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Old 04-02-2006, 06:45 PM   #1
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Help High Idle with a BB TBI

I am sure that some one else has run into this, the search functions are limited and I would like some information from those that have "been here before".
I installed the EBL with my Autoprom and was pleased with the overall engine operation with a stock 350 TBI and Injectors.
I am running a 383 (9.8:1 CR), vortec heads, performer intake.
I installed a 454 TBI unit with 55lb injectors @20 PSI and everything went south. I think I now have the IAC wired correctly my Idle speed was 2000 + and now is around 1100-1200 still to high.
I guess I need some help on how to tune the idle for now so that I can start driving to obtain some LOGS.
Thank you
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Old 04-02-2006, 10:38 PM   #2
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Quote:
Originally Posted by sbcrules
I am sure that some one else has run into this, the search functions are limited and I would like some information from those that have "been here before".
I installed the EBL with my Autoprom and was pleased with the overall engine operation with a stock 350 TBI and Injectors.
I am running a 383 (9.8:1 CR), vortec heads, performer intake.
I installed a 454 TBI unit with 55lb injectors @20 PSI and everything went south. I think I now have the IAC wired correctly my Idle speed was 2000 + and now is around 1100-1200 still to high.
I guess I need some help on how to tune the idle for now so that I can start driving to obtain some LOGS.
Thank you
To check stuff out I think it would be best to start with closing the IAC. To do this is easy: short pins A& B on the ALDL connector and key-on with the engine off. After about 20-30 seconds unplug the IAC connector (the IAC should have been clicking during the A/B short and key-on). You can then key-off.

Now start the engine. With a warm engine (up to temperature) the idle speed needs to be below the set idle speed (in the BIN). Wait at least 1 minute after engine startup before any adjustments.

If required adjust the air screw. Now, if you open or crank in the air screw far enough the ECM will drop out of idle mode. This is because the ECM maintains the lowest seen TPS value as the idle setting. To get around this turn the engine off for 10 seconds and restart it. Then wait at least 1 minute before again commencing with idle adjustments (there are after start timing and fuel adjustments, we don't want these to affect the idle setting).

Turn the engine off, wait 10 seconds, and reconnect the IAC. Now start the engine (may need some throttle opening), let it run for at least 20 seconds, and shut it off. The IAC and idle setting should now work out.

Doing all of this with the WUD active will allow one to see if the engine is in idle mode or not. Along with the IAC counts. I know it sounds like a bit of work, but the IAC learns in where the idle is.

As the VE and SA tables get tweaked in closer the IAC steps at idle my/will move around. A slight tweak on the idle screw isn't unusual.

Re-reading this post it sounds convoluted. However, setting up the IAC steps with the air screw sorta' is convoluted.

RBob.
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Old 04-03-2006, 09:29 AM   #3
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Thanks Again RBob

I will follow these instructions.

A few questions that some one may be able to help me with:
Are there many differences with the idle circuit on the BB TBI unit? It looks totally different when compared to a stock TBI unit that comes on a 350?
I have the 454 manifold adapter that came with the BB engines; it is mounted on the performer intake, I pluged all the holes. The IAC passage is very large and seems to pull vacuum from the left rear of the adapter. There is a tapped hole here that is blocked off now with a pipe plug. where does it get its air from?
I purchased a Wiring adapter from Turbo City the one that goes from the square to flat plug. It was apparently wired wrong. The engine would idle around 2000-2500 rpm. I found your (RBob) wiring pin outs on a previous post made the changes and the idle went down to 1100 or so. I still don't know if the wiring is correct as I tried to reset the IAC and never heard any sound from it. Is there a way to verify the wiring by testing voltage or resistance?
Using the WhatsUp display the IAC counts were 0 during Idle but seemed to change with throttle movement.
The idle speed increases when the engine goes into Closed Loop 250-400 RPM. Normally doesn't this cause the Idle speed to decrease when it goes to closed loop mode?

