Technical Diagnosing ignition problem

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Technical Diagnosing ignition problem

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Mar 11, 2008
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Hi,

This relates to my Multipla, not my Bravo, but since this forum sees more traffic and the motor is essentially the same, I figured it would be fine to post here.

1999 1.6 16V petrol Multipla. 150,000 km. For a few months the car has had intermittent hesitation problems during very rainy weather, and occasionally also in wet weather, it would not start in the morning. Waiting an hour or so and trying again would usually result in a running motor. Worst case the wait was two hours.

Yesterday it decided that enough was enough, and now won't start.

I suspected ignition problems, so I tried a little start-spray in the intake with no results. I removed a spark plug and it smelled like fuel and was wet. I also had someone crank the starter while I held a connected spark plug against the block to check for spark. No spark. I checked the resistance across the coil HT terminals, and across the LT terminals and the numbers are comparable to those I found when I checked my Bravo, so I suppose the coil is fine. My Bravo uses a different coil, so I didn't swap to see if that was it, as it won't fit.

So what should I do now? I thought about checking for current at the LT connector while someone cranks, but I don't know what I would be looking for. I did check that the LT ground is properly grounded, and it is.

Please help! My wife is abusing my Bravo until I get her Multipla back on the road!

Thanks,

Joseph
 
Hi Joseph.

If you had said no spark and no fuel I would have said crank sensor fault,
As you have another 1.6 in the Bravo I would try the coil pack or check for sparks on your other plugs, if two are down it most likely would be the coil pack.

You have already done the resistance test on the coil pack but I know some people have had good results and its still been at fault.



https://www.fiatforum.com/gallery/data/2312/sm-coilpack-01.JPG

Has the ECU error light shown at all? When where the leads and plugs last changed?
 
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Hi Adrian,

Thanks for the reply. Unfortunately (for more reasons than just this!) my Bravo is a 1.4 so the coil pack is different. I don't know for a fact that there is fuel getting there, as the smell and wetness could have been the start spray. And from the times when I just waited an hour, when the motor started it would start entirely fine in a clean manner. If it had had excess fuel I would expect it to burp and cough a bit upon starting when it finally got spark.

The crank sensor sounds like it warrants checking. When I had hesitation problems it was often after driving through huge puddles. The coil is well out of the way of splashing, but the crank sensor perhaps is not. Do you know where that is? If I'm lucky it's a poor connection only!

I changed the HT leads and the plugs only a few weeks ago in hopes that would solve the problem, which it didn't.

Joseph
 
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I would check the other plugs for a spark first.

The crank sensor is very low down, the same design is still used on the latest fiat engines. Your 1.4 has it in the block.

If you remove the sensor make sure you remove it in the right way as shown, removing just the sensor not the sensor bracket.

People have simply cleaned the sensor and its sorted problems. You can do a resistance test but if its the magnet that is at fault resistance tests wont prove anything. If water has a definate effect perhaps the housing/Wire or conector block is damaged and letting water in. If you check it have a look at the connector pins and put a bit of WD40 on.

You can also check the gap between sensor and phonic wheel




 
That looks very promising. The issue was certainly water/damp related earlier so I think a faulty connection down there could very well be the problem. I'll check the other plugs for spark, but since the motor hasn't even given the slightest hint to want to start, I doubt there will be spark to be found there. At first light, I'll go grovel in the gutter and see how that connection is doing.

Thanks!

Joseph
 
This morning I tried to start without first fiddling with anything, and somewhat to my relief, it didn't start. So I checked the wiring to the TDC sensor, and pulled out the sensor itself to see if the tip had been damaged by a piece of gravel stuck between it and the pulley. It looked fine. I debated pulling the sensor from my Bravo to swap, but it is in a not so accessible place, so I didn't do that. So I pulled the connector which was very dirty with spilled oil and muck. The connector didn't have any obvious corrosion, and the wires didn't have any obvious wear from hitting the intake manifold and other nearby stuff, but there was no rubber boot at the top of the connector, just some dried up electrical tape. I don't know if that is original or not.

After fiddling with the wires for a bit, I reconnected it all and the motor started right up.

Adrian, looks like you found my problem. A poor connection for the TDC sensor.

Thanks!

Joseph
 
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