Random cutting out, possible causes?

[Mr MXT]

Ok techies, I am at the end of my tether,

Turbo'd Mx5, randomly cutting out without warning on relaxed motorway and A road driving. If left in gear, engine will restart after around 10 seconds. If stationary, it will sometimes start on the key, and sometimes take a number of attempts.

Also have a long standing issue with revs dropping and cutting out at junctions. Have massive injectors (550cc) but have been fitted for 12 months without problem.

Also have a pretty major exhaust manifold leak for which I am waiting for a new manifold to be fabricated.

Can sometimes be difficult to start from cold, requiring a number of attempts.

I've changed the plugs and coil pack which appeared to have fixed the issue for 2 weeks, but now it is back.

My thoughts:

Cam or Crank Angle sensor - I don't know enough about them, would they cause these symptoms?

ISCV needs cleaning / replacing - Would explain the idle droop, but not the cutting out while in normal running?

Leaking manifold needs to be replaced (obviously!) - Could the leaking gasses be causing the lambda sensor to misread, thus giving these symptoms? This doesnt really make sense to me as the fault is random, rather than when flooring it for example.

Any thoughts / options / other ideas?

Thanks all

[jamessealey]

I've had this before with a Fiesta 2001 shape.

I fixed all those things you have mentioned and it still didn't fix it, in fact they were all working perfectly fine. In the end I found it to be an earthing out problem, however mine was basically on any road it would, but it loved cutting out at junctions.

Either way, I guess look around engine bay making sure there's no loose wires and try the Idle Control Valve and Cam Sensor as you mentioned, I'd imagine they would be the cheapest options to begin with.

[stevensdrs]

Fuel pressure regulator faulty?

[stevieturbo]

Mr MXT said:

Ok techies, I am at the end of my tether,

Turbo'd Mx5, randomly cutting out without warning on relaxed motorway and A road driving. If left in gear, engine will restart after around 10 seconds. If stationary, it will sometimes start on the key, and sometimes take a number of attempts.

Also have a long standing issue with revs dropping and cutting out at junctions. Have massive injectors (550cc) but have been fitted for 12 months without problem.

Also have a pretty major exhaust manifold leak for which I am waiting for a new manifold to be fabricated.

Can sometimes be difficult to start from cold, requiring a number of attempts.

I've changed the plugs and coil pack which appeared to have fixed the issue for 2 weeks, but now it is back.

My thoughts:

Cam or Crank Angle sensor - I don't know enough about them, would they cause these symptoms?

ISCV needs cleaning / replacing - Would explain the idle droop, but not the cutting out while in normal running?

Leaking manifold needs to be replaced (obviously!) - Could the leaking gasses be causing the lambda sensor to misread, thus giving these symptoms? This doesnt really make sense to me as the fault is random, rather than when flooring it for example.

Any thoughts / options / other ideas?

Thanks all

Ok...without sounding cheeky, you're at the end of your tether, but have you actually tried to fix it yet ? And 550's aren't massive.

So is this a new to you car, or something you've had for a long time ? has it ever ran properly ? Sounds like there is a string of problems nevermind the cutting out problem. So has it ever ran properly in order to rule out that the entire thing is a mess ?

And by cutting out. Do you mean a total engine cut in an instant ? Missfire then stop ? Does the rev counter cut at the same time, or if the engine is still turning does the rev counter still work ( as it would coasting down in gear )

If you're changing or have changed injectors, what ecu is the car using ? Are there any logging or diagnostic abilities there ? has it ever been tuned properly for this turbo kit ?

[Mr MXT]

Thanks James

Steve - If it was an FPR issue would I not get stuttering or some such as I went to WOT?

[Mr MXT]

stevieturbo said:

Mr MXT said:

Ok techies, I am at the end of my tether,

Turbo'd Mx5, randomly cutting out without warning on relaxed motorway and A road driving. If left in gear, engine will restart after around 10 seconds. If stationary, it will sometimes start on the key, and sometimes take a number of attempts.

Also have a long standing issue with revs dropping and cutting out at junctions. Have massive injectors (550cc) but have been fitted for 12 months without problem.

