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Discussion Starter #1
I have 87 Elko 305 V8 automatic with OD. Does anyone know if I can use the PROM or the complete ECM out of a Monte Carlo SS to improve performance a little on my 305? What do people mean by the service number of the ECM and where do I look for it? Does the PROM have a number?
 

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Jim, a long time ago, I asked a similar question and I believe Darbysan had some information specifically about this. Unfortunately, I can't find that thread. As for the service number it is the 8-digit number for the ECM along with 4-letters which identify the PROM programming. As for where to find this information, it is printed on a label attached to the ECM.

If you want to learn A LOT about messing with ECMs and reprogramming these computers, checkout the site gearhead-efi.com.
 

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The ECM has a number on it, I believe you will find that the Monte and El have the same ID number and are interchangeable. I looked into this awhile ago and that's what I remember.
 

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Discussion Starter #4
I have 87 Elko 305 V8 automatic with OD. Does anyone know if I can use the PROM or the complete ECM out of a Monte Carlo SS to improve performance a little on my 305? What do people mean by the service number of the ECM and where do I look for it? Does the PROM have a number?
Thanks
 

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Jim, a long time ago, I asked a similar question and I believe Darbysan had some information specifically about this. Unfortunately, I can't find that thread. As for the service number it is the 8-digit number for the ECM along with 4-letters which identify the PROM programming. As for where to find this information, it is printed on a label attached to the ECM.

If you want to learn A LOT about messing with ECMs and reprogramming these computers, checkout the site gearhead-efi.com.
Thanks
 

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Since you have an '87, the ECM should be the same as the Monte, so a PROM swap will work, no issues. Just may be easier to get the whole ECM as just the prom. You can also use a ZZ4 prom, which eliminates the EGR function ( a known problem area). From another site:
" Swapping to a 1228079 ECM is a good choice. But remember the PROM is year specific, 87-88 only PROM that works. Caprice and Camaro both used the 079 in 87-88, they are donors{if you can't find one from another G-body}.. The 079 is really the only choice for an upgrade. Any of the 87-88 PROMS are good"

Here's a good thread. Get's into detail about the chips, even re-programming them.

For the prom, here's a pretty good chart. Look at the 4BBl lines with the 1228079 ECM. Might find one with the same gearing that you have.
 

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Discussion Starter #7
Ok guys a lot of info to digest. To recap I have a 305 with mild Summit #1102 cam, 2:56 rear 200R4 trans. All pollution equipment is still on engine including the EGR, No engine lights on now. So it sounds like I need a LG4 if I want EGR to work or ZZ4 to eliminate EGR. Will either of these PROMs improve my engine performance? If I put a block off plate on my EGR will my current ECM know? Will blocking EGR off improve preformance?
Thanks, Jim
 

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Blocking off EGR will cause Check Engine light. It will not improve performance. Using EGR actually improves mileage just a bit, and also keeps the engine a little cooler. The L69 prom is the one that will improve your performance ( but only just a bit- may not even be able to measure it. Stock difference was 10 hp, but that also included Cam, piston and head differences too). LG4 is the standard engine. With the L69 chip, expect to get an EGR light ( Code 53), as it was a flaw in the software. Only known fix is to go with the ZZR chip, which can eliminate EGR on some versions. Can be expensive to buy this chip, unless you find someone who can burn a chip for you. I have the BIN file if you find you want to do this and find someone to burn the chip( Check my webpage for the files).

For a significant improvement in performance, change out your rear gears to at least 3.08. 3.23, 3.42 or even 3.73 will work great with your 200-4r and be even better. 3.42 is a stock MCSS rear gear, as is the 3.73 in later years. It will feel like you've added 100 hp, and you won't have to change your ECM. Just the driven gear for you speedo in your trans ( easy).
 

