Sudden high fuel trims - help please!

[cawith]

Hi guys,

I've been running OFT tunes for almost a year and have of course tweaked my tunes a bit since then. Have been running both gas and E85, but mostly E85 for the past 6 month. In addition to that I installed a catless UEL header in the beginning of July and have been very happy with it.

Then this week my LTFT started to climb for every time I went for a drive. In the beginning not by much, but during the last couple of days it has been increasingly much. It's mostly during idle or slow cruise but is starting to show higher trims under light acceleration as well. When I parked the car just a few minutes ago I had LTFT 18% at idle and AFR mostly mostly hitting a bit less than commanded right around 14-15.

Now, I have read about the vacuum leaks on boosted cars but mine is NA. I also can't seem to hear any loud hiss or suction in the engine bay. I guess it would be very obvious..? Wouldn't the car run much leaner with AFR up at 18 or higher with a vacuum leak?

Could it be an exhaust leak due to the new header? I used new gaskets but don't know if I torqued them correctly. Tried to do it with the same force that I had to use to get the original header off with.

Another theory is a bad blend of E85. Because there is no E85 close to me, I'm actually bringing jerry cans to the gas station that I then fill up and keep in my cellar, so that I don't have to go to this specific gas station more than once or twice a month. Initially I used some plastic jerry cans but switched to some metal ones not that long ago.
My theory is that maybe the alcohol in the metal jerry cans reacts or vaporizes leaving only little alcohol blended with fuel and water. Would that be possible? I have had no problems with the plastic jerry cans that I've used since december.

I hope it's an easy fix and that you guys can help me.

[cawith]

Ok, after having popped the hood again and having a look around, it doesn't seem like a vacuum leak.

However the very strong exhaust smell coming from there (don't smell anything behind the car) suggests it's an exhaust leak. Will have to lift up the car again and probably reattach the header with some new gaskets.

I think I'll be able to get some new gaskets tomorrow, but not before the 160 km roundtrip I have tomorrow. Would it be okay to drive that trip with the leak or would it be dangerous for the car?

[aagun]

what is ur STFT ?
is it move while idle. or rev at 3000rpm ?

[cawith]

Well it's mostly in the positive numbers as well. Depends, all morning with 12.5 LTFT it fluctuated between 0 and 10% and now with LTFT 18.9 it's 0%.
Doesn't move that much when idle. At 3000 rpm it's mostly 5% or below when not accelerating.

[aagun]

it looks like vacuum leaks

[DarkSunrise]

Probably an exhaust leak either at the header or OP (based on your description of a strong exhaust smell from under the hood and positive LTFT's). When you pull your header, you should be able to see signs of a leak from the old gaskets. Look for carbon deposits (i.e., black soot).

It's probably safe to drive. It'd be more of an issue if LTFT's were large negative values.

[cawith]

I hope you're right! I guess it's the connection to the OP that causes problems because I remember having trouble with the gasket alignment there. In that case I don't need to take the whole thing off by myself.

I will try to get some new gaskets in the morning and see if I can fix it quickly.

So the only negative thing with driving around with very large trims would be unburned fuel running through the system or are there other downsides?

I've read that if the leak is occurring in the manifold gasket or the manifold flange gasket area, excessive heat can build up which can quickly burn an exhaust valve, which will be an expensive repair bill.
How quickly would something like that happen? Just from driving around town or on the highway below 3000 rpm?

[steve99]

Originally Posted by cawith

I hope you're right! I guess it's the connection to the OP that causes problems because I remember having trouble with the gasket alignment there. In that case I don't need to take the whole thing off by myself.

I will try to get some new gaskets in the morning and see if I can fix it quickly.

So the only negative thing with driving around with very large trims would be unburned fuel running through the system or are there other downsides?

I've read that if the leak is occurring in the manifold gasket or the manifold flange gasket area, excessive heat can build up which can quickly burn an exhaust valve, which will be an expensive repair bill.
How quickly would something like that happen? Just from driving around town or on the highway below 3000 rpm?

If you have high positive ltft at low rpm its usually an exhaust leak or o2 sensor leak or crook sensor.

senosor sees fresh air in exhaust signals ecu engine is lean when it not, as a result ecu injects heaps of fuel trying to correct perceived lean condition.

if you changed header recientlt it likly an exhaust leak, make sure sensors screwed in correctly, you will damage them if they are forced in, retap threads in header m18 by 1.5 if sensors tight and dont screw in by hand

[cawith]

Originally Posted by steve99

If you have high positive ltft at low rpm its usually an exhaust leak or o2 sensor leak or crook sensor.

senosor sees fresh air in exhaust signals ecu engine is lean when it not, as a result ecu injects heaps of fuel trying to correct perceived lean condition.

if you changed header recientlt it likly an exhaust leak, make sure sensors screwed in correctly, you will damage them if they are forced in, retap threads in header m18 by 1.5 if sensors tight and dont screw in by hand

Well, the sensors have worked correctly for more than 2 months and haven't touched them since install.. But what du you mean with "retap threads in header m18 by 1.5 if sensors tight"? I didn't screw them in by hand...

