TBI to TPI conversion (MPFI)

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pro17

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(I am still gathering pictures and documents and will add update this post when I get them)

Below isn't necessarily a how-to but just a general overview of what I found I needed and had to go thru in order to put a TPI on a 1995 L05. If there are any mistakes or clarifications needed, let me know and Ill fix.

Recently, I purchased a 1992 Z28, and was curious if the TPI setup could be used in a 88-95 truck. So I started to do some research. It turns out that people have been doing the replacement for years.
In my case, it was going into a 1995 c1500 silverado, 5.7, 4L60E, and 3.42 rear. The truck uses the 16197427 ECM and BJYL prom.
Below is a list of everything I had to purchase, and any issues I had to go thru during installation (which may be different with your vehicle).
Note: Initially, I thought I was going to have to replace all of the wiring/harnesses and ECM but it turns out that wasn't the case. The existing harness, ECM, and most sensors can be reused.

- Lower intake
- Stay away from the Corvette intakes. Apparently there are issues lining up with the heads, and if you have to still pass emissions testing, there are no EGR passages.
- The coolant outlet to the heater core is in the front, unlike the TBI which is in the rear. You will have to run a coolant line if you want to keep heat all the way from the front of the engine.
- The TBI’s coolant sensor sits in the front on top. The TPI’s sensor (same part number) sits in front. You will have to extend the wiring.
- I would also stay away from the intakes that have the 9th cold-start injector which seems to always cause problems. I don't have any experience with them, but supposedly they can be deleted and ignored though.

- Upper intake
- TBI trucks use a MAP. TPI was used from 85-92 in the F-body. 89-92 use a MAP sensor. So I chose an intake from an 89 Firebird simply because the passenger side rear of the intake has a bracket that holds the MAP sensor in place. Obviously the MAF intakes (85-88) have no need for this bracket. So, it’s up to you if you want to purchase a MAF intake, and drill a place to hold your MAP sensor, or purchase a MAP intake and mount your MAP in it’s stock location.
- Upper intake plenum, with MAP sensor bracket and rear plenum extension. Throttle cable bracket optional
- The bracket is not needed. I used a new bracket and cables from Lokar to hook up to the cruise control and throttle cable.

- Fuel rail
- The rail may come with the factory grey “multi-tech” injectors. 305 engines are 19 lb/hr and 350 22 lb/hr. They are known to clog, especially after 30 years. A company called Southbay makes replacements.

- Thermostat housing

- TPI or LT1 throttle body
- TPI TB

- Uses the same idle air controller that the TBI uses. But the 4 wires must be extended, since the TB now sits at the front of the motor.
- The throttle position sensor is different. Both TPS sensors use the same 3 wires though. So you can cut and rewire for the new sensor, or get an adapter off of eBay. The wires must also be extended to the front of the motor.
- Has provisions for throttle, cruise, and TV cable for 700R4 trucks
- LT1 TB
- The throttle body uses the same TPS that the TBI throttle body does. The 3 wires must be lengthened.
- Uses a newer style idle air controller that the LS1 also uses. You can rewire or get an adaptor from ebay. The wires must also be lengthened.
- The throttle body coolant inlet must be shaved off. It’s in the way of the thermostat housing.
- The idle air passages are built into the TPI TB, but not into the LT1 TB. In order for the engine to breath at idle, you will have to dremel out some breathing room.
- Only the first year or so LT1 throttle body came with the TV cable provision. So if you have a 700R4 and want to use a LT1 TB, you will probably need to get a LT1 TB from a 93 or 94. A 95 and newer LT1 only has throttle and cruise. If you have a 4L60E like me, a 95 and later is fine.

- Intake “runners”
- Mine came with dents. Almost all of them seem to. There are repair kits on eBay. Or take them to an instrument repair shop. They have tools that can take the dents out.

- Driver and passenger side accessory brackets
- The TPI throttle body breathes air from the front, similar to the LT1, LS1, and all modern GM truck engines. The TBI’s idler pulley is in the way of the TPI throttle body. The TPI accessory bracket moves the idler pulley to the passenger side enough so that the throttle body can sit where it needs to. The drivers side bracket must be purchased also because the brackets sit an inch further from the engine. The belt will not go on unless both brackets are installed. The power steering pump can be reused. The water pump can be left alone. The accessory bracket may not hold the existing TBI hose. Due to the brackets swap, the next 3 items I had to purchase:
- Air compressor
The passenger side bracket will not hold the TBI’s compressor (at least it did not my 1995). Also, since the brackets sit an extra inch further from the motor, that also made the compressor lines squeeze a little further closer to the condenser. It becomes a little more of a tight fit, but it seems to work.
- Alternator
The drivers side alternator would not accept my 200 amp alternator. The holes just would not line up. So I had to purchase a new 100 amp alternator for a 92 camaro.
- Smog Pump Delete pulley
The passenger side bracket holds the smog pump at the bottom. TBI motors have no smog pump, therefore need the pump delete pulley. You can get an OEM part from a dealer for 20-30 bucks.