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Discussion Starter #9
Blocking off EGR will cause Check Engine light. It will not improve performance. Using EGR actually improves mileage just a bit, and also keeps the engine a little cooler. The L69 prom is the one that will improve your performance ( but only just a bit- may not even be able to measure it. Stock difference was 10 hp, but that also included Cam, piston and head differences too). LG4 is the standard engine. With the L69 chip, expect to get an EGR light ( Code 53), as it was a flaw in the software. Only known fix is to go with the ZZR chip, which can eliminate EGR on some versions. Can be expensive to buy this chip, unless you find someone who can burn a chip for you. I have the BIN file if you find you want to do this and find someone to burn the chip( Check my webpage for the files).

For a significant improvement in performance, change out your rear gears to at least 3.08. 3.23, 3.42 or even 3.73 will work great with your 200-4r and be even better. 3.42 is a stock MCSS rear gear, as is the 3.73 in later years. It will feel like you've added 100 hp, and you won't have to change your ECM. Just the driven gear for you speedo in your trans ( easy).
darbysan if I get the L69 PROM will it work with my 2:56 rear end? Also
I think I will start looking for a 3:08 rear end. I know a old guy that builds rear ends for a living. he will put New 3:08 gears in my rear end for ~$400 or new posi and gears for ~$800 only problem is he will not do it on the car. Must remove complete rear end and bring it to him. I would go with steeper gears but my Elko is a cruiser not a hot rod. If I feel the need for speed I have another hot rod to satisfy that itch.
 

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Jim, if performance is not your goal, why even think about changing ECM's or getting performance chips? Every change has it's benefits, but also it's issues. As for the L69 prom, I believe it should work, but at most you are going to gain 3-5 hp, and with that you might run into issues (pinging, for one). If a little better performance is your desire, change the gears. You will gain nothing from the engine that you will be able to feel without getting inside of it. The L69 had higher compression pistons, better heads, better cam, and better timing from the ECM, and all that got you was 10 hp.

Some Elky's came with 3.08 from the factory ( mine did). Might find one. I went from 3.08 to 3.42, and it felt like a new engine was installed. I later moved up to 3.73, but in reality I think 3.42 was a good choice. With your 2.56 gears and OD, you are essentially running with 1.79 gear ratio at cruise- just lugging along, and definitely below the RPM power level of the engine ( 1600-1900 is where the power just starts to come in). You might even find that with a higher Gear ratio ( like 3.08 or 3.42), you mileage might actually improve because your engine will be running in a "Happier" rpm range.
 
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Darbysan, I agree with you regarding 3.42 gears making the car peppier and would be better than messing around with a different ECM. I swapped out my stock rear end assembly with 2.56 for a GN 3.42 posi unit. My motor is a bone stock 305 and trans is a plain Jane 2004r.

Jim, I don't know what your level of familiarity/knowledge is with changing or modifying ECMs and performance tuning. My apologies if I appear to be speaking below your knowledge level.

First, the ECMs in our 87s have the PROM soldered directly to the circuit board. Second, these ECM versions use the spade-style connectors which were changed to plugs-with-pins later in the evolution of using computers to control engines and transmissions. Third, in order to change the PROM (or ECM programming), you have to find an ECM (correct service number) with the desired PROM (also known as a chip) already installed--soldered to the circuit board OR modify the ECM with a PROM holder that enables easy chip replacement. Lastly, if there isn't a chip or programming readily available, then your set up will have to be tuned by someone knowledgeable in performance tuning.
 

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Discussion Starter #12
All, Thanks for the input. Now don’t laugh, but my experience with changing proms is related to slot machines of the same 1980’s era that I have repaired and collected. The PROM chips on a 1980’s slots can be changed and erased with UV light just like the the ones used in the 87 ECM. My knowledge of engine tuning is more toward the older pre computer cars. But I am a excellent technician and have always accomplished whatever I put my mind to. That said, I will take the information I have so generously received here and use it wisely in my decision making.
Thanks again,
Jim
 

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Jim, if you like challenges, then I say go for it! More than once, I have considered installing a ZIF (zero insertion force) socket in order to accept PROMs with new programming. Ultimately, I decided to simply go the non-computer route. Good luck!
 
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