Tested tps with multimeter according to these instructions....

[jimdigs]

Well then whats up with my little car... I fill her up and the most I can get on a tank is around 360 miles and lately its 320 to 340. Something is going on but I don't know what. I don't smell a leak of fuel or anything else. The gas is getting sucked out somewhere. Any ideas?

[dalebwilson]

When you pull your spark plugs....what do they look like?

http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp?mode=nml

[tooldude]

Well then whats up with my little car... I fill her up and the most I can get on a tank is around 360 miles and lately its 320 to 340. Something is going on but I don't know what. I don't smell a leak of fuel or anything else. The gas is getting sucked out somewhere. Any ideas?

How many miles are on your engine? I believe your main problem is with the valves. The pistons and rings seem to be in good shape pulling 25" vacuum, engine winding down, but the valves are not holding full compression and therefore not holding full combustion power. I have put larger tire sizes than stock on 6 cyl & 8 cyl vehicles and I always could detect a loss in acceleration, and with larger engines. It "feels" like a loss of power. It's the equivalent of increasing the final drive ratio. It causes you to put your foot on the gas more to get the acceleration you're used to having and keeping it there longer to wind through the gear to speed, or overwinding a gear so the next gear doesn't feel so underpowered. This happens when the engine doesn't enough power for a higher gear ratio and all this costs mileage. If the base timing is off, or there is any condition that is affecting the timing curve it will add to the problem. My engine is apart now with this same problem, the valves are not sealing well. It knocked the mileage down from a consistent 44 to 36-38 (18%). The engine was running very smoothly with sufficient power, but noticeable power loss.( An engine with low compression can run very smoothly) The last time it was turned off it would not restart. I checked things and theorized this condition, which it has - the compression became low enough that the starter could not spin the engine fast enough to run. I proved this by pushing the car and with just a little more RPM the engine cranks right up. Also, you could find erratic compression readings, as I did, if any valve is burned or has a very worn valve guide. This shows up by checking compression on a cylinder multiple times. Eventually you will be forced to fix this but it can't be said how long it can go.

[dalebwilson]

Tooldude is right on. I had 2 burnt exhaust valves and was averaging 33-35 MPG's. After I replaced and lapped the valves....my numbers increased by 10 MPG's.

How many miles are on your engine? I believe your main problem is with the valves. The pistons and rings seem to be in good shape pulling 25" vacuum, engine winding down, but the valves are not holding full compression and therefore not holding full combustion power. I have put larger tire sizes than stock on 6 cyl & 8 cyl vehicles and I always could detect a loss in acceleration, and with larger engines. It "feels" like a loss of power. It's the equivalent of increasing the final drive ratio. It causes you to put your foot on the gas more to get the acceleration you're used to having and keeping it there longer to wind through the gear to speed, or overwinding a gear so the next gear doesn't feel so underpowered. This happens when the engine doesn't enough power for a higher gear ratio and all this costs mileage. If the base timing is off, or there is any condition that is affecting the timing curve it will add to the problem. My engine is apart now with this same problem, the valves are not sealing well. It knocked the mileage down from a consistent 44 to 36-38 (18%). The engine was running very smoothly with sufficient power, but noticeable power loss.( An engine with low compression can run very smoothly) The last time it was turned off it would not restart. I checked things and theorized this condition, which it has - the compression became low enough that the starter could not spin the engine fast enough to run. I proved this by pushing the car and with just a little more RPM the engine cranks right up. Also, you could find erratic compression readings, as I did, if any valve is burned or has a very worn valve guide. This shows up by checking compression on a cylinder multiple times. Eventually you will be forced to fix this but it can't be said how long it can go.

[jimdigs]

Is it a difficult job to replace valves if I have never done anything like this before? When I did do the compression test #4 cylinder that checked the lowest at 115 was the only one that started to lose pressure on the gauge as I watched it. The others held there readings. What does this say? Would that be the place where the valves are not sealing? Can I just replace the bad ones or do you do them all while you have it open? Thanks for the help, this has been a long thread.

Wanted to add that the spark plugs have a dried out look to them.

[dalebwilson]

Jim:

There are really 2 issues here. Low compression caused by bad rings or by valves. You need to do another compression test on all 4 cylinders and add a teaspoon of oil to each cylinder before testing. This will tell you whether the rings are worn or valves are the issue. You can simply remove the head and replace the bad valves or take it to a machine shop for a rebuild. If your rings are worn and your valves need also need replacing...I would opt for another engine or a rebuild.

[jimdigs]

I think your just sick of replying to this too long thread. LOL Just get a rebuild and be done with it. Can't do it. I'll just live with 30 mpg til it blows up I guess.

