GM TPI Swap
This page is for information about GM Tuned Port Injection EFI swaps. TPI is a fuel injection system that uses individual injectors for each cylinder that are mounted in the intake manifold and usually ends up looking much different than a traditional carbureted setup.
Goals for this Project and Web Page
This page is where I'm gathering information and details about the GM TPI swap I'm working on for one of my 1973 Buick Electra. If it goes well on the first one, I'll likely try to replicate the swap onto my 1970 Buick Electra and possibly even my 1958 Buick Special.
My main goal here is a "DIY" style EFI swap using as many low-cost pieces as possible. If you know something about wiring and basic EFI bits (or can read up and learn), then this is something any person could replicate. Basically, I am trading my time to think about things and learn how stuff works for the money I could pay someone else to do that work for me. I like to learn about stuff, and I'm always short on cash, so this is a good set of trade-offs for me. If you have more money than common sense, the thought of building your own wiring harness scares the hell out of you, or you don't want to invest the time or energy into thinking about this too much, then go pay someone else for the right parts.
A secondary goal is to avoid cutting and hacking at the vehicle to actually do the swap - particularly in the case of my 1970 Buick Electra, where being able to return the vehicle to "factory stock" for a later restoration help retain the car's value. This means no cutting or changing of the gas tank or the firewall. This pretty much dictates a weatherproof computer that can be mounted in the engine compartment.
As part of an aggressive focus on low-cost, I am attempting to build my own harness out of factory bits. If you do not want to go that route, various sources for custom "EFI swap" harnesses are available, go Google for them. I prefer to wire things myself and want to be able to take a pile of wire stubs and connectors and turn them into a wiring harness for just the cost of the wire and some new terminals to go into the connectors.
This page is focused on the "hardware" for this swap - the computer, sensors, actuators, solenoids, pumps, relays, and the wiring harness to tie it all together. It is not meant to address how to tune the resulting TPI system after you create it. That topic already fills many books and many websites, and is far too much to cover here.
First up, many people will be asking "Why TPI instead of TBI?", and it's a valid question. It's true that TPI (Tuned Port Injection) is a bit harder to swap on than TBI (Throttle Body Injection) because it requires an intake manifold capable of holding the individual fuel injectors for each cylinder. TBI mounts much like a carburetor, and can be added using an adaptor plate, so it's simpler to mount. They both use the same basic sensors, though the computer used to drive each one is a bit different. TPI also requires more fuel pressure, so it needs a different fuel pump, but the fuel system requirements/designs are pretty similar. TPI does allow for finer fuel control in more advanced systems, though TBI does a pretty darned good job on a stock or reasonably-close-to-stock engine. I prefer TPI for the potential added control, though I fully admit than in my circumstances that may be more of a "looks cooler to me" type of decision and your thoughts may vary. But, since this is my page and my cars, my opinion counts for a lot no matter how biased it may be. :-)
In my case, I have chosen a TPI system that uses a computer that is weatherproof and is placed in the engine compartment - see the next section for more details on that. That means the huge bundle of wires that usually has to go through the firewall is not needed - you just need a few key wires to go into the passenger compartment, mainly the park/neutral sensor, SES (Service Engine Soon) light, and the ALDL (Assembly Line Diagnostic Link) connector. On an older vehicle where you want to avoid cutting holes in the firewall, this is a very big deal, and to me, this helps make it worth it for the added hassle that TPI brings.
Also, mounting a TPI system onto an engine that was never offered with TPI means you have to make up some custom hardware to get it to work. Getting the fuel rails fabricated, the intake manifold modified to accept the fuel rails, and getting a throttle body mounted to the intake manifold are all difficult tasks. I say "difficult" not because these are insurmountable goals, rather that they are hard for the average DIY-er to do in their garage. That translates into having to spent money to pay someone else to do the work for you, which is at odds with the need to make this as DIY and low-cost as possible. Welcome to the world of tradeoffs. The good news is that once you get the basic hardware in place, upgrades to larger injectors, sequential injection and other higher-end goodies are as "simple" as swapping out the wiring harness and computer. And yes, I do realize that using the term "simple" for that will strike many folks as very odd. Remember, wiring doesn't scare me and is something I can do easily. Machining parts is something I find a lot harder to do.
