I had my ECU tuned with the uprev software a few months ago and everything was perfect. Yesterday I had a Cosworth Plenum installed and the car would cut power at 4500 rpm like it was hitting the rev limiter. Reinstalled the original setup and problem gone. Def was not vaccum leaks or improper install.

I am just amazed that the Cosworth makes such a big difference that the tuned ECU can't adjust for it. I figured on an N/A vehicle the tune wouldn't be so offset by a plenum change?

Experts please give your opinion, I will be taking it in for a tune but I have a track day tomorrow so I had to go back to original setup.

 

Help..bump

 

Although it wasn't to the degree you are referring to, Gabe had something a little bit similar.
https://my350z.com/forum/na-builds/4...zcargarge.html

In your case, it almost sounds like its going into safemode. What codes are you getting (if any)?

 

Hey,

Are you sure that you're not running it on the valet map at the moment? That (from what I recall) is how it behaves... Have you tried other maps?

 

Great question^

 

I do not get any check engine light or codes and car runs fine until I get into the 4500 rpm range. Then It just bucks and stutters its way further up the tach.

I am on the correct map.. double and triple checked that Also tried a reset but made no difference.

We swapped the original setup on the next day and yesterday I was running at the track with no problems at all.

 

I've seen similar symptoms before.
When I was doing exhaust R&D I tried all kinds of different exhaust pipe diameters and merge locations for the Y-pipe.

I've seen that when the exhaust system was very improperly tuned it did the same thing. Bucking, stuttering and a significant loss of power on the dyno.

 

What would you suspect is the problem? A few people are saying its a small vacuum leak which is why I won't notice at idle or lower rpms? The installer and myself suspect the tune but gabe3d mentioned he swapped in the Cosworth with no problems on his uprev tuned ECU.

 

A vacume leak won't cause that. If you did have a leak you would notice it at idle. The first thing a leak does is ruin a good idle. If you don't have a stumbling idle, you don't have a leak.

The cause may simply be the intake resonance is out of phase with the engine. If that's the case, there isn't much that can be done other than different cams or a tune. But even then, its not necessarily a sure bet.

Very few people have the Cosworth installed NA.

 

We have installed the Cosworth manifold on a bone stock 350Z with the stock ECU and no reflash. It ran perfectly fine with zero stumbling, all the way to redline. This was done in a comparison test to show the effects of a plenum spacer vs. Cosworth manifold on such a stock car. The results weren't anything noteworthy (as expected), but it is an extra data point showing that the manifolds have indeed been known to cooperate fine on NA cars.

 

I wonder if there can be unit to unit runner geometry differences. Different people seem to get significantly different results from it.

I don't really know if the bucking is related to runner geometry (resonance), but I do know I saw something similar with R&D exhaust parts. ..Just a trouble shooting thought.

 

I have the manifold on N/A with the uprev dyno tuned. and 0 problems runs great all the way to redline. If I were you take it back and make sure that he down loaded or programs your proformance mode were he told you. Thats just a easy way to start searching the problem. Because if im in val. mode it does that after 4500. Thats with my SSV and COSWORTH. Ya had the SSV move on.lol

 

A big thank you to everyone in this thread. I sent it to Cosworth after my installer found a leak following a pressure test. The manifold was sent back to Cosworth for inspection and they found it to be a bad casting and will be sending a replacement soon.