This guide is intended to help all those GMC owners who are interested in installing EFI or upgrading their existing systems.
It is an attempt to capture, in an organized and easy-to-understand format, the accumulated knowledge and wisdom of the many talented people who have worked with EFI on the GMC Motor Home. I know, an impossible task. Still, so many newbies, myself included, have struggled so much to understand the complexities of these systems, that there has long been a desire to put something like this together to help the learning curve.
Initially, almost all of what's here relates to the Howell EFI system. The Howell systems comprise by far the largest installed base of EFI users for the GMC MH.
Disclaimer:
This Guide was created Jan 17, and as of now, Jan 20, lots has been cleaned up, but still much of the info here is incomplete if not wrong. I just kind of waved my hands at it, trying to capture as clear an overall picture as I have in my head, which frankly is pretty fuzzy. Hope everyone can see the benefit of such a guide and can contribute corrections and additions to clean it up. Thanks.
Almost all of what's here has been extracted from the GMCMH-EFI forum on Google Groups (http://groups.google.com/group/gmcmh-efi), moderated by Ken Henderson. That group was formed when the EFI discussions on the GMCnet (http://gmc.mybirdfeeder.net/) got so large that a separate group seemed appropriate.
This is intended to be, must be, a living document, and all members of the GMCMH community are asked & encouraged to please make contributions and corrections and share their experience. Anyone can edit any of the sections. Or, if you prefer, you can post your edits to the GMCMH-EFI group or send your corrections/additions/suggestions in a private email.
When you're done making changes, go to the bottom of the page and click on "Show Preview" to see how your edited page will look. You can scroll back down to make other changes if needed.
When you're satisfied with your edits, scroll to the bottom and click on "Save Page."
But again, if you don't want to go through the hassle of the learning curve, email your contribution or post it to the EFI net. Thanks!!!
EFI is a fuel control system that meters the fuel to the engine much like the OEM QuadrajetTMcarburetor has done for years on the GMCMH engines. The Quadrajet, when set up correctly, does a very admirable job of metering fuel. The main difference is that the EFI system checks to see how much fuel is actually burning and makes real-time adjustments. It is also able to monitor the engine temperature and the altitude. These variables make a big difference in the amount of fuel an engine needs. On-the-fly correction for these variables can give higher performance and better mileage.
EPROM = Electrically Programmable Read-Only Memory File:WUD-KenH.jpgWUD from EBL on KenH's Lenova
Howell Inc (http://www.howellefi.com/customer/) manufactures a complete line of aftermarket EFI products for most V6, I6, & V8 engines. The ECM is the heart of the system. It contains a PROM or EPROM that contains computer code used by the ECM's microprocessor to control the injectors (at the basic configuration) and the spark advance (with more advanced configuration and sensors). The program version that is used most successfully for the GMCMH is 7747.
The Howell computer can monitor inputs from a variety of sensors, and according to the program in its PROM or EPROM, it calculates a response and controls certain outputs. With just the basic system, and no extra sensors, the inputs are: [what????], and the output is [what?? - fuel pump pressure?].
In this configuration, only the ECM 7747 is installed. This mode gives you some of the advantages of the EFI, such as [what???], but that's all.
ECM with CCD, ESC, and KS:
Adding the Computer Controlled Distributor gives a huge step up in improving the system, reportedly the single most effective add-on. The CCD requires an ESC module, and the ESC module requires a Knock Sensor. The 7747 ECM that is standard with the Howell kits is pre-programmed with code to allow controlling the spark/distributor, meaning that the chip does not need to be reprogrammed to make the CCD work. [Is this correct? Saw one note that a new chip was indeed needed???] Once spark is being controlled and monitored, real improvements can be seen in the system. By monitoring ping (pre-detonation) with a knock sensor, the spark can be advanced as much as possible without pinging (which can damage the engine). This can increase fuel mileage and performance.
ECM with EBL:
The Embedded Lockers (EBL) kit is a piggy back board that mounts on the mother board of the 7747 computer. This accomplishes a multitude of improvements. First, without the EBL, any changes to the programming (for optimizing Fuel, Spark, Highway Cruise, etc.) require the chip to be pulled out of the computer and re-burned/re-programmed with the new settings. (See Programming) With EBL however, a new program can be “flashed” to the EPROM in seconds, without removing the chip from the computer.
EBL has a What’s Up Display (WUD) that gives you X-Ray vision into the operation of your engine. If you have VSS, the WUD tells you how fast you are going. It tells you how many RPMs you are running. In addition it reports on over twenty other parameters - MAP, Throttle Position, Temperature, Spark Advance, Knock Count, Injector Duty Cycle, BLM readings, Closed Loop, Idle, DEFCO (fuel shutoff), Lean Cruise, etc. A second screen gives instantaneous and trip miles per gallon, fuel used, MAP reading and Lean Cruise at a glance. (See VSS, in Improvement 3 below.)