The computer I chose is computer part #1227727. This computer is electrically identical to one of the most popular GM TPI computers - computer part #1227730- except that this one is in a weather-proof housing that can be mounted under-hood. The #1227727 computer was used in both V6 and V8 models - most notably in the Corvette for 1990 and 1991. The V6 applications are various W-body vehicles from 1988 through 1993 on either the 2.8L (1988-1989) or 3.1L (1989-1993) engine. Sometimes the computer carries #16197128 or #16198260, but they should all be functionally interchangeable for the purposes of this swap. Other I4 and V6 engines with different computers were available in the W-bodies during this time, so double check the engine and computer info before you grab any parts. More information can be found via Googling for the computer number. The W-bodies in that era include the Buick Regal, Chevy Lumina, Oldsmobile Cutlass, and Pontiac Grand Prix.
My research indicates that the V6 and V8 units on this computer are identical except for the MEMCAL (Memory Calibration Unit) and specific programming burned onto the main "chip" that is on the MEMCAL. The MEMCAL itself is available from the dealer for a reasonable cost, as well as being around used. The chips are readily available from various sources, and I'll need one of those no matter what. That means the biggest issue here with using a V6 computer is tracking down a V8 MEMCAL - I'll be burning a new chip for it with my custom program no matter what. Given the cost difference between a "common V6 computer" and a "rare V8 Corvette-only" computer, starting with the V6 computer should be a much better deal. At the very least I got an actual #1227727 computer to do my mock-up work with for only $40. :-)
All of the sensors and injectors are pretty much standard fare for the V6 and V8 units, so if you find one of these cars, I'd say you should just grab as much as you can including the entire wiring harness and every sensor you can find/reach/remove. One thing to note is that the lb/hr rating on the injectors might not be appropriate for your needs, but they're fine for mock-up and maybe even initial testing of the system. If the injectors are too small, they will not be able to "keep up" at higher RPM and/or engine loads and the engine can go very lean causing costly engine damage. Basically, be sure you get an appropriately sized set on injectors for your engine.
I eventually found a running 1992 Chevy Lumina for sale locally for $100 and bought that to use as a source for the various parts for this swap.
Below is a "crib sheet" you can print out for use in any junkyard hunting for the computer and associated EFI parts. Millions of these cars were built, so finding one to grab parts from shouldn't be too hard. On the other hand, if you happen to come across a 1990 or 1991 Corvette you can pirate for these parts and the stuff is actually reasonably priced, then by all means, grab what you need along with the rest of the Unobtanium you find at the same time. The rest of us will stick to something we might actually find for a decent price - and we'll also continue to hate those of you who somehow manage to find a great deal on real Corvette parts. :-)
Here are some external views of the GM #1227727 computer I purchased with a wiring stub, connectors, and connector cover. Looking closely will show the 3 bolts that are used to hold the computer to a mounting bracket - one on each side and one at the top. These bolts are part of special clips that slide and lock into various slots in the housing that allow for different mounting options. The dust cover just slides off by moving it away from the wiring harness - there is a small wiring clip that may need to be removed from the dust cover first - in my case the clip had already come loose from the harness tape, so the dust cover slid off easily.
Here is the MEMCAL removal sequence and some details about the MEMCAL assembly. Note the weather seals around cover and under bolt heads - do not lose or damage these! The bolts used a 1/4" socket on this example. Make sure you ground yourself before messing around inside the computer - static electricity can be deadly to sensitive and often expensive electronics.
Once the cover is off, just push each of the two side clips down and away from the MEMCAL and it will rise out of it's socket. Install the MEMCAL by aligning the socket properly (it will only fit one way) and then by simply pushing down on the MEMCAL - the clips will re-seat automatically. The blue cover removes by gently prying the end clips out on one end and lifting it off. It installs by clipping it into place.
In the final picture of the MEMCAL, you can see the ESC on the left and the EPROM is on the right. The "limp home" circuitry (CALPAK) is two smaller chips underneath the ESC circuitry. This particular MEMCAL is a V6 unit - V8 units should be visually similar. One surprise was that the EPROM seems to be permanently mounted to the MEMCAL - that I was not expecting based on my original research, live and learn I guess. Further research indicates that they are soldered down, which makes sense given the environment they live in - lots of vibrations and heat cycles could easily cause non-soldered components to back out of their sockets and cause problems.
Here is the main computer connector removal process - aka, "unplugging the computer". You have to squeeze the red clips on the side of each connector pretty tightly and then lift each connector out one at a time. The weather seals on the sides of each connector make them a pretty tight fit - it will take some wiggling and you will likely have some sore fingers afterwards, but it will come out with very little "pulling" force. Don't yank and act like a gorilla - you'll break things and be unhappy later on when you try and put things back together. The final four pictures are close-ups of the front of the connectors - the part that goes towards the computer. If you look closely, you will notice that each one is labeled with a letter in the top middle - Orange is A, White is B, Grey is C, and Blue in D. You will also notice that the individual pins are also labeled with numbers, starting with 1 in the upper left hand corner. The wiring diagrams and descriptions will talk about wires with a notation like "pin B2" - now you know how to find them on the computer connectors once you have things apart. Remember that the numbers are reversed when staring at the back of the connector - it's easy to get confused.
