Car has low MPG for some reason.

[Sorainzo1]

Hello. For some odd reason, my car has recently gotten really low MPG. When I bought the car, the MPG in the city was about 19, but now it's only 9, which is VERY annoying, since the car HAS to use octane 91+ gas and it gets to be pretty costly. And it's not a ton of stuff in the trunk that's straining the car as it drives. Also, my last oil change used 10w30 oil and I have a 2002 Lincoln LS V8 at about 117,000 miles.

I was wondering what are the possible factors to this happening? Here are some things that I have yet to get fixed with the car that multiple shops are recommending be serviced:

• Cabin Air Filter needs to be replaced
• Fuel filter needs to be serviced
• Rear Differential fluid needs to be serviced
• Auto transmission fluid exchange
• Radiator power purge service
• Ignition coil #3 needs to be replaced since it's causing a misfire

Would any of those or something else be causing the MPG to be that low?

 

[joegr]

...

• Ignition coil #3 needs to be replaced since it's causing a misfire

Would any of those or something else be causing the MPG to be that low?

Yes, that last item. You are not only just pouring fuel out, you are damaging your $thousand catalytic converters and they may already be clogging up. If you have been running this way for long enough to be able to see the mileage change, then probably they are already toast. Please be aware that unless you are the exception to almost everyone else here, you really need to replace all of the coils and all of the spark plugs, not just #3. I strongly recommend that the replacement coils be Motorcraft and not any of the cheaper brands. I would (and in fact I do) go with the 5w-20 oil that Ford recommends/requires for this car.

How many miles on the unknown year LS with an unknown number of cylinders?

 

[Andrizzle]

Jesus dude, 9?!

Your car must be shaking at idle from those misfires, this is not to be ignored. At first sign of coil failure, I place an order for 8.

 

[Sorainzo1]

Yes, that last item. You are not only just pouring fuel out, you are damaging your $thousand catalytic converters and they may already be clogging up. If you have been running this way for long enough to be able to see the mileage change, then probably they are already toast. Please be aware that unless you are the exception to almost everyone else here, you really need to replace all of the coils and all of the spark plugs, not just #3. I strongly recommend that the replacement coils be Motorcraft and not any of the cheaper brands. I would (and in fact I do) go with the 5w-20 oil that Ford recommends/requires for this car.

How many miles on the unknown year LS with an unknown number of cylinders?

Yeah, sorry about that. It's a 2002 Lincoln LS V8 with 117,000 miles. Should I do an oil change and ask the oil to be filled with the original Ford recommended oil, regardless of the mileage? And when I replace the coils and all that, does the catalytic converter need to be replaced?

When I bought the car a few months ago, the check engine light was on, but I didn't notice any misfires until a few weeks after I bought the car. Then I got the coils replaced a few weeks back, engine light went off, now it's back on again after a few weeks with coil 3 now causing problems.

Jesus dude, 9?!

Your car must be shaking at idle from those misfires, this is not to be ignored. At first sign of coil failure, I place an order for 8.

Yeah and it just went down to 8 mpg like it's getting worse. I'm about to take it to the shop tomorrow and get that coil changed and the rest of the engine's cylinders looked at.

 

[1LoudLS]

And when I replace the coils and all that, does the catalytic converter need to be replaced?

that depends on two things...

#1 how fukced up the cats are now? if they havent been too damaged, they may be fine (not likely from the sound of it) or they may be OK (see #2) or they may be completely fukced by the time you get the coils replaced that maybe the engine wont ever run...

#2 do you like seeing a yellow light on the dash all the time?

the check engine light was on, but I didn't notice any misfires until a few weeks after I bought the car.

just out of curiosity, did you scan the car before buying it, or did you just buy a car that clearly had some sort of problem and you were just hoping it wouldn't be bad?

Then I got the coils replaced a few weeks back, engine light went off, now it's back on again after a few weeks with coil 3 now causing problems.

more questions...

did you replace all of your coils, or just the one/s you "thought" were bad?

did you also replace all of the plugs for each coil you replaced?

and if you replaced any plugs, did you gap them or at least verify that the gap was correct or did you just hope all was good (if even any plugs were replaced)?

