Gas mileage on the 450

[ptoro01]

Hey everyone,

Could someone get me tips on how to fix the horrid gas consumption on the 450. Is there any special little bolts that make it run better. Right now its running really strong and it seems to be fully up to par except the gas tank emptys too fast or am i just feeling poor. I usually get anywhere from 12 to 6mpg. I dont romp it because of those reasons and when the engine is running 3k rpm, I can literally see the needle move to the E position.

Any advice is welcome, selling it is almost not an option, a 560 sounds like the right thing to do.

Thanks,
Peter

[WANT '71 280SEL]

I think you should be able tog et up to maybe 15 if it's timed right. Have you done anything with the timing and does it have any vacuum leaks? How about the common fuel leaks at the injectors?
Thanks
David

[MunichTaxi]

Jack up the car, and spin the wheels by hand. You might have a sticky brake caliper.

[300SDog]

Fabric covered rubber fuel lines gone porous underneath handling maybe 20 lbs of constant fuel pressure over 25 yrs exposed to road salts, etc??

The rubber underneath the fabric cracks after a couple of decades, then fuel bleeds through tiny cracks into the fabric and evaporates instead of making puddles. I found this on my 6 cyl 116 last Summer, when the car was getting horrible gas mileage.

Chucking the car on a lift, I walked around underneath then poked and squeezed a few of the fabric fuel lines, litterally feeling them get wet with fuel.

Cheapest and best fix is to buy about 10-12' of regular American fuel line @ $1.89 per foot, then crawl around underneath and cut'n clamp new rubber fuel line sections in place..... replacing ALL the old fabric stuff whether it looks bad or not.

[ptoro01]

Thanks, Ill try to lift the car and see if thats the problem. Would you not be able to smell it if there was a leak somewhere? The car is in a garage without much ventilation, and doesnt reek of gas...

I did the chain tensioner and rails a little back, the chain is sitting in my closet. I will replace that as of next week. I haven't had a chance to play with timing yet. Is there anything easy that I could do to fix it?

Thanks,
Peter

[psfred]

Peter:

What year is that 450?

Makes a difference as the eariler ones had D-Jetronic injection, later ones K- or KE-jetronic, and troubleshooting is different.

Have you done a complete tuneup yet? That is, plugs, wires if old and hard, points if you have them, timing check, mixture check and adjustment?

Very likely you have a serious rich condition -- you should get around 12 in town and 16-17 on the highway. 6 is way too low.

However, you won't get much better -- these cars were designed for power and reliability, and gas milage wasnt' much of a concern.

I'd love to get a 2.65 rear end and a four speed auto in mine....

Peter

[ptoro01]

hey,

I have a 78, i think its the k jet. I havent heard of the ke jet tho. The plugs were changed but a while back I played with the mixture screw so that might be messed up. How do i adjust it right. I am changing out the timing chain next week at the shop and hopefully getting a new cap and rotor at the same time. The wires seem fine and the car doesnt misfire.

The 4 speed tranny is the reason why I wanna put a 560 in there. Not to mention that I will have better gas mileage with that. Anything more than 6 to 8 in town would be nice to get. The car seems to drink gas way quickly while cruising at highway speeds.

Peter

[psfred]

Peter:

The 560 won't do much better unless you change the rear end ratio, too -- the main reason the 450 eats so much gas is the high (3.23 or so) rear end.

You probably have "plain" K-Jetronic (no feedback, no oxygen sensor, no freqency valve). If you have an oxygen sensor and a frequency valve on the return line after the fuel distributor, you have KE-Jetronic. I know the 1980 had KE, but don't know when it started. 76 has K-Jet.

To set the mixture you will need a CO meter, there isn't really any other way to set it properly. I don't remember which way is rich on the screw, either, but I'm betting you have it set somewhat too rich.

What color are the spark plugs? I'm betting dark brown to almost black. Tailpipe would have a black ring if you had a plain exhaust instead of catalytic converters.

Make sure the vacuum retard on the distributor works properly and set the ignition timing correctly (set it 12 degrees "faster" if the vac retard isn't working). Then make sure you don't have any vacuum leaks, and set the mixture with a CO meter to the value specified on the emissions label. You will have to stick the probe into a hole provided on the exhaust in front of the catalytic converters to do this.

