1997 Chrysler Concorde backfire

Tiny
TANKK2014
  • MEMBER
  • 1997 CHRYSLER CONCORDE
  • 147,000 MILES
I changed spark plugs, spark plug wires, changed oil and filter. Drove the car for about 30 minutes after I was done. Pulled into the driveway, killed the engine. Went back out this morning to start it, made one revolution and backfired. Now it just spins. I'm pretty sure it jumped time, but what would make it backfire like that.
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Thursday, September 19th, 2013 AT 8:39 PM

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Tiny
CARADIODOC
  • EXPERT
Need a lot more information including the engine size. Does it sound normal when you're cranking it or does it spin real fast with little compression? Have you checked for spark? If there's no spark, the next thing is to determine if the automatic shutdown (ASD) relay is turning on. I can tell you how to do that with a test light or voltmeter.
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Thursday, September 19th, 2013 AT 11:36 PM
Tiny
TANKK2014
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It is a 3.5 and it just spins with very little compression. About the 4th rev, it sounds like it tries to fire but no go. I am out of town working for the weekend so cant check anything yet but your advice is greatly appreciated
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Friday, September 20th, 2013 AT 9:37 AM
Tiny
CARADIODOC
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Rats. That's an interference engine. The valves will be bent if they're hit by the pistons. Try looking through the oil fill cap to see if the camshaft is turning when a helper cranks the engine. If it's not, the timing belt is broken. If it is, the belt may have just jumped a tooth or two and no valves are damaged yet.

Check for diagnostic fault codes too. Chrysler makes doing that yourself real easy. Cycle the ignition switch from "off" to "run" three times within five seconds without cranking the engine, leave it in "run", then watch the code numbers show up in the odometer display. If we get a code for no signal from the camshaft position sensor, suspect the broken timing belt. If the belt has just jumped one or two teeth, the code will be "cam and crank sync" meaning the two signals are arriving at different times. When the belt jumps one tooth while you're driving, that is the code that will set. At two teeth, the Engine Computer will shut the engine down to protect the valves. At three teeth, (or when the belt breaks), is when the valves get bent.

When signals arrive from the cam and crank sensors, the Engine Computer turns on the automatic shutdown (ASD) relay which sends power to the ignition coils, injectors, and fuel pump relay. If the timing belt broke just as you started the engine, the camshaft position sensor's signals would stop arriving and the computer would turn off the ASD relay. That would remove power to the ignition coils just as if the computer were switching them off like normal. All six coils would produce one last spark, and you know for sure five of them would be at the wrong time. That could explain the backfire.
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Saturday, September 21st, 2013 AT 2:33 AM
Tiny
TANKK2014
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Ok, finally was able to work on it, pulled radiator, crankshaft pulley ad checked belt and timing. Al seem to be in good order. But still wont start and acts like no compression
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Wednesday, October 2nd, 2013 AT 3:47 PM
Tiny
CARADIODOC
  • EXPERT
We probably shouldn't overlook an obvious observation. Do a compression test first to eliminate a valve timing issue. Next, we need to see if the automatic shutdown, (ASD) relay is turning on during cranking. You can check that with the front cover off as long as the camshaft position sensor is in place and connected. Measure the voltage on one of the wires that is the same color at every ignition coil and every injector. That is usually a dark green / orange wire. You will see 12 volts there for one second when you turn on the ignition switch. Many digital voltmeters don't respond fast enough to catch that so you might have better luck with a test light. Next, what is important is that voltage must come back during engine cranking. If it does not, there is a problem with the crankshaft position sensor or the camshaft position sensor. There will be no spark, no injector pulses, and the fuel pump won't run. There also should be a diagnostic fault code stored in the Engine Computer. Chrysler makes reading codes real easy for you. Cycle the ignition switch three times from "off" to "run" within five seconds, leave it in "run", then watch the numbers show up in the odometer display. If you disconnected the battery or ran it dead, those codes will be erased. A code for the cam or crank sensor may not set again just from cranking the engine. Then you need a scanner to view live data. Each sensor will be listed as "no" or "present" during cranking.

That's the most common failure, with one of those sensors. If you DO find 12 volts on the dark green / orange wire during cranking, both sensors are working, and the ASD relay has been turned on by the Engine Computer. Then you have either a loss of spark. A loss of injector pulses, OR a loss of fuel pressure. A failed fuel pump is pretty common. Banging on the tank often gets them going again. Loss of spark is rare because there's six ignition coils with six driver circuits in the computer. Failure of the computer is pretty rare. Same with the six injectors. More commonly you would find that 12 volt wire to the injectors is cut. The clue is you'd still have spark, and the engine would run on starting fluid. For the fuel pump, you should hear it hum for one second when you turn on the ignition switch. If you do, it hasn't failed.
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Thursday, October 3rd, 2013 AT 12:55 AM

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