cjoy63

Hi All,

I installed MBH headers recently with no cats, loaded V5 header tune and ran flawlessly. However, I got sick of the exhaust fumes and decided to put in the optional high flow cats. After doing so, the car ran horribly. Idles rough, power was not linear, slight hesitation when accelerating. Check engine light popped up this morning.

My first diagnosis was possibly a damaged O2 sensor. The car had a rattling sound underneath the car, after investigating I discovered that the O2 sensor at the high flow cat was loose. I tightened up thinking it would solve the issue, but it didn't. I e-mailed Jerry from Eurocharged, and he too thought it could be a damaged O2 sensor due to all the rattling.

So I picked up a downstream O2 sensor. Went underneath a car to replace the suspect damaged O2 sensor at the high flow cat. The sensor I pulled out had a longer harness length, and the connector was different. I think that the upstream and downstream O2 sensors were reversed! Can anyone confirm:

My car is:
Shorter length harness O2 sensor upstream of high flow cat
Longer length harness O2 sensor downstream of high flow cat

Should be?:
Longer length harness O2 sensor upstream of high flow cat
Shorter length harness O2 sensor downstream of high flow cat

If what I suspect is correct, then I should swap the O2 sensors from downstream to upstream and vice versa. BUT, the downstream O2 sensor is too short and does not reach the high flow cat. This is because the high flow cat is much farther away then the original primary cat.

I know I'm not the only one running high flow cats with the MBH header set up. How did you guys do it?

Thanks,
Chris

siemon

what is your plan now

cjoy63

Was hoping someone with the same setup would chime in. Other than that plan, thinking about looking for an extension for the harness or aftermarket O2 sensor with a longer harness length.

Merc63

I don't think they will reach if reversed?

You need an extension for the secondary sensors with headers in my experience.

Cut the sensor wires one at a time and solder in a longer wire. Heat shrink wrap and tape the wires in a bundle.

cjoy63

Oh it reaches if its reversed alright. Just checked the part number of the long O2 sensor I found in the cat and it should be for upstream the cat.

It seems like some of the other header kits (ie MHP) comes with an extension for the rear O2 sensor. Been searching online for one. Really don't want to cut wires and solder right now, heh.

I am Jeff

My MHP LT headers come with all the necessary O2 extensions and bolts for the installation. No need to source or fabricate any cables.

cjoy63

Jealous. Maybe I should contact them for the rear O2 sensor extensions because not finding it on the web. Any chance you recall the manufacturer of the extensions? Or maybe It's made in house at MHP.

cjoy63

Looks like I'll be cutting and extending the sensors. Hopefully all goes well. Thanks for the input guys.

cjoy63

Last spam for the night, MHP rep just e-mailed me back. Quick reply is awesome, they sell the extensions. Will probably go this route now. Was thinking if the sensors ever go bad, having the extensions will make replacement easier.

Khan 55

Hello there. I don't own a 63 but a 55. I have all my cats removed as one went bad on me and finding replacement was negative in my country. So they fitted straight SS pipe in for me with adapters/foulers/spacers at the 2nd O2 sensor. The CEL comes up now and then and goes off now and then when I drive decently. I thought of maybe using a small mesh screen in front of the sensor and then fitting it to the spacer and then to the exhaust. I haven't done it yet but I have heard of people doing the wire lengthening and just fitting the sensor further down the line.
Let me know your results with the extensions and what you paid for them and if you could include a pic or two of the setup from where the cats are.


Hadta remove my battery terminal every now and then just to remove the CEL on dashboard which has become a pain cause no matter what one does, it always has a tiny spark when reconnecting the negative terminal last as is the norm with batteries and electrical.


What Merc63 said would be a good alternative. I would cut all the wires provided they are all diff colours and push a wider diameter heat shrink far over. Then a smaller diameter preferably the same diameter as the wire and push it back as well on the new longer piece of wire needed (NB you would need two pieces of small diameter heat shrink and two big diameter ones) then join the wire with the new wire and existing ones and heat shrink the smaller sections first. Thereafter you can use the two bigger heat shrink pieces to cover both ends where new wire was fitted. That way its bound to look professional and should last forever perhaps.