Loose battery post has fried my car - HOW THE HELL!!

[Silver Bullet]

I new to this site but please help me -

I have an 88 Si Accord, I have EFI, extractors, lowered to the ground and low profiles. Had it for six years and not a problem - goes like thunder and drags most cars.

Till yesterday, when I was doing some work on the body and jump started my car with a portable power pack (which i have done million times before) and while running I took off the Jump starter of the positve lead and the car crapped itself and started running beserk.

Then i noticed the + terminal was very loose, as I was using an old, dead battery as my good one was in a van I just bought. (just to hold the posts and complete the circuit)

I immediately turned it off and tried to restart - dead.

I had blown 3 fuses in the underhood compartment - which I replaced and then put my good battery back in and tried again.

Immediately fuse 1 blows in the underhood relay box as soon as the ignition goes to on. (when the fuel pump primes)

My fuel pump no longer primes as the fuse blows immediately - which to me means a short somewhere. When I disconnect the wiring harness from the MAIN RELAY under the dash, the fuse no longer blows.

I still have spark and the engine cranks, but the engine light does not go out. It is not throwing any codes, and i think I may have caused a voltage spike which has fried the ECU (NO NO NO HELP ME)

If this is the case how come the ECU is not protected by fusible links and how come all of this can be caused instantly by disconnecting a power pack from a dead battery with a loose positve terminal.

I don' t understand as I and many other people have had loose posts and not caused this kind of damage.

Anyway - how much is a new ECU (worst case scenario)

Please help me as the car has completely fried itself. I will continue to check the MAin relay and all other components of the fuel system and electrical system, but I would be much apprieciative if someone with more experience could help me out.

[cruznz]

well you already have figured out you have a short between fuse box and main relay,so you need to sort that out first, sounds like wiring has got hot,so you need to find out why

Did you try to start it with main relay disconnected?(you say it still had spark and was cranking)
Did you connect the fuel pump to 12v if you did?

[Silver Bullet]

Thanks for replying so fast!

I only cranked it for about 3 seconds with the spark plug out to see if it cranked and had spark cause I thought I had fried everything including the ignition system.

I'll hook up the pump to 12 volts but do I need to loosen the fuel pressure relief valve or will it be alright for a few seconds.

The 3 fuses that blew were all in the underhood relay compartment and were no. 1, number 5or6 (15 amp) and 10 or 11 (7.5 amp) Im not too sure about the others as I changed them frantically and they haven't blown again.

It's just No.1 everytime ignition hits on ( when it's normally primes the pump). It doesn't blow when the main relay is unplugged, or when the main relay is plugged in and the computer unplugged.

I'll check the operation of the main relay tomorrow morning, and fuel pump and let you know, but is it possible the ECU is shorting the fuse - that scares me (expensive).

What is the exact purpose of fuse 1 - is it for the fuel pump or lots of things including the ECU. I cannot get a clear definition of what those underhood fuses do. (relays?)

I'll check for a short from fuse 1 to the main relay and when checking the harness to main relay I got 12 volts on the black/yellow wire when ignition is on.

So is it safe to power up the fuel pump to a 12 volt source and try start it with the main relay disconnected, or is this gonna cause more problems (just to see if it runs when getting fuel pressure.)

Thanks for any help

[88LXi/87CRXSi]

Not sure if the car will start without the main relay even with the fuel pump wired direct to run! That's because fuse #1 that blows when you turn the ignition to "on"has nothing to do with the fuel pump. What fuse #1 powers is the injector resistors (and injectors) and unfortunatly, like you mentioned, the ecu.
Now let me mention that I'm not sure if this applies to your car since the only information I have pertains to my USDM A20A3, So wait till Pete or someone else confirms that what I'm saying applies to your car!
Here's part of a diagram that shows what I'm talking about:

88 LXi injector wiring

*edit- it could also be the main relay itself, another relay in the main relay also uses power from fuse #1 to energize. That relay's contacts are the ones, when closed supplies 12v from fuse #1 (underdash) to power the fuel pump.

[Silver Bullet]

Now you're scaring me

[cruznz]

I'll agree with steve here,...with luck,the fuse protected the ecu so try changing main relay first

What engine is in your car ?

[Silver Bullet]

I have the A20A4.

I will go right now and check the operation of the main relay as stated in the Workshop manual and repost in 30 mins or so (hopefully)

[Silver Bullet]

Yep the relay is fine, I can hear it clicking when I power it to 12volts and there is continuity between all the terminals as stated in the manual.

I also hooked the fuel pump up to 12 volts for a couple of secs (directly at the pump) and it was whirring - so I think the pumps fine.

I also checked the continuity of the yellow wire which runs to the fuel pump from main relay harness (instead of shorting it to yellow/blue 12V). It's not earthing out and can carry the yellow/blue wire's 12v to power the pump. I wouldn't be able to hear it from the front anyway as my street is too noisy.

So whatever it is that is shorting the fuse is coming from before the main relay.

I will now check the fuel resistor and also study the vacuum and electrical connections page on page 12-7 of the workshop manual.

Hopefully I am getting closer to my problem by eliminating the main relay and harness to the fuel pump.