EBL has a Learn Mode for the fuel tables that allows the computer to learn slight adjustments that were relegated to trial and error before. And of course these new bits of programming can be flashed onto the chip for permanent use in seconds.
Adding an EBL to an existing ECM can be done, but it is not trivial, and requires significant disassembly and some careful soldering (See instructions at: http://www.dynamicefi.com/EBL_Install.php). Instead, it's lots easier to buy an already integraged ECM/EBL from Dynamic and keep your existing ECM as a spare. Be sure the new ECM/EBL you get has the same connector pinouts as your existing ECM or else swapping them will be complicated.
ECM with EBL & VSS:
Vehicle Speed Sensors (VSS) are devices that tell the computer how fast the GMC is going. The 7747 computer that came with the Howell kits is able to receive pulses from the VSS in a limited way. With the addition of EBL the system moves ahead years in technology. Once the computer knows how fast the vehicle is moving, it can add important features. The WUD will now tell you how fast you are traveling and give instantaneous MPG and trip MPG. It can turn off the fuel injectors when coasting. The computer can now switch into Lean Cruise or Highway Mode. Because the computer knows the vehicle is at highway speeds and the engine is not pulling extra hard, the fuel ratio can be leaned out, so less fuel is used at the same speed.
ECM with EBL & IAT:
The EBL system has the ability to monitor the intake air temperature if an IAT sensor is installed. Because warm air is not as dense as cold air, this information can help the computer more accurately adjust fuel usage. While all modern automobiles have this feature, at this time there is not enough experience with using this sensor in the GMC to say whether it is going to make a great deal of difference in drivability or mpg.
Men's Mall: Any 307 Olds engine will have a CCD. Those engines were used in a lot of different GM cars. If you get one from a junkyard just disassemble it and clean and lubricate the shaft. Also be sure to get the connector that mounts in the outside slot of the distributor.
Important: junkyard and rebuilt distributors not done by Paterson or other GMC experts may have reversed coil polarity. [???how do you check to be sure???]
[don't know if all or which of these above is usable/best, whether there are tradeoffs to any of them...]
AC/Delco 213-324 or KS7T or Airtex 5S2158 ($25 - $35)
These parts were used in many GMC vehicles, including the 1993 Buick Roadmaster Estate with a 5.7L 350 engine, and the 1989 GMC K3500 truck with a 7.4L engine.
[??? Available from Ray Swartzendruber? He can be reached at redruber-at-gmail dot com???]
[???From Men's Mall???]
Important: The VSS must have a square-wave output to work with the EBL.
VSS pulse rate:
Originally the EBL required 2000 pulses per mile. Now, however, the programing allows you to adjust the system to use other pulse rates. Many systems are installed using a 4000 ppm VSS. This is convenient if you are now or later going to add a cruise control [which mfr???], which requires the 4000 ppm.
Disclaimer: This section is VERY rough and needs a LOT of work for clarity and completeness. I only have a very rough idea of the process, but have tried to put down what I think are important headings and categories.
Everyone please help by correcting mistakes and adding your 2c.
General
The program that calculates spark and fuel flow [and other outputs???] resides in a PROM or EPROM in the ECM. The microprocessor in the ECM reads the program and calculates the outputs needed to run the engine.
No two GMC engines are the same. Most of them are 30-35 yrs old. Mileage on them varies from that lucky find that was in a barn for 25 yrs and has only 20,000 mi on it, to engines that have well over 100,000 mi, and some even more with a rebuild or two thrown in. Some rebuilds have been to stock, and some have been over-bored. Different exhaust systems, headers, exhaust pipe and muffler configurations, different radiator and cooling system configs, and different transmission and differential gearing, all have an effect on how the engine operates. Add to this the great variety of driving conditions, with temperatures from Alaska to Arizona, elevations from Death Valley to the Colorado Rockies, loading from a light-weight 23' to a 26' with a 3500# Towd, and it all adds up to the fact that every engine has to have a custom-tweaked program in the ECM in order to run well.
First you have to figure out what you want the new program to be.
"Learns"
[???Trial and Error???]
[???Other ways???]
Once you figure you what you want, you have to burn or flash the new program into the PROM/EPROM. This can be done in a variety of ways:
Burn a new chip: This requires a piece of hardware called a "Prom burner." If you do not have your own burner, there have been a number of GMCers who have kindly burned new chips for many of us. In addition, the technicians at Howell and Affordable FI (http://www.affordable-fuel-injection.com/) have been very helpful in these areas.
Use EBL to flash a new program. This is the easiest and recommended method.
