ECU (Chip) Basics - Team Integra Forums - Team Integra
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ECU (Chip) Basics

Posted 02-27-2002 at 12:00 AM by MichaelDelaney


1. Should I get a "one size-fits all" or "off the shelf" Mugen, Jet, Spoon, Skunk2, Comptech, Neuspeed, FF Squad, Inline4, Power XS, Bayou Performance, or Dinan ECU which are "best guess" chips? How about getting one of those chips I see for sale on ebay all the time?

1A. First, Don't Chip Too Early

There is no point in getting a new ECU program early in your engine build up and then later upgrading to bigger lift and duration cams, or larger injectors, bigger fuel pump, or an aftermarket IM/bigger bore TB , etc. , since these parts just render your "new" ECU program obsolete and useless (ie. any power gains from the chip are eliminated).

So please do not get your chip reprogrammed just after i/h/c/e , if you later plan on going for bigger & better things in the future. It's supposed to be one of your last modifications and not one of your first, to prevent the need for multiple chip reprogrammings after each addition of a new modification.

The reason you see so many chips for resale on ebay?:

Other enthusiasts made the mistake of buying a chip too early that was not programmed correctly for the unique way their engine package breathes. It made very little power for them , or likely made their engine run too rich, or both. They are now trying to recover the money lost from an obsolete or incompatible chip.

Then there are the programmers who take advantage of import enthusiasts who do not understand the performance difference between a pre-programmed, mail-order chip versus a chip tuned and programmed on your car at a dyno. They are selling them based on the attractiveness of convenience for unsuspecting people who don't have a local programmer and dyno, the hyped hp gains from the magazine articles or ads, and a lower cost compared to other significant hp gain modifications, like cams or an intake manifold (IM).

1B. Second, What does an ECU do and what am I doing when I get a new chip ?

The ECU controls:

- the fuel map (ie. program commands for how much fuel to add at each rpm) and sequential firing of the injectors

- ignition map (program commands for how much spark timing to advance or retard from the baseline ignition timing you set at the distibutor cap at each rpm)

- VTEC switchover

- Redline

- Speed limiter (JDM and European models)

- Knock sensor warning

- Second O2 sensor CEL warning in OBD 2 and OBD 2b cars for testpipes and high flow cats and closed loop operations

- Activates the opening of the secondary runners' valves based on the IAB vacuum input, if you have a dual stage IM (eg. 3rd gen. GSR)

The ECU also activates your other CEL error codes and controls A/C & Idle/EVAP inputs/outputs.

When you get a new chip, the programmer has changed the program's commands of the ignition map and fuel map in response to a change in air flow and rpm (ie. both are indicators of "engine load"). The amount of ignition timing and fuel delivery is changed for a given air flow and rpm compared to the stock program. The programmer can also remove or inactivate the sensor CEL warning codes and move the VTEC point, redline, and speed limiter points to anywhere you like.

What do these ECU program's commands look like?

Example of a 3 dimensional ignition table of program commands (or "ignition map"):

Manifold Absolute Pressure or MAP which monitors air flow (Y axis), RPM (X-axis), and Ignition Advance/Retard from Baseline Timing (Z-axis).

There is also a 3-D fuel table (or "fuel map") which has Intake Manifold Pressure (Y-axis), RPM (X-axis), and Fuel Values instead of spark Advance (Z-axis).

The program commands can be entered on 2 dimenional tables.

Example of a 2-Dimensional fuel table's commands during a GSR's VTEC cam lobe operation . :

RPM down the Y axis to far left, MAP (mBar) across the top row, and fuel values for the injector duty cycle in the table cells.

Originally posted on the Hondata Website

Most (but not all) plug in chip replacements claim to be a 'Mugen' program. Typically these chips disable error reporting for most sensors and give about 40 % worse fuel economy. The chips are popular with engine swaps because they eliminate most error codes caused by poor wiring....The stock knock sensor is designed to compensate for different qualities of fuel, and has a limited scope of adjustment. It is not designed to co for detonation under boost and may be fooled by forged pistons rattling into retarding the ignition when knock is not present. Mugen recognizes this and does not have a knock sensor (input on their ECU).
1C. Third, "Best Guess" programs are not as good.

An "off the shelf" or mail order ECU is a programmer's best guess at trying to make a program that will fit as many different engine combination of mods as possible...that's why I call these "one-size-fits-all". These usually get you in the no gain or 5% disappointment gain ballpark. You will not get major gains with these "best guess" chips. Save your money.

So you want to make major power gains (ie. 13-15% or at least 7 whp from midrange up) with an ECU reprogram?

