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Bosch III injectors are NOT interchangeable w/o tuning

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Old 03-21-2016, 09:07 AM   #1
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Bosch III injectors are NOT interchangeable w/o tuning

Just had another experience which convinces me of this... (my earlier experiences can be found with a search on my user name)

A friend of mine with a bone stock 305 TPI (7730) just swapped out his old Multecs for Bosch III's he bought from a well known injector vendor. Same advertised flow rate as the OEM's => 19 lb/hr.

BLM's immediately pegged at 160. He spent some time trying to fix other things that he thought were the issue...

Vendor said to bump fuel pressure to 46 psi to solve the problem... so he bought an adjustable regulator and set it to 46, but BLM's didn't budge.

Later on he engaged me to try to tune it...

All I did was set the injector constant to 17 lb/hr, put in the closest Bosch-III injector PW vs battery voltage correction values I could find, and zero out the low PW correction table... boom... BLM's back to hovering between 124 and 134.

Anyway, just a heads up for anyone considering upgrading to Bosch-III's.

Last edited by ULTM8Z; 03-21-2016 at 01:49 PM.
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Old 03-21-2016, 10:38 AM   #2
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Re: Bosch III injectors are NOT interchangeable w/o tuning

Thanks for posting this. This is interesting, upon discovering a few of the OEM fuel injectors in an 89 trans am I bought a month ago were dead I bought a set of Bosch Gen II 19lb injectors from South Bay after reading here they were a direct replacement, no retuning required. Since then I've been chasing down a persistent high idle and running rich with no success. Do you think this could be a tuning issue as well? If so, any tips for things to look out for while scanning beyond BLM?

Thanks for any tips or advice you could provide.

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Old 03-21-2016, 12:57 PM   #3
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Re: Bosch III injectors are NOT interchangeable w/o tuning

I'm not sure about Bosch-II's. My previous set was Bosch-II 24lb injectors that I got with my Miniram kit from TPIS many years ago. Those are the only injectors I ever ran before embarking on my injector swap to Bosch-III's (which itself was an extremely painful learning experience), so I never had the experience of going from OEM's to Bosch-II's. I always thought I had those Bosch-II's running well, but even at part throttle the Bosch-III's run way better... Since I don't think it's anything to do with the injectors themselves, it has to be that the tune wasn't optimal for the Bosch-II's. I also never had a wideband on at the same time as the Bosch-II's, so it's all speculation at this point.

However, I do know that, in addition to the inejctor flow rate constant, the other two tables I mention above are critical with Bosch-III's... Whether starting from the OEM Multec's or from Bosch II's.

Nevertheless, I'd recommend making sure all of the above tables and values are correct when swapping for any non-OEM injectors (even if the advertised flow rate is the same).

Last edited by ULTM8Z; 03-21-2016 at 01:47 PM.
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Old 03-25-2016, 03:57 PM   #4
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Re: Bosch III injectors are NOT interchangeable w/o tuning

ULTM8Z, can you post the Bosch-III injector PW vs battery voltage correction values that you used? Thanks.
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Old 03-26-2016, 07:15 PM   #5
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Re: Bosch III injectors are NOT interchangeable w/o tuning

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Old 03-28-2016, 11:12 AM   #6
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Re: Bosch III injectors are NOT interchangeable w/o tuning

Cool, Thanks ULTM8Z.


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Old 04-11-2016, 12:38 AM   #7
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Re: Bosch III injectors are NOT interchangeable w/o tuning

In my case, I will be basically starting from the ground up on Lazarus ('61 GMC w/ 5.0 TPI and 4-speed manual). It sounds like it will be worth the purchase of the Bosch Gen 3s and make the software adjustments for the improved drivability.

Does that sound like a better path than the simple Gen 2 swap?
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Old 04-11-2016, 07:45 AM   #8
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Re: Bosch III injectors are NOT interchangeable w/o tuning

I'd go with the Bosch III's. They're not at all difficult to tune for once they're understood and they do run very well.

