Diagnosing Ignition Problems

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rridge
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Diagnosing Ignition Problems

Post by rridge » Wed Jul 11, 2018 2:42 pm

Here's a link to an old article from "Classic Motorsport" that well applies to our cars. The author makes the point tracking down non-start and poor running complaints should start on the ignition side. "5% percentage of carburetor problems really are carburetor problems".

https://classicmotorsports.com/articles ... n=CMSDaily
Richard
'81 Turbo Spider
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Re: Diagnosing Ignition Problems

Post by spider2081 » Thu Jul 12, 2018 5:49 am

Thanks, good read.
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Re: Diagnosing Ignition Problems

Post by jseabolt » Thu Jul 12, 2018 2:08 pm

I actually had a fuel injection problem I thought was ignition related and busted my balls trying to figure it out. This misfire would come and go over a course of 2 years. One of those intermittent problems caused by a faulty device you hope will eventually just die so it can be identified.

The first, cheapest (and usually) the best place to start with is new spark plugs. Still a misfire.

So I moved onto replacing the plug wires. I thought it was a bad "#2 plug wire. My timing light showed a misfire. So I installed new plug wires. The problem came back.

Then I noticed that the #1 plug wire showed some chapping against the hood. Not long ago I replaced the exhaust to head cambox gasket. So I thought I may have gotten the distributor off a bit. So I pulled the distributor out, moved clockwise and reset the timing. Problem went away for awhile but came back.

Swapped the rotor button and distributor cap.

By this point the engine would run fine as long as the hood was up but once I closed it, the car would start idling rough. HMMM must be a bad wire somewhere.

At this point I had a bunch of engine diagnostic stuff rigged up. remote starter button, timing light, tachometer, etc. I noticed that some of these cables were laying against the connector going to the temperature sensor. Upon inspection, I noticed the wires were not only green but one of these was about to break. This sensor was actually leaking antifreeze between the brass and the plastic (not the copper washer) at one point.

A new connector and the problem was solved. This makes the second connector I've installed on this car. It's in a stupid location. Too close to the hood and if the copper washer does leak a bit, antifreeze turns the wires green.

I think it was you, who relocated this sensor to the cylinder head by drilling and tapping out the overheat "switch". I've been meaning to do this but one of those things I have not gotten around to.

I've owned this car for over 25 years and that one component seems to be the most problematic due to it's location.
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Re: Diagnosing Ignition Problems

Post by rridge » Thu Jul 12, 2018 5:35 pm

At the end of the day a misfire can be a symptom of either improper mixture or ignition malfunction or both. Its just usually easier and cheaper to rule out the ignition first. Many people begin trouble shooting by replacing the FI components. The FI coolant sensor is a very weak point most of the other FI stuff is not.

Yes, the FI temp sensor is in a vulnerable position. The wiring harness is exposed to physical damage and the sensor and contacts are exposed to coolant leaks from the poor fitting bleed port plug. Every used tee I've looked at has had corrosion in the bleed port threads and signs of leakage. It doesn't help that the tee is the high point of the coolant system and prone to holding air or that the tee is cast aluminum and the plug is brass. But beyond all that, I had a '78 VW bus with 2L aircooled engine and Bosch L-jet injection and the well protected head temp sensor was the well known weak point of that system as well.

Dave Voss had located the FI temp sensor in the overtemp switch location when he converted that silver 131 to FI many years ago, the one he brought to Detroit and Pocono FFOs and then sold it to Jon Ranney. What are the odds that some current or former forum member still owns it? I was converting my '81 to an internal thermostat and eliminating the second upper hose and coolant tee. So I needed another location for it and Dave provided that suggestion which has worked well for me.
Richard
'81 Turbo Spider
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baltobernie2
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Re: Diagnosing Ignition Problems

Post by baltobernie2 » Fri Jul 13, 2018 9:14 pm

rridge wrote:
Wed Jul 11, 2018 2:42 pm
... and poor running complaints should start on the ignition side.
True for modern cars as well. Fords, for example, are notorious for Coil-On-Plug problems. And it's not just humans getting fooled into thinking it's a fuel problem; OBDs will often throw a fuel-related code when in fact it's ignition related.
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Re: Diagnosing Ignition Problems

Post by kmead » Sun Jul 15, 2018 6:29 pm

jseabolt wrote:
Thu Jul 12, 2018 2:08 pm
I actually had a fuel injection problem I thought was ignition related and busted my balls trying to figure it out. This misfire would come and go over a course of 2 years. One of those intermittent problems caused by a faulty device you hope will eventually just die so it can be identified.

The first, cheapest (and usually) the best place to start with is new spark plugs. Still a misfire.

So I moved onto replacing the plug wires. I thought it was a bad "#2 plug wire. My timing light showed a misfire. So I installed new plug wires. The problem came back.

Then I noticed that the #1 plug wire showed some chapping against the hood. Not long ago I replaced the exhaust to head cambox gasket. So I thought I may have gotten the distributor off a bit. So I pulled the distributor out, moved clockwise and reset the timing. Problem went away for awhile but came back.

Swapped the rotor button and distributor cap.

By this point the engine would run fine as long as the hood was up but once I closed it, the car would start idling rough. HMMM must be a bad wire somewhere.

At this point I had a bunch of engine diagnostic stuff rigged up. remote starter button, timing light, tachometer, etc. I noticed that some of these cables were laying against the connector going to the temperature sensor. Upon inspection, I noticed the wires were not only green but one of these was about to break. This sensor was actually leaking antifreeze between the brass and the plastic (not the copper washer) at one point.

A new connector and the problem was solved. This makes the second connector I've installed on this car. It's in a stupid location. Too close to the hood and if the copper washer does leak a bit, antifreeze turns the wires green.

I think it was you, who relocated this sensor to the cylinder head by drilling and tapping out the overheat "switch". I've been meaning to do this but one of those things I have not gotten around to.

I've owned this car for over 25 years and that one component seems to be the most problematic due to it's location.
You can move the temperature sensor to the bottom of the neck instead of the top as there is the drain mount underneath as well. This way you can use the upper opening to bleed the system.

This will reduce the tendency for the connector to rub against the hood.

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1969 850 Sport Coupe
1970 124 Sport Coupe
1985 X1/9, ugly but fun to drive. Olive trees are hell on paint and interiors apparently. Who knew?
1987 X1/9 slowly coming back
And a few appliances for day to day
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Re: Diagnosing Ignition Problems

Post by spider2081 » Mon Jul 16, 2018 6:43 am

You can move the temperature sensor to the bottom of the neck instead of the top as there is the drain mount underneath as well. This way you can use the upper opening to bleed the system.
The "T" is directional the small opening faces the external thermostat (passenger side) The bleeder belongs on the top and the sensor in the lower opening. If the sensor is in the top opening there is a chance the "T" is installed incorrectly.













































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kmead
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Re: Diagnosing Ignition Problems

Post by kmead » Mon Jul 16, 2018 6:59 am

Agreed, I often see them the opposite way, bleeder on the bottom with the sensor on top. Thus how the sensor can be rubbed or have force on it from the hood.
1969 850 Sport Coupe
1970 124 Sport Coupe
1985 X1/9, ugly but fun to drive. Olive trees are hell on paint and interiors apparently. Who knew?
1987 X1/9 slowly coming back
And a few appliances for day to day
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