Hey, wanna thank every one for there replys on my problem. But ya gotta help me out before I go to Mech. My adverage mpg right now is showing 13.5, that can not be right! I filled the tank, and drove about 49 miles on highway and the rest city traffic. On hwy it got up to 20 mpg and slowing came down to 13.5 I change 02 senor (which was in bad shape) and spark plugs were replaced (or so mech said) Oil changed, ck the relays and they all look good. Put back stock chip in computer. Preowner had an upgraded chip for more HP. I think I get the lowest mpg adverage out there. No gas smell, passed emmisions. I don't know what to do. I HATE to bring it to a mech with out hearing all of your responses out there. Car is 85 w/54K orig miles, all stock. I am beginning to hate it now. It even feels a bit sluggish at slow speeds. ANY feedback or idea's what can help me on the right track before I go into a MECH shop. they kill me with a huge bill and car is same as when I took it there! Thanks.

 

How mechanically inclined are you? You could do a diagnosis on your own with minimal tools and little TPI knowledge. I do ALL my repairs on my '86-late and I've encountered many problems before.

First, take your vehicle to Kragen, Checker, Schucks, Autozone, etc. and have them scan your OBD1 computer. Even if your "check engine" light is not on, your computer still stores preliminary trouble codes in it's memory. That will give you a lot of insight.

Second, use a timing light and fuel pressure gauge to make sure your timing is on (compare your engine's timing to the emissions sticker under the hood). Also, your particular L98's fuel pressure should be around 34-38 PSI. Remember, when checking both of these, your engine must be at operating temperature. When timing, disconnect your Electronic spark control connector near the firewall next to the driver's side cylinder head. And when checking your pressure, disconnect the vacuum line from the fuel pressure regulator (pass. side fuel rail).

Third, is your thermostat stuck open? Your operating temp should not be below 185F degrees. Does it take a long time to warm up? Also, the previous owner may have installed a 160F degree thermostat as required by some performance chips. Make sure it's a 195F degree thermostat in your stock engine. If it isn't, replace it with one.

Fourth, check your exhaust for any excessive restriction. Are your catalytic converters too hot? Signs are glowing red after a long drive or a "baked" finish on the cats.

Lastly, a good old tune up goes a long way. I've composed a list of regular maintenance procedures you might haven't done yet:
Replace Air/Oil/Fuel/PCV filters; Check or replace ignition dist. cap/rotor/spark plug wires; clean your mass air flow sensor GENTLY while out of the engine with Electronic contact cleaner; Clean your IAC and EGR valves and passages with throttle body cleaner and replace their gaskets; check and service ALL vacuum lines.

Please post your test results or any other info and I'll be glad to help as much as I can. There are so many generous people on CF, we're always happy to help. Good luck!

 

WOW
Thanks so Much. Wish you were here in Vegas!!! I'd pay ya to get my vette running like a top! It is so hard to find an honest mech or even one who knows what he is doing here. Thanks to you and every one out there I have so much more knowlege about this car. It is my weekend toy and I want to keep it forever and pass it down to my nephew that is if I can get it perfect! I will take ALL your great advice and with all that imformation I can go into a good mech and talk the talk like I know the car inside and out. It helps, it really does. Wish I could work on it myself but changing the 02 sensor and putting back the orig. chip in computer (thanks to CF) I do not think I can go beyond that. THX I will be in touch and let you know the progress! NIK

 

The 85 is incredibly easy to work on! Save yourself money by using the money you would spend on a mechanic and buy some hand tools from Craftsman and a new repair manual from www.helminc.com. She is your weekend car....use the weekend to learn more about it than you ever thought possible. The repair manual from Helm is the GM repair manual and has all of the schematics from wiring to basic tune ups to dismantling the car to put on your driveway if you like. Turning your own wrenches isn't all that hard and at least with the 85 there is plenty the weekend wrench turner can do himself. I love my 85 and do all of the work I can on my own and save the stuff that I know that I can't do for the experts but it has to be pretty complex for me to farm it out to someone else. The forum is a great place to learn but a manual in your hands from GM will get you closer to the direction you want to get.

 

I agree with goldeneye_vet, and a great source of info is a repair manual like a Chilton's or Hayne's available at any auto parts store for about $16. It will give you step by step instructions on just about EVERY regular maintenance job on your car. First thing to do is scan that computer at the auto parts store, all they do is go out in the parking lot and hook up the scanner under the steering wheel and while the key is in the on position, it takes a few seconds and you're done! Why don't you get the repair manual while you are there?

I myself am an industrial diesel mechanic, and I agree an auto mechanic WILL rip you off. These corvettes are SO easy to work on, please feel free to contact me for any other info, it's my pleasure to help. Thanks!

 

Even if you do end up taking it to a mech - make sure you know exactly what you want done. I think that when people take their cars in and all they say is "it's not running right," a less-then-honest mech can hear the cash register cha-ching.

 

I started off like you, thinking I would find a good mechanic for my vette - since then I've learnt that the jobs I've had to do myself , with heaps of help from the forum, have been jobs that lasted and were done well - jobs farmed out to workshops generally get done 2 or 3 times, and other problems occur - I've had the leather steering wheel ripped by someone gettin out of the car with the keys in the hand on the wheel - paint scratches, just got 2 big gouges in the windscreen from a head reconditioning job and a runner dented, had a hole punched in the brake booster while getting an exhaust leak fixed !!!!

When I got my 88 I knew nothing of fuel injection. Thanks to the forum I'm now doing all the simple things - which includes exactly what you need done right now.

