As I've mentioned in previous posts, my recently acquired '98 Blazer is showing intermittant SES codes that come and go every few days.

The engine has 154,000 miles on it, but runs great. Except for the poor gas mileage! I'm only on my second tank, and I put a bottle of injector cleaner in this last tank fill-up.

My initial trip to the dealer to fix a failed 4 wd encoder ($720.00 installed) was dissapointing when I asked them about the SES codes and poor gas mileage. He started rambing about how many miles it had, blowby, worn rings and valves, and was talking about $6,000 for a replacement motor. Can you believe it? I guess they don't do tune-ups on anything over 100,000 miles anymore. But he did mention something about the engine running rich, which would explain the gas consumption.

So, I'd like to know a little more about reading SES codes, and what I can do to get better gas mileage. I don't drive with a heavy foot, and I only do local or "city" driving.

I also replaced the aftermarket locking gas cap with a factory cap, so I hoped I eliminated that as a possibiblity of these SES lights.

The dealer wasn't interested in doing any kind of a tune-up, but besides a set of plugs and an air filter, what else could you do to improve mileage? Does this thing have an EGR valve that might need cleaning or replacing? (My Haynes manual sucks).

If I had an O2 sensor going bad, wouldn't the SES light stay on all the time?

The dealer mumbled something about disconecting the airbox, to get rid of those SES lights, but he said that wasn't ethical, and they didn't advise it. But it would cause your oil to get really dirty really fast.

So, I can either invest in a code reader, or take it to my local mechanic (not a dealer - it's someone else I use regularly) and ask for help.

Any comments on improving gas mileage on this vehicle?

Thanks.

 

Your local Advanced Auto or Autozone will read codes for free. It almost sounds like you have a evap purge code, which has to do with the sealing of the fuel tank. Replacing the cap usually makes them go away though. How many times do you click the cap when you refill? Do you fill it until it clicks off, or do you round up to the nearest dollar when you are filling? 2-3 clicks should be the norm, and you shouldn't fill it up COMPLETELY. This may cause the vacuum line to get some gas in it and set an evap purge code.

It is quite possible that the EGR valve is not seating properly. It is located on very front/center of the engine. It is about the size of a soda can and will have an electrical connector on top of it. Just take some decent throttlebody cleaner and an old tooth brush and clean it up. You'll want to have a new gasket ready and it will require a 10mm socket and atleast a 10" extension to remove the bolts. You'll want to make sure that you clean the gasket surfaces very well before reinstalling it.

It is also possible that the O2 sensors have gotten lazy. You are talking about O2's with over 100k on them if they haven't been changed before now. If the sensors have gotten lazy, then they take more time to adapt to changes that are made by the PCM to the fuel injection system. It is possible for them to be going bad, but not bad enough yet to set a SES code. An O2 sensor related code will set a constant SES light that will be there even after restarting the vehicle. I ONLY recommend AC Delco O2 sensors in GM vehicles. They may cost more, but they are worth it!

I wouldn't go back to that dealership EVER. If they are telling you that the only way to get back your mileage is to replace your motor, they are COMPLETE IDIOTS! Blowby and all that other horse crap they were feeding you can easily be checked by doing a compression check. If you had excessive compression loss, you'd know it. You're truck wouldn't run right and you'd be replacing plugs right and left due to the oil that would be getting sucked up into the combustion chamber and burned.

A full tune up should include plugs, wires, cap, and rotor. If you really want to do it right, replace the O2s as well. A bad O2 sensor can ruin new plugs just the same as bad plugs can ruin a new O2 sensor. A new PCV valve wouldn't hurt either. It presses down into the top of the driver's side valve cover.

I don't know what good disconnecting the airbox would do... Disconnecting the battery for ~10-15 minutes will clear the codes.

Good Luck

 

Thanks - boy, what a wealth of knowledge here.

I'll print this stuff out and drop by my local mechanic I've been doing business with for the last few years.

That GMC dealer may have Saturday hours, but I'm really disappointed in them.

Thanks again.