Hi,

My car is running lean between 3500 and 5000 RPM @ WOT. Any ideas why this is happening?

It is a 2001 MT LS1 with 90k miles.

Any idea is appreciated ...

 

Moved to C5 Tech.

 

how do you know it's lean?... do you have a wideband?... if it's only in that rpm range and richens up after 5k then it might be your tune, sounds like it may need to be given more fuel to meet the target afr

 

OBDII ... The O2 readings starts around .8V which is where it should be. That should be around 13. When it hits 3500, the reading goes all the way down to .2V. That is about 15. If I keep my foot into it, the air fuel ratio jumps back.

My thinking is, it is either the fuel filter, which I changed a while ago, or the pump because the issue is happening @ max torque. Unfortunately, the C5 does not monitor rail pressure.

 

Did this just happen??

 

I have been battling it for some time. I always run the car with octane booster to avoid spark knock.

Let me answer the $60 question before someone asks it. I can't remember if this happened directly after changing the filter/pressure regulator.

 

Well if fuel filter rericted it will go lean but u said after 5k its fine so i would rule that out. If u had someway to adjust the the tune bet that would work. HPTUners or what ever.
I cant think of anything else because it gos normal after 5k. If u had a gas psi gauge to watch the psi to see if the psi falls off then it might be ur fuel pump.

 

 

The car is stock and I can't adjust the tune because I run it in SCCA B Street. Maybe it is time to move it into STU :P

 

I recorded the O2 values for two pulls.
I hope that would help.

 

Can you do that again? This time just one bank, and include the Injector pulsewidth.

If the Injector PW stays flat, but it’s lean, there is no fuel there.

Agree with also measuring fuel pressure at the same time. You will have to figure out how to get a long hose on the gauge. Tape the gauge to the outside of the wind shield.

Can you feel it going lean?

 

Yes, it spark knocked a couple of times in the first pull and quite a bit in the second .... I don't know how long the pistons are going to take it :/

 

If the spark knock sensors are working, they should tell the PCM to pull timing to prevent continued knock. So, how about hitting the rev limiter, when you hit the rev limit, it can sound like spark knock. For sure you need to look at fuel pressure at WOT and under load. Hard to do. I have a homemade pressure transducer, but to use it effectively you really need a ‘scope. You could look at voltage with a really good volt meter. Some how you need to measure pressure with you behind the wheel, and the hood down driving down the road.

Usually, vacuum leaks like leaking intake gaskets will cause lean and will have less influence at higher rpm and load When the TB opens up, the manifold vacuum goes down, so such vacuum leaks lose their influence.

Can you look at MAF and MAP as a function of TB opening ti see if they are reporting correctly. You might look at MAF output to see if it is under-reporting air flow into the engine. Look up Justin Miller’s YouTube vids. He is an automotive instructor and has a great 6 minute video on measuring MAF performance. You should get linear response of air flow with increasing RPM.

 

No spark knock at the top of the rev range. It sparked knocked when it went lean and afterwards a bit. Regarding fuel pressure, I have to start on such contraption.Hopefully I won't end up in flames!

Vacuum leaks cause drivability issues. WOT solve these issues :P

I will do another run with much more info on display. On another note, does the LS1 WOT map is MAF or MAP dependent? And could the fuel rail dampener cause such an issue? Have someone faced any issues dampener?

 

the issues you are asking about: Lean condition at mid to high throttle, the engine in knocking when it goes lean, and then questions about how the MAF, MAP works.

Mid range lean condition. probably a fuel pressure issue, if it is consistent, or something to do with the MAF, since you have a "factory" tune. So basically, your PCM takes the air flow reported by the MAF along with "corrections" from the IAT , MAP the the TPS (throttle position sensor) to establish pulse with for the injectors and timing. Then this is corrected by reports from the O2 sensors. Mostly the IAT and MAP are offering corrections for barometric pressure and altitude. Obviously, at WOT, the MAP will be the same or about the same as the atmospheric pressure. So this is why I suggested you check the MAF performance vs RPM, to see if the MAF is reporting correctly.

