Engine misfire? And a couple other odd issues

[L1011tristar17]

sly, I'll have a look at those. My next item is to check the fuel pressure, so hopefully I can find some inexpensive sensors while at the parts store.

Here's a video I took of my car running. You can see the hood dancing and a bit of the engine shaking. Listen for some of the odd sounds I heard when putting the camera close to the engine.

[IPreferDIY]

My only experience with misfires has been with spark plug and coil-on-plug issues that clearly showed up as obvious 'bucking' at certain points while driving, so I can't really offer anything substantive. As for the sound in your video, my impression when you did the tailpipe close-ups was that the passenger side sounded different. I have no idea whether that might be relevant. I do believe that someone with lots of experience and an ear for it could potentially diagnose problems by how the car sounds, so it will be interesting to see what happens.

[L1011tristar17]

Did a fuel pressure test. Got 31 psi idling, which seems to be too low. I replaced the fuel filter a year ago, so could it be the pump going bad? The pressure also dropped as soon as I shut the engine off. I don't know if that's normal.

[gadget73]

31 psi with the vacuum line connected is about normal. It should be around 40-42 with it unhooked. It should not drop that quickly, nor should it come up that slow. The usual reason is either a leaky injector, or the check valve in the pump is bad. A leaky injector would show up as bad fuel economy and fouled plug(s). If the pump is original, it may be tired. I'd change the fuel filter first though because its 10 bucks and takes 20 minutes to do. The pump is rather more expensive and time consuming. If the injectors are original, they may also be due for service or replacement.


I don't see anything there that would worry me. Remember you're talking about an engine that was designed in the late 1950s with an injection system from the mid 80s. Its not going to run as flawlessly smooth as a modern car. I've never seen a 302 that didn't have enough vibration to make the hood shake a bit when it was up. I do hear a 302 with miles and a slightly loose bottom end though. Its whats to be expected with that kind of mileage. If the oil idiot light isn't on constantly, its not loose enough to worry about.

Have you ever put a timing light on it to confirm its correct? How stable is the timing? If the timing chain is worn, you'll see the mark tend to dance around at idle. You can also do the crankshaft rock check to see whats going on. basically you remove the distributor cap and rock the crank back and forth. If the rotor doesn't follow crank movement immediately, the chain is worn. At 243k, I'd say its unlikely that there isn't some wear. Whether or not its serious is another story. Mine at 225k had slop in the chain, but it wasn't causing any problems. I changed it because I was already into it for a water pump and balancer replacement, and pulling the timing cover was not much extra work at that point.

The Mark VII had random slight misfires when I got it. It was fine under load, idle wasn't amazingly smooth but not enough to be concerned about. Replacing the chain helped a little bit, but not much. Replacing the injectors with a mismatched but supposedly rebuilt set helped a tad, but also not much. When the lower intake came off, it was pretty nasty inside and the injector bungs were mostly crusted over except for a tiny hole for the spray. Replacing that helped quite a bit, and then replacing the injectors with a matched set helped some more. It idles about as good as you're ever going to find on a motor with 247k miles on it, and a damn sight better than many with half that mileage. Long story short, if the intake is packed full of crap to the point that the injectors are half blocked, its probably not going to run well. If you replace the injectors, shine a light in the hole to see what it looks like. If it looks like peanut brittle growing over the bung, at least knock that loose and try to vacuum it up before putting the new ones in.

[L1011tristar17]

Thanks gadget. That's a lot of really good information. I think it's best for me to not worry about it right now since the car still drives just fine. When I last set the timing (2 weeks ago), the timing mark was pretty steady on 10 degrees BTDC. I can't remember the last time I had the injectors out, but it was when I swapped intakes and I cleaned out the JY one pretty well. I might just run a tank of injector cleaner and see if anything improves.

[gadget73]

are they the original injectors? A fresh or fresher set may be of some help.

if the timing light holds steady, and the intake isn't all packed up with crap that eliminates a lot of possible issues. At some point you may just have to settle for "good enough". If the only issue is a slightly rough idle, but it runs down the road fine I'd say to drive more and idle less

[L1011tristar17]

Would a code 94 cause a misfire?

[L1011tristar17]

Still haven't found out what is causing the misfire. The engine runs and accelerates fine, but after about five minutes the car starts shaking pretty badly. When accelerating, the car bucks and has a difficult time going any faster. I've replaced a lot of parts, so I'm not sure what could be left. I did get a code 94 but I don't know how that might contribute to the misfire.

I also took a video of the car idling in park. I heard a ticking sound coming from the rear of the engine. Not sure what that could be. I set the timing a couple weeks ago but this noise seems to be new. I can't hear the ticking from inside the car. Bad lifter? Rockers? Another thing to note: I feel like the engine surges sometimes when I press on the brakes. It kicks up the idle too every now and then when the car is in park (with the a/c off)

[slack]

Ticking might also be coming from one of the pulley's. Not sure on that one.

The car surging when you hit the brakes... I had that problem with my old Fleetwood. I believe it was a vacuum leak that caused it.

[Pretty much broke]

It sounds exactly like the issue I've been having / had. I put in a new TPS, ignition coil, coolant temp sensor, fuel filter, new plugs and wires, new vacuum lines, IAC, EGR, cap and rotor etc. And it still did it, mine was to the point where it was essentially undriveable though. To me it sounds like a dead TFI module. Even if you replaced it once doesn't necessarily mean it hasn't broken again. My car did the same thing, run great for 5 to 10 minutes and then on queue it would just start misfiring hard. Push on the gas and it felt like the pistons were gonna fly out of the block. But it would idle decent, only slight missing. I got a new distributor + TFI module as a kit for $58 bucks and it made all the difference. Runs like a car with 97k miles should now. And improved gas mileage pretty significantly. Best investment I've ever made in this car for sure. Here's a link if you want it, if not, best of luck searching for the issue. Misfires are the worst. https://www.rockauto.com/catalog/x,c...,parttype,7108

[L1011tristar17]

Ticking sound seems to be coming from the rear of the engine, so I don't know if the pulleys would be causing that sound.

I think it's a vacuum problem as well. I'm looking to replace the hose to the MAP sensor as well as the one from the upper intake to the air pump. Other than that, I don't know which other ones to look at. The vacuum port on the intake seems to be a bit bigger than the port on the MAP sensor, so I'm not sure which size vacuum hose to buy?

I'll definitely look into replacing the TFI module. Not sure if I need a whole new distributor though. Do those things usually go bad on these cars? And I don't know what gears mine has.

[gadget73]

replace all of the vacuum hoses under the upper intake. If you're taking it off, may as well do all of it.

two ways to do the MAP vacuum line. Buy one that fits the MAP and stretch it, or buy a line that fits each end and use one of those plastic connectors that goes from one size to the other to couple them.

[sly]

ticking sound from the rear may be the PCV valve. That's normal for an all metal one.

[miamibob]

Like the ticking of an artificial heart valve....

[L1011tristar17]

Car seems to surge/stumble occasionally when cruising at a constant speed (between 65-70MPH). What could be causing this?

And an unrelated question: Are the white markings on the headlight switch illuminated?