Have you repeated the tabular fuel trim data since repairing the exhaust leak? Does it run any different after this?


George

 

He claimed it still ran "rough as hell". Don't know if fuel trims changed any.

 

Thanks Les and George, I watched fuel trims right after putting the gasket in, they are the exact same as before pegged rich. Now I have been thinking more (of course) and I have a lot of bets placed on the restricted exhaust right now, it isn't misfiring, but running rough, and running rich without a fuel delivery or compression problem, and running hotter than it should at times. I will be getting a back pressure tester and testing in the upstream o2 sensors ASAP, I can't believe I didn't do this before as the only code it has is P0420, I will see soon enough for certain if my exhaust is restricted or not from the back pressure reading. I have the MAF reading here in a video Les, maximum reading was 131.3g/s, I wasn't able to calculate a volumetric efficiency number that made sense based off this. Guys, you may notice on the TPS it never read 100%, 84.3% max, and sometimes reading negative? That is the first time I've seen that, but I'm guessing it's because the blade is adjusted further closed than it's supposed to be? Still not sure why it doesn't read 100% at full throttle though, the pedal was definitely held down to the floor. Okay so based off the o2 sensor readings at wide open throttle, I can say even further I will be chasing an exhaust issue, with them pegged rich the whole time I'm on at wide open throttle. I will need to do a back pressure test here next and let you guys know how I make out with that, but with the history of the engine (driving around for a long time with a leaking spider and misfiring, and also I drove it with no compression on one cylinder for 120km, I was on a road trip and got home ASAP) it's looking very possible. Fingers are crossed here guys I have good hope for this test, if it is indeed the cat that would be truly great news to me as I will just cut them out myself and weld straight pipes in and it will hardly cost me anything (no emissions testing here).

 

When you floor it while driving the computer ignores the O2 sensors and commands a rich fuel injector setting which causes the O2 sensors to peg rich. That’s how the system is supposed to function and is one of the very few times that emissions are ignored.

A VE calculator:

https://www.otctools.com/ve

I personally like the back pressure test in the upstream O2 port.


George

 

Air density is dependent on temp, pressure, and humidity

https://www.omnicalculator.com/physics/air-density I used this calculator
https://airdensityonline.com/track-h...ay/2022-07-16/ Here are my conditions at 4pm the day I did my testing (Osceola is 5 miles from my house). Don't know if they have a location for you or not, but you should be able to find out historical data somewhere online.
https://www.thefreecalculator.com/physics/air-density Scroll down to see "How to calculate air density" if you're interested.

My air density was calculated to be 0.0010176 g/cm3 = 1.0176 g/liter

Theoretical for mine = 1.0176g/liter * 4986rev/min * 1min/60sec * 4.3liter/2rev = 181.8 g/sec at 100% VE

Mine = 156/181.8 * 100 = 85.8% VE Which fits with the around 80% of a typical stock engine.

If conditions were the same for you (hot and humid), that would put you in the lower 70's for % VE. If you actually calculate yours, remember the temperature variable is the actual air temp entering the engine, so the MAT reading is what is used there. Also use dew point, not relative humidity (because you will be using MAT for temp - the relative humidity will automatically populate in the calculator).

I think this VE is the only solid thing that we have to go on. I'm suspicious of plugged exhaust somewhere, but could be MAT and MAF sensor, or even still a mechanical problem (but I can't think of why). Still not sure how all this could cause goofiness at idle and engine will still go 5000 rpm at 70+ VE.

 

Note corrected calcs above

 

For reference, the GM shop manual calls for 130 g/sec minimum for the 1-2 max throttle shift point. I measured mine a few years ago and believe that I was around 155 g/sec. I’ll have to go dig that up. Les’ discussion confirms that 130 does seem conservative and should be considered the minimum and not optimum. You might have some breathing problems but not catastrophic levels it would seem. A severely plugged cat causes way more performance problems than this but if you do have some restrictions, repeating the full throttle 1-2 shift point MAF reading would show an improvement in VE with an upstream O2 sensor removed.

Also, your back pressure test will help with that.


George

 

To Reway..... Unless you are doing the O2 sensor removal test same day as normal testing, different weather conditions for the two tests may invalidate your testing. But doing the two tests back to back should prevent you from having to buy a tool (unless you want to have one). But be careful about 5000 rpm blowing out of a hole ahead of the cat - could be a flame. Make sure it points in the right direction or is shielded. Don't need a fire. Also, if removing an o2 sensor does make a significant difference, I would break the exhaust apart at your connection ahead of the muffler and retest to isolate the problem to the cats or further down the line. Exhaust pipes can be double-walled and I once saw one nearly completely internally collapsed. You can run a garden hose down them them to check. Also baffles in mufflers can come loose and get out of place.

 

All good points.

 

Here is the tracks in Air Density Online where they have historical weather conditions in British Columbia. Any one of these match your location? Unfortunately we don't have the MAT temp in your video to complete the calcualtion. You might want to consider repeating.

BC

• Greg Moore Raceway
• [F] [H] [M]
• Chilliwack, BC

• Mission Raceway Park
• [F] [H] [M]
• Mission, BC

• Nitro Motorsports Park
• [F] [H] [M]
• Prince George, BC

• Northern Lights Raceway
• [F] [H] [M]
• Fort St. John, BC

• Saratoga Speedway
• [F] [H] [M]
• Courtenay, BC

• Vancouver Island Motorsport Circuit
• [F] [H] [M]
• Duncan, BC

• Western Speedway
• [F] [H] [M]
• Victoria, BC