FAQ: Improving Bad Gas Mileage

jordynarz wrote:

Yea I have a 95 It's been getting pretty poor gas mileage lately. like 13 or 14 in town. I replaced all the coil packs. and last year i replaced the plugs and wires. it has 121,000 miles on it. its a 1995 S/C.

You running premium?

L67 wrote:

jordynarz wrote:

Yea I have a 95 It's been getting pretty poor gas mileage lately. like 13 or 14 in town. I replaced all the coil packs. and last year i replaced the plugs and wires. it has 121,000 miles on it. its a 1995 S/C.

You running premium?

Yup I am running premium. I always go to Chevron lol.

jordynarz wrote:

L67 wrote:

jordynarz wrote:

Yea I have a 95 It's been getting pretty poor gas mileage lately. like 13 or 14 in town. I replaced all the coil packs. and last year i replaced the plugs and wires. it has 121,000 miles on it. its a 1995 S/C.

You running premium?

Yup I am running premium. I always go to Chevron lol.

Service Engine Soon light on?

im pretty much the same as u.
i run 93, everything is clean inside and out...
what im narrowing mine down to is a crracked exhaust manifold. run the seafoam and u can see if a bunch of smoke comes out the front.

I'm resurrecting this thread because I'm in the same boat as supergman. I'm getting 16 mpg on a tank. Same year, mods, and color even. So what did you find? My engine bay is loud, so I know I need a new dougnut, maybe new exhaust gaskets. I will be checking the plugs and putting seafoam in the tank soon. I just ordered an air charge sensor too, as mine is broken and had tape wrapped around it, does that affect mpg? I have already run seafoam through the intake. Is there a way to check the O2 sensor with a multimeter?

ok,but just a WOA,check to make sure your cat aint clogged before you do the seafoam thing.
on another note.do the obvious. change the fuel filter,clean the AIC valve.clean the PCV valve.clean the throttle body.clean the MAF.check all vac lines. u can clean the EGR valve while your at it too. ive been told a clean one helps.

Robb wrote:

I'm resurrecting this thread because I'm in the same boat as supergman. I'm getting 16 mpg on a tank.

What kind of driving?
Unless I take a trip (and get 27 MPG) I drive lots of short, cold-start, stop & go trips and all I've ever gotten is 16 MPG...

Robb fix all exhaust leaks before any further troubleshooting.

Ok, so I found out I have an intake leak somewhere on the bottom of where the TB attaches to the SC, AND an exhaust leak somewhere in the header after the collector. So, I'm going to get a TB gasket today and put that in. Headers may have to wait unfortunately. Anyone have any used headers? I also found I have Delco platinums in the car that are slightly used, like .005" more gap. Is it better to keep these or go with Autolite coppers for mileage?

Well, a TB leak would certainly F things up... As for the plugs, if your motor is stock, don't throw away the platinums, just re-gap them.

Robb wrote:

Ok, so I found out I have an intake leak somewhere on the bottom of where the TB attaches to the SC, AND an exhaust leak somewhere in the header after the collector. So, I'm going to get a TB gasket today and put that in. Headers may have to wait unfortunately. Anyone have any used headers? I also found I have Delco platinums in the car that are slightly used, like .005" more gap. Is it better to keep these or go with Autolite coppers for mileage?

Robb, if you don't fill out your signature and post it with at least what year car you have, how would anyone know if they have a spare set of exhaust manifolds for you.
You are running manifolds aren't you or do you have Headers installed.?????

If you are indeed using the term Collector correctly, then that would be aft of the header and need welding anyway.
You have to be more specific or use the correct terminology to be helped by anyone.

FIRST a SIGNATURE, or no more answers for you....

I just did my signature, sorry. Its a 95 SC. The stock manifolds are welded headers right? This is my first 3.8, so I'm not sure what they came with stock, but I definitely have mandrel bent welded headers. I usually think of manifolds as cast iron. Here is a pic of what's on my car.

I still see no Signature nor any Pic's.

Sorry can not help you, nor can anyone else.

Robb go into your user preferences and enable the signature.

95 SC had a series I 3800, whose stock manifolds closely resemble headers. They are tubular pipes and not cast iron.

Robb,
With a 95 and the way your manifolds or headers are made, you are much better off bringing it to an custom exhaust shop and have the stock headers welded up tight.
The only reason I say a custom exhaust shop is they usually have very good welders on staff.
You will need to determine that for yourself, or if you know someone that can do a good job.
Remember they are only so thick, so chose your welder carefully.
Finding a good used set may be a challenge.

Ok, changed it so people can see my sig. Sorry, didn't know I had to do that, I'm a noob on here. I got other pics to upload, I don't know why this one won't. Anyway, its already been answered.

I have what I would call stock headers, but I'll call them manifolds for simplicity. I will just get these welded, unless someone has a stock or aftermarket set cheap. I actually have a shop that is amazing at exhaust, and they're cheap. The biggest problem is going to be getting them off because its my only daily driver. I'm going to do some more reading to understand what I need to do better.

Nobody, or should i say, no company makes headers for the 95 that i know of.
That engine is unique unto itself.
If you can find a used set to replace yours with, or a used set that also needs welding, you will be able to do the swap when not needing the car hopefully.

As with any exhaust system, there are always other connections and joints that need to be considered when doing an R&R.

Maybe someone that has done a 95 can chime in.

I know there is a lot of info on here that helped me prepare for the Manifold to Header swap on my 98, but they are totally different than the 95. Sorry.

Wow, I had the chance to get this one or a 98 and the guy with the 98 didn't get back to me so I went with this 95. Seems like a 95 Riv is an odd duck for a lot of things. Oh well, anyone want to trade?

Ok, thanks Rick. I'm only going to need the manifold gaskets and a doughnut I think, they PO replaced the entire manifold back exhaust. I actually got off the phone with a guy that has a parts 95 SC thats 45 min away from me, and said he can scan my car FTW. I just have to figure out if I want to have yet another car to work on.....

dont give up buddy. the 95 has her charms too. sinister perf. can customize a chip for u,a few xtra ponies.

Ok, so I have 2 leaks on the TB. Is there a replacement for the metal heat pipe that goes from the exhaust to the SC? Mine has a crack in it. Do you need this or could I just block it off? I have a lot of aluminum flashing that could work goo for that. Thanks.

My car's gas mileage has plummeted recently but I realized that I've been only doing city driving for the most part. Couple that with holiday traffic... YUCK. I need to calculate how bad the mileage is next fill up. Right now my gauge is a couple ticks under half full and the trip says 185 miles. That seems ridic low.

I typically drive pure city driving, with lots of cold starts, and only the occasional 10-mile highway run...
I get 16MPG that way, but 27+ on a 'pure' highway run.

I think I'm right about where you are for my mileage. Will find out in a few days when I fill up again. These cars get awesome highway gas mileage but around town driving kills them even when you stay out of the gas.. Guess the same could be said for any car though unless it was a very small compact or hybrid.

Yeah, I've noticed that my tune doesn't like the cold weather. Well, actually it loves the cold weather lol. But I have noticed a significant MPG drop since the climate change. All my driving is city. Not very fun to watch the fuel gauge drop......