Blowing ECU fuses

[Bauceman]

Alright guys, despite hours of searching I have yet to find any thread that covers my situation so I had to start this one. I'm not sure this is a beginner level problem but I have to post it here so here goes. I apologize ahead of time for the length.

The car is a 1990 EX coupe with an Accord Euro Swap controlled by a P28 with an S300 chip. The car initially had a P72 running the same chip/tune. The car was professionally tuned (not dyno'd unfortunately) and ran flawlessly as far as the engine was concerned.

One day in January of 2016 I went to start the car and nothing, no clicks, no priming sound. It had battery power as all of the lights and radio would work perfectly. I consulted my Helms manual and after checking all fuses checked the main relay. I thought I heard it clicking when powered up so I assumed the pump had gone bad which wouldn't be out of the question since the car had 240K miles on it.

Fast forward a bit and I finally received the correct Walbro pump kit,I decided to go with this because I have plans in the future which will require more fuel anyways so I figured to kill two birds with one stone. I also replaced the fuel tank as it was gunked up and this was suggested by some knowledgeable friends. So fuel pump wired up and installed in the tank and the tank installed and filled with fuel I attempted to start the car. Still not priming so obviously still not starting. I had at this point a fresh battery because the old one had gone dead.

I checked all fuses and re-checked the main relay and decided maybe it was the culprit. I pulled it, smelled it to see if it smelled burnt and couldn't really smell anything like that so I opened it up and didn't see any damage. As an added measure I purchased a new OEM main relay ( the one installed was some Chinese junk). New relay installed, same issue, no priming of the pump.
I pulled the pump and after letting it dry completely I checked it with 12 volts direct using a short temporary harness and it was good to go. I also checked the factory pump and it also was operating.

So at that point I know the fuel pumps are good so it's a matter of power not getting to them, which means either a break in the harness that goes to the trunk (possible but not likely since I had done nothing that would have caused that and the car had run literally the day before it went dead). It could be a fuse or relay but all of the fuses in both boxes checked out and a bad Honda relay from my experience isn't very common. So I checked the ECU and sure enough there is a small burnt spot on the ECU. So I ordered a new ECU (hondata socketed P28) install it and give it another try. I am sure I heard priming initially but the car would not crank over. The next day it did not appear to prime (maybe I just didn't hear it) but there was a clicking sound from under the dash (I'm thinking relay). The battery was getting low with all the cranking attempts so I had it charged.

On a side note I also tried wiring the pump opposite to how it was wired initially thinking maybe I had wired it wrong and it wasn't able to prime or was priming in the wrong direction. This didn't make any difference and I have re-wired it back to the initial way it was wired which is how all the picture show the wiring done.

Currently with a freshly charged battery the car will not prime however I have found that the under dash ECU fuse is blowing. I have checked the ecu and it is all fine and well.

So I am now asking for help as the symptoms are not helping me track down the problem. I think it possible that something is grounding out but as far as other causes I can't think of any. Any help would be appreciated.

[Raf99]

(I have the same ECU and S300)

So from the battery the power is flowing to the fuse box and then to the ECU - fuse #28 (I think it's 28/ECU fuse). If that fuse is blowing then you have a short in the power wire between the battery and the ECU. If your battery is in the engine bay then that wire is pretty short, check it out.

Does the fuse box get 12V from the battery? (check with a volt meter on the main power wire, if yes then also check to the new fuse)
Can you check the continuity of the same wire? (may not be possible)

If you need help with these things, let us know and we'll do our best to help!

[Bunta]

I am Bauceman. Just to avoid confusion (this is my permanent account.)

I'm assuming you are talking about the dash fuse box, if so I'll check all the wiring. I do not have a way of checking voltage or continuity right now but I'll get a muiltimeter and check these.




*edit* I checked the wiring and nothing looked or smelled burnt. There was an unplugged sensor on top of the tranny that I plugged back in. I put a new fuse in and the car primed (an fired up) There is a constant hum/whining noise from the engine bay that I can't quite place, it sounds almost like it's coming from the firewall. I'm also throwing a CEL but I do not have a laptop to check it. Is it possible to check it the oldschool way of jumping the wires and counting the CEL light blinks and pauses?

[Raf99]

Hmm not sure on the jumping the wires. I think you can still do that as that was a part of the ECU circuit.

I wouldn't trust this is fixed though because you didn't really fix anything or find the cause. I think I need to correct myself here too. There is a large 80amp fuse for the power wire leading from the battery to the fuse box. Then fuse #28 goes to the ECU. If you are burning up fuse 28 then your problem is the wire between the fuse box and main relay. It is shorting out somewhere or the main relay is shorting out.

