Yet another thread about poor gas mileage? I'm afraid so.

[haux]

Ok, I know there have been a lot of these threads. I also know that the lack of a specific problem makes it harder to diagnose.

That being said, I've been getting about 23mpg for the past month. I'd say it has been 75% highway, 25% city.

I know some of you will say... "that sounds about right, there's no problem." At the same time, other members will boast about 450-500 miles to the tank.

I think there definitely is a problem. I used to get 29mpg with a passenger and a FULL car. I should be getting more than 185 miles out of 8 gallons.

Here's what I know:

1) Tire pressure is normal
2) Front tires are bald, rear tires are getting there
3) There are alignment issues
4) Catalytic converter is bad
5) Low idle [below 700] due to an unknown "problem"

Can 2 or 4 lower gas mileage? I can only assume that 3 will. But by so much?

[haux]

Originally Posted by pgmomni

Haux,
At some point when compression drops too low combustion efficiency drops off sharply.

Could be the cat is clogged up to the point its increasing backup pressure and impeding flow.

I would do a compression test and a vacuum test to see if its got enough "life" left.

300K for a gasoline engine is alot even if its a CAMRY!

Pete

If this is indeed a compression issue, might it also explain the low idle?

Regarding the possibility of "backup pressure." What route does this pressure go through? Does it have anything to do with the EGR system? All of the vacuum hoses having to do with the EGR system are new. The one going from the EGR modulator to the EGR VSV has popped off a few times from the modulator side. It was strange, because when I tugged on the hose it seemed tight enough not to come off on its own, but after a couple days, it would come off again. Finally I just fixed it with a zip tie. Would any backup pressure from the cat have any affect on the amount of pressure going through that hose... in a way that would cause it to come off if it was loose?

Just trying to get some ideas. I wouldn't be surprised if it was indeed a compression problem.

[camry6]

O.K, here is my opinion, take it for what it's worth. If your tires are bald, especially in the front (drive wheels), then your engine has to turn a total of more times to cover the same distance than if you had new tires, due to the smaller diameter created by tread wear. Another thing to consider is- are you clocking your MPG using your odometer, or a known measured distance between point A and point B? If you are using your odometer, and your tires are worn to a smaller diameter, then your tires will cause your odometer to clock up MORE miles than you actually traveled. This will make it appear that your MPG is actually increasing, when in actual fact your MPG is decreasing....do you follow me here? If this is the case then this is probably not your cause of higher fuel consumption because you would notice an apparent INCREASE in MPG when you calculate. However, if you are filling up at the pump and noticing an increase in fuel consumption- your Camry is needing more fuel this trip to fill than it did before for the same trip (known distance), then likely your tread wear is at least some of the cause.

The poor wheel alignment will also increase drag on the car as it travels down the highway, and no doubt is causing accelerated tire wear. This can noticeably increase fuel consumption depending on how much the alignment is off.

If your catalytic converter is restricted (as they often do) it WILL decrease engine power and efficiency. You will have to be constantly giving it more pedal (fuel and air) to get the same go from it. If you can, depending on emission laws, cut the damn thing out and put in a section of pipe. If you can't do this, then get yourself an after market universal ceramic core catalytic converter. Magnaflow makes them, around $100 dollars.

Your low idle speed will not directly affect your MPG, unless it is caused by a restricted catalytic converter (another good reason to first check your converter), it may only be due to a worn idle stop. This is a small "NON ADJUSTABLE" screw that can be adjusted to compensate for the wear. It is the point that your throttle linkage rests on at idle.

Finally, it could be due to the high mileage finally catching up to the Ol' girl. Low compression can cause low idle speed, more fuel consumption but usually accompanied by engine oil consumption. If it's not smoking or using an abnormal amount of oil, then it is likely not the issue. A compression check is a good idea. Good Luck!

[TCam01]

yea if it was me i would focus on the converter sounds like that's where the most of your problems are coming if you know its bad either replace it or cut it off its not doing you any good right now

[camry6]

The back pressure is the amount of pressure that exists in an exhaust system. Some is normal, but too much reduces engine scavenging which is what reduces power and efficiency. This pressure exists in the exhaust system and recirculate circuit of the EGR valve. This pressure will not affect the emissions system hoses or components, and should not affect the hose that pops off of your vacuum valve.

[hill8570]

Originally Posted by haux

If this is indeed a compression issue, might it also explain the low idle?

