People with Longtubes...

leakyfaucet · Nov 19, 2004

Did you ever notice problems with getting trouble codes 41, and 91 (oxygen sensors showing lean mixture), or any problems related to oxygen sensors or running rich when you installed the longtube headers? I've heard that this can cause the oxygen sensors to show a lean mixture, causing the engine to run rich. I believe I'm currently having this problem, and was wondering how you guys solved the issue.

I have MAC longtubes and I didn't use the o2 sensor extenders, by the way. My harness was long enough, apparently.

Thanks! Any and all responses are much appreciated!

notchman90 · Nov 19, 2004

yea i have mac l/t's as well and i get those codes. I learned to live with it. I was told that moving the o2 sensors closer might help.

leakyfaucet · Nov 19, 2004

So you've noticed your car running really rich and having black tailpipes? =\

I'm curious, what kind of mileage do you get?

Ourobos · Nov 20, 2004

I had mac 1 5/8s, rerouted my harness also, and no problems whatsoever.

NCStang86 · Nov 20, 2004

I'm running BBK longtubes and I've never gotten any codes like that.

Michael Yount · Nov 20, 2004

leakyfaucet - your gas mileage is bad I guess? Black tailpipes don't necessarily indicate a rich mixture on contemporary cars. My car pulls a consistent 13:1 a/f on the dyno; gets 18-20 around town, 24-26 on the highway with 3.73 gears. My wife's newer BMW runs perfectly - 38-40 mpg on the highway. Both have black tail pipes. Unleaded fuel looks that way. Isn't like the old days of leaded fuel and a nice light gray tail pipe meant you had it running really good. Similarly, white spark plugs don't mean it's running too lean. Those same two cars I described above both have white spark plugs. In fact, at 60K I did a plug change on the wife's Bimmer and except for the grime on the threads, I couldn't tell the 60K mile plug from the new one. Both were completely clean/white.

Have you had the car on a dyno with a wide band? What kind of injectors/maf are in the car?

leakyfaucet · Nov 21, 2004

Michael Yount said:
leakyfaucet - your gas mileage is bad I guess? Black tailpipes don't necessarily indicate a rich mixture on contemporary cars. My car pulls a consistent 13:1 a/f on the dyno; gets 18-20 around town, 24-26 on the highway with 3.73 gears. My wife's newer BMW runs perfectly - 38-40 mpg on the highway. Both have black tail pipes. Unleaded fuel looks that way. Isn't like the old days of leaded fuel and a nice light gray tail pipe meant you had it running really good. Similarly, white spark plugs don't mean it's running too lean. Those same two cars I described above both have white spark plugs. In fact, at 60K I did a plug change on the wife's Bimmer and except for the grime on the threads, I couldn't tell the 60K mile plug from the new one. Both were completely clean/white.

Have you had the car on a dyno with a wide band? What kind of injectors/maf are in the car?

Oh, my gas mileage is terrible. I'm talking 15 mpg or less. And no, I don't go WOT 90% of the time. You can smell the excessive fuel coming from the car at idle. You can smell it from 10 feet away. Althought black tailpipes don't necessarilly represent the car is running rich, I think it is excessive when the tailpipes go from squeaky clean to jet black in about 3 days. And although this isn't really necessarily a perfect comparison, my brother has a 2001 GT with the same exhaust system after the H pipe that I have (I have a 2002 GT exhaust) and the insides of his tailpipes stay squeaky clean. And it's not from cleaning it. Although the fact that he has 4 cats may have something to do with that.

I have an adjustable fuel pressure regulator as well as a pressure gauge. I've had it set to 40 lbs with the line off, about the same as stock. So I know I'm getting proper fuel pressure. I haven't been on a dyno with a wideband, however, I'm so sure the car is running rich I don't feel I need to.

My sensors don't get warm if I leave the key in the on position. I've let it sit there for 20 minutes or so. They're heated, so they should warm up, right? Can anyone else verify if this happens? I'm just trying to track down the problem, I'm having trouble affording the gas for this car with the rising prices. I fear if I can't fix this sometime soon I may have to sell the car.

Thanks for the help, guys!

JamesB88 · Nov 21, 2004

I have the same exact problem, runing rich, bad gas mailage, Is your car also cold blooded like mine?

leakyfaucet · Nov 21, 2004

JamesB88 said:
Is your car also cold blooded like mine?

Huh? My car reaches normal operating temperature, if that's what you mean. If your car is running too cool, it won't ever reach closed loop operation and you're guaranteed to have bad gas mileage.

Michael Yount · Nov 21, 2004

"If your car is running too cool, it won't ever reach closed loop operation "

Not true - although many think it is. The engine/ecu is designed to get to closed loop asap because it reduces emissions - especially during cold operation which is one of the dirtiest operational times for the engine, and the EPA testing protocol. The engine goes to closed loop as soon as the O2 sensors are warm enough to provide a signal - between 500-600F. This rarely takes longer than 90-120 seconds even on a cold start with unheated O2's. With heated O2's it can occur as quickly as 15-30 seconds after start up.

The parameters for cold running are different than once things warm up (ECT/ACT based) -- but the ecu goes to closed loop just as soon as the O2's are warm enough. It doesn't care what the coolant or air temps are. Contrary to popular belief, a 160 t'stat won't keep you out of closed loop - although that's no reason to use one.

leakyfaucet · Nov 21, 2004

Interesting. I've been told that closed loop was related to coolant temp so much I believed it. I always wondered why the ECU cared what the coolant temp was when it started looking at what the o2 sensors were saying.

So, any word on if the o2 sensors heat up just from switching the key to "ON"?

Michael Yount · Nov 21, 2004

Don't misunderstand - the ecu definitely cares about ECT; just not with regard to closed or open loop function. I take that back - if the engine gets too hot, the ecu drops out of closed loop, and injects more fuel (rich) to try and cool the combustion chamber. On cold start the ecu richens the mixture until the engine warms enough -- just like a choke on a carb; but much more finely controlled. But, it gets into closed loop just as quickly as it can - because it does a better job of controlling emissions in closed loop.

JamesB88 · Nov 21, 2004

By cold blooded i mean it doesnt want to idle or run good util you warm it up for atleast 5-10 minutes.

leakyfaucet · Nov 21, 2004

JamesB88 said:
By cold blooded i mean it doesnt want to idle or run good util you warm it up for atleast 5-10 minutes.

Nope mine idles fine when it's cold. I used to have a warm idle surge problem for the last year and half but it seems to have disappeared with my recent battery unplugging. It's been 3 days and not one surge.

Hydrocarbon · Nov 22, 2004

Check for 12v KOEO at the gray/yellow wire on the connector for the o2 harness. This wire is the power for the heating elements in the o2's.

I had a broken gray/yellow wire. With my long tubes, the o2's would cool at idle, and stop producing voltage. That would cause the computer to read lean and throw codes 41/91.

leakyfaucet · Nov 22, 2004

I'll do that if I can get my hands on a voltmeter. But by the connector, do you mean the part that plugs into the o2 sensor or the connector at the main harness that plugs into the o2 sensor harness?

John98-4v · Nov 22, 2004

When you install longtubes, you move the 02 sensor downsteam, this makes it difficult to reach the temerature it should be reading, thankfully I don't have that problem cause I have heated 02's.

leakyfaucet · Nov 22, 2004

I have heated o2 sensors too. Althought I don't think they're working...

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