Now the knocking condition. It may or may not be the lean condition. Your O2 sensors should be correcting for lean conditions independent of injector pulse width and air flow through the MAF. (Provided this isn't a fuel pressure issue and the injectors have no more to give). If you see short term fuel trims adding fuel evenly for both banks and it is still lean, it would sort of seem to be a fuel shortage from the injectors. A true engine knock can have a several sources. First is lean fuel delivey. Next is crappy gasoline that burns too fast. Then after that the next usual culprit is carbon deposits on the piston and combustion chamber that ignite. Timing too advanced is a possibility, but unlikely.

Combustion chambers on a port injected engine are usually clean, but at 90k miles, if the engine overheated badly, sometimes will allow oil to be burned unnecessarily. A non working PCV system is also a likely culprit, particularly for a car that is AUTO-X'd. The oil tends to stay high in the engine because of sustained high RPM, and will slosh to the PCV pickup tube in the Rt valve cover.. That oil goes right into the combustion process. That will carbon up the CC really quick.

If it is a true knock, then this begs a big question why the knock sensors aren't doing their job. They are usually pretty aggressive at pulling timing and holding it pulled to save the engine. The knock sensors live below the intake valley cover, a place that gets really warm and full of combustion blow-by gases, which condense along with the water vapor when the engine cools. This forms an organic acid that is rather corrosive and no way to get it out of there. Over time this will attack the insulation on the knock sensor wires, harden the sensor seal and then attack the sensors them selves where they screw into the block. If you have to go after the sensors be prepared to replace both, the wiring harness AND the sensor seal. Yes they can fail and never throw a code.

Now what I use for measuring fuel rail pressure. a 0-100psi sensor bought on Ebay. Then you need a regulated 5VDC power. This, again an Ebay purchase. They sell a 5VDC power supply for powering dash cams that can in turn be powered by a 9v battery or 12V from the car. After you rig it up, you need to develop a pressure vs voltage plot so you will need an air supply with which you can regulate pressure. My rig is show below. I mad an adapter to fit my fuel rail pressure gauge and used that gauge to develop a calibration curve for the transducer.

 

I went out again last night. A/F looked OK, not great, but it did knock because it pulled some timing. Given it is a cooler night, I am leaning towards fuel pump.

Several data traces I am concerned about:
1. I don't like how the MAF reading jumps around. Is that the norm?
2. I don't like how lean the engine function while not in WOT. Maybe some of the injectors are tired being injectors?
3. I still have spark knock! You can hear it in the videos.




And the videos for anyone feeling like it.

 

K24556,

Thanks for helping me out. I answered your questions/concerns below.

WOT Fueling Tables: according to what I read, the LS1 relies on MAF table and corrects it with other sensor signals
Lean Fuel Delivery: It was reported by the O2 sensors several times, but it isn't repeatable.
Crappy Gasoline: It is all I can get in a small town :/ ... I supplement it with octane booster. The tank has 3 bottles at the moment! Having said that, I had this problem when I lived in the city too.
Carbon Deposits: I am too lead footed for that
Timing too advanced: timing looks stock to me until the knock sensors start pulling timing. According what I read here, 28 @ WOT is the norm. The small graphs don't show it well though.
Clogged PCV: I re-plumed the PCV system this spring ... And can we call it a PCV system if it only has a restrictor plate, not a valve?
oil goes right into the combustion: I have an oil catch can. The C5 fill it in a day of competition!
knock sensors aren't doing their job: They are pulling a bunch of timing. Unfortunately, I can't monitor them at the moment.
be prepared to replace both, the wiring harness AND the sensor seal: when I started having this problem, I thought the same. They were the first parts I changed. Funny enough, the ones I changed to pulled a code and I am back with the old ones.


Maybe it is time for a MPVI2 and moving the car into STU.

 

I think you are discounting carbon build up too soon. I don't hear a knock in your videos, and WOT no load is a lot different. Having a heavy foot will not "clean up" the CC. It may be pulling oil, catch can or no. If the catch can gets full and you are Auto Xing, I would expect it to slosh in the catch can too and if full, get pushed up into the engine. I can't read too much into the graphs since they are a no load condition. Bottom line hard driving at high RPM will work against a clean CC.

