2.8V6 Carburetor to TBI Swap, Tips and Tricks

A pinout list of the two factory ECMs used in this swap. I think this is accurate, but if there are errors I would appreciate a note.

I converted my 2.8V6, Federal Emissions (non-ECM controlled) carbureted engine to TBI in the summer of 1995. It is easier to repair, easier to perform routine maintenance, easier to start in all conditions, has more power, better throttle response, and gets better fuel economy. It is also cleaner looking underhood than the stock carbureted system. I can't think of any downsides! If I were given the opportunity to do it over again, I would do it without hesitation.

Here's a few things I learned while doing the swap that may help those that want to do the same to their truck. This isn't a complete step-by-step howto, but it will get you started.

The parts list looks long, but it's not as bad as it sounds. TBI has been around since 1982, and since 1985.5 on the 2.8 S-series so parts are readily available and cheap. If you can find a *complete* donor truck in the salvage yard, that's the best method since the more you get from once source, the more likely you are to get everything at once. This also reduces your cost, since many salvage yards charge less when you grab a bunch of stuff at once, rather than a piece at a time.

Get the Helm manual for the donor truck. Dealers often will let you photocopy pages from their shop manuals if you don't want to buy it, but a used Helm manual won't cost that much ( http://www.factoryautomanuals.com used, http://www.helminc.com new) and the diagrams, explanations, and service procedures are excellent. Haynes, Chiltons, and their ilk don't come close.

Other reading that is nice is "How to Repair and Modify Chevrolet Fuel Injection" by Ben Watson.

California 2.8 carbureted trucks have an ECM already. It won't work with TBI, but some of the parts used with it will. I'll note them as needed. The California ECM system will be referred to as the CCC system (GM's term).

DISCLAIMER: There are several things you can do during this conversion that, while it will work, is not emissions-legal for vehicles driven on the road in the U.S. Even if there aren't inspections in your area, the law still applies and missing equipment may hamper resale, or you may face huge fines or worse if you're caught. If you're driving on the highway in the U.S., make sure you retain all emissions equipment from the donor. If you're not driving the vehicle in the U.S., consult local laws for emissions regulations. Racing is usually anything goes, but check the rules for your particular racing organization.

Parts list:

2.8V6 TBI unit, complete meaning injectors are still on it, TPS is on it, IAC is on it. Throttle cable bracket bolts to it, so make sure it's on there, too.

2.8V6 TBI intake manifold. The carbureted intake won't work.

The TBI intake should have the coolant temperature sensor (CTS) in it, as well as the EGR valve and the thermal vacuum switch (TVS). Make sure you have these if they've been removed.

When removing the intake, take the steel line to the power brake booster and the steel line from the intake to the heater core, too.

The throttle / transmission / cruise control cables should come from the TBI donor, too. You can bend the bracket so that your existing cables will work (the TBI throttle cable is a little longer than the carbureted one) but it's easier to use the right cables. They are not hard to install.

The TBI distributor. The CCC distributor will work, too.

The TBI ignition coil and bracket. You can make your stock or aftermarket one work if you change the plugs on your harness to match.

The EGR solenoid. This is mounted on a bracket on back of the intake. It has plastic vacuum lines to the TBI and the EGR valve that are nice to use.

The valve covers. They're much nicer since they don't have a bunch of brackets on them. Grab the studs, hold-down washers, and nuts, too since studs make it much easier to install valve covers than the carbureted valve cover's bolts.

The fuel filter bracket. It's bolted in place where the fuel pump would be on a carbureted truck. When you remove your old mechanical fuel pump, you can use the fuel filter bracket as a block-off plate. I added a piece of aluminum behind it on mine because it didn't completely cover the hole, but the bolt holes in the bracket exactly line up with the mechanical fuel pump mounting holes.

The fuel lines from the TBI to the frame. There are two fuel lines (feed and return) that connect to the TBI. The feed line comes from the filter bracket, and the return line ends next to the bracket. The return line connects to the line on the frame with a rubber hose. The fuel filter connects to the line on the frame with a rubber hose as well.

All 2.8V6 carbureted trucks have both fuel feed and return lines already installed from the tank to the frame. The hardest part about a fuel injection conversion is fuel plumbing, and all the TBI parts are bolt-on to a carbureted truck, and you don't have to run any hard lines. Doesn't get easier than that!

The in-tank fuel pump assembly. Get one that matches your current tank, or just take the whole tank. Trucks have different tanks than SUVs, and the tank capacity may matter, too.

