Engine stops randomly, but restarts after a minute or so.
Discussion
My 350 has just started with a problem. It keeps stopping. Engine just dies, no coughing or spluttering, just cuts out.
My first thought was the connection from the ingnition amp to the AFM. But I've got rid of the crappy connecter and crimped the wires together. Still cut out twice on the way to work today.
Usually happens after about 20 minutes running, so it might be heat related, but once restarted it usually runs fine (this morning being the exception). Could be related to vibration as the roads around here are absolutely s
te at the moment (well in reality some of the potholes are WW2 bomb craters that haven't been fixed yet 
)
I think I've probably got some sort of loose connection, or possibly the ignition amp going down (recently replaced this but it has been fine).
I guess it's going to be a process of elimination, and a thorough going over of the ignition wiring circuit looking for poor continuity / breaks / loose connections.
Has anyone else had a similar problem, and if so what was the cure?
My first thought was the connection from the ingnition amp to the AFM. But I've got rid of the crappy connecter and crimped the wires together. Still cut out twice on the way to work today.
Usually happens after about 20 minutes running, so it might be heat related, but once restarted it usually runs fine (this morning being the exception). Could be related to vibration as the roads around here are absolutely s
te at the moment (well in reality some of the potholes are WW2 bomb craters that haven't been fixed yet )I think I've probably got some sort of loose connection, or possibly the ignition amp going down (recently replaced this but it has been fine).
I guess it's going to be a process of elimination, and a thorough going over of the ignition wiring circuit looking for poor continuity / breaks / loose connections.
Has anyone else had a similar problem, and if so what was the cure?
Not sure if its any help, but on my 400 I had an issue a few years ago where the car would cut out ... and refuse to start, then start and run, only to stop again at random
I traced the fault down to the injector wiring having worn though on the top of the one head .. it was earthing and stalling the car. On one occasion, it even blew a fuse .. which is how I was able to isolate and identify the problem.
I traced the fault down to the injector wiring having worn though on the top of the one head .. it was earthing and stalling the car. On one occasion, it even blew a fuse .. which is how I was able to isolate and identify the problem.
pwd95 said:
Had a similar thing with my old 450i after I put it back together after the head gasket. There's an earth bolted to the back of the block & it was loose. It was cutting the engine dead as it was jiggling over bumps. Just get it idling & start jiggling things.
Cheers Wyn, I've already checked the earths, when I swapped the alternator last month, but it might be worth double checking the connections.Right chaps, an update.
Set off home from work, got about 20 minutes into the journey and she cut out again.
Swapped coil for a known good one (although the other one wasn't too hot) - still wouldn't bloody start.
Left it a couple of minutes and it fired up.
200 yards later it cut out again.
This time I swapped back to my old ignition amplifier. Fired first time and ran OK all the way home (just over 5 minutes).
I'm not saying that the amp is the problem, but it did get me home.
I guess I need to take her out for a really good blast to check.
Set off home from work, got about 20 minutes into the journey and she cut out again.
Swapped coil for a known good one (although the other one wasn't too hot) - still wouldn't bloody start.
Left it a couple of minutes and it fired up.
200 yards later it cut out again.
This time I swapped back to my old ignition amplifier. Fired first time and ran OK all the way home (just over 5 minutes).
I'm not saying that the amp is the problem, but it did get me home.
I guess I need to take her out for a really good blast to check.
Well, all was going well, a good half hour run and then she started to stutter, but cleared. Went and filled her up with go juice and ran for a about 5 minutes after before she cut out.
No voltage at the coil, so I hot wired her to get home. Checking through and the fuse for the coil had popped.
Of course I only checked that after doing continuity checks on the wiring.
Mental note to self check the Fing fuse first next time.
So time to try and find a Lucas Ignition Amp...
No voltage at the coil, so I hot wired her to get home. Checking through and the fuse for the coil had popped.
Of course I only checked that after doing continuity checks on the wiring.
Mental note to self check the Fing fuse first next time.
So time to try and find a Lucas Ignition Amp...
I had this same fault on my Cosworth and it ended up being a temp sensor. It used to stop at the same place to and from work and as it got to a certain temp it would cut out, then after about a minute I could restart it and have no problem again until the next time it was started from cold. This may not be the case on a TVR though but you never know.
This post hase been Edited to correct my prior mistaken observations, sorry about that!
Its good the fault seems fixed now you have replaced the fuse, but that sorta implies that the fuse was the culprit even before it blew. Thats no so likely, more probably an intermittent wiring fault that eventually blew the fuse making a permanent but diferent fault, and easier to find, therefor.
Been watching progress and early on it was not at all clear if you had established whether this was an intermittent ignition fault or a fuel problem.
It had connectivity connotations though, as your surmised, and if so, no amount of component swapping would fix it. So diagnosis was in order, methinks.
In the thread - I couldn't see anywhere saying you found the sparks had gone when the fault occurred. Perhaps I just missed it??
ie, car stops, immediately test for missing sparks, cant find sparks therefore it must be ignition.
