HELP!!! I recently left my drivers door ajar a few daysā¦interior light flattened my battery. In my rush to get out for an evening drive in the sunshine i decided to bump the car in reverse down the drive. It started no problem, ran for 10 seconds and died. All ignition lights out, completely dead.
Found 100A fuse blown. Replaced it and all seemed ok. Engine turning over but not starting.
Turns out the fuse marked āroomā which powers the interior light, clock and stereo was blown. Tried replacing it but blows straight away.
Also found the āengineā fuse blown. Again when i replace this it blows as soon as i turn the ignition on.
So far iāve disconnected the coil pack, ecu and several sensors on the engine but fuse wonāt hold.
Any suggestions? Is there any link between the āroomā and āengineā circuit
Itās Rob, we spoke on the phone about this issue yesterday.
As per our conversation and Robbieās posts a shorting lambda can take out the 15 amp engine fuse but would be a big coincidence if this occured at the same time as the bump start. Havind said that the spike blew a 100 amp fuse so possible collateral damage. Disconnect it where it joins the loom to test theory. Ā
I have had another thought. Try disconnecting the ecu completely and see if the fuses still blow when ignition turned on. Just thinking that there could possibly be a direct short where the main connector pins join the PCB. As discussed this sort of damage should be very visible. Ā
Thanks Rob. I removed the ecu last night, pins and socket look good, fuse still blew. Disconnected the coil packs as well. Ive also pulled the main relay. Looking through some very detailed wiring diagrams atmā¦shocked at how many circuits the ROOM fuse feeds. Scratching my head. What about the immobiliser part of the circuit? i cant find any details on it or indeed where it is situated?
I cannot quite understand though, what could have happened to cause this problem just because the owner jump-started his car ! Ā Coincidence perhaps, but curious all the same.
Agreed,something doesnāt add up here.the Op said he bump started the car in reverse down the drive.So there must have been enough power in the battery to fire up the electrical circuits,but not the starter.How can you do so much electrical damage without any interference from an outside power source? Confused
Key post here, the OP didnāt define what he meant.
From my POV, a BUMP start is āold schoolā, either manually pushing a car or pushing it with another car, not possible in this day and age since steel bumpers went out the door. Other alternative is towing, but thatās fraught with danger if the car starts and the driver doesnāt hit the brakes fast enough.
Then thereās a JUMP start, which Iāve done several times - using a back up battery to boost the low battery in the car.
Once done by a good friend, who wasnāt sure which was negative and which was positive, and connected the back up battery the wrong way round. Result - Blown main and room fuses. At first I thought the PCM was shot, but checking soon revealed the main 100 amp fuse had blown, but when I replaced that, the car still wouldnāt start, so more checking revealed the ROOM fuse had also blown. Fortunately no more damage, in the OPās case, it sounds like the immobiliser took a beating too, which points at an existing possible fault in it. Certainly it has one now.
My friend - who shall be nameless, is a good mechanic but a lousy sparks (Iām his back-up and heās mine!)
At the end of the day, as the + and - markings on the Panasonic are very hard to see, when the battery is in location, then the only guide on my car is a red rubber boot which fits on top of the positive battery connection, and Iām surprised my friend didnāt notice that. So the question is āIs there a red rubber boot on the end of everyone elseās car battery positive connection?ā If there is on a Mk2, then it has to be pulled back in order to stick a back up battery clamp on the bare connection, so if the OP did use a JUMP start, then the fault is his own. A BUMP start would NOT cause this problem. The implications are expensive. He has my sympathy, but that doesnāt help him.
Thereās a pointer for anyone with a jump start/restart problem. GET IT RIGHT! This comes up every so often Thatās apart from the one a few years back where his mate connected a 24V battery charger to his car - if IIRC also the wrong way round. (0oops)
No Chris, no mistake, as I said, the only way anyone can blow the Main and Room fuse is by connecting a back-up battery the wrong way round. As I also said - your post contained the key word which evoked my comment.
