Question : 1994 3.1 Bad mileage, fouled plugs.

[Mole1333]

I recently bought a 94 Sunbird 3.1 with 110,000. It was sitting for about a year. It ran a little rough but just at idle and kinda choked at 55-60 on a steady cruise. I checked the plugs, carbon fouled but recently put in, still had anti-seize on them. The plug wires I replaced they spec'd bad. New IACV, I cleaned the plugs re-installed. I get 12.8mpg. Major problem, no Trouble codes and the computer showed nothing stored. The fuel pressure is steady at 40 not running and it drops slightly with vacuum applied to the regulator.I ran a can of sea-foam in the gas tank to clear up, new fuel filter and I ohm tested the injectors all at 12.6-12.7V the harness is steady at 12.0V. Still haven't ruled out plugged injectors. Coolant temp sensor checked ok, and the crank sensor checked ok, so I have the knock (doesn't ping anyway) the TPS and possibly suspecting the coils, or a plugged catalytic? Any input appreciated.

[robertisaar]

i think you nailed it with a plugged cat.

as for the knock sensor: you'll never, and i mean it, never hear it knock before the sensor does. but codes would get set if it was acting bad.

[IsaacHayes]

If you hear a knock on the highway going WOT and it's still slow, the that could be a clogged cat and the backpressure opening the spring loaded downpipe flange and it snapping closed... My friends Impala did that when his cat was clogged.

[Mole1333]

Thanks guys, I will cut the cat out asap, its in a billion pieces now (the motor) so its gonna be a while before we know the results. Thanks. Just out of curiousity what should my mileage be? 20? I haven't owned a MPFI 3.1 since high school.....

[robertisaar]

on the highway you should be getting at least 25, especially in a J-body, but it wouldn't be too hard to get at least 30, if you know how to drive to save fuel...

[Mole1333]

Ok, well I Ohm'ed the coil packs and one was bad...It wouldn't even give me a reading, put it back together with a new coil and no change yet, runs rough and bogs, I will cut the cat out tomorrow at work where I have a lift and pipe bender.

[Mole1333]

Cut the cat out, straight pipe....the cat was pretty clogged, but still no change. Smells really gassy now. Assuming the injectors are stuck open. I found a complete motor for $100. Gonna buy it for parts.

[Mole1333]

Ok, I replaced the injectors and rail assembly, still runs bad, swapped out the Module and all 3 coil packs, no change. It runs extremely rich and I just can't seem to stop it. Possible the ECM is fubar'ed? I do have a small water leak on that side of the firewall, but it seems to run behind the sound deadener, but who knows it if ever came into contact with the computer. So far I have done Module, coil packs, wires, plugs, injectors, rail, fuel pressure regulator, IACV, tested the crank and temp sensor and catalytic. So I have the TPS, O2 sensor, harness and ECM left. Any other guesses? I'm stumped, just gonna swap out the rest of the parts and hope for the best.

[pmaniac69]

did you replace the sensor the tells the computer what the water temp is? I can't remember wtf its called, but its right below the TB pretty much

[1988GTU]

You could buy my motor for 300.00 if you are into that buying motors mood. ??

I'd hop on that CTS and replace it. Located right under the T stat just under the throttle body assembly.

[pmaniac69]

^ THATS it, CTS sensor

[robertisaar]

putting sensor behind CTS is like saying ATM machine...

Coolant Temperature Sensor...

[1988GTU]

^ THATS it, CTS sensor

Say it with me.

Coolant... Temperature... Sensor.

[pmaniac69]

lol, hey, I can't remember everything, least I remember what it did

[1988GTU]

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