Engine Mechanical problem
1996 Chrysler Town and Country 6 cyl Front Wheel Drive Automatic 137000 miles
96 Chrysler T& C, 3.8, no start. Van was driving fine, then for two days started slow but drove fine, then would not start. Battery good, turns over good, Checked fuel pump – working, checked spark – pulled three plugs in front and had friend watch laying plug on engine block – no spark, pulled out map sensor, still no start, checked codes, no codes with diagnostic tool, rpm when engine turns over is 160, when battery is weak- barely able to crank over the engine- engine fires and I believe it will start but no start. This only happens when the battery is very weak. Rpm’s jump to 400’s when this happens.
How are you determining the fuel pump is working? If you hear it run for one second after turning the ignition switch to " run", that might be a misleading clue. It must run again once the engine is rotating, (cranking or running).
When you said it starts slow, but the battery is good, do you mean it cranks slow or it has a long crank time before it starts?
The lack of spark is obviously a clue, but if the battery is weak or has a shorted cell, the Engine Computer can shut the coils down due to the initial bog of the starter motor drawing battery voltage down for an instant. Once the starter starts spinning up to normal speed, spark will not come back until the computer is reset by turning the ignition switch off and back on.
Based on your first observation of " started slow" for two days, I really think you don't have a spark problem. I'm leaning, for now at least, toward a weak battery. Try starting it with a battery charger connected. If that works, remove it and use a cheap digital voltmeter to measure the voltage between the two battery cable clamps, (not the posts for now), while a helper cranks the engine. If you see the voltage drop momentarily to less than 10 volts, the Engine Computer is turning off the coils. Replacing the battery and cleaning the cables should take care of it.
Before you replace the battery, measure the battery voltage again while the engine is running. It must be between 13.75 and 14.75 volts. If it doesn't change once it's running, the charging system is not working.
March, 19, 2010 AT 10:07 PM
Battery is good, it cranked over for about an hour before getting weak. I charged it on a charger and it charges 100%, so battery is fine.
I checked the fuel pump with my diagonstic computer, had it turn on and off several times, could hear it turn off and on when I told it too with snap-on diagonstic computer.
I meant that it starts slow, that it had a longer crank time, it cranked over fine, just did not start right away like normal. LONG CRANK TIME
March, 19, 2010 AT 11:16 PM
Couple of things to check. First, if you have a gauge, measure the fuel pressure. By commanding the pump to run with a scanner, or by listening for that one-second burst when the ignition switch is turned to " run", only proves that the pump is working. The important next clue is if it turns on during cranking.
Based partially on your comment about rpms jumping to 400 during cranking, I suspect there is a problem with the crankshaft position sensor. If I'm wrong, the fuel pump will run during engine cranking. Since you're using a scannner, you obviously know what you're doing. There are some key places to take some voltage measurements, but if you can read the Automatic Shutdown (ASD) relay state (on or off), under " Inputs / Outputs", watch which state it is in right after turning on the ignition switch and again during cranking. It should turn on for that initial first second. That's how the scanner turns the pump on.
Once the relay turns off after that first second, it should turn on again during cranking. If it doesn't, suspect the crankshaft position sensor. When pulses arrive at the Engine Computer during engine rotation, the computer turns the ASD relay on. The relay sends battery voltage to the coils, injectors, oxygen sensor heaters, alternator field, and fuel pump or pump relay.
March, 19, 2010 AT 11:33 PM
It only reads 440 rpms when the battery will barely crank it over and it fires. Otherwise, when the battery is charged and cranks strong but no fire, it reads 160 rpms.
Why would it fire over with a weak battery and not with a strong battery?
I will check the other items you brought up and reply back on that.
March, 20, 2010 AT 1:07 AM
My best guess is the Engine Computer is getting confused due to low voltage.
I can share a story about my '88 Grand Caravan. When the original battery was 8 years old, it wouldn't start on a 30 degree below zero morning. Ma cranked on it off and on for hours. Later that day, it fired right up after I replaced the battery. 50 miles later the engine " exploded". Wrapped a connecting rod around the crank. Found the oil two quarts overfull, (full of gas).
It wasn't until about 5 years ago that I had the same problem, again on a real cold night. Wouldn't start at work, but fired right up with a booster pack. That's when I figured out that the starter was drawing the battery voltage down low enough to stop the Engine Computer from running the ignition coil. There was no spark, but the injectors were working just fine. That's why the fuel in the oil the first time. Once the starter got up to speed, the battery voltage came back up but there still was no spark. No matter how many times I cranked the engine, the computer would not reset and fire the coil until the ignition switch was turned off first. The next time it was cranked, the same thing happened. The battery voltage got drawn down momentarily and the spark quit.
This was one rare case where the ASD relay was turned on but only spark was missing. Ten degrees warmer and the battery worked fine.
