Need help with fuel pump or ECU problem

**dancoco808** · 21-03-2010 01:47 AM

hi guys,

have a eg civic with b18c and hondata s300. car is unable to start. previously no problems. today when doing some interior work on the car and removing loosely run and unused audio cables;

i noticed the positive wire from the ecu relay to fuel pump had been poorly installed (under the seats and along side raid) and the insulation had been worn right through. the wire had made contact with the body/ground. im suspecting this caused a short and possibly caused damage to the fuel pump or ecu or relay?

i have checked all ECU fuses in the engine bay and kick panel (although box says 7.5A, but has 15A fuses in it), and none of the fuses were busted.

all accessory power works, engine cranks fine, but does not start/fire. im unsure if i am meant to hear the fuel pump prime when turning the key to acc/on, but i cannot hear it.

anyone have any experience on the matter?

cheers,
- dan.

**chowdaa** · 21-03-2010 12:33 PM

Dont want to jump to conclusions, but have seen few eg ecu capacitors leak, short the board and blow the fuse, i found a 10a where my 7.5 was meant to be after smoke had poured out of my ecu. From what you are telling us, sounds like previous owner had issues with old motor or current motor blowing fuses, whether it be from short or faulty ecu and just kept upgrading the fuse. Possible ECU damage.

How is your main relay, just trying plugging in and out with ignition on and see if you can hear the pump.

Does is smell burnt? can the top be opened for visual inspection?

**dancoco808** · 21-03-2010 02:17 PM

hey mate, thanks for the reply. tried taking out relays in and out, no difference. i have a slight burnt smell thats very very faint, vague and non-specfic from the engine bay fuse box.

here's a shot of the ecu

the big red wire from the relay goes to the fuel pump under the back seat.

the red wire from the relay to fuel pump that was ran dodgy, worn through and made contact with ground.

**GenesisEG** · 21-03-2010 03:19 PM

If that's the wire the powers the fuel pump, then it won't blow the ECU (or at least it shouldn't). The ECU should only be controlling the coil, and is electrically separated from the contacts themselves. It's more likely that if the power cable shorted out, you'd have a problem with either the fuel pump fuse, the relay, or the fuel pump itself. The ECU should only have a problem if the coil or the ECU cables short out, which it doesn't appear to have done.

I assume you understand how a relay works, you seem to know what you're doing.

First, try measuring between the coil contacts and ground, you should get some voltage there if the ECU is firing up the relay.

Then, if you are getting voltage, check the continuity between the contacts on the relay when it fires up. When the coil is energised, the contacts should close and you'll get power through to the pump. If the power is hitting the coil but the contacts are not closing, the relay is kaput.

If you're still not getting anything, but the relay is working fine, check to see if the line side of the relay is getting power, it should be getting power all the time.

If you are getting power, and the relay is working, then the pump is probably gone.

If you're not getting power, the fuse may be gone.

Please keep in mind, I'm saying all this from a purely theoretical standpoint, as I don't really know for sure how cars are wired up (I'm an electrician and security technician). It just makes sense to me that when the ECU wants the pump to work, it fires the coil, which closes the contact, which turns on the pump. If it's not working, then check it in that order. Make sure it's firing the relay, then check the relay contacts, then the power source, then the pump.

Get rid of that fuse too, put the right capacity fuse in there.

Oh, I just realised...

It looks like that bracket on the bottom might be the ground for something, probably the coil. I only see 3 wires on that photo going into the relay, and that doesn't make sense. There should be 4 wires, otherwise you don't have a circuit. If it is the coil ground, then it won't work unless it's grounded. I might be mistaken, but just something else to think about.

**dancoco808** · 21-03-2010 04:27 PM

thanks for the reply mate, ive already tried replacing the relay with a new one, and no change.

will test each of the coils/contacts for a more detailed idea of whats going on as you suggested.

turns out the bracket on the bottom of the relay isnt used for ground as it doesn't reach into the relay itself... i thought this also, but was able to unclip the bracket quite easily and noticed it didnt have a connection to the relay. there are actually 4 wires connecting to the relay, the 4th is behind in the picture. the central pin 5 is unused. but the thing is, prior to this event, the car has started fine.

is there a way to test the fuel pump? i.e. supply it with another 12v source and see if it primes? is this safe to do?

