Troubleshooting a Honda P28 Chip Installation

Did you install a performance chip in a Honda P28 ECM and it is not working? Having problems?

This situation is more common than you think, as many people choose to install a chip them selves, even if they have no experience with electronic parts soldering. These ECMs are small and somewhat simple, but still, are computers with fragile sophisticated and sensitive circuits. Once in a while, even professionals face some problems doing these installations, so here are some basic methods to troubleshoot your installation.

NOTE: This article covers not only the Honda P28, but also the Honda P05, P06, USDM P30, P72, P74, P75 and OBD-I PR4 computers family

The installation consists of adding some parts to the circuit of the ECM, where the space where those parts belong is empty in the circuit board as an unused option built in when the ECM was manufactured. There are even footprints in the circuit board, indicating where parts belong.

The parts added are; two capacitors (for filtering electronic noise), a resistor, the new EPROM chip (a socket will be installed), a small 20-pin chip (74HC373 latch) and a jumper (J1). The jumper “J1”, enables the new chip when installed and disables it when cut, just like a switch. When J1 is installed, it will make the ECM microcontroller (MCU) ignore its internal program (engine calibrations) and will look at the external EPROM chip installed. So if the installation is good and all parts are good and installed correctly, you may switch between “Power” (external chip) and “Stock” or “Normal” (MCU internal program). The only thing is that it will work just like that, but the engine must be turned off and then on for the changes to take place every time you switch programs.

That being said, one good test to do if you have problems with your installation is to cut the jumper. The ECM should go to “stock” mode and all should run fine. If it does, it means that the installation is presumably right, but the chip is either damaged or the program on it is not right or not compatible with your car. On the other hand, if problems stay after cutting the jumper, then something went wrong (physically) when installing the kit.

Possible common causes are:

  • A short circuit was created with soldering.
  • A broken trace (copper trace) created by excess soldering heat.
  • The 74HC373 latch chip is either bad or installed backwards
  • The 27C256 EPROM is either bad or installed backwards
  • The program in the 27C256 EPROM is no good or not compatible.
Possible problems you may confront:

1. Short Circuits by Accidentally jumping two or more connections with soldering.

The first thing to check if having problems with an installed chip is the soldering. You should check for accidental bridges, jumping contiguous pins or connections of the installed parts. Do this first by visually inspecting the installation, using a good magnifier. If nothing wrong is found, then you should use an ohmmeter to check for continuity between every pair of contiguous pins you suspect may have been jumped. This is important as the circuit board is a multi-layered board, meaning that it has connections above, below and in between its layers, making some connections not visible. When too much solder is used, it tends to absorb it through the integrated tubular connections that join all the layers and possibly accumulating an excess, jumping two or more points. So, if any two contiguous pins of any of the installed parts shows a resistance reading of less than 1 or 2 ohms, then somehow those two connections got accidentally jumped.

2. Broken Connections.

The next thing to check is possible broken connections. This often happen on these jobs due to overheating when soldering. This computer circuit boards are VERY sensitive to excess heat and this accounts for the majority of the problems that show after an installation.

If a connection was broken during installation, it must be between the chip, the latch (small 74HC373 chip) and the MCU (64-Pin microcontroller unit), because that is the area involved on the job.

Below is a chart that will help you corroborate all involved connections. All the connection should measure continuity (less than 1 ohm) with an ohmmeter or continuity checker. Any reading over 1 ohm is indicative of a faulty connection. If any of the connections displayed in the table fails the continuity test, it means a broken connection and must be corrected before going further with the test. Do so by checking the circuit to see if the connecting trace is visibly broken so it can be fixed by soldering. Otherwise, just run a thin insulated wire, soldering between both points that failed. The wire should be kept as short and close to the board as possible. This Will prevent the wire from picking or generating electronic noise.

Before the chart, there are two pictures. One identifying the involved components and the other, showing a guide for identifying the pin numbering on every respective chip.

Identifying involved components:

Pin Identification of involved chips:

Connection test chart:

EPROM Check Points
EPROM Pin# Connects to:
1 #20 of Latch
2 #13 of MCU
3 #15 of Latch
4 #12 of Latch
5 #16 of Latch
6 #19 of Latch
7 #9 of Latch
8 #6 of Latch
9 #5 of Latch
10 #2 of Latch
11 #3 of Latch
12 #4 of Latch
13 #7 of Latch
14 #1 & 10 of Latch
15 #8 of Latch
16 #18 of Latch
17 #17 of Latch
18 #13 of Latch
19 #14 of Latch
20 R54 (at left side)
21 #11 of MCU
22 #23 of MCU
23 #12 of MCU
24 #10 of MCU
25 #9 of MCU
26 #14 of MCU
27 #15 of MCU
28 #20 of Latch

The only connection that is left out that table is the following, so please also test that one:

Pin#11 of the HC373, connects to Pin#22 of the MCU

When “J1” Test Fails and all connections are good:

If cutting “J1” test fails and all connections on the table test OK, we have seen that sometimes the latch chip (74HC373) goes bad by overheating when soldering it or by static electricity. Also, as mentioned before, backwards insertion of any of the chips can damage either one or both, but being this one the more susceptible to such problem.

The less possible but has happened before, is the MCU getting damaged for the same reasons.

