The stock 85 computer setup has got to go. My car runs like hell. I've already got an 86 ECM and an 87 L98 PROM to get started, along with Mike Davis' website to aid me in repinning my harness. But then there's speed density. Since I eventually plan on a Super Ram with AFR heads, I may wind up exceeding the capabilities of the MAF setup. I'm also not real fond of chopping up my whole harness. So... rather than chop up my harness, let's say I get a SD harness & computer from a doner car. How do I integrate all of my dash wiring (gauges, ignition, SES light, etc) with this harness. In some places I see people say that it's a separate plug into the ECM, other places say it's completely separate, and others say it's all part of 1 harness. So... which is it, and what do I need to do to put that SD harness into my car and make all of my dash-related equipment work?

I have switched to speed density in my 89'. The gauges and everything should work fine yet. I didn't have to change a thing with the dash. The speed density system requires a different vehicle speed sensor, Painless Wiring part number 60116, about $55. You will get a ses light if you don't wire up a vss. You will need a map sensor, snag one from a tbi car, and the computer, and chip.You will need a different knock sensor to. I don't know what is different with it other than part number. I used the tbi harness, but if you can find a speed density harness, your all set. Painless wiring has a list of all the sensors, which are the same and what's different. I think it is somewhere in the faq section of there site. Good luck

I have switched to speed density in my 89'. The gauges and everything should work fine yet. The speed density system requires a different vehicle speed sensor, Painless Wiring part number 60116, about $55. You will need a map sensor, snag one from a tbi car, and the computer, and chip. I used the tbi harness, but if you can find a speed density harness, your all set. Good luck

You should already have a instrument harness dissconnect that ties to the engine harness (it's the C207 connector if you have a diagram). It will be a clear connector by the computer, it's two rows. That is what goes to the fuse panel, SES, ALDL and a few other places.
the SD harness (if you can find one) will have this connector too. It should be plug and play. Might have a wire to swap, probally not since you're already TPI.
I would stay away from the "painless" harness if I was you. It's more trouble then it's worth and you won't have factory wiring anymore.
If you can't find a SD harness, I can mod yours to SD status and it will be just like factory. No splices, I de-pin and replace connectors.

The guy that had the harness & computer sold the harness.
John, I'll let you know what I decide. I still havent' decided if I'm going to stick to the later-model MAF or go to SD, and if I do, whether I'm going to try the harness myself or what. Doing the harness is well within my capabilities, I've just got to muster the time and motivation.

One thing I'm considering is to make a system like Mike Davis' that can be quickly switched between MAF and SD.

why go through all that trouble to swap. i dont think youll exceed
the MAF system. unless your going to go alcohol or 25lb + boost.
usually the drawbacks of MAF is the MAF itself restrictive. tuning it
might be a lil more tricky. if you tuning yourself.. learn it and the
tweaks will be cheaper. figure $300-500 to swap you still gotta tune it.
just asking...
airdeano

Im thinking of an aftermarket SPFI harness and ECM myself. I don't think i'd go through the trouble of swapping one bad GM harness for another.

Not to say its "bad" for most normal everyday street use for a 1989 car, but for what I'd "like" its bad.

-- Joe

$300-500 to swap to SD? Are you nuts? j/k

I got a SD computer from a junk yard for $50 with connectors. I modded my engine wire harness and bought a knock sensor and a MAP sensor. Added a new prom from the dealer for $50 since the computer came from a non-fbody.
Total to swap from MAF to SD is $150.

The other "bonus" of swapping to SD is no more MAF to replace every couple of years! One of my winter projects is a MAP conversion too. A '730 costs about $45 on eBay. I bought a used MAP (with pigtail) on eBay for $20. Others have successfully retained their '165 knock sensor by simply adding a resistor in series. And a new memcal was $45. CHEAP.

85's have a mechanical speedo, you will need a VSS

you probably already know...just tossin it out there

-peace

The swap yes, around 150-200. In order to swap your going to tune, and tune alot. Its pretty easy and fun to tune it but it takes time, I don't know if you want to add the cost of prom tuning hardware/software into the conversion or not but either way you'll need it. Bottom line, SD ROCKS!

Brendan

No he won't.
I have an '86 with mechanical speedo and am not running a seperate VSS, there's already one in the instrument cluster.

Yes, MAF cars already have a VSS, just not the same as SD cars. The SD ECM has a "switch" in the eprom so you can change it to recognize the VSS used by MAF cars.