The oil pressure switch assembly. The fuel pump is run by both the fuel pump relay (part of the ECM harness) and the oil pressure switch. The switch is there in case the relay fails. The switch is a two-pin switch that threads into a T fitting on the oil filter adapter. The gauge/light sending unit also threads into this T fitting. Remove your old sending unit, install the T, and install your existing sending unit into the T along with the fuel pump oil pressure switch.

Get the knock sensor. It's threaded into one of the coolant drain plug ports on the block. Get the ESC module (flat, black box) that goes with it.

The air cleaner. The MAP sensor is mounted on it, so make sure you get it too. The TBI has a standard 5" round throat, so almost any 4bbl. air cleaner will work. You're limited to about 12" diameter with A/C, though. AC-Delco sells a chrome open-element 10" air cleaner that takes the same AC PF-773 air filter that the stock TBI air cleaner uses. Your stock 2.8V6 carburetor air cleaner will not work, since it has a rectangular throat. If you use an open-element air cleaner you'll have to relocate the MAP sensor. That's easy -- just mount the MAP sensor, run a vacuum line to it, and extend the MAP sensor harness wires so you can plug it in at it's new location. I mounted mine inside the cab next to the ECM -- just ran a hard plastic vacuum line through the firewall with the ECM harness.

The charcoal canister. The TBI charcoal canister has two lines -- one to the tank, the other to the TVS on the intake. The canister doesn't cost any horsepower and keeps fumes out of the truck, so why not use it?

The ECM. 1227429 or 1228062 are the 2.8TBI ECM service numbers. My conversion used the '429 ECM, but either is valid. Make sure it has a chip (MEMCAL) in it. You can get one for a reasonable price from GM to match your application (auto or manual) if the donor ECM doesn't have the right one.

If you have a 1227429 ECM, it will have a small box bolted to it called the Elapsed Timer Module (ETM). Make sure you get this and the harness that is attached to it. I don't know if 1228062 ECM systems use this module. There are four wires to the ETM. Constant power, keyswitch power, ground, and one wire to the ECM. The power and ground wire color codes on the ETM are consistent with the colors in the harness. The dark blue/white wire on the ETM goes to the ECM, pin C12.

The VSS. This is mounted in the back of the speedometer by a single screw. It is a small block with a ribbon cable to a small box (the VSS Buffer). CCC trucks, or trucks with original-equipment vacuum/electronic cruise (i.e. no speedometer cables running to the cruise control servo under-hood) already have a VSS. If you don't have a VSS, plenty of cars 1981- and trucks have them in the speedometer; if a GM car in a salvage yard has an ECM and a speedometer driven by a cable (newer cars have electronic speedometers), then it has a VSS you can use. Get the whole VSS -- block and buffer, and try to get a piece of the harness too since it will make connecting to the VSS buffer easier. The buffer gets keyswitch power, ground, and the third wire goes to the ECM. If your non-CCC truck has as VSS installed already (part of cruise control), then you can simply run a wire from the cruise control module's VSS input to the ECM's VSS input.

This comes up often, so I'll address it here. Yes you need the VSS. It's easy to install and cheap. With the VSS, idle quality is better, fuel economy is better, and the VSS data is nice to have for the scan tool if you're looking at scan tool data logs. If you have a 700-R4 transmission, the ECM can control it if you have the VSS connected.

If your carbureted, non-CCC vehicle has a 700-R4 or a THM200 with a lockup torque converter, you have two choices. You can leave your existing transmission wiring in place and it will work fine. The transmission will still work like it did before (a combination of brake switch and electrical vacuum switch) and the ECM won't throw a code if it's not connected to the transmission; in other words, you can choose not to hook the ECM to the transmission and it will work fine and won't light the "Check Engine" lamp. You can also choose to remove your existing TCC wiring and parts, and connect the TBI ECM's TCC connector to your transmission. This gives the ECM control over the torque converter and may help performance and fuel economy.

The ECM harness. This harness is almost completely separate from the rest of the under-hood harness. The only exceptions may be the connections to battery power. If you're taking the donor vehicle's harness this rule helps: if you unplug it, take it with you.

Note that the AIR system is not ECM-controlled (at least, on the 1227429 systems). Your existing AIR system can be retained at your discretion. Non-emission applications can remove the AIR system without consequence to the ECM -- it won't cause a "Check Engine" light if the AIR system is removed.