I first ran the engine with the BB TBI unit / 80LB injectors @20 PSI and it looked like a F4 jet exhaust when I took it for a test drive. Pulled these and put the 55LB @ 20PSI. What should my (BPC - BPC vs VAC) be set at with this combination? (BB TBI UNIT)

I do love the EBL system, kind of complicated for me now, but I hope to become proficient with it in the next life. Ha Ha
Just a lot to take in at once.
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Old 04-03-2006, 11:25 AM   #4
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I think the BB TBI unit received IAC air at the cutout on top of the unit, same as the 350 unit. Take a look at the top of the passenger side behind the bore. There is an irregular shaped opening. With the air cleaner off and engine off you may be able to look down into the opening and see the IAC pintle.

With the engine running you can place your finger over this opening and block the air flow through the IAC. If the IAC is open at all then blocking this will cause the noise level to decrease (this is where the loud hissing comes from on a cold start), along with a decrease in idle speed.

An IAC count of zero is closed, according to the ECM. It will not try to close it any further. The increase in counts as the throttle is opened is the throttle follower action. This is normal and can be adjusted in the bin.

Going into closed loop fueling won't affect the desired idle speed. It is probably leaning it out a little which will tend to increase the engine speed. With the IAC counts at 0 the ECM can't bring the idle down.

With the IAC fully closed (will need to check that), if you can't get the idle down with the idle air screw, there may be a small vacuum leak.

BPC: 80#/hr @ 20 psi is 106 #/hr (using 11.5 psi for the 80# rating).

383 ci = 6.2l, 1 cyl vol = .7797 l

This comes out to a BPC of 85.

The 55's at 20 psi is 72.5 #/hr for a BPC of: 125

If using a standard regulator (constant pressure), use that value trhoughout the BPC vs. Vac table.

The 55's won't be enough fuel, although for starting out getting tuning experience they will be easier to tune for. Just watch the WOT stuff as it will lean out. Be careful.

RBob.
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Old 04-03-2006, 02:38 PM   #5
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THANKS

EBL 225.00
Spare ECU 40.00
Autoprom 325.00
Chips 25.00
Support from RBob PRICELESS
THANKS
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Old 04-03-2006, 08:12 PM   #6
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Almost there

I followed the IAC reset and idle adjustment procedures and it made a world of difference.
My idle was holding nice around 800 until the throttle was depressed.
After this the idle would stay around 1000-1100 RPM.
Turn off the key-restart and good idle, press pedal and idle stays high.
I checked the throttle and it is returning all the way.
RBob is there some things that need to be set in the bin for the BB TBI unit.
I set the BPW to 130 with the 55lb injectors @17 psi.
I changed the SA tables to a votec table that I found for a 1998 truck 5.7 vortec (fairly close to what you had). Only changed the bin in the areas that are noted in your documentation.
I am running a 4l60 trans.
Again the engine mods are
383 6" rods
9.8:1 CR
vortec heads
Headers with flowmasters 2.5" pipe
Performer intake (vortec style)
TBI adapter from 454 truck
350 Ram Jet - 383 GM Hyd. roller Cam
454 TBI unit.

I have not yet set any of the VE table data yet.
Do you think this is most of my problem?
Got any sugestions on where to start with these maybe a % factor across the tables?
You were running a 305 correct?
Thanks again!!
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Old 04-04-2006, 04:51 AM   #7
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Only real way to get the VE tables right is just to drive, log and make changes. Use the learn VE feature, that's why its there, you'll be able to rough it in pretty quick. I'd get that straightened out at idle first, it should make it a bit easier then to get your IAC movements straight.

Also, did you set the Airflow Displacement constant for your 383? It's set for a 305 straight from RBob, make sure you do that.
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Old 04-04-2006, 06:45 AM   #8
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OK

383 is set for the displacement
I data logged my idle and used the learn ve.
Will start making corrections this week. I have been following this thread
http://www.thirdgen.org/techboard/tb...free-tune.html (Come in for a FREE tune!!!!)
and it is really helping.
Thanks for your response
Man do I feel like a dumA$$
Looking through RBobs Docs he explains using the VE Learn. I guess I got a little impatient and thought this would be easier. After re-reading everything on the EBL I should be able to get a decent tune using the tools that are incorporated into this package.
Again thanks for all the help, I will try and limit any questions to more complex issues that I may need help with later on as I tune more for performance.
Thanks

Last edited by sbcrules; 04-04-2006 at 10:38 AM.
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Old 04-06-2006, 05:12 PM   #9
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Explain learn VE feature

Quote:
Originally Posted by BronYrAur
Only real way to get the VE tables right is just to drive, log and make changes. Use the learn VE feature, that's why its there, you'll be able to rough it in pretty quick. I'd get that straightened out at idle first, it should make it a bit easier then to get your IAC movements straight.