[Silver Bullet]

Ok - I checked the resistance in the resistor an they all fall between the specified resistance,

I also checked the Harness going to the resistor to see if any where earthing out.

The terminal A (yellow/black) has continuity with earth - which I thought was abnormal but I could be wrong. This is without a battery in the car and no fuse in fuse 1.

Does this mean this is a closed circuit at all times. Or is this a short and should only have continuity when the circuit is closed by something else (maybe ecu) and be open when battery is disconnected and not earth out.

I gonna rip this car apart and check everything eventually, maybe even solving my problem in the end hopefully.

[cruznz]

sounds like you found the problem,.....disconnect the ecu plug and check for short to earth..pins A13 or 15...either one......remove main relay plug too

[cruznz]

oh...if wiring checks out ok....then i'm afraid you've probably fried the ecu as it's sending a constant earth each time main relay is turned on....hope this isn't the case...

[Silver Bullet]

Thanks, I'll check tommorrow.

I hope that is not the case either.

I don't have a harness checker - but I checked the continuity of the yellow/black, black/yellow wires of the white harness that goes into the ECU (which I presume are A13 and A15 according to the diagram in the workshop manual) and there is no continuity to earth. which means that wiring is fine right.

But I understand the ECU troubleshooting guide now, and I'll plug all the parts back in and check for voltage at the A13 and A15 pins tommorrow with the ignition on, and I presume if there is voltage there, and there are no shorts between the green/ red wire and the combination meter, then my ECU is .......

DEAD!!!!!

I can't believe such a simple action as jumpstarting with a only slighty loose terminal - (it didn't come off, just move a bit on the post and spark as I removed the lead) can blow my ECU.

I must be that guy everyone has heard about - you know - blowing up his EFI car by jumpstarting it incorrectly.

I wish I had of realised that the post was slightly loose and tightened it first, but I had already jumpstarted about 4 or 5 times that week (exactly the same way) as it has been off the road for a month getting some simple panel work done.

And I was driving around in it a bit during this time, and not a problem. I must of yanked the gator clip off to hard or something that time, (It was pretty dark)

Oh well, its all a learing experience and Im glad you guys are here to help me and everyone else out.

CHEERS, I'll let you know how it all is tommorrow.

[88LXi/87CRXSi]

Hopefully, it won't be the ecu! I really didn't want to be the one who sorta confirmed your suspicions about it! Your troubleshooting procedure will confirm what's going on. But if you don't get 12v at those two pins, and the fuse still blows, this might help! Just for some additional info, I went out to my car, and at the contacts that fuse #1 plugs into, one has 12v and the other contact, with the other probe connected to ground was infinate resistance (open)with key off. With the key turned on, and main relay energized, the resistance reading I got was 1050 ohms. I would guess that the resistance in your circuit would be close to zero. Then by process of elimination, unplug till you locate the short.(still could be the main relay, too) Good luck!

[Silver Bullet]

Alright. I have 12V at A13 and at A15 with the main relay plugged in and key to on from the A4 terminal and vehicle ground.

Starting to sound bad.

Now with the green/red wire at B6 terminal to the combination meter. That terminal holds 12v when earthed to ground. But - what is exactly the combination meter. I presume it is the Instrument cluster as this has a circuit board behind it.

So failing a short there - which I doubt it, I will go with my original diagnosis of a voltage spiked ECU.

So in order to fix this I shall find an axe and carefully aim for the A13 and A15 Terminals and splice the ECU down the middle, laugh endlessly at my stupidity and go to the wreckers and find a new ECU.

I just called them and I can get one for A$330 with specs for my car.

But one thing scares me. What if I plug in a new ECU and It blows up again from a short. So I'll have to check every wire and Harness won't I. Sounds like fun.

[cruznz]

not sure what you mean about the A4 terminal as it is a ground point anyway,....could you explain more........check to see if ecu pins A13/15 are grounded to earth....you should get no reading when checking these

[Silver Bullet]

Sorry It does sound confusing.

I meant when I put the positive on A13 and the Negative on A4 - I got 12V, and the + on A15 and - again on A4 I get 12V. And I also checked A13 and A15 to chassis just to make sure A4 was earthed properly.

And no, unfortunately I get not continuity from A13 and A15 to ground at any time. So problem isn't there.

Does it sound like ECU to everyone else. And what about the combination meter. Should I bother pulling the dash out to check the green/red wire or is it easy enough to check without pulling the dash out.

All wiring seems normal to me and the troubleshooting guide just leads to "change ECU with a known working ECU.)

Like I said I will have to go over everything with a fine tooth comb just to make sure I don't fry the next ECU instantly.

[88LXi/87CRXSi]

I think that the green/red wire at B6 terminal goes to the PGM-FI warning light. When the key is on, the other wire on the light is connected to 12v, so you would read 12v on your meter at B6.
If you can turn on the key, with every thing but the ecu plugged in and the fuse doesn't blow....well, I think your very close to finding the problem.

[cruznz]

be interested to know what voltages you are getting at main relay plug connection with ecu plugged in

[Silver Bullet]

No Worries - I'll check it out for you.

But I can't right now as It's been raining for 2 days here now and I wont get a chance until it stops.

Hopefully tommorrow.