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vrsoft 08-24-2013 03:41 AM

No Start After Bad Jump Start Attempt

My 1993 Jeep YJ 4.0L no longer starts. Starter cranks, and fuel pump primes, but Jeep does not fire up.

Background Info

Jeep was in storage. Installed brand new Optima Red Top (AGM) battery. Jeep started and ran for one day until battery drained (alternator fuses were unknowingly bad).

Replaced both red 50A fuses in PDC and attempted to jump start, but didn't realize jumper cables were reversed on vehicle with good battery (my YJ was + to battery and - to engine ground, as it should be). Both 50A (alternator) fuses blew again as a result.

Replaced them with new ones and checked all other fuses with multimeter, both in PDC and interior fuse box. Now, when attempting to jump start, engine cranks and fuel pump primes but Jeep does not fire up."

Areas to Inspect / Test

Checked so far...
  • Fuses (in PDC) = all good now
  • Fuses (Interior Fuse Box) = "Dome" fuse, that can cut link to PCM, fried due to bad jump start. Replaced it. All good now.
  • Starter = cranks engine when ignition switch in "Start"
  • Fuel Pump = primes when ignition switch in "Run"
  • PCM codes checked...
    12 means the battery has been disconnected. This one is nothing to worry about.
    33 is for the a/c compressor relay. This one will always show up if you don't have a/c.
    55 means end of test.

    I don't trust the codes though, as I believe they reset when the battery has been disconnected for a short time. New codes are not being "tripped" as I'm trying to start the vehicle.

NOT (thoroughly) checked so far...
  • ASD Relay (in PDC)
  • Battery
  • Fuel Injectors
  • Spark Plugs
  • Secondary ignition cables
  • Ignition coil
  • Distributor (contains rotor and camshaft position sensor)
  • Crankshaft position sensor
  • Powertrain Control Module

Next Steps
  1. Temporarily swap-in the ASD relay (in the PDC) with a known working one from my 1999 XJ
  2. Battery should probably be charged to full, although I have been able to jump start successfully in past years with a dead battery so I don't anticipate this to be a problem... but I could be wrong
  3. I checked for spark and I'm not getting any, but I used the screwdriver method and I'm not confident in the result. Will try with a proper spark tester.
  4. Will check for a 5V reference voltage coming out of camshaft and crankshaft sensor wiring connectors. Is 5V the right voltage to expect feeding into each of the sensors?
  5. I'll see if I can do the sensor component testing procedure(s), that the factory manual suggests

I have the factory service manual and I've also reviewed countless forum posts over the past several days, so I think I'm on the right track, but if anyone has any suggestions please share!

My goal is to post the solution to this problem once I can figure it out, as I haven't been able to find a lot of forum content covering an engine ignition failure due to a bad jump start.

Que89YJ 08-24-2013 08:43 AM

Reverse Back feeding will almost always take out the pcm. You have power to the pcm because you can check codes. Does the fuel pump cycle when you turn the key to start? Do you have fuel pressure at the real when you push the valve on the fuel rail? Do you have spark?

kloppk 08-24-2013 08:52 AM

My guess would be that the cam sensor or the CPS is bad resulting in the no spark condition.

I believe it's 8 volts to the cam & CPS sensors.

DirtKar 08-24-2013 09:04 AM

Excellent 8th post! This is what every help me post should look like. You are obviously trying to help yourself as well. :thumbsup:

You say that the fuel pump primes, have you checked the pressure at the rail via the Schrader valve? We'll know a bit more when you do a proper spark check too. Do you have anyone near you to temp swap sensors?

Que89YJ 08-24-2013 09:28 AM

I reread the post. Sorry I asked for info you posted. Cam and crank are powered through regulated supplies inside the ECU. Not likely to have killed one if it was able to run before you jumped it. Power from the asd is getting where it needs to go or the ECU and fuel pump sequence wouldn't function. The cps will give you the symptoms you describe. Check power at the coil. If you have power at the coil with three key on then I am thinking you need to check your cps and see if anyone near by has an ECU you can try out.

DirtKar 08-24-2013 09:37 AM

Do you believe there could be a link to the miswired jump start and a failed sensor or merely coincidental? I am not a fan of coincidence although it most definitely exists.

