Space Horse
Another thing I have run into, when I haven't driven my car for a weeks or months. There is quite a lot of condensation build up within the exhaust and the car will spray out a load of water and struggle to start and then continue to spray for the next 30mins. I think it is impossible for a hot exhaust to have any water that isn't a very hot vapor, but we are talking about an unknown.
I think it is on the fuel side, even though a failed ITB test might point to an air issue. Maybe it is a fuel pump issue.
A lot of water in the exhaust is usually a common issue with cars that do a lot of short journeys where it hasn't warmed up enough (assuming no head gasket or EGR cooler problems!). Most of the water comes from burning fuel, although I guess if you're in a high humidity climate that's going to add to it.
Anyway, in my years as a mechanic I've not come across this water build up in the exhaust causing any running or starting problems. Any water that is obstructing the exhaust would be blown out in seconds as the engine is fired up.
My M3 doesn't normally do short journeys anyway, the trip to the workshop is about the only one, which ordinarily would be once a month at most (for levels and pressures, but I normally do them at home now).
I wondered about a fuel pump too, but discounted it for 2 reasons, no fault codes and under full throttle (once past the hesitation) from (say) 2000-8300 RPM their is no problem with power delivery.
Also, on Bedford Autodrome circuit in May, along the longest straight I accelerated to ~142mph
, redline in 4th gear, obviously WOT, their were no performance issues there either. This will be far more demanding on the pump than a brief snapping open of the throttle at ~1500 RPM.
Further to my octane comment earlier, according to Wiki, apparently the US (Canada, Brazil and Mexico) uses AKI/PON rating for petrol, where as the UK and most of the rest of the world uses RON.
Petrol equivalents.
Standard (regular UL): 95 RON (equivalent to 91 AKI).
Premium _____ (SUL): 98 RON (equivalent to 93 AKI).
SUL 99 RON = 93-94 AKI (confusingly! So maybe 93.5 AKI? lol).
I would suggest your SC M3 could benefit from using 93 AKI octane petrol
.
Re power/power+ setting, curious, you'd think the quick acting throttle would make the hesitation worse.
I could try that for diagnostic purposes, but not a permanent thing, as something is clearly getting worse.
Quote:
Originally Posted by DrFerry
My two cents about a possible root cause: - Fuel quality makes a difference
- Carbon deposits in/on the injectors and plugs
- Fuel pressure sensor
- Manifold pressure sensor
- Differential pressure sensor
- Carbon deposits in the ICV
. |
Hmm, well point 1, I usually fill up using Tesco's (supermarket) SUL 99 RON petrol, depending what sources you read, it's either a 'meets bare min standards', or is '
just as good as premium fuels'. So who knows!?
But the problem has only been noticeable past 2-3 years and only more significant over the past year or so.
I've been using mostly Tesco fuel since I bought the car end of 2019.
Re point 2.
Injectors, is this even likely with port injectors? I know it certainly can be with DI injectors, but I thought port injectors pretty much avoided that.
Plugs, guess I'd have to take them out and have a look, but seeing as I do very few short journeys and do a couple of track days each year, I would've thought any carbon would get burnt off?
Point 3
Would need to test that, I'm pretty sure we have a fuel pressure gauge at work, but hooking it up is probably going to be easier said than done.
But this would also have the benefit of eliminating the pump.
For my future reference, from ISTA :-
13 31 Fuel Pump with Drive and Pipe S65
Fuel pressure when starting 5.55 - 6.85 bar
At idle approx. 800 rpm (engine at normal operating temperature) 3 bar
Point 4
Already tested, well at least as much as ISTA asks, which is basically to compare the IM press sensor reading to the ambient pressure reading with the engine off, they match, so seems good.
Point 5
What's that? lol
Point 6
(Idle control valve, right?).
Well that's interesting, I recently posted the following at m3cutters, but forgot to here.
"I did find a couple of weeks ago that I had forgotten to plug in the air intake feed pipe for the ICV from some months back!
That said, when I plugged it back in it made no difference to the problem (and as far as I can see, the only issue that would cause is to have unfiltered air going into the ICV/engine
)."
Perhaps some dirt has got in and is causing the ICV to stick open briefly? Although, that said, their is no problem with idle control.
On a separate issue, I earlier said that these don't have a MAF, but it actually turns out they do, not for the main inlet system, but the secondary air system. So something else I need to check!
[edit]
On further reflection, something I mentioned at m3cutters previously, I think I'm going to take the plenum off and check for air/vacuum leaks before going through the above items.