As with the example in my original post in this thread, I had his car dialed-in in about 15 minutes.
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Old 05-19-2016, 09:29 PM   #9
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Re: Bosch III injectors are NOT interchangeable w/o tuning

Are these the injectors you guys are talking about: http://www.southbayfuelinjectors.com...rvette-c4-l98/

I bought those for my 350 so I just want to be 100% clear that this thread is referencing the Bosch D3 injectors. I want to be prepared for odd tuning issues
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Old 05-19-2016, 10:03 PM   #10
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Re: Bosch III injectors are NOT interchangeable w/o tuning

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Old 05-21-2016, 09:09 AM   #11
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Re: Bosch III injectors are NOT interchangeable w/o tuning

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Originally Posted by Dartht33bagger View Post
Are these the injectors you guys are talking about: http://www.southbayfuelinjectors.com...rvette-c4-l98/

I bought those for my 350 so I just want to be 100% clear that this thread is referencing the Bosch D3 injectors. I want to be prepared for odd tuning issues
yeah thats them
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Old 05-25-2016, 01:20 AM   #12
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Re: Bosch III injectors are NOT interchangeable w/o tuning

In the EBL bin I'm using as my base tune, I found the table you were talking about (Injector correction offset). The bin I'm using has a higher resolution on the voltage axis vs the offset than the table you provided. Did you notice a similar difference when working on your friends car and how did you decide to round the values?

My table attached.

I'm planning on changing the injector constant to 20#/hr to match the -2 you did with the 19#/hr injectors. I'm also assuming the PW table you zero'd out was "small PW correction"?
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Bosch III injectors are NOT interchangeable w/o tuning-capture2.png  

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Old 05-26-2016, 07:27 PM   #13
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Re: Bosch III injectors are NOT interchangeable w/o tuning

I believe there's some linear interpolation you have to do when voltages in the injector datasheet don't match the values in the x-axis in the bin.

But, there was such a difference between the Bosch-III values and the $8D factory values, that percentage error between what you enter (which may not fit the Bosch-III curve exactly) vs the ideal value for the injector is very small.

In other words, as long as you're pretty close to the Bosch-III values, should see a marked improvement in driveability and power over hte factory $8D values.

Yes, zero out the small PW correction values.
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Old 05-27-2016, 02:54 PM   #14
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Re: Bosch III injectors are NOT interchangeable w/o tuning

I just spoke to Southbay about this and they are aware of this thread. I'm kind of hoping they chime in here with some information for us.
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Old 05-27-2016, 09:19 PM   #15
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Re: Bosch III injectors are NOT interchangeable w/o tuning

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I just spoke to Southbay about this and they are aware of this thread. I'm kind of hoping they chime in here with some information for us.
Yeah I'd be curious to get their take as well.
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Old 05-29-2016, 08:40 PM   #16
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Re: Bosch III injectors are NOT interchangeable w/o tuning

Hmmm. I have the SouthBay TPI modified Bosch III injectors I bought from them about 7 years ago. They are 30lb. I had Accel 30lb injectors for about 8 years prior until they ate it. Swapping from the Accel to the Bosch III after readjusting my rail psi at idle to be stock (it had gone off by a couple psi over the years), I didn't even need to change anything in my tune. I did spend allot of time tuning for my Accel injectors originally though.

I don't recall allot of issues going from the original Multec injectors to the Accel injectors but maybe I'm just forgetting because it's been so long.
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Old 06-01-2016, 07:02 PM   #17
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Re: Bosch III injectors are NOT interchangeable w/o tuning

how would I convert this info to fit an $6E bin ? the offset area seems to be different values ..... thanx
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Old 06-06-2016, 10:09 AM   #18
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Re: Bosch III injectors are NOT interchangeable w/o tuning

See post #5:

https://www.thirdgen.org/forums/diy-...gn-iii-pw.html (Bosch design III PW offset tables)

For the 0 volt offset entry, use the same value as the 12.8 v entry.

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Old 06-06-2016, 07:51 PM   #19
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Re: Bosch III injectors are NOT interchangeable w/o tuning

I don't mean to hijack. Are these the same but just at 30#? I cannot find the offsets that will work in $6E.

https://www.fuelinjectorconnection.c...impedance.html
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Old 06-06-2016, 07:53 PM   #20
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Re: Bosch III injectors are NOT interchangeable w/o tuning

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I don't mean to hijack. Are these the same but just at 30#? I cannot find the offsets that will work in $6E.

https://www.fuelinjectorconnection.c...impedance.html
Are these what people refer to as "SVO" injectors? Can't answer your question tho, I know nothing about Fo*d stuff lol.
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Old 06-07-2016, 08:28 AM   #21
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Re: Bosch III injectors are NOT interchangeable w/o tuning

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Originally Posted by IROCThe5.7L View Post
I don't mean to hijack. Are these the same but just at 30#? I cannot find the offsets that will work in $6E.

