Fuse keeps blowing - won’t start

[Simple]

Hi folks, after some help.

My chimaera keeps blowing the 25amp fuse for the ignition switch and won’t start. The issue started a while back but the garage couldn’t find anything wrong and as it was intermittent the simple solution became to carry a spare (which I do anyway). However today it just keeps blowing them so I can’t get it started.

I’ll call the garage tomorrow but has anyone any ideas what the issue might be? Just before this issue started my car had started having the hot start issue and they did something to fix it. Timing is suspicious but they assure me it’s unconnected - it’s a well know TVR specially so they should know what they’re on about, I've used them for years without an issue. All help much appreciated. Was looking forward to a drive having just taxed the car as it was SORN through winter and lockdown. Feeling frustrated now.

[David Beer]

The starter solenoid is not fused So agreed with your people, not connected.
Do your ignition lights, oil , come on before cranking, ?

[Simple]

Thanks David, that’s helpful. All the dash lights come on and the pump primes but as soon as I turn it to actually start it all goes dead. Starter motor never turns.

[O mage]

Sounds like your starter is cooked tvr did make a revision for this and introduced a heat shield that clipped on to the starter body.and introduced 100 amp fuse to alt on later griff early chim

[Simple]

That’s interesting. The starter had been getting a bit lazy over the last year.

[O mage]

Case closed. there is nothing else that could drag that much all things being equal.

[David Beer]

The solenoid supply is not fused ( as standard). The main supply to the starter does not go through any fuse, the two big fuses 80 & 100 amp Have nothing to do with the starter circuit. The big fuse in the footwell is the main fuse for all the fuse box, the one under the car would stop the charging of the battery.
You say ignition fuse, is it in the main fuse box ?

Edited by David Beer on Monday 10th August 16:10

[Simple]

Yes it is a 25amp fuse in the fuse box which the bible labels as being the ignition switch.

[David Beer]

So did they modify the solenoid circuit because of the hot start problem ? If they have and tapped into that 25 amp fuse supply, it could be enough to blow it captain !
Any mods for the solenoid should be direct from the fuse box or battery direct, not through any shared fuse , the solenoid circuit is around 15 amps. So say that 25 fuse was happy at 20 amps, adding 15 would pop it.
I would ask what they have done, you may of ?

[Steve_D]

Which fuse number?
Does it blow when you turn on the ignition or when you turn to start?

Steve

Edited by Steve_D on Monday 10th August 22:21

[Penelope Stopit]

Steve_D said:

Which fuse number?
Does it blow when you turn on the ignition or when you turn to start?

Steve

This

Deleted my posts, don't know what got me thinking it was blowing a fuse when cranking

[Simple]

Steve_D said:

Which fuse number?
Does it blow when you turn on the ignition or when you turn to start?

Steve

Edited by Steve_D on Monday 10th August 22:21

It’s the end fuse labelled ignition switch. Blows when you move the ignition from position 2 to crank - but blows immediately, it never actually cranks the starter.

[Penelope Stopit]

Disconnect the thin crank cable from the starter

Does it still blow?

Déjà vu

[ChimpOnGas]

Simple said:

Steve_D said:

Which fuse number?
Does it blow when you turn on the ignition or when you turn to start?

Steve

Edited by Steve_D on Monday 10th August 22:21

It’s the end fuse labelled ignition switch. Blows when you move the ignition from position 2 to crank - but blows immediately, it never actually cranks the starter.

Thus proving the starter solenoid is indeed fused, what TVR failed to fit was a dedicated starter solenoid relay which contrary to what some will try to tell you is used in the world of auto electrics to take the load of the ignition switch contacts, it's not there to deliver more current to the starter solenoid as the maker of the 'Hot Start Kit' claims. TVR didn't deem it necessary to fit a starter solenoid relay because they ran that circuit through the immobiliser that itself has two relays inside it, one is rated at 10a and was designed for the low amp ECU and one is 25a Meta specifically intended for the much higher load starter solenoid circuit.

TVR's idea to save themselves the cost of a 30a relay could have worked too, sadly they wired the low amp ECU through the 25a Meta relay intended for the starter solenoid, and the higher amp starter solenoid through the little lower rated 10a relay intended for the ECU. Now, a new starter solenoid should only pull 10a so they kind of got away with their mistake, but after a few years that little 10a relay often started to give out under all the load it was never designed to handle, and to compound the issue over time the load became greater as the solenoid and circuit became corroded ect.

