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Offline r4pinto

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misfire at cruising speed
« on: August 08, 2017, 08:02:25 AM »
Got a question for those that might know.

My car is a 1980 Pinto. Carburetor and engine from a 1977 Pinto. At high speeds (like 65-70) I am on the freeway & I hear what sounds like the engine cutting out. Any suggestions what to check? Seems to be OK at lower speeds but could hear it cutting out when driving down the freeway.

Plugs, cap and rotor were new when I installed the engine last year. Carburetor was a replacement on the 77. Last I knew it was fine. Haven't checked anything or see if there is an issue even at idle with a cylinder misfiring with the timing light but will be doing so.

Plug wires were last replaced in I think 2011. I've put about 3-4k on the engine since replacing them, if that.

I appreciate any suggestions.
Matt Manter
1977 Pinto sedan- Named Harold II after the first Pinto(Harold) owned by my mom. R.I.P mom- 1980 parts provider & money machine for anything that won't fit the 80
1980 Pinto Runabout- work in progress

Offline dick1172762

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Re: misfire at cruising speed
« Reply #1 on: August 08, 2017, 09:17:38 AM »
After its really dark, put the hood up, start the engine and look for sparks, glowing, anything that should not be there. Time tested trick.
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Offline r4pinto

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Re: misfire at cruising speed
« Reply #2 on: August 08, 2017, 09:22:35 AM »
I live in an area with street lights so it doesn't get "dark. what I might be able to do though, open the garage door about a foot or two, start the car, and leave the lights off. worth a try
Matt Manter
1977 Pinto sedan- Named Harold II after the first Pinto(Harold) owned by my mom. R.I.P mom- 1980 parts provider & money machine for anything that won't fit the 80
1980 Pinto Runabout- work in progress

Offline Rawdawg510

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Re: misfire at cruising speed
« Reply #3 on: August 08, 2017, 11:07:09 AM »
that was happening with my maverick before. it turned out to be a sparks plug that was cracked and as soon as I replaced it the car ran fine. I would check all of the spark plugs, one by one.
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Offline r4pinto

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Re: misfire at cruising speed
« Reply #4 on: August 08, 2017, 11:10:22 AM »
Since they are so cheap I might go ahead and replace them. They are an autolite platinum AP104 which was showing as for a 79 mustang turbo 2.3. Plug for the Pinto was an AP105. The AP 104 was a four pack on clearance at Meijer. I didn't see any difference in reach or heat range so I figured it would be ok. Perhaps not though


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Matt Manter
1977 Pinto sedan- Named Harold II after the first Pinto(Harold) owned by my mom. R.I.P mom- 1980 parts provider & money machine for anything that won't fit the 80
1980 Pinto Runabout- work in progress

Offline Rawdawg510

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Re: misfire at cruising speed
« Reply #5 on: August 08, 2017, 11:13:26 AM »
new plugs wont hurt but check for really fine cracks on the porcelain that is what was causing mine.
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Offline dick1172762

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Re: misfire at cruising speed
« Reply #6 on: August 08, 2017, 12:00:12 PM »
I'm running those same plugs in my 2300 Pinto with no problem's at all. Those plugs are made to run in an engine with higher cylinder temp than stock. That's all. No big deal
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Offline r4pinto

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Re: misfire at cruising speed
« Reply #7 on: August 08, 2017, 12:01:47 PM »
I'm running those same plugs in my 2300 Pinto with no problem's at all. Those plugs are made to run in an engine with higher cylinder temp than stock. That's all. No big deal
Good to know. I'll be sure to inspect them and see what happens before replacing then. Thanks. Couldn't tell from autolites website before


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Matt Manter
1977 Pinto sedan- Named Harold II after the first Pinto(Harold) owned by my mom. R.I.P mom- 1980 parts provider & money machine for anything that won't fit the 80
1980 Pinto Runabout- work in progress

Offline r4pinto

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Re: misfire at cruising speed
« Reply #8 on: August 08, 2017, 08:27:08 PM »
Opened the garage door when nearly dark, turned on the shop light when walking to the car and started the car. No arcing anywhere. Checked out the spark plug wires as well and no signs of arcing on them either. They were also good and tight. I might go ahead and pull the module off and have it tested. I will also inspect the spark plugs themselves.
Matt Manter
1977 Pinto sedan- Named Harold II after the first Pinto(Harold) owned by my mom. R.I.P mom- 1980 parts provider & money machine for anything that won't fit the 80
1980 Pinto Runabout- work in progress

Offline dick1172762

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Re: misfire at cruising speed
« Reply #9 on: August 09, 2017, 08:45:28 AM »
Water in the gas will cause misfire too. Try some "heat" they sell at the parts store and wallie world.
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Offline r4pinto

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Re: misfire at cruising speed
« Reply #10 on: August 09, 2017, 08:47:22 AM »
It's not constant and only while cruising. I haven't pulled the spark plugs yet. That'll come tonight to see how they are. I did put in a bottle of carb cleaner with water remover so we will see how that helps


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Matt Manter
1977 Pinto sedan- Named Harold II after the first Pinto(Harold) owned by my mom. R.I.P mom- 1980 parts provider & money machine for anything that won't fit the 80
1980 Pinto Runabout- work in progress

Offline r4pinto

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Re: misfire at cruising speed
« Reply #11 on: August 09, 2017, 08:12:09 PM »
Think I found the issue. I pulled the plugs and 1-3 were very good and firing perfectly but 4 was another story. It was very dingy, and didn't seem to be firing constantly. The plug wire itself was broken at the plug itself, and the plugs were also gapped larger. Specs show .034", and they were over .040". I didn't have a wire feeler gauge when I installed them but it was running well. The bigger issue was the bad plug wire. I found out at 8:55pm est and parts stores closed at 9pm est.


I will get a new set of plug wires, and keep the other three for spares in case something happens. I also have a new set of spark plugs on standby, and will also have the ignition module tested as well, just to be safe.
Matt Manter
1977 Pinto sedan- Named Harold II after the first Pinto(Harold) owned by my mom. R.I.P mom- 1980 parts provider & money machine for anything that won't fit the 80
1980 Pinto Runabout- work in progress

Offline robertwwithee

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Re: misfire at cruising speed
« Reply #12 on: August 09, 2017, 09:11:53 PM »
Congratulation s on the fix.

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Offline r4pinto

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Re: misfire at cruising speed
« Reply #13 on: August 09, 2017, 09:13:37 PM »
Thanks. Hopefully that's all that is wrong. I won't know till I get the new wire set. I looked in my garage for spare wires or even a set from a different car to see if that was the issue but I tossed them out when I got rid of the old car.


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Matt Manter
1977 Pinto sedan- Named Harold II after the first Pinto(Harold) owned by my mom. R.I.P mom- 1980 parts provider & money machine for anything that won't fit the 80
1980 Pinto Runabout- work in progress