91 Q shake and shudder

[dbellmoose]

My 1991 Q45 not doing well. 105,000 miles, I've babied this car and love it. Two mechanics are stumped with a couple problems. Any advice would be appreciated.

Problem #1. In December 05 engine turned over one morning but wouldn't run smoothly; there was a repeated slamming of the engine, whole car shook violently. Had it towed. Mechanic #1 replaced spark plugs, cleaned fuel system, got it running but it has been rough ever since. He said compression #6 cylinder was low, gave it a fuel additive and said wait two weeks. Didn't help.

Mechanic #2 said compression was fine on all cylinders, but that cylinder #2 wasn't getting spark command. Plugs OK. Replaced wire loom for ignition coil. Didn't help. He traced wiring back and said all was OK to ECU. I purchased used ECU which he installed without charging for labor (starting to feel sorry for me?), but that didn't help either. Engine still runs rough. He said cylinder #2 not firing but the coil is getting the signal. He said he didn't know what to do next and referred me to auto electronics specialist. Is it time to wend my way back to the dealer...?

Problem #2: For years there has been a shudder as car accerates through 1700-2000 rpm in all gears. Everything above and below that is smooth (except for the rough engine mentioned above). Shudder always been there but is now very pronounced.

I've been test driving new cars, but nothing measures up to my Q...

Thanks. DB

[Rex]

I'm going to move this, as it would be better suited for the Infiniti Online Mechanic sub-forum ...

Additional information would help as well ...

Have the timing guides ever been changed?Have the injectors ever been replaced or ohmed?

As much history of the cars entire service record the more helpful we can be.

Thanks and Welcome to NICO.

[dbellmoose]

Thanks for your reply.

Repair records show no change of timing guides. Five fuel injectors have been replaced over the years, but both mechanics have ruled that out in the present case. I don't know about them being ohmed. I'll ask mechanics in a couple of days when I get a list of questions together.

All services and oil changes done at appropriate times. Lots of repairs (more than I realized until I went through the repair records in my file!), but nothing related to this.

DB

[Rex]

If the timing guides have not been changed it's very possible for the chain to have jumped a tooth which could create the condition you're describing. If that's the case, you're talking guides and pan drop.

[Clyons0203]

The acceleration shudder\shake maybe due to the drive shaft being out of line. Worn joints maybe??

I would just take it to the dealer and let them run the usual test.