The result being the infamous 'Hot Start' issue, so called because the problem often (but not always) typically first manifests itself when the car is hot, as we all know from school resistance in a circuit increased with heat so while you might get away with cranking a cold engine as soon as the starter relay and its associated wiring gets hot you can easily reach critical mass at the weakest link in that circuit. In the case of a Chimaera and Griffith that weakest link is that little 10a relay potted inside your immobiliser because quite simply it was never designed to take the load generated by the starter solenoid, in essence TVR hard wired the hot start problem into every Chim & Griff they build during the 90's.

All that said don't just assume the immobiliser relay is your issue, actually that problem typically just manifests itself as an open circuit 'No Crank' condition with none of the fuse blowing you describe, so I'd start your diagnostic work elsewhere. The reason your fuse blows is because it's doing it's job, but you do need to find out why, quite simply you are looking for a point of high resistance that's placing excessive load on that circuit.

This could be at many points in the circuit so any forum based speculation will just that, speculation! To locate the point causing excessive load you need to follow the circuit using a multimeter, its the only way to professionally pinpoint where the issue resides, anything else will be pure guess work.

Key potential areas of high resistance/load are:

1. The fuse board on the starter solenoid circuit

2. The ignition key contacts (sprung start position)

3. The immobiliser

4. The starter solenoid

5. The starter solenoid actuated shift fork mechanism

6, The starter motor armature bearings

7. And of course the starter solenoid circuit cables themselves including any connector blocks

Don't succumb to the temptation of blindly replacing components like the starter motor in the hope you may stumble on the issue, test each point in the circuit to prove where the fault truly resides. However, if you wanted to improve your chances of finding the issue quickly it makes sense to start your testing at the component that has the highest probability of being a fault, to this end given the probability is high you have a mechanical issue such as a binding solenoid shift fork mechanism so I'd be starting my test sequence there.

Heat from the offside exhaust manifold can bake the grease hard in this mechanism causing it to bind, but don't just assume, test the theory as it's just one point of potential load. If you do find this is your issue it's possible to strip the mechanism, clean and re-grease with a high temp grease. However, if the resistance is on the main armature shaft things get a little more complicated as you'll need to completely strip the starter motor at which point given a perfectly decent brand new starter motor can be had for £65.00 you may as well just replace the whole unit.

Measuring current with a basic multimeter is very simple, but if you're unsure here are some simple and easy to follow instructions:

https://www.hagerty.com/media/maintenance-and-tech...

Happy hunting

[Belle427]

I'd suspect the start solenoid circuit, must be related to the work done.

[DangerousDerek]

I recently had a similar problem but mine cranked for a split second before blowing the fuse.
Turned out to be something to do with the wiring to an after market ignition switch. As soon as I disconnected that all was fine.

[Penelope Stopit]

Don't use a multimeter

Multimeters burn out or blow an internal fuse when connected in series with a short circuit

Keep it simple simple, disconnect the starter solenoid crank cable, if fuse still blows there's a wiring fault, if fuse doesn't blow there's a starter fault

[Steve_D]

Penelope Stopit said:

Don't use a multimeter

Multimeters burn out or blow an internal fuse when connected in series with a short circuit

Keep it simple simple, disconnect the starter solenoid crank cable, if fuse still blows there's a wiring fault, if fuse doesn't blow there's a starter fault

This is the most time effective diagnostic route.

Fuse 21 (the one on the end) is the supply into the ignition switch not out of. There is no other fuse in the start circuit.

Steve

[O mage]

David Beer said:

The solenoid supply is not fused ( as standard). The main supply to the starter does not go through any fuse, the two big fuses 80 & 100 amp Have nothing to do with the starter circuit. The big fuse in the footwell is the main fuse for all the fuse box, the one under the car would stop the charging of the battery.
You say ignition fuse, is it in the main fuse box ?

Edited by David Beer on Monday 10th August 16:10

It has provision for this as (standard) by tvr of course it does and its all worked out. If you take your solenoid wire off and dead short it then go to crank it will blow fuse 21 ignition every time.

[David Beer]

O mage said:

It has provision for this as (standard) by tvr of course it does and its all worked out. If you take your solenoid wire off and dead short it then go to crank it will blow fuse 21 ignition every time.

Did not know that. Surprised the immobi wiring could pass 25 amps !