Also have a pretty major exhaust manifold leak for which I am waiting for a new manifold to be fabricated.

Can sometimes be difficult to start from cold, requiring a number of attempts.

I've changed the plugs and coil pack which appeared to have fixed the issue for 2 weeks, but now it is back.

My thoughts:

Cam or Crank Angle sensor - I don't know enough about them, would they cause these symptoms?

ISCV needs cleaning / replacing - Would explain the idle droop, but not the cutting out while in normal running?

Leaking manifold needs to be replaced (obviously!) - Could the leaking gasses be causing the lambda sensor to misread, thus giving these symptoms? This doesnt really make sense to me as the fault is random, rather than when flooring it for example.

Any thoughts / options / other ideas?

Thanks all

Ok...without sounding cheeky, you're at the end of your tether, but have you actually tried to fix it yet ? And 550's aren't massive.

So is this a new to you car, or something you've had for a long time ? has it ever ran properly ? Sounds like there is a string of problems nevermind the cutting out problem. So has it ever ran properly in order to rule out that the entire thing is a mess ?

And by cutting out. Do you mean a total engine cut in an instant ? Missfire then stop ? Does the rev counter cut at the same time, or if the engine is still turning does the rev counter still work ( as it would coasting down in gear )

If you're changing or have changed injectors, what ecu is the car using ? Are there any logging or diagnostic abilities there ? has it ever been tuned properly for this turbo kit ?

Hi Steve - good questions. So far only attempted to fix as per the OP - this thread is for a bit of guidance as to what to change next or if I am barking up the wrong tree entirely!

I've had the car coming up to 2 years now. It has been running fine until a couple of months ago, so can rule out it isnt just a dog!

By cutting out, I mean total. No misfire as a warning. Rev counter cuts out at the same time, although car is in gear so engine still turning.

ECU is a Dastek Unichip Q+, mapped and tuned properly at the same time as the injectors were fitted. Been running that set up for about the last 18 months. I'm not sure what logging / diag options there are to be honest.

[stevensdrs]

A failing crank angle sensor would result in the symptoms you report. If it starts ok from cold and you only get the problem with a hot engine which completely dies with rev counter going straight to zero and ignition lights coming on then it is likely to be this sensor.

[stevieturbo]

Although ecu losing power could give similar symptoms. Take note of which lights come on the dash when the engine stops.

If the EML/CEL light illuminates, then you can assume the engine is still getting power.

And as above, losing the crank signal will cause engine shutdown and loss of rpm signal. Cam signal may cause engine to stop or run badly. But rev counter may still work ( as rpm signal is taken from crank trigger usually )

Of course...the Dastek will have piiggybacked onto these sensors so a faulty unit there could cause problems. Or dodgy wiring.

[Mr MXT]

Thanks Steves, the plan for this weekend is to change the cam and crank angle sensors and clean the ISCV too. I'll report back!

[Steve_D]

Mr MXT said:

Thanks Steves, the plan for this weekend is to change the cam and crank angle sensors and clean the ISCV too. I'll report back!

Don't forget to do these one at a time otherwise you will come away with a fixed car but no idea why.
Crank sensor first.

Steve

[gowmonster]

i had our mk2 mx5 cut out when i didn't connect the maf sensor properly and it kept connecting and disconnecting depending on bumps.

[Mr MXT]

Update as promised:

Crank sensor changed
cam sensor changed
ISCV and Throttle pos sensor cleaned

....and its still doing it. Some might say, its worse than ever!

Good shout on the MAF, will be trying that next

[Dodd90]

Mr MXT said:

Update as promised:

Crank sensor changed
cam sensor changed
ISCV and Throttle pos sensor cleaned

....and its still doing it. Some might say, its worse than ever!

Good shout on the MAF, will be trying that next

Alright Russ was guna mention mine completly cut out a while back and didn't start at all after cutting out. That was crank sensor. They tend to just completly go when they fail

[Mr MXT]

For completeness - Stevieturbo wins the prize. It turned out to be a loose connection at the piggyback ECU due to poor installation by a reputable tuner

All sorted now and running for the past month without issue