Regarding the possibility of "backup pressure." What route does this pressure go through? Does it have anything to do with the EGR system? All of the vacuum hoses having to do with the EGR system are new. The one going from the EGR modulator to the EGR VSV has popped off a few times from the modulator side. It was strange, because when I tugged on the hose it seemed tight enough not to come off on its own, but after a couple days, it would come off again. Finally I just fixed it with a zip tie. Would any backup pressure from the cat have any affect on the amount of pressure going through that hose... in a way that would cause it to come off if it was loose?

Just trying to get some ideas. I wouldn't be surprised if it was indeed a compression problem.

This just came up on the Toyotas_Only yahoogroup in the last week or two -- the hose blowing off the EGR was due to a clogged cat. Looks like any major exhaust restriction would cause it. Is your performance in the toilet, too?

[camry6]

Originally Posted by hill8570

This just came up on the Toyotas_Only yahoogroup in the last week or two -- the hose blowing off the EGR was due to a clogged cat. Looks like any major exhaust restriction would cause it. Is your performance in the toilet, too?

Interesting...... Are they talking about the vacuum actuator hose for the EGR power head, OR the EGR Recirculate pipe and/or Gasket. The pressure from the exhaust acts on the recirculate pipe, and can possibly blow if too much pressure is built up in the exhaust system. The VSV hose, VSV valve and EGR power head (which is a sealed diaphragm chamber) is placed under vacuum negative pressure created by the intake. It has to have vacuum applied to operate. The EGR power head is seperate and sealed from the exhaust system pressure. From what I can gather, it is the VACUUM hose that kept coming off, NOT the EGR Recirculate hose (pipe). Clarification is a must.

[camry6]

Originally Posted by pgmomni

Knock on wood here, so far the only thing I have ever needed was the VSV on my '97.

But, the fact that a EGR to VSV vacuum tube has popped off would lead me to believe your EGR system is out of whack somewhere. 1st thought is a couple of hoses are crossed!?

It was not long ago that you changed your VSV.
Has your mpg been slipping slowly or was it all of a sudden?

I calc my mpg every tank so I know exactly when somethings is wrong.

I only got 24mpg on the tank that included a 240 mile drive back up to Maine from CT during a Nor' Easter gale! 40-60 mile head wind with gusts to 70+ the whole way.
The mpg for that half a tank was probably like 18!

When I 1st got my '97 yrs ago it was getting like 18-20 mpg hwy. Needed front A/F sensor,
timing belt and temp sensor in radiator to get it up to 35 MPG hwy.


My 00 with only 115K idles real low too. In neutral at lights sometimes it dips as low a 600.
As my driving doesn't involve alot of city driving its not a issue.

I agree. Compare the hose connections and routing to the emissions label on the under side of the hood. There may possibly be a hose crossed over, causing positive pressure to be applied to the valve, instead of vacuum negative pressure. This is especially suspect if hoses have been replaced.

[hill8570]

Originally Posted by hill8570

This just came up on the Toyotas_Only yahoogroup in the last week or two -- the hose blowing off the EGR was due to a clogged cat. Looks like any major exhaust restriction would cause it. Is your performance in the toilet, too?

Originally Posted by camry6

Interesting...... Are they talking about the vacuum actuator hose for the EGR power head, OR the EGR Recirculate pipe and/or Gasket. The pressure from the exhaust acts on the recirculate pipe, and can possibly blow if too much pressure is built up in the exhaust system. The VSV hose, VSV valve and EGR power head (which is a sealed diaphragm chamber) is placed under vacuum negative pressure created by the intake. It has to have vacuum applied to operate. The EGR power head is seperate and sealed from the exhaust system pressure. From what I can gather, it is the VACUUM hose that kept coming off, NOT the EGR Recirculate hose (pipe). Clarification is a must.

OK, I'm going to be a bad boy and just file the serial numbers off part of the thread and post the most relevant pieces. Y'all are welcome to join the yahoogroup and examine the archive yourself, if interested.

haux, let me know if this describes the problem you're seeing

Hey guys, I'm on the road with a 2001 Camry with the 5s engine. there are two plastic valves for, I believe the EGR system. As you are standing over the radiator the valve on the left has a hose that goes down behind the engine somewhere. I was unable at the time to really look at it and it's night now and I'm in a motel. Well the hose on the bottom of the left valve keeps blowing off. Can a bad PCV valve cause this or am I looking at something else. BTW it looks like the hose is not broken.

