Vibration 90 CDV

[TJ Hopland]

Having trouble tracking down a vibration in my fairly new to me 1990 CDV.   Its the 4.5 with mulitport injection so more like a 4.9 than most 4.5's or the 4100.   

Issue its had since I bought it not running is a vibration in the 40-65 mph range when you are on the gas.  Its a rumble like vibration kinda like driving over rumble strips on the road.  I'm not sure if the frequency changes based on road speed or engine speed, it almost seems like its always the same.  It happens exactly like pinging/detonation.  If you are lightly accelerating it starts.  If you let off it quits instantly.   If you step down harder it kinda fades out. 

It does seem to be getting worse but its also getting colder so maybe the temps have something to do with it?  I have maybe 2000 miles on it now.  We got ice and snow recently and I noticed it it does it if you get the tires spinning into that 45 mph range.  It starts good and idles fine.  Seems to accelerate smooth and strong. It seems to do it in 2nd, 3rd, or OD.  Trans fluid is looks and smells decent.

Always running premium non ethanol gas.  Has the correct new AC copper plugs.  Cap, rotor, and wires look good and fairly recent.  All 8 injectors are new along with fuel pressure regulator.  Timing and other tune up items are within factory specs.   CV assembly on the left is new, right looks fairly new.   Both front wheel bearings new.  4 new tires.

Previous owners appeared to be randomly throwing parts at it to try and solve the barely running issue it was having so its got several new sensors and I think that is where all the new ignition parts came from.   What turned out to be the main issue was the computer would freak out and show several sensor reading incorrectly after it had been on for about 5 mins.   Only thing I could find wrong externally was one injector was showing almost shorted when cold so maybe when that was warm it was stressing something on the computer?   I replaced the injector and computer keeping the original prom.  Eventually I replaced all 8 injectors as a set because their ohm readings were all over the place so I figured the rest were likely to fail soon too.   

Several things that could have easily caused it got addressed and didn't change it at all.  Original tires were dry rotted.  Left CV had cracked boots with grease leaking out.   Injectors weren't electrically testing good.   About the only thing I can think to check is hook up the scan tool and see if it only does it when the torque converter is locked.  If it does then I will figure out a way to keep it from locking to try and prove that is the issue.   Even then it may not be the converter, when locked it could just be letting a engine vibration through.   I thought about doing a compression test but just doing spark plugs was over a 3 hour job so a compression test would likely be all day. 

Open to hear any thoughts on the subject.   Too cold to work on it now.   I only have enough heat in the garage to get it maybe 20-30 above outside temp and today that would get me to zero F.   Maybe next week.

["Cadillac Kid" Greg Surfas 15364]

TJ
Did you ever think you car might just be shivering in the cold?
Greg Surfas

[TJ Hopland]

Its lived up here its whole life so when I first got it and it was in the 50's it should not have thought that was that cold.    I should look and see where it was built.   Maybe it was built in Mexico so even 50F is cold for it?  I'm trying to remember what the coolant sensor was reading when it went wacky,  I don't remember if it was going high or low.   Maybe it was wishing it was warmer?

[rajeevx7]

Are you leaning towards an engine vibration or bad balance/bent wheel? Start the engine and stare at that harmonic balancer to see deviation.
0* 

[TJ Hopland]

I don't think its a wheel sort of issue because it goes away as soon as you lift off the gas.  Wheels are turning at the same speed.  I can go on gas vibrate.  Off gas smooth.  On vibrate.  Off smooth.   On hard it smooths out seemingly before the speed significantly increases.    I know tires can create a pull related to torque or braking but it did the same thing with the old dry rotted tires.

[TJ Hopland]

Oh ya forgot to ask,  what am I looking for at the balancer?   There is an oil leak up there so its kinda a mess.  I cleaned it enough to check the timing but otherwise have not spent much time down there.  Its pretty cramped there, looks like removing the tire and inner fender would be required to do anything in that area.

[rajeevx7]

Just see if it has a walk/wobble ON throttle. Check all pulleys while there.
Is the CEL on? Have you ruled out a misfire? As difficult as it is, a compression check may be on the docket

[TJ Hopland]

No check engine light.  I would have to look to know for sure but I don't think its got misfire codes.   I suppose I could look and see what it has for options to do things like shut down individual injectors.  If dropping a cylinder when its doing it doesn't make it worse that would maybe point to a missfire.

