97' Camry V6 gas mileage falling fast

[97camryMD]

I am the original owner of a 97’ Camry V6 XLE with 71 k miles and have experienced a drop in gas mileage from roughly 20 to 14 mpg (70/30 city/highway) in the last 10 months or so. The rate of drop seems to be accelerating. No check engine light ever. Car idles and runs smoothly - no terrible loss of power, although I don't usually push it that hard. Initially I thought it needed tune-up/new plugs and had a local trusted shop put in Bosch +4’s in mid Dec. 2004 and used some BG cleaner in the gas. The old (original) plugs looked normal in both my opinion and that of the mechanic. At the time it was getting about 250 miles per tank. Seemed to drop to about 225 mpt immediately thereafter. Some internet posts suggest maybe the OEM plugs would have been a better choice, but I think there must be more going on.
Investigation suggested some oil sludge build-up in the engine and last week the dealer did an engine de-sludge under warranty (just under the 8 year deadline!). This entailed about 20 hours labor to clean the engine and replacement of the valve covers and PCV valve. I didn’t manage to talk directly to the mechanic, but the desk representative claims the mechanic said the engine looked to be in good shape other than some sludge. Said the sludge was moderate – I never had the blue smoke symptoms, etc. (btw – checked my oil changes receipts – OCI’s at about 4200 miles – regular non-synthetic oil). The engine seemed smoother after the desludge (my imagination?) but early results suggest I’m down to 200 miles per tank.


Any ideas what I should look for and what approach to take to solve this - easiest, cheapest, etc? I have ordered a new fuel filter and will put it in this week, but I’m not convinced that is the problem. What would cause a severe mpg drop without a rough running engine? Oxygen sensor failing but not enough to trip the check engine light? Bad EGR valve? IAC valve? (what’s the normal idle speed for this engine when cold/warm?) I intend to get the cylinder pressures checked but don’t have that info yet (the engine has never burned oil or showed smoke symptoms, however). Would an emissions test provide useful info? Any experts or similar stories out there?

Sorry for long post but wanted to give adequate data. Thanks for any help.

[whocares04]

make sure ur air filter is clean...and maybe replace...
also, i started using premium (91,93 grade) gas about a month and a half ago (used 87 before for about the 2yrs i've owned it) and noticed not only a little better performance but better gas mileage....

but it's still horrible because one of my o2 sensors has been dead about 8 mos.....

try air filter and have o2 sensors tested (repair manual should say how)

[MadDawg]

give this a shot... i had 100% good success with it...

http://www.tornadoair.com/

[Edmond]

That really sucks.

Has the weather changed for the colder? If it has, you would be running the heat and get less per tank.

How about the tire pressure? Are you making sure they're properly inflated, everything is aligned and balanced?

[ekim55121]

its gotta be your o2 sensors bro in my rolla i was getting worse mileage than my dada caddy and my moms mountaineer and it was a 1.8 liter when my sensors went bad go to autozone and get new sensors dont bother with the dealer they will cost you an arm and a leg auto zone should only cost you your arm

[Toysrme]

Is your fault... If you would work out more often you could pedal harder!
Jesus christ 225mpt!? That like... (equating) What an Audi S6 gets without the kewl 2.7L turbo AWD 6-speed performance

In all seriousness... Get on ebay and buy two new o2 sensors. They're like 25-$30 usd a pop. Install them yourself (takes a 12mm socket and a long arm with a long sleeve shirt for the rear one).

Then reset the ECU. (pull the EFI fuse for a min put it back in... blah blah) Actually... Pull the EFI fuse for a min and put it back in. The last person on AIM that I told to do that went from 250 to 325mpt LoL!

had a local trusted shop put in Bosch +4’s

Next time don't do that. "flashy American plugs" tend to run shitty in non-Mazda(ford) Japanese engines. Noone knows why... From now on either buy Denso, or NGK iridium plugs (expencive) Or buy the "classic" generic platium NGK (6779) or Denso plugs for like $1.50 each. Nothing works better!

This entailed about 20 hours labor to clean the engine and replacement of the valve covers and PCV valve.

Bawahahahahahaha!!!
I could replace that in 1/2 an hour tops, and pour some cleaner into the oil to take care of the sludge over a few oil changes. I'm glad it was under warrenty 'cause I think they woulda taken you to the fucking bank!!!

It's defiantely not a bad EGR valve... Hell killing off EGR shit is the BEST thing you can do for mileage/preofmrance because it'll run hotter (more self cleaning) and the entire engine won't be caked with carbon deposits. Besides... 1mz-fe's are OBD-II. They tend to throw a fit when the EGR isn't operating.

Don't worry 'bout oil... I would swap to a synthetic, but I like them better. If you want, you can buy a sample oil kit, send it off to a lab and they can tell you all about your engine wear. They can also tell you about how long that aprticular oil formulation will last under the same driving conditions before it needs to be changed.



My questions for you:

1. Are you driving the car flat out?
2. Do you have ECT on and/or the transmission overdrive locked out without realizing it???

[Infinit]

I also have problems with my gas mileage, I don't have it that bad, I used to get about 20 on the road and 24-25 on the highway. I now get about 18/20. I have 76k miles on it, it was tuned a month ago, and I think there is something wrong. Same car too, V6 '96 Camry.

