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Wanna go MPFI? Can't find a decent harness anywhere?
1228746 to 1227730 For TBI F-body
1227747 to 1227730 For TBI Truck/Caprice.
I originally wrote this 2 years ago. I recently upgraded to a '91 Firebird, and had use for my own article.
Lets start:
Gathering parts:
1) 8 Injector plugs and some wire
2) 1227730 ECM _AND_ v8 memcal!
3) 1227730 ECM connectors
4) MPFI Fuel pump
5) MPFI Fuel hoses if needed for your application (TPI)
6) IAC, TPS connectors for some applications.
7) MPFI Manifold, throttle body, injectors
8) New fuel filter
Step 1: Fuel pump
You will need to remove the fuel tank, and fuel pump sending unit. Replace the TBI fuel pump with a MPFI fuel pump. This is a good time to contact APE and get a Walbro 255lph in-tank pump. The connections + sending unit for TBI/TPI are the same.
Step 2: Fuel hoses in engine bay
The TBI fuel hoses are a little shorter than the TPI hoses. The fittings are the same, lines are the same, fuel filter are all the same. If going with TPI, you should really get the correct length hoses.
Step 3: Intake manifold
You should choose your intake prior to repinning the harness. Once your intake and sensors are in place, you will know how long to extend wires (if you have to). I am using a singleplane intake with center-mounted throttle body. The wires end up being pretty much in the correct spots.
Splice the right bank injector wires to 4 injector plugs. All the grounds go together to one wire, all the positives go together to the other wire. Now, splice the left bank in place to the left 4 injector plugs. If using TPI plugs, the green plugs go on right side, the red plugs go on left side.
Remove the ESC module. Cut the connector off, and splice wires C and E together. Tape up, and hide someplace neat.
Connect MAT, TPS, CTS, and IAC. Extend wires if needed.
Step 5: Repin
Now, repin ECM connector using following table:
Step 6: Calibration changes
At minimum, you will need to change the VSS constant from "magnetic" to "optical" because the 4-out buffer box outputs 2k pulses per mile, vs the 4k pulses per mile that the $8D calibration expects.
You may need to disable VATS, EGR, etc depending on how you did your swap.
People typically don't source '749 ECM's much anymore. They *MAY* have the IAC wires differently. Consult your schematics and test as needed. Most people use a '730 donor ECM and run whatever code mask they need ($8D, $59, etc).
This assumes you've swapped out the fuel pump, and hooked up the TPI intake. This covers the wiring. An issue with some people is locating a good harness, then getting it in the car.. This should make that process a 45 minutes job. (once you've got the TPI setup actually in the car)
****! so this means I can just take out my TBI computer box , slap in a V6 computer box w/90-92 L98 Prom chip, re-pin the harness (in under an HOUR?) and voila?
pictures? Sorry, its VERY hard for me to picture things from text, I'm a visual person.
I'm having a hard time locating a good harness and was thinking of just saving up for the TBI to TPI wiring harness from hotrodlane.cc but that is over 700 dollars for shipping which is completely ridiculous!
A lil bit more than hour, but yeah it is that easy. I went from MAF to SD on my IROC in about an hour with only one screw up. lol
The only real problem with the TBI harness is, as mentioned already, the injector connectors, also you'll have to lengthen the TPS and the IAC wires. I beleive that the CTS wire is long enough already. Another thing is too, you'll have to change your knock sensor to the 90-92 style, or put a 6.1k ohm reisitor in the loop for the KS and you'll have to jump out pins C and E ( I think those are the two) together of the ESC behind the two relays on the firewall behind the power brake booster. Then take out the ESC module and toss it.
So its about 2.5 hours worth of work to go from a TBI harness to a SD harness.
So how in the world do it take two injector wires and create 8 injector wires from that is my main question.
Each side is only 2 wires. GM spliced 4 injectors per side in. If you peal back a v6 cars harness at the junkyard, you'll see what I mean. Thats the easy part.
Yeah a few wires may need to be extended.Thats why I said get some wire.
I'ts about an hour to repin carefully. A little more time under the hood connecting stuff. But thats all trivial.
ohh ****ing sweet...Disregard the other thread...Thats all I wanted to hear. Any type of electrical wire works? Happen to know what guage?
You can go buy some 16 gauge wire and a 8 new injector plugs at napa, autozone, etc. best bet is to goto the junkyard, and rip 'em outta a few v6 cars.. Then tape 'em together.
1)So I would cut off the two blue connectors from the 730 ECM box at the junkyard,
2)remove the box and two blue connectors from the yard V6 car
3)Go home, remove the TBI ECM
4)slip out all the wires from the TBI connectors
5)insert the TBI wiring harness wires into the 730 connectors
6)attach the V6 ECM with L98 prom inside and be done with it.
Thats pretty much it. You'll need to remove the ESC connector and jumper pin C to E like I said, to make your knock sensor work. And you may need to extend the TPS and IAC wires. But otherwise, its fairly straight forward.
