Stuttering...igntion? valves? something else

blueroo

Well-known member
Hey all,
My Fairlane has just started a very annoying habit. Right now, it's a lot worse because the air cleaner I just put on is interfering with the choke. With the old air cleaner though, it had this odd habit between 3400RPM and 3800RPM.
When I would be in second gear, right around 3400RPM, the car would start to stumble, sort of like ignition breakup, but not too badly. This would last up until roughly 3800RPM. Then it would go away. And it was only in second gear. First gear and third gear at those RPMs with no problems at all.
I can't figure out what it is. Usually, when ignition breakup occurs, it continues through the rest of the RPM range and I can't see how second gear would be the only gear it's in. I have solid lifters, and they need a bit of adjustment since they're starting to "tick", but then also, I don't see how it could only be in one gear.
At idle, with all the windows down, if you listen closely, it has a slight exhaust "pop" It's small though, just snapping your fingers is basically louder than this pop from the exhaust. But it is in a sort of pattern, like it's coming from just one cylinder

I figured I might add this bit on info as well. This has been going on for a long time though. If I start the car, warm it for about 5 minutes, and then drive for about 10 minutes, stop the motor, go into the bank for an example, come back out within 15 minutes and start the motor again, the oil pressure really fluctuates. Normally, I run around 45psi, but when it starts to fluctuate, it goes down to 25, up to around 35, down to 25, up to 45, and so on. My normal idle is about 800RPM, but when this happen it goes back and forth between 500 and 900. My voltmeter, with all the accesories off and the only lights on being the brake lights, would normally run around 15.5-16 volts. It fluctuates betwen 8 and 14 when the car has the oil pressure and RPM changes. However, once I get rolling and above 1500RPM, the oil holds steady at 45psi and the voltmeter steady at 15 or so. Again, I'm not sure if this last piece would have any ties to the problem, but I thought I would give the info just in case.
 
I don;t know ab out your engine issues, but the oil pressure gauge and temperature sound like a faulty instrument panel voltage regulator, provided that they are stock...

Kirk
 
If your RPM is fluctuating then your oil pressure and volt meter will probably fluctuate with them. Focus on the surging idle. when you fix this the other should smooth out.

The other problem might or might not be related. I would hook up a vacume guage and consider engine load and mixture when diagnosing.

You say it's worse with the new air filter. Maybe it is too close and choking the engine. Try it without any filter at all.
 
First off, sorry bout the double post. Just noticed that. As for the gauges, no they're not stock. They're aftermarket sunpro and with the exception of the tach and voltmeter, they're mechanical gauges.

As for the new air cleaner, I removed that and went to a new 4 inch, the old 4 inch was pretty dirty as well as checked to make the sure the plug boots were tight, and tightened the one that was ever so slightly loose. The problem of the stuttering went away for a day, but now it's back.
 
Ok, I've noticed something new. I was sitting at a stop light the other day and after about 30 seconds of idling, I heard a kind of pop. It happened about every 7-10 seconds then. When it makes this sound, the RPMs drop about 100RPM, then go up again. To better define the pop, imagine a gunshot from a 12 gauge, but it's far away enough that you can just hear it and there's no echo. Just the initial shot. The car only does this after 30 seconds of idling.

One other sound I've noticed is a lot more prevalent now since I've been able to cut down on windnoise substantially. At first I thought it was my speedometer cable. The problem with that theory though is even when I'm idling it doesn't change the sound at all. It's easier to hear on the driver's side than the passenger's side.
 
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