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89 S10 Blazer 4.3 tbi vin z 700r4 4x4
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First time on a forum so pls forgive if I'm posting in the wrong place. I've got an 89 s10 blazer 4.3 tbi and I'm hoping for some obd1 knowledge. At operating temp, in gear with foot on the brake, I can watch the iac count step all the way to zero and the engine stalls. I've replaced all vacuum lines, checked for vacuum leaks with map gas, replaced the cts, tps, iac, egr and egr solenoid. O2 sensor has maybe 5000 miles on it and the voltage oscillates pretty consistantly between 100 ish to 780ish. Block learn in closed loop sits around 90 at cruise and might climb to 110 at idle so I know its rich. The pressure regulator has a new spring that is supposed to be 12 psi but I was only seeing at best 5 so I installed an aeromotive regulator in the return line between the tbi and the tank. Set it to about 14.5 and it maintains a consistant 14.5.
1st question: is 14.5 too much pressure causing a rich condition and the computer is trying to cut fuel to maintain proper a/f?
2nd: any idea why the ecm doesnt maintain idle with proper iac count? (Iac does seem to be functioning otherwise. 120ish at highway cruise or more depending on throttle input. Also when ac is engaged, the ecm will respond with about 20 steps up on the iac to compensate for the added load but then will creep back to zero and stall)

Sorry for the long post, just trying to provide someone with as much info as possible. Any advice or ideas will be greatly appreciated!
 

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1st question: is 14.5 too much pressure causing a rich condition and the computer is trying to cut fuel to maintain proper a/f?
It may be but it would do it by adjusting injector PW (INT/BLM), not closing the IAC. EDIT: Yes 14.5 may be a little high for a stock engine.

2nd: any idea why the ecm doesnt maintain idle with proper iac count?
It almost sounds like you have a vacuum leak, EGR, TB plate shaft bushings, TB gasket, hoses, etc?

When you changed all those parts did you calibrate your base idle, IAC, and TPS? Here's a link to a .pdf that shows how to do it.

How-to-Tune-a-GM-EFI-System.pdf
 

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89 S10 Blazer 4.3 tbi vin z 700r4 4x4
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Discussion Starter #3
Awesome info, thanks! And sorry, I probably didnt word that question very well. I was referring to the blm/int numbers. They both show a correction for rich condition. I thought it would be a vacuum leak too so I used the map gas and found the Chinese egr was actually leaking by so I replaced it and could find no more vacuum leaks. The tbi is a reman unit and doesnt seem to be leaking past the bushings. New base gasket as well. I'm not sure how to find out what the target idle is for my chip...(its all stock) I did use a similar article to set base idle at 575 and still had the same issue. Tps has good ground and signal voltage is .61 at closed throttle. Smooth transition while opening throttle. It maxes out at around 3.5v at wot. I will lower the fuel pressure soon and see if I can make my block learn happier. Also I am using aldldroid and the 1320electronics bluetooth adaptor. Thanks!
 

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Sounds like you're on the right track. A word of caution, if your IAC drives down to zero, it may burn up the stepper motor and become useless. If you look at the ECM and/or open it up to see the BCC (Broadcast Code Chip)
167128

You can probably find it here,

Or you can get the Moates Burn2 and read it using TunerPro RT v5xx

You can get your ECM chip holder converted to a ZIF (Zero Insertion Force) socket to accept the 27SF512 (EEPROM) chip so you can "flash" your own .bins instead of the old 2732A chip.

OR - go with the EBL Flash2 - much better, expanded tables, 8192 baud rate as apposed to 160 with the older ECMs.

Lots of fun, enjoy, HTH!
 

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89 S10 Blazer 4.3 tbi vin z 700r4 4x4
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Discussion Starter #5
Thanks very much for all that info. Now I have lots of homework and some purchasing to do. I'll post progress as I'm able to work on this. Also thanks for the warning about the IAC. Hopefully im not causing damage.
 

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89 S10 Blazer 4.3 tbi vin z 700r4 4x4
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Well I went with the EBL flash2. Should be awesome. I swapped a known working stock ecm into my truck today and it ran exactly the same. Iac still counts to 0 in gear. Checked a little more thoroughly for vacuum leaks and hearing a little change at the throttle shaft bushings. It's a reman unit with about 50,000 miles on it. Kinds hesitant on another reman unit. Holley makes one for a 90 and up 5.7. Think I could make it work on my 4.3? Seems to be a non ecm issue at this point. Still excited for that ebl flash2 though.
 

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Holley makes one for a 90 and up 5.7. Think I could make it work on my 4.3?
The Holley TB has a 50mm bore, IIRC. That'll be too big for your 4.3. If you're getting vacuum leaks at the shaft bushings, that needs to be corrected before tuning. Keep in mind you can't properly tune to correct a malfunctioning hard part. You may be able to mask the issue but it'll never be right. I don't know where you got the reman TB but there's a good chance you got ripped off. You can send it in to one of these guys or just get one from them, they're both reputable and knowledgeable with TBI systems. I've bought stuff from both and haven't been disappointed with either.

Enjoy the EBL Flash-II, I hope you get yourself a WBO2 to go with it!


 

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Still excited for that ebl flash2 though.
LOL, I'm guessing you just joined GearHead-EFI, or someone else is using your handle! Another website/thread you may want to research, lots of support and dedicated to the EBL going back to 2006, 97 pages and still going strong.

 

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89 S10 Blazer 4.3 tbi vin z 700r4 4x4
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Discussion Starter #9
Haha yep that's me on gearhead. I wish I would have joined years ago. I'd be a lot farther ahead in this whole diagnostic and tuning world. Thanks for the link for the tbi, that's exactly what I needed and I didn't even ask for it! Definitely agree that hard part issues need to be resolved first. I will definitely be on that ebl site soaking up info as well. I read the pdf you posted about tuning tbi. Awesome and very thorough. I'll be re-reading it multiple times. I'll probably be ordering a tbi and a wbo2 here very shortly. I have no car payments...just parts expenses!
 

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89 S10 Blazer 4.3 tbi vin z 700r4 4x4
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Just ordered a tb from R.V. Morse Machine. Way less expensive than that holley unit. Thanks again!
 
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