2002 S80T6 CEL Long Term Fuel Trim Cat Efficiency

syrotchen · Post by **syrotchen** » 08 Apr 2014, 13:57

I've been chasing these codes for a couple of months now trying to find the problem. Long term fuel trim goes to the lower limit (doesn't stay there). Cat Efficiency throws a code as well. My assumption has been they have the same cause. A little history, the engine blew a head gasket and overheated enough to warp the head. I rebuilt the engine, replaced the head with a rebuilt one. The oxygen sensors were replaced both sets of front and rear with the same Bosch sensor. All the vacuum hoses were replaced. I've placed a vaccum gauge on the intake and I'm reading 19 in hg at idle initially, climbs to 21in hg after approx 60 sec and 22 in hg at approx 1500 rpm. The needle does oscillate approx +- 1/4 in hg at idle with no fluctuation at 1500rpm. I've monitored the rear oxygen sensors and they switch between ~0.7v and 0.1V. The old sensors read similar values. The front oxygen sensors move between .98 and 1.01 V with the only deviation coming with a large acceleration and response back to ~1.0V is within a couple of seconds. MAF and Boost sensors are also brand new. I've graphed both and response looks reasonable compared to my wife's xc70. Injectors were sent out for cleaning, fuel filter is brand new, and the fuel pump was replace less than a year ago under a recall. The CAT is an aftermarket DCS bolt in unit, the previous cat failed with the head gasket. All the exhaust gaskets were replaced with the rebuild, and I've run a stethoscope around the engine looking for exhaust and intake leaks. I've also used Carb cleaner to check around the intake and hose connections for leaks. Gas mileage is normal and the car has more power after the rebuild. Call it a point of foolish pride, but I'm so close to bringing this car back from the dead, I hate to admit defeat and drive it into the local dealer. I have VIDA with a DICE unit, so I can look at any data, if someone can point me in the right direction.

BradF80 · Post by **BradF80** » 08 Apr 2014, 14:58

What do you mean by fuel trim goes to the lower limit. Are you talking -25%?

syrotchen · Post by **syrotchen** » 08 Apr 2014, 15:46

diagnostic codes for long term fuel trim are set ecm 261A and ecm271a. Codes for the Cat efficiency are also set ecm4801 and ecm4901

syrotchen · Post by **syrotchen** » 08 Apr 2014, 20:13

Well, I set up a little test rig with compressed air. Plugged the air filter end of the intake using duct tape, removed the larger of the two vacuum hoses coming from the evap and pushed compressed air through the intake starting at 5 psi and slowly increased the pressure until I found the leak. I found the leak on the crossover tube, where it had split at the seam. Its a healthy leak, I'm surprised the carb cleaner didn't pick it up, but I do believe that is the source of my codes.

BradF80 · Post by **BradF80** » 08 Apr 2014, 21:37

It very well could be. A lean condition on the intake side will definitely show lean on the exhaust side, it will also throw a catalytic efficiency code if it stays below threshold too long.