Please get a true custom chip instead, programmed on YOUR unique car with its own combination of mods, on a dyno using a wideband exhaust O2 sensor/Air:Fuel Ratio meter. This is the only way to go, if you are serious about getting the most out of a computer program upgrade for a street/race setup. If you got your chip by mail then, please understand that you did not get the most out of it...even the custom pre-programmed, mail-order kind of chips. The only correct way is to do the reprogramming on the dyno. And this leads us to who do you go to?

If you are lucky like me and have a couple of local programmers with Honda experience near your town, then your local programmer will go with you to the dyno and work his experience in tuning on the laptop and EPROM or EEPROM burner.

If you do not have a local programmer or race shop that does programming, then I strongly recommend getting together with some friends and investing in a Hondata Stage 4 or P200 system. It allows YOU to tune YOUR car on the dyno or at the track using elapsed times between known rpm points.

It comes with a chip burner, chips ($25/each), emulation laptop capability, instructions, and tech support. Investing in a wide band O2 sensor like the MOTEC they sell is also a good idea. This takes the guess and disappointment out of ECU upgrading.

If you want to go at this alone, then an AEM EMS is worth looking into, since it has base programs and laptop emulation. This is a serious investment for serious people.

If neither of these appeal to you and you insist on getting a mail order chip knowing that it won't be the best program, then stick to the known programmers (PM me if you want recommendations from people I've known who do a decent "best guess" chip). Most people who buy a mail order chip usually have a piggyback tuning box, like an Apex fuel controller (SAFC or VAFC) or Field SFC VTEC/fuel controller, and use those to further tune the fuel delivery on the dyno with a wideband O2 sensor.

Chip reprogramming at the dyno requires a wideband universal exhaust gas oxygen sensors (called an UEGO that you can get from dyno shop or race shop) to measure air:fuel ratio at each rpm. Expect at least 3-4 hr dyno time minimum to tune these even if you are experienced at partial and wide open throttle fuel tuning.

Other systems to consider are the Motec M4, Apex Power FC, Accel DFI, SDS EF3, and Electromotive Tec3. Compare processor speed (16 bit, 16 MHz versus 32 bit, 33MHz ), available baseline programs to get you going without startin from scratch, sensor compatibility, emulators availability, and a good track record for tech support/customer service (not just whether they have one or not).


2. Why will an "off the shelf" mail order ECU Disappoint?

From FAQ/Tech

...on most naturally aspirated engines operating on pump fuel, the only way to achieve tangible power gains is by increasing airflow through the engine. Chips cannot do this. Therefore they cannot make much difference in power output. Chip reprogrammers can richen the mixture slightly at full throttle and advance the ignition timing slightly perhaps but this would be at the expense of lowering the factory safety factors for detonation and emissions. The absolute maximum gain in this instance would be on the order of 5% and could be as little as 0%. Most independent tests that I have seen on performance chips for naturally aspirated engines have indeed shown minimal or no gains in acceleration.

Some were slower than the factory chip.

Chips for use in factory stock turbocharged applications can increase power substantially in some cases by raising the boost pressure. This again reduces the factory detonation limits and you risk engine damage. Without increasing fuel octane, you are asking for trouble especially if your engine does not have a knock sensor.

Finally, we have chip companies doing "custom" chips for modified engines. What does this involve? This is a technically sound modification only if your engine has the same mechanical mods as the motor on their dyno that the chip is being developed for. If your cams, heads, turbo, exhaust, intercooler, injectors, throttle body or fuel are different, the chip will not be correct for your engine. A chip made for an engine slightly different from yours will be slightly wrong under some conditions. In some cases, poor driveability and performance are the result.
SDS and Hondata agrees with me that the best way to rechip your computer is to program your ECU instead on the dyno on your car rather than buying a previously programmed "best guess" chip made to fit as many different engine packages as possible.

The only way to get good results on a modified engine with different mods from the base engine is to take your vehicle to the tuners facility and get a true custom chip burnt for YOUR engine. This must be done on a chassis dyno then tested on the road also for driveabilty faults which often don't show up on the dyno. This will cost more.
Here is some very good advice when buying a pre-programmed , "mail order" performance chip from SDS' website that I have found to be true:

Before buying, do acceleration testing with a stopwatch, Vericom (or a GTech Pro) or at the strip. Have an objective measure of performance as your baseline before programming so that you have something unbiased and not subjective (like a butt dyno impression) to compare to afterwards.

Get the chip maker to guarantee the performance gain IN WRITING and make him understand that you will return the chip to him if the chip does not work as claimed. If emission compliance is a concern, ask if their chip will pass the test and get it IN WRITING.

Follow all of the instructions provided by the chip maker when installing it.

Stick to reputable companies. Some people in the chip industry really don't know what they are doing. Talk to some people first who have used a certain chip and see if they are satisfied.

