Marelli V12 idle stumble

[poprivet]

The screen has done its job well, its protected the pump while the finer cartridge filter has protected the injectors.

Unless the pot was filled with rubbish I doubt you will have to clean it again for a few years

Hopefully it helps with the current engine running problem, if not, at least its another piece of important maintenance completed!

[oldtimer]

Thanks DavidR and folks

[steve_m]

Going back to the idle stumble mine has started playing silly buggers.
It has been intermittently hunting on start up; I'm not sure what revs it starts at as the counter is u/s but it drops significantly before picking up again and will do that for a few minutes before settling down. It doesn't seem to hunt if I drive straight off.
Last week it seemed to stop completely for half a second or so which was a bit worrying as I was booting it past something at the time; interestingly the speedo started working after that (most of the anyway).
Today it decided to stop completely in the rush hour in Hungerford high street which was a bit embarrassing especially as it was on the rise with traffic behind me.
It took about 4 or 5 attempts to get it going and then it seemed fine. When it stopped the only light that I saw was the oil light; I didn't notice if the battery light came on or not.
Doesn't bode well for my trackday in 3 weeks.

[Phil 18]

This is all made for very interesting reading. I have owned my 3.6 for about 9 years now, it has not crossed my mind to clean the swirl pot and filter, but after reading BB and David R's posts I think it is time to take apart and have a look at state of play. Have not had any problems but who knows what waits ahead after all it is 25 years old. This did remind me after looking at David R's pictures of a problem I had many years ago with a cortina inline filter to carb, would drive for a couple of miles and for no aparent reason would stop. Just goes to show the knowledge that can be gained through reading the BB. Sharing the knowledge great stuff.



Phil

[steve_m]

Anybody got any ideas on my little hiccup? I don't think that it is the swirl pot as the tank, pump and lines were changed last year plus I had a full tank of fuel (lotto win!).

[Brakebuster]

hmm



BB

[steve_m]

Ok, so I uploaded a video on YouTube, https://youtu.be/dwuBMOCIlBM, which shows the car hunting and smoking like the Flying Scotsman.
This only happens on the first start of the day and clears as soon as it is up to temperature.
Any ideas anyone?

[Brakebuster]

have you had a comprehensive compression check carried out, as this will determine what condition the piston rings and the valve seals are in

the hunting HAS to be the AAV , this is on the left back coolant pipe and is a known issue, when up to temp it shuts and allows the the idle adjust screw to regulate tick-over ,

the smoke is concerning me , though mine ' smokes ' at start but its actually condensation burning off for about three minutes at each morning start , this is totally normal , but ' smoke ' is not normal , so hold a clean white rag or paper towel over the exhaust to see what is being thrown out the back when its doing this , you could find the majority of it is steam

hope this helps in some way

BB

[steve_m]

Thanks for the reply Vince
Compressions 2 years ago were as follows:
Readouts for Cylinder Compression :
1A 201 2A 199 3A 200 4A 202 5A 201 6A 204
1B 198 2B 210 3B 202 4B 195 5B 205 6B 200
I haven't done any significant mileage since then so I don't see that there should be any noticeable wear; all 4 pipes are pumping out the same volume and pressure of exhaust so unless all the compressions have dropped equally it must be something else.
It is more like steam than smoke but seems to be getting worse although it is quite cold and very damp at the moment.
I was wondering about the AAV; if this is playing up could it cause the car to just cut out and then be reluctant to restart?

[Brakebuster]

compression seems fine , so the majority must be ' steam ' and yes, the colder and damper the day the more visual this gets

as for the AAV , no, this will not cause the car to stall unless your TB's are set at less than 2 thou , so the engine could be starved of air , but slight pressure on the pedal would negate that

ensure the vac pipe to the ecu in the boot by the battery is correctly connected, as this does effect fuelling as indicated on the other site , the modulator for the gearbox can as stated allow ATF into the induction system, but this would be very white smoke all the time ,

cutting out engine could be anything electrical , such as capstan position sensor, loose wiring, poor each to the engine etc etc

process of elimination I'm afraid

BB

[steve_m]

Ta for that. Off to work tomorrow for 3 weeks so I'll attack it then but I'll order a new AAV.

[BigCatXJS]

An incorrectly set AAV (and whatever thst valve is called that allows extra air/fuel in when the air con compressor kicks in) can stall a car in traffic. I can only relate to my own experience some years ago. We were travelling through central London en-route to a hotel the night before a Jag London to Brigton event (the Dulwich college start). I had only got the cat back from the garage literally the day before. Seemed that the AAV had been adjusted (tightened) when the engine was not at full operating temperature. The effect was 500rpm tick-over with both fans running and the air con running hard (it was a hot day - unusual for April). At one point, I approached a junction slowing down and the cat stalled just as the air con compressor kicked in! So I adjusted my AAV (slackened) and all was well. I still suspect that there is an issue with a lack of off-set/compensation for when the air con compressor kicks-in but I cannot recall what the valve (or circuit) is called that controls this behaviour.

Ta, Rich

[Brakebuster]

Rich , the theory is perfect

but there is however an EAV ( extra air valve ) on the right bank airbox that electronically opens when the aircon kicks in to allow the idle to stay the same, I'm not saying your wrong, but that another device that might have failed may well be contributing to the issue

as i said, there are lots of small issues that could result in such behaviour, all of which need checking out

BB

[steve_m]

Ok then, plenty to look at when I get back; hopefully it will have warmed up a bit in 3 weeks.
In the mean time I have ordered a stethoscope to check out the injectors, only a couple of quid and a useful tool.

[BigCatXJS]

Rich , the theory is perfect

but there is however an EAV ( extra air valve ) on the right bank airbox that electronically opens when the aircon kicks in to allow the idle to stay the same, I'm not saying your wrong, but that another device that might have failed may well be contributing to the issue

as i said, there are lots of small issues that could result in such behaviour, all of which need checking out

BB

Thanks Vince - EAV - that's the one I could not recall! I suspect that still may not be right on mine as the revs do drop when the air con compressor kicks in. I'll need to check...