Mechanics

CAR SPUTTERING AT LOWER SPEEDS

1995 Geo Prizm

Engine Performance problem
1995 Geo Prizm 4 cyl Front Wheel Drive Automatic

My wife has a 95 Geo Prizm LSI and last sunday she found it would not start.
Well I had been needing to change the fuel pump on it for awhile since it had been going in and out for a few days. So we changed the in tank pump, screen and in line filter.
The car then started and ran but would start to spit and sputter badly after 10 - 15 minutes driving and finally would die. Would have to let it set for up to 30 minutes before it would restart. Replaced the coil, rotor, and distributor cap, we also removed the catalytic converter and just put a pipe in its place for the time being since the converter was going bad according to pressure test. The car now runs fine but when in low rpm range driving from 1st to 2nd gear it will sort of chug like its trying to die for a moment. If you let off the accelerator it will stop and run fine once past 2nd gear. It does not do this at idle only while moving. Could this be caused by the O2 censors since there is no cat converter? The car has two 1 in front of and one behind the converter. If not a censor does anyone have an idea what it might be.

Thanks in advance
J.W
Avatar
Oiii88
May 10, 2009.



I think the sensors are the problem, and they should set a SES light.

Upstream measures A/F while downstream measures CAT effeciency, since it has none the readings would be out of range.

Mmprince4000
May 11, 2009.
Yes it tossed a Service Engine Soon light. My issue with the light is my local mechanic cant test it because he only has a ODB II and my cars ODB I or so the connector says. I guess I will weld on a new catalytic converter sometime this week if the rain stops and see if that stops it. If not should I check the MAP and MAP sensors? Thanks for the response.

Tiny
Oiii88
May 11, 2009.
MAP or MAF should run, although badly. On ODBI cars the diagnostic connector should have two ports, Te1 and E1. Short these ports, with a piece of wire, turn ign. On and SES light will flash codes.

Mmprince4000
May 12, 2009.
Do I just run a wire from each connector to cause the short and count the flashes? Also would it matter if it was the port under the dash or under the hood? I believe while working on it I seen an ODB1 connector under the hood. Sorry I have never messed with the OBD-I testing. And I would prefer not to pay the local garage 90$ to test if its something I can do. My other question is there a list of fault codes that I can reference after retrieving the code?

Also could anyone recommend an OBD-I scanner for this model of vehicle. I have searched and am not sure if a GM reader to 1995 will work or if a Toyota one is needed. And if Toyota is needed where can one be found I have only located up to 1993.

Tiny
Oiii88
May 12, 2009.
There should be a diagnostic port in the engine compartment, that is where you short the connector.

OBDI scanners are available from Innova, OTC etc. They are combination OBDI and II.
OBDII scanners have a common connector, prior to OBDII the connectors came in all shapes and sizes, that was one of the problems with OBDI.

The pins in the diagnostic port are close together, so you could use a small paperclip.

When you get the codes, post them, I have an OBDI library for Toyota, Geo.

Mmprince4000
May 13, 2009.
Well I shorted the ports today and the stupid light never flashed. Assuming I was doing it wrong I drove to my friends shop and he tried also using a wire and still the light never flashed just stayed solid. Since its my wifes care I had not driven it much since the issue started. But today I noticed it never chugged till that car had been running for about 20 minutes and only at around 35 - 40 mph and only did it while accelerating if I let off the peddle it would idle down and cruise fine. My dodge truck did something like this when the cat was plugged. So I am assuming my original assumption was right in that it was the missing cat converter causing this by allowing the post O2 sensor to send bad data streams. So I am putting in a new converter in the morning and hopefully this will fix it. Thanks for all the help so far.

Tiny
Oiii88
May 14, 2009.
Good luck, but you have a solid premise, the O2 sensors.

The downsream measures CAT effeciency, since there no CAT, it would give a code and default to a reading predesignated by the ECM.

Most manufacturers will build this into the ECM, when a sensor is out of range it will default to a setting within the ECM, this reading is usually rich to prevent a lean condition than can quickly cause engine damage.

Mmprince4000
May 15, 2009.
Welp put new catalytic converter on it still nothing. Took it to the shop they scanned it and found what was causing it to still toss the SES light was a bad connection. But are having issues figuring out what the heck is causing the spuddering while going from around 3000 rpm to 4000 rpm. Its only doing this once the vehicle warms up as I mentioned so its even more bothersome. Guess I will just keep treating the symptoms and hope for a cure. Anyways if anyone has anymore ideas what it might be I am all ears.

Work done so far

New Fuel Pump
Fuel Screen
Fuel Filter
Ignition Coil
Rotor
Distributor Cap
Spark Plugs
Plug Wires
Catalytic converter

Tiny
Oiii88
May 15, 2009.
Just figured I would post the fix in case anyone else runs across this post with the same issues. After taking it to a local shop and having it scoped it was found the pickup in the distributor was going out which was causing the sputtering I assume from misfiring or not firing at all. After replacing the distributor the issue is resolved. To bad the pickup in the distributor wasn't replaceable. Thanks again for all the suggestions they were much appreciated.

Tiny
Oiii88
May 20, 2009.
Glad you got it running.

It is actually cheaper to replace the dist. Is this car. The ign. Module alone costs more than a reman'd dist.

I have a spare dist. I got for $200, that I keep for my 91 Corolla. The original dist. Still works.

Mmprince4000
May 21, 2009.