Here is the main computer connector disassembly process - aka, "getting the individual terminals out of the connectors". This is what you need to do to build your own wiring harness, or replace damaged wires. First, you remove the red "terminal lock" (also called a Terminal Position Assurance or "TPA") by prying the two side clips on the TPA up and away from the connector body. Then, you lift the TPA up slightly and slide it to the side (it has grooves for each row of wires to slide through) and off the connector.
At this point you can remove individual terminals from the connector. I found that using a small paper clip works well, but I had to sand the paper clip to make it slightly smaller in diameter so it would fit inside the space in the connector. Form the paper clip into a "L" shaped piece and wrap a piece of sandpaper around the end you want to stick into the connector. Grip the sandpaper and paperclip between your thumb and forefinger, and rotate the paper clip 20-40 times to sand it down some. Do this until it fits in the smaller section of each opening in the connector and you can "wiggle" the paper clip in without much force. In the "head on" picture with the paperclip in the connector, the paper clip is inserted into the smaller "bottom" part of the "T"-shaped opening. Once the paper clip bottoms out, you should be able to remove the wire and terminal by pulling on it gently from the back of the connector. If you have to force it - stop and wiggle the paper clip around some more. You are trying to depress the small "tang" in the terminal the is holding it into the connector body. You can see this tang very clearly in the last two pictures.
When inserting a terminal, make sure the tang is bent out slightly as shown in the last few pictures. If it's one you just removed, it may not be bent out much if at all. Make sure the paper clip has been removed, and that the tang is aligned with the smaller portion of the opening, and then slide the terminal and wire in from the back of the connector. You should hear a soft "click" as the terminal locks into place.
These pictures are of the actual terminals and seals inside the connectors. In the first picture you can clearly see the weather seal the is crimped onto the wire and terminal assembly as part of the wire crimping process. This seals the back of each terminal in the connector, and it is important to not damage it. If you are crimping a new terminal onto a wire, you must install the correct size seal for the wire size you are using onto the wire before you install and crimp the terminal onto the wire.
I am still looking for a source for these terminals. The seals on each wire appear to be fairly standard MetriPak style units (MetriPak 150, perhaps?) , but the terminals are a bit different than what I have seen before.
Fuel Delivery System
The pump and plumbing were mostly covered on my EFI Basics page - I'm planning on using the basic twin pump system with a surge tank that's been detailed there, so go read up on the basic design of the system. The routing of the plumbing, the location for both fuel pumps, and the location and exact design of the surge tank are all specific to the final vehicle the system gets installed into and as such are not going to be covered here.
The fuel rails and injectors need some special discussion, however, need more discussion as for my Buick V8 TPI swaps there are no production intake manifolds with fuel rails available. That means I am automatically heading to the aftermarket or to a custom fabrication source for the intake manifold modifications and the matching custom fuel rails I will need. I can use standard GM injectors in a size appropriate for my engine, but the intake manifold needs to be modified to have injector bungs in each runner as well as have a way to mount a fuel rail on each side. The fuel rails need to be fabricated to match the injector bung spacing on the intake manifold, and they need to have the correct fittings on their ends to hook up the system. That usually means fittings for a "crossover" hose in one end of the rails and fittings on the other end of the rails for the fuel input on one side and the regulator on the other. The return line connects to the regulator.
In theory, I could do the conversion myself, but 1) it requires welding the injector bungs to the manifold and I don't know how to weld aluminum and 2) it requires very precision machining on the fuel rails in both size and location for each injector. I'm not ready to tackle that kind of fabrication, so I've pretty much resigned myself to the fact that I'm going to have to pay someone else to do it.
I checked with Arizona TPI when I was talking to them about the throttle body adaptor (see below) and they said they will do the conversion on my intake for about $300-$400. I need to get prices on doing the conversion on my manifold from a few other places to see what the "going rate" for this is.
As for the manifold to use as the basis for the conversion, I happen to have an older Edelbrock Performer intake laying around that I could use on my first conversion - it's available and "free". That intake would be fine to use on my 1970 Electra. I've also thought about using a Poston "S-Divider" intake (part #B-455) on my 1973 Electra because it has an EGR provision and that vehicle was originally EGR equipped. I like the idea of starting with a dual-plane intake on the 455 engines because my research on camshafts indicates that the dual plane intakes have benefits in low-rpm power production and allow you to run a slightly larger cam. That, and the intake I have lying around already (read: free) is a dual plane intake. :-)
If I ever get around to converting my 1958 Buick, that would likely be a totally custom arrangement. One idea I had would be to use spacers that would go under the existing intake manifold that would have injector bungs in them and use a throttle body on top of the original intake manifold. Another idea I had was a totally custom "mini-manifold" for each side of the engine (made out of tubing with short runners down to each intake port) with separate throttle bodies on each side. That would definitely look cool, but would be a bear to create for someone with limited fabrication skills such as myself.