March, 20, 2010 AT 10:28 AM
This did not happen on cold days, but happened over a warmer spell when overnight was 30s and daytime temp was 50s. A week earlier, we were sub-zero temps and everything was fine.
Also, I do not think that explains why it will fire over when battery is weak not strong? It seems like your story is the other way, the battery is strong you get the van to fire up, but the battery is weaker and no fire.
March, 20, 2010 AT 8:47 PM
Let's back up a minute because I'm probably not reading what you're typing.
Describe " fire over". Does that mean the engine cranks / turns over, or do you mean the spark plugs fire?
When you said, " It seems like your story is the other way, the battery is strong you get the van to fire up, but the battery is weaker and no fire.&Quot, after rereading it, I think you meant MY van will fire up, right? If I read that right, then yes, yours is doing the opposite.
So I don't send you on a wild goose chase, instead of " fire over" refer to having spark or no spark, or the engine cranks well or cranks slowly. I have some ideas of what might be happening, but I don't want us to be talking about two different symptoms.
Cranking with a weak battery is not the normal way the system should work, so, even though that might be an important clue, lets pursue this as a no-start with a charged battery, or with a charger on it. If you find no spark then, try to find one of the switched power wires to take a voltage reading. Look for the dark green / orange stripe wire on the coil pack or on the injectors, or, if you can get to it, on the back of the alternator.
You should find 12 volts there two times. First, it will be there for one second after turning the ignition switch to " run", then it will go back to 0 volts. During that one second, you should also hear the hum of the fuel pump in the tank. That is proof the Automatic Shutdown (ASD) relay is working, the Engine Computer has control of it, and the wiring to the coil, injectors, alternator field, oxygen sensor heaters, and fuel pump or pump relay are good.
Next, that voltage should come back when the engine is rotating, (cranking or running). In the rare chance that it does, we have to troubleshoot the individual inoperative circuit, spark or fuel. More commonly, the voltage will not come back during cranking. That would suggest a problem with the crankshaft position sensor. It's his pulses that tell the Engine Computer the engine is rotating and would he please turn on the ASD relay.
If you think it's a problem with the crankshaft position sensor don't replace it yet.
March, 20, 2010 AT 9:19 PM
When I checked the fuel pressure, the scanner read INJ(ms) 82.2 and TPS(v).78.
I listened for the fuel pump during cranking but either I did not hear it over the cranking or the fuel pump was not on during cranking but I know it was working right before cranking and right after because I could hear it then.
In my scanner I did not see Inputs/Outputs to scheck the Automatic Shutdown Sensor, I will look around in the scanner tomorrow for it.
When I say fire over, I mean the spark, fuel, O2 engine is starting and seems to hit a few times but does not stay running.
When I turn the ignition switch to run, the fuel pump kicks on for a second.
I will have to check voltage tomorrow.
March, 21, 2010 AT 2:30 AM
Based on your observation of hearing the pump right after you stopped cranking, it sounds to me like the pump is running. That means the Automatic Shutdown (ASD) relay is working. That means the crankshaft position sensor is working. Going back to your first post, the 160 rpm during cranking would also indicate the crank sensor is working. I see too you were able to run the pump with your scanner. I apologize for repeating steps. I'm in the middle of about two dozen on-going conversations and I get confused sometimes.
Next, head to the coil pack. There are actually three distinct circuits. The fuel supply circuit, the trigger circuit which is the crankshaft position sensor, and causes the most trouble, and the ignition coil circuit which causes very little trouble. It looks like that's where we're going to end up. Measure the voltage on the dark green / orange wire in the coil pack connector during cranking. It should be full battery voltage which, during cranking, should be a good 10 to 11 volts. If it's there but you still have no spark, the problem must be the coil pack, the Engne Computer, or the three wires in between. I doubt three wires would be broken all at the same time, but for that matter, it would be odd for all three coils or all three coil drivers in the computer to fail at the same time too. About the only two things the three coils have in common is that green / orange feed wire and the power supply circuit inside the computer. I've seen a single coil go bad in the assembly, but I wonder if a shorted one could shut the entire circuit down in the computer.
Assuming you have voltage on the dark green / orange wire, and you don't see anything else obvious, I would be inclined to try the coil pack first and hope you don't have to try the computer next.
By the way, if the trouble is all related to no spark, the injectors have been firing all this time. There is going to be raw fuel washing down into the oil. Once the engine is running, change the oil as soon as possible. I had a different problem, ... Oh, wait. I told you about that already. Only lasted 50 miles with all that gas in the oil. Funny thing was, it was common practice at the dealership to change oil every time we fixed a no-start related to no spark. &Quot; Do as I say, not as I do!&Quot; caradiodoc
April, 2, 2010 AT 1:13 AM
Just to let you know, it ended up being the computer. PCM.