Poor starting then cutting out.

[peanut]

Frenchy
if you have another go at the pig next w/e might I suggest you try removing the DME relay altogether and replacing it with a 3x wire bypass whilst you test (as described on clarkes garage.)

The beauty of testing with this in place is that you then know with some degree of certainty that both the fuel pump, ECU and Injectors are getting a continuous power supply plus if the engine now runs you've identified the faulty component and associated circuitry .If it doesn't run any better then you can probably eliminate the DME relay and associated wiring being the culpret.

The more components you can eliminate the closer you'll get to the culpret/s

Good luck ! I know just how frustrating this sort of problem can be from personal experience [&o]

 

[Frenchy]

Cheers Peanut, will give it a go fella, hopefully another session tomorrow, i WILL get there in the end.

 

[sulzeruk]

Jim, is it maintaining the correct pressure in the fuel rail? What are you getting with the engine cranking? Could be a reference sensor in the bell housing is going open circuit? They do get roasted at the back of the engine? Also may be worth checking the damper if the pressure is low on the fuel rail.
If the plugs are way rich, there is obviously excess fuel being burnt (or not) so be wary of fuel dilution of the oil as it is very easy to seize or trash a piston with all that fuel draining down the bores. I would be changing the oil when you get the fault fixed.
Alasdair

 

[tartan_rob]

My problem is similar but I don't seem get so far as the engine running! Cough, splutter and die.

On the Audi's you can disconnect the AFM and the ECU swaps in default readings. If the Porsche is the same,. maybe try this to finally eliminate the AFM?

 

[Frenchy]

Cheers people had another go today, it will not start at all, changed out the throttle position switch, no joy as i fitted it to the 220 this evening and it ran fine [] noticed that the DME was chattering when the spare ECU was tried but okay on the donor,still not starting though.
3 bar fuel pressure showing at the fuel rail gauge (Aftermarket jobbie) and staying at that pressure throughout cranking, checked with a spare plug and getting a spark, crank sensors has to be next, any tips ?
Also what does the third sensor on the bracket do, it terminates at the back of the cam cover in a blanked off 3 pin plug, is it used for setting up TDC ?

 

[tartan_rob]

How are you checking you have a spark? Pre or post distributor cap?

If its post cap, then your crank sensor is likely to be working. May be wrong though...

 

[peanut]

ORIGINAL: Frenchy

Cheers people had another go today, it will not start at all, changed out the throttle position switch, no joy as i fitted it to the 220 this evening and it ran fine [] noticed that the DME was chattering when the spare ECU was tried but okay on the donor,still not starting though.

Frenchy I know how difficult it is to decide which advice is pertinent and which is not but you need to trust me about fitting the 3x wire bypass in place of the DME relay. Its standard practice when troubleshooting the Bosch Motronic Fuel and ignition systems.

Until you do this there will be a whole raft of stuff that could be giving you intermitant faults and you'll not know what it is. If its definitely the DME relay chattering then you definitely have an intermittent fault like a bad connection with either the DME relay earthing or the ECU earthing or the relay itself or the ECU and its connector or the power supply and wiring associated with these components, not forgetting the ignition switch and wiring of course that supplies the DME relay.

If I were you I would forget the ignition side of things for now and make sure that the DME and ECU are working correctly because they control your ignition and fuel delivery .

I would remove all the fuses and relays and the fuse board and clean and check all the connectors .Whilst you are there under the dash there are two large Earthing points which are for the DME relay and the ECU strip them and clean them really thoroughly (MPll and MPlll )

Do the same with the CPS sensor connector and the Hall effect connector at the back of your distributor cap.
The Hall effect sensor works in conjunction with the flywheel (reference) sensor to tell the ECU when No1 piston is coming up on its firing stroke and allows the ECU to control the ignition accordingly. If its not working properly the car will hard start and run badly or not at all.

Hope this is helpful

 

[Frenchy]

Cheers Peanut,
My next move this weekend will be the DME bypass and then strip and clean earths and relay blades etc, i will also remove the crank sensors for a clean and a coat of looking at, dark nights, miserable weather and the fact that the car is stranded at my other garage means that progress is slow at the moment.

I was checking spark at the end of a plug lead with a spare plug, it would not start at all yesterday and whipping a plug out found a dry plug but i have 3 bar fuel pressure,fuel pressure but no injectors driving ?

 

[peanut]

if you had a Noid light you could check that the ECU is pulsing the injectors . They are quite cheap on ebay usually in sets of 4x

Alternatively you could use a multimeter to make sure that 12v+ is getting to each of the injector connectors with the ignition on.

Forget about spark and ignition for the present. The ignition spark comes from the ignition amplifier which is pulsed by the ECU and the timing of the ignition comes from the ECU in conjunction with the hall effect sensor which you queried located behind the distributor .

You need to concentrate on getting power to the ECU , fuel pump and injectors first .The ECU internally controls the earthing of all the vital components ,If the ECU is not being powered you'll get no ignition or fuel
.
With the 3x wire bypass in place of the DME relay you should get a constant 12v+ to all of the above even with the ignition switched off. Check with your multimeter.The result of those tests will determine where to test next.

 

[Elliot]

sounds like failed diaphram in the regulator / dampner on the fuel rail to me.
remove vacuum line - check and if fuel coming out replace regulator
replace oil as fuel in oil will thin and not coat the engine parts sufficiently

cheers