93 4.0 no start...

[guyd]

Its not actually MY car - its my friends (whos in germany on work for the foreseeable) - so please excuse the ignorance..

we have been having some problems with the immobiliser - the original TVR one, not the foxguard one (which is now disconnected).

The foxguard one has the larger of the two plugs unplugged, and the smaller one left in. It is totally unresponsive to the zappers.. thats why its unplugged. It has run like this, so Im fairly happy that its not the problem.

the fuel pump primes quite happily, and i get a spark (fat and healthy) - but i dont appear to get any injector pulse (multimeter on an injector plug shows nothing)

I'd like to remove the foxguard alarm completely - but - as has been said several times on here - I am unlikly to get an answer on this until I have done some more mileage...

So - any tips? Anything non-security compromising?

[chassis 33]

What setting have you got the multimeter on, if your simply measuring for 12vDC its doubtful you'll see anything, try AC, or hook a bulb up to the connectors.

Is the cold start injector firing?

Regards
Iain

[guyd]

i had it on 10mV iirc - the minimum setting. Checked that it would show by connecting to my volvo 940 injectors - yes, i get a reading. but not on the tvr -

wheres the cold start injector?

[GreenV8S]

Does the engine turn over?
Do you get a tacho reading when it turns over?
Do you get a spark when it turns over?

If the answer to all these is 'yes' then it may be that the ECU isn't seeing the signal from the dizzy. In this case you would also find that one side of the injectors was at 12v ish when the engine was cranking, and the other side was floating (the ECU pulls it down to open the injector). The signal from the dizzy is carried by a single wire from the dizzy that runs along the near side rocker cover and into the passenger's footwell. It should have a diode in series somewhere near the bulkhead.

[guyd]

GreenV8S said:

Does the engine turn over? Do you get a tacho reading when it turns over? Do you get a spark when it turns over? If the answer to all these is 'yes' then it may be that the ECU isn't seeing the signal from the dizzy. In this case you would also find that one side of the injectors was at 12v ish when the engine was cranking, and the other side was floating (the ECU pulls it down to open the injector). The signal from the dizzy is carried by a single wire from the dizzy that runs along the near side rocker cover and into the passenger's footwell. It should have a diode in series somewhere near the bulkhead.

yes - it turns over!
Yes - I get a fat healthy spark (i thought i mentioned that?)
ish - I get a slight wobble, very slight, from the tacho.

I have seen the diode - is that the flat one with spade fittings on either end?

So the ign ECU is separate from the fuel ECU? I'll check the signal from the dizzy next then.

The voltage on the injectors was floating (wavering around a couple of millivolts) until cranking, when it went to zero (hard zero)... this seems to support the statement above, if both ends are floating etc


hmmm

[Nuggs]

GreenV8S said:

Stuff

Sir, I salute you. Your knowledge and willingness to share it is really very impressive

You deserve one of these:

[guyd]

seconded...



(ill buy ya one if it works )

[GreenV8S]

guyd said:

I have seen the diode - is that the flat one with spade fittings on either end?

That's the one. Sometimes the diodes give trouble. As a saity check, if you connect a volt meter on the ECU side of the diode you should see the voltage going up and down when you crank the engine over. If not, work back towards the dizzy and see where it is getting lost.

guyd said:

So the ign ECU is separate from the fuel ECU? I'll check the signal from the dizzy next then.

It doesn't have an ignition ECU as such, just the clockwork dizzy. All that requires is an ignition switched 12v supply to the coil+, so if you are seeing a good spark that proves that the ignition supply, dizzy, coil and ignition module are OK. That leaves the fuel side as the main suspect. The fuelling is managed by the ECU. The only connection between the fuel and ignition systems is the signal wire from the dizzy which tells the ECU how fast the engine is turning.

guyd said:

The voltage on the injectors was floating (wavering around a couple of millivolts) until cranking, when it went to zero (hard zero)... this seems to support the statement above, if both ends are floating etc

That doesn't sounds quite right. What you *should* see is that when cranking, one side of the injector gets 12v and the other side toggles between floating and pulled down to earth. If you don't see 12v this points to a supply problem. That could be a simple electrical fault, wiring, fuse, relay etc or it could be caused by an immobiliser.

Sanity check, do you hear the fuel pump run [1] for a second or two when you switch the ignition on? Does the fuel pump also [2] run while you are cranking the engine over? If so this proves that the ECU is [1] powered up OK and [2] seeing the signal from the dizzy.

[rfisher]

Talk to your ECU.

www.pistonheads.com/sales/54383.htm

[guyd]

hmmm - 12v at the sockets for the injectors with ign on - as soon as i spin it over, it drops to near enough zero volts. On both sides of the socket...

I get a pulse of sorts (difficult to tell with a slow digital multimeter) on the diode (both sides) - so I assume the ecu is getting a signal.

Left indicator is stuck on now.... (as in stays on, not blinking)

any ideas???

[GreenV8S]

No power to the injectors while cranking is a fundamental problem which you need to track down. It may point to a problem with the main power relay, or an immobiliser playing up, or a fuse/wiring fault. I suggest this is where you need to focus your attention.

Indicator sticking on is wierd, might suggest the indicator relay has got stuck or you have a wiring fault. Alarms are often wired into the indicators so the alarm is an obvious common point of failure for these two symptoms.

The only alarm problems I've had to date have been simple wiring faults in easily accessible parts of the loom. Once you get past these trivial problems, alarms can get very tricky to diagnose because by their nature they are designed to be obscure and tamper proof. If you come to the conclusion that it is an alarm related problem, this may be time to call in a specialist. Is the alarm generally behaving as normal in terms of beeps and flashes etc?

If you get really stuck, you only need a couple of basic systems to getthe car running and it would not take a huge time to hotwire the car sufficiently to get it driving. This is really only a last resort though, for example if you *have* to get the car to somebody to fix it, or you are left stranded.