- Electric fans, fan controller
- I had already done an electric fan conversion with flex-a-lite fans and the VSC 15 years ago. In my opinion, I dont think it would be possible to do the conversion and still have enough room up front to work.

- Fuel pump
TPI requires at least 40psi. The TBI pump supplies 10-15. I purchased an ACDelco EP381 from amazon for $60. It was a direct drop in. It’s a 60psi pump designed for a vortec truck, more than enough for the 45psi. I would recommend getting a ACDelco TS7 strainer as well. The one I took out was completely destroyed.

- 6AN PTFE steel braided fuel hose and fittings
The factory TBI feed and return lines run up the transmission tunnel and end up at the back of the motor next to the distributor. The factory TPI fuel lines on a camaro/firebird run down the side of the car, come around across the drivers fender, and in between the alternator and valve cover (front of motor). So not only do new lines need to be ran, but those existing lines at the back of the motor near the distributor need to be removed or moved out of the way (they sit in the way of the rear of the TPI upper intake plenum, when installed).
Some people choose to remove all fuel lines entirely, and run brand new fuel lines, similar to how the F-bodies are ran, and feed fuel at the factory location between the alternator and valve cover. Others take the TBI lines at the distributor and slightly bend them out of the way, and then install adaptors onto the ends to convert them to 6AN, and run new lines around towards the front of the intake.
I chose to cut off about a foot off the TBI lines, TIG weld 6AN bungs onto the lines, and then run 6AN hoses to a modified fuel rail. The feed and return lines no longer stick out towards the alternator and almost inaccessible from behind. Google search modified TPI fuel rail, and you will find even better ideas on how to move fuel feed/return from front to rear.

- Air intake modification
There is emissions testing in my area, and a simple cone K&N air filter attached on the end of the end of the throttle body will not be enough. Even a tube coming off of the TB, going off to the side with a K&N attached to it will not work either. I was given two different stories by two different inspection stations.
One said that they would approve of any custom made intake, just so long as it made use of the heat-riser hose that comes off of the passenger side manifold/header, or if I had installed any aftermarket intake setup that was CARB approved (such as the 94-96 K&N Impala SS). The Impala SS setup wouldnt work because of the radiator hose being in the way.
The other station said they would approve of any intake as long as it used some sort of OEM air box, and not open-air filter.
So I decided to use an air box in either the passenger or drivers side corner, similar to how the newer trucks do (especially since the intake of air is from the front of the motor). The problem is that the 88-98 truck platform was designed for intakes that took in air from on top, and for the air box to be above the wheel well, passenger side, and the battery in the front corner. The drivers side corner was open, but the radiator hose was in the way. So my only option I decided was to move the battery to the drivers side (many people do this, and GM offers a drivers side battery tray and factory mounting holes) and then find a place for the air box on the passenger front. The battery was moved, and I used new cables. I searched for an air box that would fit where the old battery tray was and eventually landed on a GM 99+ 5.3 box. It does not sit square against the fender without drilling holes. But even if I did drill holes to make it sit, it would not clear the hood, and it would also not have room to breath air, since it intakes air from the back side. The box had to have been rotated slightly in order to clear the hood. This actually worked perfectly, because there was already an existing spot at the bottom of the box that lined up with a battery tray bolt hole in the fender. That allowed me to bolt the box down. Once bolted down, the air box sat perfectly. It cleared the hood, and the bottom of the box just slightly rested on the condenser lines at the bottom of the radiator. It also barely cleared the transmission cooler lines. Moving the battery required relocation of the charcoal canister. The canister is so tall, there is no real easy place to put it, but I found that many GM vehicles (specifically the camaro/firebirds and some oldsmobiles from the 80s) used canisters that fit the bracket perfectly, and were half the height. Mounting it and the bracket above the fender well where the old air tube used to be barely cleared the hood. An added plus is that the canister comes with the solenoid built in. So the TBI solenoid and bracket no longer has to be relocated – just run the wires from the harness to the canister (the harness is the same).

