gti 8v not starting

[rutter123]

removed the inlet manifold to fit new gaskets (of which none were fitted) and gave the throttle body a good clean up as well, re assembled as per disassembly checking everything twice, and now point blank refuses to start, there is agood spark, there is fuel in the rail, and it turns over ok, but dead as a dodo, i only disconnected the coil the throttle pos sensor and the ecu, the fuel pump runs and the plugs have been cleaned and gapped, does it matter which connector goes to which injector? everything else is exactly as it came apart as i took photos,

any ideas?

[sdelasal]

Are the plugs getting wet i.e. is fuel getting injected? If so, there should be at least a hint of something firing - unless the plug leads are incorrectly connected. Perhaps try spraying some easy-start into the intake manifold to identify whether you have a fual or spark problem. steve

[rutter123]

the plugs are dry, no hint of firing, plug leads are correct, sure its a fuelling prob but still no joy. and cant see where i went wrong, if i did?

[rutter123]

have removed the inlet manifold again and can see that the injectors are bone dry, not even a hint of any petrol?? poss cause? tho the rail is full of fuel it seems its not going any further than that for some unknown reason.

[bx petrol auto saloon]

Dear rutter123,
First question is, does the car have a fuel pressure regulator fitted to the fuel rail ?
Second question is, is the fuel pressure regulator vacuum operated or electrically operated ?
It may be that the fuel pressure regulator is only allowing fuel into the fuel rail, but not at a sufficient enough pressure to open the injectors.
Vince,

[mat_fenwick]

It doesn't matter which plugs go to which injector, as they are fired as a batch not sequentially.

[rutter123]

there is a fuel pressure reg fitted on the rail, vacuum type, this has not been disturbed so dont see y it would cause any probs, there is fuel pressure in the rail but i dont know how much.

car was previously running/starting up until, im stumped as my petrol engine knowledge is limited.

is there any way of checking the injectors are getting power?

[mat_fenwick]

There will be an ignition switched 12 V to one side of the injectors (easy to check), and a switched earth (less easy to check!) to the other. Search eBay for noid light, or you can make your own with an LED & resistor.

I think the injector supply is shared with the fuel pump so if that's running it's likely the injectors also have power.

[Tinkley]

Personally I would check the fuel pump. Unless it is all high pressure (steel tube) just ensure a reasonable flow to rail. The small orifices in the spraying nozzles on injection are pretty small and may have become gummed up, at least partially if it has been allowed to dry out. You should be able to remove and clean out with carb cleaner, at least I have been able to on my only inj machine an Aprilia. A real cheeky one might be to take off inlet air manifold and squirt carb cleaner in there to see if it fires on that. It would then eliminate the need to test the current supply to the injectors.
I would think a test meter (or even a 12v bulb) to the injector power lead would test for current OK. No reason for it not to be 12v DC.

[rutter123]

thanx for that chaps i shall be re fitting the inlet manifold this eve and will check the injectors for power, also have a can of dampstart to hand to hopefully "prime it" into life.

[Way2go]

I would think a test meter (or even a 12v bulb) to the injector power lead would test for current OK. No reason for it not to be 12v DC.

Beware!!! The injectors are not raw 12v, they are fed from the ECU which puts out a mark-space ratio controlling at least 4 different spray patterns for different engine conditions/demands. A test meter or bulb will not tell you anything meaningful, an oscilloscope may but connections are critical if you want to avoid damaging the ECU.

[Tinkley]

Thanks W2G, would it be best to use one of the remote (horseshoe shaped) current detectors? and what current would you expect to get? I suspect you just need to check that there is input to the injector. The ECU is obviously controlling the injector pattern/fuel feed but will need current to power the internal mechanism. There's more than one way to actually achieve different flow patterns mechanically and electrically so different manufacturers have different designs. How would you suggest testing the cable feed to the injector is 'live' with relatively simple ie garage/home diagnostic stuff?

My Aprilia has twin injectors each with its own feed of cables. The 'plug in' is similar to the BX ignition system (carb version) push on black plastic rectangular item with springy stainless wire release/lock. Pretty much every other petrol injection system I have looked at has been similar.

The ECUs seem to be just a bit pricey, I've heard of £800 to over £3k+ (new) depending on vehicle. Older ones might be a bit better on price, but a lot of MGs' had trouble with them - after the spares dried up!.

[mat_fenwick]

As I mentioned before, you can check the live feed to the injectors fairly easily, as on the BX it's a switched earth. Just a meter set to voltage with the negative probe on a good earth, and the positive probe on one leg of the injector wiring. I'm pretty sure the 12 V supply is fed not via the ECU, only the switching side but in light of W2G's comments I'd want to check before using anything that draws significant current such as a test lamp.

To check that it's actually switching, the cheapest way is with what's termed a noid light - you can get a set to cover different vehicles for just over a tenner. I made my own from a spare injector plug and a couple of LEDs and resistors (I wired mine with LEDs in both directions to cover vehicles that are wired the other way around). I do have an oscilloscope, but the battery life is frustratingly short and you don't always have a mains power supply available when tying to diagnose a sick car!

[Way2go]

It does seem unlikely that all 4 injectors would spontaneously fail. Maybe one has gone permanently short circuit? Check out resistances or disconnect one by one and try for a start.

Also you say the rail is pressurised? Are you sure its not a fuel issue? The electric fuel pump is controlled in two ways as I discovered during my own faultfinding (1) via the cranking position of the ignition switch and then (2) after a start by separate circuits. You can see whether fuel is being pumped by disconnecting the feed hose (care) and placing it in a clear bottle. It will only spurt fuel in the cranking position. It will only continue to run in the "ignition on" position after a successful start which you cannot see when testing this way.

[rutter123]

will be trying a start again tmrw, no time to do anything in last few days, need to finish re assembly and try again.