So me and a couple of buddies installed LG street headers on NYE. There was a log of belly-aching about the lack of room in a C5, primarily getting out the plugs (and plug wires), by this over 50 crowd. But things actually went pretty smoothly. Guys also noted that the headers and plugs don't get torqued down very tightly. But they did all to spec's.

We reinstalled the old plugs and wires since the vert has only 10k miles.

Now we're not rookies to this kind of stuff, but its been over 20 years for each of us.

SInce I am still waiting for the correct cats from LG, we bolted on the off-road setup and I wired up the O2 sensors exactly matching the stock setup.

Well, we fire her up and she starts running rough after warmup (seems to run fine while warming up). So I double check the O2 sensors, plug wires, turn out lights and look for arcing. Nothing.

With the help of a couple great folks on this forum, I check a few things this week, figure out that its throwing codes, p171, 300, 500. So then I call LG and Mike tells me that its either a plug wire or plug. Makes sense so I order a new set of plugs and wires from Gene at Fred Beans.

I'm still waiting for the plugs/wires and the cats. And the C5 is still up on the jack stands. (Hell, its winter here in CHi-town and C5 is in dry dock.)

Well, I pull the plugs out today and what do I find? Wires are clean. No cracks, nicks, anything. No cracks in any of the plugs. MY BUDS DID THEIR HISTORICALLY GREAT JOB. But.......... All four plugs on the drivers side are sooty black, while the plugs on the pass side were pretty brown/clean. (The plugs were all decent when pulled out.)

So now I'm a little hesitant to button her back up without becoming a little more comfortable that a new set of plugs/wires is going to address this. (I must admit goofing around with the plugs is a PITA!)

ANybody had this kind of problem before? ANy ideas on what else to check.

Thanks for any advice.
Dick

 

With the LG's the o2's do not cross, the drivers side goes to the driver's side and the passenger's side goes to the passenger's side.

That should clear it up.

 

I assume you are speaking about the front O2's, RIchie. Yes, that is the way that mine are wired up. Exactly like stock. And the fuse is good too. And all wires are well off the headers.

D

 

its a spark plug, bolt her back up and try it.

 

your faults are for:171 left bank[1],running lean,500 vss [vehicle speed],300 random misfires.first,make sure the 02's are plugged in correct.if they are,look for the air leak on bank 1[left/drivers],that will explain your 4 sooty plugs,they all came out of the bank with the fault],for it to fatten up all 4 cylinders, you have a air/vacuum leak,you will hear it,it's big enough to hear if it fattened the whole bank[are you sure you have the brake booster plugged all the way in?].
if no leak,check for crossed o2's.300 is because of above.500 is a vehicle speed sensor fault.

 

Thanks for comment, Don.

I agree. THat's why I started thread. Whole bank appears affected.

Looked for vacuum leak on dr side and could not find any. I listened and did not hear anything. In fact, when I pulled plugs today, I yanked booster (after 3 days not running) and it still had vacuum. Not sure what else on that side is connected to vacuum "system". But will recheck all connections.

I ignored the 500 code since vert is still up on the jacks.

I guess I'm about to cross the O2's out of frustration and see if they work that way.

D

 

are the crankcase hoses back on the valve cover[assuming you pulled them to put the header in],is the header tight?,exhaust leaks near the o2,loose o2,etc.something is telling the o2 it's all air.
on the o2's.the ones in the collectors are the fronts.the left collector goes to the left side and the right to the right.

 

I'm beginning to tri-angulate this................

I will recheck, but yes, the hoses were reinstalled like stock. When I pulled the drivers side apart to get at the plugs, all was well. On the pass side, we pulled the valve cover, but there were no vacuum lines pulled.

Now you have gotten me to thinking. Is it possible that I might have put the front O2 sensors into the back connectors? THat might explain the prob, but I labeled everything as I took apart. Duh.................

Us 50+ folks have been known to err......................

 

your car is a 04 so you HAD to use your ORIGINAL 02's up front,correct.if that's the case you can't plug fronts into the rear plugs,because they are different shapes.how many 02's are you using?
if you took off the right valve cover,you had to have taken off 1 or 2 pcv vent hoses[i can't remember if it's 1 or 2 ,but i know they're there on my 03]

 

I did not know they were different shapes. I'm not under C5 right now, but my recollection is that all 4 O2 connectors were the same. SO you just told me something new.

I had labeled all connectors when I took apart (could tell things were getting complicated), so that I would know how to put back together.

Stupidly, I WAS using all 4 O2 sensors. Then I got corrected by guys on this forum, since I don't have the cats installed yet. SO the rear ones were disconnected, but I was also told that this would not cause the misfire.

Yes, I used the original O2's sensors up front, with the LG extensions. Dr side to Dr side and Pass to Pass (the rear ones go to the reverse side). I was given a hint to reverse the fronts, but have not doen so yet.

 

DO NOT CROSS THE FRONTS! plugging in the rears doesn't matter as they only monitor the cats,sounds lke the fronts are right.i still thing you have some type of leak on the left bank[air/vacuum,etc.].if you plug in the rears,cross them.start up the car and spray carb cleaner around the intake/valve cover,etc.]f you have a air leak you will hear the rpm's pick up.

 

Based on what's going on, I agree with you Don. I'll check tomorrow morning. thx

 

Double check and make sure the passenger side front O2 sensor is routed and plugged into the connector on the driver's side and visa versa. Check your coils too, I don't know if it matters but when I did my header install I marked which coil unit went on which side of the motor and reinstalled accordingly. Good luck!

 

Since I have made a mistake with the same symptoms :bb You might want to check and see if the FUEL RAIL on the PASSENGER SIDE is plugged in correctly. I forgot to completely seat the plug for the injectors and had the same issue, drivers side rich car missing like crazy.
Bob

 

This is the opposite of the way I have the wires installed, which were labeled when I disassembled. In fact, the wires on the front O2 sensors are too short to reach to the other side on a stock install.

Thanks, Bob. Yes, I checked and both dr and pass side plugged in correctly.

Just went over everything again. All seems consistent with above recommendations with the exception of my answer above (terlox).

I should point out that she starts right up and runs fine until she warms up. Then sounds like she is "loading up" and runs rough. If I rev 'er up she loosens up and runs smooth, only to get rough again back at idle.

Guess I'll have to wait for new plugs and wires, button her up and fire her up again.

 

That is not correct Drivers side to drivers side, passenger to passenger side. The confusion is that they point in opposite directions.
There is a reason for that.

 

i don't think plugs and wires are going to fix it.if you still get p0171,plugs/wires are not going to fix it.if EVERYTHING checks out ok[no air/vacuum leaks],etc.did anybody drop any of the o2 sensors?
here is a test,swap the front o2 sensors side to side,if the right bank[bank 2] now shows the lean fault you know you have a bad o2.

 

I was just about to swap them. Great minds think alike. :-)

 

Did you look at my idea ? There were more than 2 hands in there. Check each connector, unplug them then plug them back in

 

On my '00 C5 the FRONT O2 sensors cross over eachother and plug into opposite sides (pass side plugs into driver's side, driver's side plugs into pass side). The car runs awesome so I know it is correct - I've heard the kinds or problems people encounter when they get the front O2's mixed up.