Installing Timing control on a Howell TBI FAQ

[FSJ Guy]

Modifying an OEM Howell TBI system to control ignition timing FAQ

INTRODUCTION

The Howell TBI system is actually a very nice fuel injection kit. It is entirely turnkey, meaning you can install it and be driving almost immediately after you make the last connection. There is no programming required and no need to send chips and datalogs back and forth through the mail.

Unfortunately, the system does not control ignition timing unless you ask for that to be included and of course, it will cost more.

If you want to do this addition yourself, you can. You will need a willingness and capacity for learning as well as knowing how to solder, drill and work comfortably with a Windows based laptop computer.

As with any modification on your Jeep, proceed with care. Read the entire FAQ and if you are not comfortable with the job, it might be best to have someone else do it for you.


EDIT: A few pictures were added. There is already a lot of info out there on the 'net so I tried not to duplicate too much. I wanted to show a nice mounting point for the ignition module, however.

[FSJ Guy]

What you will need:

Aside from the Howell TBI kit, here is what you will need to acquire:

8 pin GM ignition module (BWD Part # CBE28P)

GM dual connector coil (BWD Part #E46P or MSD Part #8226)

This shows a dual connector coil hooked up via an MSD box. An OEM connection would have TWO connectors going to the coil. See the next picture for the connectors


Connectors for both the ignition module and the coil (These are pricey if bought new, but can be found in junkyards.)

This picture shows the black and gray connectors plugged into an MSD harness. An OEM connection would have these two connectors plugged into the actual ignition coil shown in the picture above this one.


1/4” x 1/2” x 6” aluminum bar (heatsink for the ignition module)

Heatsink grease (A good electronics parts store should have this in stock)

Extra ECM (Electronic Control Module) connector (from a junkyard or ebay) for spare pin connectors

And of course, you will need some nice wiring, a soldering iron, solder and some heat shrink tubing.

G2 Adaptor from Moates (see posts below)

Burn2 EEPROM burner to erase and reprogram chips.

27SF512 EEPROMs. You will need two since you will probably put one in backwards at once point and ruin it. You can use the second one while you wait for the new one in the mail.

Laptop computer with a USB port, running Windows XP or better. I have used a 600 MHz pentium computer with no problem.

Access to a MIG welder, or a twenty dollar bill.

Nice to have, but optional: An ALDL cable to log data from the computer. Not required for adjusting timing, but EXTREMELY helpful if you’re going to adjust the fuel table.

[FSJ Guy]

Backstory:

Read this to understand what we are doing and more importantly, WHY.

Most Howell TBI kits use the GM 1227747 ECM. This number is what is known as the ?Service? number. There is good support for this ECM in the aftermarket community.

The ?7747 ECM uses a removable PROM (Programmable Read Only Memory) to allow for different parameters for different engines to be stored in memory. This way, different engines can use the same ECM simply by changing the PROM.

This ECM is found in vehicles with a 4.3 6 cylinder as well as the 454 big block Chevys. The difference is the chip.

The stock ECM uses a chip that is erasable by UV light. As far as I know, the stock chips from GM can not be reprogrammed. Aftermarket chips, known as EPROMS (Erasable Programmable Read Only Memory) can be reprogrammed. However, they do have a finite number of times they can be erased and erasing a chip can take up to 10 minutes, depending on the UV eraser.

Fortunately, there is a faster way.

Enter EEPROMS. (Getting tired of acronyms, yet?) These are ?Electronically? Erasable Programmable Read Only Memory chips.

Point your browser over to http://www.moates.net and you will find the G2 adapter that will allow you to modify your ECM to accept a 27SF512 EEPROM. This chip is popular with the Honda crowd and as of 2011, is not obsolete like the old UV EPROMs. One of the biggest advantages is that you can reprogram this chip virtually instantly. It takes SECONDS, no minutes, to change the data on this chip.

[FSJ Guy]

OK, so you?ve read through this entire FAQ and you?ve gathered up all your parts. Ready to proceed?

REMOVING TACH FILTER

The first thing you will need to do is find and remove the ?tach filter? that is buried in your wiring harness.

