Andre,
You appear to have enough fuel pressure that would get the car to start.

Don't check the fuel pressure yet, unless you can get a gauge.

It doesn't sound like the ECU is the problem.

I would check that you do have compression...............

The green wire that is being referred to is on the earlier engines, not yours

 

Having the compression measured will be the next step. Problem is I have to arrange a flatbed to get it there. And although it would not be like riding around our cosy little village naked on the back of a truck myself, the feeling will not be far from that.
When searching the archives, I found a couple of other things to check, but they also give me more questions.
Here they are in random order:

The spark plugs spark. Can it be the tension isn’t high enough, for instance caused by one of the coils?

I think the battery drains pretty fast while starting the car. It takes about 1 minute of starting before it won’t crank anymore. Could this be related?

Could a faulty Alternator/AVR cause a lack of power to fire up?

What do the vacuum lines do and could a serious leak prevent the car from firing up?

Can a faulty O2 sensor prevent a car of starting at all.

I disconnected the MAF so that the car would go to “limp home” mode. No start. Does this rule out all sensors and info the brain gets, or only the MAF?

Could the engine speed reference mark sensor be culprit in my case?

Hope you can help me out.

 

Having the compression measured will be the next step. Problem is I have to arrange a flatbed to get it there
>>>>>>>>>>
Try and get the garage to let you borrow a compression tester, it's not expensive, you could even buy one for yourself.

The spark plugs spark. Can it be the tension isn’t high enough, for instance caused by one of the coils?
>>>>>>>>>>>
Theoretically, it requires a "bigger" spark to fire the compressed gas than in open air. But the 928 system is very powerful. As there are two independant systems in the 928, it should show life on at least 4 cyclinders..

I think the battery drains pretty fast while starting the car. It takes about 1 minute of starting before it won’t crank anymore. Could this be related?
>>>>>>>>>>>>
You need to know the state of charge of the battery before you can say that. Disconnect it from the car, and give it a good charge - at least 15 hours at a 3A rate.

Could a faulty Alternator/AVR cause a lack of power to fire up?
>>>>>>>>>>
A very high alternator output voltgae can cause misfire, but I don't think it would give a no-start.

What do the vacuum lines do and could a serious leak prevent the car from firing up?
>>>>>>>>>>>>
It would have to be a very large leak of false aitrinto the manifold to stop it even trying to start....

Can a faulty O2 sensor prevent a car of starting at all.
>>>>>>>>>>>
No, the ECU will go to stored defaulyt settings. Under normal conditions, it does this until the cat warms up anyway.

I disconnected the MAF so that the car would go to “limp home” mode. No start. Does this rule out all sensors and info the brain gets, or only the MAF?
>>>>>>>>>>>
Only the MAF. Again, when the MAF is disconnected, the ECU reverts to a stored program "limp home"

Could the engine speed reference mark sensor be culprit in my case?
>>>>>>>>>>>
The Hall sensor on the end of one of the camshafts is used as a back up timing signal if the main flywheel sensor fails........so it should still start.

Beg, borrow, buy or steal a compression tester, see what that tells you.

When you try and start, after the first few attempts, do you then open the throttle ? This may be necessary if it is starting to flood.

Hope this helps

 

Wow John,

You keep amazing me. I didn’t expect you to come up with all the answers! (I have to make up harder questions).

Every time I charge one of the batteries (I have two) I keep em charging for 12 hours minimum at 9A. That should fill em up I recon.

I haven’t tried starting the car with full throttle. That’s what I’m going to try next and then try to get my hands on a compression gauge.

Thanks again!

 

Andre,
Take a look at the crank sensor on the flywheel. The connector gets brittle and can fall apart and result in an intermittant contact. The connector is under your air intake under the MAF.

 

Although the fuel pump is humming, the spark plugs are wet and smelling after fuel after cranking, and the exhaust smells a bit like it too, I took the fuel line loose from the fuel rail. The fuel came gushing out untill the rail was empty. I asked my girlfriend to crank the car but no fuel came out.

I was a bit irritated that all the signs for a fuel flow where there, but still that seems to be the failure. Even the WD40 trick in the inlet didn’t work. On the other hand I am relieved that my straitjacket can be put in the closet for the time being.

So resuming;

I took of the black cap of the right fuel rail. On the front, going to the left is a black hose (see picture (not my engine)) This is the one I unhooked. We started the car 5-6 times for about 5 seconds. No flow. Is this definitely a fuel problem? What should I check first, the pump or the valve?

Thanks Ernest,

I’ll check that sensor anyway, because the air-filter housing is already off and I heard that sensor can cause nasty failures.

 

Andre,
Were you lowish on fuel when you span the car ?

