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Discussion Starter #1 (Edited)
The car was running fine before some repairs. I changed the water pump and disassembled and restored the wiper system. Didn't disconnect any wires or disturbed the distributor or coil. Got everything back together and no start. Fuel pump cycling, fuel pressure light off, but no spark. Coil is recieving 12v on both poles, but no spark from the coil. One side pulses as I crank which leads me to assume it's not the distributor. I had a problem with this earlier this summer which turned out to be the ignition module (Cresent shaped GM part) and replaced it with a new one. Can these things go bad that quickly? I checked my work and saw no pinched or disconnected wires. The ignition I have is a Marreliplex. I'm stumped. Any suggestions? Thanks Allan
 

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Discussion Starter #2
Replaced the ignition module again and still no spark. I have three wires on the negative side of the coil, one from the ignition module, one to a condensor that is bolted to the side of the coil, and a white wire that I assume may be the tach. The positive side has the green wire from the ignition switch, and the other ignition module wire.

My understanding of how all this works is when the positive side is charged via the ignition switch, it builds a electrical field in the coil's primary. Then when the distributor triggers the negative side to ground, it collaspes the electrical field and sends it through the secondary coil resulting in a high voltage/low amp spark to the distributor. I am getting 12v to the positive, and the negative is cycling to ground when I crank the engine, but no spark.

I have a Marreliplex ignition and I'm not quite sure what is amiss. From all accounts, I should be getting a spark from the coil. I swapped out a new coil I had laying around with the same results. What I don't know is if the Marreliplex is sending a good enough ground signal, or if the condensor has anything to do with the spark. I assumed it was for radio reception, but not sure. Any help would be appreciated as I'm now lost without a clue. Thanks Allan
 

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It took me a while to find my plex instruction manual, the condenser is correct on the negative side, for the electronic tach. From what you've said the module is giving a pulse when you crank and there is power at the coil, so I don't think it's the module. The coil, I believe is specific to the system, if you have a coil with the wrong impedence it might not work? Anyway check and make sure the ground to the engine is good. Have you done this test: unplug the coil wire from the distributor, wearing heavy leather gloves and wearing rubber soled shoes hold the unplugged end 1/4" from the valve cover while someone cranks, you could run a test light in paralell with the iginition circuit, at tthe same time, to re-establish that the circuit is pulsing, if you get a spark check the cap and rotor, if you don't first try another coil-wire. One other thing, for longer life of the module, the bottom side should be slathered with di-electric tune-up grease where it mounts to the housing.
 

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Discussion Starter #4
Thanks for the input. I removed the coil wire to the distributor and attached a test light directly into the coil. I grounded the other end to a known good ground on the engine. The test light didn't even blink. I'm perplexed as from all I know, the coil should be sparking given the power to + and plusing on the - side. The second coil was from a Formula Ford I use as a spare and it did not spark either. I don't believe the Marreliplex specific coil would not spark other coils, but don't know for sure (I hope this would be the case since a coil would be cheaper than a new distributor if available). So the only thing I could think of is that somehow the distributor is not producing a sufficient ground pluse, or it is "leaking" ground all the time so as not allow the primary coil to charge up. I just don't know enough about this system to diagnose any further.

Prior to this, the car ran fine. Then I changed the water pump and replaced the oil pressure sender. The replacement was an AC Delco that looked different from the orginal, but fitted fine. I doubt this was the cause, but I'm grasping at straws here. Any Marreliplex gurus out there? Thanks Allan
 

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I save too much stuff, the replacement module (Standard brand, Nienhoff I believe) says: "a) clean module terminals with an eraser or abrasive and b) connect and disconect the and harness several times to insure good contact."
also :" apply a liberal coating of the enclose silicone compound to the module's metal mounting plate, to prevent heat build-up."
The module I replaced had the GM # 146 1D14, I believe Marellli installed the GM modules when new. I don't know the specs on the plex, I do know if you have the wrong impedence coil on other electronic systems, it won't fire. Very specifically the Marelli installtion manual says: "An eventual check for the presence of the H.T. in the plugs by means of sparking, should be done by placing the H.T. cable end at not more than 5mm from the engine" I do not think the test light method you are using on the H.T. circuit is appropriate. There are other prohibition listed in this document. I can make a copy and mail it to you, maybe someone can scan and post.
 

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Discussion Starter #6
Does anyone know how to test the Marreliplex distributor and coil? To review everything I have checked so far:

1) Ignition powers the + side of the coil
2) I do get a ground pluse on the negative side of the coil when the car is cranking
3) New ignition module
4) All contacts clean and good contact
5) No spark at coil
6) Battery charged
7) engine has good ground

What I need to know:

1) Ohm readings for the primary and secondary coil
2) Is it possible that the distributor is not sending a strong enough signal to collaspe the primary electrical field so it could arch to the secondary this causing a spark?
3) There is a relay attached to the side of the coil, it "clicks" when power is switched on, but could this cause a no spark at the coil.
4) Should I toss the system and get a aftermarket dist and coil, or go to points?

Thanks in advance, I'm sure someone has gone through this before and has the answers (I hope), Allan
 

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I experienced almost the same problems with my plex. There must be dielectric grease on the module between the coil heat sink and the back of the module. Otherwise it will not work.

Have you done this?
 

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Discussion Starter #8
Yes. I had a problem with the module earlier this summer when it wouldn't spark, a new replacement took care of it at that time. I had replaced it with another module recently when I experienced this no spark problem with no avail. Both times I used the dielectric grease liberally. I got the diagnostic chart from International Auto Parts from a Fiat manual which I am told is the same system. Everything appears to be within range, except for the secondary windings on the coil. Manual says it should be 10K to 11K Ohms, mine is 7800 Ohms. So I bit the bullet and ordered a new coil and distributor trigger, which pretty much covers the ignition system. Reason I was so confused with this system was that I never had a coil go so quickly. Usually it would fail intermitently when hot for awhile and then then fail completely after giving you plenty of notice. Plus the coil had continuity which meant no broken wires. This car started fine and then overnight stopped working. I didn't think it was the distributor, plus it checked out fine on the ohm meter, but I bought the single trigger (mine had a double system) just in case. I should be getting the parts tomorrow and will post my findings. I'll start with the coil first and if that works, the trigger will go into the glove compartment, along with my spare module. Thanks, Allan
 
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