Are my plug wires bad and if so would that cause stalling after the car is hot? - Alfa Romeo Bulletin Board & Forums

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post #1 of 301 (permalink) Old 02-15-2017, 08:35 AM Thread Starter
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Are my plug wires bad and if so would that cause stalling after the car is hot?

My car wants to die after a while. It'll start strong, idle smoothly, rev freely, run fine. After a while, though, it'll start to miss. It'll chug a bit. It'll probably die. I ran it at idle in the garage this past Sunday and regardless of where I set the idle it would eventually start missing to the degree that my digital rev meter was freaking out and bouncing all over the range.

The battery is new, the coil is new, the ignition amp is new, all of the sensors are new, the wiring to connect them is new, the plugs are new, the injectors have been serviced and flow cleanly, the electricity to fire them is consistent and adequate, the fuel pump is new, the fuel pressure regulator is new and confirmed to be at spec, the AFM checks out and the mix is good (if a tad rich). I've literally gone through every component and either checked/confirmed it's good or replaced it, if not.

All that's left is the plug wires, and they're $150 or so. I don't know if the plug wires on my car are original, but they are old. However, the resistance readings are all withing spec when cold. I can't seem to be able to determine if they lose conductivity or if the resistance goes wonky when they get hot. I assume MAYBE that's what's happening?

Thoughts? Every time I drive the car for more than about 15 minutes, as soon as I come to an idle stop it'll die and take several minutes to restart. Let me tell you, when that happens at an intersection at a major highway, it's not good. Not good at all.

as good as a car can be... briefly.
'82 GTV6
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post #2 of 301 (permalink) Old 02-15-2017, 08:42 AM
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What about your coolant temp sensor? Might that give a false signal when the car is warmed up?

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the resistance readings are all withing spec when cold. I can't seem to be able to determine if they lose conductivity or if the resistance goes wonky when they get hot. I assume MAYBE that's what's happening?
I just don't know the answer to that one. From my experience, bad plug wires begin to show symptoms on acceleration and going up hills. But don't know how much temperature has to do with it.

Jay Mackro
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post #3 of 301 (permalink) Old 02-15-2017, 08:47 AM
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at night with the car running and the hood open look for electrical leakage (sparks) you can also mist the wire with a spray bottle and if you disconnect the wires you can check the resistance. That said your problem sounds like fuel supply to me not plug wires, maybe filter(s)or intank pump?
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post #4 of 301 (permalink) Old 02-15-2017, 08:48 AM Thread Starter
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The CTS is BRAND new and checks out. My experience with that one is that if it's bad, the car will just die. This is more of a gradual decrease in smoothness and power, to the point it just stalls. Let it cool for a few seconds and it starts right back up, but will again start to go downhill pretty quickly. I feel it HAS to do something with temperature though. Heat does cause a decrease in conductivity in electrical components.

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post #5 of 301 (permalink) Old 02-15-2017, 08:49 AM Thread Starter
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Fuel filter is BRAND new, hoses are new, sock is clean, pump is new and fuel pressure checks out regardless of how well the car is running.
This problem has been an issue for a while now. Maybe I'm just stubborn for not replacing the plug wires...

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post #6 of 301 (permalink) Old 02-15-2017, 09:18 AM
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The ignition wires have carbon filament conductors which develop cracks as they age. You may be able to identify a bad one by measuring the end to end resistance. Each lead should read about the same resistance. Watching the cables in the dark may reveal loss of electricity through degraded insulation. That is a second failure mode. Either of them will make your engine run badly. I have replaced my ignition wires with wire core types but they require CD ignition and will not work with the stock ignition system.

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post #7 of 301 (permalink) Old 02-15-2017, 09:19 AM
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With all the other things you've replaced, why not the wires?

