Re: Running great, but 12MPG, Update 11/10/05

In regards to this post.


Brand new carb, not rebuilt by me (so I take the me screwing up factor out of it), and adjusted properly, and I'm still getting 12.5 around town. I'm not positive I have the idle mix set right, but if anything I have it idling on the lean side.

• Brakes are not dragging
  
• Fuel system is clean
  
• Timing is unknown, but unchanged for who knows how long
  
• Doesn't ping, or backfire (some burble and pop, but no backfire)
  

At this point, I'm ready to attribute it to a combo of sea level, lead foot, crappy gas, and all city driving. I really don't know what else it could be. I had the cat off not that long ago, and it didn't look clogged. You could barely see light through it, but the honeycomb was clean and free of deposits.

<img src="/forums/images/graemlins/frown.gif" alt="" />

I do have a long freeway trip coming up soon, so we'll see what happens then.

If it makes you feel better, city driving really does hurt you. I'm all over Providence and it sucks my gas up. are you throwing any new codes? doesn't sound like a timing issue, but I'd get it checked. most places will put a light on it for free, mabey a small fee if they suck.

I am wondering the same thing....is it throwing codes? Oxy sensor still intack? black smoke out the exhaust(richness)?

Carbed - no check engine light. Oxygen sensor is new, doesn't seem to be black smoke out the exhaust. The thing runs like a top, just gets crap mileage.

There is an ECU of sorts, so I would wonder about a check engine light, but it's never come on, even when you start the car. Not to mention, there is no check connector where you could jumper it to pull codes.

With the price of gas, it would seem like an FSM would be a good investment. I am not sure about the check light....seems like there must be some way to check engine health....you might not have injectors but you still have an oxy sensor. Remove the air filter and inspect the choke plate while it's running. Try some acetone <img src="/forums/images/graemlins/wink.gif" alt="" /> ZUK

Believe me, I'll try damn near anything at this point. <img src="/forums/images/graemlins/drunk.gif" alt="" />

I do have an FSM, but unfortunately, mine being the last of the 4WD carbies, and being a Cali model... Probably one of the more obscure ones out there. I'm not even sure it has a pinout for the "ECU"

The one other thing I remembered, is I do have a very small leak between the cat and the cat-back at the flange; I need to get a new crush gasket. I really don't see how that could be affecting this that much, though.

why do you have an 02 sensor on a carbie??? is that some freakish california thing?

Ding ding! We have a winner!


I'm really not sure what all the ECU does on this truck, I think Josh probably understands it the best. I did find the pinout just now, and here is what's hooked up to it:

• O2 Sensor
• Temp switch 1
• Temp switch 2
• Vacuum switch 1
• Charge light
• Tach signal
• Vacuum switch 2
• Speed sensor
• EBCV
• EACV
• CMH
• Fuel cut solenoid valve
• VSV
  

According to the FSM it actually has a way of adjusting the A/F mixture.

Before going to FI..Toyota had O2 sensors and carbs...and all those other goodies on Tercel engines up to '88.

With these cars several people with poor mileage have found that the vac advance diaphrams on the dist were leaking...not allowing the right vac advance. Also helps to redo ALL the vac lines...or at least redo the ends. EBCV?

For the Tercel there is no diagnostic...you just have to check each component.

Some just put a Weber on the car.

I have one of those want to be fuel injection carbs on a mazda. for me it was the electronic main jet.
$$$. got a junk yard one that worked finally and I am back up to 22 mpg.

You said the 02 sensor is new... Is it factory Toyota or aftermarket? I ran into a problem on an 85 Toyota 22re w/ a bad sensor, so I threw new one at it. Mileage was HORRIBLE after. Turns out the aftermarket sensor was 1/2" shorter than the factory sensor and didn't even get into the exhuast stream.. So the computer was all confused and dumping tons of fuel in to compensate.

Worth a check if it's aftermarket... if it's factory Toy... then I don't know what to tell ya.

I've heard the horror stores about aftermarket... It's OE identical. Same company, same size, same everything.

But thanks for the suggestion.

Have you verified that the vacuum and centrical
advance are working properly inside the distributer?
They can get gummed up. Mine did. When I corrected
that, my highway mileage went from 19 to 23 <img src="/forums/images/graemlins/smile.gif" alt="" />

Are there any exhaust leaks in the exhaust line?
My Carsound Cat blew one of it's welds and my gas milage went down to about 10-12mpg.
I rewelded the line and it went right back up to 19 mpg.

You know, the vacuum advance feels kind of gritty, like whatever that fiberglass looking thing is is disintegrating and gumming it up.

A) What is that thing?
B) Can it be replaced?

The distributor looks OK otherwise, no real play in the shaft, and the governor advance still feels fine.

*EDIT*

Heh, duh. Just an insulator. I pulled it off and repainted it, and shot about half a can of brake cleaner in there to try to clear everything out. We'll see.

I removed my distributer from the motor to clean
it. The vacuum breaker plate should move with no
resistance. That assembly has to be removed to get
further down to the little weight-spring thingies.
Make sure they move freely. I used brake cleaner
(I think) to free it all up, and then some silicon
lubricant. Adjusted the gap while I was in there.
Make sure you start at TDC before removeing the
distributer (I assume you know that)

Well, here's an update:

Before I made the trip home (360 miles, all freeway), I played with the idle & timing some, didn't really change it.

I pulled 21MPG on the trip home, so city driving was most of the problem, BUT...

I did take it to the dealer for lube/oil/filter and a general lookover, and here is what they found:

1 ruptured diaphragm in the vacuum advance (I asked them to check)
1 small vacuum leak between the intake manifold and the head in the vicinity of the #4 cyl (found when they set the timing and idle)
Leaking cat to exhaust flange, I knew about that, and had them throw a new gasket in

So I guess the moral of the story is a lot can be attributed to city driving, but if your mileage drops, it's still a good idea to look into it.

Now I'm wondering how much it will improve when I fix the diaphragm and vacuum leak... if I can pull 21MPG doing 75-80 on I5 with those problems and an exhaust leak, I can only wonder what it will do afterwards.

Thanks to everyone for all the helpful ideas and good suggestions. This board continues to be the greatest resource for shadetree mechanics I've ever found.

Cool; nice to know where to look for other trouble spots on these old ponies. Let us know what your gas mileage does once you're squared away.

Would a 92 truck has this vacuum advance on the distributor? Does anybody have a picture of it?

Thanks

The round gold colored thing directly under the hand in the picture is what you're looking for.