MIL Tech Question

Dark_Horse · Mar 6, 2008

Is there any concieveable way for a pair of MIL eliminators to screw with the a/f ratio of the engine? I have been having this probelm with the car since I put the Mac o/r pipe and MIL eliminators on it a few months ago, where the car seems to spit out some colored smoke on occasion. Now it never did this before, either because the cats were masking the problem or there was no problem in the first place. Either way I'm getting bad carbon deposits on the tailpipes (I cant keep them clean) and after it has idled for long periods it will blow out bluish funny smelling smoke: http://forums.stangnet.com/showthread.php?t=739896

So bottom line, I'm thinking it's because of these new parts that im getting this response from the motor. Clearly it was not doing this before. Im thinking that the car is running too rich because it is not detecting the rear sensors, therefore spewing out rich carbon exhaust. I could be wrong on this.

The other explaination is a bad valve seal or bad piston ring as I found out in my first thread. But I cant shake the fact that the motor was sound before the install, and after it I'm having these problems. Am I completely wrong about the MILs or could there possibly something happening with the a/f ratio??????

281CI96Coupe · Mar 7, 2008

what kind of MIL's you have. I know my upr made my car run rich as hell. It felt faster but i had horrible gas mileage, and the car wouldn't get up to operating temp because of how much fuel was being dumped.

Superhereaux · Mar 7, 2008

the rear o2's do not effect the A/F ratio

AdRock · Mar 7, 2008

The rear O2's are there ONLY to tell the ecu whether the cats are doing their jobs or not. They have no bearing on how the ECU controls the air fuel ratio. The front O2's are what the ECU reads to determine things.

4.6andSlicks · Mar 7, 2008

The rear O2's or MIL's wouldn't effect how rich or lean the engine is but the lack of Cats sure would. That's a big drop in back pressure.

SilverBullet00 · Mar 7, 2008

As stated, your rear "02's" are just monitors, they onlything they do is throw a check engine light if you dont have cats...

281CI96Coupe · Mar 7, 2008

I beg to differ with all you guys, rear o2's do more than you think, it makes the ecu act different. Everyone says it doesn't do anything but shows a CEL. I think its the opposite, from my experience it made the car act different. Went i took them off, everything was back to normal.

Smokeurhonda · Mar 7, 2008

What most people are unaware of is that Ford actually does use the rear O2 sensors to control fuel trim. Of course the upstream is the primary monitoring, but there is a slight effect coming from the downstream. Anyone with a predator of scanner can see a reading under diagnostics that says REAR FUEL TRIM. For some reason when I read it, it will say either 7.99% or 0%. Not sure if this is because I have MIL's or if that's how the factory FOrd programming works.

Smokeurhonda · Mar 7, 2008

Dark_Horse said:
Is there any concieveable way for a pair of MIL eliminators to screw with the a/f ratio of the engine? I have been having this probelm with the car since I put the Mac o/r pipe and MIL eliminators on it a few months ago, where the car seems to spit out some colored smoke on occasion. Now it never did this before, either because the cats were masking the problem or there was no problem in the first place. Either way I'm getting bad carbon deposits on the tailpipes (I cant keep them clean) and after it has idled for long periods it will blow out bluish funny smelling smoke: http://forums.stangnet.com/showthread.php?t=739896

So bottom line, I'm thinking it's because of these new parts that im getting this response from the motor. Clearly it was not doing this before. Im thinking that the car is running too rich because it is not detecting the rear sensors, therefore spewing out rich carbon exhaust. I could be wrong on this.

The other explaination is a bad valve seal or bad piston ring as I found out in my first thread. But I cant shake the fact that the motor was sound before the install, and after it I'm having these problems. Am I completely wrong about the MILs or could there possibly something happening with the a/f ratio??????

Hey dude, don't worry about the black smoke. Cats clean up alot of fuel that gets dumped under wide open throttle. You remove the cats, you see the smoke. Maybe some MIL's do richen up the mixture, but some smoke is normal. As far as blue smoke goes, that is oil. If you think you have a compression issue that is probably it. Or check PCV to see if your pulling oil in through the intake.

