96 Accord is a Mover & Shaker

January 2, 2009 11:18 AM

96 Accord is a Mover & Shaker? Mysterious problem.

My '96 honda accord will vibrate for ~1 second if i actuate the power locks or windows while the car is at a stand still (for ex. at a red light). I can definitely feel the tremor pass through the car. If i put the car in neutral (auto transmission) and actuate the power locks/windows, the vibration can still be felt, albeit to a lesser extent.

For example: The car is stopped at a red light. It is in drive. I push and hold up on one of the window buttons. Even though the window is up, a tremor will pass through the car for about 1 second and then die down. I am still holding up on the button. Lather, rinse, repeat.

Is this indicative of any problem? What more can I do to better diagnose the issue other than take it to a tech?

I am technically inclined and love getting my hands dirty, so feel free to offer all suggestions.

posted by FusiveResonance to technology (9 comments total)

Sounds like you are drawing electrical power from the spark plugs to the locks/windows. You might also see a very slight dimming of the headlights when you do this.

You might start at your plugs and work your way up the electrical system checking everything out. Things to note among other things: worn/dirty plugs, worn wires, alternator and generator shorts/wear, lose or worn belts, an old/dying/corroded battery or cables, and last fuse box and (if all else seems good) the wires leading to the door switches themselves.
posted by Pollomacho at 11:55 AM on January 2

Dunno if this is it, but it's something to consider: I've had two Hondas, and both had to have the motor mounts replaced after a few years.

As explained to me, "motor mounts" or "lifing mounts" are usually 3-4 mounts that actually hold the engine in place and help control vibrations. They tend to crack and break over time. When they're cracked or broken, the engine can vibrate more and continue moving forward when your car has stopped, both of which are sub-optimal, as you can imagine.

I recommend taking it to a Honda-specific dealer; every time I've received estimates from non-dealers it's ended up being way more expensive and time-consuming to go through a regular mechanic (apparently the parts aren't always on hand) for my car's specific problem.

I was told that the work is somewhat expensive because they literally have to lift your motor out of the car to see the mounts or to replace the mounts. Recently, I paid $800 to have two of the three replaced. YMMV.
posted by answergrape at 12:04 PM on January 2

Your motor mounts may be worn out, so you notice more, but they're not the problem. I'd stop by an auto parts store and get your alternator checked out - if the power locks are drawing too much for the alternator to handle, the ignition won't get enough juice, etc. I'd also take a voltmeter and see what kinda voltages you're getting when the locks are switched. If I had to guess, I'd suspect the relays for the power locks are sticking or pulling too much power down to ground (that or the window motors are grounding out).
posted by notsnot at 12:15 PM on January 2

Or maybe your idle speed is set really low. Like, about-to-stall-any-second low. So you put an additional electrical load on the system, which ultimately loads the engine. Just for a second, the speed drops and you almost stall, which you can feel as a shudder in the car.

That would be amplified if your electrical system were drawing way more current than normal, like notsnot said, but I would think that would blow a fuse also. Maybe not.
posted by ctmf at 12:33 PM on January 2

I should then add, after ...which you can feel as a shudder in the car: Then, the speed picks back up to the idle speed and the shudder goes away. Which exactly describes your symptoms.

Try this: put the car in neutral with the parking brake on. Rev it just a bit with a slight toe press on the gas pedal while you try the window switch. See if the same thing happens.
posted by ctmf at 12:38 PM on January 2

A larger electrical load can be perfectly normal without any chance of blowing fuses. That only happens when the load on an individual circuit is too high - not on the system as a whole.

Do you have air conditioning? If you turn on the air con in the same idling scenario, does the engine shudder or kick in the same way as when you use the power windows? All of these (and the rear window heater) are pretty high loads, but the air con is more of a physical load (it kicks in the compressor pump and will make the engine mounts more likely as the cause of the shudder than the electrical system).

Does the engine make any different noises? Like a cough and a splutter? Does the car have a rev counter? If the cause is loss of electrical power to the ignition system (the least likely of the two options) then the engine revolutions will drop and the car will hesitate. As a double check, with the car in drive, do the same actions that produce the shudder, but try and pull away at the same time. If the car stalls, then it is still potentially either situation, but if it pulls away with no issues, it is most likely the engine mounts.
posted by Brockles at 12:48 PM on January 2

ctmf:
Try this: put the car in neutral with the parking brake on. Rev it just a bit with a slight toe press on the gas pedal while you try the window switch. See if the same thing happens.

Nope, I'm not noticing it at all.


Brockles:
Does the engine make any different noises? Like a cough and a splutter? Does the car have a rev counter? If the cause is loss of electrical power to the ignition system (the least likely of the two options) then the engine revolutions will drop and the car will hesitate. As a double check, with the car in drive, do the same actions that produce the shudder, but try and pull away at the same time. If the car stalls, then it is still potentially either situation, but if it pulls away with no issues, it is most likely the engine mounts.

Car is in drive/neutral (doesn't matter - same effect) and needle is static on the tach. Actuate windows/doors and the needle drops slighly (1 or 2 degrees). Returns to previous position in ~1 second.

I'm not hearing any different noises, neither am i able to stall the vehicle.

So based on viewing the tach isn't it apparent that this problem is loss of electrical power to the ignition system? If this is the problem, should i be concerned? Should i take the vehicle to a mechanic right away?
posted by FusiveResonance at 4:06 PM on January 2

Should i take the vehicle to a mechanic right away?

No, I think you're fine. If all the electrics are actually working, and no fuses are blowing, and it's just a transient effect (goes away, like you say, even holding the switch), then it's probably not a grounded window motor or something like that. Also, if you can reproduce it with a variety of different electrical loads, that doesn't (to me) indicate an electrical fault.

If it bothers you, you could have someone (maybe your mechanic, maybe a friend with a multimeter) check it out as Pollomacho said. You could call your mechanic or Google around for how to improve a rough idle. A general tune-up would probably not do the car any harm.

I would avoid mentioning anything about motor mounts to a mechanic I did not know very well. I don't like volunteering BS stories that I might believe if they tell back to me. If that's what it is, they'll know whether I tell them or not. Just saying.
posted by ctmf at 5:10 PM on January 2

So based on viewing the tach isn't it apparent that this problem is loss of electrical power to the ignition system

Quite the opposite. Such a small drop, and the inability to stall the engine, suggests it is almost certainly engine mounts to me - not in the slightest bit urgent. I would have expected a 500rpm or so drop from an electrical issue at least, and some attempt on the engine's part to stutter or try and stall. Certainly the extra load of being in gear should have made a difference. It is worth noting that the electrical load angle that people were focussing on is almost unheard of and would have shown other, more obvious, signs first, in my opinion.

When the engine is cold, grab it firmly at the top and try and move it (forward and back in the car as you stand at the front). If you get anything like appreciable movement, then that will confirm the diagnosis of engine mounts. Another way is to stand in front of the car (or to the side, if you don't trust it!) with the bonnet open and have someone (with the e-brake and footbrake firmly on) drop the car in and out of gear while it is stationary. My guess is you will see a sizeable kick of the engine position (like half an inch of movement or so). It shouldn't really move much at all if the mounts are in good condition.
posted by Brockles at 12:32 PM on January 3