Techno Duck

Just curious what effect exhaust leaks, both pre and post turbo have on what i am seeing with my wideband. I noticed my AFR's have been running richer than normal after a hard run i did a few weeks back. Full boost in 3rd and 4th i used to see in the 11.2-11.5 range which was nromal due to running the Vitesse MAF with no piggyback support yet. A few weeks back i noticed it was running 10.8-11 AFR's at the same boost. I pressure tested the intake and had one minor leak at the fuel vapor thermovalve which i bypassed. With that fixed the rich AFR's were still happening. I recalibrated the wideband also (Innovate). Anyhow i smoke tested my exhaust and found a number of leaks both pre and post turbo.

The pre-turbo leaks are at the #1 header flange (probably cracked at welded flange) and at the headers / crossover flange. Both are leaking a decent amount. The only post turbo but pre wideband leak is the downpipe to midpipe flange which is leaking a huge amount. Ive read before that exhaust leaks before the wideband can cause inaccurate readings, but i was under the impression it would read lean, not rich? Also would the stock O2 have an effect on this, i was WOT so i figured the stock O2 had no effect here.

My main question was can pre-turbo exhaust leaks cause the car to run richer than usual? My guess is during my hard 2nd - 4th run i may have blown out one of the gaskets worse which may be causing the change in AFR's.

Not overly concerned about the leaks really. Everything pre-turbo will be mostly cured when i pull the engine over the winter and put in new headers. The downpipe flange just needs a new copper gasket.. i have reused the one on the car now probably 5-6 times now so im not too surprised its leaking like crazy.

Rogue_Ant

Pre-sensor leak will cause a leaner reading. Post-sensor will not affect the reading.
Stock 02 is not used at WOT.

Paulyy

clean the MAF and see if it goes back to normal

fast951

I doubt a leak in the exhaust is causing the rich mixture. A bad ground will cause the rich mixture, check the ground connection, especially the one at the MAF.
Of course, there are many things that could cause the rich mixture (Engine temp, fuel pressure,...)

Techno Duck

Thanks for the input. I will double check all the grounds, including the wideband ground. I did make some changes under the dash a few weeks back so its a possibility. The intake is getting pulled when i get home again aswell to fix a few nagging issues.

Forgot to mention i also replaced the plugs. I had the NGK BPR7ES for about 6k miles in there, replaced with the same heat range plugs. Was running rich before and after the new plugs.

DME temp sensor appears fine, car idles rich on cold start and comes out of it as it usually had when watching the wideband; usually high to low 13's, where it eventually starts to dither toward 14.7. Also on my list of things to change.. as its original as far as i know and probably not a bad idea to just change with the intake off. Along with that ill also probably change the also original TPS when i reseal the throttle body. FPR is a 3-bar with probably under 15k miles on it..also being replaced with an Aeromotive when i replace the fuel rail.. jeez i just realized how much things are replaced on this car..

Techno Duck

Cleaned all grounds on the front left frame rail (including MAF ground) and still rich on boost.

Here are some particulars,

-FPR installed with MAF back in July '08, has 13k miles on it.
-Cap and rotor have less than 5k miles, will pull tomorrow to see if its burned up..but i checked about 1000 miles ago and they looked fine.
-Ignition wires and ignition coil replaced less than 1200 miles ago
-Plugs have sub 100 miles on them..will pull tomorrow to see how they look

Here are what my plugs looked like after 5k miles. They are NGK BPR7ES, .29 gap. I have since replaced them with new ones. Too me it looks like 2 and 3 were lean?





Close up of plug #3 which looks lean?

Chris White

Yep, looks a little lean.

TurboTommy

Techno Duck;
You're describing an air/fuel ratio change of about a half a number (richer). The assorted gas stations all vary in their ethanol content these days. It can easily make a difference of half a number, if you let the tank get close to empty before filling at a different gas station, for example.
But, maybe your observations are all from the same gas; I don't know.

Techno Duck

Gas is Sunoco from the same station, though not one i usually goto.. usually i do Sunoco or Mobil.

What has me puzzled now is i pulled my new plugs again with ~150miles and plugs #2 and #3 appear to be lean, while #1 and #4 are acceptable. There is not much i can think that would cause two lean cylinders. Tested the injector harness but not sure of what the results are telling me (see my other thread about that).

gcb951

Techno Duck,
You're describing almost the same thing that just happened to me tonight. I drove the car kinda hard for a few pulls and ran fine. I had it parked for about 4 hours and started back up when the wideband went rich. I have the Vitesse chip and SMT-6 so I went on the computer and leaned out a few of the cells. It seems to have corrected the problem for now. I noticed that my fuel pressure gauge was a little low at about 41psi when I got home and was thinking all this was happening because its about 100 degrees out?

BTW: I have exhaust leaks too.

Techno Duck

Well my problem is only on boost, cruise and idle all are still normal. I did some more 'testing' last night.. mostly 3rd and 4th gear pulls and my issue seems to have gone away. AFR's stayed in the 11.2 range which is what i was seeing previously as i do not have the piggyback yet. And yea.. my car does not run particularly well when its this hot out.

What does have me concerned is the lean #2 and #3 plugs.

fast951

How could a problem fix itself? Either there was no problem to start with OR something changed to fix it..
- How accurate is your WB system? When did you calibrate and how old is the WB O2 sensor?
- Does the AFR change if you run the AC and/or headlights? If it does, check your grounds.

Swap injectors between #1,4 and #2,3 see if the lean condition follows. If it does, you might need to clean the injectors. If it does not, I'll start looking at the wiring harness. If using Ballast resistors, make sure to inspect as well.

Techno Duck

Hi John, again i really appreciate the tech support on this.

The wideband is something i have been suspecting. I am using the Innovate setup and it has been re-calibrated atleast twice in the last 2k miles, the last time being about 2 weeks ago. My plan today or tomorrow (way to damn hot out) is to replace the sensor which has approx. 16k miles on it (about 2.5 years old). My buddy has a WRX with the same wideband and when he replaced his sensor (30k miles on it) it was reading nearly 1 point richer at full throttle, idle and cruise afr's were normal. I am thinking possibly i am seeing the same problem.

No change in AFR with the headlights, a/c has been deleted (days like today i wonder why i did that).

I did check the MAF ground after emailing you yesterday John and saw no voltage at the ground pin on the MAF harness with ignition on or off. I also visually checked the wiring to the resistors on the injector harness and all looks ok.

I did test the injector harness but not sure how to interpret my results. I am not sure if it should be tested with all 4 injector connectors disconnected or by disconnecting 1 at a time. With all 4 disconnected, i get 12v on 1 pin and 10v on the other pin indicating i probably have a harness issue. Testing with only one disconnected at a time i get the normal 12v on each pin.

I am going to install a LR injector harness when i get home again, but was hoping to find a smoking gun on possible causes of the 2 lean cylinders. Will swap injectors today or tomorrow and see what happens. Injectors have about 15k miles on them and are going on 2 years. The car has sat for probably close to a year in that time though.

Thom

I see (insignificant) irregularities on my AFR as well and despite John's excellent support I haven't been able to pinpoint the issue - that is assuming it is even a real "issue" as the engine performs faultlessly and is very healthy.
So will be interested to see if you get to see different AFRs by replacing the harness, as mine is also still original.

gcb951

Interesting find. After hearing what John had to say I noticed my A/Rs went rich when I turned my headlights. So, going by what John said I must have a bad ground. My question now is, what ground do I need to check? The black wire from the MAF? If so, where should I ground it?