Stumbling after start up

[Big Moose]

Had a similar issue on one of our trucks. Sometimes it did it and sometimes it was good. When it was stumbling the truck would vibrate. Are you able to tell from your live data on your scanner if some cylinders are misfiring? On ours, one side (bank2) was showing a lot of misfires. The front O2 sensor was showing different voltage readings than all the others. Pulled it out and it was really black. Put a new one in and still did the same thing. But I had previously pulled the spark plugs and noticed they were really black as well on that bank. So I decided take it for a good hard drive to see if the plugs would clear themselves off. Well, didn't have to drive to far to accomplish that. Truck runs so smooth now, issue fixed.

What I'd recommend is pulling your plugs and inspecting them, that should tell you something.
One other thing to note, 42 psi is to low, should be around 52 minimum with the return type fuel system, it could be you're starving a little bit. it could also be that the strainer on the fuel pump is plugged or the inline filter.
Good luck

[Wgesnerjr]

Thanks for all the replies. I have checked plugs and all seem good. even replaced the wires because i ripped an end off. no change.

when I pull the fuel pressure regulator vac line, the pressure goes up but stumble is still there. I don't think it's starving since bank 2 is super rich. exhaust smells confirm rich state. Tank, strainer, pick up and fuel pump are all brand new.

tried swapping all injector left to right. still no change.

lastly, this only happens for first 45 to 90 seconds. after then, rich condition goes away on scan tool and truck runs fine the rest of the key cycle.

no check engine lights either, no codes in computer. staring to think it's an O2 heater issue on the right side. figure the heater should run for the same amount of time im having the issue. going to try this soon: https://www.motor.com/magazine-summa...cuit-failures/

[BR3W CITY]

Did we ever discuss if ASE (after start enrichment) was an issue? I can't remember.

FWIW ASE is a setting in the ECM designed to add fuel (enrich) during the cold cranking period. Too much ASE and it runs rich or potentially floods on mid-temp starts. Too little and some motors (usually w/ heavier mods to intake/heads) won't want to catch. Its not something a tuner should/would be playing with on a standard swap but sometimes does get used as a crutch if another issue is making startup headaches.

[Wgesnerjr]

We have not discussed this, but sounds entirely plausible. With the timing of the issue, I thought it could be something along these lines. One thing that keeps me thinking otherwise is that only one side of the engine runs rich. Would a bad program for the ASE cause a rich condition on one side of the engine?

The other thing is that my set up is very stock. I did not ask LT1swap to do any tuning except VATS, delete rear O2 and Speedo calibration. so I wonder if he would have touched the ASE anyway? And for what reason.

The only parts I thought would affect just one side of the engine would be injectors, O2, or the program in the PCM. Things like MAF, vacuum leaks, PCV or EVAP I have been shying away from as they would affect BOTH sides of engine.

[BR3W CITY]

ASE just adds fueling, it has no control side-to-side that I'm aware of, and its not something I would typically think that Lt1swap would touch on a regular email tune. ASE is something that a tuner would use upon road testing and cold/hot starting the car, and its entirely meant as a useability/driveability feature.

[Wgesnerjr]

Thanks BR3W CITY. That's what I thought too.

I have read where the O2 is not used during open loop. I wonder if the O2s are completely ignored or used to adjust the fuel trim but to a less precise extent until it enters closed loop operation?

[BR3W CITY]

STFT has no correction factor applied in open loop on stock operating systems.

[Wgesnerjr]

Well, crap. I'd hoped it had some connection.

So I read this article on how to test the o2 heater circuit. https://www.motor.com/magazine-summa...cuit-failures/
Thought it might not have been working.

I built the test harness and tried on the right side o2 sensor. The light lit up but blinked every 2-3 seconds. Should the heater circuit work continuously? There is not much info before closed loop operation. Guess it could be the o2 sensor took a crap. Just replaced it when I dropped the engine in.

Next stop, new o2 sensor.

[Wgesnerjr]

Here is the test harness.

[BR3W CITY]

The 02 heater is controlled on the ground side by PWM (this is according to an article on 02 sensor heaters), so the pulsing wouldn't completely surprise me.

Same article references this: "On many GM models it can be done with the sensor hot, and the PCM will relearn the real value at the next cold-start."

[Wgesnerjr]

Thanks BR3W, That sounds interesting. Could you post a link to the article?

Just to be 100% sure, I have ordered a new ac delco o2 sensor. This side was replaced during the swap as the original one was damaged in the Tahoes accident. Just the sensor was damaged, wires looked good. I checked during the rewiring process. Not sure what brand o2 sensor I bought before, but I've heard of Camaro and Firebirds not liking Bosch ones. That could have been what I bought.

One last question. Before it was roadworthy I did start and run the truck around the block to do some troubleshooting. This was done WITHOUT exhaust. (My neighbors love me) The manifolds had 3 inches of pipe with the O2 screwed in. Could that have recalibrated the ASE enrichment? If so, once the full exhaust (with cats) was installed would it not have recalibrated?

[BR3W CITY]

Its a little mish-mashed. The guy has lots of information but it overlaps multiple makes so you have to glean through to fine applicable stuff.

https://www.autoserviceprofessional....t-code-is-real

[Wgesnerjr]

I see that. Good information though. Thanks for the link.

