so i've had a CEL and "service emissions system" message that comes and goes (mostly sticks around to annoy me) that has been with the car since i got it in November. i've been told by a few sources that the o2 sensors on the earlier years of V8Vs can go back, which would trigger this fault code. i've had the CEL scanned a couple of times, and each time it comes up as a cat inefficiency error.

a couple Saturdays ago was a dyno day at a local shop that just opened up. so i had my car dyno'd to see what it was putting down compared to my buddies' cars. after the 3 pulls, the guy at the shop told me my car is running really rich and it's robbing me of a good chunk of power, maybe about 20 hp.

based on all the above, and some phone call diagnosis from elsewhere, i had the primary o2 sensors replaced last Friday and the fault code reset ($706 ), then went to Road Atlanta for an HPDE on Saturday and Sunday. Saturday, while putting to a nearby Wendy's for lunch, the CEL and fault message came back.

on Tuesday i had the car re-dyno'd to see if the new o2 sensors fixed the rich fueling (the answer is "marginally"). turns out i'm down about 10 whp and 10 wtq. this could be due to the temp/humidity difference between the two days the pulls were done, or because the traction control wouldn't turn off on the second session (and possibly preventing power from being put down as well). more than likely, though, it's because the universe hates me.

i was going to order a new pair of secondary o2 sensors and see if that fixed the problem, but then i saw this in another thread:

if anyone has any ideas at all about what could cause the "service emissions system" fault code, and if anyone has any ideas as to why it's running so rich, please give me your thoughts! my error code is due to "cat inefficiency" but it could be caused by something elsewhere.

here are my engine/power mods, and the dyno pulls:

AM Power Pack
RSC Green filters
RSC 200-cell cats
RSC Sport exhaust

first session, traction control off.


second session, new primary o2 sensors, traction control on. notice the slightly lower hp at 6k rpm and the slightly lower torque at 3k rpm. also, we did a fourth pull after clearing the fault code and that pull was identical to the others.

 

I have seen V8V cars were the catalyst comes apart. I would get the catalyst tested before I change any more parts. The catalyst come apart and can clog up the exhaust giving you lack of power. Esp, because you have catalyst efficiency codes.

 

i've got RSC cats on it, and i haven't heard of any of them failing (nor has RSC, except for one batch that mine didn't come from). i still have the factory cats, so if i can't figure anything else out, i'll swap them back in and see if the CEL stays off for good.

 

I've seen this on other cars
The high flow cats are less efficient so the secondary O2 see more unburnt fuel in the exhaust and comes up with the CEL you have
Easy solution is a spacer on the secondary O2 sensor to back it out the gas flow a bit

 

That's one of the solutions I thought of a while back. But RSC said their cats are designed to flow within the ECU's specs so I shouldn't be getting a CEL. (Still, I'd be surprised if that was feasible, given the difference in flow.)

Has anyone had spacers made for the o2 sensors? Or do I get to be the guinea pig?

 

I've also heard that these errors can crop up with high flow cats, particularly when the car is cold (one of the posters here who sold his car recently had that issue - it was a PITA as he had to get the codes cleared at the dealership - now however, if you decide to buy the RSC ECU tune, it comes with a Livetune unit so u could clear them yourself). However, if it was just a sensor problem, would that explain the loss of HP?

 

I don't think the loss of power was due to the sensor, since I had the CEL for both sessions. I think it was a combination of the temp/humidity difference and the traction control being on for the second session. The traction control button works fine, he probably wasn't holding it down long enough.

I've still got the original pair of primary o2 sensors so, as long as the size and thread is the same, I can have spacers made without having any down time. I'm going to find a local machine shop and see what they can whip up.

I want to have the CEL fixed before getting RSC's tune so that I don't end up using that as a band-aid for a different problem. If the spacer fixes it, I'll go ahead and get the tune (I'll do before-and-after dyno pulls, too).

 

Telum-
Sorry to hear about your issues. That is frustrating.

Regarding the RSC Cats, mine have yet to throw a code (knock on wood) and have been on for a couple of months.

Regarding the dyno numbers being down, I was told that you absolutly want to have the traction control off....I believe that was your issue. The humidity/temp etc are all factored in by the machine I believe.

Also, try doing your pulls in 4th....I tried 3rd, 4th and 5th and 4th was by far the highest.

 

yeah, it's frustrating (and expensive) trying to figure it out. but mostly it's just annoying to see a CEL popping up when the car is otherwise perfectly fine. when i do my next dyno session, i'll be certain to take the traction control off. pretty sure all the pulls have been in 4th.

so if i get some spacers made, would anyone else be interested?

 

Potentially yes. I've got my cats ready to go on, just waiting on spring to get the car out of storage. PM me with details. Thanks.

 

I had RSC cats put on about a 1.5 years ago and initially had issues with the CEL light coming on. If the cats are not installed properly and there is a slight exhaust leak where the cat connects it can through a code, happened to me. Also, had one of the O2 sensors replaced and I believe after that it did not come back. I am not a mechanic but it might take the car awhile to adapt to the new readings the O2 sensors are sending as well. I had probably 4 or 5 instances of the code popping up and it was very frustrating. Hope this helps.

 

Sounds like you have a catalyst leak before the downstream o2 sensor(bank 1 or 2)..what is the exact code you have?? This will tell also which bank is leaking/faulting. Doesn't mean the cat is bad/leaking but rather could be mal-installed causing a leak at the flange..same fault would be simulated..I don't see a cat inefficiency below threshold coming from the o2's unless damaged during the install of the cats..but then you'd have other faults stored if this was the case..

 

You really should not see any CEL with these catalyts. We did have an isolated run of catalysts where the supplier of the cellular matrices changed the specs without notifying us, and these all threw CEL's but we quickly identified them and replaced them.

Notwithstanding that unique production run, we don't get CEL's with these cats unless something underlying is not functioning correctly. Often it is O2 sensors, but I have even had a customer who's installer shorted out an O2 wire and blew a fuse. That same fuse controls the variable cam timing so it was running with the cams permanently retarded... or at least, they weren't advancing at higher RPMs.

If you are getting P0420 & P0430 codes, then the O2 sensors this correlates to are not the primaries, more likely the secondaries. Because of their location on OEM cats (sandwiched between the primary & secondary cats) the secondary O2's are the most likely of the two to fail. Vacuum leak is possible as well, but the catalysts really should not throw a CEL.

 

thanks for the input, guys.

any ideas as to where a potential vacuum leak would be?

which fuse would blow if that was the case?

i didn't notice any exhaust leaks while under the car (would've seen a bit of blackened blow-by, right?) but i won't rule that out.

 

Leak is usually at the gasket from header-to-catalyst..a nut can be 1/4 turn off and a leak occurs, or gasket is faulty..which will flag the same fault. You could really need to lift and run the vehicle and listen right next to the possible leak areas..if nothing then datalogging the sensors is needed to see where you will be going..catalyst/sensors/leak more upstream..etc