Jrice116

For some reason my car is extremely snappy and powerful when I first start driving. Say for the first 15-20 minutes. (Of course i'm not running the car until the car warms up) but after being in traffic or driving for a while, the car takes off extremely sluggish, and feels like it revs much slower when pulling. When I pull the clutch, it revs normally. No engine lights, no other problems. Any ideas? Everything i've searched says clutch plates, but it's not the clutch plates as the clutch isn't slipping. The rpms don't climb faster than the car is moving. any help would be greatly appreciated.

CK_32

iTrader: (1)

Is your idle at like 1-3k RPM when you first take off?

That's because your engine is running rich to warm up. When it's sluggish that's because it's back to its normal mixture and 1k RPM...

It's normal with all direct injection cars. It's for cold starts and something else I can't remember off the top of my head. And yes it does it even if it's 90° outside. Which is why you should always let your car warm up on idle for a min or two to move the fluids around and find it's normal idle.

Jrice116

I realize that. I always let the car warm up for a minute or two before I move it. But the car is INCREDIBLY slower after 20 minutes or so of driving.

CK_32

iTrader: (1)

Have you done regular maintenance?

Check air box and filter, serviced oil, injectors, plugs etc ect?

Any codes?

I remember reading something a while back saying Z's have a ECU that detects routine driving habits and programs it self to that after a while. Ie if you drive slowly on commuting it down graded the tune to a more leisure performance.

Not sure how much of that is true or not tho.

I'd start with the basics tho. Check all your regular maintenance items. But IMO it sounds like your ECU is giving you a nice A/F then backing it down some this the reduced spirit output of the engine.

I still want to just say warm up tho. My truck did it yesterday on my way to work. I was in a rush and started it then went. I tapped the throttle as per normal and literally it almost did a burn out for the first 5 or 6 taps.

Then as soon as I left my track it was back to 4,600 dog slow Silverado. And I'm driving a 2015 with 10k miles so again it's super normal cause my car is still literally brand new lol

Jrice116

Regular maintenance has been done since I bought the car a month ago. It runs great except for that issue. I researched the ECU thing. That may be it. It's worth a shot anyway. Thanks for the help!

CK_32

iTrader: (1)

Wait you just bought it?

Oh boy hopefully you didn't buy from a weekend warrior mechanic. Make sure the car isn't in limp mode or something from something they did to it.

If I were you and did all the basics and couldn't find the issue I'd have a mechanic do a look over inspection and see if anything is wrong with the car before it's too late if something is wrong with it.

Hopefully you had them sign a in good working condition BOS when purchased.

iideadeyeii

iTrader: (6)

Butt dyno isn't going to prove anything. Test it at the quarter mile.

If you don't have a strip a Kat Matrix 3-axis accelerometer works well(I tested it at the track and it was only off by .1 sec) though you will reach illegal speeds.

zakmartin

If you know how to interpret engine data (especially live data graphing), doing an open loop closed loop test with data logging could show you exactly what's causing the problem. If you don't know how to interpret engine data, I strongly recommend you take it to someone who does and have your car evaluated. If the car's running fine in open loop and then becomes "INCREDIBLY slower after 20 minutes," then I'd start by checking how the various systems are performing in closed loop. You're being a bit too vague about EXACTLY what the car is doing in your description to lead me to the conclusion that your car is going into limp mode. You also left out the fundamental information you should include in a help request: MILEAGE and MODS. Also, unless it's really cold outside, it should take less than 20 minutes for your car to go closed loop.

EDIT -
Here's a good write-up on open/closed loop and how it affects engine performance:
http://www.obdii.com/articles/Unders...n_Sensors.html

Jrice116

I guess I could've been more specific. 140k miles. No mods other than a mishimoto radiator. I have a family of mechanics. They looked over it before I bought it, and It's been a great car. I can't really give specifics other than it feels like it's seriously lacking power once it gets hot.


I bought it at what I thought was a good deal. 04 with 132k miles and for $5,000.

I'll look into that write-up. thanks!

knuckles899

iTrader: (1)

Get a compression leak down test performed. Maybe the rings are starting to wear. I'm just guessing but maybe when it's cold all the engine tolerances are tighter and as the engine warms the tolerances between the cylinder wall and piston rings is not great causing the slight power loss feeling when at full operating temperature.