https://www.fuelinjectorconnection.c...impedance.html
This should be the correct data for those injectors:

Injector Data Sheet: M-9593-BB302 (EV6 30 #/hr) 280-155-759

Fuel Pressure: 44 psi
Flow rate: 32.3 #/hr

Offset Compensation versus Battery Voltage:
6.4 Volts: 3193 usec
8.0 Volts: 2163 usec
9.6 Volts: 1618 usec
11.2 Volts: 1278 usec
12.8 Volts: 1031 usec
14.4 Volts: 821 usec
15.0 Volts: 784 usec*

RBob.
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Old 06-07-2016, 05:59 PM   #22
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Re: Bosch III injectors are NOT interchangeable w/o tuning

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Originally Posted by RBob View Post
This should be the correct data for those injectors:

Injector Data Sheet: M-9593-BB302 (EV6 30 #/hr) 280-155-759

Fuel Pressure: 44 psi
Flow rate: 32.3 #/hr

Offset Compensation versus Battery Voltage:
6.4 Volts: 3193 usec
8.0 Volts: 2163 usec
9.6 Volts: 1618 usec
11.2 Volts: 1278 usec
12.8 Volts: 1031 usec
14.4 Volts: 821 usec
15.0 Volts: 784 usec*

RBob.
You seriously rock. You help this forum out so much. Thank you very much. It's much appreciated.
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Old 06-07-2016, 10:54 PM   #23
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Re: Bosch III injectors are NOT interchangeable w/o tuning

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You help this forum out so much.
Ain't that the truth!!
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Old 06-08-2016, 07:35 AM   #24
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Re: Bosch III injectors are NOT interchangeable w/o tuning

much thanx--- will give it a try !!!
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Old 06-17-2016, 05:34 PM   #25
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Re: Bosch III injectors are NOT interchangeable w/o tuning

Just a heads up to everyone: changing the injector flow rate matters a lot. When modifying my bin I changed the injector offset correction table and the small pulse width correction tables to the values stated earlier in this thread. But I made a stupid mistake and forgot to adjust the injector flow rate from 22# to 19#.

That small error had me chasing lean issues for 2 weeks. At idle my VE table values were in the low 70s to get a BLM around 128 while still trending towards the lean side. Because my idle VE table values were so high, I ran out of room quickly when going into higher RPM and MAP values.

Then last night I thought to check the injector flow rate value and sure enough, I had forgotten to change it. Once it was set at 19#, my BLMS looked MUCH better. I went back to the original bin I started with before modifying the VE tables for the lean issues, and my fueling was almost spot on. Rich in a few areas even - something I had never seen before making this adjustment.
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Old 09-11-2017, 06:24 PM   #26
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Re: Bosch III injectors are NOT interchangeable w/o tuning

Well son of a gun... I have been chasing this... hopefully this is my problem... but dang, lotsa dollars and elbow grease replacing just about dang near everything...

https://www.thirdgen.org/forums/tech...e-stumble.html (Help Me Chase This Stumble Down)

So, should I reinstall my Multecs or find someone to pay to program my ECM for these things? I suppose I could learn myself.

Kinda ticked. I spoke to SouthBay and they didn't mention anything about this.

It's like I created a new problem when trying to fix another... BUT I am excited, maybe this is my problem. The car is so close to running perfect OEM.

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Old 09-11-2017, 07:39 PM   #27
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Re: Bosch III injectors are NOT interchangeable w/o tuning

I've got a 1988 L98 350 TPI Mass Air Flow car and bought a new set of Bosch 3 24lb injectors.

In the future I will replace the stock 165 ECU with a new Haltech Platinum GM Sport ECU.

My question is, while still using the stock MAF 165 ECU would I need to reburn the PROM or would the MAF system be flexible enough to handle the new injectors?
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Old 09-12-2017, 09:56 AM   #28
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Re: Bosch III injectors are NOT interchangeable w/o tuning

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Well son of a gun... I have been chasing this... hopefully this is my problem... but dang, lotsa dollars and elbow grease replacing just about dang near everything...

https://www.thirdgen.org/forums/tech...e-stumble.html (Help Me Chase This Stumble Down)

So, should I reinstall my Multecs or find someone to pay to program my ECM for these things? I suppose I could learn myself.

Kinda ticked. I spoke to SouthBay and they didn't mention anything about this.

It's like I created a new problem when trying to fix another... BUT I am excited, maybe this is my problem. The car is so close to running perfect OEM.
My friends car also didn't run terrible either... just high BLMs and some mild stumbling.

