Sunday, April 7, 2013

Jeep Wrangler Has No spark

Troubleshoting No Spark Issue On Jeep wrangler



The Problem Description Of The Vehicle:

Having trouble with  93 Jeep Wrangler. I have fuel (I can hear the fuel pump charge the system when the key is turned on, don't know after that) but no spark

Also getting  power to the plug going into the coil for about one second when the key is first turned on, no power after that or when cranking. This is with the plug removed from the coil with a test light contacting inside of the plug. 

Tried Replacing:---
I have replaced the ECU, the coil, the battery, the wiring harness both under the dash and in the engine compartment, the crank position sensor, I think the O2 sensor (just restarting the project) and the water temp sensor.

Vehicle Details:
Make (manufacturer): Jeep
Model: Wrangler
Year: 1993
Engine (optional): 2.5L


Expert's Reply To This Problem:

As Per The Problem described:

Because the coil has power when the key is initially turned on its clear that the powertrain control module (PCM) is awake, it's commanding the ASD relay on, and the relay's output circuit is ok. 

Then What's The Actual Problem?

The ASD relay is initially turned on for about a second. When the PCM sees that the engine is turning and is in time then it will turn the relay back on when cranking. It looks at the crankshaft position sensor, which is mounted in the bellhousing. I see that you've replaced the crank sensor already.

Yes,Its Replaced,Then What's The Other Possibility?

Along with the crank sensor it looks at the cam sensor, which is also referred to as the pickup plate and is in the distributor under the rotor. The PCM looks at cam and crank signals together and determines whether the engine is in time, if it is then the ASD relay is turned on to power the coil and injectors.

Assuming your crank sensor and wiring are ok, possible problems at this point would be the cam sensor, the engine is out of time, or the distributor isn't turning for some reason. If the timing chain was broken it wouldn't turn, but you should also note the engine cranking faster than normal.

Ok,But What About Distributor?

If the distributor drive gear was damaged or the distributor shaft is broken then it won't turn either, but this isn't very common. 

Ok,Then What Is most Possible Problem In This Case?

It would take some electrical testing to know for sure, but if the PCM, wiring harness and crank sensor are new then the problem almost surely lies with the pickup plate. Pop the cap off and make sure the rotor does turn when the engine turns. If so then most likely the pickup plate is causing your issue.


Also I Got Error Codes?
12, 33 and 11.  What This Error Codes Indicate?

For Error Code 12 it sets when the battery has been disconnected and error code 33 sets for the a/c clutch relay, which would be a normal code if you don't have a/c. The code 11 is for lack of distributor reference signal, so that's more evidence that the pickup plate isn't working. 

Ok,So What You Suggest?

Start by popping the cap and see if the rotor does turn, if it does then the pickup plate is likely your issue. Some basic testing of the sensor can be done with a digital voltmeter and you may be able to prove the sensor bad with a few minutes of testing if you have a meter.

How Should I Use Voltmeter To Start Basic Testing?

  • Let's go to the crank sensor first. Turn the key on and unplug the sensor, ground the black meter lead and set it to the 200 ohm scale. Measure the resistance to ground on the black/light blue wire.

Then flip the meter over to the 20v DC scale and measure the voltage on the other two wires.

  • Do you get the same readings at the cam sensor connector as you did at the crank sensor?
To check these voltages you want to leave the black meter lead grounded and probe the terminals with the red meter lead. If this wasn't the way you tested at the crank sensor let's go back and check those voltages again.

Please Note: The crank and cam sensors are the same with one wire reading 3.37 and one reading 5.02 on each using the negative battery post as a ground.
That's the reference voltage wire which comes from the PCM. 

Now Let's disconnect the vehicle speed sensor. It will be on the back of the transfer case assuming you have a four wheel drive. It's a three wire sensor and it will have the same orange wire in it. Unplug that and see if the voltage on the orange wire jumps up.


Now Measure the voltage:
What is it at the cam and crank sensor now? See if it jumped up there too. If it did then the engine should start. This is the 8v reference circuit and it's usually right around 9v.

But If The orange wires at both the cam and crank sensors are both still 3.37. Or Not more then 5 volts.
Then There's a wiring problem somewhere on the circuit. The orange wire at all three sensors is the same wire coming from the same place at the PCM. It's ok down at the speed sensor but not at the others so somewhere we're losing about 6v in the harness. We'll need to dig deeper into the harness to troubleshoot the problem.

This Details Will Help.
Thanks.

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