Odd shake that went away

[GngrBeardMan]

I'm not sure if this is something that I should be worried about or if I should just watch for it to happen again but as the day is Veterans Day the wife and I are running all around town trying to get as many freebies as possible along with the many doctor's appointments that she ended up getting scheduled on this day. I was coming off the freeway and had to accelerate to get up and over into a lane before I stopped at a stoplight. Once I did that as I was sitting there I noticed that I could feel what seemed like a pretty strong Shake while I was sitting there at the red light. I could feel it in the driver side door in the center console, keep in mind I'm a fairly big guy so my knees are constantly resting against those spots. It lasted for all of maybe a minute and then went away right before I started to accelerate and she began to run smooth again. Didn't notice any difference in the idle and the only code that I seem to be getting from the engine is just a p430. I've known about that one for a while and narrowed it down to I believe the catalytic converter, the rest of the signs are there for bad cat and the previous owner told me they replaced all the O2 sensors to rule that out. Not getting any other codes or lights on and I drove for about a half an hour after that with no issues. Any ideas what might have caused that shake? Could I have an engine mount that might be starting to go bad? Any ideas would be appreciated.

 

[whtbronco]

Sounds like a misfire to me. For an intermittent misfire my experience on these engines leads me to first suspect a coolant leak dripping into the coil/spark plug recess. Besides it's easy to check and free. For instance the heater valve is a fair common thing to leak. Mine only leaked intermittently with pressure so when the engine was running and it didn't leave any coolant on the intake/head, I guess it baked off. The #3 plug recess had a bunch of coolant in it though. Maybe a bit of water in the fuel. Using Heet fuel treatment with injector cleaner(the red bottle) 1-2 times when it's cold sure can't hurt and it's fairly cheap, $2-3.

Other, I think less likely, things could be fuel flow from either a failing pump, clogged injector/s or clogged fuel filter, fouled spark plug, slight chance of a dirty MAF, internal coolant leak or a piece of carbon broke loose in the exhaust holding the EGR open a bit.

EDIT: Other than checking things over not much you can do, but wait and observe.

 

[GngrBeardMan]

Thanks for some ideas. I'll check around see if I can see any coolant pulling up anywhere. Don't know if it's potentially related or not but I do have a fuel disconnect switch in the back of this thing that is finicky. There's been a couple of times where she wouldn't start at all and I had to go back and push the button down a couple times on that stupid thing. Doesn't happen very often but I have a feeling that it's just going bad and I haven't had a chance to looking into what kind of work is going to take to replace that thing. Did cause about one afternoon of head scratching and pointless testing lol. And it wouldn't start I thought of all things that might be wrong but luckily I wasn't in the mood to start tearing anything apart before I spent hours online trying to figure out any possible cause. Is actually first vehicle I've ever had that has had a field disconnect so that one threw me for a loop

 

[whtbronco]

Do you have an aftermarket switch in the fuel system you're referring to?

I am aware of the inertia fuel shutoff switch that's in a little cubby in the left rear trim panel. A lot of vehicles have these now days, if not all, though some are easier to reach than others. It's supposed to shut off the fuel supply if you're in an accident.

 

[Dustin Gebhardt]

@whtbronco is on the right track. You state that the shaking happened after a highway run and acceleration, then stopping at a red light. Your engine likely high a slight increase in coolant temperature and pressure, which caused a slight leak. The coolant tee over the passenger side of the engine is a common source for this type of leak, which then drips onto the coil for cylinders 3, and sometimes 2 and/or 4.

 

[GaryH]

Was the check engine light flashing while it was running rough?

 

[GngrBeardMan]

Check engine light wasn't flashing or on. And it hasn't done it again since I posted it. I can't find any coolant leaks and haven't needed to add any coolant either.
The fuel cutoff is what I was talking about. I've had to push the red reset button on top twice in the past year and a half but the last time was 6 months ago.

 

[Gary Waugh]

If it was the fuel cutoff, the engine would have died completely, due to lack of fuel, it would not cause poor running. Whilst it sounds like you have an issue with the fuel cut off switch, I don’t think it was the cause of your poor running. How low was the fuel level when the vibration occurred, if the level was very low then it could be that with the car coming to a stop at the traffic light, some water was sucked up into the fuel pump. This can cause vibration until the water has passed through the engine. There are some additives that you can add to the gas tank to help bind the water to the fuel and remove it from the gas tank, or just don’t let the gas level get really low.. just food for thought.