XJ93 08-24-2013 11:34 AM

If the battery was completely dead use a proper charger to recharge it before using it. You can kill an alternator quicker than you can spit if you let the car charge a dead battery.

Que89YJ 08-24-2013 01:06 PM

The sensors are isolated. The ECU and electronics are designed to take a reverse feed. Load dumping its the killer for most yjs.

vrsoft 08-25-2013 04:09 AM

Update (more troubleshooting completed...)
Thank you everyone for your great comments! I did some more troubleshooting tonight and this is where things stand so far:

Checked so far... (note, items in BLUE are things I've checked this evening in addition to what I already checked previously...)
  • Fuses (in PDC) = all good now
  • Fuses (Interior Fuse Box) = "Dome" fuse, that can cut link to PCM, fried due to bad jump start. Replaced it. All good now.
  • Starter = cranks engine when ignition switch in "Start"
  • Fuel Pump = primes when ignition switch in "Run"
  • ASD Relay = GOOD (I tested it by following the factory service manual test procedure, as well as temporarily swapping it out for a known working relay from my '99 XJ.
  • Fuel Pressure = LIKELY GOOD (definitely pressure present so I didn't bother checking the actual psi)
  • Fuel Injectors = LIKELY GOOD (all injectors read 14.5 ohms perfectly, exactly per FSM diagnostic procedure spec)

I also checked the following tonight, but I'm not 100% on the results:
  • Camshaft Position Sensor

    FSM schematic confirms 8 volts supply from PCM on this circuit. Unplugged the wiring connector and checked the pins...

    A* = 9.55V
    B* = n/a (varies)
    C* = 5.03V

    *I can't find the exact pin ID's in the FSM for this connector, but what should really matter is consistent voltage readings on the circuit.
  • Crankshaft Position Sensor

    FSM schematic confirms 8 volts supply from PCM on this circuit. Unplugged the wiring connector and checked the pins.

    A = 9.55V
    B = n/a (varies)
    C = 5.03V

    Notice how the voltage readings match for both sensors. This is expected since they are on the same circuit. I am however not sure if 9.55V is too far away from the reference voltage of 8V that the FSM indicates for this circuit.

    I also completed the FSM procedure for testing the crankshaft position sensor @ the pigtail harness built into the sensor itself (which is a simple test involving checking that the resistance reading between two of the 3 pigtail connector pins is *open*, meaning no resistance). It says to replace the sensor if low resistance is indicated. Test passed, no resistance at all (open). I'm not sure that this is a full-proof test, but I'll take what I can get as I work through resolving this highly frustrating problem! :(

Next steps:
  1. I still want to get the Battery fully charged just to rule that out completely. I may even swap in my known working XJ battery as a last resort somewhere down the line.
  2. The Vehicle Speed Sensor (VSS) is also linked to the same circuit as the Camshaft & Crankshaft Position Sensors. I should probably check the voltage to that sensor as well, and also check the sensor itself somehow. I changed my speedo gear just prior to the bad jump start that started this mess. I can't help but think this may be related to something. I need to rule this out somehow.
  3. Check for spark. I purchased the wrong spark tester today. It's for HEI ignition systems and not standard systems, like in my YJ. I'll exchange it tomorrow so I can do a proper
  4. If I can confirm that I am indeed not getting spark, which I don't believe I am, I should then somehow check the ignition coil, distributor and secondary ignition cables.

Last bit of info for tonight...

The very last thing I did before I called it quits was to re-check my PCM codes after all of my diagnostic fun this evening... the PCM is now giving me additional codes, in the exact order that I started unplugging and testing connectors...

12 = battery was disconnected [Reason: I've been disconnecting the battery, so this is expected)
33 = a/c compressor relay [Reason: expected code… my YJ doesn't have a/c]
54 = No fuel sync (camshaft signal) detected during engine cranking [Reason: I unplugged it and was testing voltage at the connectors]
24 = Throttle position sensor (TPS) sensor or circuit (outside of max/min acceptable voltage) [Reason: I unplugged it and was testing voltage at the connectors]
11 = no ignition reference signal detected during cranking [Reason: I unplugged it and was testing voltage at the connectors]

55 = end of test

So it appears that my PCM is working, although I'm not ruling it out just yet.