...You have a plugged catalytic converter or a restriction somewhere in your exhaust. Make sure no kids poked a potato in your exhaust first

...if you speak of the larger hose at the bottom of the EGR modulator that runs to the base of the EGR valve, I have seen this twice in my career, both times, plugged catalytic converter.

...Yes it is the large hose which goes to the egr valve and there is a fair amount of exhaust pressure being emitted from the hose. Not to mention the hose gets pretty hot.

...Two things...I limped to a place that diagnosed the problem. In fact it was the converter; however, there are two of them and of course the upper one, located in the exhaust manifold, was the problem. Unfortunately Toyota is truly in love with the part. I didn't quite budget for $1188 just for the part. So I had nothing to loose by putting it on a hoist and gutting the converter. This solved the problem and my hole in the gas tank miraculously disappeared.

[haux]

Originally Posted by hill8570

This just came up on the Toyotas_Only yahoogroup in the last week or two -- the hose blowing off the EGR was due to a clogged cat. Looks like any major exhaust restriction would cause it. Is your performance in the toilet, too?

For a few months now I have felt that something just isn't right. Nothing so hugely noticeable that I could pinpoint the problem. But it just feels like performance could be better, yes. I wouldn't describe it as in the toilet though.

[haux]

I'll post one response going off of the various posts above.

Every component of the ERG system is new. But, the "new" hoses are not OEM, and they are not metric sizes. At first, it wasn't really a problem because everything fit nice and tight, or there was already a clamp there anyway. The one that was just a bit loose was the hose from the modulator to the VSV, on both ends. I already zip tied the VSV end a while ago. But I never did the modulator end. And like I said, although it wasn't on as tight as it probably should have been, tugging on it felt like it would not pop off. Everything is hooked up correctly. I followed the diagram on the hood.

Also, the only other thing about the VSV is that I relocated it to the firewall. I also rerouted the two hoses involved with it, so the lengths are different from the original setup. But I already posted about that a while ago, and the conclusion was that it wouldn't be a problem.

I know for sure the cat is bad because of a reoccurring P0420 code even after both o2 sensors were replaced (with Denso's). My exhaust also stinks, which I believe is also a possible symptom of a faulty cat?

I have a new magnaflow cat at home, but I didn't get around to removing that pipe and getting the cat cut out and rewelded before leaving town. If that is indeed the problem, I definitely regret it now!

Could this bad cat damage the new o2 sensors?

[haux]

Originally Posted by hill8570

haux, let me know if this describes the problem you're seeing

Everything is accurate except it was the hose on the side of the modulator that kept popping off. The hose is also indeed very hot. In fact, the whole area is. It feels like whole engine bay gets hotter now than it ever used to. I thought I was just loosing my mind... and I thought those hoses may have been getting hot because of the intake manifold?

Could hot exhaust be backing up so much that it's causing the entire engine bay to become hotter?

By the way, here's a picture of the new hose routing I posted in another thread a while ago:

[carsrus]

Originally Posted by haux

Could hot exhaust be backing up so much that it's causing the entire engine bay to become hotter?

Yup. Look under the car at night after a good long drive. If the cats plugged enough itll be glowing. No joke.

[haux]

Originally Posted by carsrus

Yup. Look under the car at night after a good long drive. If the cats plugged enough itll be glowing. No joke.

I will check that out.

I feel like I should have someone mail me that new cat and get that thing put on ASAP...

[camry6]

If your engine bay is noticeably getting hotter, and your exhaust stinks (larger amounts of NO2 created by hotter combustion temps) and yes the recirculate hose on the modulator valve (not the VSV connections as I thought you were describing earlier, sorry 'bout that) then a catalytic converter is most likely the cause. In a worse case scenario, if the converter plugs, it can damage your engine (burn exhaust valves, warp the cylinder head or even melt pistons). Even worse than this is a possible fire due to extreme temperatures under the hood or around the exhaust system. This actually happened to a Hyundai Tucson just a week ago here where I live. The guy was driving on the highway on his way to work. He felt a gradual loss of power over 5 or 10 minutes, then he heard a funny sound in his exhaust system, then other drivers with panicked looks on their faces were blowing their horns and pointing at his under vehicle area. He pulled over only to find flames under his Tucson and around the hood. It burnt to a crispy critter. No one was hurt. The catalytic converter internal core was found shattered and blocking the exhaust. I suggest driving easy and get it checked ASAP.