Car won't start after headgasket change...

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Old 04-23-06, 01:00 AM
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Car won't start after headgasket change...

1) 1996, Eagle, Talon, Manual, 2.0L I4 Non-Turbo, coupe.

2) One day my car was shutting off on me and didn't start from time to time , so I checked everything. I found that my oil was mocha in color, so...a head gasket blew. As soon as I could, I changed the head gasket and followed "Chilton's" car manual for Mitsubishi Eclipses and Eagle Talons. It took me two weekends to do it all, but I did the change (because of school), but the grand Finally wasn't as planned. The engine cranks but won't fire. I checked the electrical, and most seem fine. The car is a distributorless car and igniton is computed by the ECU electronically and runs off of just the coil. I checked the coil as stated in the book to see if voltage are correct...the are. I checked for any missing plugs...there aren't any. I tried a new ignition coil, alternator, and even the battery...and still nothing. there is no spark...checked the fuse and fuse is ok. then found this forum for help... please help me...
 
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Old 04-23-06, 10:32 AM
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Are you getting any spark out of the coil tower as you should?

Have you opened up the distributor cover to see if the cam inside is turning?

On your coil low voltage (12 volt) check, did you see if one of the smaller 12 volt wires is reducing it's 12v voltage during the engine rotation, as it should? so that the coil can build up high voltage inside? If not, then that would mean that you have an issue in the distributor magnetic pickup/cam *if* you are getting 12 volts coming into one of the coil's small wires. Did you even have to monkey with the distributor in the head removal operation?

(I have been out of practice worrking on cars for many years, but I remember a few things regarding the spark formation for an engine.)
 
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Old 04-23-06, 06:05 PM
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OK, So you've had the head off.........2 things I'd be looking at. ....1) compression.........test compression will confirm you put the timing belt back correctly........If you didn't, you'll probably be pulling the head again to repair bent valves..........
2)..With a scan too connected, crank the engine and confirm an RPM reading.........I once had a Talon I'd done head work to have a seperated wire in the crankshaft sensor circuit.......
 
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Old 04-23-06, 08:16 PM
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OK... thanks wrench47, All I know is that I don't have bent valves because I marked the cams with the timing belt along with the crank when at tdc. but the ideas of both you and daveboy about the a sensor has "sparked" an idea for me. can you guys tell me more? I keep looking at Chilton's car book and reading about the sensor that sits right next to the exhaust camshaft. it detects the rotation of the camshaft and operates electornically/megnetically. but maybe not. I don't know. Compression is good, i just tested it, and I'm getting fuel for sure because I can smell fuel from the exhaust. but still no spark. um... is there a sensor I should be focusing on? daVeBoy "distributor magnetic pickup/cam" wrench47 "I once had a Talon I'd done head work to have a seperated wire in the crankshaft sensor circuit" can you tell me more?
 
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Old 04-24-06, 03:17 PM
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I really can't help you any more than the suggestions I have already made. I am of the old school mechanics and all these sensors they put on cars today are new to me (although I am picking up on some of these, more and more).

*I* was referring to a possible problem in the distributor itself. The camshaft *I* was talking about is the distributor camshaft whose workings, unlike the old cars which had points, are electronic and the pulse occurs when the camshft lobe that is in time with a particular cylinder creates a draw-down in the primary voltage... which then allows the voltage to build up in the coils secondary windings, which then causes a high votage discharge to occur out of the coil tower , and then on to each plug.)

If you are not getting that proper operation to occur where the 12 volt primary current collapses so that the coil can build up that secondary high voltage charge...you aren't going to get spark. I am assuming that these newer cars all still work on this principle and that if your thin wires serving the coil are not doing this where the current is alternating between a full 12 volts, and then collapsing down to almost no volts...then you are probably having a problem in the distributor is my guess.

Regarding a "crankshaft sensor"?: To be honest...that is a new one on me. Never heard of one. I have no idea what possible function it could perform; what it would "sense".

This is simply the way I would look at it: You say you have 12 volts coming into the coil, I believe you said. If current is doing that, that means you are simply one step away from creating the high voltage spark. And that should occur with proper magnetic pickup of the distributor cam which then would collapse the 12 volt 'field' (when the distributor cam shaft turns, only) and create high voltage (like 30,000 volts) in the secondary windings of the coil. And then you should have spark. I can't see how any other sensor could be interupting or stopping this once you already have 12 volt current flow to the coil primary, like you claim...IMO.

I never did expalin though how one would go about doing the test. The way we *used to* do it , in the days of the points was, you would put a volt meter or a 12 volt light tester (that was like a sharp awl that could literally puncture a hole in the wire to get a reading...and you can still buy these... and you would pucncture one of the two small primary 12 volt wires at the coil, or, hookup a voltmeter to the terminal instead...and then ground the other end of the tester. Then with the engine on and being cranked, with the coil wire pulled out so the engine would not start...you would watch the light or test meter and see if the current would oscillate between the full 12 volts and almost no volts. If it did this, then it meant the points were at least opening and closing as they should. A more accurate test of this very nature could be done with a "dwell meter" which actually measured the duration of the collapse of the 12 volt current field. The only difference is that today, their are no points that cause this oscillation, but rather this magnetic pickup in the distributor as the distributor camshaft rotates. But that same effect with the oscillating voltage should occur, I would imagine. And if it doesn't, then you wouldn't get secondary high voltage to cause the spark.
 

Last edited by DaVeBoy; 04-24-06 at 03:34 PM.
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Old 04-24-06, 03:37 PM
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The sensor behind the cam is the cam sensor............which by the way has a couple of bulletins out on it.......mainly for oil leaks.......
The crank sensor is in the block on the back side of the engine compartment towards the front of the engine.........
 
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Old 04-24-06, 03:53 PM
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wrench47,

What does the crank sensor do?

And realistically, do you think this could possibly be contributing to lack of spark?
 
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Old 04-24-06, 06:41 PM
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crank sensor lets the PCM know when the crank is at TDC and which cyl is up so it can time spark and fuel injector pulse. no crank signal = no run
 
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Old 04-24-06, 10:33 PM
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ok.. that's a lot of good info... thanks on all of the input DaVeBoy and wrench47.... i'll let you guys know how it goes after I try all of the advises... any more advises are welcomed...thanks
 
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Old 04-25-06, 03:37 PM
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Originally Posted by towman501
crank sensor lets the PCM know when the crank is at TDC and which cyl is up so it can time spark and fuel injector pulse. no crank signal = no run
Interesting. I just learned something new; a hobby of mine. Now let me ask you this. If this is the case, then what is the sequence of when the 12 volts gets to the coil to then start to allow the coil to build up it's powerful secondary voltage. The poster said he had 12 volts to the coil. If that sensor was not working, would he still have got the 12 volts as far along as to the coil? *I* wouldn't think it would. But you tell me. Thanks.
 
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Old 04-26-06, 06:38 PM
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12v is always applied to the coil or coil pack when ignition is on. PCM controls ground side of circuit to trigger firing the coils.
 
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