Boatnut

I didn't know that a simple harness was available. Would you suggest to changing the ECM to GM aftermarket computer MEFI4 controller? Aslo I take it that the Optispark module is controlled by the ECM as well. Is this true? After spending yesterday afternoon removing the stock harness and marking all the sensors it looks more and more like a simple carb. replacement would be the easy way out but I think that there would be a considerable horesepower loss increased fuel use and a big step backwards from the multi port injection it has on it. Now that it is apart would you suggest any different intake manifold or cam? For running a jet I need all the torque that I can get at around 3000 to 4000 RPM . On the ZZ4 engine they boost the torque and horsepower by puting in GM "Hot Cam" and 1.6 to ! ratio roller rockers. Whatr do you think about any mods. like that or is money better spent in other places?

55ChevyMan

I wired mine like you but i got volt at the starter cabel but that it nothing when I turn the key I got new + red cable new black ground cabel plus new ground straps and on the old corvette red + cabel it has two extra red wires where do they go? and at the starter the purple wire there no voltage and also on the 94 vette wire harness there a fuses box that stays right? I thought that the wire harness got the power from the purple wire at the starter thank for your help my e mail is brioneschevybelair@yahoo.com

55ChevyMan

where does the fuel pump relay go on a 94 Corvette LT1 go is it part of the engine harness?? help

Boatnut

Sorry I can't help you. I am looking for wiring help myself

chevyowner02

iTrader: (3)

It gose on the inside of the car on the passenger side. I would think if you did not take the harness off it probally got sniped.

55ChevyMan

took out the starter to look behind it no luck dont know if I should pull the headers off on the harness on right where big black connector block like the comaro harness where it go inside the car I would think that where it should be, the Corvette relay I got is small black and square I am sure I the right one

55ChevyMan

I need help I followed trans amm #5 on the LT1 wiring and the engine cranks but the fuel pump is not work at all if anybody can help how would get the fuel pump to run it a 94lt1 out aCorvette I am using the 94 lt1 harness how would I wire the fuel pump from the PCM ? and are the fuel pump wire on the firewall ? and what color are they pink and Tan???

91_RS_Vert

hey there guys. i think this is a good thread so ill start my questions on here.
I have a 91 rs car with an l03 305 tbi. i have my engine and transmission out right now, im having my 700r4 rebuilt with b&m rebuild street strip kit and a transgo shift kit. I got to looking on here and saw where people were swapping in lt1s in their thirdgens, this interests me very much. I know ill need a 93 intake to use my 700r4 and im fine with that.

I have been reading up on the different threads for about two weeks now and there are still a lot of things i am confused on i would like some help with. first of all i keep hearing that the painless wiring harness for the swap is 350 dollars in jegs. The only one im seeing in jegs is 700? can i get the part number for the one that is 350? And on that note is the painless wiring harness even needed if i can get my hands on the entire wiring harness from the donor lt1 car? When i do this swap is all of my original wiring completely removed or do i keep some of it or what? I have done a lot of auto wiring and its not difficult i just need to know a general basis of where to start from. i appreciate all help i can get because i want lt1 speed after driving my buddy's 94 car. the engines are easy to bolt on mod and have them in the 350 hp range. Later.

mechanic58

You ask a lot of good questions. If you can even half-assed wire up a car stereo, I would not recommend you buying a painless harness...as long as you have access to the donor car's harness. Weeding them out and making them work is EASY, way easy compared to forking out $700 and then still having to do just as much "wiring" work.

You will discard most of the 91's original under-hood wiring that pertained to the engine. That whole harness that originates from the passenger's side kick panel can be removed and shitcanned. The only wiring from the '91 that you'll use is the starter ignition wire, the fuel pump wire and whatever guages you'd like to have working in your stock cluster. All those wires originate on the driver's side bulkhead connector.

Send me a PM if you have anymore questions.

