Fairly simple question...

I've got a 94 Z28 A4, the motor is pushing 170k and starting run pretty sluggish. At high RPM's my motor almost completely dives, loses any sort of power. I just had fuel injection cleaned and that help on a the smooth ride but im still very worried about the dive at high rpms. Fuel pump? Spark? Please give me some things to check... and not to mention in other mods that will help bring life to my extremely high mileage car.

only performance mod would be the K&N Cold air...

 

maybe time for a valve spring change?
weak springs could drastically affect performance

could be fuel pump too

sounds like your car is a good candidate for a fresh and complete tuneup

 

Possibly the opti.

 

Could you tell me the price range on a valve spring change? ...and forgive me lack of knowledge, what is an opti?

 

The opti-spark is the pancake distributor for an LT1 located beneath the water pump. I'm on my third opti at 198K.

As with any high mileage engine, problems could arise anywhere, anytime. I pulled my heads at 160 to get them freshened up, and that helped with performance. Your tappets could be very loose. Mine were.

Now my current dilemna is I thought I spun a bearing. But I just found a hole in my exhaust manifold. So I will put headers on and hope that fixes it. If not, then I know I need a rebuild.

Point is, These cars are finacially worth it if you can do the labor yourself.

Price on springs is about 80 - 120. Then's there's labor, add 200. Guessing.

 

how many miles are on your plugs?

 

How difficult is it to change the opti? I do have a general knowledge of replacing and repairing (enough to keep those labor costs down)...

 

Not difficult, just time consuming.

 

Bought the car a year ago and haven't change the plugs yet...

 

I am having the same problem with mine at 125k miles. before i can redline the engine actually cuts out for half a second then it kicks in again.

 

when i pulled my LT1 springs out at 70k miles they measured in at 75 ft lbs seat pressure at 1.8 inches. New is 90 ft lbs seat pressure... So at such a high mileage i can see how your spings have gotten weak.. and at the high RPMs is where you'd feel the loss of power with weak springs. With so many miles it could be lots of things.

 

get some lt4 valve springs. They dont cost much. I picked some up for $40 from the local dealer.

 

If you don't know when the last time the spark plugs were changed out then that should be your first step to trying to fix your problem. It is cheap if you do it yourself.

When I first bought my car it it ran like crap in the upper rpm, it was so bad that it wouldn't accelerate over 5k rpms in 3rd gear. I changed out the sparkplugs and wow what a difference.

 

Time for a stroker

 

If any of these havnt been done in a long time (or ever) I would replace them:

Plugs
Wires
Fuel filter
Coil

I'd do the above items first, they are all fairly cheap if you can do them yourself. Try replacing them then see how it feels, if they don't fix the problem maybe replace the opti. If its the original opti in a 94 with 170k theres a good chance it needs replacing. I would also check the fuel pressure to see if the pump and fuel pressure requlator are ok, if the pressure is not in the correct range they may need replacing.