Test your car to be sure that you got what you paid for. This is all good advice when buying any aftermarket devices such as ignition wires, ignition products, oil or fuel additives etc. which advertise a performance gain.

If it doesn't do what it is advertised to do, you just got hosed and with some chips costing $300-500. This is something that you should not put up with.
Be careful. Some unscrupulous programmers will promise to sell you a "Mugen" like chip but in reality, all they have done is moved the redline higher and removed the CEL warnings. The advice to stick to known reputable programmers is wise, if you plan on mail orders.

What about standalone computers like a Hondata instead of a redone chip ?

If all of this doesn't sound too good to you (in terms of chips), the alternative is a (standalone) programmable engine management system . These allow you to tune your engine yourself. This can be good and bad. The same things apply as above for the mail order chips.

If you don't have a fairly thorough understanding of the system, engines and tuning plus a dose of patience, DON'T buy one of these.

Understand that you will have to program all of the values to make the engine start, warm up, cruise, accelerate and run at full power. This can entail entering hundreds of points in most cases and you will require either a dyno or a long deserted road plus some indication of mixture strength to properly tune such a system. These systems are great for the knowledgeable person and a nightmare for the lay person.

Remember, both the chip that you buy or the chip in your (standalone) programmable ECU must have the proper values entered for your engine to run properly.

The main advantage of user programmable (standalone) systems is that they can be quickly changed, if a new mod is done or if not quite right whereas the factory type (mail order) chip must be changed or sent back to be redone, sometimes, several times at great cost.

If you are contemplating a strictly race situation, don't bother with the factory ECU or chips at all. These were not designed for performance use and you will usually not get the kind of power required with factory hardware. This is when a programmable system is a must.

When considering buying a programmable system, here are a few tips:

Discuss your goals and needs with the tech people selling the system.

Make sure that the system will do what you require it to do. Don't expect the impossible - you can't expect a 400hp, 4 cylinder street car to have factory driveability, fuel economy, emission compliance, a smooth idle or long life on pump fuel. If you do, you are a nut and no one will talk to you. There is a reason why there are no factory cars like this driving around your neighborhood.

Removing the factory system and installing a stand alone system can be a lot of work. What hardware, skill and tools will you require to install the system? Can you handle it or do you know someone who can?

What factory options will you lose when removing the factory ECU?

If emission legality is a concern, find out if their system is legal and if it will likely pass in your area when properly programmed. Many systems are not legal for street use and many manufacturers will not guarantee emission compliance because they cannot control the programming.

Find out how easy the unit is to program and if you can handle it. If it is difficult to use, either don't buy it or find a place where you can go to have it properly tuned.

Make sure that the company has good, accessible tech support, you may need it.

You are responsible, if you program the system too lean and melt your engine, don't blame the system maker. If the engine runs like crap, you are probably asking the system to do something that it was not designed for or have not programmed it correctly. This is your problem now.

Read, understand and follow the manufacturers instructions. LISTEN. It will save you a lot of time. Remember, that the people who design and build this stuff likely know a hell of a lot more than you do about it.

If all of this discourages you, sell the present car and simply buy a
faster one, you will probably be happier in the end.

3. Some Basic ECU Info for OEM Honda ECUs

Originally posted by

Most ECUs up to 1996 hold their program information and data in small chips called ROMs. These are 28pin chips 1.5 inches by 0.6 inches. If we want to change either the program information (how the ECU behaves) or the data (usually the fuel and ignition tables), we need to replace the factory ROMs with our own. There are several different types of chip which can be used to replace the factory ROM.

3A. Terms To Know


ROMs are read only memory, which cannot be re-used once programmed(e.g. Atmel AT27C256 ROMs). ROMs are most suitable for the final tune for an engine, which is not going to be altered.


EPROMs are like ROMs except they have a quartz window which allows the EPROM to be erased and reused. Like ROMs, EPROMs are suitable for the final tune.


EEPROMs can be electrically erased and re-programmed, usually much quicker than EPROMs (e.g. Atmel AT29C256). The advantage of EEPROM is that it is can be programmed in 20 seconds without erasing it first. EEPROMs are most suitable for use when tuning a car, but can be used as the final tune as well.

EPROM emulation

An EPROM emulator is a device which emulates (acts like) an EPROM. It is a box of electronics which plugs into the ROM socket on the ECU, and a laptop or PC. The advantage of using an EPROM emulator is that the tuning information in the ECU can be changed quickly without unplugging or swapping ROMs.

There are two types of EPROM emulators: normal and real-time.

Normal EPROM emulators will shut the ECU down while the information in the ROM is updated.

Real-time EPROM emulators allow you to changetuning information while the engine is running.

