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Understanding the warmup of cold Tbi..

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only 31s

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My question is...during cold start on tbi(factory settings. No mods) what sensor inputs is the computer waiting for before it lets the idle come down....1990 suburban......currently it's taking 7 mins to idle down..just looking to see if I can speed it up? Thanks
 
  1. Briefly, on starting mode, the ECM/PCM checks the coolant temp. sensor(CTS),throttle position sensor(TPS), manifold absolute pressure(MAP),and crank signal, then determines the proper air/fuel ratio for starting. Run mode has either open or closed loop.When the engine is first started , and it is above 400 RPM,the system goes into open loop -the ECM ignores the signal from the O2 sensor, and calculates the air/fuel ratio based on inputs from the coolant temperature and MAP sensors. The system stays in open loop until the O2 is hot enough to operate properly ,the CTS is above a specified temp, and after a specific amount of time has elapsed after starting the engine.........
 
So , it being still very cold where you live, I'm sure, it must take 7 minutes or so for the O2 sensor to heat up good enough to tell the ECM to come out of open loop and into closed loop, when the RPM's drop. When it starts getting warm out , it shouldn't take as long to take the engine to warm up, assuming the system is operating properly .
 
only 31s said:
My question is...during cold start on tbi(factory settings. No mods) what sensor inputs is the computer waiting for before it lets the idle come down....1990 suburban......currently it's taking 7 mins to idle down..just looking to see if I can speed it up? Thanks
Click to expand...

Seven minutes of idling, or driving? Since it IS coming down, does not seem to indicate a failure, unless the CTS is sluggish, but that's unlikely.

Idling is a waste of time, you are better off getting in it and starting to drive. It will heat up far faster being driven than sitting.
 
What engine is in the burb? Some have different ecm programming for the iac (idle air control) and wont fully idle down till in D.
Also, it will idle down regardless of closed loop operation or not.

These will idle faster longer than most modern vehichles.
 
dyeager535 said:
Seven minutes of idling, or driving? Since it IS coming down, does not seem to indicate a failure, unless the CTS is sluggish, but that's unlikely.

Idling is a waste of time, you are better off getting in it and starting to drive. It will heat up far faster being driven than sitting.
Click to expand...
I have tried to jump in it and go to try warming it up quicker....it out smarts me! I have to either stop in d and foot on brake or just pull up to fuel or park and wait her out...I'm too close to the highway.....if I don't idle her down proper she,ll stay 1100 rpm until I hit a light... I don't mind too much the wait but hate the thought of the fuel waste. ( 20 to 30 mins after I hit the highway.).I have just always strived to get my vehicles close to factory operating and basically wanted to get an idea of how far off I am...
 
black dawg said:
What engine is in the burb? Some have different ecm programming for the iac (idle air control) and wont fully idle down till in D.
Also, it will idle down regardless of closed loop operation or not.

These will idle faster longer than most modern vehichles.
Click to expand...
Don't have the ECM part number handy but 350 Chevy motor in it..bought out of Texas,brought to Mass, 11 years ago.. I know it won't ever be as efficient as something modern......that's me...different...there may be 50 or so of these in my state, maybe 5 in as good as condition as mine......Rust is an arch enemy here...
 
MEANSTREAK K30 said:
So , it being still very cold where you live, I'm sure, it must take 7 minutes or so for the O2 sensor to heat up good enough to tell the ECM to come out of open loop and into closed loop, when the RPM's drop. When it starts getting warm out , it shouldn't take as long to take the engine to warm up, assuming the system is operating properly .
Click to expand...
I hope so... If not I do get a kick out of knowing when it will do its thing.
 
dyeager535 said:
Seven minutes of idling, or driving? Since it IS coming down, does not seem to indicate a failure, unless the CTS is sluggish, but that's unlikely.

Idling is a waste of time, you are better off getting in it and starting to drive. It will heat up far faster being driven than sitting.
Click to expand...
black dawg said:
What engine is in the burb? Some have different ecm programming for the iac (idle air control) and wont fully idle down till in D.
Also, it will idle down regardless of closed loop operation or not.
Funny how you mention the idle down until put in drive....did that for years , thought that was just how it went, until I was in it idling in park one snowy day 20 mins or so defrosting the windshield,accidentally moved my column shifter(not out of gear but closer to reverse)and didn't that bitch drop down to 700 from 1100.....oh happy day, I figure misadjusted neutral safety switch, I now get in it, slightly move my column shift,start it, 7 mins later,bout 750 idle. So now I chase the time....I think I'm anal.....or at least addicted...lol
These will idle faster longer than most modern vehichles.
Click to expand...
 
Unfortunately I don't have the data in front of me, someone might be able to tell you what engine temp those are supposed to idle down at.

Do you have any idea what the RPM's are while it's idling? All vacuum lines are in good shape and hooked up properly?
 
Get the goddang ALDL data...that's the mantra with TBI (well, my mantra anyway). It tells you an immense amount about what's going on with your engine, and it's cheap to obtain.
 
dyeager535 said:
Unfortunately I don't have the data in front of me, someone might be able to tell you what engine temp those are supposed to idle down at.

Do you have any idea what the RPM's are while it's idling? All vacuum lines are in good shape and hooked up properly?
Click to expand...

I thought it was 150-160ish??
 
I timed my 87 stock DD today. 4:35 to idle down. It was 47 degrees out. When it is below 32 degrees, I bet it is around seven minutes. The Jimmy is the same. And I eill let it sit for a full 10 minutes, with the heater on full. Nice and toasty when I get in.
 
dyeager535 said:
Unfortunately I don't have the data in front of me, someone might be able to tell you what engine temp those are supposed to idle down at.

Do you have any idea what the RPM's are while it's idling? All vacuum lines are in good shape and hooked up properly?
Click to expand...
Yeah I have a tach on it,bout 675 after first c old idle down, bout 725 when warm start, then575-600 in d ...very little stumble...very satisfied on that end...all vac lines except-cruise good. even to the charcoal can
 
dyeager535 said:
Unfortunately I don't have the data in front of me, someone might be able to tell you what engine temp those are supposed to idle down at.

Do you have any idea what the RPM's are while it's idling? All vacuum lines are in good shape and hooked up properly?
Click to expand...
Yeah I have a tach on it,bout 675 after first c old idle down, bout 725 when warm start, then575-600 in d ...very little stumble...very satisfied on that end...all vac lines except-cruise good. even to the charcoal can
 
dyeager535 said:
Unfortunately I don't have the data in front of me, someone might be able to tell you what engine temp those are supposed to idle down at.

Do you have any idea what the RPM's are while it's idling? All vacuum lines are in good shape and hooked up properly?
Click to expand...
Yeah I have a tach on it,bout 675 after first c old idle down, bout 725 when warm start, then575-600 in d ...very little stumble...very satisfied on that end...all vac lines except-cruise good. even to the charcoal can
longbedder said:
Get the goddang ALDL data...that's the mantra with TBI (well, my mantra anyway). It tells you an immense amount about what's going on with your engine, and it's cheap to obtain.
Click to expand...
I'm so anal about all that info....one of these days...it would make me giddy..lol
 
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