Dark_Horse · Mar 7, 2008

That's really good to know. So the rear o2s do actually effect fuel trip, allbeit not by much. Either way I'm going to be changing the spark plugs in a couple of weeks and doing a compression test and seefoam while im in there. That should give me a good idea of whats going on with the motor. If I dont find anything after that I'm just going to put the stock h-pipe back on and take the MIL eliminators off.

BTW I bought the MILs off the guy on ebay, which I think he's based out of Tulsa or something. I'll keep this thread updated with video/pics of the compression test and seafoam. Surely after that we should know whats going on.

But clearly I cannot rule out that the new pipe did this to the motor as 1) its an ebay brand MILs and 2) rear o2s do have an impact on the fuel trim. Great info guys, much appreciated.

jstreet0204 · Mar 8, 2008

Dark_Horse said:
That's really good to know. So the rear o2s do actually effect fuel trip, allbeit not by much. Either way I'm going to be changing the spark plugs in a couple of weeks and doing a compression test and seefoam while im in there. That should give me a good idea of whats going on with the motor. If I dont find anything after that I'm just going to put the stock h-pipe back on and take the MIL eliminators off.

BTW I bought the MILs off the guy on ebay, which I think he's based out of Tulsa or something. I'll keep this thread updated with video/pics of the compression test and seafoam. Surely after that we should know whats going on.

But clearly I cannot rule out that the new pipe did this to the motor as 1) its an ebay brand MILs and 2) rear o2s do have an impact on the fuel trim. Great info guys, much appreciated.

Rear o2's are not controlling any fuel trims at all. You are getting the black smoke and carbon build up on the pipes because of the lack of cats. The EEC is programmed to run fairly rich stock during warm up and acceleration. You didn't see it before because the cats were doing their job and cleaning it up. The rich smell is just part of having an offroad pipe.

Shiroelex · Mar 8, 2008

+1. I have removed my rear o2s since i have disabled them with my handheld tuner, and nothing has changed at all. I did notice that it seemed to get better when I had the timing advanced.

varad · Mar 8, 2008

yeah what I think is that youre taking off the cats which is supposed to clean up emmissions. Without them, the exhaust is going to be like that

manpowermustang · Mar 8, 2008

I made my own MIL from numerous sites, costed a total of 11.53. I do more smoke, sorta whitish colors. Is this ok/

Smokeurhonda · Mar 9, 2008

Black smoke= Fuel
Bluish smoke=Oil
White smoke=Coolant or water
Grey smoke=you just burned up your pistons (usually on nitrous cars)

281CI96Coupe · Mar 9, 2008

Smokeurhonda said:
What most people are unaware of is that Ford actually does use the rear O2 sensors to control fuel trim. Of course the upstream is the primary monitoring, but there is a slight effect coming from the downstream. Anyone with a predator of scanner can see a reading under diagnostics that says REAR FUEL TRIM. For some reason when I read it, it will say either 7.99% or 0%. Not sure if this is because I have MIL's or if that's how the factory FOrd programming works.

This really makes sense....It does affect the car slightly, and I've noticed when the CEL is on. It feels like its holding some power back.

Shiroelex · Mar 9, 2008

When the CEL is on, it's because of the Catalyst Efficiency Below Threshold. The computer goes into open loop then, and your fuel trims go crazy. If you tune it properly to not have cats, it will be fine. The MIL eliminators just simulate a change in signal between the front and rear o2's so that code won't pop up, but it does nothing for the timing that must be changed due to the lack of backpressure, and the little bit of a/f ratio adjustment that also needs to be looked at.

jstreet0204 · Mar 9, 2008

Shiroelex said:
When the CEL is on, it's because of the Catalyst Efficiency Below Threshold. The computer goes into open loop then, and your fuel trims go crazy. If you tune it properly to not have cats, it will be fine. The MIL eliminators just simulate a change in signal between the front and rear o2's so that code won't pop up, but it does nothing for the timing that must be changed due to the lack of backpressure, and the little bit of a/f ratio adjustment that also needs to be looked at.

