Having some issues with my $2K super duper stepped/merge collector headers that are turning out to be not so super duper after all. Must say it wasn’t a warm and fuzzy selling my Hookers for a song and dance to find absolutely no gains on the dyno. Stuff happens right!

The issue now is getting leaks from the merge collector union and need to seal that somehow as it’s throwing the tuning off. If anyone knows any tricks besides removing the headers and welding the collectors on, I’m all teeth and ears. Another thought is to convert over to speed density, but I’m not sure of the Pro’s and Con’s of doing so.

What say you..experts?? Got a couple of cams rusting away that need to be installed but no sense until I can establish a stable baseline.

 

Are you running a closed loop tune?

 

Not that this is going to help you too much but you dont have to remove the headers to add flanges to them. Also why do you want to convert to SD?, are you having that much trouble tuning it in closed loop?.

 

Always have to stop for a second to remember open loop vs closed loop but the answer is yes.

The minor leak is not were the collectors meet the main exhaust, but where the merge collectors meet the four tubes. In fact, being a bit pissed in general and thinking it would fix my problems, had the exhaust/header slip flange welded where the slip tubes meet. I have a flange about a foot or so after the union for cats so besides boogering up the headers, it's not a big whoop.

Also replaced the 02's and added a new MAP sensor just to remove them from the equation but the car has always been inconsistent. Seems everytime I want to race it, it's down on power and usually responds to retuning but I see guys all the time put down the same numbers dyno after dyno and trying to figure out how to make the car more consistent.

 

If its a closed loop tune, the only issue the leaks should be causing would be a "false lean" condition causing it to run rich.

Are you saying you are thinking about going to speed-density to so the leaks won't cause problems? If so, that's not going to solve your problems. The change you would have to make to eliminate the leaks as an issue would be to go to an open-loop (no O2's) tune.

 

Would just unplugging the 02's do that?? What happens to the fuel/air tables during normal driving if they are unplugged?

Your exactly right that it runs rich during normal driving but the air/fuel also changed radically on WOT. I'm a little stumped as it went very lean below 6000 rpm and seems to be OK 6000-7000.

A bunch of my old F-body buds are going to a track tonite and was hoping to run with them but just going to watch if I can't figure out what this thing is doing.

 

Unplugging them will put the car in open loop. You can go in TunerCAT and check the box for SD (in the menu where you can turn DTC's on/off) and that will do it, too. You make your normal MAF calibration table and PE table adjustments, it's just the computer can't compensate for what the O2's read. Make sure you reset your PCM. Now, your INT's and BLM's will always be 128.

 

Thanks guys!!

 

If you unplug the O2 sensors, it won't go into closed loop. That's not a problem if its tuned to run in that mode, but if you haven't tuned it to run in open loop - and verified it at least on a dyno, with a wide-band - you **MAY** have some issues with the A/F ratio.

In open loop, the PCM only uses 3 "cells".... 16 for idle, 17 for decel and 18 for "load". And Cell 18 has long term fuel corrections that are calculated from the other 16 cells that are normally used in closed loop.

If you reset the PCM (pull the "PCM BAT" fuse for 30 seconds), you will clear all the learned long term fuel corrections. That means that as long as the O2 sensors are disconnected, the PCM will look at the MAF to see how much air is entering the engine (always does that), and use the "standard" calculation to figure out how much fuel to add.... air mass flow (rate / A/F ratio) = fuel mass flow rate. Still the same way the PCM would work in closed loop, but the calculation includes a multiplier term which is "BLM / 128", where BLM is the learned long term fuel correction for the cell you are operating in (the cells are defined by a grid with RPM on one axis and MAP on the other).

***IF***.... and that's the big "if".... your tuner hit the nail on the head with his tune, and "if" he has the PE mode A/F ratios correct, it will run fine in open loop with no O2's and the PCM reset. The danger is if the tuner was a little bit "off", and the PCM is using the BLM's to correct for a "TRUE" lean condition, the PCM will lose the ability to make that correction in open loop, and it may run lean.