So yeah that could be your issue.

The injector company I was dealing with wasn't at all helpful with me when I was trying to figure out the issue on my car. And frankly these modified Bosch-IIIs sometimes may not even correspond to the offset tables they're supposed to use. On my car, I had to go get factory Ford injectors and use the table for those in order to be successful. The ones i bought earlier that were 19 lb and modified to be 30 lb were literally un-tunable ( you can search on my user name looking for threads on Bosch-IIIs).
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Old 09-12-2017, 02:53 PM   #29
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Re: Bosch III injectors are NOT interchangeable w/o tuning

I think I am going to throw my old, good Multecs in and see if that fixes the BLMs. That'll help eliminate the D3s if that's the case- or not!
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Old 09-13-2017, 12:15 AM   #30
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Re: Bosch III injectors are NOT interchangeable w/o tuning

Threw in the Multecs. BLMs low-normal now instead of pegged 160. Car drives much better except for high load miss. I will check my iridiums for rich fouling.

Data file attached. I am in the camp that D3's are NOT drop-in compatible.
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Old 09-13-2017, 08:16 AM   #31
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Re: Bosch III injectors are NOT interchangeable w/o tuning


I am using the 24# Bosch III's in my car Yes you do have to play with the battery offset compensation table.


It did help a lot with mine. The Bosch III's open much faster than the Multec's and that is why it runs rich unless you make adjustments...


Attached is the sheet that Southbay sent me for the data on the 27# ones I got from them....


I did have to "wing" it a bit as the tables on this sheet and the tables in my EBL P4 do not match but it was a huge help.
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Old 09-13-2017, 09:24 AM   #32
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Re: Bosch III injectors are NOT interchangeable w/o tuning

Yep. Hopefully they will accept my return. They are sold as OEM replacements and they are not.
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Old 09-13-2017, 11:18 AM   #33
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Re: Bosch III injectors are NOT interchangeable w/o tuning

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Yep. Hopefully they will accept my return. They are sold as OEM replacements and they are not.
Yeah try to get factory injectors and then the datasheet corresponding to that p/n. That will give best results.

Even if you need only 22 lb and find a 30lb factory injector, you can tune for it. I only need roughly 26 lb, but got 30 lb and it runs fantastically.
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Old 09-13-2017, 11:26 AM   #34
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Re: Bosch III injectors are NOT interchangeable w/o tuning

You guys are crazy. Tune for them. These are freakin light years better than the factory Multec injectors. Your engine will run smoother everywhere and with a tiny increase in power and fuel economy. I can't even begin to convey just how much better these atomize the fuel.

These are as "drop in" as you're ever going to find.
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Old 09-13-2017, 11:37 AM   #35
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Re: Bosch III injectors are NOT interchangeable w/o tuning

This is my "enjoy the car" engine. Stock OEM 305 TPI. I prefer to keep it that way. So far I have been "under" the car far more than I've been "in" it. I just want to get it running right and then I can relax for a bit. Right now it's love and hate. The D3's caused another problem I did not need. Now that that is out of the way I can close in on the chronic, constant missing problem after warm up.
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Old 09-13-2017, 11:47 AM   #36
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Re: Bosch III injectors are NOT interchangeable w/o tuning

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You guys are crazy. Tune for them. These are freakin light years better than the factory Multec injectors. Your engine will run smoother everywhere and with a tiny increase in power and fuel economy. I can't even begin to convey just how much better these atomize the fuel.

These are as "drop in" as you're ever going to find.
By "factory" I mean OEM Bosch III in the flow rate you need, as opposed to aftermarket modified Bosch-IIIs.

With all due respect, you probably need to read the thread more carefully before spouting off with insults...
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Old 09-13-2017, 01:47 PM   #37
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Re: Bosch III injectors are NOT interchangeable w/o tuning

Hey Guys, I'm sure you all have this info but I thought I would post it anyway. If not, hope it helps


The ECM calculates the fuel injector pulse width on the assumption that it knows all about your engine... displacement, injector size, mass air fow, etc. It uses an equation that includes the terms:

..... x (BLM/128) x (INT/128).......

The BLM is the long term fuel correction. This is what is stored in the ECM in volatile memory. The INT is the short term fuel correction, and its not "stored". The ECM recalculates the short term correction for every cycle of the calculation - about 9 times per second. It is intentionally forcing the closed loop A/F ratio to swing back and forth between very slightly rich (14.65:1) and very slightly lean (14.75:1). It has to do that for the cats to work.... when its lean the cat stores the excess oxygen, when its rich the stored oxygen combines with the unburned hydrocarbons (HC) and carbon monoxide (CO).