MAF systems use a 2k pulse signal from the VSS generator.
MAP systems use a 4k pulse signal from the VSS generator.
glen, i am not familiar of a pulse switch switching one to the
other. what address is that switch? usually we have to use
a dakota digital splitter to use 4k pulse for the computer and
the splitter switchs the 4k pulse to 2k for the speedometer
and cruise control. that switch is useful intead of the $125
dd splitter.
thanks
airdeano

Airdeano, the switch is bit 6 of byte at location $8018 in the SD eprom. If bit 6 is set to "1" ($40 mask) the SD ECM will assume you are using the 4,000 Pulse/Mile Magnetic Sensor. If bit 6 is not set to "1", then the SD ECM will assume you are using the older 2,000 Pulse/Mile Sensor.

This switch is now defined in TunerCat's $8D TDF, so all you have to do is put an "X" in the Switch Table for the "Magnetic Speed Sensor Installed" if you have newer 4K one or leave it "blank" if you are using the older 2K one. Changing the BIN is like a 2 second change.

I have not found an equivalent switch in the MAF ECMs to allow you to use both. MAF systems can only use the older 2K one.

If you already have access to eprom burning equipment, then you can indeed avoid putting that spitter on. Also, someone has come up with a method of altering the display to the electronic speedo for a gear change. I haven't been able to test and verify it, but when I do I will let people know about that too. It isn't a "fine" adjustment (to correct small deviations). Its more for the guy who installs 4.56s where there is no gear change available and needs a large correction change, and then "fine" tunes with appropriate speedo gears. I am also not sure if this only works for the 4K Magnetic Sensor.

As I said, as I dig deeper, I will let people know as anyone wanting to run lower than 3.73s cannot make a "correction" to the speedo with a simple tranny gear change. Again, this if for SD ECMs - I have no idea if such a "correction" exists in the MAF ECMs.

thanks glen, gunna have to update 8d.tdf ver f doesnt have that
option.
again thanks
airdeano

Jim,

Just sit down with the 85 service manual wiring and the diagrams for the year harness you are using (87 would be the absolute best for you)

Instead of integrating all your wiring, let me say this: 85-87 harnesses are standalone. That means your starter, gauges, headlights are on a separate harness than the ECM harness. The 88-92 harnesses are an integrated harness.

So option one is to get an 86 or 87 harness, or option two is to trim down an 88-92 harness.

I hope that clears up your Q on it being one harness or not.

As far as SD harnesses go, you will again want both service manuals, and figure out which wires are the same. The way I put an 86 LB9 harness in my CCC Q-jet car was w/ a harness pigtail from the engine ECM harness of a CCC car, and a harness pigtail from the dash harness of an EFI car. It matches up all the same wires between the L69 / LB9 and the wires that aren't the same are free to go to what they need to go to.

You could put VATS in your column w/ the SD by using an 88-89ish firebird plastic column bowl and the added wiring, or you could get a VATS delete PROM.

Your dash equipment will work because its wiring is separate from the ECM harness. I think option two would be my choice.

If you are interested in a 91 5spd SD harness, I know of one that's prolly for sale.

If you have the 85 wiring diagrams, scan 'em...

Hey airdeano - could the Dakota Digital pulse changing box change 2 pulse to 4 from the speedo instead of splitting it off like you described? Just a thought.

Glenn - good stuff! thanks.

wow. Good info! Thanks guys.

Seems like for now swapping in an 86 or 87 harness may be my fastest option. Until I get AFRs and a bunch of induction work done to the motor, I can't imagine exceeding the MAF capabilities anyway. We'll see. I'm sure I'll change my mind 20 times before spring anyway.

Anyway, feel free to keep the good info flowing!

I have not looked at the latest tunercat file, but changing the VSS to rear the 2 pulse, would require changine the harness lead from the 4 puls to the 2 pulse pin, right?

Thanks in advance,

Paul Tholey

<b>Hey airdeano - could the Dakota Digital pulse changing box change 2 pulse to 4 from the speedo instead of splitting it off like you described? Just a thought.</b>
jmd,
nope only large pulse down to small. 128k->16k, 8k, 4k, 2k
64k->16k, 8k, 4k, 2k.
they may make an emulator or something. this is something we
use for TBI->TPI conversions. LT1/LS1 conversions.
airdeano