1996 Geo Prizm engine misfires after warm

T_BONE_U13

MEMBER
1996 GEO PRIZM
4 CYL
FWD
AUTOMATIC
175,000 MILES

When the car idles it runs fine hot or cold, and the car runs great idle to redline when cold, but she problem shows up after the car warms up. Thats when it starts to miss, and its no small miss, the motor sputters and cuts out on aceleration. I got the car from a friend who replaced all the ignition components and injectors to no avail. One other thing is that there is allot of black smoke on the bumper by the exhaust

5 Replies

MMPRINCE4000

MECHANIC
8,548 POSTS

Have the car scanned at most autoparts stores for free.

The black exhaust indicates a rich mixture, this could be from a misfire, or a sensor out of range.

Generally, when you have a hot misfire, but runs OK cold, look at the ignitor (ignition module). Even though it is new, by what you have said, it can still be bad.

You want to get this fixed, because a rich mixture will ruin the convertor.

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Wednesday, September 24th, 2008 AT 8:39 AM

T_BONE_U13

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3 POSTS

There are no codes on it. And I just replaced the ignitor and it didnt change it at all. I bought one of those obd2 recorders and it looks like the fuel system is getting goofy when it happens. The graph shows it dropping to near zero and spiking after. Could it be the fuel pressure reg, on even maby the computer?

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Wednesday, September 24th, 2008 AT 10:21 AM

MMPRINCE4000

MECHANIC
8,548 POSTS

Check the fuel pressure regulator by removing the vacuum line, if gas is present, the FP diaphram is ruptured and needs to be replaced.

Could also be a fuel pressure problem, or possibly the ECM.

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Thursday, September 25th, 2008 AT 8:42 AM

T_BONE_U13

MEMBER
3 POSTS

I looked in the line and didnt see any gas, but my nose is plugged so I will have a friend sniff it. Can it go bad even if there isn t any gas in the line?
The more I dig into it the more it seems like its the computer. I put a live scaner on it again, and it said that fuel system bank one was closed and bank 2 disabled. Are there 2 banks in a 4 banger or does it say disabled because its not present. For bank 1 it seems to allways say closed no matter what throttle position.

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Thursday, September 25th, 2008 AT 9:03 AM

MMPRINCE4000

MECHANIC
8,548 POSTS

I would still check fuel pressure with a mechanical gauge.
The FP regulator would have gas present in it (if diaphram was ruptured.
OBDII cars (96 and newer) have many codes that are not used in all cars, bank one and two would be for V6 cars.
Since you have a scanner, check the data in live data mode and make sure all the sensors are within specs.
Specs are listed in the car repair manual link in this thread or from a factory repair manual.