The throttle body is an important piece. It controls all air coming into the engine, as well as holding the TPS sensor and IAC motor. It typically has a few vacuum hoses running to it as well. You can get aftermarket throttle body units that bolt on like a traditional carburetor and make retrofitting easy, but they cost non-trivial amounts of money. Thus, I'm hunting for a solution that will allow me to start with a used TPI throttle body - they are readily available, reasonably priced, and when it's time to upgrade, there are many choices for bigger throttle bodies.
I've been thinking about ways to build an adaptor plate to allow me to mount a typical GM TPI throttle body onto a carburetor mounting pad. The trick is that the TPI throttle body uses a much different air cleaner arrangement than a carburetor does, so I would need to figure out some way to handle that. Since height is a problem in most carbureted installations, you'd want to mount the throttle body in it's originally intended forward facing position and the adaptor would be responsible for "turning" the airflow to go down into the intake manifold. A typical carb and air cleaner assembly is about 6"-8" high, which should be more than enough here. Make sure to measure your actual hood clearance to be sure, though. Assuming you have the right height, you could reasonably easily make a simple adaptor out of sheet metal and two steel plates, One plate has a carb mounting pattern on it - I'd make it a dual square bore and spread bore pattern for the most possible usage. The other has the TPI throttle body mounting pattern on it. The adaptor would basically be a box with the throttle body mounting plate on the front near the top and the carb mounting plate on the bottom. There are plenty of air intake systems for a TPI, and a simple filter right on the front of the throttle body would do to get things working at the start. Grabbing some colder air from in front of the radiator would be best, though that's getting into some fairly application-dependent fabrication for the air ducting.
I have seen some pre-made adaptors that allow mounting a throttle body to the manifold. Most of them either mount the throttle body so it faces "straight up" or they turn it to the front but are designed for a non-GM-TPI-style "single butterfly, square base" throttle body, and those are not what I'm looking for here. The one picture I have seen that looks "right" is from Arizona TPI, specifically their Big Block 1000 CFM Multiport system, using a standard single-plane manifold as a starting point and the exact kind of adaptor I am pondering building from scratch. A copy of that picture is shown below with the specific part I'm interested in called out. I contacted Arizona TPI and talked to a very nice fellow who told me that they can be sold separately, but they only have a few left for around $300 each. They were apparently made by a company that is no longer producing them, so if you want one, get 'em while they're still available. This is a very nice looking piece, but at $300 it's running a bit counter to the low-cost idea in my original plans. It is available if needed and it has the advantages of being a "bolt-on" part. You would still need to provide your own throttle body and air cleaner/air intact system, the same as if you custom built an adaptor. If you know of a readily available adaptor that allows mounting the TPI throttle body to the carb mounting pad as I'm describing, please let me know.
Another choice is a custom throttle body that mounts directly to the carb mounting pad and the air cleaner mounts on top, similar to a carburetor. These are commercially available - to the tune of around $600-$800 - and they look a lot like a traditional carb. Other than the fuel rails and injectors on the intake, they don't have that "tuned port fuel injection" look to them which could be a plus or a minus depending on who you ask and the goals for your specific vehicle. They work quite nicely and look very trick. As they say, you get what you pay for. This goes against the low-cost idea in this plan, but it is available if needed and has the advantage of being a "bolt-on" part. It also has the potential advantage of using the same air cleaner setup you were running with your carburetor. The air cleaner height and the air cleaner neck size could be an issue, but those are readily solvable the same as they are with a carburetor.
Another choice is running a different style throttle body. I've seen people try and adapt the Ford units, but I have no info on that. I did find the Edelbrock now makes adaptors to mount a Ford, or GM LS1/LS2 style throttle body to a standard 4-bbl square bore intake - part #3849 is one example. Summit sells it for about $115, so if you could adapt one of these throttle bodies, that might make some things a bit easier.
Air Intake and Filter
If you are going to use the TPI style throttle body, JTR carries some very nice pieces to make this work. You can also mount a filter right to the front of the throttle body, at the expense of some performance (somewhere around 5% on warm days) and of increased noise. I found a page about how to add a cold air-intake using some rubber elbows used for plumbing systems combined with some straight lengths of exhaust tubing. It looks a little ghetto, but it seems like it ought to work pretty well - and it's dirt cheap. Neat.