This board takes the tach signal from your stock ignition (it?s wired to the tach side of the coil or the tach output of your aftermarket multiple spark ignition) and converts it to a signal that the ECM can use and understand.

It?s a long, thin printed circuit board. It will usually be located in the main trunk, probably close to the ECM connectors, but not right next to them. There will be some wires going to the ECM and probably 1 white wire heading to the other end of the harness. Pull the board out intact and set it aside. You never know when it might come in handy again. If you want, you can trace where the wires run to the ECM connector, but I wouldn?t worry about them.

[FSJ Guy]

Here come the FUN PARTS!!

IGNITION MODULE WIRING:

Next, download ALL the files found HERE:

ftp://ftp.diy-efi.org/pub/gmecm/manuals/1227747/

These are the wiring diagrams for the 1227747 ECM. We are interested in the one with ignition module wiring on it. It is the page with the wheel on it (labeled “pickup coil”) and a graphic ignition module below it.

When you unplugged your ECM connectors, you undoubtedly noticed that one was larger than the other. Or was the other smaller than the one?



Anyway, there is a 24 pin connector and a 32 pin connector. Fortunately, you don’t have to COUNT the pins, since they are labeled on the connector. Get out the magnifying glass, because the numbers are small and hard to read! The small connector has A1-A12 and B1-B12. The larger connector has C1-C16 and D1-D16.



The ignition module wires will all plug into the larger connector.

Using the diagram, you will see the following pin locations:

Ignition Module A ------> B3 (WHITE)
Ignition Module B ------> D5 (PURPLE / WHITE)
Ignition Module C ------> B5 (TAN / BLACK
Ignition Module D ------> D4 (BLACK / RED)

Note that connection B (Pin D5) is labeled “Bypass” and “Set Timing Connector”. You will want to put a removable connector such as a WeatherPak connector in line with this connection or some other weatherproof switch.

Here is the OEM style Weatherpak connector:



If you choose to use a switch, it should be a single pole, single throw slide or toggle switch. A momentary pushbutton switch is not recommended since you will need to hold open this circuit to set your base timing.

Using your spare harness to supply you with extra pins, add new wires to the appropriate locations. I tried to match the colors by pulling the pins from the correct locations on the “parts” connector. You can use a paper clip to release the pins on the parts connector. Splice in extra wiring long enough to run from the ECM to the coil mounting location. I mounted my ignition module to a bolt on the A/C bracket.



Remember, it is better to have your wires a little long versus too short! But everything in moderation.

The wires that go from the module to your ignition coil should be fairly obvious if you got your plugs from the junkyard.



If not, the MegaSquirt site has a nice overview of the GM 8 pin module here:

http://www.megamanual.com/ms2/GM_7pinHEI.htm

Scroll about 3/4’s of the way down and you will see a pinout diagram of the GM coil as well as which color wires to hook up from your distributor.

Disconnect the distributor from the wiring harness. I replaced my connector with a Weatherpak connector. If you want to hack into your OEM harness, you can use the existing connector, but I think it is a bulky connector and unless your distributor is not original, chances are good that the connector has seen better days.

Your distributor should have an orange and a purple wire. The orange wire should go to the P terminal on the ignition module and the purple wire should go to the N terminal. If you have trouble with the timing, you can reverse these wires, but this configuration should work. Some people report good luck with twisting this pair of wires. This is supposed to help with the clarity of the signal from the distributor. I'm not an EE so I can't explain if it has an ounce of truth or not.

[FSJ Guy]

IGNITION MODULE MOUNTING:

The ignition module must be grounded in order to work correctly. Fortunately, this can be accomplished by grounding the required heatsink. The heatsink is mounted on the metal side of the ignition module with heatsink grease spread inbetween. If you have test fit the module to the heatsink already, you probably noticed that it will not sit flat on the metal part of the module due to two locating pins moulded into the plastic. Remove them carefully with a sharp knife.

Remove enough of the molded pins so that the heatsink will sit flat against the module. If it does not sit flat against the heatsink, the module WILL FAIL. It gets hot!

