Sudden drop on MPG causes?

collapsed/plugged Cat converter?

Belgique wrote:
An Update. Buried above is a post I made about my V10 all of a sudden barely getting 3 or 4 MPG when I usually get 7. My regular guy blamed winter blend.

I took it to a chap I use when we're in the mountains. I told him my problem and he asked how many miles on it? I said 40K. He said: "O2 Sensors". He said they age and will keep "asking" for more fuel long after it isn't needed.

Yesterday was my first run since he changed 2 of them and I got a solid 7.3 average MPG for a 6 hour run and the engine just ran better. I'm a happy camper again. Hope this helps someone down the road.

Right along the lines our mechanic friends say. If there is a performance issue look to the air either coming or going.

If you have an OBD code reader what you might have seen was excessive short and long term fuel trim percentages. My daily driver is a 98 Honda Accord with 212,000 miles that still has the original O2 sensors. Fuel Trim should only be a few points while I getting in excess of 15% which is causing a rich fuel/air ratio. I'm down about 2 MPG from historical numbers and replacing the sensors is on my to do list for next oil change. Worn sensors won't trip a fault code, as in my case on the Honda, but will effect fuel usage and maybe engine idle performance.

Code readers make a great Father's Day or Birthday gift and thanks for the update.

An Update. Buried above is a post I made about my V10 all of a sudden barely getting 3 or 4 MPG when I usually get 7. My regular guy blamed winter blend.

I took it to a chap I use when we're in the mountains. I told him my problem and he asked how many miles on it? I said 40K. He said: "O2 Sensors". He said they age and will keep "asking" for more fuel long after it isn't needed.

Yesterday was my first run since he changed 2 of them and I got a solid 7.3 average MPG for a 6 hour run and the engine just ran better. I'm a happy camper again. Hope this helps someone down the road.

wildmanbaker wrote:
Now wait a minute, yes, dealer shops have very good, in depth scanning equipment.
20 something kids? We all started out at some very young age. The young kids will be able to find the really hard problems without being a parts swapper. The 50 something gruff guy, may also be a good trouble shooter, or just has a lot of good experience. Lets not label people without knowing. Today's "grease monkey schools" are very good, because they know the latest technical equipment.

There is a magazine: Popular Mechanics.. Back when I was in high school they ran a story in every edition: Gus Wilson's Model Garage.

Gus was one of those 50-something who'd been working on cars darn near all his life.

He had an assistant, As I recall he was name Stan (But it's been a long time) and the local High School had an automotive technology class with the latest hardware.

Stan bet the teacher that Gus could diagnose a car's problems with little more than a screwdriver and a wad of chewing gum (I learned to do it without the gum by the way)

I should say I have seen this diagnostic method live and up close. That story finishes this post.

Well using thousands of dollars worth of the latest tools the kids had all come up with the wrong answer.. Gus got the right one and proved it. He used the screwdriver. chewing gum, spark plug wrench, modified spark plug, and air compressor however.

My story: The latest diagnostic tools said I had a blown head gasket on my 1977 AMC Horned straight six.. This was covered by the 24,000 mile warranty (I had 23,700 when I hit the dealer's bay)

He hooked up the latest hardware and confirmed the earlier diagnosis

The he removed the radiator cap (Same as GUS did)
Removed the nut on the air cleaner cover (Same as Gus did)
Replaced one (and then the other) of the affected plugs with a modified plug body (Same as Gus did)
Hooked up the air hose (Same as Gus did)
and blew the cover off the air cleaner (Different, in Gus' case it was a blown head gasket)

Then he replaced two intake valves and the engine lasted the life of the car.. And that was hastened when the car died (Years later) of a Drug Overdose.. Yup, the shuttle driver from Sentry Drugs dove his Sentry Drug truck right over my poor little car.

most scanners will do what a factory scanner will do if I was worried about fuel mixture I would look at long term fuel trim should be around 0 plus or -minus 6 if running to rich first place to look is fuel pressure regulator pull small vacuum hose off if fuel comes out that's your problem

I had this happen one time when I was at Lake Havasu City, AZ. I took my coach to Joe's the Workhorse Dealer in LHC and they did a diagnostic test and it was electronic throttle control switch. It was a $45.00 fix for parts and labor.

wildmanbaker wrote:

10forty2 wrote:

wa8yxm wrote:
Do different shops.... Well, YES.

Some shops have a bunch of 20 something kids just out of grease monkey school who basically have a problem telling the difference between a piston and a valve.

Some shops have a 50 something gruff old guy who has been working on motors since he souped up his go-cart back in his single digit age days and who can tell what's wrong with your engine just by the sound it makes as you pull into the lot.

Ok, I exaggerate a bit, but that is not far from the truth.

When my 8.1 had that same kind of problem no codes were set by the ECC, the Check Light did not come on.. But the 50 something's gruff old guy found it in less than 10 minutes.

No truer words have been spoken!!! Today's new mechanics are nothing more than parts-swappers. They have no idea how to diagnose a problem and actually fix it. They read from a troubleshooting chart either on a computer or in a book and then start swapping parts until the problem stops. And if an engine doesn't throw an error code, there's nothing wrong with it. It can't be, right? I mean the engineers designed the thing so that if something were wrong it would tell you. Technological advancement is not always an advancement. I'll take an old 60's engine without a computer any day. :D

Now wait a minute, yes, dealer shops have very good, in depth scanning equipment.
20 something kids? We all started out at some very young age. The young kids will be able to find the really hard problems without being a parts swapper. The 50 something gruff guy, may also be a good trouble shooter, or just has a lot of good experience. Lets not label people without knowing. Today's "grease monkey schools" are very good, because they know the latest technical equipment.

I respect your opinion and I know that for a majority of problems the computer can tell them exactly what to do. My experience with new mechanics today is that they don't really understand HOW the system(s) work...therefore they can't really diagnose problems. They can only compare symptoms against what a book tells them and then start replacing parts as recommended. I am an Electronics Engineer by schooling and learned to repair electronic equipment at the component level by tracing out voltages/resistances and actually finding the problem component. It may have been the component itself or it may have been the pathway to the component that was causing the problem. Electronics today involves using another computer to find the computer that is causing the problem inside the computer. And the recommended repair is to replace the entire circuit board instead of actually finding the problem component. It's just a different world out there.... ;-)

I don't pretend to know it all, but most dealer scanners can go back quite a ways recording vehicle performance parameters, actual speeds, altitude, times, braking rates, acceleration rates, etc. It was eye opening to say the least, talking to a tech, working on an actual costumers car, and showing me the research. I am saying YES.

Wildman: you're getting to what I was asking. If my reg guy or his equipment doesn't find anything, do other shops have more exotic equipment? I think you are saying yes?