If you are going to use a custom throttle body that looks/mounts like a carburetor does, then you can use any of the readily available carburetor-style air filter and/or cold air induction pieces that are out there. Everything from your original air leaner to a chrome "open element" air cleaner, on up to a custom cold-air induction system is available.
Here's the list of "stuff" you need to hook the computer up to so it will all work - including all of the sensors, actuators, and solenoids. (If you don't know what an actuator is, go read my EFI Basics page for a description of them.)
Some of these things can be omitted on some installations. Emissions related items are marked in purple, items for options you might not have are marked in blue, items that can be omitted if you desire not to use them are marked in green, and stuff you will likely never use is shown in red. More experienced tuners might want to nit-pick and claim almost anything is "optional", and to some degree they would be correct, but not here. My basic assumption and purpose for this page is to have EFI that works automatically so you can install it, drive it, and forget about it - just like a new car. Sure, you can rig the computer up to not have control of the timing, but then you have to futz with that separately and it's a pain. You get the idea.
Using my 1970 Electra as an example (since that is what this page was originally written for), it was not originally equipped with EGR, a vapor canister, or an AIR system so all of those hookups can be deleted. It does have AC, so I need to hook that up so the computer can control the idle properly when the AC is on. The original speedometer is completely mechanical, the engine fan is completely mechanical, I am not currently running a transmission with a TCC, and the cruise control is the original that is completely separate from the computer so those are all hookups that are not needed. If I choose to wire the fuel pump relay without using the oil pressure sensor, that's one more thing I don't need to hook up. That leaves me with a pretty reasonable list of things that need to be connected, and most of them are already in the engine compartment. Only the SES light (one wire) and the Park/Neutral Switch (one wire) needs to go inside the car. The ALDL connector (three wires in this application, four if you use TCC control) is also desirable to mount inside the vehicle, so if I do that I need only five wires to route through the firewall and into the passenger compartment. That's not too bad. If I left the ALDL in the engine compartment, it would only be two wires - and that's very simple to add. I don't like putting the ALDL in the engine compartment, though, so I wouldn't do that unless I had no other choice.
The diagram below is complete with all emissions equipment, the ALDL, SES and Park/Neutral Switch in the passenger compartment, and the cruise control VSS signal going into the passenger compartment. If you are not going to use a given emissions control item, simply omit the relevant wires from the harness. The electric fan trigger wires are there but stubbed out - none of my cars use electric fans. Various wires such as the battery hookup are labeled as to what they need to be connected to - the actual hookups are not shown. Lastly, the engine pictured under the harness is a typical Buick 455 with the distributor in the front. I also assumed the computer would mount in the driver's side fender area next to the brake booster. Why? Because the two vehicles I own that are most likely to get this swap done on them both use a Buick 455 and they both seem to have space for the computer in this area, so I did my diagramming with that in mind. If you need to use this on a different engine, you'll need to re-arrange some of the wires based on your engine layout and where you choose to mount the computer. The schematic stays the same, but the physical layout of the wiring harness will differ. This is trivial to change when you are making and wrapping your own wiring harness - just lay out the wires as needed and tape them up as you go.
I went out and got a 1992 Chevy Lumina to use as a parts car for what I needed here. It was super cheap at $100 because it had a rod knock, but since I don't care about the engine, that was fine by me.
What's Left To Do Here?
Basically, I need to keep chasing down open questions and unknown details. I'll keep updating the page and further refining my TPI swap plans based on what I learn. Eventually, the result will be an installed and running TPI system on one of more my vehicles.
Pics and Credit
If you want to use my stuff, I'll pretty much always say "yes", just send me an email and ask, or if it's a small usage, then just give me credit for my stuff, link back to my site, etc. I'm here to share information with folks, but I did the work to take the pictures and write this site, so if you want to use my stuff, credit me some sane way. That's all. The information itself is more or less public, so I don't care about that, the exception being if you want to use my text directly, then again, I wrote it, so please ask me, credit me, and link back to my site. It's not an unreasonable request, it doesn't involve money, and it's simple to fulfill. I don't care what the exact format is for the credit or the link, so long as it's clear to any reasonable reader that it's my stuff. I don't think that's too much to ask. I'd do the same if I used stuff from your site, and if it's extensive use, I'd ask you first. It's simple common courtesy.
Comments? Kudos? Got some parts you'd like to buy/sell/barter/swap? Nasty comments about my web page so far? See Contacting Us.
Page last updated 12/27/2011 10:23:21 AM