This is by far the most difficult problem I've ever had to fix on my YJ. I can't help but keep thinking it's going to be something obvious, right in front of my face. The saga continues :mad:

Don't ever cross your jumper cables boys and girls. It's been 3 weeks of "fun" ever since :p

Que89YJ 08-25-2013 06:18 AM

Clear the codes. Do a battery reset.

vrsoft 08-25-2013 12:12 PM

Good call Que89YJ. I didn't reset the computer properly last night to clear the codes and try to start again, to see which codes remain after the PCM reset.

Woke up determined this morning to get this resolved. Here's what I did quickly this morning:

1. Unplugged both battery cables (unplugging the negative terminal only is not enough to reset the computer) to reset the PCM
2. Checked the codes BEFORE trying to start the engine (12, 33, 55). These are all normal / expected / "clean" codes.
3. Checked the codes AFTER trying to start the engine. This is what I ended up with:

12, 33, 54, 55

54 should be the camshaft sync sensor. However, I thought it was the CPS (trying to remember the codes from memory as I didn't bring my FSM with me) but CPS should be code 11. So what I did was the following...

1. Checked for continuity on the CPS on my '99 XJ (that I know is working, as it's our every day vehicle). There was continuity on two of the pigtail connector pins, so this would lead me to believe electricity can pass into the sensor and come back out.
2. Did the same test of the CPS on my dead '93 YJ. I did not get continuity between ANY of the pigtail harness pins at all.

This makes me think the CPS is truly toast. It's a magnetic sensor so it would make sense (I think) that a reverse feed of electricity (from the bad jump start) would screw it up.

However, the engine code is still 54 (camshaft) and not 11 (cps).

SO... my next step is going to be:

1. Reset the PCM and unplug each sensor (camshaft & CPS) 1-by-1, check to see what code is "tripped" in the PCM, reset the PCM to fresh, and repeat the same step for the 2nd sensor to try and isolate exactly which sensor (when unplugged) is tripping the PCM. In theory, I guess should still get a matching code (no matter 11 or 54) when the CPS is plugged in AND when it's unplugged... since if it's really not moving electricity through its internal wiring anymore, the PCM should always think it's not getting a CPS signal in either case.

At least I'm getting closer. Trying to not to over think things, but don't want to start buying expensive parts until I'm sure I've narrowed something down. CPS isn't' cheap. Parts store quoted me ~$160 (I'll call around first if I decide to pick it up in the end).

QUESTION: Has anyone ever had a code 54 (which points to camshaft sensor) and not a code 11 (cps), but the root cause was actually a bad CPS and nothing to do with the camshaft sensor? It's really looking like a CPS failure based on what I just did.

Que89YJ 08-25-2013 12:17 PM

Yes you will get 54 by itself. If that code is repeatable then you know you have a problem there.

DirtKar 08-25-2013 03:41 PM

Is this the $160 sensor in question?

Que89YJ 08-25-2013 04:06 PM

No that is the crank position sensor for code 11. Correct me if I am wrong but I thought you had 54 cam fault. The crack sensor is the one on the back pod the engine and usually cost 60. The cam is in the distributor and you can buy it separate for about the same or if it is the cam fault get the entire distributor with it installed for 20 or so more.

vrsoft 08-25-2013 06:01 PM

Getting closer...
Cleared PCM and did some more troubleshooting...

1. Checked that PCM reset, then tried to start engine with both cam and crank sensors disconnected: 12, 33, 11, 55

2. Checked that PCM reset, then tried to start engine with crank sensor plugged and cam disconnected: 12, 33, 54, 55

3. Checked that PCM reset, then tried to start engine with cam sensor plugged and crank disconnected: 12, 33, 11, 55

4. Checked that PCM reset, then tried to start engine with both sensors PLUGGED in: 12, 33, 54, 55


I have a distributor assembly on order from my local parts store ($93+tax). Will pickup tomorrow, install, and fingers crossed...

NOTE: Apparently you can't get just the camshaft sensor for model year 91-93 YJ's. I talked with three different parts stores (Napa, Lordco & West-Can) and they all told me the same thing.

The time now is 11:53 PM.

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