Dear god man! No offense, I don't think there is a single correct statement in that entire post except for the reason the CEL comes on.

First, Computer going in to open loop has nothing to do with the CEL. You are probably thinking of limp mode, but computer does not go into limp mode for the rear o2 codes, and even if it did, it would not do anything to the fuel trims.

Second, the MIL's do not simlute anything between the front and rear o2's. MIL's are simply resistors that take the actual voltage signal from the rear o2's and changes it to a voltage that the computer expects to see if the cats are working properly.

Third the change in backpressure does not require any tuning to a/f or timing. a/f and timing are both adjusted dynamically based on upstream sensors like the MAF, TPS, and ACT sensors. The computer is programmes to adapt to changes and freeing up the exhaust some is not going to require any changes in the tune.

Dark_Horse · Mar 10, 2008

jstreet0204 said:
Dear god man! No offense, I don't think there is a single correct statement in that entire post except for the reason the CEL comes on.

First, Computer going in to open loop has nothing to do with the CEL. You are probably thinking of limp mode, but computer does not go into limp mode for the rear o2 codes, and even if it did, it would not do anything to the fuel trims.

Second, the MIL's do not simlute anything between the front and rear o2's. MIL's are simply resistors that take the actual voltage signal from the rear o2's and changes it to a voltage that the computer expects to see if the cats are working properly.

Third the change in backpressure does not require any tuning to a/f or timing. a/f and timing are both adjusted dynamically based on upstream sensors like the MAF, TPS, and ACT sensors. The computer is programmes to adapt to changes and freeing up the exhaust some is not going to require any changes in the tune.

If I happened to have a Predator or Xcal tune and deleted the rear two o2s, then you're saying there would be no change at all in the timing from the computer? You're 100% sure that the only purpose for them is to indicate that the CEL is different from the front two o2s and needs to be checked, therefore throwing a SES light?

I'm not saying I don't believe you I'm just trying to get all the facts straight. What your're saying makes complete sense but I'm just getting mixed responses so its hard for me to rule the MILs completely out at this point.

Another test that I think might be plausable would be to take off the MILs and run the car with the SES light on. If I have the same results with them off then I could assume its not the MILs, right? Or would this cause the computer to run in a safety loop? Thanks for any clarification you can give on this guys, my knowledge on the ECU is pretty finite.

jstreet0204 · Mar 10, 2008

Dark_Horse said:
If I happened to have a Predator or Xcal tune and deleted the rear two o2s, then you're saying there would be no change at all in the timing from the computer? You're 100% sure that the only purpose for them is to indicate that the CEL is different from the front two o2s and needs to be checked, therefore throwing a SES light?

I'm not saying I don't believe you I'm just trying to get all the facts straight. What your're saying makes complete sense but I'm just getting mixed responses so its hard for me to rule the MILs completely out at this point.

Another test that I think might be plausable would be to take off the MILs and run the car with the SES light on. If I have the same results with them off then I could assume its not the MILs, right? Or would this cause the computer to run in a safety loop? Thanks for any clarification you can give on this guys, my knowledge on the ECU is pretty finite.

I am possitive that you will have no changes in timing. I've been tuning my own car for years now. I also have MIL's installed becaus initially the sooftware I was using did not have access to the rear o2 paramater to turn them off. Some cars do use rear o2 partially to influence long term fuel trims only but I have never seen anywhere on any of the tuning documentation that I've read, that the mustang is one of them.

If the only issue you are having is the carbon on the tail pipe and some dark smoke, it is just part of have an off road pipe. You may also get some fuel smell. Mine has done it since the day I took the cats off and I have I wideband o2 so I know that I'm not running extremely rich.

Now if the smoke is bluish white, it could be burning some oil, and the cats most likely were masking it. Check your plugs and see what they look like. Are you losing any oil over time?

Either it isn't a problem at all or removing the cats revealed some oil burning but if you are not getting the CEL the MILS are working and are not an issue either way.

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