Jump to content
CaddyInfo Cadillac Forum

Severe vibration under load


Chris

Recommended Posts

Starting a few months ago, I noticed my STS vibrating at highway speeds. Over time, I began to notice it on acceleration and (to a much lesser extent) at city speeds. It seems to have gotten worse in all conditions, and is less noticable when just starting to drive.

The engine idles a bit rough, but it always has been this way, even after changing the plugs and wires together (years ago).

I found a few posts suggesting the following:

1) change the wires

2) change or regap the plugs

3) change the transmission fluid

I did the "spray test" on the wires and didn't notice any arching. They were changed (with the plugs) about 50k miles ago.

The transmission fluid is probably due for replacing, but could this actually be a problem?

I took a video to help me explain the problem to a friend: HIGHWAY VIBRATIONS QUICKTIME VID (you may need to right-click and select Save As... to view this).

Please let me know if you have any suggestions. I'd like to try and figure it out this weekend, so am looking for anything that might help. :D

Thanks!

-Chris

Link to comment
Share on other sites


Starting a few months ago, I noticed my STS vibrating at highway speeds. Over time, I began to notice it on acceleration and (to a much lesser extent) at city speeds. It seems to have gotten worse in all conditions, and is less noticable when just starting to drive.

The engine idles a bit rough, but it always has been this way, even after changing the plugs and wires together (years ago).

I found a few posts suggesting the following:

1) change the wires

2) change or regap the plugs

3) change the transmission fluid

I did the "spray test" on the wires and didn't notice any arching. They were changed (with the plugs) about 50k miles ago.

The transmission fluid is probably due for replacing, but could this actually be a problem?

I took a video to help me explain the problem to a friend: HIGHWAY VIBRATIONS QUICKTIME VID (you may need to right-click and select Save As... to view this).

Please let me know if you have any suggestions. I'd like to try and figure it out this weekend, so am looking for anything that might help. :D

Thanks!

The file is 44.2MB by the way. Platinum spark plugs are known to lose the pads. I do not think the transmission can cause vibrations at those speeds because the TCC is locked up.

The saddest thing in life is wasted talent

Link to comment
Share on other sites

I had a strange vibration a few years ago with my Oldsmobile. A little searching found a missing bolt on an engine mount. Once I replaced it, everything was fine. An engine/transaxle combo is a living and wiggling entity that has vibrations in several different directions when it is running, and it has to be carefully tied down before it really seems smooth.

Link to comment
Share on other sites

It could possibly be a bad CV joint.

I agree Jim

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

Link to comment
Share on other sites

I had a strange vibration a few years ago with my Oldsmobile. A little searching found a missing bolt on an engine mount. Once I replaced it, everything was fine. An engine/transaxle combo is a living and wiggling entity that has vibrations in several different directions when it is running, and it has to be carefully tied down before it really seems smooth.

Hmm good suggestion, thanks... One thing I forgot to mention is that the severity of the vibration seems to be somewhat related to the road surface (its not nearly as bad on newly paved roads), so this could explain that.

It could possibly be a bad CV joint.

CV joint was actaully the first thing I thought of but I understand a bad CV joint will cause clicking or other noises when making sharp turns at low speed? Is there anythign I can do to check the CV joints aside from visually inspecting the boots?

-Chris

Link to comment
Share on other sites

it will audibly click if the boot is ripped and the grease has been spun out, but if the boots are intact the axles can be loose or out of balance and cause vibration.

Sometimes its difficult to determine if its suspension or ignition related. I think if it was igntion related you would get a misfire code, but I dont think a P300 will get set in the 1993 PCM, you might need an engine analyzer. Check your engine mounts also, my front engine mount was separated and I got a vibration on acceleration.

Check your COILS, clean the towers, and check their primary and secondary resistance

Use an ohm meter to check your ignition wire resistances

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

Link to comment
Share on other sites

it will audibly click if the boot is ripped and the grease has been spun out, but if the boots are intact the axles can be loose or out of balance and cause vibration.

Sometimes its difficult to determine if its suspension or ignition related. I think if it was igntion related you would get a misfire code, but I dont think a P300 will get set in the 1993 PCM, you might need an engine analyzer. Check your engine mounts also, my front engine mount was separated and I got a vibration on acceleration.

Check your COILS, clean the towers, and check their primary and secondary resistance

Use an ohm meter to check your ignition wire resistances

I took a look at the CV boots, they are in perfect condition.

As you say, I dont think the 93 has a P300 code. The only powertrain code that is set occasionally is P027 - Open throttle position switch.

I checked all the engine mounts I could see, and they were ok - 2 of them were replaced a couple years ago.

I found that some of the wires werent clipped onto the coils properly... this didnt solve the rattling problem, but couldnt have been good.

The probes on my multimeter arent long enough to contact the wires on the spark plug side, Ill have to go to the store tomorrow to get something for that so i can report back on resistances.

-Chris

Link to comment
Share on other sites

Measured wire resistances: 1.64 to 2.77kOhm for the odd-bank, and 4.36 to 5.78kOhm for the even-bank. Not sure if these are reasonable, but at least they are generally inversly related to the wire length (only exception being cylinder 4, which has a slightly higher resistance than cylinder 2).

Found some corrosion on the contact for cylinder 6, cleaned it off, but didnt make any difference.

Pulled the plugs and they look acceptable. Its been about 60k miles (not 50k as mentioned earlier) and they are Champions so i think i will replace them with ACDelco to see if that helps. Can't believe the local dealership is wanting to charge $16.40/plug... will have to take a drive over to detroit or buy from rockauto (US$9.10 shipped).

BodybyFisher: To clean the towers, do I need to remove them and clean the terminals (I assume there are terminals underneath?)

If that doesn't help, do you think wires could be shot? Come to think of it, they were changed with the plugs when I first got the car (7 years ago) and at the time I wouldn't have insisted on Delco parts. The resistances (as mentioned earlier) appear to be ok, but not sure the insulation will be in tip top shape.

Thanks again for your help guys!

-Chris

Link to comment
Share on other sites

did you try putting you car in neutral when it is vibrating. if it's the CV/wheel, you will still have the vibration. if it's engine. it will stop

I havent actually put the car in neutral while driving, but as soon as I let off the gas, the vibration disappears immediately.

-Chris

Link to comment
Share on other sites

My 94 suddenly (as I experienced it) vibrated under load and as it nearly disappeared when cruising

I put in a new drive axle with CVjoints on the right side as I got a feeling of that it was on that side.

Now the vibration is gone -I also rebalanced the wheels. The axle that I took out felt a little stiff

in the CVjoints but I could not see any fault on it (there is probably 160000 miles on it). I did no further

investigating as I am no expert on CV-joints.

/Jan L.

Link to comment
Share on other sites

  • 2 weeks later...

Thanks guys for all the suggestions.

Texas Jim, BodybyFisher, and jlinde all had it. I finally got around to take it in... CV joints were toast. I had both halfshafts replaced, and its as good as new :D

-Chris

Link to comment
Share on other sites

Thanks guys for all the suggestions.

Texas Jim, BodybyFisher, and jlinde all had it. I finally got around to take it in... CV joints were toast. I had both halfshafts replaced, and its as good as new :D

Glad you got it fixed and that was all that was wrong with it.

:D:D:D

Posted Image
Link to comment
Share on other sites

Glad to hear it Chris, consider becoming a supporting member to help maintain this great resource, its very reasonable.... Mike

There actually are some benefits, and you can do it via paypal

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...