Oil sending unit riser
On the back of the block, the oil pressure sensor screws into a riser that sits about as tall as a cigarette lighter. The riser screws into the block near the china wall. This riser sits in the way of the TPI lower intake. The F-bodies dont have this problem because their pressure sensor is above the oil filter. There are several ways this could be solved.
One solution on thirdgen was to modify the riser (cut it in half):
Another could be to relocate the sensor to above the oil filter.
I went with neither and instead went to home depot and put together this little setup. The block is 1/8 pipe fitting, and the sensor is ¼. I have yet to have any leaks, but am still looking for a better solution.

Coil relocation
Coil and bracket will stay mounted to TPI manifold just as it is on the F-body. Reuse 2 of the intake bolts from the TBI manifold though in order to mount the bracket, and use an extra pair of nuts in order to raise the bracket slightly higher (or move the transmission dipstick a little towards the passenger side). The TBI harness is a direct plug into TPI coil, although the connector coming from the engine harness will need to be extended about half a foot (since the coil on the TBI intake sat center-drivers side of the TBI intake, and TPI sits passenger side).

Fuel injector wiring – Replace each TBI injector connector with 4 TPI injector connector. To do this, both connectors to the TBI fuel injectors must be cut. Then, create Y connections where the connectors used to be. Then wire in the positive/negative wires feeding all 4 injectors in parallel. The TBI injectors have 1 negative (either a blue or green wire) and a positive (pink) wire running to them. TPI/LT1 fuel injector connectors can be purchased off of eBay.

PCV – The TPI PCV valve is on the drivers side valve cover in the rear. The TBI drivers side rear, though, has a port that the throttle body used for vacuum which, with the TBI removed is no longer used. This can be used to place the PCV valve for the TPI.
The TBI PCV is on the passenger side front. I left the PCV there, and plugged that into one of the ports in the throttle body.

Brake booster – Purchase new rubber hose (same size that your TBI came with) and run it from the brake booster to the upper plenum. There is a port on the drivers side rear of the upper plenum that connects a rubber hose to your brake booster. Its the same port that the F-body’s use.

Air intake sensor (underneath the upper plenum)
Its not needed by the truck ECM. Just leave it in and unplugged. I had to leave it in and shave it off as far as possible since fuel line is running very near it.


ECM modification and tuning:

The TBI ECM is hard wired to bank fire the two injectors. (Each injector alternates firing as the coil sends a spark). So the passenger’s side injector covers cylinders 2 4 6 8 and driver’s 1 3 5 7. On a full rotation of the crank, that means each bank will receive 4 injections of fuel. On the TPI batch system, all 8 injectors fire 1 time all at the same time, and then each cylinder ignites. So that means, if you were to run this TPI setup directly off a TBI ECM with no modification, each cylinder would receive 4 times as much gasoline as it needs. And I found there is more than just burning a new chip to overcome this issue. 2 resistors have to be removed from the ECM, and a jumper wire added to the MEMCAL on the PROM.

Once I made the ECM and MEMCAL changes, I began burning chips. I used tuner pro to edit parameters. Attached to this post is an XLS of several of the changes that need to be made to the bin that’s burned. These are just basic value for multiport conversions. For TPI, you will have to go a step further and change other variables. The injector lb/hr for example I used set to 22. I also had to go a step further and decrease the values in the VE at idle table, because my scanner was showing the motor running rich at idle (INT and BLM was showing near 105 at most idle speeds). My scanner also showed knocking at higher RPMS (2500rpm+, and 70+kpa). This is apparently due to timing adjustments that are required for TPI. I retarded the timing in around the 70-100kpa and 2500-4000rpm range slightly. I have also attached my XDF and BIN for reference.


Final thoughts:

- The project turned out being much more expensive than I thought it would be. Mostly because there were items surrounding just the intake that needed to be replaced in order for the whole system to work. But I didnt know what those items were until getting into the project. I guess it would be called a domino effect. For example, I knew I would have to replace the accessory brackets. But I never realized I would have to also replace the AC compressor.

- I didn't do this project with an expectation to gain much in terms of power. I just wanted to see a TPI under the hood. But I notice now that the truck is no longer useless after around 5 minutes of driving. With the TBI and the engine warm, a heavier foot was needed in order to keep the truck moving. With TPI, its much more consistent when both cold and after running for long periods of time.