Pulleys should all be good.  I ended up changing an idler when I had things apart to do the injectors.

[Roger Zimmermann]

Bad CV joint?

[James Landi]

I had a 61 Cadillac that acted in a similar manner-- turned out that flex plate was cracked on several of the "flange ears" so that when torque was applied that roughness between the engine and tranny would occur.  Was easy to see the problem in that model car as there was an inspection plate at the bottom of the bell-- perhaps this is your problem?   James

[Eric DeVirgilis CLC# 8621]

My guess is a bad front axle. Had this issue in the past w/FWD Cadillacs of this era.

[TJ Hopland]

The axle I replaced due to cracked boots appears to be a new design and new production.  I did drive the car before I replaced that side and it had the problem.   The other side was recently replaced and appeared to be the same design as the one I bought.   I suppose they could easily be poor quality and bad out of the box or easily damaged with regular use.

I'm pretty sure the inspection cover is missing so it would be easy to look there.   Also makes me wonder why it is missing, I wonder if someone else was looking in there?   I have glanced in there but didn't look real close.   

[V63]

Might check motor mounts?

[wrench]

Since you are brainstorming, I will throw this out there with the caveat that I know nothing specific about your vehicle.

I troubleshot a similar problem on a car I had and it turned out to be the brake booster. The vacuum changes during Throttle operation affected the front disc brakes somehow. It did not vibrate the steering wheel it shuddered the car.

Also, did not see exhaust mentioned, but a good look at the exhaust might reveal something.

[corey raub]

I’m not saying I have the answer to your problem, I can only tell you of a problem I had about 8 years ago with my early 90’s Coupe Deville.  I no longer own the low mileage beauty.  My car felt like it was missing when it was in higher gears and lower RPM’s.  Any other time, the car ran perfect.  I took the car to my mechanic and he told me something that made me think you might be having the same problem as I was.  And this is the only reason I decided to comment in the forum about your issue.  He told me that all of my fuel injectors needed replaced, something you mentioned that you needed to do.  Because the car was immaculate with less than 50,000 original miles, I just couldn’t accept his diagnosis.  I took matters into my own hands and decided to replace the computer (ECM).  I don’t remember if my brother (former auto mechanic) gave me the idea, if I researched the internet to get the idea or if I was just in one of those moods, but replacing the ECM fixed my problem.  I do remember the part was not terribly expensive, and I was able to replace it myself.  I hope this helps you in some way.  If nothing else, it will give you some food for thought.  I remember being terribly frustrated at the time.  Good luck.
Corey

[TJ Hopland]

I should look at motor mounts.  I'm not even sure where they are, they must be pretty well buried.  I could imagine a bad mount causing this since it appears to be load related.

This car doesn't have a vacuum brake booster, its electric.

Exhaust is original except for the muffler which I just replaced.  It has pretty good clearance so I don't think its rubbing and the vibration is much stronger than just a pipe rubbing.

I do have an extra computer and prom I could try.  I'm not sure if it works.  I know the prom will run the engine but not the accessories.  I tried the computer with its prom and it would not start.  I had a working combo so I just didn't bother to keep testing.  It was apparently a pretty common computer model, just the prom was specific.     

[Eric DeVirgilis CLC# 8621]

Does the car do the same thing at same speed with the gear selector in 3rd gear instead of normal OD position?

Highly doubt motor mounts could cause vibration like rumble strips.

[V63]

Original posting does mention it does it in all forward selections but speed not specified

I wonder if the catalytic converter could be getting restrictive? We replaced one ‘seeming good’ at 90k miles (4.9L) and it made considerable drivability improvement.

Fuel pumps have a pretty high failure rate and can generate  some strange anomalies before complete failure. I have had interesting experience with ‘aftermarket’ fuel pumps and have learned to avoid them at all costs.

[TJ Hopland]

Doesn't seem to do it in 1st or 2nd.  3rd 4th doesn't seem to be different.  It seems to be road speed more than engine speed.   I will have to get the scan tool out and see if maybe its only during lockup or something like that.