Drill two mounting holes to match the ignition module and attach it to the heatsink with a pair of nuts and bolts. DON?T FORGET the heatsink grease. Yes, this is important. Without it, your ignition module WILL overhead, die and leave you dead in the water. Or more likely, dead in the middle of a busy intersection.

As mentioned before, I mounted my module and heatsink on one of the bolts of the A/C bracket. Location isn?t terribly important as long as you don't try to bolt it to an exhaust manifold. Just don?t let it lay around unattached.

Now you have your ignition module wired up to the ECM, the coil and the distributor, right?

The next step is to modify the distributor.

[FSJ Guy]

MORE FUN!!!

DISTRIBUTOR MODIFICATION:

Set the engine to TDC, remove the cap and then remove the distributor. See, aren’t you glad you kept a removable plug on the distributor wiring?

What you want to do now is disable the vacuum advance and the mechanical advance.

Disabling the vacuum advance was already done when you remove the distributor. How? You removed the vacuum advance hose. That is all that needs to be done there.

Disabling the mechanical advance is a little more involved. This is where your buddy with the MIG welder or the twenty dollar bill comes in handy.

Remove the rotor and set it aside. Remove the two screws that hold the pickup module in place. Remove the pickup module.

The starwheel is attached to the rotor via a roll pin. Before you remove the starwheel, match mark it with a permanent marker. You will want to replace it in the EXACT position that it came out. It can install 180 degrees opposite of its correct position, so marking it is important. Using two screwdrivers on opposite sides, carefully pry the starwheel off the rotor. Try not to pry on the "fins".

Below you will see the weights and springs that make up the mechanical advance. As the rotor spins faster, the weights are flung towards the outer edges against the springs holding them in. As they do this, the timing is advanced. The rate is controlled by the springs and the total advance is controlled by the stops. Note the position of the rotor and the distributor drive gear when the springs are at the least tension. This is how you want the rotor to be welded to the bottom half once the springs and weights are removed.

Remove the weights and springs.

You will now see that the top of the rotor is free to rotate slightly, independent of the distributor gear. It is these two sections that you want to weld together. Now you know why you observed the “at rest” position of the rotor and the bottom half of the distributor.

A MIG welder makes short work of this job or you can bring it down to a shop and have them do it for you.

Assembly is reverse of removal. Honest. Since you match marked the starwheel to the rotor, pressing that back on will go off without a hitch, right? If that unconnected port on your vacuum advance bothers you, you can buy plugs at your local parts store in the Help! section.

Now you have your distributor modified and your ignition control module wired up and mounted. Don't stop now! You’re halfway there!

Besides, you just made a rather permanent modification to your distributor!

The modified distributor below. Note the Weatherpak connector for the pickup. Much easier to connect/disconnect than the OEM connector.

[FSJ Guy]

KNOCK SENSOR BYPASS:

Now that your ECM is controlling the spark timing, the computer will also be looking at something else; the knock sensor! You could install an actual knock sensor, but the sensors are tuned to particular engines and frequencies. Instead of spending tons of money on sensors and modules, it is easier to simply ignore it. However, the computer doesn?t like to ignore things. Instead, we can ?fake it?.

Looking back at your ECM wiring diagrams, you will see the knock sensor (labeled as ?Electronic Spark Control Module?) module hooked up to pins A6 and B7.

Pin A6 is a 12V supply. Pin B7 is monitored for the knock signal.

By supplying Pin B7 with a 5V reference voltage, the computer will think the knock sensor is working and NOT sensing any knocking. This will prevent a knock sensor trouble code as well as any retarding of the timing due to sensing any knocking.

Tap into Pin C14 and run a wire from that splice to Pin B7.

You are almost there!

[FSJ Guy]

Modifying your ECM to accept the 27SF512 EEPROM chip

Now you can work on modifying your ECM to accept the newer EEPROM chips.

You?ve already ordered your G2 memory adapter from Moates, right?

