S&S Header Tuning Help please?

[jibbby]

Need help fellas, and I figure there is no better place to ask then the Lextreme Forum....

Here is the deal, I recently installed my S&S Headers on my 1992 SC400 and got a engine choking effect going on only at idle launch under full throttle...The car just bogs and hesitates a little, and I got the engine check light coming on every now and then......I have been driving it for a while hoping the ECU will learn and adjust and it has some but not %100......It doesn't bog all the time but atleast more then half the time..It doesn't bog down under a nos run either....I deleted the two cats at the down pipes and I think that has something to do with maybe a bad ECU read or something......

I just tried tuning the car using my Apexi piggy back ECU and had no success the bog remains.... It seems the engine flows so well there is no back pressure or something so the engine chokes when punched.... Is this a bad ECU read, timing problem, how to fix fellas?

The MIL eliminator system was mentioned by my tuning mechanic for a timing change that may correct the problem...Does anyone concure with this?

I need to correct this bogging effect PLEASE HELP ANYONE, what to do????.....

 

[new big400]

Do you have a code for the light?

 

[jibbby]

Check engine light comes on, have not run a diagnostic check yet......I believe the ECU is getting a bad read because the car does not bog from launch all the time but only half the time as apposed to all the time before.....So it seems the problem is getting better as weird as that sounds...

I am going to look into the sensor reads from the dual cat deletion...That probably is the where the problem is at........

I am just hoping this is not a timing fix, or lack of back pressure from the wide open exhaust..... Thanks for the reply big....

 

[stevechumo]

John,

You can have a free diagnostic check at Autozone in your area. Autozone does it for free. I think something might have been missing, such as the O2 sensors weren't installed correctly, especially the one after the cat. You may try to disconnect the battery so the ECU will learn the new reading. I've installed many hi-flow headers on Honda/Acura but I never had any problems, but I never deleted any cats before. However and recently, my cousin opened up his Honda's cat and took out the filter inside the cat and he got a check engine light. He then had to reinstall it and the light was gone. Also, I believe that deleting the cats will foul up the after-the-cat-O2 sensor very quick. I think James deleted the cat on his swapped SC, but he didn't mention this problem. If the problem isn't soved, then I think a dual hi-flow cats (I prefer 2 singles) are in order.

 

[jibbby]

Steve, I think you are right...It seems to be a timing problem at low rpms when cold..It defenitely misfires or something to that effect and bogs or hesititates..When that car has been running a while and heats up the problem lessons or is gone at times......Oh, and yes the check engine light is always on now.......Still looking into those O2 sensors...It's just too damn hot to get under the car right now in this heat as you know..I don't have a garage with fans or A/C.......However, thanks for the input buddy I will figure it out.......I started to see evidence of this bog when I first changed out the large center cat 6 months ago to the Magnaflow......Now with the Header install and the two smaller cat deletion this problem just made the same situation worse...It's got to be the sensors and ECU..

 

[GSMnow]

You need to find out whatcode the ECU has set. You may help the sub O2 sensor situation by locating them after the rear cat. This way they will see post cat exhaust while the front O2 sensors are seeing pre cat exhaust. They should both go rich when you are under full power for a while, but the post cat sub O2 sensors should see a slower change and reduced swing. A proper working cat actually stores excess oxygen when running lean and releases this stored oxygen when running rich. This is what the rear O2 sensors are looking for. With the sub O2 sensors in the same pre cat reading, the signals will follow each other directly. This looks like a totally failed cat.

All that being said, this should not kill performance unless the ECU is going to a backup mode because of the code, and I don't think a sub O2 or bad cat code would force a limp mode.

My guess is that you are going either very lean or vey rich on throttle tip in. Put a good digital volt meter on the primary O2 sensor. You should see it swining from lean to rich at idle and light load. This will be from below .2 volts to over .8 volts. Then when you get on the throttle, it should swing up over .8 volts and stay there until your load is reduced by either reaching a steady speed ir lifting off of the throttle. If you see the O2 signal dip under .2 volt on tip in, then you are going lean. Increased air flow could cause this, but I doubt it since the AFM should detect the increase in air flow and add fuel to make up for it. You may also want to check the TPS sensor signal. The ramping up voltage is used to activate the equivolent of an accelerator pump. This adds a shot of extra fuel when the throttle is moving quickly. On my TEC II ECU I used to run, it had a huge number of parameter to set for acceleration enrichement. It was very east to get it wrong and either starve or flood the motor since even a small rate of change on the throttle could mena a huge increase in air flow. You can test the low back pressure theory by partially plugging up the exhaust and see if it makes the car pull harder. Fixing the fueling issue is the better cure though.

Gary M.

 

[jibbby]

GSMnow - Thanks for the write up.... Apparently after the header install and the relocation of the header 02 sensors the bog problem has completely dissapeared...After a week of driving it's gone...However the check engine light is on all the time, and the car idles just a bit low but doesn't stall...That is a direct effect of the Header install and O2 sensor relocation..That I know for sure...No biggie......

In regards to the hesitation or bog at take off, I don't know if the ECU learned and corrected problem or if the 02 sensor relocation worked it out, but what it wasit is gone for good...The car runs fantastic....Thanks...