Also, did you set the Airflow Displacement constant for your 383? It's set for a 305 straight from RBob, make sure you do that.
I read your message and am very interest in the "learn VE feature". Can you please descibe this and is it mechanized in software? Please explain in depth. I need to modify the VE table in my 16197427 0E mask ECM for a 454 Chev bored and stroked to 489cu in.

Rolland Sicard
Tucson, Arizona.
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Old 02-13-2007, 05:02 PM   #10
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Quote:
Originally Posted by rsicard View Post
I read your message and am very interest in the "learn VE feature". Can you please descibe this and is it mechanized in software? Please explain in depth. I need to modify the VE table in my 16197427 0E mask ECM for a 454 Chev bored and stroked to 489cu in.

Rolland Sicard
Tucson, Arizona.
Your truck must be a 94 or 95 huh? They have the newer ecu's, the one you forementioned. Talk to Dimented24x7 (Cofounder of a source with designed to take advantage of addition of a maf), and Fast355 (running same system), and other than that i personally am not sure who else besides oh yeah Haulin@ss. Search for your ecu and mask because the EBL isn't compatible with your ECU, (yours is newer, you'd have to downgrade your ecu to use the ebl).

- B
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Old 02-24-2010, 07:13 PM   #11
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Re: Help High Idle with a BB TBI

Quote:
Originally Posted by RBob View Post
To check stuff out I think it would be best to start with closing the IAC. To do this is easy: short pins A& B on the ALDL connector and key-on with the engine off. After about 20-30 seconds unplug the IAC connector (the IAC should have been clicking during the A/B short and key-on). You can then key-off.

Now start the engine. With a warm engine (up to temperature) the idle speed needs to be below the set idle speed (in the BIN). Wait at least 1 minute after engine startup before any adjustments.

If required adjust the air screw. Now, if you open or crank in the air screw far enough the ECM will drop out of idle mode. This is because the ECM maintains the lowest seen TPS value as the idle setting. To get around this turn the engine off for 10 seconds and restart it. Then wait at least 1 minute before again commencing with idle adjustments (there are after start timing and fuel adjustments, we don't want these to affect the idle setting).

Turn the engine off, wait 10 seconds, and reconnect the IAC. Now start the engine (may need some throttle opening), let it run for at least 20 seconds, and shut it off. The IAC and idle setting should now work out.

Doing all of this with the WUD active will allow one to see if the engine is in idle mode or not. Along with the IAC counts. I know it sounds like a bit of work, but the IAC learns in where the idle is.

As the VE and SA tables get tweaked in closer the IAC steps at idle my/will move around. A slight tweak on the idle screw isn't unusual.

Re-reading this post it sounds convoluted. However, setting up the IAC steps with the air screw sorta' is convoluted.

RBob.
will this same procedure work for a 1991 silverado? my chiltons manual does not show how to reset the iac
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Old 02-25-2010, 08:26 AM   #12
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Re: Help High Idle with a BB TBI

Quote:
Originally Posted by bucklee00 View Post
will this same procedure work for a 1991 silverado? my chiltons manual does not show how to reset the iac
Most likely it will work. Not sure which ECM is in it, although most likely the '7747. This ECM does an IAC reset at key-off after the engine has been running. That is, it fully closes the IAC, then opens it to the park position. At this point the ECM now knows where the IAC is.

RBob.
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Old 02-25-2010, 02:54 PM   #13
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Re: Help High Idle with a BB TBI

Quote: Are there many differences with the idle circuit on the BB TBI unit? It looks totally different when compared to a stock TBI unit that comes on a 350?

Make certain you are using a 7.4L TBI base gasket. Mine covers entire base of unit plus some. Otherwise vac leaks can occur.
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Old 02-25-2010, 02:54 PM
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