My country is not big on car modding or tuning, so I couldn't get the gaskets today. I'll have to either get some OEM Subaru or Toyota ones on monday or order some from abroad.

I decided still to lift up the car today to see if some bolts needed tightening and if there were signs of a leak. I noticed some black dirt close to one of the bolts at the cylinderhead. See the picture with the red mark. I was also able to tighten this bolt a bit more, maybe half a turn. I check all the other bolts but they were almost as tight as they could be. No other signs of leakage that I could find.

So I thought I had it fixed without even taking off the header but I hadn't. With steady 130 kph on the highway it looked quite alright. But when I drove home through the city later in the afternoon I still had large trims - but it looked a bit better though with a total trim of around 10% mostly.
Do you think I need new gaskets no matter what?

[steve99]

Originally Posted by cawith

Well, the sensors have worked correctly for more than 2 months and haven't touched them since install.. But what du you mean with "retap threads in header m18 by 1.5 if sensors tight"? I didn't screw them in by hand...

My country is not big on car modding or tuning, so I couldn't get the gaskets today. I'll have to either get some OEM Subaru or Toyota ones on monday or order some from abroad.

I decided still to lift up the car today to see if some bolts needed tightening and if there were signs of a leak. I noticed some black dirt close to one of the bolts at the cylinderhead. See the picture with the red mark. I was also able to tighten this bolt a bit more, maybe half a turn. I check all the other bolts but they were almost as tight as they could be. No other signs of leakage that I could find.

So I thought I had it fixed without even taking off the header but I hadn't. With steady 130 kph on the highway it looked quite alright. But when I drove home through the city later in the afternoon I still had large trims - but it looked a bit better though with a total trim of around 10% mostly.
Do you think I need new gaskets no matter what?

with the car idling you can usually smell exhaust fumes in engine bay if gaskets are leaking.

also try spraying some soapy water on connections when car is cold then start and see of any bubbles.

That dirt looks normal.

[cawith]

So, some weeks have passed while I waited for my new gaskets..
In the mean time I've had the car on a lift several times, mainly to tighten the bolts. Didn't seem to help

The gaskets arrived last week and with the help of a friend, we took off the header and mounted it again. I applied 30 N-m torque to the cylinder head bolts and 35 N-m to the OP bolts. After a few minutes on the road I could smell, hear and see (on the OFT) that it hadn't worked.
I took it off again and did a reinstall but this time with exhaust sealant. Initially I applied the same torque, but after 24 hours and everything having cooled down, the first cold start sounded like I had installed the meanest straight pipe. The problem was one of the two OP bolts wasn't tight at all.

So I went back to over tighten all the bolts and placed an order for some Grimmspeed gaskets. Hope they'll be shipped quickly.
After having left the garage, the fuel trims look fairly well, but I'm a bit paranoid now.

One thing that I don't understand is, why my AFR always is 0.2-0.5 below command AFR under low load and low rpm..?
Example at cruise or idle: AFR - 14.69; Command AFR 14.94; but fuel trims combined are still 4-5% (positive) -- why? I'm running Shell V-Power.
In open loop in usually within +-2% LTFT.

Btw, does anyone have any advice on good ways to remove sealant, when I receive the Grimmspeeds?

Also, should I apply the exhaust sealant with the Grimmspeeds as well? What about the torque - it seems like very little...?

[steve99]

make sure you put some high temp anti seize on the threads of nuts and bolts and work them a couple of times so they run nice and smooth, else most of the torque gets used up overcomming the friction on dry corroded bolts and they dont torque correctly. Then when they get hot they work loose.

[cawith]

Originally Posted by steve99

make sure you put some high temp anti seize on the threads of nuts and bolts and work them a couple of times so they run nice and smooth, else most of the torque gets used up overcomming the friction on dry corroded bolts and they dont torque correctly. Then when they get hot they work loose.

Would copper paste be suitable?

What do you think about my positive fuel trims even though AFR is richer than commanded? Would that be due to 5% ethanol in V-Power?
Is the AFR calculated with data from the O2 sensor or the MAF sensor?

[steve99]

Originally Posted by cawith

Would copper paste be suitable?

What do you think about my positive fuel trims even though AFR is richer than commanded? Would that be due to 5% ethanol in V-Power?
Is the AFR calculated with data from the O2 sensor or the MAF sensor?

Copper paste should be fine

AFR is measered by front o2 sensor.

you will get AFR leaner than commanded some times as you open/close throttle for a short period event though the average may be positive as shown in ltft.