cumbercr

I installed a Jim Barth 396 Super Ram in my 85 two years ago. Since then I have never been able to get the tune quite right. I feel like the 870 ECM just doesn't have enough tuning parameters. So I'm planning on upgrading the ECM to a 165. I've researched threads on the subject and I think I have a handle on what needs to be done. But I have to believe there are forum members who have run into glitches. I'd appreciate any tips or lessons learned from those have made the swap.

By the way, I am documenting this modification to hopefully provide a comprehensive procedure for others to follow.

John A. Marker

Did you have a non-stock cam put in the 396?

I ran the stock bottom end L98 on my 85 with 180 AFR heads and the SuperRam for several years with the stock chip. When I changed over to the ZZ4 with a Lingenfelter cam keeping the AFR heads and SR I had a chip made by TJ Wong and had no problems at all. It might be your tune.

cumbercr

I'm using a Crower 221/230 with AFR 195 heads and 42# injectors. Ed Wright did the initial tune and it would be OK if I lived anywhere but California. But my current tune is borderline legal at idle. I have to increase the idle RPMs to just under the legal limit to sneak by. Ed told me at the time that it would be iffy with the 870 ECM.

I also ran my Super Ram with AFR heads and a near stock cam with a stock chip. But I couldn't leave well enough alone.

MrWillys

Have you considered just upgrading to the 1227727 speed density? An independent harness can be had for about $250, and I think the tuning is easier.

Aardwolf

If it were me I would probably get a MegaSquirt kit. Even if you buy it assembled it's still a decent price. Having spent plenty of time and money on tuning the self tune computers have been looking so nice. Tell the computer the A/F and let it work!

cumbercr

Frankly I'd rather stick to a conversion that has been done by others. Making harness modifications bothers me enough. But I'm OK with it because the process has been documented by others and I feel confident I can succeed.

cumbercr

Thanks for the tip. I checked out their website. There's a lot of info to go through. The biggest stumbling block is CA smog.

powerpigz-51

Sign me up. I have the 870, and tuning capability (Hardware wise), and was always under the impression that the 870 could be tuned. Where it seems to be lacking is in the data logging department, with info being updated at "whatever" speed. My lack of tuning knowledge, combined with lousy scan feedback, has left me with pretty much a stock tune. My next round of mods consists of Edelbrock RPM heads, Hi flo intake, 24 # Bosch 3's, Comp XE262 114 and 1.6 roller tip rockers, Pacesetter shorties and chambered exhaust. I have fully siamesed stock runners, but am considering some ported out SLP's. So what is actually different (or lacking) in the 870's tuning parameters? Do I just need the knowledge to be able to tune it (which is what I would like to do)? If it is simpler, meaning less stuff to get you in trouble, maybe it is a good ECM to learn on. Now if someone can just explain what the dang tables do and what to do to them to make your car run better..........

cumbercr

I've compared the 85 and 86 BINs and there a lot more parameters in the newer ECM. In fact, way too many to list here. So I think there's more to the swap than just data log speeds. The question I have is why do so many tuners refuse to work on the 870 ECM? And I'm with you. I wish there was a tutorial on all these tables.

powerpigz-51

Some tables are air, some tables are fuel, some are timing. Engine load vs. all of these. I want a carb lol

vetteoz

Because it is a one year orphan with a slow data rate that anyone doing serious tuning would want to get away from

Comment below from Mike Davis that documented the 870 - 165 ECM swap
http://www.eecis.udel.edu/~davis/z28/ecm_swap/

" '870 diagnostic data is transmitted at only 160 BAUD!.
This works out to about a 1.25 second interval between the 25 Bytes of data.
I have only been able to get about 6 to 8 data samples during a Quarter-Mile DragStrip run which you can imagine does not
provide much feedback for tuning

The ALDL data rate for the 86 - 89 '165 ECM can supply diagnostic data at 8192 BAUD.
The data stream of 64 Bytes cycles through every 62.5 milliseconds (16 per second) at this BAUD rate."

cumbercr

I don't disagree with the diagnostics advantages, but why would a well known tuner tell me he could tune for smog with a 165 ECM but not with an 870. There's more to this than diagnostics.

GREGGPENN

I think he's saying the shear speed improvement for sensor feedback (aka diagnostics) is what makes the newer ECM a better computer for correcting AFR. That would translate into emissions improvement.

I like the idea of converting to a 165 ECM. I've seen it mentioned and suggested several times. I thought it was a fairly simple plug/play kind of swap. Will you plug off and not use your CSI? Beyond that, I can't remember if/what sensor differences there are.

I wish I could help you.

Once you get hooked up, I can at least help with any questioned on 165 ECM tuning.

powerpigz-51

Here is a good question....just because the ALDL info is slow, does this really effect the part of the ECM that is running the engine? Isn't the ALDL info a separate function?

Cliff Harris

The slow data rate affects your ability to data log. You're just seeing snapshots instead of a movie. That's why the tuners don't like it.

The 1227165 ECM was used from '86 through '89, so it's quite possible to retain the cold start injector (which was eliminated in 1989). It only works while cranking so it doesn't affect the tuning while the engine is running.

The swap to the 1227165 ECM requires some "repinning", which means moving some of the pins to different positions in the ECM connectors. All this has been well documented in several places.

vetteoz

well documented
http://www.eecis.udel.edu/~davis/z28/ecm_swap/

Other than the ECM ,
the major difference is the expensive ( $150 + ), hard to find ,burn off module under the dash that was replaced
by a couple of $15 relays on the '165 setup

cumbercr

Since I'm running a Super Ram the cold start injector port is already blocked off. So I hadn't considered that. But I assume if I was to use it the 86 ECM should be compatible.

I've researched the harness changes and conversion of the burn-off module to relays. That part I understand. It's not plug and play but it's not rocket science. Unfortunately, the article vetteoz referred to is based on conversion of an F body ECM. I've already discovered some minor wiring differences between the F and Y bodies. I also seem to recall someone running into issues with the BIN settings. So while there is a good bit of information available, I have not found a comprehensive guide for the Y body conversion. That's why I want to document the process for others.

cumbercr

I've been told the ALDL is separate. I'm curious why GM made the conversion. I doubt the factory was concerned about data logging. I can see why they would want to replace the burn-off module with inexpensive relays. But I suspect the additional tuning parameters had other advantages.

matts85vet

this is what i used when i did minehttp://forums.corvetteforum.com/c4-s...m_id=82&arch=1

just needed to buy the 2 relays and harnesses. i cut off the old C12 pin and used it for my new D12 connection. i used a recycled ecm from a tpi f body i think. it was really pretty simple if you have all the re-pinning connections and the relay wiring worked out

i do my own tuning and data logging with a Moates Autoprom and Tunerpro RT along with a wideband o2 sensor in the passenger header collector.

GREGGPENN

From what I've seen, better control of warm-up performance was likely the biggest gain from 85 to 86. IOW, most of those extra BIN parms are in areas of warm-up control. I think there's also a couple of extra for idle control too. I would suggest that emissions and AFR control had to be better as well...especially when they went to the 2-stage converter system that came on my 89 car. (I've never had any other car with such a clean looking exhaust pipe.)

If somewhere you read that ALDL is separate, I could believe the storage locations...and even the interface to the ALDL connector are separate modules. Though theoretically possible for modules to be significantly slower than the main "CPU", I would doubt it. I GOTTA think clock speeds improved greatly (as implied above) providing a huge step in sensor feedback. That's GOT to translate to a cleaner-running motor. Probably better response/power too. (I don't remember power increase numbers between 85-86.)