Electronic interference with ECU - is this possibly?

[roseytvr]

Hi Guys

I have just had a new ECU and associated gubbins fitted and now have a real weird problem.

For some reason the car is running fine in the garage with no issues but as soon as I drive it it cuts out when slowing down at junctions or stopping in traffic. A quick on off with the key and it fires up fine and off I go until slowing down at the next junction! I have noticed that it will bump start immediately if I just switch ignition on and off whilst rolling but unless I switch the ignition off and on again it will not start. Its almost as if I am having to reset the ECU via the ignition to start it again.

However I have noticed that if I pull the ECU, relays etc away from the foot well by the battery (its a grif) and spread all the electronics out on the passenger side floor I do not have any problems. It seems the electronic shutdown only occurs when everything is squeezed into place above the battery.

Is it possible or feasible that electronic interference could be occurring with everything crammed together tightly in a real small space? If so how would I go about identifying the culprit and resolving the problem?

I can take it back to installer but he has already had the car 6 weeks and not identified the issue. I would prefer to identify/solve the culprit/problem before I take it back.

Any help appreciated.

Thanks
Ian

[danbourassa]

Hi Ian,
The ECU is fastened to the chassis in Land Rovers. This grounds the case of the ECU and adds shielding properties. TVRs are an even harsher environment since the FRP body does no shielding at all. Try running a ground wire from the ECU to battery ground. The wire should be fairly thick (maybe 16 gauge). Just attach it under an ECU corner screw for a quick test before bothering with a permanent installation.

[blitzracing]

Sounds like you need RoverGauge plugged in with someone reading the values as it fails. The 14CUX is pretty tough spike wise, as long as you dont run silly low resistance plug leads. Id suspect its more likely you have a fractured wire in the loom, thats simply making connection as you move the loom.

[taylormj4]

blitzracing said:

Sounds like you need RoverGauge plugged in with someone reading the values as it fails. The 14CUX is pretty tough spike wise, as long as you dont run silly low resistance plug leads. Id suspect its more likely you have a fractured wire in the loom, thats simply making connection as you move the loom.

+1, sounds like fractured wire, or something touching the exposed battery terminals. I've covered mine to prevent any inadvertent contact, e.g. metal relay cases onto the +12V terminal etc

Weird that you can reset it by turning on/off though. It might be coincidence: the braking is causing the wires to move and fracture to open or inadvertent contact made. Presumably you only do the off/on thing when you come to a halt. The fact that you have stopped braking could be the actual reason it restarts. ALthough you did say you can do it whilst braking too...very odd.

Could be something to do with the fuel pump or ignition relays. If they are tired, the different angle when you ram it back into the footwell could cause problems, would be very unusual though.

Edited by taylormj4 on Tuesday 3rd March 23:22

[roseytvr]

Thanks guys, I am running DTA Fast ECU with a new bespoke loom, twin lambdas etc. the ECU is earthed, albeit light gauge.

I have put the ECU back in the footwell protected with rubber roofing material but the problem has now reappeared. I appreciate your opinions and the difficulty of a forum diagnosis but I don't think it is a fracture as the symptoms are predictable and consistent.

I can drive like a looney braking and pushing on without problems but as soon as the revs drop down below c2000 rpm and the gearbox is engaged the engine just dies and the car will come to a stop unless I turn ignition on and off and it bump starts immediately. Obviously I can't bump it when stationary but it will start immediately on the key.. As mention previously it's like an electronic shut down that clears when I turn off and on ignition.

Will my ECU software give me any clues, I am not that good at understanding what it tells me!!

Will keep you updated as I try moving stuff around. Any material recommended to reduce possible interference?

[TV8]

Hi Ian,
How old is the battery and what is the alternator putting out? I had a couple of wierd things happening with mine in recent months. For un-related reasons, I changed the battery and they have gone away!

