Howell TBI Install - installation tips

[tgreese]

I'm poking along with my Howell TBI install.

This thread is not meant to be complete instructions, but instead cover some issues that I found either interesting or may be useful to others.

Note that this is the kit with a CARB number (California Air Resources Board), and is 50-states legal in all regions when installed according to the instructions. You have to keep your catalytic convertor, EGR valve with CTO, PCV system, and vapor recovery (charcoal canister) if so equipped.

The first is a link to this thread viewtopic.php?t=24558 showing how I plugged the air injection ports in my exhaust manifolds. As Stuka points out, you must remove the air injection with one of these systems. They rely on an oxygen sensor (O2 sensor) in the exhaust pipe to control fuel mixture, and adding a bunch of fresh air will prevent the system from measuring the air-fuel ratio.

[tgreese]

Second topic is the hole in the firewall. The computer (ECU) is installed in the passenger cabin, and there is a wiring harness that must go through the firewall to the engine compartment.

J20TBIharness.jpg

This is the harness laid out on the bench. The computer end is next to the gray box and blue connectors in the foreground. The engine end has three groups of branches - one group goes to the top of the engine and controls the injectors and reads the engine sensors for temperature, throttle position and manifold pressure, amongst others. The second group is much longer and goes to the vehicle speed sensor, starter trigger and 02 sensor. The last group manages power with some fuse holders and the fuel pump relay.

You want the middle part where everything is in the same bundle to go through the firewall. Howell gives you a grommet for the firewall and says to make a 1.5" diameter hole in the firewall. I did some tests to mock up what this firewall hole needs to be. MysticRob at IFSJA https://forums.ifsja.org/forum/tire-kic ... -o-d-452-2 tells how he took the harness apart and carved away some of the fuel pump relay socket to make it all fit through the prescribed 1.5" hole.

My first test (on my mock-up) was to file a couple of notches in the 1.5" hole to clear the corners of the socket. This still did not give enough room for the "octopus" of the harness to pass through - I would need to take all the tape and split loom off of the harness, as did Rob, to make this work.

Instead, I went to a larger hole. McMaster-Carr offers a larger grommet for a 1.625" hole that has a 2" diameter and a 0.875" center hole for about $5 https://www.mcmaster.com/9600K222/ I found this will fit in a 1.75" hole, and everything will go through without a lot of dismantling of the harness.

Here's my mock-up in a panel I scrounged from a discarded dishwasher:

J20TBIharnessMockup.jpg

You need to pay attention to the order that you pass the various items through the hole: fuel pump relay socket first, then the fuse holders, the injector sockets, and so forth. The octopus will fit through the hole if you squish the split loom some and walk it through. I used my huge step drill, but a hole saw would work and is cheaper than the big bit. I split the grommet to fit over the harness.

J20TBIsmallerGrommet.jpg

This is the larger hole with the grommet that Howell supplies.

[tgreese]

Air cleaner revision.

The throttle body is shorter than the original carburetor. Howell suggests adding a spacer. The throttle body is the same 5.125" diameter as the original carburetor, providing many options.

First I went to Summit and looked at what was offered there. All of the spacers had some comment from buyers that claimed it would not fit on this or that application. Next I went to Amazon and bought a cheap aluminum spacer, resolving to make it work. https://www.amazon.com/dp/B09K7S4M4D?ps ... ct_details

When the spacer arrived, it was a loose fit to the existing air cleaner and had no provision for a seal at the air cleaner. I made some little brackets and fixed the two parts together rigidly.

J20TBIairCleanerSpacer1.jpg

I sealed the air cleaner to the spacer with some silicone (brown is what I had on hand).

J20TBIairCleanerSpacer2.jpg

The bottom edge sits on the original-style paper gasket that came with the Howell kit.

[akguy09]

Looking good so far

[tgreese]

Thanks - more progress.

MAP sensor.

Not a lot of time available for this during the week, but I had a few moments this afternoon. The MAP sensor is for "manifold air pressure" and provides an input to the computer (ECU). The part that Howell supplies appears to be for an LS engine, with the sealing grommet removed.

DelcoMapSensor.png

Apparently this plugs into the Chevy LS manifold. In its original application, the sensor looks to be held in place by the sealing grommet and some clips on the manifold that fits into this part. Good picture of a Chevrolet truck manifold with this type of MAP sensor here: https://www.streetmusclemag.com/image/2 ... 40x639.jpg (top half is the factory manifold). Supplying this part rather than the earlier part that mounts on a bracket is likely a cost issue. I'm sure this part is fine functionally, but this version of sensor does not have any bolt holes or other means to attach to a bracket or such.

