getting around 240 per tank and need some suggestions please

[jruppert]

I have a 93 ATX with around 125,000 miles. The car was purchased in late summer and I changed the plugs, wires and o2's. The car seemed to of gotten better during the summer which is understandable. Since the mileage has gone down I have noticed two problems. One of them is an EGR code. I cant remember the code number but it has to do with excessive exhaust pressure. The CEL representing this code appears when I run WOT up to around 70 mph and stays on for around 5 seconds. The other problem is that I have a hole in the passenger side cat. I am wondering if its possible that fresh air could be sucked into the exhaust here and causing a lean condition which may tell eec to richen that bank. I dont know if its possible but just an idea. What do you guys think? I am unaware of any internal tune ups that may have been done before me from previous owner. If the rocker adjustment hasnt been made could this also affect the mileage?

 

[LJRuddy]

Well, i dont know about your EGR problem but for me, i get around 250 miles per tank... a tank is usually 60/40 highway/city. I dont drive the shit out of my car nor do I drive like grandma...

I dont think a hole in the cat would cause much of a problem other than a little rasp from escaping exhaust though.

 

[mlatten]

Well, firstly, the SHO doesn't have rocker arms (DOHC). Secondly, I was getting about 270 miles to the tank so I did a full 60 k at 99k. Now, even in the cold weather, I easilly get over 350 miles to a single fill up. Check for any leaks - vacuum or the like, and drop in some fuel injector cleaner at your next fill up. A little carb cleaner here and there will also go a long way.
Keep well posted about anything you do or anything you think has been done.
Best of luck - Matt

 

[jruppert]

Thanks for the replies. Yes you are correct about the rocker arms. It was late and I really wasnt thinking about it. What I meant is from what I understand of that 60k tune up, there is an adjustment in the valve lash. I wasnt sure if this is enough to cause issues. Like I said before, I have no knowledge of prior history before me. I should go ahead and do the tune up anyway but will have to wait until spring. I have noticed when cold there is a slight clatter but is gone after it warms up.

 

[BeautifulDisasterSho]

The slight clatter could be due to valve lash, hard to tell. Sometimes when rod bearings are getting close to the need of replacing the engine will noticably clatter when cold.

 

[mlatten]

Yeah, a chatter can come from many places - and if its from the bottom, well... Just make sure you have plenty of oil in the system and always let the car warm up for a few minutes, and even after that try to drive her as easy as possible. If it's from the valves, they'll make it to the spring.

 

[95IVSHO]

i get 240 to a tank and im on it alot

 

[SonicRiot]

The other problem is that I have a hole in the passenger side cat.

uh, this could be a blatant and obvious issue. You have a hole in your cat, indicating your cats are shot. Stop chasing your tail and replace them. They are probably all clogged up creating excessive backpressure.

 

[seraphiem]

Figure out what your actual mileage figures are. Using miles per tank as a metric is a quick and easy way for your own mileage comparsions but absolutely sucks when you compare to others or other vehicles.

IE, I often fill up at a 1/4 tank, way before the light comes on. Others drive over 100 miles after the light comes up.

Depending on who you talk to your mileage sounds about right for winter driving.

If you have lots of city driving you'll get as low as 14 ~ 15 mpg with the ATX. Much worse if your car has problems.

First get your exhaust fixed! If you have a simple leak due to age then the fix should be cheap and you'll gain some low end power back! If the cats are clogged (and thus leaking out the side) replacing them will result in restoring lost power and getting your mileage back up.

Other common things to go bad on the SHO are a cold blooded engine or stuck rear brakes.

#1 The cooling system diagnosis requires testing the ECT and verifying you truly have a proper working thermostat. If it is running cold expect to replace the T-stat or ECT. Both easy jobs.

#2 Checking your rear brakes is super easy. Put the car in neutral on a slight incline and see if it rolls back like a MTX.

If not figure on at least on of the following;

Stuck Rear Caliper Pins - Pull em Out and Regrease
Collapsed Rear Brake Hoses - Replace
Stuck E-Brake Cable/Mech.

Other common probs are tired O2s and vaccum leaks galore (all that old tubing).

Also you didn't say what kind of driving you do or the mileage you obtained in the summer.

Winter gas (10% ethanol) along with longer then normal warm ups and idling the car to warm up really does hurt a cars mileage. Figure a few mileage points right there. If you do a lot of short trips figure that your car never fully warms up and your mileage will absolutely get killed.

Unless your getting consistently under 14 ~ 15 your in the average for the winter.

 

[jruppert]

Thanks for the suggestions. Yes I understand that a leaky cat is a sign of problems. I would just as soon replace them but you know that they arent cheap. Today put it up on some blocks and checked exactly where it was leaking. It was the front cat and there was a small pencil tipped hole on the bottom flat section of the cat. I took a hose clamp and some header wrap along with a piece of sheet metal and did a quick fix. This was only to keep it quiet and it worked great. Tomorrow I plan on checking codes. I have noticed this.. If I am traveling at 55 and go to pass, when I kick it into 3rd it accelerates but not very quickly. It feels like its running out of power. It will hold at a certain point til it shift back into OD or unless I let off the pedal. At this point the rpm's drop and it begins accelerating again. It is at this point that the CEL light comes on. I never did replace the fuel filter so this will be the first of any work done. Like I said previously, the o2's, plugs, and wires are new. The 240 is all around driving.