That said, it was reasonable to assume ignition. This procedure would help you or anyone establish where and how an intermittent ignition fault is occuring.
First, the circuit would be something like this.
Guaranteed Foolproof Intermittent Ignition Fault Finder.
Rig up two 4/5 watt 12 volt bulbs (or better still, 2V, 15mA LED's + 680 ohm resistors) on test leads into the cabin and connect one between coil +ve and earth and the other to coil -ve and earth. Mark the bulbs POS and NEG. Beware cables dont foul hot/moving parts.
Start the engine and observe:
POS sensing the ignition input voltage is permanantly on,
AND
NEG sensing the pulsed voltage across the Ignition Amplifier flickers in sympathy with engine rpm, or is dimly lit (LED's flicker better).
Now drive the car and have a helper note what happens when the engine misbehaves.
If POS and NEG go out together there is an open circuit interruption of the 12 v feed such as a faulty wire/ignition switch,
OR
A short on the same circuit due to burned insulation.
If NEG comes full on the Ignition Amplifier (due to excess internal heat) or its associated wiring/earth has failed in open circuit mode,
OR
The pulsed input (ie Hall Effect or Reluctor) to the amplifier from the dizzy has failed or the associated wiring is faulty/shorting to earth,
OR
The Coil has failed in a short circuit mode (unlikely cos it would surely kill the amplifier methinks?)
If NEG goes out the Ignition Amplifier has temporarily failed in short circuit mode due to excess internal heat,
OR
the local wiring is shorting to earth,
OR
The coil has failed in open circuit mode due to insulation breakdown or internal heat
If POS stays lit and NEG show signs of flickering instability not sympathetic with engine rpm, then the Ignition Amplifier or its connections are on the blink.
Moving on to fuel related intermittent possibilities
1 Check the engine running signal from coil negative goes to pin 1 of the ECU via the 6800 ohm resistor is not being disrupted intermittently.
2 Check the wiring around all the key Efi system components such as coolant temp sensor, AFM, ECU, etc.
I realise that now you seem to have found the fault, none of the above is needed, but the lack of a process meant that guesswork was the main resource, or looking for similar events in other vehicles.
Its good the fault seems fixed now you have replaced the fuse, but that sorta implies that the fuse was the culprit even before it blew. Thats no so likely, more probably an intermittent wiring fault that eventually blew the fuse making a permanent but diferent fault, and easier to find, therefor.
Been watching progress and early on it was not at all clear if you had established whether this was an intermittent ignition fault or a fuel problem.
It had connectivity connotations though, as your surmised, and if so, no amount of component swapping would fix it. So diagnosis was in order, methinks.
In the thread - I couldn't see anywhere saying you found the sparks had gone when the fault occurred. Perhaps I just missed it??
ie, car stops, immediately test for missing sparks, cant find sparks therefore it must be ignition.
That said, it was reasonable to assume ignition. This procedure would help you or anyone establish where and how an intermittent ignition fault is occuring.
First, the circuit would be something like this.
Guaranteed Foolproof Intermittent Ignition Fault Finder.
Rig up two 4/5 watt 12 volt bulbs (or better still, 2V, 15mA LED's + 680 ohm resistors) on test leads into the cabin and connect one between coil +ve and earth and the other to coil -ve and earth. Mark the bulbs POS and NEG. Beware cables dont foul hot/moving parts.
Start the engine and observe:
POS sensing the ignition input voltage is permanantly on,
AND
NEG sensing the pulsed voltage across the Ignition Amplifier flickers in sympathy with engine rpm, or is dimly lit (LED's flicker better).
Now drive the car and have a helper note what happens when the engine misbehaves.
If POS and NEG go out together there is an open circuit interruption of the 12 v feed such as a faulty wire/ignition switch,
OR
A short on the same circuit due to burned insulation.
If NEG comes full on the Ignition Amplifier (due to excess internal heat) or its associated wiring/earth has failed in open circuit mode,
OR
The pulsed input (ie Hall Effect or Reluctor) to the amplifier from the dizzy has failed or the associated wiring is faulty/shorting to earth,
OR
The Coil has failed in a short circuit mode (unlikely cos it would surely kill the amplifier methinks?)
If NEG goes out the Ignition Amplifier has temporarily failed in short circuit mode due to excess internal heat,
OR
the local wiring is shorting to earth,
OR
The coil has failed in open circuit mode due to insulation breakdown or internal heat
If POS stays lit and NEG show signs of flickering instability not sympathetic with engine rpm, then the Ignition Amplifier or its connections are on the blink.
Moving on to fuel related intermittent possibilities
1 Check the engine running signal from coil negative goes to pin 1 of the ECU via the 6800 ohm resistor is not being disrupted intermittently.
2 Check the wiring around all the key Efi system components such as coolant temp sensor, AFM, ECU, etc.
I realise that now you seem to have found the fault, none of the above is needed, but the lack of a process meant that guesswork was the main resource, or looking for similar events in other vehicles.
Edited by honestjohntoo on Wednesday 19th May 21:03
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