st185 3sgte dump pipe/catalytic converter/oxygen sensor question...

[drumerboyben]

Hey All,

I've just picked up an st185 but it doesn't seem to be going as hard as I would have expected, planning to check through the timing and valve clearance and do plugs and maybe new leads etc soon, but what I wanted to know is this:

It came with an aftermarket dump pipe on it which is (I assume) where the original catalytic converter went, with the oxygen sensors at the top and bottom of the pipe. Wouldn't this mean that without the cat there anymore (it appears to be now further down the line) that the second oxy sensor would be getting exactly the same reading as the first one as they're both before the cat? Wouldn't this then result in a whacked fuel mix because the ecu would be trying to reduce the emission reading in the second sensor? I'm wondering if this could be part of the sluggish performance issue?

I've I've got something all wrong here please feel free to straighten me out....

Cheers,
Ben

[thechuckster]

O2 sensors are only used at cruise and warm idle.

Not quite sure about systems that have pre-and post CAT sensors but you'd only notice any change when at cruise. Once you got to accelerate, the ECU goes open-loop and uses the base maps for accel enrichment and fueling (and spark).

Might be worth giving the engine & turbo a decent inspection (e.g. look at turbo, air filter, plugs, coolant, oil, etc) plus what you planned (check base timing, pull plugs, etc).

[jonathan yee]

the 3sgte only has 1 O2 sensor at the top of the dump. some have a cat temp sensor down the bottom, but they don't do anything.

after checking your ign components the other most likely cuase is the AFM. some people stuff with the idle mix screw.

[drumerboyben]

Thanks for the replies fellas, gotta love toymods community =D

Replaced the air filter, cleaned the AFM checked the timing(was fine) changed the plugs tonight, was going to do the leads as well but found the ones I bought are 7mm at the distributor end when it looks like I need the 5mm ones so hopefully can sort that tomorrow.

Thanks for the tip on the AFM idle mix screw, wouldn't surprise me - whoever worked on the car before I bought it has done some pretty stupid things so there's a good chance that's it. Coolant is good, oil changed last week, haven't had much of a look at the turbo yet, will check that too...

I think what's really not helping is this though:
When I pulled cooler off to get at the plugs the rubber hose between the turbo and the cooler tore about a third of the way around just under the hose clamp, I have a feeling that it may have been leaking air already and I just hadn't noticed what would have previously been a small tear. Gonna pick something up from here tomorrow or the day after and see how it all goes.

Cheers,
Ben

[jonathan yee]

ah yeh a boost leak will make it run bad esp with the AFM.