Hey guys, I'm new to the z ownership as I just picked up a used 03 touring about a month ago. I am having an issue I can't seem to solve and I need some help. My car is slow. It feels like it has about 200hp. I know 'feels' is subjective, but the best 0-60 Ican do is 6.8 and the best quarter mile is 15.9. I drove my friends Z and I can achieve stock 0-60 and quarter mile times in his car(1yr newer). My issue is, I don't know whats wrong with the car. Repacled the knock sensor and sub harness which helped. Had code for it being bad. Also had a misfire in cylinder 4 and 2. All new plugs, and two replaced coil packs solved the problem. I have no more engine codes, no stalling, no bad idle, no hard starts, haven't noticed any vaccum leaks, everything appears to be working, but the power just isn't there. I'm not interested in racing, I just want stock performace back. What could be causing my issue? Car has 120k miles.

 

Do a compression test and respond once you have the numbers

 

This.

 

let me gaze into my internet mechanic crystal ball......

 

Sounds about right.

 

 

Bboy is onto somthing here.... the signs are all adding up now...

 

Right, sorry it took so long to reply. I work nights.

Compression as follows- #2-152 #4-154 #6-152 #1-180 #3-160 #5-160

Could it possibly be a bad crank sensor, or cam sensor? I would expect those to throw a code though... but maybe not

 

Cleaned the pvc, coolant is running at 91 degrees so temp sensor is working, cleaned maf, tried resetting the ecu. only other thing I can think of is the throttle position sensor..?

tail lights are stock.

 

That 180psi on cylinder 1 doesn't sound good. Limit between cylinders on a VQ35 is 14 PSI. The rest seem fine for the age of the engine.

 

Thank Cthulhu

 

Idk what would cause that cylinder to be a higher compression. I wouldn't think that could be robbing power from the engine though?

 

How many times did you run the compression test? How long did you crank each cylinder?

 

Since my compression is pretty much normal for the age, any other suggestions? Things to check? I'm willing to put in the work.

 

Cranked each cylinder for about 4 secs. Twice

 

Compression seems fine other than the one cylinder. Maybe carbon build up.

 

Standard compression is 185psi max 14psi between cylinders
So, simple math
185*6=1110
152+154+152+180+160+160=958
958/1110=.863*287=247.68hp

You're losing approx 40hp based on your compression test.

 

So to regain lost power I need a engine rebuild? I thought the minimum tolerance was 142psi.