Probems after new exhaust

[97GSTee]

Ok, so i was installing my new HKS cat-back exhaust. In the process i broke my downstream o2 sensor, well i replaced that and the spark plugs as well. But when i start my car up it idles extremely low, and has a lot of trouble revving over 2000rpms when i gas it. I ran my obd2 and it came up with these codes:

MAF or VAF Circuit malfunction
Engine Coolant Temp malfunction
IAT sensor malfunction
MAP / BARO Circuit malfunction

Any help will be appreciated

 

[super97gst]

Ok, so i was installing my new HKS cat-back exhaust. In the process i broke my downstream o2 sensor, well i replaced that and the spark plugs as well. But when i start my car up it idles extremely low, and has a lot of trouble revving over 2000rpms when i gas it. I ran my obd2 and it came up with these codes:

MAF or VAF Circuit malfunction
Engine Coolant Temp malfunction
IAT sensor malfunction
MAP / BARO Circuit malfunction

Any help will be appreciated

well, that only gives you 2 options. the coolant temp. sensor and the MAF. The MAF contains the IAT sensor and Barometric pressure sensor.

 

[97GSTee]

Do you know what could have caused that? I never got any CEL's before the exhaust so i'm confused and thinking and it has something to do with the new exhaust, but then again, i don't see how that could cause all this. Also...do you think this would be an easy fix? if so, how? thanks

 

[97GSTee]

any ideas?

 

[kenamond]

any ideas?

Are you sure you wired the new rear O2 sensor correctly? Some of the ECU gurus might have to chime in, but I believe the rear O2 has a sensor signal ground and heater ground. The sensor signal ground is much more sensitive to noise, and all sensors share a common signal ground that is separate from the other grounds to keep the sensor signals clean. If you mess up the wiring and get the heater voltage going to the shared sensor signal ground or the sensor signal voltage going to the normal ground, that might cause problems for all of the other sensors (you've contaminated the ground used by all of the sensors).

 

[super97gst]

Are you sure you wired the new rear O2 sensor correctly? Some of the ECU gurus might have to chime in, but I believe the rear O2 has a sensor signal ground and heater ground. The sensor signal ground is much more sensitive to noise, and all sensors share a common signal ground that is separate from the other grounds to keep the sensor signals clean. If you mess up the wiring and get the heater voltage going to the shared sensor signal ground or the sensor signal voltage going to the normal ground, that might cause problems for all of the other sensors (you've contaminated the ground used by all of the sensors).

While searching on my po300 situation i ran across several threads where this was discussed. However the way i see it, it's a case by case situation. For example, when i installed my Greddy Evo 2 catback and test pipe I eliminated the cat. While this of course threw a rear 02 sensor code immediately it didn't affect any other sensors. But I have read some that somehow cut or frayed the ground or the heater signal wire, the car went haywire.

There is a ground strap that runs from the subframe to the downpipe. Did you re-attach it to the new exhaust?? That one small strap does make a small difference for grounding the rear 02 sensor. That also seems to be different from car to car.

 

[super97gst]

Do you know what could have caused that? I never got any CEL's before the exhaust so i'm confused and thinking and it has something to do with the new exhaust, but then again, i don't see how that could cause all this. Also...do you think this would be an easy fix? if so, how? thanks

The exhaust install probably doesn't have anything to do with your problem. But it of course is possible it could, you could have loosened something accidentally. Engine parameter sensors are very sensitive to certain temps and vibrations. Most of the time however sensors just go wear out just like everything else. As to the difficulty of the sensor installs, you shouldn't have any problems installing either of those. Like i said before the IAT and barometric pressure sensors are in the MAF, so on those you will just replace the entire MAF. The coolant temp. sensor is located on the thermostat housing. It's the 2 pronged connector. Just drain the coolant level down below the thermostat housing and unscrew the CTS. Wrap teflon tape around the new sensor and install. Easy.

 

[i r teh winnar]

I would check your MAF and make sure that the clip is entirely hooked up. I have experienced a similar problem, come to find that the plug had come loose from the clip and thus freaking the MAF out.

It was dumping fuel, wouldn't idle without me on the gas, and sputtering. Just check and make sure all your connections are tight! Your CTS may have also come loose on your exhaust install. Very feasible.


Keep us posted!

 

[97GSTee]

thanks for the advice...great ideas...i looked at the MAF sensor and unplugged and plugged it back in to make sure it was secure..
Super97Gst:

Engine parameter sensors are very sensitive to certain temps and vibrations.