**GenesisEG** · 21-03-2010 04:51 PM

If it's a 12VDC pump, which I guess it would be in a car, then yeah, should be fine. Just take a lead straight from the battery to the pump.

Before you try that though, have you tested the relay to see if it's being fired up?

Measure your DC voltage on the line side of the relay to make sure that your fuel pump positive cable is powered, and then measure from the load side of the relay. The load side SHOULD get 12V when you turn on the car.

If you're getting 12V constant on the line side, and 12V on the load side only when you turn the car on, then you know the ECU and relay are fine, and you can put it down to the pump.

At least that way, you can eliminate an ECU problem before you risk frying your pump! =P

**dancoco808** · 21-03-2010 06:09 PM

went down and poked the relay with a multimeter... still nothing

but heres some results that may help diagnose.

(btw following is all with car on 2 clicks 'on', not ignition)

old relay has power

old relay, but no power to fuel pump line

new relay has power

new relay but also has no power to fuel pump line

so regardless of relay, there appears to be no power to the fuel pump line

other pics:

kick panel fuse box, noticed alot of wrong fuses, slowly replacing them

engine bay fuse box, replaced ECU and backup fuses to correct, does it matter that the battery fuse is 100 instead of 80 as it says on the sticker?

.

**90LAN** · 21-03-2010 06:16 PM

looks like you dont have a main fuel relay

look for a silver/grey box with brown end on it

see if you have one

**GenesisEG** · 21-03-2010 06:23 PM

The fuses should be rated no higher than the specified rating.

If it's too high, then it's not protecting the cables and equipment as it should. It'll allow too much current to pass through in the event of a fault. The point of the fuses is to provide a controlled weak-link in the circuit so that in the event of a fault, the fuse will melt first, protecting the components on that circuit. If it says 80A, put an 80A fuse in. It's not worth risking it for the sake of something so cheap and simple.

If the new relay is not allowing the 12V through to the load side of the contacts, then the coil is not firing, which is probably controlled by the ECU. Unless you're really unlucky and the new relay is a dud too.

Can you identify which wire provides power from the ECU to the relay? If you can, try measuring the voltage on that wire. The ECU should fire a small amount of current down the wire to energise the coil in the relay and close the contacts. It looks like the ECU is not firing up the relay, so double check the ECU positive wire just to make sure. If you get no voltage on the coil circuit when you turn on the ignition, then the ECU might have been damaged.

Sucks, but at least you've isolated it down that much.

**dancoco808** · 21-03-2010 06:27 PM

Originally Posted by 90LAN

looks like you dont have a main fuel relay
look for a silver/grey box with brown end on it
see if you have one

yeh i cant seem to locate one either, is that because of being an non-efi stock eg4 breeze, that now has an engine swap by any chance? will look again. are you referring to this lan? (pic taken from http://www.tegger.com/hondafaq/mainrelay.html)

you reckon at this point in time its safe/a good idea to run a 12v to the fuel pump to see if it works? or given the fact that it receives no power is pointless?

Originally Posted by GenesisEG

Can you identify which wire provides power from the ECU to the relay? If you can, try measuring the voltage on that wire. The ECU should fire a small amount of current down the wire to energise the coil in the relay and close the contacts. It looks like the ECU is not firing up the relay, so double check the ECU positive wire just to make sure. If you get no voltage on the coil circuit when you turn on the ignition, then the ECU might have been damaged.

Im not too sure of the wiring colours etc, as im a toyota guy and ive just owned this honda for about 2.5 weeks, also its got an aftermarket computer to confuse me even further. i will try tho...

**GenesisEG** · 21-03-2010 06:48 PM

If it's not receiving power, then it really doesn't matter if it works or not.

Try it, I mean the chances of breaking it are slim. Just run a lead from the battery positive to the lead where it plugs into the relay. If it fires up, then it's probably an ECU problem.

**dancoco808** · 21-03-2010 06:51 PM

Originally Posted by GenesisEG

If it's not receiving power, then it really doesn't matter if it works or not.

Try it, I mean the chances of breaking it are slim. Just run a lead from the battery positive to the lead where it plugs into the relay. If it fires up, then it's probably an ECU problem.

so by that theory am i able to run a 12v positive lead from ignition switch wire to the fuel pump as a band-aid fix to move the car around?

its currently stuck underground 2 levels in my apartment carpark.

are there any other relays/fuses that i've not located?