C5's are getting some age on them so at 90k miles, someone has pulled the drive train to work on the clutch, etc. The fuel line leaves the tank area and follows the torque tube forward to the engine bay. Most C5's will have this line bent, as the shifter box will always drag this line and pinch it unless you know to protect the lines in the tunnel with a big putty knife. If it is kinked you will have restricted fuel flow. Bottom line yes you may have a bad fuel pump but there is more to getting enough fuel to the engine than just the fuel pump. New fuel lines are still available, and a total B&%$H to change.

Regarding the orifice slit, that means you have the "late model" valley cover. the plastic orifice box is usually better than the PCV valve systems, but two things can happen. The slit can be plugged up so crankcase pressure builds up, or it becomes separated from the valley cover and a vacuum is pulled on the system all the time. both of these are age related problems, with the first suggesting your car passes a lot of oil. If the valley cover is a fresh install there should be no worry.

I think your engine sounds pretty good revving up with no load.. You could have a lazy lifter that is clattering at high RPM causing the noise you hear. I don't hear it, but knocks are very distinctive and I would not expect to hear a knock at WOT and no load on the engine. Timing will advance only so far, so as you get to higher RPMs the advance will not increase. knock usually develops in third gear, not no load situations. So to confirm you have a knock, you should drive the car and get up to 50-60mph and pull a hill with a heat-soaked engine and in a high gear to lug the engine. If the knock sensors are working, you should feel a loss of power, if not working noisy knock develops.

1. check fuel delivery under load. This will take some plumbing and electrical work to safely get a reading into the cockpit. Then Drive the car and put it under load where the fuel delivery is really challenged. If pressure drops off then you need to look for kinked lines or possibly a fuel pump.
2. Check your throttle body and your intake for oil deposits. If you are pulling oil, the bottom of the intake runners will have oil laying around. The intake should be as dry as a popcorn fart. If you find oil that is a problem to solve. Catch cans are SUPPOSED to stop this, but some of the products out there are crap and work poorly on an engine that has other problems.
3. Take a bore scope and look at the combustion chambers through a spark plug hole. Look for carbon deposits. The spark plugs may tell a story, they did in the old days, but not so much today. The center electrode insulation should be a light tan and no black deposits on the plugs .

 

Whatever you are using to scan this is confusing.
Timing for instance. 12 degrees at full throttle is certainly wrong. The timing at cruise is also certainly wrong. Most definately not follownin the timing tables.
MAF looks correct. It's always somewhat jagged.
I'm not seeing Knock Retard in the data.

Not a fan of Octane boosters, they turn the spark plugs orange in color.

Reading the narrow bands for enrichment is a crap shoot.

So, HP Tuners scanner is an excellent diagnostics tool. Especially with the pro feature set so you can log a Wideband O2 sensor.
Of course the investment will be around $1000.

Any dyno tuners in your area? Just running and data logging it would tell a lot. They can sniff the tail pipes to get wideband readings.

You mentioned changing the fuel pressure filter regulator, just before the issue started. GM or Wix part? I wouldn't trust anything else.

Ron

 

Thanks for helping out guys ...

K24556, regarding CC, it is worth pulling the spark plugs to check the combustion chambers. Hopefully I will do that soon. The clutch on the other hand is original and I don't look forward to changing it. As a matter of fact, I am having a problem with that too! The clutch pedal disappears when I run the engine @ high RPMs. Thankfully I need to shift once in competition. Anyway, everything looks as factory as it can in the tunnel. Lastly, all the videos I shared so far are underload.

Ron, I am not a fan of octane boosters as well, but my choices are limited. I agree with you too about narrow band O2s. Having said that, if you are seeing .4-.7V, you know that you have a problem. Regarding the graphs, the Y-axis isnt accurate. Lastly, the fuel filter I installed is a premium grade! It is time for new filter ...