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Tbi timing guru’s for cold stumble issue

bp71k5

bp71k5

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cold weather here lately has let me notice that the engine has an annoying stumble when the engine is cold and I stab the throttle. Runs fine when warm, and doesn’t stumble if I slowly hit the gas pedal.

For reference, it’s a 454 with 1227747 computer, no EGR, no codes set. I tuned it myself so I’m guessing I only tuned it to work well in the summer.

My searches lead me to think it’s either too lean or too rich. But I have no way to check which one it is. Anyone got a smart way with a scanner and tuner pro to see what’s going on?
 
Without a scanner I would bet too lean. Watching the AFR cold on the aftermarket systems, I’ve seen 11.7:1 at 0*
 
The best I think you can do with that situation is to datalog it, and hope you can get some readings from the o2 that indicate rich or lean for a consistent period. Better to be rich and back down towards lean imo. Ime the o2 will heat up pretty quick and start reading, even if the ECM isnt using it. It's a crutch, but if there is a timer for closed loop and coolant temp settings for closed loop, you can try and force it into closed loop a bit faster.

I dont know TBI so well, but if there are some settings for AE based on coolant temp, you might take a gander at those and bump the settings up for a bit more fuel when the engine is cold.

Cold settings are hard to do because you only get one or two shots a day to tune.
 
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dyeager535 said:
The best I think you can do with that situation is to datalog it, and hope you can get some readings from the o2 that indicate rich or lean for a consistent period. Better to be rich and back down towards lean imo. Ime the o2 will heat up pretty quick and start reading, even if the ECM isnt using it. It's a crutch, but if there is a timer for closed loop and coolant temp settings for closed loop, you can try and force it into closed loop a bit faster.

I dont know TBI so well, but if there are some settings for AE based on coolant temp, you might take a gander at those and bump the settings up for a bit more fuel when the engine is cold.

Cold settings are hard to do because you only get one or two shots a day to tune.
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I’ve got a heated o2, so maybe I can turn the ignition on and wait for a couple minutes to see if it’ll heat up enough to switch. I could also shoot the AE based on coolant temp up a ton and see if it gets better or worse.
 
Bent77 said:
Without a scanner I would bet too lean. Watching the AFR cold on the aftermarket systems, I’ve seen 11.7:1 at 0*
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Is 11.7 what I should shoot for at 0* or do the other systems treat that as too lean? Mine is set to be closer to 8 at 0*
 
bp71k5 said:
Is 11.7 what I should shoot for at 0* or do the other systems treat that as too lean? Mine is set to be closer to 8 at 0*
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Hard to say, but I agree with @dyeager535 that you really almost need to data log it to see, but 8:1 sounds fat
What is the RPM set to at that temp?
 
The engine ultimately will govern what it likes. I have mine set to go closed loop very quickly with a heated o2 based on time, but on mine unless I got crazy with the coolant temp vs closed loop setting, it still takes time to go closed loop on a cold engine.

When warm, but restart, does it run correctly if you just hop in and go? If it doesnt, forcing it into open loop for tuning may be a valid idea as well, and might give you an idea which way to go with the folder settings.

Since o2 isnt being used when the engine is cold, an afr setting isnt going to matter unless the ECM somehow uses a strategy to extrapolate what injector pulse width is needed to get that afr at a given engine speed and load. I dont know as that is how it works, vs just using engine temp, load, AE, rpm, etc. to guesstimate what the injector settings need to be.
 
dyeager535 said:
The engine ultimately will govern what it likes. I have mine set to go closed loop very quickly with a heated o2 based on time, but on mine unless I got crazy with the coolant temp vs closed loop setting, it still takes time to go closed loop on a cold engine.

When warm, but restart, does it run correctly if you just hop in and go? If it doesnt, forcing it into open loop for tuning may be a valid idea as well, and might give you an idea which way to go with the folder settings.

Since o2 isnt being used when the engine is cold, an afr setting isnt going to matter unless the ECM somehow uses a strategy to extrapolate what injector pulse width is needed to get that afr at a given engine speed and load. I dont know as that is how it works, vs just using engine temp, load, AE, rpm, etc. to guesstimate what the injector settings need to be.
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When it’s warm, runs fine after restart. I suppose datalogging it while cold might not be perfect, but it could give me a clue. I’ll have to see what other data is valid in open loop since BLM is a constant 128 until it goes closed loop.

Edit: checking the tuner software, the system does try to extrapolate what the AFR should be even in open loop mode using a couple coolant temp based tables.
 
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bp71k5 said:
Idle is 800 at 55C. That’s the coldest end of the table.
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My old TBI was 1100 at lower coolant temps. Not sure the exact temp that changed, but it may be worth noting
 
Bumped up the cold idle a little. Didn’t seem to make a noticeable difference.

But I did hook the scanner and just watched the numbers as it warmed up and stabbed the throttle every so often. Even before it goes closed loop, the stumble goes away around coolant temp = 60C. That’s helpful to know since I can add or subtract AE at that temp and see if the behavior gets better or worse.
 
Am I wrong but could that just be condensation or is it definitely raw fuel?
 
Scribbles said:
Am I wrong but could that just be condensation or is it definitely raw fuel?
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Could be both, but it hasn’t evaporated so I assume there’s some oil or gas in it. It did smell a bit rich while warming up but I’m never quite sure how to tell the difference between normal old car burning exhaust vs overly rich smelling exhaust.

I also noticed a cracked PCV hose fitting so I need to fix that before doing anything else. Seems like I have to replace all the rubber plug fittings on the throttle body every year or so. Anyone got a link for some more durable stuff? Oreillys had some silicone plugs that seem to work better, but only had one size.
 
Pull the fittings, tap the port, and use set screws. Was never a fan of caps on those type fittings. As you've found, most materials those caps are made of fdont hold up, and are a vacuum leak invitation.

If it idles ok you can play with fueling there a bit, and see what the exhaust does for smell, but for me that is an inexact science and you can have similar results too rich or too lean.

Agree on fixing PCV first of course.
 
Fixed all my potential vacuum leaks and tried to start it this morning, wouldn’t even start without my foot on the floor of the gas pedal. Would idle ok after 30 seconds of running. I made a bunch of tweaks yesterday so not sure what I did.
 
Foot on floor is clear flood mode, so theoretically no fuel being injected. Kind of hard to know what's going on if you made changes to the tune at the same time. Would make sense if you had tuned with vacuum leaks that it would be rich now that they are gone.

I always save my bins with the date and version as part of the file name, so I dont have to remember what I did, just go back one if it runs like crap lol.

I also keep the last known "decent" prom in the truck so if something unexpected crops up in the tune, I can swap back.
 
dyeager535 said:
Foot on floor is clear flood mode, so theoretically no fuel being injected. Kind of hard to know what's going on if you made changes to the tune at the same time. Would make sense if you had tuned with vacuum leaks that it would be rich now that they are gone.

I always save my bins with the date and version as part of the file name, so I dont have to remember what I did, just go back one if it runs like crap lol.

I also keep the last known "decent" prom in the truck so if something unexpected crops up in the tune, I can swap back.
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Yea, I can go back one, but the new one was done in emulation so lots of little tweaks while running. It’ll start without my foot on it but chokes and dies immediately until it warms up. Too rich when cold?
 
Success. I was able to undo some of the choke tweaks I did and got it to at least start up again. Then turned the AE vs temp way down. Now it starts right up and the throttle is responsive right away. Thanks for the help pointing me in the right direction fellas.:thumb:
 
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