Hi all,

I recently noticed my car driving and starting differently, almost as if it was wounded or misfiring and was stumbling on startup. Since I wasn't sure if it was just the Phoenix summer heat or if something was actually wrong so I took it in for a compression test. A bit more information than is probably needed...

2005 GT with 74k miles on the original engine
I've owned it for the past 3 years and 30k miles, daily driven for the past two.
It's been in Socal or Phoenix it's entire life, it is a USDM Cali spec.
Oil Changes have been every 3k or less usually with 5w-20, premix .5oz/gallon since 60k
BHR ignition @ 55k
AP tuned by MM @ 69k

A quick note, when changing the plugs last I noticed that the trailing plug on rotor 1 had not been firing, after testing with a new BHR coil and plugs it was just determined that the coil had stopped working but it could have been ran up to 10k miles without firing the trailing.

Results in kgf/cm2, elevation ~1100ft

Rotor 1
7.8
8
7.9

Rotor 2
8.6
8.8
8.6

Compression is above spec on both rotors but the difference between the two rotors is above the max difference.

Driving it seems to stumble or act like it's misfiring <4k, but above that seems to be okay and any loss of power I would normally just attribute to the summer heat.

I'll try to upload video of the cold and hot starts, both are pretty much the same but it seems to stumble once or twice whereas it didn't use to 1k miles ago.

Any advice is much appreciated!

 

A picture of my 8 for your enjoyment.

 

If it were me, and it started suddenly, the first thing I would do is hit it with a can of injector cleaner / fuel treatment. The number of times my wife or kids come home with a poorly running car after a fill-up is surprising.

A can of seafoam in the tank works great.

 

Search for the rotor balance test, there is a thread on it here. I would try that and report back with the results.

 

I'll give the seafoam and see if that helps clear up some symptoms. The dealership did a decarb about 20k miles ago under warranty and did a fuel injector cleaning about 10k ago although since they don't flow test them I have no idea if it did any good.

Will try the rotor balancing out this week. Would you guys recommend getting the cat looked at? It is original with 74k miles, no CELs.

 

Seafoam is a waste of time. You can pull the cat and do a visual inspection and shake it around see if you hear anything rattling around but a cat efficiency test is the best way to check it.