The V8 Owners Forum -

No, not me!

A mate of mine has a V8 in his MGB.
As you know I'm no good on EFI stuff


Here are his comments.

""The car is not starting! It turns over, I have spark and petrol, but obviously not in the right way cos it's not showing an inkling of starting. Not even the odd 'nearly'. Nothing. Zilch.

Reminder: car is a V8, EFI, Lumenition Optronic ignition.

I'm happy with all the 'normal' checks, my question here is very specific.

Are there any EFI checks I can do? Such as any voltages I can measure across sensors, injectors, ecu or anything?""

First make sure the feed from the coil negative (via an in-line resistor) to the ECU hasn't got unplugged. With no tach signal, the injection won't.

Is the fuel pump running and pressuring the fuel rail? Just how it runs on starting depends on whether flapper or hotwire. If in doubt, jury rig a supply to the pump relay so it can be made to run all the time.

If that is ok, unplug the EFI coolant sensor. This will cause the mixture to go fully rich as for a cold start. When they fail, it is usually short circuit so the system thinks the engine is hot, and won't start when cold.

Ramon Alban's site has lots on flapper fault finding.

http://www.vintagemodelairplane.com/pag ... nts01.html

Hi Perry
There are various checks but first can yu smell petrol at the exhaust pipe? It eill tell if there is anything being injected or not. - My guess would be not.

Then when you turn the ignotion on you should hear 2 relays click and the HP fuel pump should whit for about 5 seconds to prime the system. If this does not happen check the relays next to the Ecu

After that you are down to checking resistances between pins on the multiplug - check on Ramon's Model aircraft site for what resistances between wat pin - that will aim you at a faulty sensor or similar

Ian

Must type faster!

ian

How is he sure there's fuel? has he put a pressure gauge on it?

Worth checking that the coil -ve signal reaches the ECU. I can't remember which pin, and I dont' know which EFi setup he has. But I'm sure it's the same pin on the ECU for SD1 and Range Rover EFi's. If there's no coil -ve signal on this pin, the ECU doesn't realise that the engine is running.

Chris.

ChrisJC wrote:How is he sure there's fuel?

Chris.

Hence my question can you smell petrol at the exhaust ?

Ian

its always worth checking the over run valve .. that cuts the signal from the coil neg ?????????

Thanks for the replies chaps. I'm passing them on. Jimmy has tried to register on the forum but says he cant for some reason ??

The various advices have a few subtle differences.
The Hotwire runs the fuel pump for 5 seconds, the Flapper doesn't. It only runs the pump when either cranking or when there's air flowing through the AFM. You can test it by poking the flap in the AFM.

I think that only the Range Rover EFi had the overrun cutoff valve, but I stand to be corrected on this point!

Chris.

And the most important question.....

Has this setup ever started and run ? Or is the fitment of the Lumenition a new thing ?

hasn't flooded it has he?

Sorry I should have said. This setup has been running for 2 years so far until the other day.

Right, I'm registered, at last. Thanks Tony.

Thanks everyone for your replies. And thanks Perry for posting it for me.

Yes, it's been running for about three years now. It literally started running lumpy one day, took it home, in the garage it was running lumpier and lumpier, then stopped.

Fuel pressure is around 37psi.
Spark is present
Petrol at exhaust and on spark plugs, although I would expect a stronger petrol smell on the spark plugs.

I have found a great note with various voltages to check on the ecu.

How do I check the voltages with the ecu plugged in? Do I need to roll back some wire somehow, or somehow undo the plug whilst leaving it plugged into the ecu?

Thanks for all your help to date.

Jim

If it's a flapper, the cover can be removed from the plug giving access to probe the contacts while plugged in. Not familiar with the hotwire setup.

It would help if you said whether it is a flapper or hotwire. However, I'd check all the sensors etc individually while not powered up before anything else.

TBH, if you have a good strong spark at all plugs and seeming to be at the correct time.

There isnt a lot of point probing voltages all over the place. The ignition system can be deemed working.

So then you need to establish if the fuel side of things is working. ie are all injectors getting triggered ? Does the fuel pump actually run and supply fuel at all times when it should ?

Are the plugs wet or dry ? Or soaked.

If soaked, bin them. I never trust soaked plugs. Sometimes drying them with a blowtorch works...often it doesnt. But when it doesnt, you never really know and that could be a further problem causing a non start when in fact everything else is fine.

If you've covered the above, and the engine can actually get air...then it should be making some attempt to fire.

if it isnt making an attempt to fire, then it cannot be getting spark to all 8 at the correct time, and it cannot be getting fuel injected.