Violent Shake!

[ILuvNkdChx]

Alright first off I just want to say THANK YOU to everyone who takes so much of their time to help everyone on this site. I have had this car (94 Q45t 155,000 mi.) for about 2 years now and since I discovered the power of the SEARCH button I can't get enough of this site.

OK so here is the thing. the engine has a bad shake to it. The car is from California, it had a transmission and a radiator flush about 3K miles before I purchased it (18,000 mi. ago). At the same time as the flushes the car had a new fan and a new MAF put in. Also new brakes and shocks but I'm not sure that that is pert anent. I wanted a Cali. car because I live in Mass and all the Q's here are rusted through. But buying a car from Cali. I could not test drive it(I'm an idiot, I already realize). When I got the car the first thing I noticed was the shake. After consulting this site I took the plenum off and replaced the knock sensors. At the same time as the knock sensor replacement I tested all the fuel injectors and found that surprisingly only one was bad. I replaced the fuel injector the fuel lines and the fuel filter. After the work was done, the shake still remained. The check engine light is NOT on but it shakes too much to be any bad mount or bushing. I have slowly come to realize this is no "normal" car and I feel the more I read the more complex the car becomes, but I'm slowly cracking the puzzle that is the "Q".

I like to take leave from work and get all the work done on the cars (Q45t, I30t, 260z) that I need to all at once in a big "fixathon". I already need to replace the blue relays for the TCS on the Q, and the ignition switch on the I30 (both diagnosed by the power of SEARCH) and I have recently purchased a full body kit, 18 in. rims, a full alpine navigation system with flip out screen, 2 12in. type R subs, and V12 amps for the Q...pics to come to "represent " the G50 community.

Anyway I wasn't sure what I could check or do to resolve the violent shake? I have been searching and reading for the last 2 1/2 hours and could not find anything to define what the problem may be. I'm sure I left things out on the info so just anyone let me know and I'll get back. Thank you threaders! Any help is appreciated. Adam Powis.

P.S. I have been using Mobil 1 oil and Lucas brand petroleum oil additive for the past 3 oil changes. Not sure what previous owner used because he wont get back to me, as he does not answer my calls and he has deleted his user name on e-bay.
Modified by ILuvNkdChx at 2:59 PM 2/12/2007

[ScottJackson]

Ebay is the great lemon dumping ground. Next logical step, after checking for any vacuum leaks, is to pull out the spark plugs. Inspect them for any signs of something bad, ohm test the coils, and do a compression test.

[ILuvNkdChx]

Sorry I forgot to mention I replaced the plugs with the NGK's and tested the coils when I replaced the knock sensors. Also the shake does happen ALL the time but gets even worse up hills, even slight inclines. I have also run injector cleaner or ISO through it, about 1 cycle every few weeks for the past 3 months, and she has seen nothing but Sunoco 93 since I got her. . Sorry again if I remember anything else I will post. But I'm off to check compression.
Modified by ILuvNkdChx at 3:36 PM 2/12/2007

[maxnix]

I have been using Mobil 1 oil and Lucas brand petroleum oil additive for the past 3 oil changes.

To see why to not use Lucas, read http://www.bobistheoilguy.com

Well, if it is from SoCal, you might suspect motor mounts.

You know you can obtain the dealer performed service history?

How abut the under plenum hoses, EGR and IAC valves, TB and the interior of the plenum itself?

Fuel pump/pressure?

I think we need a little more information.

[ILuvNkdChx]

1.) HOLY CRAP! I did not realize how bad Lucas can actually be. No wonder they have no high speed test in the over the counter displays.2.) The owner before me did not use the dealership for service.3.) All the under plenum hoses were treated or replaced when I took the plenum off. And the plenum itself was cleaned. I had not suspected the EGR or IAC because the check engine light has not come on. And the fuel pump has not been making any out of the ordinary noise but I will check for sure.Thank You guys KEEP EM COMING. I'm half ignorant and whole stupid so all info. is appreciated!

[maxnix]

Very little throws a CEL in OBD I except imminent failure items.

A power balance test would tell you a lot.

[ILuvNkdChx]

I did not know that. I will add it to the list. Also since Lucas is no good, do you know of any other oil additives that help or is Mobil 1 good enough on such a high mileage engine?

[maxnix]

Mobil 1 is fine by itself. The best oil is fresh oil.

BG Quick Clean just before an oil change (read the posts) is the only other thing you may want to consider. Or perhaps in light of the Lucas, an envirolution flush.

[Q451990]

Anyway I wasn't sure what I could check or do to resolve the violent shake?

Does it feel like a "bounce" at idle? Sounds like a dead cylinder to me... probably an injector. My next steps would be to ohm test each injector, and then check each leg of the exhaust manifold with an IR thermometer to try to narrow down the dead cylinder. Of course, the best option is a Power Balance test with a Consult - but you seem pretty well DIY oriented, so that would be a good place to start.

Good luck!

Heath

[Dabizzo1]

I recently brought a 94 Q45 I purchased from Dallas from Dallas back to mechanical happiness under the hood and after replacing injectors, replacing knock sensors, plugs, MAF, pcv, vacuum lines, all fluid flushes, and thoroughly cleaning the plenum and the entire air intake system, I found 2 main culprits that would affect the car at speed, especially under an inclined load. First, if the IAC is dirty and if the seal is not perfect, the car will have fluctuations at idle...a vacuum leak basically. But at speed, only assuming the rest of the vacuum and fuel systems are in order, a completely blocked EGR pathway will cause a wonky vibration under load. Mine was literally blocked shut with carbon at tghe 90 degree neck inlet in the plenum itself. With a flathead screwdriver, long allen wrenches for the sharp bend, and long bristle brushes from a gun cleaning kit, I literally strongarmed the carbon out until the passageway was clear. To my understanding, the purpose of the EGR system is to introduce cooler exhaust air into the airbox in order to prevent detonation within the cylinder at speed, which could be manifested by a violent shake while in motion. Now also, even though the injectors ohmed within range on your car, something I discovered when I removed mine for replacement was rust on the diffuser tips, which not only restricts a good spray pattern, but is also a strong indicator of water in the fuel. Such a physical failure of a crucial part will manifest itself at all speeds. My car is a testament to the damaging effects of ethanolized fuel on a fuel system. The first things I had to change were the fuel pump (very rusted in some areas) and the fuel injectors. With the guidance of this site, my car now runs as close to perfect oem as a 13 year old car can get.

I'd recommend you do a full plenum cleaning (especially the EGR pathways) and if no change, continue your diagnosis from there. As the veterans of this site have preached through experience, perfect engine operation begins with clean internals in the air/fuel mix systems. Without that first, any diagnosis will have much difficulty in pinpointing the culprit. Good luck. Boris P.