P0171System Lean Cosworth Supercharger

[weederr33]

Originally Posted by sly

Took the header off. Heat shields are crazy. I can find no sign of a leak. No burn marks, no cracks and the gaskets looked good. I pressurized the header some and did not see any leaks either.

Would failed DI seals really cause this problem? Car idles fine. No shudder at all. The hesitation I described is only slight and only under certain circumstances. I can't even get it to do it all the time.

Just throwing it out there you could always try someone else's tune.

Or try replacing the DI seals just to make sure (depending on your year model and miles). I think they were a known issue on the earlier cars, though I think that was rectified after the 2014 or '15.

[sly]

What about a plugged fuel filter? I did upgrade the fuel pump awhile back and it's possible there could have been some dirt get into the tank.

I tried reflashing the ECU with the original Cosworth tune and got the same problem. High LTFT. I'm back on the custom tune Matt did for me. No difference between those two tunes. I have a copy of an old log from the original tune and the fuel trims were normal.

[sly]

Got it back together. So far no CEL. On the off chance that it might make a difference, I think I'll pick up a bottle of injector cleaner and see if it helps.

Is there a test you can do for the injectors? I'd hate to pay someone to replace the DI seals and take everything apart without knowing if that really is the problem. Maybe I sucked some dirt up in them...

[sly]

Been driving it for a day and still not CEL. I noticed I only get the CEL when I am data logging. If the Ecutec is not plugged in, it seems to run fine. I wonder if there is a problem with my laptop or cable and maybe the car is actually fine?

I noticed when I datalog the car seems a little sluggish. I run my laptop in the passenger's seat and log until the battery dies (old battery). I can tell when the laptop disconnects because suddenly the car feels more responsive.

I measured the exhaust while idling with a portable exhaust oxygen analyzer. At idle I measured about 14.7:1 which agreed with the ECU. So I don't think the car is rich, which would indicate an exhaust leak. I took the intake apart and pressurized all the hoses and there were no leaks. I also disconnected all the vacuum lines and plugged them. No leaks. Brake booster has no leaks.

I'm kind of at the point to where I think there is a problem with the data logger or I have a fueling issue. I can find no intake or exhaust leaks anywhere. I've taken the whole thing apart. Retorqued the intake manifold bolts and made sure everything was sealed.

Car runs fine when the datalogger is not connected. Maybe it's just the laptop...

[gtengr]

Has it thrown P0171 since day 1 of the supercharger install? If not, how many miles/days later?

[sly]

Originally Posted by gtengr

Has it thrown P0171 since day 1 of the supercharger install? If not, how many miles/days later?

I installed the supercharger 5 months ago. I initially got a code for the EVAP system leaking. Repositioned the hose and it went away. CEL started about a week ago. About 5,000 miles.

I may have finally fixed it. I took the intake tube, all vacuum lines and the throttle body off. Noticed a slight amount of oil on the underside of the throttle body. Cleaned it with some throttle body cleaner spray. This car needs a catch can. The PVC vacuum lines did not have a hose clamp on them so I reinstalled them with one. I noticed that the EVAP line was not completely seated against the throttle body. With the body off, it was much easier to get in place with the hose clamp. Got it on tight and put everything back together.

Ran it today and no CEL and no missing or spark knock. Runs great. AFR is down in the 11's under WOT. Previously they were in the 13's Fuel trims are still high though. I did switch to ethanol free just for this tank and put a can of seafoam in it so that might have something to do with it. The car was tuned on Exxon 93 octane E10.

So long story short, I think I had a vacuum line barely leaking. Probably the EVAP line. It's hard to get on and could stand to be a little longer. I may replace it and the brake booster hose as they are both tight. Fuel trims are still high but I'm running different gas. No spark knock, no missing and no CEL.

[sly]

I think I finally got it fixed. I took apart every vacuum line and added hose clamps to the ones that didn't have them. I ended up adding a hose clamp to both sides of the PCV hose, Crankcase Breather hose and EVAP hose on the throttle body. I also took off the air cleaner box and noticed that the hose clamp had slightly deformed the outlet to a D shape. I heated it up with a heat gun and used a funnel to make it round again. I reattached the hose clamp so that it did not squash the air box.

So long story short, I think I had multiple small leaks on the intake. Attached are 2 logs. One from October when everything was running fine and one from today. My fuel trims in October were -25%. But my intake air back then was over 100F. My fuel trims today are +25% but the intake air is now at 70F. I noticed my MAF reading is lower now than it was then. Cooler, denser air will need less flow to achieve the same volume. So today when the weather is colder, my throttle plate is opening less to keep the engine running. The ECU sees less airflow but then compensates for it by increasing the fuel trims. Back in October when the air was hotter and less dense, the ECU saw more airflow and so the fuel trims went negative. The median trim between these 2 values is 0%. It went from -25 to +25 depending upon outdoor ambient temperature.

I ruled out exhaust leak. Both screen shots are at 850RPM. The injector pulse width is nearly the same as well as the AFR. If I had an exhaust leak, then the system would think it was lean and would widen up the injector pulse width to send more fuel. But since the injector pulse width is nearly the same, the engine is getting the same amount of fuel then vs now to achieve the target AFR. This also rules out an injector failure. If an injector was partially plugged then the ECU would widen the pulse width to compensate. The differences in pulse width could be accounted by differences in fuel temperature and summer vs winter gas. Winter gas is more volatile to account for the colder temperature and so has a higher vapor pressure than summer gas.

My MAP reading is also the same. 0.31 bar. So at 850 RPM the engine is seeing the same vacuum then vs now. My MAP was reading 0.33 bar previously, indicating a small intake leak. Now it's back down to where it started.

Fuel pressure then and now is nearly identical. Spark timing is the same. So after tearing the car apart to find the problem, I learned how to read ECU logs and to remember the fact that you must install hose clamps on each and every vacuum line, even if it didn't come with one. And never overtighten the hose clamp on the plastic air box or it will deform it.