Got an 85 mustang gt automatic. I recently noticed on the highway around 65mph around 2k rpm, my rpm gauge will stutter and the car with jolt quickly like a misfire. It did it about 10 times in 15 seconds yesterday. I then made sure my spark wires were routed correctly (1 and 3 far apart, 5 and 6 far apart). That greatly improved the issue. Now on highway, it only does it once or twice every few minutes. I replaced the spark wires, ignition coil, distributor cap, distributor rotor today trying to fix it but that stuff didn’t help. It still does it once or twice every few minutes. Very subtle and you might not notice unless you’re looking at rpm gauge the whole time. What else could this be?
85 GT intermittent miss at highway speed
- Thread starter rwordenjr
- Start date
No. Wouldn’t spark plug be a lot worse of an issue ? I’ve got it down to very rarely happening and you probably wouldn’t even notice unless you were looking at rpm gauge as it happens. For example, say the rpm gauge is at 2k… it will drop to 1800k then come right back.
I did try that but didn’t see anything abnormal. I’ll try again in bit once dark to double check… what did significantly help the issue was spark wire routing. Here’s the area you’re talking about just for reference.
You're not pulling the plugs to see if [they] are the issue although that possibility does exist. You are pulling the plugs to [read them] so you can see if any cylinders are running fat or lean.
If you are not certain how to read plugs, take a pic of each one and keep track of where they came from. Post the images here. Make sure they're sharp and not blurry. It's best to take photos of them laying flat on a table with a profile of the strap. Be sure to show any parts with dings, etc...
Also: When it's dark outside. Start it up and let it idle until it's completely heat soaked. Look for lightning leaks around the hoses, boots, and coil.
Thanks. Will be running it in dark shortly. Ignition wise, the only items I haven’t messed with are ignition switch, spark plugs themselves and PIP in distributor.
For reference, here’s the rpm gauge. This was shot before I was able to improve things. Now it dips like you see in video once every few minutes under load instead of 10 times in 15 second video.
View: https://youtube.com/shorts/Cc9bCzCNKZU?si=pZt-HD3IBIbQA5ZN
View: https://youtube.com/shorts/Cc9bCzCNKZU?si=pZt-HD3IBIbQA5ZN
Put a timing light on your balancer. If the thing looks rock steady while you're tach is bouncing around... I win!
That’s going to be tough… it only does that every once in awhile now and it’s always under load. Never at idle. In the video above, when the tach was tweaking, I could feel the car jerking very light while it happened so I thought was miss.Put a timing light on your balancer. If the thing looks rock steady while you're tach is bouncing around... I win!
Hmmmm.... Well the jerking is [def] a miss. I couldn't hear it in your video though.
Def look around for the aforementioned lightning leaks. We can press on from there. It's important that everything is [hot] when you do it.
Maybe? You have a Temp gauge that gives you degrees?
If not, maybe run it it with the rad cap off until the thermostat opens then let it idle for 2 to 3 minutes after you put the cap back on.
Let it run for 10min… no sparks or anything coming out of engine bay with lights off. Probably not related to my issue but I’ve noticed since I’ve had this car… quite a bit of smoke coming out of pipes and it smelly. Smellier than my 91 for sure.
View: https://youtube.com/shorts/H_pxQw8ANQY?si=leMGZng68m146OaI
View: https://youtube.com/shorts/H_pxQw8ANQY?si=leMGZng68m146OaI
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