My engine is sick....

a few problems:

high idle around 800-850 (checked with a scan tool)
medium strong vibration all the time.
slightly higher vibration at 1600-1700rpm
the vibrations and (maybe knocking sound) seem to be coming from the back of the engine
pool gas mileage
poor power
when coming to a complete stop, engine rpm will drop to about 700rpm when stopped, then quickly raise an additional 500rpm and drop back to 800 or so.

the G35 sedan has 73,000 miles..... changed the spark plugs a couple of days ago; didn't help........... engine oil level is good.. (used mobil 1 since 40,000 miles)

any ideas?

 

Plug in a diagnostic scanner, and see if you are getting any misfires, bad sensor readings, etc.

In my other car, the car is mildly shaking at idle, stronger at 1200rpm, and then smooths out after 2000rpm, so I plugged in my scanner, and I'm getting mis-fires in cylinder-6. I think I narrowed it down to a faulty fuel injector.

 

Plugged in a scanner and it doesn't show any codes...

The scanner in itself can't check for misfire...........

 

Yes it can. You need an OBD-II scanner, not just a code-reader. Misfire counter for each cylinder, history and current, are the fields I'm talking about. A code will only get thrown if the number of misfires is sufficient to cause catalytic converter damager and/or emissions failure.

Misfire information is an OBD-II generic parameter, so it should work on any car. Some other generic parameters that may be useful, are the air/fuel ratio, the various oxygen sensor readings, etc. That way you can see if you have a lean/rich condition on various cylinders to see if that's causing the vibration/loss of power/etc.

You can also monitor fuel pressure, so if you get a fuel injector tester, you can test the flow-rate of each injector by monitoring the fuel pressure drop when activating each injector individually/manually, to see if one of them is plugged/faulty/etc.

 

I have the http://www.autoenginuity.com/ scanner...

it doesn't let you check anything other the basic OBDII codes.
rpm, air temp, maf, os2 sensors, etc......

no misfire information, etc.........

 

Hmmm. I have an autotap scanner. It has the misfire information I was talking about. Since it said it was a generic OBD-II parameter, I assumed all OBD-II scanners would be able to access that....

 

is the car still under warranty? if so, and here's the forum's most popular response, bring it into the dealer so they can check it out.

 

while I'd freak too, its probably just a bad O2 sensor.

 

can the autotap check cylinder misfire?

warranty just ran out I am at 73,000 miles right now...........

I checked the os2 sensors and they seem to be okay

 

Yeah, that's how I diagnosed a bad fuel injector on my other car. It registered something like 242 misfires in cylinder 6 within a couple seconds of starting the car.

If you have 73000 miles, dealer may be nice, since you are so close to the warranty period.

 

maybe it registered a misfire because you actually had one...

maybe mine doesn't have a misfire..

I am wondering if changing my belts (drive and a/c) has something to do with my problems. The service manual give basic instruction on who to change them and I followed them just correctly. However, looking more into the manual is shows how to adjust the camshaft pulley for timing adj.

Maybe the camshAft pulley moved when I was switching the pullies.
Throwing off the timing?
What do you guys think.

IS THAT POSSIBLE?

 

I doubt it. You said you just changed the belts right? None of the belts connect to the camshaft. They are all driven by the crankshaft.

As for the misfires, yeah I actually had misfires. However, I think I might know what your problem is (as far as the scan tool now showing misfires). It doesn't (at least on the Autotap), get monitored by default. You have to select it. So in the case of the autotap, I have to manually add the misfire types into the table.

Does your vibration get worse with higher RPM, stay relatively the same, or smooth out?

 

not too bad at idle... kind of bad at aroung 1600-1700rpm,, after that around 2000 same as at 1600...... higher then 2000 is hard to tell, but I don't think it gets any stronger...... just the engine sound and normal vibrations make it hard to tell after 2000..rpm..

it looks like my trip to the dealer tomorrow morning will be postponed, my wife just went into labor...........

later,

 

av007,

My idle is gown to 725 rpm this morning, my timing is between 9-10 deg..
isn't this a little low.. .I thought it should be around 15 at idle....

I check my wifes lexus and it idles at 650 and timing aroung 15 deg...

manual i think says 15 deg...

Since I don't know much about timing on cars, is it possible that is some how changed and my car runs funny now.....

thanks for any info

 

Kind of pissed.. Dealer didn't find any problems with the car...

they can't feel the vibrations, even though, they are always there.
dont' see anything wrong with my bad gas mileage on the last few tanks,
loss of power, etc.... and the 850rpms and idle is not up normal according to the service manager.............even thought the manual says, 650rpm is what is should be ...

and any problems I might have had, they blamed on the oil, because I was 1/2 a quart low....... only half of a quart.................

don't know if I should take my car to that dealer anymore.