1997 V6 poor gas mileage troubleshoot

[kenratboy]

About a month ago, I posted about my 97 V6 5-speed Camry getting consistently poor fuel economy. I used to get 26-28 MPG all day, every day, and life was good.

Over the past 6-12 months, I have dropped into the very low 20's (20-23 MPG), and the car does not feel as strong as it used to.

--Just replaced the fuel filter, and I am not sure that did it (it will take a few tanks to be sure, but that will take weeks with as little as I drive!).

--Tire pressure is not an issue, I always check it and keep it in the low-30's (even if this is somehow wrong, this is the same pressure that was giving me the higher mileage).

--Air filter is checked and changed more often than needed (takes all of 30 seconds!)

Now a few things I am wondering about:

--Plugs and wires - been well over 40,000 miles since this was done. Would this have a meaningful impact?

--O2 and other sensors - there are too many and they are too expensive just to replace on a whim, is there 1 or 2 that are known to go bad and screw with fuel economy?

--What about things like a clogged PCV valve, bad EGR valve, or something related?

I really appreciate any help, gas prices are creeping back up, and I have some road trips this summer, if I can figure out what is happening, I would be happy.

Thanks!!!

[96paseo]

I wouldn't worry about plugs and wires just yet. Seafoam your TB first. See if that helps improve your throttle repsonse. If your EGR has never been cleaned, i would suggest doing it. I picked up 2 MPG on my 4 banger gen3 after fixing the EGR. To check your PCV valve, pull it out of the gromett on the valve cover and shake it. If it rattles, its good. Unless you have a CEL and have O2 sensor and/or MAF codes, they probably aren't hurting your fuel economy. A bad ECT can hurt your fuel economy as well.

[kenratboy]

How hard is the EGR to 'clean'? I see it is literally right on top of the engine, but the Hayes manual goes on for four full pages about the system. Is there something quick and easy I need to look at?

Dumb question - my Hayes manual does not show me where my PCV valve is - where is it? It is a sub $20 part, worth replacing just because (13 year old car)?

My mechanic said not to replace sensors until I get a CEL, as they are expensive and there are too many of them to just go to town.

What symptoms would a bad ECT sensor give?

Thanks!!!

[ASG14]

Plugs and wires very well could be it.

The EGR won;t be the cause. It would throw a CEL if so, The O2 sensors could be, but I'd wait untill they cause the CEL to come on (as your mechanic said). They are $150 each, and you have 3. The PCV won;t be the cause, but it's a sub $10 part, and I would just replace it. It;s located ont he firewall sid bank, on the top/passenger side od the valve cover.

What Spark plugs do you have in it? And how many miles, or only know over 40k?

I's say 1st thing is start with seafoam throu8gh the brake booster hose. Then I'd change the plugs and wires (depending on what brand and mileage). While your at it, I'd also gat a can of carb cleaner and clean the throttle body butterfly well, to get off all the carbon and oil. As well, I'd probably just spend $7 on a can of Electronic Parts Cleaner and clean the MAF sensor. They get dirty over time.

[kenratboy]

For the Seafoam, I see most videos for new cars, they:

-Warm up engine
-With the engine running, SLOWLY put ~1/3 in the brake booster
-Stop engine and let sit for 5-15 minutes.
-Start engine, rev it up and down, lots and lots of smoke. Do that for maybe 5-10 minutes.
-Pour the rest in the fuel tank.

What is missing is pouring some in the oil, while I see this on the Seafoam video, I don't see many people doing this. Not a good idea on a modern car?

As for the plugs, whatever the Toyota mechanic put in (no reason to think they are crappy). I will take a look for the PCV, funny the book does not show it anywhere (just says, "Remove").

Any risk of damaging the MAF with parts cleaner?

Thanks! Great advice.

[ASG14]

For the seafoam, I put it in my oil a long time ago. I honestly think, if your engine is fine (oil wise, no sludge), you really don;t need to.

For putting it in the brake booster, you don;t really pour it in, you suck it in, semi slowly. There are a couplke DIY vids around for it.

For the plugs, if the Toyota mechanic did it, and used OEM Toyota plugs and wires, they should be fine at 40k miles.

As for the electronic parts cleaner, it's meant to be used on items such as the MAF. I got a CEL from my MAF not working correctly around 30k miles ago. Sprayed it with electronics parts cleaner form the auto store, and been fine since.

I'd say 1st, replace the PCV valve (if old). But you can check if it is good by shaking it. If you head it rattle, that means it is GOOD. If it doesn't rattle, it's bad.

I'd say start with doing the seafoam, in both the tank AND brake booster line, clean the MAF, and plead the butterfly in the throttle body. My Nana has a 1995 Corolla with 19k miles (17k at the time I did the seafoam). A couple months afte rI did the seafoam, she called me and said ever since I drove the car, the gas needle has gone down slower, lol. Cleaned all the carbon out of the engine.

[kenratboy]

Sounds like a good plan. The cost of the Seafoam is nothing, and it is easy to do (as long as it doesn't wreck my engine!) I did see the video, just the tiniest trickle you can manage (saw someone doing an Accord).

Can the PCV valve affect mileage, or is it just to keep things running properly?

Thanks again!

[ASG14]

PCV is to keep things running properly and let gasses out of the cylinder head to reduce pressure.

[kenratboy]

One more question on Seafoam - just worried about making the (currently) very small oil leak from the head, worse. By not putting any in the oil, isn't this supposed to leave these areas alone, and not exacerbate oil leaks?

[ASG14]

Do you mean the valve cover gaskets leaking? A bad PCV can make that worse. The seafoam would only effect that is put into the engine oil, NOT from the fuel tank or brake booster line.

[kenratboy]

Yes, I believe my mechanic said that gasket is leaking, and that it is not uncommon on that engine. Not a bad leak, but a leak none the less. I do not want to make it worse.

And thank you for confirming that could be made worse by putting it in the oil.

[ASG14]

The Valve Cover gasket leaking is actually expected, and considered part of normal maintmence for the Camry's (BOTH I4 and V6). Thats nothing to get worried about. BUT, it will slowly get worse. So look into gettign them replaced (along with the spark plug tube grommets) int he future. But it should like your mechanic knows what he is talking about.

[kenratboy]

Originally Posted by ASG14

The Valve Cover gasket leaking is actually expected, and considered part of normal maintmence for the Camry's (BOTH I4 and V6). Thats nothing to get worried about. BUT, it will slowly get worse. So look into gettign them replaced (along with the spark plug tube grommets) int he future. But it should like your mechanic knows what he is talking about.

I assume that job requires dropping the engine on the V6? I do love my mechanic, gives me breaks on jobs, and always tells me NOT to do things that would make him money "Yeah, no reason to do that..."

[ASG14]

Nope, all done with everything on car. The pic below is with the valve cover's removed, along with addition item's removed that is not needed to be when the work is done. The covers just cover the cam's and vavles. I THINK the book time on the job is 3 hours labor, and under $100 in parts. I've done it for several V6 Camry's/Solara's.

[kenratboy]

Very nice. I would hate to have to rip the entire car apart to fix this.

Also sounds like a good time to do the plugs!