[Hajoca]

One thing that you did not mention is tire pressures that can be 2mpg right there, and driving in snow... you may spend time warming the car, idling and also winter gas can contribute to the milage decrease.

Aside from that do you have any vacuum leaks??

[95camguy]

i lose 3-4 mpg in the winter. but i still get about 350-425 out of a tank. i use 91octane if that matters.

a few months back i replaced my o2 sensor(cel came on) and i got a noticable bump in mileage. but other than that some suggestions might be:

- just keep up with tuneups(stick with ngk plugs like toysrme said, bosch plugs suck)
- tire pressure(i try to keep it right around 30psi)
- try using 91 octane as recommended by toyota in the owners manual for peak performance in the 1mz-fe(50% of this forum will disagree with me on this, so take it or leave it)
- and i tend not to carry 300 pounds of junk in my car.
- checked for clogged airfilter(very cheap to replace anyway)

unfortunately, you probably wont average more than 20mpg if you drive more city than highway. my mileage is around 23-24 on average with 90% highway 10% city. i drive a 95 1mz-fe with 133,000 miles on it. in the warmer months it was getting 27+mpg.

k.i.s.s and check out the simple things first

[jhbhatia]

I can't believe no one suggested this - BOSH plugs, for us 1mzfe camrys your not the only one who has experienced reduced milage with those plugs. I know other people who did the likewise and experied the same fate. I have denso-platinums on mine. I still get 24-25mpg on my xle 97 w/ 77K miles.

[97camryMD]

General things I forgot. Air filter is new. Tires (BFG Traction T/A’s – nice) are new in November 04 with alignment. Air pressure checked regularly and OK (30-31 psi). I switched to 91 octane several years ago cause of pinging when the car was pushed hard. Overdrive is not locked out. ECT – don’t think this car has it. I would expect small drop in mpg in winter but I have 8 years with this car and have kept track of mileage – it ain’t normal.

Driving habits: I try to be fairly fast but efficient – i.e. if the upcoming light is red I don’t accelerate hard and then brake hard (why do people do that?).

On the dealer desludge – I agree a simple valve cover and PCV valve swap would have been quick. They claim to have done much more physical engine cleaning (wires, brushes etc.) to remove sludge from all small passages, which I assume is the labor. Parts alone (valve covers, lots of gaskets, etc.) would have been $1185 (dealer list). With labor nearly $100/hour here it would have been a major reaming if not under warranty. BTW they kept the car 8 days … major grrrh, except it was free.

The O2 sensors seems like a good thought. I don’t quite understand the interaction between the pre- and post- cat sensors, however, and how to check if they are weak. Does it make sense that both would fail at once? Could either be bad or is the A/F mix only determined by the manifold sensor? If they were completely bad I assume (?) it would generate a check engine light. I ordered a Chilton’s guide and a Toyota Service Manual PDF off e-bay – maybe that’ll help. I’ve heard the post-cat sensor is a bitch to remove. Cheapest I could find OEM sensors were $110 each shipped – otherwise I’d just swap’em out and see. Couldn’t find any on e-bay. Is it worth looking for a cheap OBD2 scanner – any recommendations or are the cheap ones worth it?

One other thought – is there a temperature sensor that, if bad, would make the system run as if cold (i.e. rich)? The dash temp gauge reads normal but I’m not sure if that is controlling or not.

Plugs - I do wonder, although the mileage was failing before (course the plugs were old...) and the mpg drop is so extreme. What happens if I swap the front 3 plugs with NGK/Denso as a test, (only front cause the rear plugs are a bitch to get to – have to pull the manifold). I kinda think swapping only 3 might be asking for trouble but not sure….

[Toysrme]

You have three 02 sensors. The two that tell the ECU how to tune are in the manifolds. (one rear, one front)

The o2 sensor after the cat doesn't really do anything tuning wise unless there is a problem. It's sole purpose in life is to let the ECU know when the cat is working, and when it is not.

is there a temperature sensor that, if bad, would make the system run as if cold

Yes, the lower the ECT temperature, the ECU will add to the fuel trims. However it is a veeery small change. 5% at most and it will add .5 to 1* of timing. Which would probably offset the mileage loss in fuel. (I actually wrote a guide a few months back on how to use a rheostat to lower the ECT signal so the ECU thinks the engine was colder, increasing fuel, and timing a hair)

You could do it. Wouldn't hurt anything.

Might try buying a can of seafoam, and cleaning the intake with it twice, then putting the rest in with your oil to clean things out. (forget a second can for the tank, you've done the injectors all ready) It'll defiantely be more peppy and run a little smoother.

[97camryMD]

2 manifold sensors ... So does the ECU somehow treat the front and rear A/F mixtures and timing independently? (I show my ignorance) I do remember 3 of the old plugs were more worn than the the other 3, which might suggest something.

[Edmond]

Originally Posted by 97camryMD

2 manifold sensors ... So does the ECU somehow treat the front and rear timing independently? (I show my ignorance) I do remember 3 of the old plugs were more worn than the the other 3, which might suggest something.

How differently worn were the other 3 plugs? Lighter? Darker?

[97camryMD]

How differently worn were the other 3 plugs? Lighter? Darker?

They were definitely a little more rounded. I think they may have also been slightly grayer & darker, but the difference was not huge and its from memory. I kept the plugs for several weeks but finally tossed them while cleaning up. The mechanic thought the plugs were "unremarkable", but I'm sure there was a slight difference.