Won’t idle after long drive
Thread Starter
Racer
Joined: Oct 2020
Posts: 416
Likes: 76
From: Atlantic Beach, FL
Won’t idle after long drive
Recently rebuilt everything LT-1. Car starts immediately when cold, kicks down from fast idle after warming up and idles beautifully at 950 RPM.
Drove around town about 15 miles to a friends house, idled fine. Shut down for about 5 minutes then back on the road for another 10-15 miles. At some point something changes and the car will not idle. If i lift off at a light it dies, but can be re-started. So to get home, i use a lot of heel and toe to keep it above 1500 RPM.
Checked all the vacuum lines, made sure the anti-diesel solenoid was working, snugged up carb bolts, nothing amiss. After about 15 minutes, starts right up and idles beautifully again. So i checked vacuum - solid needle at 16. Fuel right at the bottom of the sight plug….
Drove around a bit and again about 5 miles in, it starts dying at idle.
I’m at a loss for where to look next - the first 30-40 minutes are great and then i loose the ability to idle.
Anyone have any suggestions where to look next?
Drove around town about 15 miles to a friends house, idled fine. Shut down for about 5 minutes then back on the road for another 10-15 miles. At some point something changes and the car will not idle. If i lift off at a light it dies, but can be re-started. So to get home, i use a lot of heel and toe to keep it above 1500 RPM.
Checked all the vacuum lines, made sure the anti-diesel solenoid was working, snugged up carb bolts, nothing amiss. After about 15 minutes, starts right up and idles beautifully again. So i checked vacuum - solid needle at 16. Fuel right at the bottom of the sight plug….
Drove around a bit and again about 5 miles in, it starts dying at idle.
I’m at a loss for where to look next - the first 30-40 minutes are great and then i loose the ability to idle.
Anyone have any suggestions where to look next?
Race Director
Joined: Nov 2006
Posts: 13,248
Likes: 7,840
From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
2024 C3 of the Year Finalist- Modified
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Cruise-In VIII Veteran
Seen that exact symptom with a failing coil many times. If you keep the R's up it'll keep running. But let the R's drop and she dies. Happens after 30 - 40 minutes run time generally. Let it cool down and problem goes away. But if not totally cooled down returns quicker.
Put a bag of frozen peas on the coil the next time. Give it a minute or 2 for the frozen peas to cool the coil. Fire it back up. What happens?
Put a bag of frozen peas on the coil the next time. Give it a minute or 2 for the frozen peas to cool the coil. Fire it back up. What happens?
Team Owner
Joined: Jan 2007
Posts: 53,648
Likes: 878
From: Southern Cal Ca
St. Jude Donor '22
hate it when that happens.
you say the carb has gas to bowls when looking at sight plugs.
leaves spark.
you could check spark in a couple ways.
put coil dist wire in cap loose looking for cranking spark.
an inline spark tester
have an ex hold the coil wire
good luck
you say the carb has gas to bowls when looking at sight plugs.
leaves spark.
you could check spark in a couple ways.
put coil dist wire in cap loose looking for cranking spark.
an inline spark tester
have an ex hold the coil wire
good luck
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Thread Starter
Racer
Joined: Oct 2020
Posts: 416
Likes: 76
From: Atlantic Beach, FL
1967 Pedal Car Champion
Joined: Mar 2020
Posts: 9,137
Likes: 4,248
From: US-PNW
Thread Starter
Racer
Joined: Oct 2020
Posts: 416
Likes: 76
From: Atlantic Beach, FL
Yes, but with the new one there was very little sloshing as it was mostly full. The old one seems to have lost a fair amount, leaving more room for sloshing around. The difference was pretty obvious
Thread Starter
Racer
Joined: Oct 2020
Posts: 416
Likes: 76
From: Atlantic Beach, FL
Here’s a fun update. Replaced the failing Pertronix flame thrower coil with a new one last week. Advance stocks them so it was an easy replacement. Today when i was changing my carburetor i notice some oil around the base of the coil and pooled in the manifold near the coil. Cleaned it up and after running the car a bit, found more oil. So the new one was leaking quite a bit and would have eventually caused problems like the last one.
Quick trip to the parts store with the old one for an exchange and back in action. Let’s see how long this one holds up.
Quick trip to the parts store with the old one for an exchange and back in action. Let’s see how long this one holds up.
Race Director
Joined: Nov 2006
Posts: 13,248
Likes: 7,840
From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
2024 C3 of the Year Finalist- Modified
2022 C3 of the Year Finalist - Modified
Cruise-In VIII Veteran
Oh Gawd! Ain't that enough to frost your tail!
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
69rx7,
I am afraid your quick repair will be short-lived. That's two band-aides recently but no permanent fix.
Sometimes when you fry a coil, its sending a message that something is amiss downstream. You cooked two coils so far. Might be headed for another.
How old is your plug-wire set?
I am betting the resistance of the plug-wires is not in the proper range and the coil(s) is protesting by overheating and failing, twice!
I am afraid your quick repair will be short-lived. That's two band-aides recently but no permanent fix.
Sometimes when you fry a coil, its sending a message that something is amiss downstream. You cooked two coils so far. Might be headed for another.
How old is your plug-wire set?
I am betting the resistance of the plug-wires is not in the proper range and the coil(s) is protesting by overheating and failing, twice!
Safety Car
Joined: Sep 2007
Posts: 4,458
Likes: 331
From: Indy Indiana
dang.. in my home mechanic lifetime I have never seen a leaky coil.. guess it can happen though and does describe your symptoms...
don't know of you are points or not, but I have seen lack of a resister circuit in front of the coil roast a coil. you should not have 12V, it should be resisted to .. I dunno.. 8 or 9 volts... to the front of the coil.
I have petronix, and therefor 12 volts to my coil, and it gets pretty toasty after a long drive. petronix's instructions say to bypass resistor and run 12 volts to the coil.
i bet the secret is to get you a nice well built non Chinese coil. but those are hard to find.
Maybe mount your coil on the firewall instead of your hot manifold too.
don't know of you are points or not, but I have seen lack of a resister circuit in front of the coil roast a coil. you should not have 12V, it should be resisted to .. I dunno.. 8 or 9 volts... to the front of the coil.
I have petronix, and therefor 12 volts to my coil, and it gets pretty toasty after a long drive. petronix's instructions say to bypass resistor and run 12 volts to the coil.
i bet the secret is to get you a nice well built non Chinese coil. but those are hard to find.
Maybe mount your coil on the firewall instead of your hot manifold too.
Thread Starter
Racer
Joined: Oct 2020
Posts: 416
Likes: 76
From: Atlantic Beach, FL
69rx7,
I am afraid your quick repair will be short-lived. That's two band-aides recently but no permanent fix.
Sometimes when you fry a coil, its sending a message that something is amiss downstream. You cooked two coils so far. Might be headed for another.
How old is your plug-wire set?
I am betting the resistance of the plug-wires is not in the proper range and the coil(s) is protesting by overheating and failing, twice!
I am afraid your quick repair will be short-lived. That's two band-aides recently but no permanent fix.
Sometimes when you fry a coil, its sending a message that something is amiss downstream. You cooked two coils so far. Might be headed for another.
How old is your plug-wire set?
I am betting the resistance of the plug-wires is not in the proper range and the coil(s) is protesting by overheating and failing, twice!