DIY Honda ECU Repairs- P30 P08 P27

Jul 28, 2012
Kuala Lumpur
I came across this forum while searching for answers regarding my ECU problem. Sorry for the long post as I don't want to leave out important details. The ECU is a chipped P28 running Crome. The car is an SiR with a boosted B16 engine.

Note:there was a very small black(burned) mark below the c19 capacitor, the one beside NF1 and the "D" terminals when I first bought the ecu. Before using the ecu, I replaced all the caps and check the slightly blackened part for continuity and it was good. I was able to use the car for more than 2 years before this problem occurred.

The car stalls while driving and I thought it was the ICM because our CRV experienced similar stalling issues before but the CEL would lit up and gave a code 15 while there's no CEL in the Civic. We replaced the ICM anyway.

After replacing the ICM, there were no stalling anymore for about 2 months though the car is seldom use. But one day, the car stalled again while cruising on the highway. I tried putting it in 2nd gear and popping the clutch with the gas pedal pressed but the car doesn't want to start. I had to wait for about 20 minutes before the car started up again and I was able to continue driving. About 2 kms to my house, it stalled again. I saw the tach needle move a bit while cranking so I thought it wasn't the ICM. I removed the rear seat to check if the pump is priming. The fuel pump wasn't priming. I tried starting it every 5 minutes and sometimes the pump will prime but the engine would stall after 2 seconds. I had to let it sit for 20 minutes again.

I thought my Walbro fuel pump was going bad so I swapped the stock fuel pump in but to no avail because it still primes intermittently. The CEL lits up but giving a solid CEL when the service connector is jumped. I checked the inside of the ECU but everything is good. I tried checking the main relay according to the Helms manual and it checked out good but I re-soldered the solder joints anyway. After doing the solder joints on the relay, the pump no longer primes intermittently. BUT I noticed that when I moved the ECU, the idling speed would get affected and the engine is closed to stalling.

The next day, I started the car to check which ecu wire is affecting the idling but suddenly the idling was at a low 500 rpm and surging. I used a wooden bbq stick to poke around the wires and as soon as I touch D21 (SG1) the engine was close to stalling while D22 (SG2) only has a slight effect and other wires are ok. I thought to myself that this will be an easy fix but I was wrong. I depin and repin SG1 and SG2 and even bought another "D" ecu socket but after fixing the wires, the engine is idling like crazy. Sometimes it will idle at 2000 rpm and slowly creep up but most of the time the idle will surge like an invisible person is pumping the gas pedal. I re-soldered the main relay again but still the same thing. I was so frustrated at this point.

The following day, I decided to swap in the original stock OBD2 ecu. The idling was low at 500 rpm and there's smoke coming out of the tail pipe but idle speed is not surging anymore. I guess the stock ecu was having a hard time idling the 450cc injectors. At this point, it also gave a code 3 which is map sensor. So i thought the MAP sensor wiring must be having issues so I wired it directly to the OBD2 ecu and there's no more CEL. I also wired the MAP sensor directly to the OBD1 P28 but the idle speed still surges. I swapped in the MAP sensor and main relay from the CRV but still no luck and the idling speed continues to surge.

I decided to check the MAP sensor wiring but there was no short so I use the stock harness again with the OBD2 but this time no more CEL. I switched to the OBD1 ecu and idling speed continues to surge. At this point, I decided to check the capacitors carefully and though there were no leaks on the board, I noticed that the markings on 47uF 16v caps are easily rubbed off. Perhaps from heat? But I'm not sure. I also read the C14 (220uF 35v) is the main cap so I decided to replace 3 caps (33uF, 47uF and 220uF). After that, the idling speed was normal again and I let the engine idle until the radiator fan turns on twice.

After several hours, I tried starting the car again to confirm that it is indeed fixed. Unfortunately, the idle speed would jump to 2000rpm instead of the usual 1500rpm and then the engine stalls and the CEL will lit up. I jumped the service connector and solid CEL again. I tried starting it a couple more times but it will just stall after idling for 2 minutes. So I decided to replaced all the capacitors and it will be good again until it has rested for a few hours and the madness will start happening again then it will just continue stalling. Idling would blip then stall over and over again.

I decided to check the ecu again and used a jeweler's magnifying glass to check every component and solder joint on the ecu but everything checks out good except the NF1 or the 3 legged EMI filter capacitor which seems dirty and corroded in the soldered area so I bought new NF1. Since the ecu had a blackened spot from the previous owner I rechecked the continuity of the tracks again and it's all good. But since I'm at a lost already and facing a blank wall, I decided to hook up the NF1 and the 33uF capacitor OUTBOARD and the engine started up normally again and was able to idle until the radiator fan turns on twice. I was really hoping it would be fix since I'm feeling desperate already. So after 3 hours, I started the car again and it idle smoothly and as soon as it passed the 2-3 minute mark without stalling I thought it must be ok already. I let it idle for 10 minutes before shutting it down. I decided to let it sit overnight and see what happens in the morning before I put back NF1 and the 33uF cap in their right places.

The next morning was hell! The car started up with the correct idle speed of 1500rpm but stalled after idling for 2 minutes and CEL lit up. As usual, it's a solid CEL. I was heartbroken and pissed as hell at this point. I check the outboard parts and I noticed one leg of 33uF had come off. I soldered it back but the problem persisted and it continue stalling. I decided to solder the OUTBOARD parts (NF1 and 33uF cap) back in but to no avail. I even used a new NF1 AND 33 uF again but nothing. At this point, I honestly don't know what to do anymore. I just grabbed the magnifying glass but don't know what to look for anymore. I decided to solder the top lead of 3 capacitors which I think doesn't have enough solder since original ecu have solder on the component side and solder side and as soon as I did that, it has gotten worse. The engine will start and die after only a few seconds unlike before where it will stall after 2 minutes. Not only that but after it stalled, the fuel pump and main relay will continue priming and clicking respectively until I turn the key off.

I did a quick search and it said that QM3 is responsible for the fuel pump but the pump is priming and working. I was about to remove the QM3 from my previous burned out P08 ecu but hesitated because I'm not sure it will work PLUS the QM3 on the P28 is clean with no burn marks. So I decided to post the problem here and hope that someone knows what's going on. Buying another OBD1 ecu is not on my mind yet because the car is still starting up unlike other problems that I read online where the car is not starting at all and the pump is not priming. I still believe that it can still be fixed so any help or info will be very much appreciated.
Try to use a known good working OBD1 programmable ECU and see if the problem will go away. If it's running fine on a good working ECU, try to re-do the repair on the problematic ECU by removing all the capacitors, cleanup all the traces around them (no black spots, no lead drops, etc), then solder brand new capacitors accordingly in their correct spots.


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Jun 28, 2005
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