The procedure then, is to replace the 74HC373 first as it is quite inexpensive (about $2.00) and do a test. If problems persist, then it is best to replace the ecu, as a spare MCU is hardly found, adding to this that it is a discontinued product. Also, replacing it will take a greater effort than the the whole installation job and might really ruin the ecu, loosing the money spent in that part anyway.


Q – Will a chip with an incompatible program damage my ecu?

A – No. The ecu will activate the check engine light steadily and go to protection (limp home) mode to avoid engine damage. To achieve the purpose of protection, it won’t allow the engine to rev more than 4000 RPMs and fuel mixture will go very rich to avoid destructive lean conditions.

Q – I have had many problems buying chips like these on eBay and other places. Do you know where to buy a real good chip?

A – Yes. We know about problems with eBay. Most chip sellers don’t know about mechanics or racing, neither programming. The ones that sell a chip that doesn’t fail, are just selling the same copies of the same chip, nothing new, and those chips are only fairly good. We only recommend our chips. They are tested and will make your car pull real hard:

Racing Chips

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9 Responses

  1. Tom Humes says:

    Nice Site layout for your blog. I am looking forward to reading more from you.

    Tom Humes

  2. admin says:

    Thank you Tom. I’m glad you liked it.

    Thanks for reading.

  3. Racer_Phaser says:

    I did all that is said here and still having problems, so i conlcude it is the chip i bought from ebay, as cutting j1 makes the car works good.

  4. admin says:

    Hello. If cutting “J1” solves the problem, definitely the problem is the chip. It may be that the chip program is not compatible with your ecu, it may be that the chip architecture is not compatible with your ecu electronics, it may be that the chip electronics are damaged (static electricity or other factors) or it may simply be that the chip is garbage.

    Please, before buying chips on eBay, make sure that the seller knows what he or she is selling. Make technical questions. Simple answers like “yes” or “no” to your questions is simply not acceptable. Many chip sellers on eBay don’t know a thing about electronics, programming, mechanics or even driving safety.

    Be smart and be a step ahead.



  5. admin says:

    I forgot to mention some history about chips.

    Some time ago many forums on the INTERNET that shared technical information about modifying chips for different car models, used to post the modified file along with the original file and all information about it, including algorithms to accurately make the calculations for customizing chips. Then the eBay boom began when forum users, specially “newbies” started to download the modified files (prototypes from forum users)and using them as good and completed, to make and sell chips on eBay. As it should be expected, many chips that were sold this way, failed and some caused damage to engines. When people started to complaint on eBay, the word spread out and Forum administrators started to restrict users because of this behavior and some of the admins even prohibited sharing modified files at all in their forums. Those chips are still on eBay and are now sold for cheap in an attempt to sold the greatest quantity possible without caring about customers.

    To prevent from being banned or avoided by buyers, they started putting bogus information on auctions like “We have been chipping ecus since xx year, and we know what we are doing”. But facts go further than words and people realized otherwise, but only after having spent their money in such a garbage.

    The real problem on eBay are buyers. People leave feedback before even trying the product. Only a few were brave enough to test first and then give feedback. That is why there are many feedbacks that state “nice looking”, or “fast shipping” and many more that doesn’t speak for the product, but for the service.

    A few also tested the chip and felt something, but didn’t realized that it was the “placebo” effect, fooling them into thinking that it is a good product, even when the car ran the same as before. Yes, many stock chips were and still are being sold on eBay as performance chips. This placebo effect was also caused by the infamous IAT resistor in most cases. This happens often to people that have not tried any chip before and didn’t know how a real good chip should feel.

    About the IAT resistor, many buyers had no other choice, as these resistors and fake modules, are offered to every car, even new ones, while real chips are only available to few models and are limited in Manufacture Year, since most car computers from 1996 and up (OBD-II) don’t use those chips in their circuits. A sure sell was obvious.

    Other chip buyers, were not fortunate enough and their cars didn’t even start. Some started, but blew their engines when test driving because of a hard knocking in the pistons caused by a too advanced ignition timing and a too lean AFR mixture induced by the chip. Of course, the seller didn’t know about this, so If you would ask him, they would have said otherwise.

    About Honda, many sellers say they sell “Mugen”, or “Spoon”, “JUN”, etc., but if you call every one of the mentioned Companies, they either say that they didn’t make those chips or that they don’t make chips for those cars or applications. Some of those Companies complained to eBay and eBay forced sellers to change the name of their products as they were violating the VeRo rules by copying a trade mark. That was the birth of M-Gen, instead of Mugen for example. After some years, I guess that those Companies got tired of trying to eradicate those trade mark infringements because once in a while, you will see their trade names again on eBay for chips.

    I think part of this began for Honda chips when someone published a list of chip files that were sold by a Malaysian guy named Richard Wong. They advertise chips that will tune your car like “Mugen” or “Spoon” do, but those were not from such Companies, but an adaptation of some “supposed” read codes from them. Whatever happened, those Wong’s chip files were intercepted by today’s eBay sellers (with exception of a few of them, like Auto-Motivo) and are the same chips that have been sold as of today, though each one claim different and add supposed attributes. The only attributes that they can really add are VTEC change over and revlimiter in many cases, thanks to free softwares that have been freely distributed by a few talented people that were kind enough to let everyone have it. Still, today exist many parameters of chips’ program codes that are still not understood in full or at all, either because lack of knowledge or special tools, or simply because of lack of interest, so even those free softwares are not the complete solution.

    Any question, please post in the “comment” area below.


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