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post #8 of 301 (permalink) Old 02-15-2017, 09:23 AM Thread Starter
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Great question! Up to this point they've always checked out on the bench. Good conductivity, correct resistance. And weirdly, every other repair I've made has actually been a. Otoceanle improvement. So maybe this is THE final R&R job? I just wish the wires weren't $150 +tax and shipping!
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post #9 of 301 (permalink) Old 02-15-2017, 09:38 AM
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I just measured the resistance of an almost new set of factory wires that I keep as a spare in case my Crane Hi-6 fails and I have to revert to stock ignition. Each one is about 2200 ohms. Yours should be within a few hundred ohms of 2200 if they are any good.

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76 Suzuki GT500

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post #10 of 301 (permalink) Old 02-15-2017, 09:47 AM Thread Starter
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They're within spec when cold, and even when I yank them off the car. But given how long it'll typically take for the car to restart after a stall, I am probably not doing it quickly enough.
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post #11 of 301 (permalink) Old 02-15-2017, 10:04 AM
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Mr. Kaga

This is one of those problems that swapping parts with another car (another GTV6) can be very useful. Can a another Alfisti in Austin with a GTV6/ Milano swap cables with you? If the problem follows the cables, you have your answer.

BTW if you're feeling thrifty you can make your own ignition cables. I've never done this, but you reuse the plastic insulators that go down the spark holes, and buy new wire in a roll.

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post #12 of 301 (permalink) Old 02-15-2017, 10:19 AM
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BTW if you're feeling thrifty you can make your own ignition cables. I've never done this, but you reuse the plastic insulators that go down the spark holes, and buy new wire in a roll.
That probably will not work. Each plug lead has the same resistance even though they are different lengths. This is achieved by a balancing resistor in each of the insulators. These resistor values are chosen to match the length of the leads and are different for each plug wire.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #13 of 301 (permalink) Old 02-15-2017, 10:46 AM
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if yours has a "drive" relay, replace it. I had a similar problem on an L-jet spider, replacing the "drive" solved it. theory is: cold it worked fine, after working for a while get hot and fail (no fuel) then cool down and work. Another test would be to pull a plug on failure (stall-out) and examine, my guess not wet = no fuel

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post #14 of 301 (permalink) Old 02-15-2017, 12:15 PM Thread Starter
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The plugs are telling me it's getting gas. Interestingly, when the CTS was failing the car would run increasingly rich, causing the engine to eventually stall from flooding out. The plugs would be wet and greasy. Now they're the perfect shade of brown.
On another board, it was suggested I clip my multimeter to the wires, pop it into the toaster oven at 200 degrees or so, and see if the resistance changes with heat.

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post #15 of 301 (permalink) Old 02-15-2017, 12:34 PM
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Maybe the plugs?

I confess I sometimes read through threads too fast, but I don't see where you mentioned the plugs anywhere. I wonder if you might have replaced the plugs with some wonderful unbelievably magic newly invented spark plugs that your best friend recommended? I sold a 1750 spider to a young fellow a long time ago. He and his father came to me, bringing the car back for a refund, raging that the motor would cut out after running barely a bit. I noticed that the young man had replaced the plugs (with some allegedly wonderful split fire plugs), and without saying a word I grabbed the grubbiest old used set of NGK BP7ES plugs I could find quickly in a bucket and put them in. It ran perfectly even after he drove me thirty miles in a huff. The further we went the quieter he became. I finally told him sweetly that next time he had to check the heat range when he replaced plugs. His father apologized to me.

I confess I did have one instance where a good friend brought me his two liter that would not turn over faster than 4,000 rpm. I did everything I could with the carburetors and the timing to no avail. I finally learned the friend had decided the solid wire plug wires gave off too much static for his radio and had replaced them with graphite core (carbon track) wires used on American cars. Just could not get the spark needed to run the engine over 4,000 rpm. Solid lead wires replaced. Ran fine. But unless those are carbon track wires, and if the car ran fine before you did all that rebuilding, must be something else. Carbon track wires do work okay on american cars where 4,000 rpm is considered high. Alfas in good condition have a red line of at least 6,500. It's important to get them running at top rpm. The joy of driving one is their only real justification for owning one.

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