Sudden plummet in FE and nothing seems to fix it

[txe5502]

Well, it is uncommon that I do this these days, but the house where my grandma used to live is uninhabited now, and people were destroying the place, so I would go hide in my car in the gully in the woods to catch them, but they are in jail now, so I don't do this anymore. However, as far as the spark plugs, I just checked this, the gaps meet top specs, and they are only about a year old. As far as the warming up because it is colder, it couldn't be that because the decrease in FE happened long before temps dropped (around these parts, they just dropped last week).

Now, something you might need to know is the fact that I replaced the engine in this car Nov 27, 2006 (bad rebuild job by previous owner led to blown rod bearings, what a nightmare!), but I achieved 32mpg with THIS CURRENT engine! Now, I can get at most 15mpg

[txe5502]

Now that could be, but as far as plug wires, impossible, has direct ignition (no spark plug wires because there is a separate coil for every plug, sitting right on top of each plug), however, it could be that some of the coils are not functioning properly, or it could be an electrical problem relating to the lines going to the coils, after all, I DO have an electrical problem in the A/T Shift selector switch (It will not detect when I manually shift to 1st gear). So there ARE known electrical problems, but I have not got any misfire codes on OBDII

Some OBDII codes that pop up constantly are:

-Downstream O2 Circuit fault (but my dad says the DOWNSTREAM O2 only tests the CAT, and doesn't affect Fuel Air Ratio)

-A/T Shift Selector 1st Gear circuit fault

-A/T 1st Gear ratio or slippage problem (but I know something is fishy here because my transmission is definately NOT slipping as I would notice this)

[diamondlarry]

Originally Posted by txe5502

Some OBDII codes that pop up constantly are:

-Downstream O2 Circuit fault (but my dad says the DOWNSTREAM O2 only tests the CAT, and doesn't affect Fuel Air Ratio)

This could be an indication that the cat is clogged.

[txe5502]

Okay, but if the CAT was clogged, wouldn't that make it run like crap? It runs fine (no misfire, no backfire, no surges, no stalling, no erratic RPM at constant throttle, no erratic idle)

[diamondlarry]

You mentioned that the car doesn't seem to have as much power. This reminds me of a Plymouth Horizon that I once owned. It seemed to run fine as far as smoothness goes but it didn't seem to have as much oomph and also seemed to be running hotter according to the temp gauge. It turned out that the cat was clogged.

[txe5502]

Well, I am really hoping it is not the CAT, because if it is this, that is so expensive, that would probably be more expensive than low FE.

[txe5502]

Ok, I will check the junkyard on Old Lexington Road, which is about a mile from my house (and they are HUGE and CHEAP usually). They may sell them cheap. By the way, what is avgas?

[landspeed]

Check the cat first! I had a 1.3 litre Metro (rover) with a clogged cat - why did they think of putting a cat on a carb car?. Anyway, it lost power, but ran 'fine', with progressively less power, until eventually I couldn't go up any hills and got stuck in a valley

By the way, cats can also 'collapse' and block the exhaust, depending on the type of cat. Is there any chance that the cat may have sustained a little knock somewhere with the all-terraining?

A while back I saw a video of 'Nissan Maxima Offroading', where someone tried to drive down a ditch and up the other side, however they couldn't quite get up the other side (it was, to be fair, the kind of hill only a proper 4x4 would get up), so it reversed back - but the bumper got damaged.

This wasn't you was it? I think it was a 1996-type model!

[diamondlarry]

In the Horizon I mentioned earlier, pieces of the catalyst actually made its way into the muffler which ended up needing replaced as well. The Horizon was an '87 which was the last year that they were carbed.

[DarbyWalters]

Easy way to check the cat...drill a hole just ahead of the cat and check with a pressure guage...plug hole...drill hole behind cat and check with a pressure guage...compare and if there is a big pressure drop the cat is probably clogged.

The holes can be closed with a small screw or welded back shut.

You can find reasonably priced cats online...Randon Technologies, ect.