VR6 not starting, low voltage at fuel injector rail, can anyone help?

[Thom 1]

Hello,

 

Have done a search but can't find an answer, apologies if this has been covered before..

 

I'm having trouble with my VR6 which will crank but refuses to start. I have replaced the fuel pump and ECU relays and have tested the ignition switch, fuel pump/lines and tested for a spark and all's good there. I've found though that I'm only getting ~5v at the fuel injector rail plug whilst cranking.

 

VCDS also isn't throwing up any fault codes.

 

Has anyone had a similar problem or any advice? I'm now looking for a short between the ECU and injectors.

 

Thanks in advance,

 

Thom

[tony_ack 0]

Have you ruled out the Crank sensor? I'm not sure if a faulty reading stops the spark, but it definitely stops the fuel

[Thom 1]

Thanks Tony,

 

I have tested it for continuity and all seems ok there. I'm getting 4.7v at the fuel rail both with ignition on and also when cranking. I would have thought that a bad crank sensor would be stopping ANY voltage reaching the fuel rail and also stopping the pump running, but that's working as normal.

 

Have also checked the wiring to the cam sensor and am getting the full 12v there.

 

 

Cheers,

Thom

[Keyo 47]

Could actually be the ecu check it out for water damage on the plug housing or any cracks in the case.

[Thom 1]

Thanks Keyo, yeh literally just been out to do that, alo took off the plug to check for water ingress and it all appears fine.

[fendervg 33]

You need spark, fuel and air - the last bit is usually fine. When you say voltage at the fuel rail, is this at the injector? This might only be 5v anyway to pulse them.

 

Did you check that you are actually getting fuel delivered to the rail by doing a pressure test (there's a small test outlet at the front left)or pulling an injector to check the flow rate? I could also be that your fuel pressure regulator has failed.

 

If it's not starting buy getting fuel, you should be able to see and smell fuel when you remove a plug after cranking.

[fla 9]

Check your 109 relay. Bridge it temporarily and try and start

[Thom 1]

Thanks,

 

Yep, voltage read at the 2 pin plug to the right end of the injectors.

 

I'm getting fuel at the rail, Have put a pipe on the little outlet and am getting fuel there, just the injectors aren't firing. The fuel is coming through the rail with decent pressure.

 

Thanks again

[fendervg 33]

As per fla, replacing/swapping our or bridging the ECU relay #109 could be worth a try.

 

Fuel pressure etc. seems to be fine.

[Thom 1]

Thanks for all the replies,

 

I've just bridged the ECU relay and still nothing :-/

[Keyo 47]

Immobiliser possibility but you say it cranks.

[Thom 1]

Yeh it cranks, ..and from memory the immobiliser will let it run for a few seconds anyway before cutting out. I'm just off to check all ECU grounding points and inspect the fuel pressure regulator.

[1xshaunx1 27]

Oem Immobiliser lets it crank but it won’t fire crank all day long without a hint of firing

I had a new key because of new barrel for my old Corrado and it wouldn’t fire up, turns out I needed the old chip out of the old key into the new one then sorted. This is how I know it will crank

Edited February 2, 2020 by 1xshaunx1

[Keyo 47]

Oem Immobiliser lets it crank but it won’t fire crank all day long without a hint of firing

 

Sounds like it could be the NO1 suspect then Shaun.

[1xshaunx1 27]

I’d certainly look at it but electrical gremlins and running problems are notoriously difficult to get to the bottom of, good look matey, keep at it.

[Thom 1]

Thanks for all the replies, I'm slowly getting through the checklist.

 

Would any VR6 owners be willing to check the voltage at their injector power supply plug with ignition on and let me know what they're getting?...might be that I can rule that out.

 

Thanks again

[1xshaunx1 27]

I trust myself with a test bulb, otherwise I’d understand what you said. I’m sure others understand you and can check

[Thom 1]

I trust myself with a test bulb, otherwise I’d understand what you said. I’m sure others understand you and can check

 

Haha, no worries Shaun,...cheers

[Thom 1]

Bump....anyone with a VR6 able to check what voltage they're getting at their injector supply?

[fendervg 33]

I think it should be 12v, but measured from the + pin to an external earth - otherwise you will see a pulsed signal, which would explain the lower voltage. The Bentley just says to check for voltage level and then to carry out a flash test with an LED bulb - I think the injectors are pulsed via earth back to the ECU, which cycles the earth connection,.. but probably someone else here would know for certain....

 

Have you removed the injectors to see if they are actually delivering the rated amount of fuel with the correct spray pattern(sorry if this has been asked already) ?

Edited February 7, 2020 by fendervg

[Thom 1]

Thanks Fender, Yeh I'm getting a low voltage even if grounding at the battery or on the chassis. I think that the 12v feed is shorting to ground somewhere along the wiring harness. Injectors are firing sporadically and I have 12v at the fuse box so am now working back along the loom trying to locate the short.

Wish me luck!

[1xshaunx1 27]

Good luck

[Dox 23]

Its rare that any ECU feeds circuits with 12V, when cranking an engine from cold so much of the battery's power is consumed turning the rotating parts creating compression at the same time that voltage available for other circuits drops well below the 12v you have at rest. So manufacturers build in a safety net to allow the circuits it rellies on to achieve a voltage the circuit can operate with, typically below 9V regulated.

 

So 5V at the injectors maybe the factory setting?

[fla 9]

Yes the injectors operate on less than 1V , like Dox suggests it could be 5V. Are the spark plugs wet after cranking or can you smell any fuel?

[Dox 23]

Bentley manual 24-470 gives data for injector testing, but doesn't give trigger voltage at the injectors