calvinlc

For lots of reasons I am not into dealing with tuning a 25 year old computer with intake, cam, exhaust and cylinder head changes. For this reason I have decided I want to go with an aftermarket computer setup. I know there are arguments both ways on this, but with nobody local who actually tunes these computers and because my time is not infinite, I have chosen to change. That being said there is some functionality I would like to retain:
a. ABS
b. FX3 suspension
c. Speedometer

I believe the FX3 is fine, because it gets the VSS signal directly from the transmission. I think the ABS is OK, but I am not sure as it has a connection to the serial bus with the ECM. Does it need that connection? The CCM gets a VSS input that is processed through the ECU from a sine wave into a square wave. I need to know if the ECU scales the frequency of that sine wave at all, or is it just the same 4k pulses per mile? If that is the case then I can simply build my own sine to square wave converter and I should be fine. Has anybody pulled the ECU out of a 90 or 91 and does the ABS and FX3 still work? Thanks!
--Calvin

ch@0s

Keep the old computer and use the new one for engine management. It will be easier in the long run.

calvinlc

I thought about that, but then I have to keep the harnesses which will kind of pollute the engine area to have a double set of harness, and then it also becomes a question of what sensors and wires do I have to hook up to the stock ECU.

ch@0s

The engine harness can go Just unpin it drom the ECM connector. Look at this it may help.

http://ls1tech.com/forums/conversion...e-my-swap.html

leesvet

I've seen far too many guys that bought in to the aftermarket HYPE and regretted it......never ending tuning problems.
Its just not worth it in a street car IMO. You might go with a straight engine mngt system that leaves the stock ECU alone,. as Chaos says, just chop the engine harness, (cut and plug off JIC you ever go back). That's the best of both worlds. Still, the tuning aspect is NOT going to be as easy as you are thinking. Don't believe everything you read on the "box".

Just find a tuner that can burn a chip. Many of the online services will do you a deal...2 for 1. Do one now and get a 2nd for free within the next year. That way you can have a street chip, a full on track chip, and even buy a granny chip if you let the kid drive your car.



BTW
http://sale-fire.com/Obd1%20Scan%20T...FQQPaQodArAASA

in case you ever want to see what your engine is seeing and doing.

trackbird

I've been pondering this exact thing. I had a prom burned by one of the mail order tuners and it wasn't quite right. I'm not having any luck getting some of the preferred logging software to talk to my ECM without dropping connection so I'm not having any luck getting the info they need to tweak the tune (They will absolutely fix it, if I could only get the log files to work properly for me so I could send them in). I also have a '91 and I just ordered a prom from TPIS (not particularly inexpensive, hopefully it does the trick). I have prom burning equipment and a wideband and I've been tuning/logging/testing and I'm running out of patience for it. If this doesn't do it, I'm considering dropping a FAST XFI computer in mine with the self tuning wideband setup and giving that a try.

I know just where you are right now...and I've been meaning to get the factory service manuals out and start tracing wiring to see where and what the ECM is tied to.

C409

...... Switch to aftermarket ... I have used a Holley Commander 950 for the past three years and am delighted with how easy it is to tune with a laptop ... I just kept the OEM ECU in place and wired the 950 where it needed to be on the engine ... the Holley units control spark too ... not all of them do ... I wish I had changed over a long time ago ........

STH

I removed the ECU from my 1990 L98 Vette, and replaced it with a FAST XFI 2.0, with a harness adaptor from Dan White Racing. Did not have to change the engine harness, and everything seems to still work, except the fuel economy readout. Check him out http://whiteracing.com/about.html

esham

Cool! So the ECU is completely removed from the car? The AC, cruise control, ABS all work? Did you put the Fast unit in the same place as the OEM ECU or is it inside the car now? Any pictures?

STH

I have the manual AC, and it works. Yes my FAST is mounted in place of the old ECU. I made a new mounting plate for the FAST. Give Dan White a call, and he will answer your questions, plus if you buy from him he will help you tune the FAST.

esham

Thanks!

trackbird

That's what I did and so far it seems to be working. I removed the stuff from the stock ECM that I was no longer using (fuel injector wiring, knock sensor, fans, fuel pump, IAT, TPS, CTS, etc) and left the rest in place. I hooked the check engine light to the FAST XFI computer and left the stock ECM there to handle VATS and any remaining functions. The car started the first time and so far the dash and all functions seem to work (I am yet to hook the AC request in and output to the clutch to the fast system, but it's on my list). I haven't driven it yet, but it starts and runs and everything works so far.

calvinlc

Thanks for the update, Trackbird. Where did you mount the FAST ECM?

trackbird

We managed to fish the harness through the firewall (where the body "plug" was on the passengers side of the distributor) by taking that apart and modifying the plate. Then we took out the unused tuner module (and jumpered the switched hot wires through to the radio...or I think I did, I haven't put power back on it quite yet as I'm doing the permanent installation of the wiring right now) and pulled the harness up into the glove box. I had to take the plastic tray out of the glove box to make room and I have to build some brackets to bolt it down, but that should do the trick. I left the laptop cord in there with it and I can just open the glove box and plug the laptop into the connector to tune it.

Attached are pics of the body connector once I pulled the sealant off of it and trimmed out the wires I didn't need, the modified plate that I used to put the harness in place and the harness when it was pulled into place (before I placed it in the plate with the power harness from FAST and what was left of the body connector wiring). I don't have any other pics handy right now, but it's an idea of what I've done.

Also, the FAST harness is quite long for this application. I have to trim several inches out of most of the wires (the TPS will nearly plug into the radiator right now) to clean things up as I complete the project.

calvinlc

Thanks for the pictures. I was thinking about doing something similar, but I am now thinking about removing the air box on the passenger side firewall with the heater core and ac stuff in it because I already took off the AC and since I only run the car in the summer, the heat is really of no use to me. I will then mount it in the area created by removing that stuff.

trackbird

I considered pulling the AC parts, but I'm going to try to convert it back to R12 and keep it running. I have R12 and I have all new hoses on it as of a year or so ago (it's mostly been parked since I installed them). Here's the finished firewall plug and the wiring pulled up into the glovebox area (I removed the "guts" of the glovebox to get the new ECM to fit and I still have to fabricate a bracket to hold the ECM). I'm replacing/repairing the split loom on the wires near the body connector, that pic was just something I took while I was working to show a friend that it worked.

trackbird

Figured I've come this far, I'd post a few pics of the glovebox install. I have to do some clean up work and work on the looms and wiring a bit, but this is where things currently stand. I should be ready to hook the battery back up and do some testing and start tuning when I get back to the garage.

trackbird

Update (in case anybody was actually wondering). The gauges all work, the cruise control still works and you wouldn't know there were two computers in the car by driving it. I think leaving the stock ECM to handle VATS (and such) and using an aftermarket ECM for the engine management is a good approach and it works.

As a side note. FAST has pretty terrible tech support. I've had issues with the computer that appear to be a "math issue" about injector size and tech support has basically blown me off so far. I've tuned the car in spite of the funny readings (the highest number in my VE table is 56%, but I'm seeing nearly 80% duty cycle out of 37.92 lb/hr injectors at 13.13:1 AFR and 6,500 rpm....that doesn't add up) and it's running pretty well at this point.