Hey all, I've got an 85 SE 4 cyl auto. The original manifold blew out the bung with the O2 sensor, so I replaced it with an el cheapo (I'm so sorry I spent so little) Spectre exhaust manifold from Rock Auto. New O2 sensor too. After about 150 miles I'm getting a code 21, TPS sensor Check Engine light comes on for a minute when I first start the Fiero, so I have a new one ready to go on. The MAP sensor is on the air cleaner, didn't think that was bad... getting a lot of oil in various places in the intake. Spark Plugs are new, no arcing that I can see at night, and I get an intermittent code 44, low O2 signal, running lean. Last time the car ran lean (vacuum leaks) I got glowing hot exhaust manifolds and a melted throttle cable. Not now; The Check Engine light comes on only at sustained higher speeds, and will go out after a minute at low engine speed, under 1500 RPM. So here's my question... do you think the cat could be marginal?


Man, I want an engine swap!

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John DuRette
Custom 85 SE/86 GT
"Kinda makes you nostalgic for a Members Only jacket"

I highly doubt it. A clogged cat is going to give you an odd exhaust note, almost no power and an inability to reach higher RPMs. Now I realize that this describes a properly functioning 'duke rather well as well, but I mean more so than usual. The O2 sensor hardly cares what the cat is doing. And if the engine is having a hard time breathing, I highly doubt it would go lean.

Lots of oil in the intake might be something as simple as a PCV valve that's not working right, but it often indicates worn down rings and such increasing the crankcase pressure.

Sounds like your new O2 sensor isn't good - or maybe the wire to the sensor is shorting to an exhaust pipe or sharp edge somewhere.

When diagnosing SES codes, what it says is usualy the last thing it is, unless its just a dead sensor.

Low O2 usualy indicates a vacum leak, the ECM thinks the engine is running lean. Could also be EGR issue, maybe the valve is leaking. How is the idle?

The Cat cant cause a SES code, there is no sensors after it, so the ECM doesnt care.

Are you sure its not an EGR code, how you say the SES light is acting sounds like EGR, which only comes on at sustained cruising speeds.

How long since you changed your fuel filter? Mine would start missing and light the SES when at higher cruise but go off when I slowed down. It just kept getting worse until I changed the fuel filter.

Hudini, I agree with you on the fuel filter analysis; I change it every year, so it's only 5 months old. I had replaced the fuel pump relay a while back, I know it's working. I'm still looking for vacuum leaks. Replaced the TPS today, started it up to check everything, and within a couple minutes the idle was at 1000 RPM on the nose, no SES light. That's a good start. I did tighten up exhaust manifold bolts, and because one bolt is actually a stud with (I feel) a dodgy bolt, I'll probably replace that soon. Tightened that, the EGR, TB and some intake bolts that just seemed loose to me... and that after I torqued them a year and a half ago when I replaced the head gasket... checked the routing and connection of the new spark plug wires... you know how stuff comes loose...
If I go a day or so without the intermittent SES light, I'm pretty sure it means that solitary exhaust bolt is backing off. I'll probably just replace it on my next day off.