All Honda ECUs have a part number which is located on the side of the
ECU and inside the ECU on the connector. e.g. 37820-P72-A01

The part number consists of three components:

Honda's part number for ECU, which is always 37820

Three characters (which are loosely related to the model of car/engine). e.g P72

Three characters (which are the revision of the ECU) e.g. A01

The middle three characters are the most useful to identify what the ECU is. Different generation ECUs may use the same characters. e.g. a P72 OBD I ECU is different from a P72 OBD II ECU. Here is a list of common ECUs (and the car model they come from):

PG6 : 88-89 Integra (all makes)

PM5 : 88-91 Civic/CRX DX

PM6 : 88-91 Civic/CRX SOHC Si

PM7 : 89-91 DOHC ZC (JDM 'EF' ECU)

PM8 : 88-91 CRX HF

PR2 : 89-91 ZC (Euro)

PR3 : 89-91 JDM B16A EF8/9

PR3 -J00 or J51 : 92 JDM Integra B16A EF8/9

PW0 : 89-91 JDM B16A EF8/9 DA6-XSi

PR4 : 90-91 Integra LS/GS

PS9 : 88-91 4 door Civic EX Auto

P05 : 92-95 OBD-1 Civic CX

P06 : 92-95 OBD-1 Civic DX

P07 : 92-95 OBD-1 Civic VX

P08 : 92-95 OBD-1 Civic D15 JDM

P0A : 94-95 OBD-1 Accord EX

P13 : 93-95 OBD-1 Prelude Vtec

P14 : 93-95 OBD-1 Prelude Si (non Vtec)

P27 : 92-95 OBD-1 EG JDM Civic 1600 sohc

P28 : 92-95 OBD-1 Civic Si/Ex

P30 : 92-95 OBD-1 DelSol DOHC Vtec Si/EG SiR

P54-G31 : 1997 Honda Accord 1.8 LS

P61 : 92-93 OBD-1 Integra GSR

P72 : 94-95 OBD-1 Integra GSR

P72 : 96-00 OBD-2 Integra GSR

P73 : 96-00 OBD-2 Integra Type-R (JDM & USDM)

P74/75: 92-95 OBD-1 Integra LS/GS

P75 : 96-00 OBD-2 Integra LS/GS

P2N : 96+ OBD-2 Civic HX Coupe

P2P : 96+ OBD-2 Civic EX Coupe

P2E : 96+ OBD-2 Civic DX Coupe

P2M : 96+ OBD-2 NZ Civic SOHC VTEC

P2T : 99+ OBD-? Civic Si Coupe

P5P : 97-00 OBD-2 Prelude Type-S (JDM ECU)

PBA : 97+ US Acura 1.6EL


PCX : 99+ OBD-? S2000

ECU ROM Numbers

As further identification Honda ECUs have a software revision number inside the ECU. This is usually a two or three digit number stamped on the 28 pin ROM, or main processor. Accord and Prelude ECUs can use a letter and number code.

3B. Injector Size Limit For Stock ECU

What are the biggest injectors I can run with a stock ECU?

The ECU can be re-calibrated to suit any sized injector (make sure you match injector impedance if you are replacing you injectors). However, injectors take a finite amount of time to open and close, so the bigger injectors tend to be less accurate with their fueling at low durations, such as idle.

Much depends on the mechanics of the injector, and how quickly it can open and close. With disk type injectors (such as RC 440cc injectors) you cannot tell the difference between stock injectors and injectors which flow twice as much as stock injectors, once the ECU has been reprogrammed for the larger injectors (and there is no difference on the dyno either). With race engines we have run injectors up to 4 times the size of the stock injectors.

How come people say that the biggest injector I can run is 310
cc/min. ?

This assumes that you are not re-calibrating the ECU to the new injector size. If you don't, the bigger injector will over-fuel. If this happens then the ECU will compensate to some degree using closed loopo peration to reduce the injector duration. The limit of the long term closed loop adjustment is about 40%, which is close to the increase in size from stock to 310cc injectors.

3C. Disadvantages of Running High Fuel Pressure

Some people, instead of buying a proper size injector to get more peak hp opt to push the limits of the current injector they have by cranking up the FP and running at near or over 80% duty cycle. Once you exceed a 20% increase from the maximum FP spec, you wear out the injectors faster and the ECU fuel map calibrations for the program are no longer applicable.

Other disadvantages of extra high FP.:

- Fuel injectors require more current to open meaning they run hotter and are less reliable as a result.

- Fuel injectors can take longer to open.

- There is a greater tendency for the fuel to leak past the injector seals.

- There is a greater chance of rupturing the diaphram of the FPR (usually rated to 100 psi) dumping fuel into the intake.

So, you probably need to upgrade the injector and possibly the fuel pump (if you push FP or run high CR or boost) and if you exceed 310 cc/min then you will need an ECU re-program.
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