Been following you guys since 2011 the rear i got my 98 sc2 with 60k. as of 1mar23 she has 180k of hard driving and over a decade of car pooling. love my little car. i upgraded the suspension last year when i did a complete replacement. over a decade of 4 big ugly construction men running the roads going to fast took its toll on our backs and the suspension too! so over all these years ive never gotten that 36 mpg or even close no matter how i drive. right now i'm waiting on a new down stream o2 sensor. i put in the universal last year. just now throughing a code and something about the voltage may damage the circuit. hopefully the right sensor and the wiring info i got from you guys fixes it. i dont know where to start. i guess with the darn carbon build up. i cant get it under control!!! i've been reading the service manual bullitons and cant find anything the top of piston 1 and 4 is covered with crusty black goo. and cylinder #1(firing?) is advanced 40 degrees at highway speeds. is that right? alright enough crying for today. i'll check in later and see if anyone has any comments. now this is just whats on my mind TODAY!!! lol. thanks a million to all the fellas that put this sight together and keep the wheels rolling.

 

35 mpg in an SC2 at highway speeds is obtainable with only one person in the vehicle and no real load in the trunk. Also, tires in good condition, fuel injection system clean, catcon clear, no vacuum leaks..... Blah blah blah.

Take out whatever crap plugs you have in there and replace with stock NGK 5643 s (double check number).

Please list all codes by Pxxxx format.

Have you been pulling and cleaning your EGR valve and the inlet and outlet port piping where It attaches?

How much oil does it burn per 3000 mi?

Rough idle misfiring? Rough idle unsteady? Automatic or manual? What is idle RPM?

 

Welcome, I am also a newcomer to the forum, there are many knowledgeable people in this forum, I hope someone can answer your questions.

 

[thanks. Yeah I’ve been reading the forums for almost a decade now. These guys really do know their stuff. I’ve got the rough idle under control but the gas mileage is still not so great. I put a set of accel ignition coils on and I think it might be them. Keep getting the code loss of serial data and one other I can’t remember. I think it had to do with the module that controls the coils. So cross your fingers it’s the accel ignition coils

 

It's really difficult to help you when we ask questions and receive no answers to them.

And when things like communication codes lost aren't included in the initial description of the problems.

Ignition issues will show up as p o3 XX codes. Most people don't use stock plugs and end up with misfire codes and cam position sensor codes. There is no cam sensor in an SC2. It's usually your plugs. Use stock NGK plugs. End of story.

If your mileage sucks and you have no other codes, change your front O2 sensor. Use the denso sensor listed at Rock Auto that costs about as much as the ACDelco. Back in the day the sensors were identical, as in the OEM sensor was a denso.

If the modules in the vehicle are not properly communicating, I'm not surprised you're losing gas mileage. Without knowing the code I can't say what's not talking to what But TCM likely involved.

There are many other reasons your mileage is down. Could be worn wheel bearings, dragging brakes, inefficiencies in production of power due to reduced compression in the cylinders, blah blah blah blah.

Answer the questions above and we might be able to help you. There's a reason your thread didn't go anywhere. We asked a bunch of questions trying to help you and you never answered. It's only because I just woke up and I'm not my usual cranky *** self yet that I'm even replying to this. I generally like to help people but it goes both ways. I am a magician and I am clairvoyant but that doesn't mean I can fix your car necessarily without your involvement.

This has been a public service announcement as well as a private communication. Have a nice day.

 

Right on, derf. That post made my day. Thanks so much.