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Scott and I just went for a ride with his laptop and I was getting some strange readings.

First, my speed sensor isn't working. My speedometer is working but the ECU isn't receiving a signal. F***! How do I fix that? Does the whole gauge cluster need replaced or what? Is the sensor part of the speedometer or what?

Second, looks like my O2 sensor is on the fritz again. Double F***! I was getting readings fairly solid at .8-.9 and then out of no where, without a change in throttle or speed, it would drop to like .08. Then after awhile it actually went to 0.0 and stayed there. I hope the snesor itself is just fried and it's not a wiring problem again.

So anyways, I think the speed sensor is the main reason my car has been driving so weird lately. The O2 sensor doesn't help either but for now I'm just going to unplug it.

Can someone explain where the speed sensor is and what is required to fix it?

Arrgh, where's Vikash when you need him?!

I doubt you have an oxygen sensor wiring problem. Going straight from the ECU to the O2 sensor is as direct as it gets.

I bet the only problem your having is that it's not properly grounding on the downpipe. Perhaps remove it, wire-wheel the contact on the downpipe (remove the ceramic) and try again.

About the speed sensor, you should take it back to the shop you had replace the cable and have them replace it. Remember, it worked before you took it to him, now it doesnt...

Are you throwing an ACTIVE speed sensor code? What if you reset the ECU, then what?

Hehe, sorry, I've been at a wedding.

Luckily, you can easily inspect all your oxygen sensor wiring. If the problem is indeed the ground (your downpipe is stainless with a ceramic coating or something, isn't it?) you could attach a 20-gauge ground wire to the sensor with a hose clamp and just attach the other end to an intake manifold bolt or something with a ring terminal. Disconnecting it for now seems like a good way to go.

I haven't examined it in person, but my understanding is that the VSS is a little reed switch built into the speedometer, that clicks on and off as the cable turns. It's possible for the speedometer to work even if the VSS doesn't.

But your VSS used to work.

Maybe your ECU is indeed on the fritz. I'll bring a spare to the Feed & Speed.

Hmmm, maybe I'll try the grounding thing.

That'd be sweet if you bring an ECU to try out Vikash.

My laptop cable broke yesterday. Let me repair it and we'll go for another run.

Right on. At the rally it seemed to start running a bit better, like maybe the VSS started working again or something. The severe hesitation seems to have dissapeared but at the same time once on boost, it seems slower. My boost gauge isn't working right either, I don't think.

Man, I'm getting really annoyed. I'm hitting FC all the time! I don't understand it. I have the FCD and the Walbro 255, so what gives?

My boost gauge is only reading 9 psi too. The car feels faster then 9 psi so I don't know if it's actually 9 psi, the gauge is bad, the vacuum line has a hole in it (this is what I suspect) or the MBC is stuck open.

The thing that sucks is I have no time to trouble shoot this crap anymore. The weird electrical problems with this car are driving me mad!

I really hope the ecu ends up being the problem because at least that'd be an easy fix.

The only other thing I can think of it maybe being that is causing the FC is how I was saying the O2 sensor was putting out weird readings. It will be reading .9 and out of no where it will drop to .09 for just a few seconds, then bounce back to normal. Maybe the ECU is seeing that and cutting fuel. The thing is that we noticed that when not on boost and it wasn't cutting fuel then.

legacy92ej22t wrote:Man, I'm getting really annoyed. I'm hitting FC all the time! I don't understand it. I have the FCD and the Walbro 255, so what gives?

My boost gauge is only reading 9 psi too. The car feels faster then 9 psi so I don't know if it's actually 9 psi, the gauge is bad, the vacuum line has a hole in it (this is what I suspect) or the MBC is stuck open.

The thing that sucks is I have no time to trouble shoot this crap anymore. The weird electrical problems with this car are driving me mad!

I really hope the ecu ends up being the problem because at least that'd be an easy fix.

The only other thing I can think of it maybe being that is causing the FC is how I was saying the O2 sensor was putting out weird readings. It will be reading .9 and out of no where it will drop to .09 for just a few seconds, then bounce back to normal. Maybe the ECU is seeing that and cutting fuel. The thing is that we noticed that when not on boost and it wasn't cutting fuel then.

I think I had the same issue with the boost gauge on a previous car. I had a big ole vacuum leak and it would boost like crazy, but only show a little PSI. As far as the FCD not working, I think it is, but your injectors might be at 100% when you hit cut.

Ran new vacuum line for the boost gauge and that fixed that!

Still hitting FC all the time though. It makes me cry.

legacy92ej22t wrote:It will be reading .9 and out of no where it will drop to .09 for just a few seconds, then bounce back to normal.

This could be the oxygen sensor indicating a misfire... But a few seconds sounds too long for that.

Maybe the ECU is seeing that and cutting fuel. The thing is that we noticed that when not on boost and it wasn't cutting fuel then.

Keep in mind that when the ECU's really busy (like at high RPMs and/or high loads), it sometimes stops reporting values to the scan tool. It's possible that the oxygen sensor reading is doing the drop-to-low-values thing even on boost, and that that is triggering a fuel cut.

Hmmm, sounds reasonable. What would cause the O2 sensor voltage to drop off like that. Do you think the ground would consistantly do this?

I can't really see how a ground-through-the-sensor-body could fail intermittently for seconds at a time, no.

Is that little bullet connection between the sensor and the rest of the wire solid? Maybe it's coming loose or something.

I think it's OK. It clicks in and seems nice and tight.

I think maybe the sensor itself is just on its way out.

Well, we'll try a different sensor at shop night, then, I suppose... But it's an almost-new sensor, no?

Ya, it's pretty new but it sat out the whole time I was doing my swap too. It might be ok, but what else would cause the problem I'm seeing?

Either way, I'm not 100% sold that it's what's causing the FC issue either. I'm really hoping it might just be the ECU.

Can the knock sensor induce FC? It usually just retards timing to counter knock, right?

Yeah, we can't know for sure...

I would believe that excessive knock sensor activity could trigger fuel cut, if retarding timing wasn't effective.

Do you think your motor's knocking though? Does the scan tool show much pinging and/or timing correction?

No, I don't think it's knocking really.

This motor is much slower then my other one though too. That could be attributed to the high mileage though I guess. It's just doesn't seem 100%. I don't know what's wrong.