The ECM harness is also inside the truck. CCC trucks have an ALDL connector already, as well as a "Check Engine" light in the dash. Non-CCC trucks don't have either, though there is a place in the dash for the bulb. I installed a bulb and soldered a wire to the cluster which I ran to the ECM.

Yes, non-CCC trucks will have to cut a hole in the firewall for the harness. It's not that hard to do (hole saw) and after you do it, your fears about punching a hole in the firewall will be forever alleviated. Smear some RTV silicone around it when you're done installing the harness and you'll be fine.

CCC trucks will need to carefully examine the dash harness connector and make appropriate changes to make sure the TBI harness has the correct, fused power (both constant and keyswitch), grounds, and ALDL connections. CCC trucks have a small module in the dash harness called the Lamp Driver Module. This should be located close to the CCC ECM. It has power, ground, a wire from the ECM, and a wire to the dash lamp. Cut the wire to the ECM and the wire to the dash lamp, and splice them together. Remove the Lamp Driver Module and discard it.

Non-CCC trucks using a stock TBI harness will have to wire the ALDL connector, power (constant and keyswitch), and the "Check Engine" light. This isn't hard to do, but does take some time. Grab an ALDL connector and some of the harness from the donor truck, as well as the dash harness connectors that connect the dash harness to the ECM harness. Remember to install fuses on all power wires from the fuse box to the ECM harness.

You can also use a Painless Wiring V8 TBI harness. I used one in my conversion. You'll need to move a couple of injector wires, and add two wires for the EGR solenoid. 1227429 ECM systems will need to add the four wires for the ETM module. These are easy changes that don't take much time. The Painless harness also comes with a pre-wired ALDL and "Check Engine" light which makes installing the harness easy. Plug in all the labeled connectors, connect the fuel pump, connect the grounds and power wires, and you're done.

One thing to remember about either the CCC dash harness or the Painless harness; make sure that keyswitched power is on anytime the key is at Run or Start. Several places in the fuse box have power in Run but not Start, which makes starting the truck impossible. Check this with a voltmeter or a test light before you do anything permanent.

You'll need an oxygen sensor and a fitting (bung) welded into the exhaust. CCC trucks already have an oxygen sensor installed. You can buy a bung made for just this application, or you can make your own. Buy a spark-plug non-fouler and cut off the external threads. Weld this (or a commercial bung) into the exhaust as close to the exhaust manifold as possible. If you have Edelbrock TES headers, they already have a bung, but have a plug installed in it. Remove that plug and install your O2 sensor.

A 1-wire O2 sensor is fine for most applications -- just get one for your donor truck. A heated O2 sensor may help if you're running headers or your sensor bung isn't close to the manifold. AC AFS-74 is the 3-wire heated O2 sensor. The purple wire is the signal. The brown wires are the heater and they are not polarized. One goes to ground, the other to keyswitched 12V (the ignition coil is a good place to pull power for this). An inline fuse is a good idea on the power wire. A 2 amp fuse should be fine.

I have had the best luck with genuine AC brand O2 sensors. Many have reported that parts-store brand O2 sensors aren't as good -- they are either too slow or they switch at the wrong air/fuel ratio. An AC O2 sensor at the dealer is usually competitive -- my AFS-74 from GM was actually $6 cheaper at the time than an aftermarket one from a local parts store!

Installing the under-hood parts is pretty straightforward. Remove the old carburetor, intake, and distributor along with all those vacuum lines and pieces that were once part of the old system. Install the TBI parts and the new harness. If you can change the carburetor and intake on your 2.8, you can install a TBI system. The wiring's no harder than installing an aftermarket stereo system (and easier than many of the stereo installs going on today).

When you plumb the fuel lines, use new rubber hose. It's low pressure so special EFI hoses aren't required. Get a new fuel pump and sock filter, along with a new fuel filter, too. That used fuel pump may or may not have a lot of life left in it, and it's a pain to change the pump (drop the tank or remove the bed) so why not install a new one now?

Note that the carbureted in-tank assembly's lines are crossed compared to the TBI in-tank assembly -- the return and canister lines are swapped, and they are the same size. Make sure you hook the TBI return to the return line on the frame!!! If not, you'll force fuel through the canister, which is dangerous.

It is REALLY nice to have a scan tool when you do the conversion so you can see what's going on. WinALDL is free software that will work (choose 1227747 for the ECM type for 1227429 ECM systems). An old laptop and a cheap cable are all that's needed, and it makes installation/tuning/repair much easier.

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