91_RS_Vert

yeah ive done several car stereos as in like over a hundred so yeah i figured i should be able to just use a stock one, was just curious. from what ive read the painless wiring isnt so painless. but thanks man you pretty much answered all the questions i had. but ill get hold of you with nemore questions i might have. thanks alot.

mechanic58

You will discover when you begin ripping that engine harness out that there are several wires in it that are "married" to the other harness...that lead over towards the driver's side bulkhead connector. Cut them. Those are insignificant ****...guages, etc. You can weed that **** out later on once you decide what guages you want to work, etc. The wire for the CEL on the 91 will be located under the dash on the passenger's side...in the connector that plugs from the dash-side harness into the ECM. That wire will turn the CEL on when grounded. You'll connect it to the appropriate wire coming from the LT1 PCM. Also...don't use a '93 LT1....those engines use the earlier flash memory type ECMs, you want a '94 or a '95 model ONLY. '96s were OBDII and are a bigger pain in the *** to tune, etc. You can fab up a connection on your throttle linkage for the 700R4s kickdown cable, use a cable from a tuned port car. Or you could just shitcan the 700R4 and go with a 4L60.

91_RS_Vert

right, i heard the 94-95 engines were the way to go. and i was thinking about gettin rid of the 700 but i already have my rebuild kit and i spent kind of a lot of money on it. but if im not mistaken it says 700r4 or 4l60 ill have to look on it tomorow.

excuse me for my ignorance on this but the ecm is the computer?
pcm?
cel?

mechanic58

ECM = Engine Control Module (pre-OBD stuff)
PCM = Powertrain Control Module (OBDI and OBDII stuff)
CEL = check engine light

Most of the rebuild kit you bought for the 700R4 will work in a 4L60. All the hard parts will interchange and also the rubber seals for the clutch actuators. Bout the only **** you won't be able to use is the valve body gaskets.

91_RS_Vert

thanks for the definitions. but ya thats good to know because i was looking up some info on the 4l60 its a nice transmission, but if i i got a motor and trany from a junk yard i would just have my local transmission shop rebuild the trans before i put it all in with the kit i already have. I have bad luck with transmissions and I give my car hell so I don't wanna take any chances on a transmission from the junkyards longevity.

third_genbowtie

can you be more specific about the tuning part, because i bought a 96 lt that came out of a c4 vette. how much more would i have to do to get a good tune?

91_RS_Vert

I think what hes talking about is the 96 and up lts are obdII and they are harder to do anything to and make them run correctly such as camshafts heads or even some bolt on modifications. generaly just more of a pain and more money to work on.

91_RS_Vert

ok so today i located and removed my ecm, and the entire engine harness. I took your advice and cut everything at the point where the engine stuff was married to the bulkhead connector wires. i left the purple wire and the rest of the other ones that come off the bulk head that go to the starter alone. I hope to god I'm able to pull this off it sure does like like a ****ton of wires. I'm usually not one to be afraid of wires but idk about this one!

91_RS_Vert

someone please post and give me some wisdom lol!

cusz28

I;m swapping an lt1 form a 95 impala ss into an 83 z28, and i'm using the harness from a 94 caprice with a l99 4.3. same harness and computer, no big deal. the reason for getting the 94-95 lt1's is because they are sequential injected, where the 91,2, and 3's are batch (91 and 92 are y body only). also, 94-97 used mass air instead of speed density, much more accurate. 96 and 97 are obd2 and need a special connector to tune, and a special program which is really expensive. there is a way around it though. you can reflash a obd2 computer to obd1 as long as it's the same computer as a obd1 model. as stated above 93 and older have a chip, 94+ are flash programmed. the harnesses between f, b, and y bodies are only different in what extra sensors each model may have (b bodies used two knock sensors and an internal oil level sender). other than that the harnesses are just different lengths and the computer is located in different places. i.e., f bodies had it tucked in the upper passenger side, while b bodies are under the air cleaner in the front driver side. don't know about y bodies. all the pinouts should be the exact same at the computer no matter which computer you have. all the information necessary for modding your factory harness is available in this thread. personally, i prefer the b body harness because the factory location for the computer puts it right where my charcoal can is, and that's getting canned (no pun intended) anyways. also, i can come straight off the corner or the harness into the bulkhead connector on the drivers side. any questions, feel free to ask or pm. i'll post a pic of my harness layout a little later for reference.

