Rough running engine

[Russ]

Would advancing the base timing a couple of degrees help to smooth out an engine that's running rough under load?
I'm pretty sure the symptom is related to the ignition system (symptom didn't show up untill I had to change a distributor on it). It's a '95 Galant with 137,000 miles, new distributor (OE, includes coil and module), plugs (NGK V-grove), wires (OE). Recently replaced air/fuel filters, cleaned throttle body, new PCV valve, single Redline SI, and single Seafoam treatments.
Any input would be greatly appreciated.

 

[tpi]

Is timing to spec now? Generally out of spec timing does not cause rough misfiring engine (unless extreme

) . Too advanced: detonation. Retarded: Sluggish, throttle tip in sag.

I'd go over the other ign work again. Look particularly at the spark plug wire ends.

 

[keval85]

Just a stab in the dark,but maybe the distributor was put in a tooth off?

 

[Russ]

Thanks for the replies

The timing is within spec now (5 before; the actual spec is 5 before +/- 2, so I was thinking maybe setting it to 7 before would do anything positive. I never checked the timing with the old distributor in, but it seems to me that it was a bit more advanced than it is now - the whole assembly was turned just a bit more toward the front of the engine than it is now.)
What exactly would I need to look for at the plug wire ends? (These are brand new wires from the dealership, fit nice and snug both on the plugs and the distributor - I quadruple-checked that part

)
The distributor itself does not have a traditional gear drive - just a cam with two index studs on each side, one longer, one shorter, which correspond to indentations on the camshaft. So there's only one way to install this distributor (or so it seems).
Once again, thanks for the help!

 

[tpi]

You can advance the timing to 7 BTDC and listen for detonation in hot weather. If you don't hear any you should be OK, it is within spec. But I wouldn't expect a 2 degree advance to smooth out a misfiring engine.

Spark plug wire ends seem frequently be a failure point, from handling or strain.

I take it you have a smooth idle and it is smooth under light load. This should rule out improper firing order.

Is what you're feeling a sharp ignition miss under heavy throttle? Bucking, intermittent misfire? Maybe you have a defective or cracked spark plug or something defective with the new distributor. Can you substitute the old one back for a test?

 

[keval85]

Maybe a ohm test on the wires is in order ,I have seen a bad wire right out of the box before,or maybe a fuel problem like the pumps getting tired.

 

[Russ]

Well, maybe I gave a wrong description of the symptom. It is a vibration that is actually driving me nuts. It is most aggravating at highway speeds. First I thought it was a tire/wheel bearing problem of some kind. But the tires had to be replaced along with wheel bearings (those did produce symptoms, which were cured with replacement, but those were not the vibration in question). Then I started suspecting axle shafts, torque converter, etc. Then I finally noticed that the exact same vibration is present at idle. It is least noticeable in neutral. As soon as the car is put in gear, the vibration increases. It seems to increase with RPMs, not just the speed (although its not as bad when revving the engine in Park, or Neutral). The wheel bearings were replaced shortly after the distributor (along with plugs, wires, etc.) I was expecting a smooth ride after that, but here I am. I figured that the vibration from the tires and bearings was masking the engine problem.
The idle did smooth out noticeably after the throttle body was cleaned, but that was it, the high RPM/speed vibration did not change one bit. It also sounds like there is a surge of a sort (not a steady engine hum, this made me think that this could be torque coverter shudder, but the transmission has been flushed, fluid is fresh, and it shifts almost flawless - as flawless as a transmission with 137,000 miles on it can). Of course, this "surge" is not all that obvious, you have to listen to it (but I don't believe its my imagination).
On top of things, there's a "thump" at the start-up. Feels like there's a late spark somewhere, or something.
In short, the engine cranks, "thump" at start up, somewhat rough idle (but this IS an old and tired engine), idle speed withing spec (700-800 RPMs), vibration when put in gear, vibration increases with speed/RPMs, slight "surge" (speed/RPMs don't change a bit) at cruising speed. Good acceleration, mileage.
Oh, and I did replace an O2 sensor with a Bosch unit (Bosch was in the car when I got it, and it ran fine).
The old distributor had to be replaced because the Ignition Control Module (internal part of the distributor along with the coil) went out on it, so the engine won't run with it.

 

[tpi]

Hows the engine power? Acceleration normal?

 

[Russ]

Yes, seems perfectly normal, along with fairly smooth shifting transmission (as "normal", and "smooth" as possible on a car with almost 140,000 miles).

 

[97tbird]

Motor mounts ok?

 

[Russ]

Looks like it.
I did check the timing last night. The thing was at 2 or 3 before (have no idea how it got that way, unlesss automotive service professionals messed with it last time they had their hands on it). Set it to 5 - still vibrates, but not as bad. So it's still within spec, but a couple of degrees of advance seem to make some kind of difference.

 

[keval85]

Sell it

 

[Pecos]

I would suggest that you look closer at ALL engine and transmission mounts.If you have access to a hoist I would try the following.

Put someone in car and raise hoist.
Put a nice sized pry bar or equivalent in hand.
Have car started and put into drive,foot on brake.
Insert prybar into mount area and hold mount in opposite direction it is flexing.
If vibration changes at all,replace the mounts.

 

[Russ]

quote:

---

Originally posted by keval85:
Sell it

---

Working on it. (Although it's a **** shame - car is in pretty good condition for its age, has been pretty well taken care of while in my posession, etc.

)

 

[brianl703]

Does this engine have a harmonic balancer of some sort? (Usually part of the crankshaft pully).

Could it be in need of a new one?

 

[brianl703]

Also, does the vibration change any if you put it into neutral at highway speeds?

 

[Russ]

I don't think there's a harmonic balancer. It does have a balnce shaft, though.
Will try shifting into neutral on the highway tomorrow.

Thank you for all your responses, folks!

 

[Russ]

Oh, yeah, Fuel Power seems to be making a difference also.

 

[Gary Allan]

Assuming that you've checked the motor mounts ..which I think would evidence themselves with shot CV joints after too long (how do I know?)...

...I'd find some outfit with a Sun Interigator and perform a cylinder balance test (the full battery of what it can do).

Naturally, given the cost of such an action ...I can understand that "parts replacing" is a viable option to accurate diagnosis.

 

[brianl703]

Actually, you can perform your own cylinder balance test.

First thing to do is to get an accurate shop tach and hook it up.

Second thing to do is to is to start the engine (it should already be up to operating temp) and disconnect the idle speed control valve (hopefully the engine will still run with it disconnected. It does on my Ford vehicles).

This will prevent the computer from changing the idle speed.

Third thing to do is to disconnect each fuel injector in turn while noting how much the engine RPM drops with each injector unplugged.

A cylinder that shows less of a drop than the others is weak...possibly leaking valve or clogged injector.

Ford vehicles have this test built-in to the computer, and they do it it by turning off each injector and measuring the RPM drop each time.