GuyT Posted January 23, 2006 Share Posted January 23, 2006 Whilst travelling along, sometimes when I sound the horn, it causes the engines to miss momentarily and backfire. Can anyone suggest where I should be looking to find the fault? I doesn't happen everytime so there is clearly something loose but where might that be. Any pointers appreciated. RGDS GuyT Link to comment Share on other sites More sharing options...
andy_h Posted January 23, 2006 Share Posted January 23, 2006 Sounds like the horn is causing a dead electrical short when pressed and this starts to kill the electrics/ignition system. White road legal 2.0 HPC VX race car 😬 Link to comment Share on other sites More sharing options...
Chris W Posted January 23, 2006 Share Posted January 23, 2006 I agree with Andy's diagnosis. Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
GuyT Posted January 24, 2006 Author Share Posted January 24, 2006 Andy and Chris, Thanks for your replies. Being electrically retarded, where should I be looking for this short. The car is a '92 HPC VX, the switch is a toggle on the dash and their are two horns which look standard. Is it more likely to be in the horn units, the switch or the wiring between. As I said, it is intermitent. Many thanks GuyT. Link to comment Share on other sites More sharing options...
Jason Plato Posted January 24, 2006 Share Posted January 24, 2006 you could try shouting instead of beeping the horn 😬 C7 TOP Powered by Hellier Performance 😬 South Wales AO Link to comment Share on other sites More sharing options...
Foxy Smith Posted January 24, 2006 Share Posted January 24, 2006 Guy given the position of the horns and the corrosion they're likely to suffer I'd bet the problem was there. I'd start at the horns and pull off connections till the problem stops. That will confirm the location of the short. Link to comment Share on other sites More sharing options...
conorkaby Posted January 24, 2006 Share Posted January 24, 2006 I suspect the horn is drawing too large a load from the alternator and sapping power from the engine. Suggest you consider a bhp upgrade as a possible solution Link to comment Share on other sites More sharing options...
Martin S. Posted January 24, 2006 Share Posted January 24, 2006 If the horn is causing a short it should blow the fuse. Check your fuse is not too big, would have thought it should be 5A or less. If it is causing such a short that the engine is dying I would expect a fair volt drop to be occuring, to test this put your headlights on with the engine off and see if they go dimmer when you press the horn (they shouldn't, at least not by much), or better still if you have a test meter check the vlotage across the battery doesn't drop when you press the horn by more that say 0.5V If all the above checks out OK I would think you have a short in your wiring loom somewhere. Link to comment Share on other sites More sharing options...
Chris W Posted January 24, 2006 Share Posted January 24, 2006 It could be that a previous owner bypassed the normal horn fuse for some reason. Hence why no fuse is blowing. Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
Stijn LUYCK 1 Posted January 24, 2006 Share Posted January 24, 2006 Sorry but I can not believe a short in the horn would cause this. If it was a dead short then first of all it would not work and secondly either a fuse would blow or the switch and wiring to it would melt. I doubt it a good battery goes on its knees enough for a ECU to suffer before the wiring to the horn melts ... how would you expect 1.5mm2 to handle the curent from something like a starter motor? The horn functioning migh generate enough spikes on the supply for the ECU to get confused, esspecially if the signal from another sender is too low though (flywheel?). Check for ground and cable connections on those I would say ... My own 2P worth ..... Link to comment Share on other sites More sharing options...
Chris W Posted January 24, 2006 Share Posted January 24, 2006 Stijn What you suggest sounds correct in theory, but if the horn push is causing the engine to stutter momentarily, then it does seem most likely that the horn circuit is pulling the supply line down and affecting the ignition. I don't think it's the horn switch per se but the horns themselves, which are connected directly to the battery (should be through a fuse). The horn switch merely operates a relay and is in a low power circuit. Guy: you could try disconnecting the power feed at the horns and see if the engine still stutters when you push the horn switch. You should hear the horn relay clicking as you press and release the horn button. If you still get the effect, disconnect the earth to the horn button and try again. Little by little you can eliminate culprits. As Sherlock Holmes once famously said, "Once you have eliminated the obvious whatever remains, however improbable, is the answer" Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
GuyT Posted January 24, 2006 Author Share Posted January 24, 2006 Blimey, I first noticed this when I was driving up a long straight empty road and was bored, so sounded the horn to alleviate the monotony. The horn worked fine and the hiccough was only momentary with one backfire. Sounding the horn again to try and make it repeat the problem, the horn sounded and no miss or backfire. Tried it again on another blat and it didn't do it on the first sounding but did on the second. On another blat it wouldn't miss at all when sounded. Confused and got to learn to type faster! PS - plenty of horse power! Link to comment Share on other sites More sharing options...
LazerBrain Posted January 24, 2006 Share Posted January 24, 2006 Are you sure it's the horn button and a not button connected to one of these here More seriously - try pulling the horn fuse. You should only hear the horn relay clicking. If the horns still sound then the fuse has been bypassed. cheers, Darren. Edited by - LazerBrain on 24 Jan 2006 14:55:00 Link to comment Share on other sites More sharing options...
GuyT Posted January 24, 2006 Author Share Posted January 24, 2006 Many thanks for all the above - certainly given me some options to try at the weekend. I'll keep you posted. LazerBrain - I've put my order in for an Extreme flame kit!!!! RGDS Guy. Link to comment Share on other sites More sharing options...
acw Posted January 24, 2006 Share Posted January 24, 2006 I would also suggest the age old electriacl gremlin on the 7 - the earth! I had a weird fault on my HPC when the heater fan was turned off the engine would die, it turned out to be the earth on heater. Andrew Link to comment Share on other sites More sharing options...
Normans_Ghost Posted January 24, 2006 Share Posted January 24, 2006 What's a horn? Didn't know I had one of those. If they can't hear a 7 coming then a horn won't do much good. 😬 Norman Verona, 1989 BDR 220bhp, Reg: B16BDR, Mem No 2166, the full story here You and your seven to The French Blatting Company Limited Link to comment Share on other sites More sharing options...
andy_h Posted January 24, 2006 Share Posted January 24, 2006 Reminds me of a time when I was driving my old Land Rover. It started to get dark so I put the lights on and the engine started to die. Lights off engine fine. Lights on engine started to die..mmmmm Dash off - found light switch too close to the metal dash and when the light switch was on (toggle switch) it shorted the load side to earth. Guy, I too have a HPC (1996) but my original pair of horns I replaced with a single modern one. Your fault is intermitent which smacks of dodgy cable connection/short. Fault finding is a process of ellimination. I'd start by disconnecting one of the two horns and see if you still have the problem. If you have, swap the horns and try again. If still problem, work your way back along the wiring loom looking for a squashed cable. Good luck. White road legal 2.0 HPC VX race car 😬 Link to comment Share on other sites More sharing options...
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