If you don't have access to a CO meter, you will have to set the mixture by spark plug color -- too lean is stark white, correct is white to light tan or grey, too rich is dark brown to black.

Your milage (and performance) will be terrible if the ignition timing is late!

[ptoro01]

Wow, thats a lot of info on how to fix it. I work as a detailer in a small dealership and have access to plenty of equipment and a mechanic that seems to know his benzes. His first idea was that my fuel filter is cloged and needs replacing. Maybe Ill do that too while im at it. We will time the car properly after the timing chain is through. I think that there is an almost 12 to 15% stretch on there. The engine is running strong anyways which is wierd. I know I dont have any special meters in the car so its Kjet.

I dont quite understand how to check the vacuum system and the vacuum retard on the distributor.

Peter

[psfred]

Yeah, these are kinda complex compared to American cars of the same era.

The vacuum retard is applied any time there is vacuum in the manifold unless switched off by the AC compressor running OR engine temp of 212F or higher (the aux fan runs at the same time).

If it's stuck or the diaphram is blown, it won't retard the ignition, so if you set to specs then, you are 12 degrees late. Runs fine, but is loggy. Check by idling and pulling the vac line. If it doesn't speed up, the retard isn't working and you need to set the timing to 7 BTDC. If it does, set to 5 ATDC. I'd set it now, it's easy ad can make a big difference. You'll have to reset after pulling a new chain in, but hey, why burn all that fuel for six minutes work?

You also need to verify the operation of the mechanical advance -- rotor should turn clockwise against a spring a snap back to the starting position by itself. If not, you need to take it apart and clean it, the hollow shaft is dirty an sticking. If you get spark knock for a second on hot starts, it's probably stuck

Late valve timing will increase fuel consumption because you are way down on power at the low end. Still there, but only at high rpms.

change that chain at the first opprotunity, it's way too long and you risk breaking a plastic guide from startup chain slap -- this will usually cause the chain to break, and you then get to do a valve job.

I would also suggest a valve adjust (unless this car has hydraulic lifters -- don't remember what year they changed).

Peter

[ptoro01]

I have changed the timing chain out and now it gets much better mileage. I can go almost twice as far that before so I am happy. Althought around the time the chain was changed out, a wierd idle issue started. When its warm outside, the engine will stop choking and rumbling and then stalling at a long red light. I have to keep my foot on the gas to keep it running. I just cleaned out the top part of the intake that had a thick layer of dry black dirt. It may have helped slightly but I doubt it.

What could cause that problem? Should I maybe take the intake off and clean the inside of it because it may be clogged up just that badly? I also pulled all the plugs and took a picture. They seem to all be very very white except for 1 thats rather dark. Could you guys help me solve this idle issue before it drives me insane?

Thanks a bunch, and a happy new year to everyone!!

Peter

[MunichTaxi]

a disconnected vacuum hose. First place to check. Have you put a vaccum gauge on a vaccum port to see what PSI reading is? Should be at least 15 PSI.

[ptoro01]

Do you think that its running too lean because i did mess around accidentally with that one deadly mixture screw.

How do you adjust that to make it perfect

Peter

[Tomguy]

Those plugs do look like it's running too lean, except one cylinder. I don't know the manifold design of the K(E)jet, so I don't know if you have a vac leak at that injector, somewhere around it, or a leaking injector. I'd suggest that you get a new injector and see what happens.

Set it about 1/8th of a turn richer. With the new chain in, you're going to be using a LOT less gas. Don't want to burn a valve!

[psfred]

If you have dirt in the manifold, you have a vac leak.

Sadly, what is probably leaking is the seals between the manifold halves (top and bottom), plus the plastic connector between the air flow meter and manifold can crack. Seals are cheap, but you need manifold gaskets too, and the pipe is costly.

I suspect the seals are shot, but you also need to check the power brake booster line and the other vac lines.

I would replace the injector seals, too. They don't go bad often, but yours are VERY old.

Correct mixture must be set with a CO meter on your car.

Peter