400 dying under load
Discussion
Car hasnt been run over the winter. Car idles and moves off fine. When i accelerate to just about 3000 rpm in second / third, the car just dies and starts to coast, rev counter doesn't drop quickly, a few backfires and it coughs and splutters. If i change down it seems to pick up a bit just to run like a pig until it dies again. If i come to a halt car then idles well pulls off ok and then does it all over again. New plugs, dizzy cap, fuel pump and rotor arm last year. Does this sound like coil and / or ignition amp, or anything else??? Thanks
Edited by SwanJack on Saturday 25th March 17:39
Edited by SwanJack on Saturday 25th March 17:41
This matches the symptoms of the car running on battery rather than alternator.
Which happens when electrical contact between alternator and battery is lost.
Test it by starting the car and seeing if you are getting 14 amps at the back of the alternator.
If yes, then see if you can see 14 volts at the battery.
If no, the fault lies between the two.
The car would drive for about 50 miles just on battery, slowly dying like you describe.
Your battery probably wasn't 100% to start with.
Could be a failed alternator, but first thing to check is the 100 amp fuse.
It is under the car, directly down from the alternator, in a black fuse holder.
Unbolt it from the holder to be sure it is intact.
Which happens when electrical contact between alternator and battery is lost.
Test it by starting the car and seeing if you are getting 14 amps at the back of the alternator.
If yes, then see if you can see 14 volts at the battery.
If no, the fault lies between the two.
The car would drive for about 50 miles just on battery, slowly dying like you describe.
Your battery probably wasn't 100% to start with.
Could be a failed alternator, but first thing to check is the 100 amp fuse.
It is under the car, directly down from the alternator, in a black fuse holder.
Unbolt it from the holder to be sure it is intact.
Rather than just guessing (could be this, could be that), your best bet is to start from scratch, diagnosis is essentially the process of elimination where you set out to prove/disprove the correct function of each element in a system, in turn.
Before you can do this effectively you must 100% understand how the system is designed to work, it's impossible to determine if something is working as it should if you don't fully understand how it was designed to work in the first place.
Lets be honest, there are a thousand different things it could be, but we can simplify things by saying it'll essentially boil down to two things:
1. A loss of spark
Hook up a bulb to the +12v side of the coil and go for a drive, if the bulb goes out when the engine dies you have your answer, from there logical & systematic fault diagnosis will eventually take you to the source of the problem (bad connection at the coil, lose battery terminal, ignition amp ect ect).
2. A loss of fuel
Hook up a fuel pressure gauge to the Shraeder valve on your fuel rail and go for a drive, if the fuel pressure drops when the engine dies you have your answer, from there logical & systematic fault diagnosis will eventually take you to the source of the problem (fuel pump, connection at fuel pump, insufficient current at fuel pump, fuel pump relay, loss of power supply or engine running signal at ECU ect).
I recommend starting with these fuel pressure and live to coil tests, from there make a list of the system at fault following the path of that system from end to end, then check each stage/component in turn until you find the problem.
As already stated, to diagnose a fault in any system it's essential you first understand exactly how that system works, without this understanding you really are on a hiding to nothing. For example the ECU will only run the fuel pump while it sees an engine running signal from the coil, if the ECU loses this signal it will stop the fuel pump by taking away the switching current at the fuel pump relay.
So lets say your coil test bulb goes out and at the same time you see a drop in fuel pressure, in this case its worth checking live feed to your ECU, you can check this by hooking up your test bulb rig to the ECU relay hanging in the footwell, if the ECU retains it's +12v suspect the ignition amp or the coil itself.
If you start by properly understanding exactly how the system works, you're systematic in your approach, and you apply simple logic.... eventually you will track down the source of the problem.
Remember, proper diagnosis is a process of elimination where you set out to prove/disprove the correct function of each element/component in a system and in turn, but you must understand how it was designed to work in the first place or all you'll do is end up confusing yourself.
Before you can do this effectively you must 100% understand how the system is designed to work, it's impossible to determine if something is working as it should if you don't fully understand how it was designed to work in the first place.
Lets be honest, there are a thousand different things it could be, but we can simplify things by saying it'll essentially boil down to two things:
1. A loss of spark
Hook up a bulb to the +12v side of the coil and go for a drive, if the bulb goes out when the engine dies you have your answer, from there logical & systematic fault diagnosis will eventually take you to the source of the problem (bad connection at the coil, lose battery terminal, ignition amp ect ect).
2. A loss of fuel
Hook up a fuel pressure gauge to the Shraeder valve on your fuel rail and go for a drive, if the fuel pressure drops when the engine dies you have your answer, from there logical & systematic fault diagnosis will eventually take you to the source of the problem (fuel pump, connection at fuel pump, insufficient current at fuel pump, fuel pump relay, loss of power supply or engine running signal at ECU ect).
I recommend starting with these fuel pressure and live to coil tests, from there make a list of the system at fault following the path of that system from end to end, then check each stage/component in turn until you find the problem.
As already stated, to diagnose a fault in any system it's essential you first understand exactly how that system works, without this understanding you really are on a hiding to nothing. For example the ECU will only run the fuel pump while it sees an engine running signal from the coil, if the ECU loses this signal it will stop the fuel pump by taking away the switching current at the fuel pump relay.
So lets say your coil test bulb goes out and at the same time you see a drop in fuel pressure, in this case its worth checking live feed to your ECU, you can check this by hooking up your test bulb rig to the ECU relay hanging in the footwell, if the ECU retains it's +12v suspect the ignition amp or the coil itself.
If you start by properly understanding exactly how the system works, you're systematic in your approach, and you apply simple logic.... eventually you will track down the source of the problem.
Remember, proper diagnosis is a process of elimination where you set out to prove/disprove the correct function of each element/component in a system and in turn, but you must understand how it was designed to work in the first place or all you'll do is end up confusing yourself.
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