If the ECM finds that the long term average of the INT's is adding fuel (over 128), it ratchets up the BLM's to try and get the average of the INT's back to 128. It stores those values in the volatile memory..... that's most of what the ECM "learns". If the BLM's are above 128, the ECM is responding to what it BELIEVES is a lean condition. IF the BLM's are below 128, its responding to what it BELIEVES is a rich condition.

The BLM's are developed during part throttle/part load conditions, when the ECM is operating in closed loop (O2's are being used to modify the fuel rate). They are not learned when you are running at WOT, so they are not an indication that the engine is leaning out at peak power output. They are used at WOT to calculate the fuel rate (but only if they are above 128). A BLM above 128 indicates that something in the fuel system is not responding the way the ECM thought it would.

For example, if your fuel pressure is too low, the injectors don't flow the amount of fuel the ECM is expecting, it runs lean, and the O2 feedback elevates the BLM's above 128. If you had a vacuum leak, same result. If you have an MAF sensor and its dirty and reporting less mass air flow than is actually entering the engine, its a lean condition. If you have a speed-density setup, and have modified the intake and exhaust to improve the engine's breathing, but have not had the programming modified with changes to the volumetric efficiency (VE) tables, it would run lean. These are all "TRUE" lean conditions.

But sometimes, the O2 sensors give the incorrect feedback, indicating a "FALSE" lean condition. The main examples of this would be 1) faulty O2 sensor(s), 2) misfires, 3) exhaust leaks before the O2 sensors. All of those trick the ECM into thinking the engine is running lean, and it adds a bunch of extra fuel, using the BLM's, that the engine does not need.
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Old 09-13-2017, 03:01 PM   #38
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Re: Bosch III injectors are NOT interchangeable w/o tuning

I have the #3 injectors also from SouthBay (22#) Could I use this info for mine? This is for the 19#.
6.4 V: 3.07851247
8.0 V: 1.85340073
9.6 V: 1.30766195
11.2 V: 0.99121428
12.8 V: 0.76537403
14.4 V: 0.60906068
15.0 V: 0.55248610*

Also what else would I have to do on the top of that screen to make it a correct install.
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Old 09-13-2017, 06:06 PM   #39
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Re: Bosch III injectors are NOT interchangeable w/o tuning

Hard to say... once an injector is modified it's not clear that the datasheet of the original injector still applies to the modified one.

Often times the supplier will have to retest and come up with data specific to the modified injector.

Like i said before, my original attempt at BoschIII with modified injectors... the vendor threw some datasheet over the wall at me and it didn't work at all.
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Old 09-13-2017, 06:51 PM   #40
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Re: Bosch III injectors are NOT interchangeable w/o tuning

what do you mean by modified? What bosch lll's are modified? And to what?
I'm confused
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Old 09-13-2017, 07:07 PM   #41
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Re: Bosch III injectors are NOT interchangeable w/o tuning

Edit... double post

Last edited by ULTM8Z; 09-13-2017 at 07:10 PM.
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Old 09-13-2017, 07:08 PM   #42
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Re: Bosch III injectors are NOT interchangeable w/o tuning

The ones i had gotten earlier on were originally 19 lb and were evidently modified to be 30lb by drilling the atomizer plate. They weren't South bay injectors....

Maybe yours are not modified in which case my comment wouldn't apply there...
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Old 09-15-2017, 11:10 AM   #43
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Re: Bosch III injectors are NOT interchangeable w/o tuning

No that's ok. I misunderstood Sorry,, my bad
and no...we do not modify our bosch lll's
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Old 09-15-2017, 12:32 PM   #44
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Re: Bosch III injectors are NOT interchangeable w/o tuning

That's fine... no apology necessary... no offense was taken...

But I guess getting back to 83 Gman's question... If they're the correct values, my guess is you'll know it pretty quickly.

After having ditched those earlier modified Bosch-III's and getting the factory Fords, I recall when I started up the car with the factory Ford Bosch-III's and the correct offset values for that exact p/n, I knew immediately something was very different (and for the better) just after 10 seconds of starting it and having it idle.

From there it was pretty easy to get everything in line in terms of the fueling (not withstanding the unrelated PE drop out issue that RBob graciously helped me fix along the way).
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