If you?re remotely handy with a soldering iron, it is very easy to install. A nice description of the install is here:

http://www.binderplanet.com/forums/showthread.php?p=293613#post293613

If you?re able to solder chips to a board without frying them, you may want to try the ?chip mod? described here:

http://www.binderplanet.com/forums/showthread.php?t=80053

What Bill did in this mod is basically connect pins 1, 2, 28, 27 and 26 together. I did a similar modification but did it on a chip carrier instead of the actual chip. The result was the same. Keep in mind that this modification doesn?t lend itself well to constant chip removal. The G2 Switcher from Moates comes with a ZIF (Zero Insertion Force) socket that lets you swap chips quickly and easily without any wear and tear on the chip or the socket.

I'd recommend the "chip mod" method for when you settle in on a good tune and won't be changing chips very often. Start with the G2 switcher with the ZIF socket.

Note that you can still use your existing 24 pin chip (stock, or from Howell) in the adapter. But I don?t know why you would ever want to...

[FSJ Guy]

Burning chips and modifying things!

Now that you?ve installed your G2 adapter, you?re ready to start burning chips! (It's about time, isn't it?)

Follow the instructions from Moates and install the software on your computer. Download your favorite ?tuner? program and read the Howell bin (short for binary file) from your Howell chip.

What? You have no idea how to do that? Let?s step back for a minute.

OK, that?s better.

There are several programs out there that let you read the bin file and adjust parameters without knowing or ever seeing a single hexadecimal number. You can actually edit the bin file MANUALLY, but this is tedious even for the most enthusiastic programmer out there.

What these tuning programs do is allow for other users to create ?hacks?. A hack is a roadmap and description of all the parameters in the bin file. A good hack translates the data into useful numbers that we can interpret as degrees of advance, % of fuel, temperature, etc. Think of it as a ?secret decoder ring? that allows you to read the bin file.

I use TunerProRT, but there are others out there. They are fairly similar but some offer different features or support for various products.

TunerPro is available here:

http://www.tunerpro.net/

It is free, but has a nag screen upon launch. It is inexpensive and WELL worth the money that Mark asks for it. I suggest buying it simply because it is such a good program.

When you install your tuner program, you will also have to load a hack for your ECM. With TunerPro, it is called a ?definition?. For the ?7747 computer, you want the 42.XDF file. If you are datalogging, you will want the corresponding ADS file, too.

These are available here:

http://www.tunerpro.net/downloadBinDefs.htm

TunerPro will work with the Burn2 unit as well as the AutoProm. Either way, install your Howell chip on your burner and read the chip. CHIP ORIENTATION IS VERY IMPORTANT!!!! You did read the instructions, right?

Save the bin file to a separate folder. Copy it and do your modifications on that file, not your original.

Once you load up your bin file, you will want to change the following under ?Flags/Switches?. (You may have to scroll up and down to find some of these)

42 Knock Sensor: Enable this. If this code comes up, you know that your spliced wire has become disconnected.

43 ESC: This is the knock sensor control module. The spliced wire will make the computer think that this is working, even though it is not. You want this trouble code to set if something is wrong because if it IS sensing knock, it will try to retard the timing.

Under Constants/Scalars, you will want to change the following:

Initial Advance:
This tells the computer what you will set your base timing to. In other words, what the timing is set to without the computer controlling the timing. Chevy motors are set to zero degrees and your Howell bin will probably show zero in this field. Whatever you set yours to, make sure the actual timing on the engine is set the same. I set mine to 10 degrees BTDC (Before Top Dead Center).

Main Spark Advance Bias:
This number is used to allow negative advance timing. I have not found a use for a negative advance with either my 360 or 401 motor. The ECM takes the Main Spark Advance table value and subtracts the Main Spark Advance Bias value from it.

So if the lookup value for spark is 10 degrees and the Main Spark Advance Bias is 15 degrees, the ACTUAL calculated spark advance is MINUS 5 degrees. The table can not handle negative numbers, thus the reason for this setting.

To make programming advance easier, set this to zero.

Under Tables/Functions, you will find the Main Spark Advance table.

The X axis is the manifold vacuum pressure from 30 (high vacuum) to 100 (low vacuum, or atmospheric pressure.

The Y axis is RPM from 400 to 3600.

Remember that the OEM Chevy spark tables are calculated with about a 20 degree spark bias. So, where it reads 20.04, it is really calculated to no advance at all. Since you zeroed out the Main Spark Bias, you don?t have to do any extra math.