18 months ago I re-set the base idle and then the throttle position sensor - it's very very easy - you need some torx head sockets and a multimeter. This made a huge difference to the way the car was running.

As mine has an adjustable fuel pressure regulator (they're an add on after market part) I bought a fuel pressure guage and re-set the fuel pressure.

I fitted a new O2 sensor and new spark plugs.

The car ran better, had a bit more go and the fuel economy changed dramatically. I measure mine in litres per 100 kilometres - I was getting 19-23 and it went down to 12. 10 on a long run.- for litres/km the lower the number the better.

Hardest job I reckon was replacing the O2 sensor and you've already done that.

I think the TPS needs checking every 12-18 months so it's worth learning how to do it yourself, especially as it's so easy.

There's a big list of tech tips on the forum go to 'other' and choose C4 - that's on the bar on the main page that reads left to right - Forum - User CP - Events - Store - Vendors - Buy a Vette - Other - etc

Here's a direct link to the tech tip on setting the TPS - https://www.corvetteforum.com/techti...D=55&TopicID=2

Hope this has encouraged you to have a go!

Check out what maintenance I've done to my vette here - http://www.users.bigpond.com/mpheale...aintenance.htm

S'nut

 

"Please HELP with my 85 mpg problem!!! "

What's the problem? Sure wish my C4 would get 85 mpg...

Be well,

SJW

 

OH so sorry I wanted to say my 1985 vette mpg problem. Every one else got it, not to hard to figure out but I will edit it so it is more understandable, and you to...Be well!

 

a 1985 with only 54K miles thats great low mileage. but that also means old gas being sent into the injectors. my 1986 with 86K gets around 20 mpg. i have a 195 stat and she runs around 180, with a new rad. i was haveing a long start when it was warm, but started right up after seating all night or a day or two. so the last two time between 1/4 and 1/2 tanks of gas i ran 2 bottles of fuel injection cleaner in her. i am starting to feel a diff just in that. so far the warm starts are better, and seating idle at a stop light is smoother too. i am thinking the same could be your too, dirty or gummed up injectors, or your cat is going bad. if your going to get a 1985 GM service manual look on ebay i got mine in really nice shape for only $30 bucks. and a hayne's at pep-boys. theres also a book i think call 101 projects for your C4. i looked at it in Boarder's and its pretty good for a new to repair guy!!

 

There was no misunderstanding, my friend. I just couldn't resist having a bit of fun with that one when I read the thread title. Guess I shoulda tossed in a or two, rather than deadpanning that one.

Now if we could REALLY get 85 mpg out of our C4s, we'd be livin' large, wouldn't we?

Be well,

SJW

 

LOL... thx! I felt a bit stupid there for a second, but I know we are all here to help each other out. That is what the CF is all about. I would be happy with 16-17 mpg adverage! And I'll tell ya what, with all the help and feedback out there I am not gonna give up and I will have this Vette running PERFECT! Thanks for the support!

 

Thank you all for GREAT advice. I have my vette with a mech (friend of friend) so I hope he will he honest. He said he ran his fuel injector cleaning machine on car for an hour and then change spark plugs (which were changed a month ago). said plugs looked bad. He is gonna run it today to see how it drives now. Is he taking the right steps? My last mpg adverage with a full tank of gas was 13.5 and I had about 40 miles hwy on that tank. Can cleaning injectors help? I know also to tell him to ck and clean vacume lines too? Any thing else while it is there. I think the car was running sluggish do to what ever is causing bad gas milage. Should I tell him also to ck for codes? I believe I did when I took it to him. Still get a low volt reading at long stops only (11.4) but that goes up as soon as you hit the gas. I beleive that is because of the 4K worth of audio video, amps, dvd, cd loaded in there. Had one mech rip me off checking that out so I am afraid to go there again. Just want my gas milage right or close to it. Any more thoughts on what to to, let me know. He will be calling me today on how the injector cleaning worked. THX

 

There are a lot of great suggestions being made. The only problem I have with the hole deal is assuming there's something wrong in the first place. 1st place to start no matter what is to verify there really is a problem before throwing money at it or changing parts.

If I just drove my car around town and seldom got past second gear, I think I'd be lucky to get 10 mpg. As is, 28 miles of a 30 mile trip of my driving is down the highway so I get 25+. So, how is this car being driven? Also, it wouldn't hurt to verify the mileage through a couple full tanks of gas using pencil and paper to calculate the mileage rather than rely on the dash read out. jmo

 

driving around town in Vegas is pretty much stop and go. It seems a bit sluggish. It is an automatic and I know vettes were never considered gas guslers. I know there is a reason for only 13 mpg. That is a bit low. I fill my tank at about 200 miles and it show me on reserve. I realized that was incorrect cause when I would fill up at that point it would take 7 gallons, so the gas reserve senor is off. I have documented the fuel for three months now and it is same. Get about to 200 miles and reserve light is on about 180 so I fill up. Takes 7 gallons and mpg adverage is 13-14 even if I did some hwy driving. The 02 sensor was a mess when I changed it, so I thought that would help. I just thing I should be getting like 16-17 mpg in this city. The gas prices are killing me and this is just a weekender car but I am driving more than my suv..HA Seems like I am always filling up the tank.

 

Yes! I'm embarassed because I didn't recommend cleaning your injectors! I recommend running a can of Berryman's Chemtool B12 in every other full tank afterwards, a can costs about $3.20 at the auto parts store. Keep all your electrical equipment off when diagnosing, 11.4V is awful low! My '86L gets around 27 MPG according to the trip computer. Stick to the procedures I posted, and let me know the results. We'll get your 'Vette purring. Good luck!