I really feel this is O2 heater related, because it happens so quickly then it's gone. My thinking is that the heater is working, but not real well. Therefore the O2 sensor is waiting until the exhaust heats it up enough to start reading data correctly, instead of the heater quickly getting it to temperature. Hence the 45 to 90 seconds. Only problem with this there is NO check engine light.

The article did explain a relearn process quoted above. Since the original was damaged in the accident, I wonder if the new one never calibrated. I have had codes and reset them but will try again this weekend. (in between rain storms!)

[Rich84]

Both my swaps don't go into closed loop until 130*. My understanding is that the O2's don't do anything until closed loop.
Is this correct?
I have a similar stumble at start up as well. Hoping you get to the bottom of this.

[Wgesnerjr]

SOLVED! SOLVED! SOLVED! (I feel like the auctioneer at Barrett-Jackson)

Finally did something that made a difference. Changed the right side O2 sensor and the truck runs normal! No more stutter and stumble! No more idling like its got a racing cam! No more stinking exhaust smell!

So now, after start up, the right side bank 2 goes rich for 7 to 10 seconds and starts to lean out with the O2 sensor alternating up and down, as it should.

I know everyone says the O2s are ignored during open loop but this clearly shows it has some impact on A/F ratio during warmup. Otherwise, why bother having a heated sensor that wouldn't have input until the engine is warmed up? I am really thinking that the heater part was not working and was depending on the exhaust to bring it up to temp.

This Denso O2 sensor was installed during the swap and I want to condemn the brand. But it was installed during the custom exhaust install. If it was screwed into the bung as it was welded into the pipe, maybe something got damaged. So, not 100% sure why it happened. I did install an AC Delco this time. I was so happy with the result, I have ordered a second one for the left side, just in case. This way it will start off with both replaced at the same time.

Still wonder why no CEL or codes. Either way, its done!

Thanks to everyone for all the help. It is such a pleasure to drive now!

[mongocanfly]

Well......after all that I'm glad you got it solved.....

[jjzepplin]

Amazing! Glad you got it fixed. And something so simple. HA! Soooo what are all those pictures? I thought I would be that guy... I have not done any swaps yet but am about to embark.

[Wgesnerjr]

Thanks. Excitement has died down now.

The pics are screenshots of the Torque Lite app on my phone. It connects to a bluetooth OBD plug in the ALDL connector under the dash.

It it showing both O2 sensors. Both left and right banks of the engine. The higher the green line, the richer the mixture. Lower the leaner. The far right is the current measurement. It will slowly move left and give a line as it goes. So imagine everything slowly moving left. (Sorry, cant post a video) the whole screen is about 15 to 20 seconds of time.

This really helped me figure out where it was running rich and under which conditions. The green line would max out high on bank 2 during start up until the exhaust warmed the O2 sensor, then drop down and start alternating up and down as the PCM controlled mixture. Bank 1 would alternate like normal.

The app is customizable with different readings so I could see open vs. Closed loop, temperature, MAF, etc.

[Wgesnerjr]

This is the OBD check plug I got on amazon. Works with many different apps. It's pretty cheap at around $30.

Veepeak OBDCheck BLE OBD2 Bluetooth Scanner Auto OBD II Diagnostic Scan Tool for iOS & Android, Bluetooth 4.0 Car Check Engine Light Code Reader Supports Torque, OBD Fusion, BimmerCode app

https://www.amazon.com/dp/B073XKQQQW..._-oGrCb2TAK4Z1

[Wgesnerjr]

Got the second O2 sensor installed and the truck runs smooth a silk! Not sure what brand the drivers side was, but it was significantly different in looks. Glad I have a matched set of AC Delcos. The graphs look the same now.

[jjzepplin]

That is very good news! And didn't cost a fortune! Good job. Is it still running well?

[Wgesnerjr]

YES! Drove it to work Friday and it ran like a champ!

AM ride started at 30 degrees. Truck fired up and settled into a smooth idle. Dropped my daughter off at school and proceeded to work in stop and go I-85 standard Atlanta traffic. Plenty of power and throttle response. For the hour drive, no issues whatsoever.

Left work a 6 in 45 degree weather. And again sat in traffic on the way to a swim meet. 1.5 hours later I pulled into the parking lot of the pool and again, had no problems.

After swim meet, we ate dinner and finally go to cruise it home. Still running great at 40 degrees and purrs like a kitten at 60 mph.

I have noticed an overall degree of smoothness. Like any other fuel injected car. Before, once it was past the stumbling, it would run but slightly rough. Since I did not get to feel the donor run, I assumed it was normal. But with the O2s updated, it is like a new car even though the engine has approximate 180K on it now.

I am a BIG believer in the LS platform now! Best engine swap ever!

[oldman3]

Been following along on the thread, really glad you found the problem. I agree the LS platform is the way to go...Jim

[lutronjim]

Wgesnerjr Did you get the pro version of app? I looked at info briefly and one of the options was ' fast connect'. Does this take a special OBD2 dongle or the one shown in your link.

Thanks

[1971Stepside]

I just purchased the odb2 device. Do you recommend a specific app?