85 Vette, Terrible MPG
Thread Starter
Cruising
Joined: Aug 2015
Posts: 11
Likes: 0
85 Vette, Terrible MPG
Hey guys!
New to the forum. I recently purchased an 85 with a blown head gasket. Finally got it up and running, and I'm now working out all the bugs (quite a few).
I've noticed this thing is dumping gas. I get 9.5 average MPG (between 2 - 5 MPG on accelerating, 12 - 16 when moving). I've been using it as a daily, about 20 miles to work (40 both ways). Not bumper to bumper, but frequent stops, no highway cruising.
Is this normal? Its a stock L98, automatic. Straight tube exhaust, no catalytic converters, mufflers, etc. On the scanner, the fuel reads as burning lean, and the coolant temperature shows -39 F (although it reads accurately on the dash gauge). No AC being run currently.
I'm going to keep working to make the car more fuel efficient (my goal is 12+ mpg average), in order to make it an affordable daily. If anyone can give any tips or advice, I would greatly appreciate it! Of course, the o2 sensor is going to get replaced, and I'll post results after, but if there's anything else that might be an issue, or any general advice about fuel efficiency, I'm all ears.
Thanks in advance!
New to the forum. I recently purchased an 85 with a blown head gasket. Finally got it up and running, and I'm now working out all the bugs (quite a few).
I've noticed this thing is dumping gas. I get 9.5 average MPG (between 2 - 5 MPG on accelerating, 12 - 16 when moving). I've been using it as a daily, about 20 miles to work (40 both ways). Not bumper to bumper, but frequent stops, no highway cruising.
Is this normal? Its a stock L98, automatic. Straight tube exhaust, no catalytic converters, mufflers, etc. On the scanner, the fuel reads as burning lean, and the coolant temperature shows -39 F (although it reads accurately on the dash gauge). No AC being run currently.
I'm going to keep working to make the car more fuel efficient (my goal is 12+ mpg average), in order to make it an affordable daily. If anyone can give any tips or advice, I would greatly appreciate it! Of course, the o2 sensor is going to get replaced, and I'll post results after, but if there's anything else that might be an issue, or any general advice about fuel efficiency, I'm all ears.
Thanks in advance!
Last edited by 85BK86; Aug 2, 2015 at 03:22 PM.
Racer
Joined: Feb 2015
Posts: 279
Likes: 9
From: ridgecrest ca
you might ck to see if yor 02 sensor is working the way it should . if your car has over a 100k miles and it hasn't been changed there is a good chance that it is on its last legs. they can cause the fuel milage to go way down .
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
The dash gauge uses a difference CTS (Coolant Temperature Sensor) than the ECM. The ECM uses the one on the front of the intake manifold, under the throttle body.
You have a bad connection to the ECM CTS. It could be a corroded pin in the connector or a broken wire.
Thread Starter
Cruising
Joined: Aug 2015
Posts: 11
Likes: 0
Thanks for the responses. I have a new CTS and o2 sensor on the way, so we'll see how much improvement is shown. The car has about 160k miles, so I have my fair share of kinks to work out. If I could at least drive it without breaking the bank though, that'll be a huge step....now just need to watch the mailbox...
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Thread Starter
Cruising
Joined: Aug 2015
Posts: 11
Likes: 0
I replaced the coolant sensor, oddly enough didn't feel much of a difference driving, or see an increase in fuel economy. The scanner showed correct readings though.
Replaced the o2 sensor. Still didn't really see much of an increase (maybe .5 mpg) in fuel economy, BUT...it did eliminate the acceleration hesitation issue, as well as the super aggressive idling.
Decided to finally replace the air filter, saw immediate gains
An interesting note about the o2 sensor. I had a whole slew of codes (about 8 or 9) showing before I replaced it. The codes ran the gamut of the MAP sensor, fuel pump circuit, faulty ECM, EST, etc...(The SES light was on constantly. After replacing it, the SES light would disappear whenever I was driving at higher speeds, but would come back on at low speeds/idling. After a couple of days, checked, and 4 codes remained (2 new ones + the 2 MAP related ones)...adjusted the TPS, the SES light went off altogether. Cleared the codes, and not one remains.
I do appreciate the help. I took a quick spin around the block and saw an average MPG of 15, before oil started burning all around me...so I'll be spending a good amount of time in the tech section before finding a reason to return.
Thanks again!
Replaced the o2 sensor. Still didn't really see much of an increase (maybe .5 mpg) in fuel economy, BUT...it did eliminate the acceleration hesitation issue, as well as the super aggressive idling.
Decided to finally replace the air filter, saw immediate gains
An interesting note about the o2 sensor. I had a whole slew of codes (about 8 or 9) showing before I replaced it. The codes ran the gamut of the MAP sensor, fuel pump circuit, faulty ECM, EST, etc...(The SES light was on constantly. After replacing it, the SES light would disappear whenever I was driving at higher speeds, but would come back on at low speeds/idling. After a couple of days, checked, and 4 codes remained (2 new ones + the 2 MAP related ones)...adjusted the TPS, the SES light went off altogether. Cleared the codes, and not one remains.
I do appreciate the help. I took a quick spin around the block and saw an average MPG of 15, before oil started burning all around me...so I'll be spending a good amount of time in the tech section before finding a reason to return.
Thanks again!