I've been studying this also.
How should I control the fans, especially since I switched to dual fans.
The fans would operate as they do on the TBI. To make 'em work like a TPI car, you'd have to wire them into the ecm's fan control lead, and wire in a second coolant sensor.
Originally posted by anesthes Not really. If you use the '730 to control fans, you'll just need to jumper a wire but no biggy..
-- Joe
I have the dual fans also. I have one fan running off a relay hotwired to the ignition so that it runs as long as the ignition is on and the other fan is hooked up to the fan switch. When I install the TPI harness, do I still have to hook up the second fan to the ECM?
I have the dual fans also. I have one fan running off a relay hotwired to the ignition so that it runs as long as the ignition is on and the other fan is hooked up to the fan switch. When I install the TPI harness, do I still have to hook up the second fan to the ECM?
The ECM has 2 fan control circuits. You "can" hook it up if you want to, or you can leave it alone. If you leave it alone, it will work as it does now.
Personally, I like the fan control on '730. You can set each one to turn off/on at different temps and MPH.. Off at 80mph, back on at 50, and so on.
OK, to bring back a somewhat old topic. I will be doing this conversion on my '91 GMC TBI soon. If you are not familiar with the truck systems (as i am not familiar with the car systems) I believe it is the same style as the old f-bodys... two barrel TB... same as the '87 truck injection. Are the procedures the same as for the cars? Wires may have to be lengthened, but that is not a problem. Seems like i may only need a newer style knock sensor? Is this my first post? If so, Hello to all From CK5!!! They sent me here!!!
Originally posted by Kat A lil bit more than hour, but yeah it is that easy. I went from MAF to SD on my IROC in about an hour with only one screw up. lol
Kat
Woah, wait, you did it in an hour?
I have a 730 ECM just sitting here, I wanted a new harness, but you are saying I can relatively easily just switch over to SD? My LT1 intake already has the SD port on it and rigged up. If I can find a way to swap to 730 easy, i'll kiss you.. well maybe not because I don't swing that way, but you get the idea.
This forum answered alot of question, but i have one more...Why would you use the v6 ecm? I have 91 305 TBI. Thanks this would help me save money instead of buying the new harness/computer/sensors
I'm experimenting with a dual fan setup from a fwd Oldsmobile 88 and 3800 v6 as a cheap way to incorporate the dual fans. It takes some custom fabrication, but that's for another post.
Another tip I have is an easy way to get injector wiring is to take the quad 4 harness. It's got a 3 pin connector I just cut off. The length is near perfect, and it sure beats trying to pigtail a bunch of v6 injector wires together.
If you're doing a 5.7L swap, look for injectors out of a 91-94 series I 3800 or a 95-up series II engine. The earlier ones are 22lb/hr while the later ones are 24lb/hr. http://dtcc.cz28.com/gminfo.htm is part of a frame that has a ton of info.
The biggest thing to remember is interchangability. Mass Production has it's advantages in similar parts. (i.e. injectors, sensors, etc.) If a part looks the same, it most likely will work.
Oh, one last tip I have is mock up your system outside of the car first to get your wiring lengths right (especially on the TPS)
also have a fuel pump question. I have an 86 carbed motor. Do I need a different sending unit that holds the pump as well, or does the fuel pump mount to the carbed unit?
How would be the best way to remove the pins from the harnesses? Also, is there a way to make a adapter harness using the connectors from inside the tbi ecm?
Originally posted by anesthes Wanna go TPI? Can't find a decent harness anywhere?
1227746 to 1227730 For TBI F-body
1227747 to 1227730 For TBI Truck/Caprice.
Since i've repinned before (maf to speed density) I think its tons easier than running a new harness.
I grabbed Mike Davis's '730 swap, and hacked it up a little changing it to TBI pinouts. I'm 99% sure this will work, with only a few mods maybe to be done. (splice a ground or two)
This assumes you have allready:
1) Replaced the in-tank fuel pump with a TPI pump
2) Replaced the TBI intake with a TPI intake
3) Connected the fuel lines, and are ready for wiring.
I am really **** about having cut wires, but couldn't really cough up $150 for a harness right now. I repinned my TBI harness today while my motor was out, but I went a step further. I had a really hacked up 85 TPI harness lying around that was next to useless, and I removed the wiring for the injectors, iac, and tps (surprisingly, these were uncut). I carefully separated them from the harness, traced them through to the ecm, and unpinned them from there. I did the same to my TBI harness, traced the injector, iac, and tps wires all the way to the ecm, and unpinned them. Then I replaced them with the TPI wires (iac and tps are now the correct length). This way, I didn't have to cut any wires, all looks stock. While I was at it, I also removed the air divert and egr wiring, as I will not be needing those. Repinning the harness as anesthes outlined above was pretty straightforward. It took me about an hour and a half, but only because I purposely went slow and triple checked everything I did. I don't want to end up tracing electrical problems. Doing what I did to avoid cutting any wires took me all day, as I worked slowly and methodically. Its not difficult at all, just annoying work. I'm gonna try leaving the fan control as it is now. If I run into cooling problems, I'll look into dual fans.
