454 Gas Mileage

[jimzz2001]

Originally Posted by awarnes

OK HERE IS THE UPDATE.
After much reading on this site and others and speaking with my mechanic this week we went ahead and had a tune-up today. When speaking with the mechanic (who has a large toyhauler) he was shocked at my mileage. He did it today and boy what a difference driving home. More power, less peddle and climbed the 2 hills coming home with ease. He said I should get between 8 to 10 and have no problem on my trip over the Cascade Mtns.

The nice thing about him doing this was we found that the oil sending unit had blown off and was spitting oil on the engine. That would explain the smell and minor smoke. 2 birds with 1 stone.

Can't wait to leave on Saturday. Again thanks to all who gave me insite to the issue.

Arnold

What did he all do in the Tune-up? Plugs + wires, did he adjust timing? what was the cost of the tune-up?
The reason I am askng is I am only getting 5 at best going 55-60 mph. I was hoping/planning on 7.7 - 8 mpg with the easy going speeds? My 34' is running good but someting has to be wrong + it is sluggish up the hills

[BA-in-Mich]

Jimzz, Get the carb rebuilt and get the distributor recurved It will give you better fuel economy and better running up those hills. Been there and have done that. Talk to Jim Elliott, He'll set you straight.

[JimElliott]

Originally Posted by jimzz2001

What did he all do in the Tune-up? Plugs + wires, did he adjust timing? what was the cost of the tune-up?
The reason I am askng is I am only getting 5 at best going 55-60 mph. I was hoping/planning on 7.7 - 8 mpg with the easy going speeds? My 34' is running good but someting has to be wrong + it is sluggish up the hills

Sluggish up the hills indicates your ignition is really retarded so now you will need to find a "Guru" in your area that understands the "HEI" ignition and is willing to set it up to these specs....
(1)....Base timing 10*, NO vacuum connected at the distributer advance (yet).
(2)....Distributer mechanical setup to 22*-24* at 3,000 RPM.
(3) Stock vacuum advance hands out way tooooo much advance (25*) and will need to be cut back to 10*---15*.
Base 10* + mechanical 22* = 32* without the vacuum hooked up yet..
Now with the vacuum advance reconnected which while lite footing it down the flat & level road add in the 10* or so advance and when your foot is into the floor board and you have ZERO vacuum you have at least 32* of built in advance and your engine will love it.....

Please find this socalled "Ignition guru" and just ask him the above questions.......WALK AWAY if he makes NO sense......

Cannot get into the carb section YET until your ignition is setup and locked down (forever )

Jim

[jimzz2001]

Originally Posted by JimElliott

Sluggish up the hills indicates your ignition is really retarded so now you will need to find a "Guru" in your area that understands the "HEI" ignition and is willing to set it up to these specs....
(1)....Base timing 10*, NO vacuum connected at the distributer advance (yet).
(2)....Distributer mechanical setup to 22*-24* at 3,000 RPM.
(3) Stock vacuum advance hands out way tooooo much advance (25*) and will need to be cut back to 10*---15*.
Base 10* + mechanical 22* = 32* without the vacuum hooked up yet..
Now with the vacuum advance reconnected which while lite footing it down the flat & level road add in the 10* or so advance and when your foot is into the floor board and you have ZERO vacuum you have at least 32* of built in advance and your engine will love it.....

Please find this socalled "Ignition guru" and just ask him the above questions.......WALK AWAY if he makes NO sense......

Cannot get into the carb section YET until your ignition is setup and locked down (forever )

Jim

Thanks JIM!

Looks like some great ideas that I will have my mechanic do. A big part of my problem turned out to be plug wires, well just one actually. Number one Plug wire burnt off. Not once but twice. Im sure it was due to heat, the factory heat shield was in place but it had been bent/straightened more than once from what it appeared.

We were quite a ways from home with limited tools. Here is a link to my experience and how I was able to control the heat and preserve the wire for the trip home.

http://www.irv2.com/forums/f65/1200-...tml#post929440

Now the journey begins to get the RV ready for our next advnture.

[BA-in-Mich]

Jimmzz, if your wire burned twice, and you are still running OEM manifolds you probably have a crack in your exhaust manifold. Had that happen to me. If you listen there will probably be a ticking noise right around where that plug wire is. The one that burn't on me was the passengers side,very back plug.

[BigV]

That back passenger side plug is common.

I replaced my wires with NAPA ceramic booted ones. They are pricey at ~ $120, but you only have to spend it once.

[RVforTwo]

Some great advice here, thanks!

[ga traveler]

Originally Posted by Go Dawgs

I have an 87 Allegro 33' MH total gross weight is under 14k and I was shocked at the low gas mileage I am getting. I just filled up and I'm averaging under 5.5 MPG's. I don't expect to get great mileage and was hoping for 7 to 8. During the last 2 trips I ran the generator about 10 hours with min. load (mainly recharging the batteries). I don't pull a toad.