[jimdigs]

I just set my timing. (I think) I then rechecked my vacuum and it is better than before. Its staying close to 19, still has the flutter but better vacuum reading. This is so frustrating, the car actually seems to run good but the gas mileage is just not there. I just ran down my latest tank of gas and only got 300 miles with about one gallon left in the tank. HORRIBLE. I know its probably the valves or rings like you guys suggest though. Just wanting it to be something else somehow.

[Pu241]

Your timing can make a big difference as well as your driving habits.
See what the timing adjust does for you on your next tank.
You can also bump it just a bit and run it and see if you detect and pinging/detonation.
If you don't hear any, pump it smig more. till you do hear it then back it off. that will optimize your timing to the condition of your engine and type of fuel you use.

But if the ring and vales are worn this isn't going to cure it.
B3 can be had pretty cheap and doing a rebuild isn't hugely expensive if you do it yourself and minimize machine shop work.

[jimdigs]

Could this be what may be going on? Noticed my coil module was ticking (may be normal)? while I was checking the timing. I did some research on the coil module and was reading this.....what say you?........................

High RPM Failure

Generally speaking, the first indication of module failure is a stutter at high RPM that feels remarkably like the engine's rev limiter. As the module continues to worsen, the engine's upper-RPM limit will get lower, and the cut will get choppier. Eventually, the condition will manifest itself as high RPM misfire, which can't be mistaken for anything else.


Read more: http://www.ehow.com/list_6300728_fau...#ixzz2yoPMR5bv

[jimdigs]

So I bought a new ignition module on ebay for 21 bucks and it makes the same ticking sound as my other one so I changed that out for nothing. BUT when I was dinking with it I took the coil wire off, I also remembered that when I did put new spark plug wires on the coil wire that came with the set was to short to use so I just left the old one on. So today when I was looking at the old coil wire I noticed that the end that goes into the ignition coil was real loose and floppy. I still kept the newer coil wire and managed to connect it up by bending the metal arm thingy that the ignition coil and module set on. I know that the car starts a lot quicker than it did before. Before putting this new wire on it took a few cranks for it to start up. Will this possibly help with my gas mileage somehow or just how the car starts? Thanks, Jim

[jimdigs]

Today I decided to check my rear brakes out and found that my passenger side wheel when spun would stop pretty quick. So I went and bought bearings for both wheels and slapped em on. Both wheels spinning real good now and this will have to help with my mpg. Brakes looked fine by the way. A little worn but good enough for now. I'll be filling up with a new tank full some time next week and will report back on mpg.

[jimdigs]

I set my timing again but this time I did it right by setting the rpms wile the STI was grounded and then setting the timing. The rpms were pretty low around 500, according to the service manual it should be 700 on a manual so thats were I set it to. This will affect my mpg reading because I had to let the car run for about 15min to get it warmed up for the check. Oh well, I'll still report back when I run outta gas or get near to. If I'm still not getting 40mpg or over I'm going back to 12 inch tires and see what I get.

[jimdigs]

I filled my tank up today. At last fill up my odometer was 77,511 "0" tenths on 4/22/14. Today 05/04/14 I filled up and it took 8.17 gallons to fill her. My odometer was at 77,811 "5" tenths. Almost exactly 300 miles. So 300.5 miles divided by 8.17 = 36 miles per gallon, almost 37. What is frustrating is that I had gone 200 miles on my first half tank of gas but after the half tank it goes down fast. Don't know why? Also I was going to put my 12 inch tires back on but forgot that one of them is slashed so I couldn't do that. I guess this thread is a dead one now. I will just drive this car til she dies and try and find another one that gets the gas mileage I want. Its so frustrating because this car drives and runs nice but it must be bad piston. Just can't gain the mpg. Been a good learning experience though and I'm an old fart that should of learned this stuff when I was younger. Thanks to all who helped in this thread especially dalebwilson. See ya in another thread, Jim

[Pu241]

What is frustrating is that I had gone 200 miles on my first half tank of gas but after the half tank it goes down fast. Don't know why?

That's not unusual. All of mine do that, some more so more so than others. If you drive it a lot you know when to get gas!

Also I was going to put my 12 inch tires back on but forgot that one of them is slashed so I couldn't do that.

You know, you could just use the 12" tires on the front if you want to check for MPG, so you only need two. Just make sure all the tires are at their rated max pressure.
This maximizes your mileage, but the ride is some what less comfortable.

I guess this thread is a dead one now. I will just drive this car til she dies and try and find another one that gets the gas mileage I want. Its so frustrating because this car drives and runs nice but it must be bad piston. Just can't gain the mpg.

The thread is only dead if you let it die!
I haven't read the entire thread, but did you do a compression test on the engine?
Have you bumped the timming up a little?
Keep your speed at 60MPH or less?