The S4 has two fuel pumps, one in the tank, and one outside, under the metal cover where the fuel filter is.

If you run the car so that the pumps are starved of the fuel which cools them, one or both can fail.

This may explain why you can hear a pump running, but you have no fuel flow.

Have a look under the cover on the fuel tank, at the rear of the car. Check the wires to the external pump are OK, and also check the ones that go to the internal pump (in the outlet from the tank)

Please be very careful when fuel and spark are about !

While you are under the cover, it might be worth checking the fuel filter.

Make sure you "counter hold" while undoing the fuel line unions.

 

Andre,

Lack of fuel,... swap fuel pump relay with identical relay,... replace clogged fuel filter,... replace bad pump

 

To check the fuel flow, the manual describes taking a fuel hose loose at the back of the engine, under the air filter. The picture illustrating this method are probably from an earlier model (but after ,84), because they don’t correspond. I didn’t want to just take one loose. I think it’s kind of scary thinking of this hot engine with a dripping fuel line over it. Instead I took the cover off the fuel tank and an took the fuel pipe loose coming from the filter. Bridged the fuel pump relay for 30 seconds. Didn’t even produce half a coffee cup full. Then I took off the line before the filter. The amount of fuel after 30 seconds was even less, like the pump was going to give up any second now, although it was still buzzing. (or was that the internal pump?) I wanted to take off the check valve, but couldn’t. Therefore I clamped off the fuel line coming from the tank, marked the poles and took the pump off, to check it out. I carefully checked the pump for the markings + and – (actually I took a quick glance). I couldn’t find them so I assumed that the bigger pole should be the +. I put some juice on it and it was stuck. Right at that moment I saw the markings + an - on the neck shining right at me. I took a brief moment to accept the fact that I’m an idiot and proceeded by reversing the poles. The pump was completely stuck now. Well, one thing is for sure now, the pump is broken! Although I’m not sure that I caused it. I can’t imagine that shortly changing the poles on a DC motor would cause it to break it.
I’m going to replace the pump and filter.

John,

I didn’t realize there being a pump in the tank as well. Does this mean I can take the clamp off and it wouldn’t drain the tank? Is the internal pump also driven by the fuel pump relay?
The tank was half to three-quarters full when I spun.
It probably has not much to do about me spinning. I think this is just a case off coincidence. To bad the car coincidently had to be on a racetrack, where I was coincidently taking a racecourse I just paid 140 euro’s for, coincidently being about 200 kilometres from home.

Hmmmmm…… makes you wonder if coincidence really does exist…………

 

I didn’t realize there being a pump in the tank as well. Does this mean I can take the clamp off and it wouldn’t drain the tank? Is the internal pump also driven by the fuel pump relay?
The tank was half to three-quarters full when I spun.
It probably has not much to do about me spinning. I think this is just a case off coincidence. To bad the car coincidently had to be on a racetrack, where I was coincidently taking a racecourse I just paid 140 euro’s for, coincidently being about 200 kilometres from home.
>>>>>>>>>
Andre,
You shouldn't run the pump with fuel feed into it, or it will overheat. But it does look as though the pumps were starved of fuel and damaged.

I don't know if the in tank pump will hold back the fuel if you unclamp the hose.

Try checking the intank pump on its own, Yes, they are both fed from the same relay, and wired in parallel. You should see the wires going to it.

Take care !

 

Thanks John, I owe you one!

 

Hi Andre,

Glad to hear you found the culprit - bad external fuel pump.

You may be able to get and return an internal pump provided you never use it. I would order both pumps, fuel filter, one of each common relays. Install the external pump and filter. Start car. If start, return internal pump. If no start, install internal pump. It may have its own filter - I don't know for sure. If there is a filter replace it too. Put extra relays in spare open spots on the fuse and relay board.


Correction - 89 has only one spare relay opening.

 

Yep, that was it. I fitted a new pump (external) and filter and the car fired up on the second try. It runs as smooth as ever.
The “cage” around the tank, holding the protection plate and the protection plate itself were badly corroded. They don’t seem to have gotten an corrosion preventive treatment. I took the opportunity to brush all rust away (put on your goggles) and sprayed a thick layer of anticorrosive paint (black tectyl). It looks much better and maybe did some good as well.

Well, and of story. Thanks to all for all your suggestions and support. The saga did make me begin to wonder what to have on board when you and the car go out for a drive:
https://rennlist.com/forums/showthre...threadid=87286

 

Hi Andre,
Good to hear a stiry with a happy ending !

If you want a new fuel tank support in stainless steel, and a plastic fuel pump/filter cover to replace your rusting old ones, see www.928spares.co.uk