1.8 apt engine wont start with spark plugs in but will with one out?

[carl350i]

Hi,

My audi a4 with a 1.8 APT non turbo engine will not start. It just cranks and cranks with the odd little cough.

Ive checked sparks, fuel, compression, fuses etc.

This morning I took one of the plugs out again to double check for a spark and it fired up for a couple of seconds with the plug removed.

It doesn't matter which plug is removed or even 2 at a time, but when all 4 are in no joy.

Any suggestions or similar experiences gratefully received.

cheers,

carl.

[zollaf]

4 coil pack or 1 coil and leads ?

[Mikedelta]

Another possible cause of contaminated fuel, where an engine may cough and backfire and try to apppear as if it is about to fire, this can cause catalyist to disintegrate upon a massive backfire and this in turn can cause complete blockage of the cat, which will not enable your engine to start, you may already have your cat blocked up and so by taking one or two plugs is providing escape route for exaust gasses, through spark plug holes.

Get a sample of your petrol in a clear glass thumbler, it should be pale yellow and very clear, if you place some newspaper behind the thumbler you should be able to read all the print through this pale yellow but clear uncontaminated fuel, if on the other hand the fuel is contaminated even by a few % of oil or diesel, it can cause some problems to starting and oil in the petrol will leave a layer on plugs and hence they may not fire.

I am currently looking at a 1.6 FSI Golf which refused to start, and has baffled everyone who had a go at it, no fault codes, but just by pure chance I discovered that its fuel was heavily contaminated, already we had had a few things changed thinking it must be something else, but never underestimate garages selling contaminated fuel.

My Calibra suffered this fate, and suffered enormous damage through reluctant to start and finally a tremendous bang and the cat disintegrated, car was towed to a Vauxhall dealers, who took 4 days to reach conclusion that I had filled my tank with diesel, but i showed a receipt from the BP garage and proved the garage that I did not stuff any diesel but 4star unleaded petrol back in 1996, so I rang the BP garage, and they referred me to their head office and promptly settled about a £1000.00 worth of claim, my car needed a new cat, drain aned clean fuel tank, petrol pump, replace petrol filter and changed engine oil which got contaminated by constantly attempting to try to start the engine, unburnt fuel went down into the sump, so engine oil change, oil filter and labour, the garage had been trying all kinds of things before figuring out that soemthing was wrong with the fuel, they even tried swapping the ECU, changed a few sensors!


On another VW Polo, contaminated fuel caused one petrol pump after another to seize the next day, each time we changed a fuel pump the next day it would be seized up, so it took us 5 pumps to replace before we realised that the fuel was contaminated! We take petrol for guaranteed because it smells strongly like petrol and our nose cannot detect contaminants, even diesel mixed with petrol will smell like petrol except if you then compare two samples one being contaminated and one being normal, against each other that you can tell them apart.

Good luck, but you must check your fuel first, if contaminated, you will need to drain away all contaminated fuel, replace petrol filter, flush petrol lines, clean tank, and refill with fresh uncontaminated fuel, then disconnect your cat, and then see if it would fire up. good luck. But take precaution when dealing with petrol and fumes, highly explosive and fire hazard., keep a fire extinguisher at hand.

[carl350i]

Good morning,

Thanks for the replies so far.

In response to zollaf its got a wasted spark arrangement, there is a coilpack over 3 and 4 cylinder and 2 flyleads going to 1 and 2.

In response to mikedelta the fuel was a clear yellow colour.

Another thing I did was to disconnect the crank sensor and it wouldn't cough or fire at all, when I disconnected the cam sensor it made no difference, should it?

cheers.

[Mikedelta]

But have you determined if your exhaust system is not blocked up? be it the catalyist, which is a common problem when it disintegrates into tiny pieces and ends up blocking the exhaust.

as for cranksensor, in most cars it is essential and without it the ECU won't know when to fire up spark signals, and will usually not even attempt to start as this can create backfire.

[carl350i]

Fixed it, the problem was with the throttle body assy, its one of those fly by wires things, whats wrong with a cable.

Anyway I found it was jammed shut and a good clean out later and it started first time.

thanks again.

[Mikedelta]

really glad you managed to sort your starting problems down to butterfly stuck in your throttle body which is controlled by a wire, again I agree what was wrong with a mechanical cable linkage! at least it was I am sure far more reliable, than is electronics, and used to be far more easier to adjust idling speeds and what not, thats technology for you mate! But remember one day the old days shall return, already Valve Amplifiers are coming back with vengence! (LOL)

[zollaf]

fly by wire throttles do make an engine more efficient . with a cable throttle the ecu has control over the fuel but with fby it also controls the air, so when you floor the throttle the ecu can open it as fast as the engine wants to still keep the mixture rich enough thus making the emissions cleaner and ultimately making the car more responsive. cruise control is also easier to link up to it as well as it can then be fully electronic rather than electro mechanical. thats the advantage, you already know the disadvantages

[Crasher]

Fly by wire also makes for a more sophisticated ESP system (if fitted) where the two ECU's working together via a high speed CAN BUS can alter the engine power independently of the driver to re-stabilise the car.