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1994 Geo Metro Loses Power


jmatt.walsh
07-03-2008, 10:32 PM
I am totally lost on this one -

I have a 1994 Geo Metro, 5 spd, 1.0 L that has the oddest problem. Every now and then, when accelerating from a stop sign or light, the engine will lose power. It will idle just fine, however, when I step on the pedal it trys to rev and then backs off, then revs again, etc... it oscillates like this until I take my foot off the gas - at which point it returns to a normal idle. It is as if something is cutting the fuel whenever it reaches more than 1200 or so rpm. If I turn off the car and restart it, the problem goes away. This does not happen all the time, and when it doesn't the car runs great. The check engine light is not on (and hasn't been since I eliminated the pesky code 51)

Whats interesting is that the problem seemed to get worse after I replaced the EGR valve (was blocked and now tests fine) in order to pass smog. When the EGR valve was blocked, it happened much more rarely.

I've replaced the TPS, but that made no difference.

On the smog test, the car did run high on the HC which tells me perhaps it is running rich. Could this be the O2 sensor? MAP sensor? I'm really confused since it seems to happen mysteriously out of the blue.

Any help is greatly appreciated!

Scrapper
07-03-2008, 11:00 PM
those were suppose to be throw away motors when they came out.i believe the timming belt or you can take some seafoam and put in tank and see iff it brings it out..if you think 02 then unplug it and see if it run's any diffirent if not it could be 02.i doubt it..cat converter may also be plugging up..good luck....scrapper1 use to be scrapper but now i got to use scrapper1 after getting my computer fixed...

jmatt.walsh
07-04-2008, 04:10 AM
What is the normal resistance range for the potentiometer on the 1994 1.0L TPS? When I measure across the pot I get 3.7k.

Is it normal for the engine to quit suddenly when the MAP sensor is disconnected? I noticed that several people on here recommended disconnecting it and running the engine as a way of testing it.

Thanks!

DOCTORBILL
07-04-2008, 10:19 AM
I have a suggestion.

This kind of intermittent, unexplainable crap has happened to me several times
with older cars - VW Rabbit, Jeep Cherokee, and my Metro.

Think about it - if the gas is choked off when the engine tries to draw it quickly,
what could be keeping it from getting to the Throttle Body?

Bad Fuel Pump ? Maybe.

Something simpler, though, would be the Fuel Filter being almost plugged up...

Once on a trip from Washington State going south thru Oregon to Los Angeles,
my VW Rabbit started bucking and stalling intermittently in Bend Oregon - on a
early Sunday Morning - nobody around.

Finally it just died. Stopped. Looked at the engine - nothing!

Started right up. Tried to drive off - died. Started right up - died as I tried
to accelerate.

Became obvious once I thought about it.

I took the Fuel Filter out (VW Engineers are Smart Germans - they put the Fuel
Filter up in the engine compartment where it was readily accessable),
blew through it backwards and all sorts of red powdery crap came out (rust and dust)
and when I put it back in, I drove 2,000 more miles until I returned to Eastern
Washington and put a new one in.

Long story short - if it has not been changed in several years, the Fuel Filter
is probably full of rust and dust.

This crap falls off the filter once you kill the engine! Then as you try to drive
away or maybe a few minutes later - replugs the filter.

Like trying to breath thru a hose that somebody keeps sticking their finger over
to bug you.

Try changing it. Can't hurt.....

I bypassed mine with rubber hose (down under beside the fuel tank) and put
it up in the engine compartment (cut the incoming fuel line in the middle and put
the fuel filter there).

Now I can get at it at my leisure w/o busting my buns under the car with Fuel
squirting all over me. Very unpleasant job....

DoctorBill

jmatt.walsh
07-04-2008, 02:18 PM
Thanks for the tip! I'll be changing the fuel filter today.

Also, I unplugged the O2 sensor and started the car - it didn't make any difference. Could the O2 be bad? The only sensor that really seems to affect the car is the MAP sensor - when I unplug that, the engine dies.

MrPink
07-04-2008, 04:44 PM
Mmmm... hmmmm... sounds like a bad cat with a loose bit of catalyst bouncing around. Exhaust pressure pushes the block into the pipe or makes it form some other kind of obstruction, and as soon as you back off, everything is hunky-dory again.

Had this with an '86 Samurai, and also had it with the cat on my '96.

Hit the catalytic with a rubber mallet. If you can hear stuff rattling around inside, you got problems, Bunky.

-Pink

jmatt.walsh
07-06-2008, 01:50 PM
When I pull the codes - I get 21/22 and 46 - However, the check engine light is not on! Is it normal for these codes to appear and "not" set off the check engine light?

What is the proper MAP sensor for a 1994 1.0L, manual with CALIF emissions? Will the MAP sensor off an automatic work?

Thanks!!!

CKSan
10-20-2009, 03:46 PM
It is an odd problem. Before putting in a "new" crate engine, my 95 1.0 would on rare instances just cut out as I would corner and accelerate, it was intermittent and sometimes would cut out twice as I resumed to a normal speed. I installed a the engine but kept my intake manifold and applicable sensors. Have put on about 5000 miles since the install, the problem has returned but now I do not have to corner before the cut-out occurs. Usually, within 5 to 15 minutes after warm up. I changed the fuel filter (there are no lights on check engine bar) but had no effect. It continues to cut-out more frequently on corners, sometimes after long after engine has warmed. I want to think it is the fuel pump or fuel strainer in the tank. But maybe the MAP or the Oxy (O2). Because it's intermittent I don't think any resistance reading or fuel pressure reading would be an accurate diagnostic approach. So am trying to learn from others. Luckly, I browsed this forum and saw what appears to be an issue closely associated with mine. If the faulty part or connection was isolated would appreciate any help to guide me through the matrix in order I do not end up replacing my parts that are good with new parts chasing the problem.

CKSan
10-22-2009, 08:46 PM
Problem solved! Was ready to do a DVOM voltage check on the O2 sensor and was looking at the spark plug wires coming to the plugs from the distributor. Again (I have done this before) started checking each wire at the spark plug end and the distributor end, pushing inward and visually checking for any telltale evidence of anything unusual. When I pushed the wire at the boot into the #2 spark plug it moved in about 1/2 inch. I decided to pull that wire from the plug and examine it more closely. There it was the small wires from the interior of the spark plug wire where it is either soldered or crimped to the metal ring that encapsulates the top metal contact of the spark plug had been burnt and was not longer in direct contact. Had another wire from a previous wire change and replaced it started the engine, took it around town and freeway for about 45 minutes and the cutting out, stuttering, bucking was history.

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