 

[Sorainzo1]

that depends on two things...

#1 how fukced up the cats are now? if they havent been too damaged, they may be fine (not likely from the sound of it) or they may be OK (see #2) or they may be completely fukced by the time you get the coils replaced that maybe the engine wont ever run...

#2 do you like seeing a yellow light on the dash all the time?





just out of curiosity, did you scan the car before buying it, or did you just buy a car that clearly had some sort of problem and you were just hoping it wouldn't be bad?




more questions...

did you replace all of your coils, or just the one/s you "thought" were bad?

did you also replace all of the plugs for each coil you replaced?

and if you replaced any plugs, did you gap them or at least verify that the gap was correct or did you just hope all was good (if even any plugs were replaced)?

I have a shop check and replace the coils and spark plugs.

I bought the car hoping that the car wouldn't be too bad.

The shops just replaced only the coils that were bad. However, the shop I'm taking the car to tomorrow to replace the coil #3, they are going to check all of the coils and spark plugs, regardless of if they are currently working fine or not.

 

[LS4me]

I have a shop check and replace the coils and spark plugs.

I bought the car hoping that the car wouldn't be too bad.

The shops just replaced only the coils that were bad. However, the shop I'm taking the car to tomorrow to replace the coil #3, they are going to check all of the coils and spark plugs, regardless of if they are currently working fine or not.

To correctly check the coils they need to do a stress test. That diagnostic costs as much or more than just replacing the coils.

Do yourself a favor and replace and replace ALL the coils with Motorcraft ONLY and the plugs with a quality plug. Not one of those fancy Bosch plugs. I went with an iridium plug.

Or don't listen to those of us that have been there and spend mega bucks "cheapening" out with substandard non-OEM parts.

 

[joegr]

...Should I do an oil change and ask the oil to be filled with the original Ford recommended oil...

Just wait till the next change.

...the shop I'm taking the car to tomorrow to replace the coil #3, they are going to check ....

Bad idea.

...Or don't listen to those of us that have been there and spend mega bucks "cheapening" out with substandard non-OEM parts.

Yep, this is heading for disaster. I wonder how long before there is a post about how terrible the car is and how much he hates it?

 

[Sorainzo1]

Well, to be honest with you, I can't change ignition coils and spark plugs myself as I do not know how to do that type of work on the car and don't want to mess the engine up, I'd rather have a professional do it.

So you're telling me that I should buy all 8 Motocraft ignition coils and 8 iridium spark plugs myself and have someone I know or a mechanic install them all for me?

And even if I do all that, should I still buy another catalytic converter? If so, what brand and from what store/website?

Just wait till the next change.

You sure? I have 10w30 in there right now, you think changing the oil and putting 5w20 in there would raise the MPG a bit after I get this coil/plug situation resolved?

Yep, this is heading for disaster. I wonder how long before there is a post about how terrible the car is and how much he hates it?

Nah, I'm not that ignorant, I know that the car's performance is bad only due to how the car was being treated before I bought it.

 

[joegr]

...So you're telling me that I should buy all 8 Motocraft ignition coils and 8 iridium spark plugs myself and have someone I know or a mechanic install them all for me?...

Yes

...And even if I do all that, should I still buy another catalytic converter? If so, what brand and from what store/website?...

You should check and see if it is clogged. If it isn't, then does it trigger the check engine light for catalyst efficiency? If not, then no worries. If yes to either, then OEM ($thousands) is the best bet for fits and works with no problems. There may be some aftermarket that work okay, but there are several that don't.

...You sure? I have 10w30 in there right now, you think changing the oil and putting 5w20 in there would raise the MPG a bit after I get this coil/plug situation resolved?...

The mileage difference from the oil is down in the noise (maybe 1 MPG?) compared to the drop from 20 to 8.