Other websites where I received loads of info:
http://www.sethirdgen.org/tpi1.htm
https://www.thirdgen.org/
http://www.gearhead-efi.com/

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pro17

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I followed the attached doc (which I edited to lower in size so that it could be attached to this post, as well as fix a couple of hyperlinks) in order to modify the MEMCAL and ECM. The MPFI Definitions XLS spreadsheet goes with the doc.
The XDF I downloaded from gearhead-efi.com and loaded into tuner pro. The bin in final.zip is what I have burned onto a chip and currently running in the truck.
 

Attachments

  • Converting from TBI to MPFI v6.doc.zip
    374.2 KB · Views: 77
  • Advanced $0D TP5 v251.xdf.zip
    76.9 KB · Views: 43
  • final.zip
    30.3 KB · Views: 43
  • MPFI Definitions v4.xls.zip
    7.3 KB · Views: 38

pro17

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Hopefully the first image shows how close the coil sits next to the transmission dipstick. The second image just demonstrates what i did in order to bump up the bracket/coil a little further away from the dipstick. There may be a better way and Ill deal with it later. But this seems to work.

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Like I mentioned above, the TPI fuel lines for the rail insert right around behind the alternator. Here is an image of the lines installed on my camaro.
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There's a big distance between the alternator and the wheel well on the truck, and I didn't want to run brand new lines all the way down the side of the truck anyway, so I decided to use the existing lines. The existing lines though needed to be modified. They were in the way of the TPI runners and plenum:
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So I decided I would take about a foot and half off of those lines and have a shop TIG weld AN6 bungs to the end of the lines. Marked with a black sharpy is where I cut:
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Once welded on, new fuel lines were ran to the fuel rail (which was also modified so that lines could be ran from the rear instead of from behind the alternator)
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Here is an image of the oil pressure sensor and the riser it's plugged into along the rear china wall.
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Here it is installed with the intake off
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And here it is, with it being too tall and the lower intake unable to sit.
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This was my Home Depot solution at the time. So far I have seen no leaks and good pressure.
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Another solution by a member at thirdgen is at:
https://www.thirdgen.org/forums/members-camaros/589399-second-chance-after-12-a.html#post6027146
"had the existing elbow turned down on a lathe and new threads added"
This is his creation, in case his image ever gets wiped from his website
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I didn't realize until now I couldn't edit my first post until now (for whenever I need to do corrections).
For example, I need to add the crank pulley to the list. Here is a demonstration on how much further out the brackets are from the motor. Like I mentioned, the passenger/driver brackets have to be replaced with the F-body brackets so that the throttle body can be used. But the bracket pulleys are about a centimeter further out that the TBI ones. Here is a demo of that using the crank pulley. The first image is the F-body pulley installed which is about 8 centimeters tall. The second pic shows the TBI pulley which is about 7 centimeters tall.

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I mentioned that the water pump didn't need to be swapped. The pump pulley seems to be thick enough that even though the belt was pushed out a centimeter, it still has enough room (by a few millimeters it seems) to stay on the pulley. In the long term, it may require being swapped out. But, the heater core port is on the bottom and not on the top on the f-body pumps. So if you run heat, you might have to rethink your set up.

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Since I moved the battery to the drivers side, I had to get rid of the vapor canister. I purchased an f-body canister, which is half as tall as the TBI canisters, same diameter, so it fits the factory bracket, and then mounted it above the wheel well on the passenger side. It barely cleared the hood.
This first pic is the top of the canister on the trucks. It has vapor line into the canistor (from the gas tank), a vapor line that goes to the solenoid (mounted on the intake), and then a vent. When certain parameters are met, the solenoid allows a vacuum to pass thru it and sucks vapor from that canister into the intake to be burned.

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This next pic is the TPI canister. It has the solenoid built in. So if you decide to use it, you can throw away your TBI solenoid. The connectors are the exact same and use 12 volts. It has the hose connection for the gas tank to receive vapors, a vent, and the other hose connection that goes straight to the throttle body for a constant vacuum. When the solenoid is grounded, it allows the vacuum to pass thru and the canister is emptied.
Since the TBI solenoid is mounted on the intake, and I mounted this canister that has its solenoid built in on the fender much further away, i had to extend the wiring.