Battery > #15 fuse > fuse box > #28 fuse > main relay > ...(sends power to other things like fuel pump)

edit: you could also test voltage at fuse #28 and also at the main relay (yellow / blue wire) too.

[Bunta]

Hmm not sure on the jumping the wires. I think you can still do that as that was a part of the ECU circuit.

I wouldn't trust this is fixed though because you didn't really fix anything or find the cause. I think I need to correct myself here too. There is a large 80amp fuse for the power wire leading from the battery to the fuse box. Then fuse #28 goes to the ECU. If you are burning up fuse 28 then your problem is the wire between the fuse box and main relay. It is shorting out somewhere or the main relay is shorting out.

Battery > #15 fuse > fuse box > #28 fuse > main relay > ...(sends power to other things like fuel pump)

edit: you could also test voltage at fuse #28 and also at the main relay (yellow / blue wire) too.

I am not concerned so much about doing the factory CEL test to find out the codes as I've installed Smanager on our laptop and am gonna use that to check. Honestly I feel the same way about this being "fixed". Now when you say "fuse #28" are you talking about the one in the engine bay fuse box, because that isn't the one that was burning out.

*edit* I initially was having problems with the fuel pump not priming but now it is and the car starts and runs and obviously the ecu fuse hasn't burnt out again. I'm gonna check all the under dash wiring just in case

[Bunta]

*update, sort of*

The car starts and has a surging idle, I've cleaned the IACV and ran a can of seafoam through the engine to make sure it was degunked with little effect. I have no vacuum leaks that I can find. I still have a solid CEL but jumping the wires in the blue plug does not cause the cel to blink, despite several tries with several methods. I'm unable to diagnose the CEL through Hondata as it is having issues somehow (and I'm working that issue out with Hondata).

I double checked that my sparkplugs were a resistor type as Hondata posted that such should be used in Hondas. I have a feeling it is one or two things that will prove simple to solve (even if it means simply buying a new part).
Anywho, even with an idle surge it sounds beastly, the exhaust growls and the engine sounds like a commercial jet "idling".

[Raf99]

If it's a bad surge it is most likely a air leak. Check around the intake manifold. The CEL light should show up in SManager under the error codes section.

[Bunta]

If it's a bad surge it is most likely a air leak. Check around the intake manifold. The CEL light should show up in SManager under the error codes section.

Well it is a surge but there are no air leaks that I can find, obviously that was my first thought too so I'll keep checking. S-manager isn't connecting ride with the S300, I think due to an issue with the S300.

[Raf99]

Ya, sounds like you got some issues. I'd fix the connection with SManager first as it can tell you lots of info. Why won't it connect?

[Bunta]

I do not know, all I know is I'm getting no readings from the sensors and there is a flashing red led from the S300 port where I plug in the usb cable. I feel like the surging is a mechanical issue separate from the issues with the S300 because of how long the car sat without being run.

[Raf99]

So you don't see any data in SManager (volts, IAT, rpms, etc.)? When you turn the key does Smanager even pick up S300? (the lightening bolt becomes available)

I would first try reseating the S300 board in the ECU. Mechanical issues would not stop S300 from connecting to a laptop.

[Bunta]

So you don't see any data in SManager (volts, IAT, rpms, etc.)? When you turn the key does Smanager even pick up S300? (the lightening bolt becomes available)

I would first try reseating the S300 board in the ECU. Mechanical issues would not stop S300 from connecting to a laptop.

No I don't see any sensor values and no the "lightening bolt" isn't clickable but I read that I'm online and drivers installed in the lower corner and get a chime when I plug or unplug it so it has to be reacting in some way.. Yeah I was talking more about the idle surging being mechanical rather than caused by the S300.

[Bunta]

Problem solved. I opened up the ecu to triple check if there were any loose pins or damage I hadn't noticed. I pulled the S300 and checked both side carefully along with the pins it connects to. Nothing wrong there I made sure I could see the pins lining up with the S300 and pushed evenly. There was a lot more pressure required than before to seat the S300 and I don't remember having to push that hard on this new ecu.

My theory is I wasn't fully seating or even completely missing some connections. No CEL and my idle is rock stead. I also had to re-insert the Vtec solenoid pin into the ECU connector.

So two things came out of this for me (and hopefully the community)

1. ALWAYS check your connections to make sure they are seated correctly.

2. ECU issues CAN cause problems that present mechanical issues. I was sure that my surging issues was strictly mechanical in nature.

[Carbonaccord]

good to see you got this all figured out!

[Bunta]

good to see you got this all figured out!

Sort of, the initial issues are gone (blowing ecu fuses, the CEL, idle surging, not being able to connect with the ecu in Smanager) but I have an issue with drivability right now. At least now I'll be able to datalog and hopefully correct the problem.