 

[Sorainzo1]

Ok, I just got the ignition coil replaced and the check engine light went away. The mpg also went back up to about 17 mpg, but it's not quite 20 mpg.

Will a catalytic converter cleaner really do anything to unclog the catalytic converter, if it's clogged?

Also, are any of the services I mentioned earlier going to raise the mpg, or even a little bit?

 

[1LoudLS]

Will a catalytic converter cleaner really do anything to unclog the catalytic converter, if it's clogged?

not if the honeycomb material has been melted up solid.

 

[Sorainzo1]

Ok, how would you know that the catalytic converter needs to be replaced, other than looking at it? Because the engine is running fine now.

Does a bad catalytic converter also bring down the mpg or is there some other telltale sign that gives you a hint that the catalytic converter needs to be changed?

And thanks for the help guys.

 

[Robot]

Ok, I just got the ignition coil replaced and the check engine light went away. The mpg also went back up to about 17 mpg, but it's not quite 20 mpg.

Will a catalytic converter cleaner really do anything to unclog the catalytic converter, if it's clogged?

Also, are any of the services I mentioned earlier going to raise the mpg, or even a little bit?

Don't expect 20mpg unless you drive mostly above 55 mph and on limited access highways. Traffic lights kill the fuel economy for these cars. If you're seeing 17 for mostly city driving, you're doing pretty good.

 

[joegr]

Don't expect 20mpg unless you drive mostly above 55 mph ...

Actually, I'm getting just over 20 MPG in mixed driving. It's about 1/3 low speed stop and go and 2/3 interstate at 80 MPH.

 

[Robot]

Actually, I'm getting just over 20 MPH in mixed driving. It's about 1/3 low speed stop and go and 2/3 interstate at 80 MPH.

That's pretty good. Lucky you to have 2/3 interstate driving. I do 80% city driving and see 17 in the heat and up to 19 during cooler months. I found out my diminished return speed is only 72mph in summer though. During fall it's more like 80mph.

 

[LS4me]

Actually, I'm getting just over 20 MPH in mixed driving. It's about 1/3 low speed stop and go and 2/3 interstate at 80 MPH.

MPH??????

 

[1LoudLS]

Ok, how would you know that the catalytic converter needs to be replaced

well with m,y 1st LS, when the dealer/body shop F boned that one up, I got codes that led to the cats, with my 2nd gen, they were melted solid, and the engine would not run for more that 10-20 seconds before dying...

if the car is running well, it doesnt smell funny, and your CEL is not on, then chances are, that it is still good (not saying that it will stay that way, damage could have still been done)

 

[joegr]

MPH??????

Got me...

 

[RigsLS]

OP:

For further <tiny> improvements, you'd need to replace the fuel filter <not serviced but rather straight out replaced>. It'll make a differance in throttle response and yes it will run better and give you back a little on the fuel mileage.

Also maybe time for a fresh intake air breather element. Gently clean the MAF sensor, pull the battery cables off for longer then 30min and rehook it up, on start, let it idle for a couple minutes, it will relearn and reset the fuel/air mixture parameters. Other then that, perhaps a bottle of STP fuel injector cleaner in the tank and check tire pressure.

27-29Mpg Highway is about the best your going to see with this car, City driving all depends on how heavy your foot is. Will easily drop back down to the low tens if you stomp if from light to light constantly.

 

[Telco]

One thing I don't see mentioned is the O2 sensors. With what else has been going on it would be worthwhile to replace the front O2 sensors with Motorcraft units. After the O2 sensors are replaced disconnect the battery for about 15 minutes to zero out the learned fuel trims. This is not a necessary step as the car will adapt to the new O2s eventually but it'll go a bit faster starting at the factory settings. Rear O2 sensors are primarily there to make sure you don't remove the cats, and in later model cars (don't know if the LS does this) are used for fine tuning of the fuel mix. These aren't worth replacing unless there is a code set.

 

[Robot]

Don't forget about the tire pressure. The LS really responds well to this especially when your alignment is set up for quick response.