Geo Metro TBI question

[2bluesweptlines]

I know, it's not a Swepty, or even a Dodge, but you guys have been and continue to be a pretty good and accurate resource, so I figured I'd ask anyways.
I have a '94 Geo Metro with the 1L (60 CID-yeah, I know, not much more than most lawn mowers...) 5 speed manual. It's throttle body injected and has about 91,800 semi rough miles on it. The EGR valve has been blocked off as well (about a year or so ago, but I think it had stopped functioning long before that) Here in the last 5000 miles or so, I've been noticing this black powdery/oily looking stuff on the back bumper, above the tailpipe, and the inside of the tailpipe itself is covered in it. I know it isn't supposed to be as clean as a whistle, but there is something clearly being deposited there, and on the back of the car. It doesn't use oil (other than leaking), and doesn't smoke, so I am fairly confident it isn't oil. The exhaust smells rich and just here in the last several days (granted I've been putting about 100 miles on a day over the last week and a half), I've noticed a miss start to develop. It is pretty pronounced at idle if you just stand at the back of the car and listen, and even somewhat in the driver's seat. I've noticed no jumpiness or hesistation, but maybe a small loss in power (from what little power there is to start with). I guess the question is what do you guys think could be going on here? Is something telling the engine to run rich? Is there a way to (safely) manually lean out the engine?

I don't know much of anything about TBI/FI and am stumped. It seems pretty clearly to me that it's running rich (much more than normal), but I haven't changed anything. Any help would be appreciated.

Thanks,
Stephan

[Oldguy]

I think the oxygen sensor would be my best guess but I'm not that up on FI type stuff! Some times it bites to be old! LOL Mike

[nfury8]

I have been doing a lot of EFI research for my Magnum swap, but I am in no way an expert.
I have read several places that O2 sensors can have a life of about 80,000 miles. They
can make a motor run rough, they are really the part that controls the air/fuel mix.
The one on my Dakota has 140,000 and is doing fine, though.

Also I would run a couple cans of Seafoam through the tank. Then dump the Seafoam down
the throttle body, flooding out the motor. Let it set a while and fire it up. It will clean out
all the carbon build up from the combustion chamber. Too much carbon will raise the
compression and cause trouble.

A side note, pouring Seafoam down the throttle body isn't effective on motors like the Magnums,
it will pool in the bottom and not get sucked up the runners. Mopar sells a combustion chamber
cleaner which is similar, but in an aerosol can. It sprays in as a mist and gets sucked in.
I bought some a couple weeks ago, it was actually cheaper than Seafoam. The stuff works!

[birddog_mopar]

From my understanding of fuel injection systems the amount fuel is controlled by the Oxygen sensor and the EGR valve, if the vehicle has an electronic EGR valve. I know I had problems with my 1994 Jimmy passing emissions from the NOX being to high and they told me it had to do with the fuel being to rich. When I asked a mechanic he informed me of O2 and EGR valve being in control of the Air/Fuel Ratio, (thus rich or lean). My 94' Jimmy had an electronic EGR and those things are very expensive--like $180.00 expensive. I had no way of knowing what the correct ohms were supposed to be on that or the O2 sensor so I could check them. My point is if you have soot build-up it sounds like your car is running rich. Since you have a GM it may have an electronic EGR and they can be expensive, but the O2 sensor's are not usually that much. If you do replace the O2 sensor buy the genuine AC Delco part, and the reason is because they are meant for that specific vehicle, the Bosch or generic parts that Autozone or a local auto parts may sell do not look at all the points on the fuel map the is required by PCM. I learned this on the Blazer /Jimmy website when I was trying to figure out how to fix my emissions problem. A memeber there explained how he used his laptop with one of those programs you can use to tap into the PCM and watched the fuel map of both the Bosch and AC Delco O2 sensors and said that the Delco looked for more specific points on the map than the Bosch. I hope this helps.

[2bluesweptlines]

Thanks for the info. I have (had) a vaccuum EGR. I might try and find a good EGR and a good O2 sensor and put those in.
I've heard you need a special tool to take the O2 sensor off. Is this right? I haven't looked at it yet. Also, is the O2 sensor something that just goes out all at once?

[birddog_mopar]

As I said an O2 sensor can be checked with a ohm meter if you know the correct ohm range, and you can probably find out what is supposed to be on a Geo Metro forum (I am sure there is one, there is a forum for everything). They may even have a better idea of how to fix you car without spending any money.

[MountainMoparRobin]

your probably going to find that both will need to be replaced, and the longer you let them go the worse it will effect the computor in trying to keep the motor operating at the correct levels and eventually will make the computor go bad also, everything has to work and give correct information feed back to the computor to operate or the computor has to compensate in a manner its not supposed to , to attain the proper levels it has been programmed to have for the operation of the motor.
every sensor becomes important in maintaining proper operation, or they all will start going out because they are over burdened trying to make up the difference
or you could pull the engine and put in the riding lawm mower engine
just kidding, don't take it personel

[2bluesweptlines]

I got an O2 sensor and am going to put it in today, along with a new water pump. Hopefully that will help.

No kidding about the riding lawnmower engine. I've heard of several people putting a Honda CB 600cc in as an upgrade, even though you are going down in cc's by 400, you are increasing power by almost a factor of 2. The current engine has about 50 HP from what I have read. However, for only having 50 HP, you can still spin the tires pretty good (I love manual trans!), and while it is slow, not as slow as you'd think for 50 HP (but very close) My dad's 1950 Dodge B2B (1/2 ton) with a 230 flathead can beat it in a race...pretty sad.

[Stinky]

I had a 1999 Metro with the screamin' 1.0...Really good on gas, very poor on performance. I cut the exhuast off right after the cat, put on a 27" cherry bomb and a 90 degree, and ran the exhaust out in front of the rear passenger side tire. I also took off the stock air cleaner and put on an edelbrock triangular-shaped foam-element filters with a hole-in-the-hood scoop right above it. After that it was loud, poor on performance, and average on gas. Oh, and the stickers added almost 900 rwhp.