Upstream vs Downstream O2 Sensors

[hagar]

Oops, didnt finish the thought. It will also show if one of the sensors is pooched. If the sensor is shot and reading say -15 fuel trims, it will cause the engine to run lean and can cause pinging

 

[Dmascari1984]

I have the same “misfire/stumble”. Everyone tells me it’s normal. I can’t stand it. I did check my timing with blue driver and it bounces around while all my other cars are steady. Driving me nuts. Have you found any solution?? FYI here’s my data at 2500rpm no load


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[gpracer1]

Misfire stumble is not normal.
Your graph looks ok, upstream O2 sensors should be constantly swinging (narrowband).
Where/when is the misfire or stumble?

 

[thompsoj22]

Ditto on the stumble/tremor at idle. it does seem more pronounced as the engine is warming, not nesessarily initial startup but in between cold and op temp. after a long duration of highway speed and then coming to an idle sometimes it is smooth as glass. ill be watching also.

 

[swathdiver]

Precisely. No codes, no misfires. I've watched the individual cylinder misfire counts live and there's nothing. It's just a very random, very light stumble/miss.

It will exhibit the random detonation on the stock tune

Are you sure it's detonation and not timing being pulled? Torque Management can and does pull timing randomly even after much of it is removed. A few months back I had my tuner advance the timing while driving, chasing a mile per gallon performance gain, and the timing was being pulled while cruising, the KR meter was going off a lot so we put it back. I went back to E85 so we haven't sorted that one out yet.

I have the same “misfire/stumble”. Everyone tells me it’s normal. I can’t stand it. I did check my timing with blue driver and it bounces around while all my other cars are steady. Driving me nuts. Have you found any solution?? FYI here’s my data at 2500rpm no load View attachment 212961

Your sensors look good as Marc says. Check or change your plugs and wires, double check the gap. Bank 2 Fuel Trims are a bit high to me. Check your intake gaskets with a propane torch while watching the O2 sensor graph.

 

[HiHoeSilver]

Your sensors look good as Marc says. Check or change your plugs and wires, double check the gap. Bank 2 Fuel Trims are a bit high to me. Check your intake gaskets with a propane torch while watching the O2 sensor graph.

Trims are negative, no? Under load at 2500. What do they look like at idle? What kind of gas is in it?

 

[Dmascari1984]

Thanks guys. Did propane and carb cleaner test No vac or exhaust leaks. changed manifold gasket anyway because i heard they fail a lot($50 and 3 hrs not too bad)no change. Had already done plugs and wires. Attempted to do injector pulse test but tester broke(wtf). Went to check fuel pressure and I think I may have found the issue( and possibly a lot of other folks that have the same issue and haven’t been able to solve theirs). I hooked up a fuel pressure test kit and observed the gauge prime properly to 56psi. From what i know, when it is running the gauge should stay pretty steady. Mine was fluctuating very rapidly from like 38-45psi. I know this isn’t scientific but I pressed the purge on the gauge and noticed the fuel was coming out of the line properly and then I would get a stream of bubbles In the line. Then it would go clear(gas only) again. Then more bubbles. In my opinion that would make the gauge fluctuate(air compressing and expanding etc) and cause the lean condition( not enough fuel due to the bubbles being mixed in. Soo I’m thinking it’s a seal somewhere in the lines or the supply line is getting air in it while pumping gas up in the fuel tank. I’ll attach the videos of my gauge findings. I’m a DIYer and have limited knowledge. Just enough to get myself in trouble. Hope this will be the answer. I’m selling the truck soo the wife doesn’t want me to change it but I want to anyway just to see if it’s the problem lol. Btw my fuel trims are crazy. Sometimes negative then sometimes positive. It was in rich when I posted earlier and had been lean for a few days now. Like +9 ltft.
https://share.icloud.com/photos/0p7T_0iHkFElmOMNa1bBVGjgQ#Home

 

[thompsoj22]

Thanks guys. Did propane and carb cleaner test No vac or exhaust leaks. changed manifold gasket anyway because i heard they fail a lot($50 and 3 hrs not too bad)no change. Had already done plugs and wires. Attempted to do injector pulse test but tester broke(wtf). Went to check fuel pressure and I think I may have found the issue( and possibly a lot of other folks that have the same issue and haven’t been able to solve theirs). I hooked up a fuel pressure test kit and observed the gauge prime properly to 56psi. From what i know, when it is running the gauge should stay pretty steady. Mine was fluctuating very rapidly from like 38-45psi. I know this isn’t scientific but I pressed the purge on the gauge and noticed the fuel was coming out of the line properly and then I would get a stream of bubbles In the line. Then it would go clear(gas only) again. Then more bubbles. In my opinion that would make the gauge fluctuate(air compressing and expanding etc) and cause the lean condition( not enough fuel due to the bubbles being mixed in. Soo I’m thinking it’s a seal somewhere in the lines or the supply line is getting air in it while pumping gas up in the fuel tank. I’ll attach the videos of my gauge findings. I’m a DIYer and have limited knowledge. Just enough to get myself in trouble. Hope this will be the answer. I’m selling the truck soo the wife doesn’t want me to change it but I want to anyway just to see if it’s the problem lol. Btw my fuel trims are crazy. Sometimes negative then sometimes positive. It was in rich when I posted earlier and had been lean for a few days now. Like +9 ltft.
https://share.icloud.com/photos/0p7T_0iHkFElmOMNa1bBVGjgQ#Home

Anxious to hear from those with knowledge as this sounds possible, but how do you induce air into a system with a submerged suction pump and no return plumbing design.

 

[swathdiver]

I hooked up a fuel pressure test kit and observed the gauge prime properly to 56psi. From what i know, when it is running the gauge should stay pretty steady. Mine was fluctuating very rapidly from like 38-45psi.

That looked to me like an inexpensive gauge, one not dampened with oil. The pressure looked normal. If the fuel pressure was really bouncing around that much one would think the idle would have been terrible. I'd like to see what the scan tool sees for FP.

 

[Dmascari1984]

Anxious to hear from those with knowledge as this sounds possible, but how do you induce air into a system with a submerged suction pump and no return plumbing design.

I was thinking the line inside the tank that pushed the fuel up. Or possibly an irony somewhere.


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