[blitzracing]

Anything metal wrapped around the ECU and loom- even tin foil will reduce interference, but make sure its grounded as well to work. You cant stop spikes running down the loom from the engine bay this way though, only radio type interference. Its also always worth trying a set of resistive plugs, as these will reduce ignition spikes, and it wont cost a lot. In your case you may need to get technical and get someone to put an oscilloscope on some of the lines to look for noise. The original 14CUX loom is very carefully designed so each sensor has its own earth wire leading back to a common earth, so you don’t get spikes or ground loop issues, so who ever did your loom will need to know what they are doing, as a car engine bay is a highly hostile environment when it comes to electrical noise.

Edited by blitzracing on Thursday 5th March 14:58

[spitfire4v8]

What have DTA said about the issue ?

[taylormj4]

Why would electrical noise suddenly become an issue when the revs dropped below 2000 though ?

I think your ECU software would be a good starting point.

The question would appear to be what happens when you drop below 2000rpm that is reset by turning the IGN off, then ON.

You mentioned "with the gearbox engaged", does it not happen if you are in neutral ?

[fatjon]

It could be the crank pickup. If it loses signal the ECU detects a stall (or crash!) and cuts off the fuel pump (on most if not all systems). If the signal is weak it could be losing it at low engine speeds, seen this a few times with magnetic VR sensors when they are knackered, crudded up or too far from the teeth on the pickup wheel. When this happens it will not fire up the fuel pump until the ECU is reset with an ignition off/on.

Of course if it's an optical or hall sensor not a VR this is all cobblers.

[griff 200]

That sounds like a very feasible cause of the fault it's not that easy to fit a crank sensor close and on a non flexy brk. Worth a look for sure. Richard

[griff 200]

That sounds like a very feasible cause of the fault it's not that easy to fit a crank sensor close and on a non flexy brk. Worth a look for sure. Richard

[V8 Fettler]

Is this the standard 14CUX ECU? Does it not receive a signal for road speed to hold up the idle approaching a stop? Also need to set the mechanical idle speed and check the operation of the stepper motor.

[roseytvr]

Thanks for the responses guys, I will get back to you on progress with this but its "worse than that, shes dead Jim" - I cant start her at all now to check anything. The fuel pump is not priming and whilst its cranking like a good un clearly it isn't going to start.

All fuses checked, relays checked, immobiliser by passed and still no life. I will try +ve to the fuel pump tonight and work back from there. The car is not stock - aftermarket ECU, bespoke loom etc so no stepper motor and associated gubbins.

Cheers
Ian

[rev-erend]

It might even be simpler that that - maybe the ecu connector pins are not making full contact. Remove the main connector and take a close look at the pins to see that they are right at the front of the connector and cannot be easily pushed back into the connector.

[blitzracing]

Wont the Aftermarket ECU have an OBD port you can plug a reader into? Far better than guesswork.

[roseytvr]

It goes from bad to worse unfortunately. DTA ceased trading last month so I cant go to them and I cant even pick up a connection with the ECU via my PC. It as if the ECU is dead. All pin connections appear OK will see if I can check if the ECU is getting power tomorrow.

[carsy]

Nightmare Ian. Hope you get it sorted without too much difficulty.

[rev-erend]

My first step would be to check the ECU gets power at the correct pins.

There are likely to be 2 pins that get power. 1 constant from the battery and the other from the ignition.

Also test the earth(s).

After that I would suspect the ECU. Does it have a fuse built in ?

The DTA site is still up - so you should still be able to get information from there.

[roseytvr]

It gets even worse unfortunately - the loom configuration to the ECU bears no resemblance to the wiring diagram issued by the now departed DTA Fast. I cant even make sense of the wiring to the two relays that I assume are for the ECU and fuel pump. For example Ignition on :

Relay 1:
Pin 87 12v
Pin 85 12v
Pin 86 12v
Pin 30 0v

Relay 2:
Pin 87 12v
Pin 85 0v
Pin 86 GND
Pin 30 0v

Completely baffled so its back to the installer on a trailer when he can fit me and no doubt hang on to it for another 6 weeks. Grrrr.
Well it.At least its Friday night