Codes

I got it thank you so much.

If the car shifts good and you don't have to let up on the gas to shift that is good. If you only test the back pressure at the front manifold that will only tell you if that pre cat is clogged and if the lower cat is clogged. But won't tell you if the rear pre cat is clogged because you can only see that by testing the pressure right off that manifold. The pressure on the front one sounds normal since you have the gauge now I would test the rear one too. As far as the scan tool not showing very many line's of data I really have never used a aftermarket scanner on the L model saturn's I have only used the Tech2 with the factory software the same scanner that all the gm dealers use. It is a lot more advanced then the generic obd2 scanners the diyer's use. As far as saying you have a bad ecm because of the lack of data lines I wouldn't jump to that conclusion all the ecms I have replaced the engine didn't run the tech2 wouldn't link up to the ecm other running issue's etc. Also you can still have bad cats and setting those cat code's you have even though it's not showing a clogged cat.I would reset the cat code's and see if those cat code's come back also check the other manifold back pressure. So you have a miss fire with no code's?Another thing those early v6 L model engine's are known for are bad timing belt tenisors I have seen them just let the belt go completely loose. Or just loose enough to jump a tooth and cause a power loss or a miss fire.

Your comparing a 99 S model saturn then a 4cyl L model to a 6cyl L model. Like I said I have never hooked up a generic code reader to a L I have on a S model and I think it had like 108 lines of data I have a actron scanner. As far as the belt being replaced 10,000 miles ago was the timing belt tenisor replaced also?Because the belt's aren't the problem the tenisor's are and they can fail with a new belt or old one. Have you had a transmission shop perform a line pressure test on the transmission yet?You could have a pressure issue those transmission's are known for line pressure solenoid issue's.

If you have low pressure high pressure etc I have seen the transmissions destroy themselves inside. So was there any debris in the transmission pan?

You change it every 50,000 miles it gets pretty dirty by then though.

Those cars never really got that great of mileage 24mph sounds about right. So what was done to fix the p0742 back at 163,000 miles?

Keep me posted on what you find.

If you want
to try a ecm thats your choice I wouldnt go down that road. Its on the intake manifold drivers side there are reverse torx bolts holding it on with two connectors going to it.

The transmission computer is under the cowl at the base of the windshield passenger side and the ecm is on the intake manifold on the drivers side.

Alright keep an eye on the oil level and keep me posted.