When coming up with a timing table, try and think like your distributor ?thinks?. At idle, there is no centrifugal advance present. As the RPM increases, the advance will increase.

If you are simulating manifold vacuum, there will be vacuum advance at idle and part throttle and the effects of vacuum advance will diminish as the MAP readings rise.

Ported vacuum will only add advance at part throttle and be lower at idle and wide open throttle.

A good rule of thumb is to start off with TOO LITTLE advance and work your way up slowly. I?m sure it can be done, but it?s harder to hurt your engine with too little advance versus too much advance. If you hear the engine knocking, back off the timing in that area. (This is where datalogging comes in handy, but that?s a different thread altogether.)

Don?t forget to save all your changes to a NEW bin file. I label mine sequentially and put them in folders by month. I find it easier to keep track of all the bins this way. Trust me, you will end up with a lot of them! I also keep a written log of the changes I make and the results of those changes. It makes it much more useful when I go back a week or month later and look at what I?ve done.

[FSJ Guy]

START YOUR ENGINE!! (But read this first!)

Startup

Before starting your new system, go back and double check all your work. If you have an AutoProm or a separate ALDL cable, hook that up so you can log data and watch the different parameters such as MAP, RPM and TPS values.

Install your new ?custom? chip into the ZIF socket on your ECM. DOUBLE CHECK that the orientation is correct. You WILL fry the chip if it is installed backwards. Try to keep that to a minimum.

With everything installed, and the timing bypass plugged in, turn the key and start the engine. Listen for any knocking or other indication that something is wrong. The SES (Service Engine Soon, aka Check Engine) light should not be lit while the engine is running.

If all is well, turn off the engine and hook up your timing light. Unplug the timing bypass wire. Start the engine and turn the distributor to set your base timing to whatever number you set your Initial Advance to. Tighten down the distributor and check the timing again to make sure it didn?t move. Turn off the engine and remove your timing light. Plug the timing bypass wire back in.

You will now have a trouble code registered in your ECM because it things the ignition module is not working correctly due to the timing bypass being unplugged. To clear this code (or any code) unplug both ECM connectors with the ignition key turned off. The official word is that you have to wait 30 seconds, but I never do. 5 seconds is plenty. Plug the ECM connectors back in. You should be able to start the engine again and not have the SES light come on while the engine is running.

Take your truck out for a casual drive around the neighborhood. CAREFULLY try out different driving situations and see how it performs. Changing the timing is now a simple matter of reprogramming a chip and swapping it. No more physically adjusting the distributor or worrying about swapping weights, springs or limit stops.

You can also adjust the fuel via the same program you used to adjust the timing. But that's another thread!

[dusty]

AMC HEI conversion distributor change from your 4 pinn to 7 pinn module and plug it

IF you want to install ESC on your existing AMC HEI conversion distributor here?s some pictures to help you get it done. The 7 pinn module can be had from summit http://www.summitracing.com/parts/ACC-35363/. Hopefully these pictures showing the 4 pin plug and the corresponding wires and their colors to where they plug into the 7 pinn module will help you convert yours. The green and white wires are the trigger wires. Note that only 3 of the 4 pinn plug wires go into the module, the fourth wire, the red and black wire is the ground. just take an old vaccum advance plate cut and grind it to fill the hole where the vaccum advance diaphram pokes out the hole. All other components can be retained from your existing HEI, though i did replace everything while i was in there. Notice that the weights and springs are removed and the center shafts are locked down. This is a very simple conversion you can reference a 1981-1990 Buick LaSabre with the 5.0L motor to get this part at any parts house. Also a host of other buick vehicles from 1981-the mid-late 80?s all shared this ESC HEI design. That is also where you can get the four pin plug (if you want used, go to ebay if you want new) as well the lock down shaft ect any parts can be sourced from there. If you want ESC and have an HEI distributor already don't worry its not as much of a problem as you might think at first glance.

[FrankNB]

I love this writeup, only thing missing is a little diagram showing how to connect the MSD in there. Which is apparently being used in this article. Unless it's explained and I just missed it.

Also, why use the dual plug coil if only one is being used? wouldn't any TFI coil work?