Super low MPG in 91 Tercel

incorrect cam timing

mrcheerful

Check ignition timing, air filter and intake hose for leaks and clogs, use OEM ignition parts, check for vacuum leaks.

Finshed the compression test. decent. I did a warm test with exactly

10 compression strokes and got 187, 194, 197, 211 PSI respectively. Which is an 11% diff between the highest and lowest. The 187 was the cylinder where the head gasket busted.

My son has a 90 Tercel with 180k on it. It has a boneyard engine that wee put in 35k ago that had about 90K of it when we put it in. He has gotten as high as 44 mpg with it on the hiway but some observations we have made with it. It is very sensitive to tire size in performance and MPG and it is also timing sensative too. If he sets timing to stock, the MPG goes down a good bit but he runs it about 6 to 8 degrees betfore TDC and uses plus or better gas it does a LOT better on fuel. You might also check your cam timing and make sure that the cam is not out of alignement by one cog of the belt and that can greatly effect overall performance and MPG.

So I decided to check the cam timing alignment. It's a bit of work. I just put the timing belt back on and followed the directions in the manual exactly (I remember putting the timing belt back on last time and I did exactly the same thing). I won't know until I get everything back together, but I'm guessing I'll get the same results.

My car also passed smog with flying colors a week ago... I'll try setting the spark timing a few degrees BTDC

You said the speedo is too fast... have you calibrated the odometer using highway mile markers? I would go at least 10 miles to get a decent conversion factor between odometer miles and actual miles.

No, I used my GPS. I drove around with it on where I had a good signal and found there was about a 9.8% difference. Probably caused by non-stock tires... I'm gonna need new ones soon anyway.. so we'll see.

IMHO you should be getting 30 EASILY with that car. My 87 Camry would do 40+ on the highway (yes, I am a pretty conservative driver).

So I just finished putting it all back together and checked the timing and it waas dead on according to spec. 10 deg BTDC, I might try changing it a tad though.

I have a feeling it's going to be the same as it was before.

Check to see if the timing advances properly at higher RPM. Check vacuum - you want somewhere in the neighborhood of 14 in. hg. at idle. Check to make sure the transmission isn't slipping Check to make sure none of the brakes are dragging

The timing does advance properly and smoothly as RPM increases. Vacuum is approx 18in Hg at idle. Transmission is not slipping. Brakes are not dragging.

Damn, man, I changed my rubber on a '95 from 155/80-13 to 185/70-13 and still managed 42~45 MPG on a regular basis, 39MPG in the winter! Not only that, but I had plenty of grip! I ran out of engine before I ran out of grip!

Here's one:

This will help you get your speedo straight: And another good one:

Good

Good

Good

Good - you did check each wheel by jacking up the car and spinning the wheels, right?

Automatic or manual transmission?

If automatic, is the torque converter locking in high gear? Very difficult to fell the TC lock up. Try cruising at a steady speed in 4th & lightly tap the brake pedal enough to make the brake lights come on and see if the RPM jumps slightly.

Tires properly inflated?

I checked the wheels several months ago and no, the brakes weren't dragging, I'd imagine they'd get too hot start to burn which would be easy to smell. It's a 5 speed manual.

Yeah, the tires are properly inflated. 155 R13 78T Kumo's

Do the plugs show any evidence of a too-rich mixture, i.e., buildup?

Does the temp gauge work properly?

Nope, they look fine, no build up, and yes the temp gauge works fine.

Thanks for your help.

If everything I mentioned is OK and working fine, and assuming the car passes smog tests, then maybe your MPG calculation is incorrect somehow, either from the incorrect odometer or handheld GPS margin of error.

Your problem reminds me of a customer who came in complaining that his Corolla was only getting 14 or 15 MPG for the first 2 weeks he owned it and he was embarrassed because he had told all his friends what a great and economical car he had purchased. EPA mileage was around 28 MPG mixed. Everything checked out OK with the car and we were baffled.

2 weeks later, he comes back and now his car is getting over 50 MPG and whatever we did to the car was fantastic (all we did was check stuff out).

Another couple of weeks go by, and he is mad because whatever we supposedly did to the car didn't take and he was back to 14-15 MPG.

At this point, I figured he was filling the tank improperly or doing his math incorrectly so we put a locking gas cap on the car and told him to come by the dealership for fillups for the next 2 tanks. Lo and behold, with dealer people filling the tank and doing the math, he is getting 28 MPG like he was supposed to.

After 3 tanks, he is happy again so we take of the locking gas cap and send him on his way. Of course, on his very next tank, he is back to lousy mileage. He announces to his buddies that he is going to sue the dealer and Toyota for a gazillion dollars for unfair and deceptive business practices, selling defective cars, and anything else his lawyer could think of. When he mentioned hiring a lawyer, his buddies fessed up. It turned out that they were siphoning a couple of gallons out each week for the first few weeks so he would get lousy mileage, and then putting it back a few weeks later for unbelievably good mileage. To his credit, the customer came and apologized to the service manager and me for being such a jerk.

Calculating mileage isn't that difficult. besides, any error made in one tank would show up in the next and it would even out in the average mileage over several tanks (total miles / total gallons) that is unless of course my odometer works intermittently (unlikely) or I have a gas leak (haven't noticed any gas, nor smell).

I keep my mileage records in a giant excel file.

Sorry, I didn't mean to imply that you were making a math error. I thought that the error could be in the odometer or you have an over-rich mixture.