That would make a lot of sense haha, when i was installing my catback, i had to the cut the head of the bolt off the back of the cat...and in an attempt to get the leftover stud out to bolt in my new exhaust, i was lubing it and trying everything from channel locks to bolt extractors and of course a hammer...thats why i think the vibrations definately set something off.

and sorry for being a "noob" (i hate saying that) but by the CTS, you mean coolant temp, sensor right? This is the first car ive worked on, so im learning bit by bit

 

[super97gst]

thanks for the advice...great ideas...i looked at the MAF sensor and unplugged and plugged it back in to make sure it was secure..
Super97Gst:

That would make a lot of sense haha, when i was installing my catback, i had to the cut the head of the bolt off the back of the cat...and in an attempt to get the leftover stud out to bolt in my new exhaust, i was lubing it and trying everything from channel locks to bolt extractors and of course a hammer...thats why i think the vibrations definately set something off.

and sorry for being a "noob" (i hate saying that) but by the CTS, you mean coolant temp, sensor right? This is the first car ive worked on, so im learning bit by bit

I had to do the exact same thing when I installed my catback. The studs on the back side of the cat were rusted up badly. I'm lucky i didn't blow my car up though, I got pissed and took out the acetylene torch and went to cutting. I absolutely DO NOT recommend doing that to anyone though. Definitely one of the dumbest things I've done on this car. The fuel feed/return lines are like 6" from where I was cutting. BAD.

Hey, you don't have to apologize for anything. Everybody has to start somewhere. When I say CTS, yes, I mean Coolant Temperature Sensor. Did you install just a catback exhaust?? Or did you install a downpipe as well?? If you only did the catback then the ground strap I mentioned before doesn't apply. That ground strap is connected to the stock downpipe, but most aftermarket downpipes have a connection for them.

 

[kenamond]

Not sure how different the FWD cars are from the AWD, but I think it's easier to drop the whole exhaust and try bashing the sections apart out in the driveway where you can get a good swing on the sledge

I got mine apart without breaking anything (rounded off a couple of nuts). It was a MAJOR pain even with it out in the open, and I live in a very dry climate. But with it off the car, you have many more (safe ) options.

 

[super97gst]

Not sure how different the FWD cars are from the AWD, but I think it's easier to drop the whole exhaust and try bashing the sections apart out in the driveway where you can get a good swing on the sledge

I got mine apart without breaking anything (rounded off a couple of nuts). It was a MAJOR pain even with it out in the open, and I live in a very dry climate. But with it off the car, you have many more (safe ) options.

I think the only difference is how the exhaust piping is routed near and around the rear axle. And i'm sure your right that it's easier to just drop the entire exhaust and tear sections apart in the open. I should have thought to do that on mine since the downpipe came off easily. However, for a week before I did the downpipe install I sprayed WD-40 on the 02 sensor housing - downpipe studs and nuts then drove the car. By spraying penetrant on the bolts cold then driving the car the heat draws the penetrant into the threads of the stud. Worked really well. Definitely would have been a lot better than the fireball I was making underneath there.

 

[97GSTee]

Hey, you don't have to apologize for anything. Everybody has to start somewhere. When I say CTS, yes, I mean Coolant Temperature Sensor. Did you install just a catback exhaust?? Or did you install a downpipe as well?? If you only did the catback then the ground strap I mentioned before doesn't apply. That ground strap is connected to the stock downpipe, but most aftermarket downpipes have a connection for them.

I only installed the catback...i was about to order a new downpipe and testpipe and now I'm glad I didn't go through with it, because I'm starting to think I should take my car into the shop and I'd need the money for that. It's mind boggling to me. When i start my car up it rev's so extremely low that it shuts off sometimes, and when i give it any gas, it barely moves, i feel like im flooding it almost. And then I get all these codes from the OBD2.. Im lost

 

[super97gst]

I only installed the catback...i was about to order a new downpipe and testpipe and now I'm glad I didn't go through with it, because I'm starting to think I should take my car into the shop and I'd need the money for that. It's mind boggling to me. When i start my car up it rev's so extremely low that it shuts off sometimes, and when i give it any gas, it barely moves, i feel like im flooding it almost. And then I get all these codes from the OBD2.. Im lost

Just try swapping the CTS out for a new one. If you have a buddy that has a 2G turbo, swap his good MAF onto your car and see if it makes a difference. If so you know what you have to buy to fix the problem.

 

[97GSTee]

i wish haha, im surrounded by mostly ls1's and ws6's...do you think it could be the entire ecu? and another question...where is the cts screw at? :-/

 

[super97gst]

i wish haha, im surrounded by mostly ls1's and ws6's...do you think it could be the entire ecu? and another question...where is the cts screw at? :-/

Well, there is a possibility that the entire ecu could be a little scrambled, but it's unlikely. The CTS is located on the thermostat housing. It is the 2 pronged wire connector, on the top.