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Username Post: Cylinder Head Ground
Posts: 136

Reg: 07-16-05
02-23-20 08:03 AM - Post#2787106    
    In response to 65_Impala

Typically it's in the 100-130*F range but I've seen newer stuff even lower. The running delay before closed loop varies depending on the start. On this TBI stuff, if it's considered a cold start then it's minutes of time and if it's considered a hot start then it's typically something like 20-30 seconds.

Thanks - I've wondered about the temp range I saw. When I've seen someone mention a temp criteria it was lower. I didn't do an exhaustive check - just watched it in the datastream once or twice. It very well could be that was just the temp when the time criteria was met.
I was also wondering if the time criteria varied with temp or other conditions. nice to know.
I've also wondered if there is a O2 mV criteria to go into closed loop. I once had a lazy O2 where it would change enough driving to go into Closed loop but would not vary enough to enter closed loop @ idle after cold start or, if driving and then stopping, would drop out of closed loop. Only found it because I failed emissions @ idle. Tracking that down, it made me think O2 had to get over 700mV before it'd go into closed loop. However, I couldn't find anyone who knew.

according to my scan tool, it stays in open loop during this whole ordeal. Once it clears out and I stop and restart, say within a minute or so, it is still in open loop. Only after I drive it a few minutes does it go into closed loop.

I think important part is verifying it only struggles when it's in open loop. I don't think the fact that it's not always bad in open loop - even separated by a few minutes is necessarily that surprising. eg. fuel pressure could change slightly, temp could be slightly higher, ECM in different A/F map for some reason,

You've been so thorough on your checks/troubleshooting there's not a lot left except something assumed good is not actually good. As I had problems ~11psi (1yr old Autozone) which went away when I replaced with an ACDelco pump that gave me 13psi - that's where my mind is stuck. These engines are sensitive to fuel pressure and I've read many posts which were resolved with a new pump & filter - though admittedly never one like yours in which the problem was only during such a limited time/condition.

btw - though this would have no relation to a problem in open loop - I think it should go into closed loop @ idle if you sit long enough. Also should stay in closed loop @ idle after driving. If it doesn't you may want to replace O2. I think only about $12 and easy to replace.
65 Belair 350
68 Camaro 327
93 Suburban 5.7L TBI

Edited by Sabino on 02-23-20 08:06 AM. Reason for edit: No reason given.
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