASD relay.
  • Jumped 30 to 87 and get battery voltage at PCM connector C12.
  • While jumpered, cranks but doesn't start.
  • While jumpered, fuel pump does not pump nor does fuel pump relay click on.
-SpecMan
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Old 03-04-2014, 07:34 PM   #4
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Since fuse 6 powers the a22 wire at the PCM I wonder if pulling it, & as you say clicks the relays, that points to a bad PCM. Not sure how but that seems strange because you are removing power from the PCM.

To get fuel you can also jump the FP relay. Just remember that as long as it is jumped the pump will (should) pump even with the key off so don’t leave it jumped if the engine doesn’t start. If no start, are you getting spark? If not I would again look at the CKP. If it is bad not only will you not get spark but the FP will shut off (relay opens) in 2-3 seconds of turning the key. Maybe the ASD opens too, don’t recall off hand. All this happens through the PCM of course.




Also make sure you are getting power to & from fuse 11 in the block behind the glove box & fuse 21 in the PDC when the ASD is closed or jumped.
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Old 03-04-2014, 09:19 PM   #5
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When I pull fuse 6, the fuel relay definitely "clicks" on and I can hear the fuel pump start running. It runs and doesn't stop until I put fuse 6 back in.

I tried jumpering both the fuel pump and the ASD relays. I can hear the fuel pump go on. It cranks and doesn't start.

There is no spark with the ASD relay jumper in place and the starter cranking the engine.

I had my helper turn on the key while I was standing near the PDC. No fuel pump relay "click" and the fuel pump didn't start at all.

I had previously checked fuse 11 voltage with the key in run position but double-checked. Both sides of the fuse are "hot" when the key is in run position.

With the ASD relay jumper in place, both sides of fuse 21 are "hot".

-SpecMan
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Old 03-04-2014, 09:32 PM   #6
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Also, with the ASD jumper in place, the orange/dark green wire to the coil is "hot".

-SpecMan
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Old 03-04-2014, 10:12 PM   #7
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I checked a few other things.

With the key in the run position and the CMP sensor unplugged, I am getting .6V on the orange wire on the CMP sensor plug. Based on the wiring diagram, I would expect 5V.

I tested continuity between the PCM connector pin A17 and the orange wire of the CMP sensor plug and it is good.

I took another look at the wiring diagram and I saw that the CKP sensor, CMP sensor, MAP sensor, and TPS all receive their 5V signal from PCM plug pin A17. I unplugged all of them in case one of them was shorted. With the key in the run position and all the sensors unplugged, the voltage at the orange wire of the CMP sensor plug was .72V so no significant change.

-SpecMan
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Old 03-04-2014, 11:20 PM   #8
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Good work. It does sound like a PCM problem & I never go there first because it is usually something else but maybe this time…

This might be a long shot but there is another 5v output at b31. I don’t see what that supplies power to. Maybe you could isolate the a17 wire from the PCM connector & tap into the b31 to get 5v. Then remove the jumpers & reinstall the relays & see what happens.
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Old 03-04-2014, 11:35 PM   #9
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It looks like B31 goes to the vehicle speed sensor. I'll see if B31 is actually supplying 5V. If so, I will try to isolate the wire from A17 and jump from B31. I'll try this all tomorrow evening after work and let you know.

Thanks again.

-SpecMan
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Old 03-05-2014, 01:11 AM   #10
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Yes, I see it goes to the speed sensor, just missed it with a quick look. You may not have to isolate the a17 wire but thought it a bit safer not to back feed the b31 into the PCM at a17. You probably can pull the pin out of the connector. I seem to remember someone losing that 5v & trying this but don’t recall if it worked.
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Old 03-05-2014, 06:56 PM   #11
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Unfortunately, with key on, I get 0.8V at B31.

-SpecMan
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Old 03-05-2014, 08:08 PM   #12
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Like I said, it was a long shot. Both pins probably get power from the same source within the PCM.
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Old 04-05-2014, 09:49 AM   #13
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Thanks for the help.

I have finally ordered a re-manufactured PCM and should have it in a couple of days.

-SpecMan
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Old 04-06-2014, 09:47 AM   #14
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SpecMan:
I am having a similar problem with my 97 TJ 2.5 manual trans.
Got it last Nov. towed it home drove it twice, parked in heated garage. I went to start it last month and battery was dead. Charged battery still no luck, so far I have a new battery, IAC valve. dist. cap and rotor. I checked fuel pump relay, checked ok. I am not getting any spark how can I test coil? When I turn key all gauges work except gas and battery. I took out the PCM and took it to the Chrysler /Jeep dealer in town to have tested they said it has to be in veh. to be tested. Who did you order yours form,how much are they?
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Old 04-07-2014, 02:34 PM   #15
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I recently had these symptoms after a muddy/very wet wheeling trip. Try leaving the key in the ON position, then have someone watch the gauges while you unplug each sensor one by one. If one of them causes the gauges to come to life when unplugged, change it.

Mine was the cam sensor/pickup coil (disk under the rotor button inside the disty). Apparently when it gets nice and hot after doing some hard time, then gets a drop of cold water on it, it gets "temp shocked". Changed it out and she started right up.

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