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Old 11-13-2015, 06:37 PM   #1
kchar
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Exhaust or Vacuum Leak when Hot

Hello everyone, I've been trying to diagnose and fix an issue I've had with my car for quite a while and I'm at a loss.

My car runs near perfect when I'm on load but after the car gets hot my fuel trims start to go 10-15% positive and when I'm idling I can hear a slight tick which sounds similar to the sound with exhaust is cooling after the car has turned off. I would take a video but I know it would not come through over the boxer engine itself. I don't believe the sound is lifter tick as it has no true rhythm.

There's no signs of scoring that I can see so for a while I was convinced it was the header and overpipe connection so I fiddled with that to hell but it did not help. Last night I took the header off and the gaskets looked like new. I reinstalled the gaskets with copper sealant on both sides and did the same with the header/overpipe connection.

As for it being a vacuum leak I would think that the issue would be present no matter how long the car has been running. Like I said, the car can cool off and will not have any fuel issues until a fair amount of throttle has been given.

At this point I'm leaning towards some hairline crack in the manifold but I really have no clue. HALP PLEASE!
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Old 11-18-2015, 07:17 PM   #2
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Originally Posted by kchar View Post
Hello everyone, I've been trying to diagnose and fix an issue I've had with my car for quite a while and I'm at a loss.

My car runs near perfect when I'm on load but after the car gets hot my fuel trims start to go 10-15% positive and when I'm idling I can hear a slight tick which sounds similar to the sound with exhaust is cooling after the car has turned off. I would take a video but I know it would not come through over the boxer engine itself. I don't believe the sound is lifter tick as it has no true rhythm.

There's no signs of scoring that I can see so for a while I was convinced it was the header and overpipe connection so I fiddled with that to hell but it did not help. Last night I took the header off and the gaskets looked like new. I reinstalled the gaskets with copper sealant on both sides and did the same with the header/overpipe connection.

As for it being a vacuum leak I would think that the issue would be present no matter how long the car has been running. Like I said, the car can cool off and will not have any fuel issues until a fair amount of throttle has been given.

At this point I'm leaning towards some hairline crack in the manifold but I really have no clue. HALP PLEASE!
Could you provide the following?
1) List of engine-related mods. In particular, headers and other exhaust components (including O2 sensors), intake (especially regarding the MAF sensor), and anything that required you to tap into the vacuum system. Also, are you running an engine map?

2) Do you have a CEL? Do you have any codes (even if CEL isn't illuminated)?

3) What are you using to monitor fuel trims? OFT? Which fuel trims are changing (i.e. STFTs, LTFTs, both)? Also, when you say high you mean high positive, correct? Not negative? Any other parameters changing with the trims when car is warm (e.g. knock values, intake values)?

4) Just to clarify - the trims are normal when on throttle at all times? Trims are high only at low/no throttle when the car is warm? If you are full-throttle, the trims are correct?

5) Any changes to the cooling system - e.g. new thermostat, new coolant? Any coolant leaks - do you have to refill the overflow tank more than once every few months?

Just to share my line of thinking - if I understand what you are describing, and you have an OFT (or other) revised engine map, it sounds like you have an issue with closed loop fueling. Based on the car not having a fuel trim issue before it comes to temp (in particular before the O2 sensors come to temp), I'd say your open loop fueling tables are fine. But something is happening once your car switches to closed loop fueling - could be many things including O2 sensor faulting or leak around it, MAF sensor calibration, other exhaust leak (as you mentioned), intake leak proximal to MAF sensor, etc. IMHO, in the absence of an exhaust or intake leak, I'd say you simply have a calibration issue with the closed loop tables. If you are using an off-the-shelf map, seemingly minor things like ambient air temp, altitude, and the like can result in the closed loop fueling table being incorrect.
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Old 11-21-2015, 10:41 PM   #3
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Quote:
Originally Posted by theadmiral976 View Post
Just to share my line of thinking - if I understand what you are describing, and you have an OFT (or other) revised engine map, it sounds like you have an issue with closed loop fueling. Based on the car not having a fuel trim issue before it comes to temp (in particular before the O2 sensors come to temp), I'd say your open loop fueling tables are fine. But something is happening once your car switches to closed loop fueling - could be many things including O2 sensor faulting or leak around it, MAF sensor calibration, other exhaust leak (as you mentioned), intake leak proximal to MAF sensor, etc. IMHO, in the absence of an exhaust or intake leak, I'd say you simply have a calibration issue with the closed loop tables. If you are using an off-the-shelf map, seemingly minor things like ambient air temp, altitude, and the like can result in the closed loop fueling table being incorrect.
Heya, thanks for getting back to me.

1) I'm running the normal perrin intake with a sprintex 210 kit which is tuned through moto-east. I also have the dual radium catch cans which I've checked the connections for.

2) No codes.

3) I'm using an oft and the only noticeable change is my STFTs which are 15-20% positive after a fair amount of throttle has been put through the car.

4) The trims are good at all other times with the normal variation due to the environment.

5) I've not had to add any coolant since I installed the blower.

I would agree with you but since the issue has occurred only recently (while on the same tune) I believe its mechanical in nature. I pulled the o2 sensor and there was a bit of residue towards the top but I don't think that is related. I plan to try a friend's upstream o2 to see if that helps and then I'll have to get it smoke tested at some shop. Any other ideas of what the issue could possible be?
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Old 11-21-2015, 11:17 PM   #4
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Heya, thanks for getting back to me.

1) I'm running the normal perrin intake with a sprintex 210 kit which is tuned through moto-east. I also have the dual radium catch cans which I've checked the connections for.

2) No codes.

3) I'm using an oft and the only noticeable change is my STFTs which are 15-20% positive after a fair amount of throttle has been put through the car.

4) The trims are good at all other times with the normal variation due to the environment.

5) I've not had to add any coolant since I installed the blower.

I would agree with you but since the issue has occurred only recently (while on the same tune) I believe its mechanical in nature. I pulled the o2 sensor and there was a bit of residue towards the top but I don't think that is related. I plan to try a friend's upstream o2 to see if that helps and then I'll have to get it smoke tested at some shop. Any other ideas of what the issue could possible be?
I agree with your assessment - if LTFTs are fine, I don't think you've got an issue with the maps. Unfortunately, I know very little about forced induction-related issues. I'd see if the good people over in the FI subforum could lend some advice. I recall there being a thread or two dedicated to the Sprintex kit - that might help.

That said, STFTs normally can vary widely depending on throttle position and load, at least in NA cars. In the absence of LTFT changes more than +/-5%, this STFT variation is not a cause for concern - again in NA cars. If your LTFTs are stable and you are not running lean on WOT (e.g. high AFR compared to target AFR), I probably wouldn't worry too much. Of course, this could be different for FI and it sounds like this is a new problem, which could indicate the beginnings of something bad. I hope you are able to find the issue!
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