l28ET problem goes flat about 4500 RPM

[split-reduction]

My turbo conversion in '77Z uses a stock '82 ZXT ECCS system, with manual a boost controller running about 9 pounds of boost. The engine runs fine for most driving, although it seems to stumble a bit occasionally when starting out from a stop sign. The main problem is when accelerating hard it stops pulling at 4500 or 5000 RPM- it may rev a bit past 5000, but isn't really pulling anymore.

 

I had thought maybe the valve springs were weak, and replaced them with a set of springs from a motorsport cam kit I had in another Z. That didn't make any difference. My mechanic told me the ignition system was poor. I've replaced the coil with a replacement Echlin coil, and new 8 mm high performance wires, but that didn't make any difference either. I also replaced the fuel pressure regulator a couple of years ago.

 

One thought I had is that the fuel pump ,modulator is going bad. I've heard you can bypass that , but I didn't see any post that explained how to bypass it. Does anyone have any ideas? There doesn't seem to be anyone in my area who knows much about these or how to test them. Thanks.

[FlatBlack]

I had this problem on my N/A EFI when my TPS was not hooked up properly. You may want to check that.

 

Also read up on the stock EFI, it may help you diagnose problems a little better if you know what is controlling Fuel and Spark.

[sweetleaf]

Check your fuel pressure

[Brad-ManQ45]

I believe that you are running up against the "hard coded" or "open loop" table values for fuel/vs rpm/boost.

 

At close to 10 psi, 4500 rpm is about where the engine starts going lean on fuel.

 

Get a MS or Wolf or SDS system and pick up a lot of low speed driveability and better fuel economy once tuned.