ajlelectronics
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- Gloucester, England
This has had me perplexed for some while with the intermittent nature of it.
From cold, the engine starts and runs pefectly well. Cold idle 1500 dropping to 850 when warm. Acceleration and performance all as expected and then suddenly there will be a dead cut. Just briefly, the rev counter only drops in sympathy with the reduced output, suggesting it isn't an ignition fault. Sometimes it will cough once, other times it will cough rhythmically (interesting) about four or five times at around once a second. Then it clears and no further problem for some time. As an example it did it on Wednesday after joining the M5 north and having been driven for an hour or so round town. It was then fine all the way to Birmingham and all the way back. RPM doesn't matter, it will do it at idle once in a while or any other speed. Once it stops coughing, it can be booted and will take off as expected, suggesting that it isn't fuel starvation. It can do it from cold or when hot. Even towing the caravan was fine, suggesting it isn't engine load.
It has had multiple tanks of full spec 97 RON fuel, the tank was brand new and so is the in tank pump and filter / fuel lines.
Fuel pressure checks out, but a new regulator has been fitted anyway.
Ignition coil renewed.
Distributor (and hence ign. amp) has been swapped for another.
Timing is correct 12BTDC.
All setup has been done in service mode.
Idle air control valve has been replaced.
Throttle pot has been replaced.
Engine temperature sensor has been replaced.
All top end gaskets have been replaced and checked for air leaks with volatile spray.
Injectors have been refurbished professionally.
MAFs are clean and securely connected.
FCR shows nothing, although two digit ECUs don't store much.
Wiggle test doesn't provoke it.
Vacuum lines all brand new and not leaking.
I did start to wonder if it might be the A4LD gearbox, but that would release drive and show an increase in RPM so 99% sure it is not that.
From cold, the engine starts and runs pefectly well. Cold idle 1500 dropping to 850 when warm. Acceleration and performance all as expected and then suddenly there will be a dead cut. Just briefly, the rev counter only drops in sympathy with the reduced output, suggesting it isn't an ignition fault. Sometimes it will cough once, other times it will cough rhythmically (interesting) about four or five times at around once a second. Then it clears and no further problem for some time. As an example it did it on Wednesday after joining the M5 north and having been driven for an hour or so round town. It was then fine all the way to Birmingham and all the way back. RPM doesn't matter, it will do it at idle once in a while or any other speed. Once it stops coughing, it can be booted and will take off as expected, suggesting that it isn't fuel starvation. It can do it from cold or when hot. Even towing the caravan was fine, suggesting it isn't engine load.
It has had multiple tanks of full spec 97 RON fuel, the tank was brand new and so is the in tank pump and filter / fuel lines.
Fuel pressure checks out, but a new regulator has been fitted anyway.
Ignition coil renewed.
Distributor (and hence ign. amp) has been swapped for another.
Timing is correct 12BTDC.
All setup has been done in service mode.
Idle air control valve has been replaced.
Throttle pot has been replaced.
Engine temperature sensor has been replaced.
All top end gaskets have been replaced and checked for air leaks with volatile spray.
Injectors have been refurbished professionally.
MAFs are clean and securely connected.
FCR shows nothing, although two digit ECUs don't store much.
Wiggle test doesn't provoke it.
Vacuum lines all brand new and not leaking.
I did start to wonder if it might be the A4LD gearbox, but that would release drive and show an increase in RPM so 99% sure it is not that.
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