cusz28

here are some pics i just took of my harness. it's laid out on top of my old 305 (my lt1 is on a stand). looking at everything from the front of the car, the computer is up by the driver's side head light by the evap can like i said earlier, and the harness wraps up the block between the intake and head on the drivers side, loops around, and comes back on the other side. there's also an extension coming off where a normal dist would be for the fuse block that for now is just laying out of the way. the small loom of wires draped up is the trans harness (but you may not see it in the pictures). as another poster said, the bulkhead connector is one piece on b-bodies. i took a pic of that too just for giggles. you can see where the factory 3rd gen harness comes out from by the brake booster, and it cones really close to the corner of my harness just where the oil pressure sender is. I hope all this helps.

cusz28

more pics

cusz28

last one, i promise. also to note, the computer tag picture is the good computer to get. it has removable knock sensitivity modules, is flash programmable, and can control maf, and auto tranny. the number to remember is 16188051

dannyvera778

iTrader: (5)

hey im doing the same exact swap in my 91 except im using everything out of a 93 camaro computer and wiring harness..i stripped my old wiring harness coneected everything to the starter..and now im stuck!! im trying to conect the fuel pump..and where does the computer get its power from, no one seems to have a diagram to hook up 93 obd1 and its wiring in this kind of swap help please???

55ChevyMan

it cold up here Wiconsin so I havent work on it the last things to connect were the the fuel pump relay and daul fan relay this was my question too I got this from (Z28ricer I hope it HELPS )one side of the relay coil goes to pcm A7(red) the other side to ground (opposite the fan relays they receive ground from the PCM and get power feed from the harness) the switch side of your relay you need power and the output tothe C100,I belive it *should*be G4,tan/white how ever you may want to double check with a multimeter before quoting me on that my email is brioneschevybelair@yahoo.com let me know if it worked for you

55ChevyMan

connecting fuel pump relay one wire go (Pcm 7 red )green/white wire one and one to ignition switch and to hot battery with 15A fuse where does the ground wire go to (pcm red) are just any ground on frame? and wouldnt better to get a new wire going to the fuel pump ?? thanks for your help my email is brioneschevybelair@yahoo.com thank you what does it mean to ground opposite the fan relay on pcm red there nothing opposite of the fan relays I dont understand this thanks would one wire splice to A 18 PCM GROUND? which is tan/white RIGHT ? I use will the old connector from the 86 and the86 fuel pump relay

55ChevyMan

on your 94 pcm where is the tach out put? on the 96 97 is A13 this where you splice your tach wire right

Thirdgen89GTA

iTrader: (5)

I ended up wiring mine directly from the coil output.

Pocket

iTrader: (24)

Ground to the engine. Rear of the cyl heads are common. Stud on the ICM is stock. If in doubt upgrade your fuel pump wire. Usually its ok though

PCM grounds are A2, A18, C32, D1. Its always a good idea to run redundant grounds to the engine/chassis to remove any possibility of a faulty ground

Correct. Tach output pin is the same for 94-97 PCMs

That works fine, but the PCM output is more accurate. Stock tachs arent known for their accuracy, so every little bit helps

Klortho

Actually for some reason, the tachs can drop out if using the output when hitting a certain RPM, I've tried this with 3 different tachs and all 3 do the same thing, when the timing advances it seems that the signal goes away and the tach drops to 0, hooking it to the coil gives a direct feed and seems to work better, don't know why it does but :shrug:

55ChevyMan

on my 94 red pcm there no white wire at( A13) and I got the 94 pcm diagram from GM and it doent show any thing for A13 are a tachout put I talk to few shops and no help thanks for your help