As on Mazda supplied diagrams only show empty boxes for PCM, Immobiliser , alarm and other self contained devices itās difficult to know whatās inside - āA closed bookā - so while I believe the PCM has reverse polarity protection diodes (otherwise it would blow) I have no idea if other components have this also.
Thereās no way I can envisage a BUMP start would achieve the same result, even though the only way you can do this is by pushing the car. Many years ago, I started my first car with a push out of the garage, where fortunately there was a sloping ramp to get into the garage in the first place , and that gave just enough impetus to allow the car to start, despite having a very low battery. āOld schoolā car of course, but the point remains the same. Being in reverse gear helped a lot too.
A near empty battery cannot supply enough current to blow a 100 amp main fuse, so BUMP start does NOT compute - period. IMHO the OP used the wrong word in the first place.
If anyone wants to argue āThat a BUMP start can blow fuses because of a high charging surge from the alternator to the battery can do thisā, then they need to consider the rating of the alternator, which maxes out at 68 amp at 2000 rpm, which a bump start can never achieve.- Brings to mind that oldie - āBeep Beepā by the Playmates. 1958.
Ok, when i said BUMP start i was referring rolling the car and releasing the clutch. Car started ok for about 10s then died. Main, room and engine fuses blew.
Eventually traced back to immobiliser, plugged in a new one and fired up first time. Very strange i agree but thats the facts
Definitely didnāt connect up any sort of back-up battery the wrong way round
I have been looking at the immobiliser removed from your car. Apart from the odd spatter of solder on the case and burning smell, I cannot see any visible sign of burning, damage or even missing solder on the PCB. Plugged in the correct seven wire connector with stripped wires to check for a short, hoping to find just one. On a working immobiliser there is trace resistance that quickly disappears on one cross wire connection. Your immob show three direct shorts(beep), five partial shorts(steady resistance but no beep) and 4 trace resistances(high figure appears initially and then disappears).
The solder spatter is around a chip marked A947, 24v - I canāt find any reference to this but the PCB reference is Z1.
Given the additional number of shorts on this board I am thinking it has been completely fried.
Getting back to bump starting and jump starting. Neither are desirable as introducing electricity generated outside of the usual circuit.
Jump starting does this via the ballast of the battery so any excess charge likely absorbed through battery before other components affected.
Bump starting involves alternator generated current with circuits not authorised by the immobiliser ie. engine starts to fire before ecu/immob handshake.
As the immobiliser initiates this handshake I guess it will also got the effect of the electric spike.
Not an entirely convincing argument and more than happy for anyone else to add to it. Ā Ā Ā
Very interesting post by Rhino666 about the damage caused to Daveās immobiliser and the possible causes.
Now, Iām the first to acknowledge that my car-mechanicās experience is strictly āold schoolā, having been a motor mechanic in the 1970s when there was no such thing as an immobiliser (not on the stuff I worked on anyway !). Ā Bump starting, when needs be (and indeed jump starting), was the norm back in those days, and it never occurred to me that such practices on modern cars, with all their electronic wizardry, could be hazardous to some of these electronic components. Ā Rhino666ās explanation / theory as to what possibly went wrong does sound plausible to these old goatās ears.
A good warning then, to other āold schoolā owners of modern cars I think !
Couldnāt agree with you more Chris. My own fault for bumping itā¦the sun was actually out and i got a bit over excited.
Good investigation work Rhino666
Thanks to everyone who has contributed to resolving this problem. Got to mention the fantastic service provided by MX5BITZ
Dave - I apologise for assuming you got the term wrong, my mistake. Glad you have got the car working, so no harm done, other than a frustrating delay for you.
However, while not your concern, the comment that you plugged in a replacement immobiliser and it worked throws new light on the claim that immobilisers are paired with PCMās (ECUās) and must always be fitted together - at substantial expense.
I would appreciate clarification of this from someone, as Iāve been saying this out of faith for some time now. So have others I would add. It is a general assumption.
