Fuse blows & engine dies when I turn

[Weston]

Well, this is weird and highly frustrating... every time I take certain corners at a decent speed, an important fuse blows and it kills the engine. It started Saturday night and it does it pretty often when I pull decent lateral G's; it seems like a little bit of deceleration will help it happen, but I'm not 100% sure.

It's fuse #24 "(ACG (IG))", which is a 15 amp fuse (20 amp for GS-R) that's located in the SRS fuse block of the fuse box under the driver's side dash. It will pop 15 and 20 amp fuses when I take certain corners fast, but even a little 10 amp seems to be sufficient for going straight. The Chiltons and Haynes manuals just say that it powers the main relay and fuel pump, but the Helms manual shows it powering much more under 3 branches:

Branch 1
--------
SRS unit

Branch 2
--------
Charging system light (in the gauge assembly)
Cruise control unit
Cruise main switch indicator light

Branch 3
--------
PGM-FI main relay (power for this relay also supplies the fuel pump)
Transmission control module (I assume this doesn't apply to me, since I don't have an automatic)
Voltage regulator
Vehicle speed sensor
ELD unit (electronic load detector)
Cruise control unit


Any ideas? I'll be going to Second Creek all day Saturday and Sunday, so this is a pretty huge problem... The only things related to this circuit that I've added are a Walbro 255 lr/hr fuel pump, and a VAFC (but I think that's not on this exact circuit, just controlled by the main relay). It's been like this for 7 months with no problem. I already checked the AFC connections and undid my kill switch on the fuel pump, but no luck. I also disconnected my gauges which were powered from the cruise control wires, but it didn't make a difference.

[stu]

My guess is it's something like a certain amount of lateral G's or chasis flex or something causes it to ground out somewhere.

[Weston]

Yeah, it has got to be a short, seeing as how it can operate in under 10 amps, but blows a 20 amp fuse when I turn fast. The real problem is that I have no idea where the short is...

[hotrod]

Check the wiring on the pump and the VAFC. You probably have a wire pinch or a sharp edge that has worn through the wire insulation over time. It worked fine when you made the mod, but now it has a bare spot that shorts on those high G turns. Look first for loose connectors or connectors that have "whiskers" or wire sticking out, and then check at any place the wire passes through a panel (ie fire wall, under the dash) or goes past a raised lip in the body work.

If that doesn't find it run a temporary wire to replace existing wires and see if the problem goes away. If it does you found the bad wire.

Larry

[12seccivy]

Man, that's a lot to chew on..
Maybe try taking the main relay down out from under the dash and keep it from vibrating while trying to make the fuse blow?
other than that the only thing that comes to mind is the wiring harness under the intake might be rubbing on the support for the manifold-->this is a problem for some of the civics of the same year<--

[Weston]

I'm pretty sure I fixed the problem... The top of the secondary O2 sensor was rubbing on the underside of the car. It scratched some paint off and there was a very small hole worn in one of the black wires. Being that the wire color was black, I figured it was a ground, but sparks flew when I touched it to ground.

The reason it was rubbing was a combination of the larger than stock size of my aftermarket cat, the location of it's O2 bung, and the fact that last week, I used 3" hose clamps around the exhaust hangers to tighten them up to minimize exhaust system stress in turns. I removed the exhaust hanger mod and it gave the O2 sensor slightly more room; it's still a lot closer than stock, but it shouldn't rub now. I put some electrical tape on it and some touchup paint where the paint had been scratched off. I took the same turns that killed it every time before and it had no problem, so that must have been the cause.

I couldn't get it to pop the fuse when I was under the car making sparks, but I didn't have the fuel pump and everything else on that circuit running at the time either; just had the key in the on position, but engine wasn't running. And of course, none of my wiring diagrams show this O2 sensor being powered by the fuse that blew, but the Helms manual I was using is for a '94 (I have a '97, and there were some changes for OBD-II in '96), and the Chiltons and Haynes diagrams are simplified and incomplete.

[12seccivy]

WHEW!
Good find!

[HONDA GHANDI]

The black wire for the O2S is the heater wire. It will have power on one side and ground on the other. If you still didnt get it fixed you can try finding the branch split on the wiring harness and putting 7.5A fuses in each branch. Once the short shows up again it will blow only the branch its connected with eliminating 2/3 of your diagnosis area. I have used this method on some tricky problems and it works quite nicely.

[fozzy]

Could anyone tell me what the thread size of the secondary o2 sensor is or where I could find out? Ive been trying to find out for a while so I can get it drilled in my cat replacement pipe by the manufacturer. Ive got a POrelude but Im hoping itll be the same