I made a bracket to mount the sensor, and held it with some zip ties.

J20TBIMAPsensorOnBench.jpg

J20TBIMAPsensorOnManifold.jpg

The MAP sensor for Rochester TBI connects to a dedicated nipple on the back of the throttle body. Looking at the Howell harness, I may need to lengthen this branch a bit to reach my mounting point. Howell says no more than 12" of hose between the throttle body and the sensor. This may be 9" of hose, something like that.

[akguy09]

I am torn between Howell and The Holley, so I am curious to see your results

[tgreese]

Fuel System Plumbing

Normally the GM cars and trucks with this GM Rochester TBI use an in-tank fuel pump with an operating pressure of under 15 psi. Howell supplies a fuel pump similar in appearance to the more familiar high-pressure Ford-type pump, but operating at a lower pressure. Conventional fuel hose, hose clamps and fittings, same as used with carbureted vehicles, are supplied by Howell.
Walbro GSL395: https://walbrofuelpumps.com/walbro-gsl3 ... -pump.html

My truck has a dual tank system, so the fuel pump must be forward of both tanks and the tank switch. The truck came to me with an electric Pollak six-port tank switch, which provides for both the feed and return for two tanks. Prior to last summer, I ran exclusively on the Aux tank and the switch was not used. Last summer I repaired my factory plastic gas tank - seen here viewtopic.php?t=23694 - and then I made the valve operational.

Howell supplies an inline fuel filter for a Ford https://www.rockauto.com/en/moreinfo.php?pk=4413396 - I presume their thinking is a Ford-type inline pump (though operating at lower pressure than a Ford) needs a matching fuel filter. The instructions from Howell stress that the pump they supply must have the proper filter between it and the tank. I purchased a second example of this filter and placed both filters (one for each tank line) ahead of both my switch and the Howell-supplied fuel pump.

J20TBIFuelPlumbing1.jpg

Both the filters and the six-port tank switch are located on the gray skid plate I repurposed from part of a discarded keyboard drawer. Here you see it TBI-ready, with the future TBI connection capped with the red plastic plug. The top hose with two clamps goes to the factory fuel pump and carburetor. The line in the middle is the factory return line.

To connect the TBI pump, I removed the factory fuel line from the top of the frame rail and cut off a section of it, flared a new end, and put the shortened line back on the frame.

J20TBIFuelPlumbing3.jpg

The fuel pump is mounted on the frame rail using a conduit clamp from the hardware store. There is new tubing from the tank switch (red plug above) and the short length of hose connects to the original fuel line on the frame rail, minus the 21 inches shown above.

J20TBIFuelPlumbing4.jpg

[tgreese]

Fuel System Plumbing, continued

Howell supplies something like ten feet of rubber fuel hose that they instruct should be used to connect between the new fuel pump and the throttle body. I have seen cars burn to the ground from wandering long rubber fuel lines, and thus chose another approach.

With the plumbing modified as described above, the truck has two steel fuel lines (feed and return) that follow the top of the frame rail to a location near the original mechanical fuel pump. The mechanical pump has been removed and its location blocked off using the block-off plate supplied in the Howell kit. I now need to make steel lines that connect from the frame rail, across the top of the engine, and connect to the throttle body.

Here are the lines I made -

J20TBIFuelPlumbing5.jpg

These were made from coils of steel brake line that I bought from Inline Tube through eBay. These are Inline Tube OE1425 and OE1625, for 1/4" and 5/16" OD resp. This material is fairly cheap; if interested to purchase, suggest you search on eBay for a seller with competitive price and shipping costs.

I have a tubing bender and a flaring tool. I made the bubble flares on the tubing ends by starting a double flare and not folding it over. Works well for holding rubber hose. I made a pattern for the shape of the pipe using coat hanger wire, then copied the shape in tubing. As I said the material is cheap, and you'll probably need a few attempts till you get the hang of it. My batting average was .667 here... I started three and two came out ok.

Here they are installed on the truck:

J20TBIFuelPlumbing6.jpg

I connected the 5/16" rubber hose to the frame, but I'm out of 1/4" fuel hose, so I'll have to stop here. Note that you need a little slack in the hose between the frame and the engine, to account for engine movement.