By the way, if you decide to take a look into a Chilton's manual, don't take their diagrams for granted. The one I was looking at had a mistake or two. I believe the 746 to 730 chart in this post has an error as well. Take a look at the line with BD12 and A8. A8 was already used in the chart privously ( BA8 and A8 ), which is supposed to be ALDL Serial Diag.... Looking at the unreliable Chilton's diagram, A8 on both the 746 and 730 ecms show as an orange cable, without specifying what its for. BD12 is labeled on previously as A/C Pressure Switch, but I can't tell from the diagram I have in front of me what it should correspond with from the TBI diagram. I'm kinda tired though, so that may be my problem, I'll look at it again tomorrow.
There is one error in the repinning table, and it's important for those of us who want to keep the EGR Enabled.
730 terminal GE9 should be pinned with the wire originally on 746's A4. AGain, for those running a stock EPROM or Super AUJP with EGR enabled need to have this pin correctly installed to avoid an SES.
I am also not a fan of using a single +5ref for both the MAP and TPS, especially if there is a provision availible on the 730.
My solution was taking a pin from my old CCC wire harness that went to a MAP sensor and running it through the harness creating a seperate +5 ref like the factory intended.
Also I've found that Quad 4 motors had a seperate injector harness. I simply disconnected it, cut the plastic wetharpak connector off, spliced the two drive wires together and presto, had me an injector harness that makes a much cleaner install than the 3+1 look of the v6 cars.
Many Mild 350 TPI applications need a 24lb injector... stock on 1990-1994 3800 series I tuned port engines is a Bosch 24lb injector. These motors are finding their way into the yards more and more. I got 6 of my 8 injectors form a 48,000 mile motor. the other 2 a 64,000 mile motor. They are currently being sent to be fow matched and cleaned. I got all six form the second car, in case any were bad. I think the harnesses and the injectors ran me about $40 at the U-pull-it yard near my place.
Originally posted by 86BirdSE There is one error in the repinning table, and it's important for those of us who want to keep the EGR Enabled.
730 terminal GE9 should be pinned with the wire originally on 746's A4. AGain, for those running a stock EPROM or Super AUJP with EGR enabled need to have this pin correctly installed to avoid an SES.
I am also not a fan of using a single +5ref for both the MAP and TPS, especially if there is a provision availible on the 730.
My solution was taking a pin from my old CCC wire harness that went to a MAP sensor and running it through the harness creating a seperate +5 ref like the factory intended.
Also I've found that Quad 4 motors had a seperate injector harness. I simply disconnected it, cut the plastic wetharpak connector off, spliced the two drive wires together and presto, had me an injector harness that makes a much cleaner install than the 3+1 look of the v6 cars.
Many Mild 350 TPI applications need a 24lb injector... stock on 1990-1994 3800 series I tuned port engines is a Bosch 24lb injector. These motors are finding their way into the yards more and more. I got 6 of my 8 injectors form a 48,000 mile motor. the other 2 a 64,000 mile motor. They are currently being sent to be fow matched and cleaned. I got all six form the second car, in case any were bad. I think the harnesses and the injectors ran me about $40 at the U-pull-it yard near my place.
Fixed. Thanks. My schematic for '746 didn't have that labeled. weird.. It was from Pontiac to boot.
I removed EGR and installed a block off plate, and I also disabled it in my PROM. As a result, I didn't pay any attention to that pin.
I think there is still a bug in the table though:
A8 was repinned to BA8 for the diagnostic link.
Later, you have BD12 listed with A8.
Originally posted by 92blue I removed EGR and installed a block off plate, and I also disabled it in my PROM. As a result, I didn't pay any attention to that pin.
I think there is still a bug in the table though:
A8 was repinned to BA8 for the diagnostic link.
Later, you have BD12 listed with A8.
I'll double check my service manual when I get to the shop today.
Originally posted by Fredless ****! so this means I can just take out my TBI computer box , slap in a V6 computer box w/90-92 L98 Prom chip, re-pin the harness (in under an HOUR?) and voila?
pictures? Sorry, its VERY hard for me to picture things from text, I'm a visual person.
I'm having a hard time locating a good harness and was thinking of just saving up for the TBI to TPI wiring harness from hotrodlane.cc but that is over 700 dollars for shipping which is completely ridiculous!
Hey fredless did u try a wiring harness from Painless wiring? I got my wiring harness for $325 bucks. Im swapping from carburated to TPI, Im not sure about the price for tbi to TPI though, but im pretty sure it wont be $700 bucks
12-29-2003, 01:23 PM
