Originally Posted by BlackThunder
Just put a new exhaust system (pacemaker headers, high flow cats and a twin 2.5" system) on my XR8 and it ran sweet for about a month, but now its running like a hairy goat. It shudders at low rpm and surges when held at constant revs. I've checked all the usual things, plugs, leads, filters, etc and all looks OK. I checked the exhaust output with an AFR and it confirmed that the mixture was cycling from lean to rich. I am unsure as to whether there is something I have missed when upgrading the exhaust, or as to whether the problem actually relates to the exhaust.
Any assistance would be greatly appreciated.
Are these the large primary pacemakers using the header plate?
If so, the problem is simply plug tracking. You need to unpick the aluminium tubes that cover the rubber plug boot, use needle nose pliers. Then, when you have them bare, buy some thermal plug lead insulation, availible from rocket industries. Then cut approx 8 x 6 inch lengths, and slide them over the plug boot. That will fix the problem.
The pipes are a great header, but the header plate and header needs about 15mins work with a die grinder and a stone BEFORE fitment. Ive been through all this before.
Are you checking the AFR at idle? you wont get an accurate reading in either loop at idle. Check it under load, on the road or on a dyno.
It is unlikely that the oxy sensors will have logged a "hego not switching" code, but check the voltages to rule it out if necessary. Check it - dont rule it out. The above posts are great advice also.
If the headers are the 4099's with header plates - do this mod with the plug boots. if its not causing a problem now, it will save u a headache in the future.