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On to air intake. In TX, regardless of the age of the car, and the jurisdiction, a visual inspection has to be performed every year. That means if the car came with a smog pump then it has to be there. Or if it came with the heat riser tube that's found on the TBI (that goes from the manifold to the metal intake housing) then it has to be there. I was told that if those items were missing, then the only exceptions were to ether find replacements, or install CARB exempt items with a K&N sticker in plain sight for the inspector to see during inspection time. Incidentally, the 94-96 Impala SS K&N CAI kit happens to be CARB exempt, and can be slightly modified to fit the TPI or LT1 throttle body. The only problem is that the unit turns towards the drives side, directly into the radiator hose. So, that wouldn't work for me. Flipping it around towards the passenger side sort-of works, but it sits somewhat loose, and flops against the AC. The filter is also large and doesnt clear the hood well anyway. Plus, its an open K&N filter right in the middle of the engine bay. So I wanted to find something different.

Installing OEM equipment was the other option. So I had the idea to use a NBS 4.8/5.3 air box on the passenger side, and relocate the battery to the drivers side (the air box idea was backed up by another guy at thirdgen.org). The box fits fine, as long as its slightly tilted, as you can see in the pics below. I had to tilt it for several reasons. First, if it sat flat against the fender, it had no way to breath. It sucks air in from the rear, and if it sat against the fender, it would suffocate. Second, the box is not aligned perfectly square, so if you try to align it square with the fender, it will not clear the hood. Third, if its not tilted, the cover of the airbox will not screw on because the upper transmission cooler line is in the way. Finally, if not tilted, the angle of the exit of the air box leads more towards the air compressor and makes it harder to run air tubes to the intake.

Incidentally, with the box tilted, it sat perfectly flat on the wheel well, where the battery tray mounted. All I had to do is drill a hole in the bottom of the plastic box, align the box with the existing battery tray hole, and lock it down. There was no drilling into the frame or body necessary.

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Going from the air box to the throttle body was the next issue. Airaid makes DYI tubes that you can cut up and form your own intakes. You can purchase your own couplers, or theirs as well. I went with their 3 inch tubing.
The tubing used:
https://www.amazon.com/gp/product/B0026K42MY
I ended up cutting a 45 degree angle piece, a 90 degree piece and 1 longer straight piece with a 45 degree bend at the end. I was planning to glue them together for a cleaner look, but they came out somewhat crummy in the end. So I went with couplers instead. I found spectre couplers on amazon. The reviews said that if you have 3 inch tubing, then get 3.5 inch couplers, which I did.

The first pic shows a coupler on the air box. The output on the airbox is 4 inches. So the coupler is a 4 in to 3 inch reducer. The tube coming out of the box has a 45 degree turn, then goes straight into a 3x3. Its then connected to a 45 degree tube. Finally a 90 degree tube, which goes into a 90-92 Camaro Z28 air filter bellow. The bellow then connects as normal to the LT1 throttle body.

The tubing lays on the fan shroud and the hood rests perfectly on top with hardly any wiggle room around it.
Someday I will revisit gluing the tubes together and getting rid of the couplers.

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This picture hopefully shows how the bottom of the airbox slightly rests on the condenser lines. I haven't pulled a vacuum on the system yet to check for any leaks to see if this has caused any issue yet.

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Maybe this shows how close the box comes to the transmission cooler line.

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Battery cable
Cable length - I stayed with the factory sized 2 gauge. Even though I was almost tripling the length of the cable due to moving the battery to the drivers side, the voltage loss wasn't that much. The factory length is about 3 feet if I remember. According to the calculators I found a 400 amp draw on 12 volts on 3 feet 2 gauge wire brings you down to 11.62 volts. The length that I needed to get to the other end of the truck was 8 feet. That comes out to 11 volts. I figured that wasn't much of a loss and decided to just take the gamble. Those that live in colder climates may need every volt they can get, I'm not sure.

I bought 2 gauge welding cable from amazon and connectors. I used the TMS hydraulic crimping tool filling with solder to put on the connectors. I also reused the factory heat shielding that sits hear the manifolds.
The flex-a-lite fan bracket's had a perfect location to mount the cushion clamps that I used in order to secure the cable in place. The cable is held in place at the 2 factory locations, passenger side of the fan shroud, drivers side of the fan shroud, and one spot next to a connector on the drivers side (all held in place by cushion clamps).

Passengers side, the 2nd clamp right after coming from the starter:

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A ziptie to the transmission line, although it's really not needed because of the previous clamp. The cable barely moves in that location

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The passenger side fan bracket has a nut/bolt that holds a clamp perfectly.

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Drivers side bracket and clamp

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Next to the power steering lines was a perfect place to bolt in a clamp as well. After this, the cable runs straight to the battery.

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