I feel I drive with a light foot. Freeway about 58 and 2 lane road I try to keep it under the posted speed limit by a couple of miles per hour. I ease out of stops and ease into stops. I use my tranny to slow me down and keep it in 2nd until I'm at about 35 -40 MPH.

What can I do to improve my mileage?

Thanks
Arnold

1987 was the year Chevy went to the TBI instead of the carburetor. Yours could be a split year. It could be a 1987 coach and a 1986 chassis. If you have a split year, your problem is most likely the carburetor. The float was made of plastic. Over several years the float gets soft and absorbs fuel. This causes the float to not shut off the fuel at the correct level and the carburetor to run very rich. In fifteen years as service manager we had dozens of carburetors rebuilt because of this complaint.

[RVforTwo]

Originally Posted by ga traveler

1987 was the year Chevy went to the TBI instead of the carburetor. Yours could be a split year. It could be a 1987 coach and a 1986 chassis. If you have a split year, your problem is most likely the carburetor. The float was made of plastic. Over several years the float gets soft and absorbs fuel. This causes the float to not shut off the fuel at the correct level and the carburetor to run very rich. In fifteen years as service manager we had dozens of carburetors rebuilt because of this complaint.

Now this is interesting! My Chevy 454 is in a 1990 model Fleetwood Southwind (made in 01/89) and it has a carb. Are you saying that someone changed the TBI unit out and replaced it with the carb?

[GOLDWINGER2]

Originally Posted by RVforTwo

Now this is interesting! My Chevy 454 is in a 1990 model Fleetwood Southwind (made in 01/89) and it has a carb. Are you saying that someone changed the TBI unit out and replaced it with the carb?

1989 MH still had a carb. You have a 90 on an 89 chassis.
J

[udid]

Originally Posted by BA-in-Mich

1990 was pretty much the last year for carbs. Some were throttle body some were carbs that year. After that throttle body, unless someone changed it over.
GM that is.
I had my carb gone over and my distributor recurved this spring. I went from 7-7.5 to 8,75mpg. Not pulling a toad.

I concur...95 with a carb? LOL! That would be a bit tricky given the rig likely would also have a electronic transmission. No one is getting that mpg with a carb set up. No one. 5-8 mpg is more likely.

[udid]

Originally Posted by PalmSprings

I had an 84 pathfinder 36 ft 454w/headers.
i consistiently got 10 mpg. i did drive less than 50-55 and kept rpms at about 2000 rpm, I accelerated very slow from stops,no passing etc.
Around town it was 5-6 mpg as i recall

BTW my 01 rex (pic on the left)w/ v10 gets 10-11 driven same way

3 speed trans in it you'd be over 2k rpms (84-454) likely over 3k


1994 Southwind Storm 28ft@ 60mph will be right at 2700-2800rpms (4L80E trans) Go north of 60mph and the mileage tanks. That was the gearing in those days.

[Latech]

One Item, I consider a tune up Item , is an O2 sensor
The older one wire sensors dont heat up fast and can slow down on reaction time fast, get fouled easy and read wrong causing poor mileage and performance.

Any EFI system on a GM 454 will have an electronic distributor and control the timing advance to stay as far advanced as possible.
It does this by monitoring the knock sensor
If you think your timing isnt advanced far enough, hook a scanner to your rig and watch the knock sensor counts.Listen for audible knocks.
If you dont hear knocking it could still be pinging/knocking which will result is retarded timing.
A defective Knock sensor could cause poor mileage if it is over reactive.

Each time the Computer (PCM) gets a knock signal from the knock sensor , it retards the timing by 3 degrees , until the knock clears up and the sensor stops generating a knock signal. The PCM will eventually "learn" to keep the timing pulled back ( adaptive strategy of the PCM) and mileage will suffer.

Plugs , wires , cap and rotor is a must on a tune up.
An O2 sensor is a tune up Item ( at least the old 1 wire sensors are) and should be replaced at 60 -80 K miles.
A throttle body system is actually a pretty economical system.
Throttle bodys do have issues though. The pressure regulator is in the back of the throttle body , and have been known to leak raw fuel into the intake air stream.
Cleaning the throttle blades will improve Idel/starting.

lots going on in a GM TBI. They are good systems . Not bad to work on.

On another note , worn rings can leak combustive gasses and create poor mileage

Checking the blowby pressure can give an indication of ring health.

[Fiesta48]

I had a 78 Dodge C-class 26' It had a 38 gallon tank. Had a Dodge 440 ci , with a 3 speed. On a good day it got 7 but usually 6. Had to fill up before 200 miles. PIA.