S13 running rich--Exhaust Manifold Leak To Blame?

[mhosey33]

I have a 92 240sx all stock and I have been having intermittent problems with it running rich and running rough for several months.

It will do it once or twice and then not do it for a couple of weeks, but recently it has been acting up alot more.

Here is what I have done to it, new plugs, wires, cap and rotor button, O2 sensor, tried different MAF sensor and put in new coolant temp. sensor and all of this has not helped.

I took it to my local mechanic and he checked it out and he is pretty much at a loss, he did say that since the exhaust manifold was leaking that it may be messing up the air/fuel ratio in some way, but he was not positive in this.

I am getting ready to take it to the dealership to see if they know what is going on and I was Just wondering if anyone had any suggestions or had encountered this problem before.

Thanks in Advance Guys

[DAEDALUS]

Does it seem to be temperature dependent? Like do it when it's cold out, or when the engine is cold?

"he did say that since the exhaust manifold was leaking that it may be messing up the air/fuel ratio in some way, but he was not positive in this"

That scares me. I don't see how it could be related unless your exhaust manifold is somehow in front of the intake.

[mhosey33]

It really doesn't matter what the temperature is outside or what temp. the engine is, it does it at start up sometimes and after driving 40 miles sometimes.

This thing is driving me crazy, I figure it is about dealership time unfortunately

thanks for the help

[DAEDALUS]

I saw Cav's post in technical. Didn't think about the leak actually drawing air in. I suppose that is possible since there is a partical vacuum after each exhaust pulse.

If it's a potential cause, why not fix the exhaust leak first, since you should anyway, and then see if it changes anything?

[mhosey33]

Well I went and had my exhaust manifold looked at today and there were a couple of welds needed to stop the leak. Also the mechanic found there was a exhaust recirculation tube(going to sensor?) that bolts into the manifold was loose and not screwed into the manifold.

Got it welded up and the tube fixed and so far it is running good

I hope this does it, I have my fingers crossed

Anyway thanks for the replies DAEDALUS , I appreciate the input