55ChevyMan

whar year lt1 do you have? an do you have AC on yours

55ChevyMan

Just thank you all for your help I will hook the tach to the coil I never tryed anything like this before on the 55 belair I put a Painless wire harness it was easy

Pocket

iTrader: (24)

B-bodys didnt always have a tach wire. No matter, just add a new one and connect it directly to your old tach wire

http://www.lt1swap.com/pictures/100_1590.jpg

http://www.lt1swap.com/95impalalt1.htm

Bookmark that site, VERY helpful

You can see the tach output here

http://www.lt1swap.com/pictures/100_1780.jpg

BiggTrav

im tryin to wire up the oil pressure switch and the problem i have is i cant find on any of the scematis is where the tan wire of the switch goes to i know orange is spliced int to the relay and the computer and the grey goes to the computer but where does the tan or brown wire go??????????

Pocket

iTrader: (24)

Correct for 90-92 cars

New2Chevy

iTrader: (11)

The LT1 I am looking at is a 97, and it will include the entire wiring harness and ecm for that exact engine, right off the car it's in now. It seems it would be easier to hook up to my 86 with all that stuff already included....I could be wrong, though.

New2Chevy

iTrader: (11)

Of all the stuff I've read and viewed, this is the easiest for me to understand, for the LT1 harness prep.

http://www.lt1swap.com/all_lt1.htm

Pocket

iTrader: (24)

Glance over these

https://www.thirdgen.org/forums/post...009-post4.html

55ChevyMan

On the Pcm connector C2 black 8 green/white VSS output 4000 pulse/mile its high lighted in blue where does it go ? and 15 ?and 30and 31 ?? my swap is into a 86 IROC Z thanks for your help

Klortho

This one normally goes to the speedometer input in the dash harness, but since the '86 Iroc has a mechanical speedo, it would goto a Cable X box input so it can convert it to a mechanical output to the speedo.

New2Chevy

iTrader: (11)

I'm swapping an LT1 into my 86, too.

I'll have to check back here when I am at the point of wiring the darn thing.

55ChevyMan

I have the 4L60e Trans but changed the gear to a mech speedometer and I dont know what a cabel X box is ? thanks for your help

Klortho

http://www.abbott-tach.com/cablex.htm

a cable x box

Pocket

iTrader: (24)

If you changed it to cable VSS, then you need an inline VSS to feed the signal to the PCM. The speedo output wire from the PCM can be ignored then

Night_blade897

Ok im wanting to do this in my 92 RS, i havent got anything for it yet. but im reading all of these and i just wanted to clarify what i know b4 i go and get the stuff. All i need to get is the engine, the computer, and the wiring harness from my LT1 donor car right? if so can i use them from any body type car, or does it have to be a camaro?
but anyway. your just talking about cutting the old connectors and putting the wires from the LT1 harness onto them?
oh and you keep mention the A/c thats the air conditioning right? im 99.99999999% sure it is but i want to make sure just incase its something really inportant lol. but i was gona delete my A/c anyway so would i still have to worry about it?

thanks

Thirdgen89GTA

iTrader: (5)

Only way to keep A/C is with a Tubular K-member, vette accessories, notch the stock k-member, or to go without.

Night_blade897

ok, planned on deleting it anyway lol.

dannyvera778

iTrader: (5)

yea you can use the impala,firebird or camaro wiring harness...i went with a painless so i didnt have to deal with old wiring and it tool me only a couple hours to hook everything up..all you have to do is connect that wire harness to the connector on the firewall on your driver side...dont mess with under the dash unless you really want to get into a real hectic project

Night_blade897

ok now you got my confused. what do you mean not to mess wih the wires under the dash? wouldnt i need to to get the computer hooked up? or would the LT1 computer hook right in?

Thirdgen89GTA

iTrader: (5)

You won't be using your old computer. You'll just be rewiring the harness connector and eliminating unused wires.