Quote:
Originally Posted by Assimilator1
No I'm not in the habit of lugging it before anyone says that   .
So this started a couple of years ago, initially only when the engine was stone cold (say upto 30s running) + cold temp's, pull away in 1st, roughly 1/4 to 1/2 throttle ~1500 RPM, it'd hesitate for about a second.
Because this scenario was rare and brief I just ignored it.
Fastforward to today and it has gradually got worse and worse, happening at increasing engine temp and ambient temps, and at less throttle (but always up to about 1500 RPM).
The other week the engine was a needles width from fully warmed up, when a work mate asked me to rev it up (of course I was willing to oblige!  ), it spluttered (hesitated) then revved up (slightly embarrassing, lol). So it's getting to be quite a problem now.
Blipping the throttle from idle (to say 2k RPM) will replicate it, the colder the engine and ambient temps are, the worse it is. More throttle makes it worse too (obviously I don't give it full throttle when cold!).
It reminds me of 2 cars I had when I was young (Mk1 Fiesta's), these had carbs with a manual choke, if I pushed the choke in too soon, they would hesitate just like that! lol. So it seems like a weak mixture misfire on snapping open the throttle from low revs.
No EML has shown, there are no engine codes (pending or current), I tried to read live data from the o2 sensors, but apparently that's not possible with these  (I used ISTA, an old version, and my work's snap on tool).
I did do a primary o2 sensors check with ISTA, and it found no problems, giving the sensors a very good score of 0.9.
I also did a spark duration check @idle, which was mostly in the range of 0.65-0.75 (which is in spec, spec 01.-1.5ms). And I checked combustion quality @ idle, which mostly was between 0.4 -1.3 (which is in range too, spec 0-5).
I use SUL fuel (99 octane), spark plugs have done 25k miles, IIRC the OE change interval is 36k miles? I was planning to change them at 30k.
If it is a weak mixture issue, then unmetered air could be getting in. I suppose I need to check air and vac hoses.
Standard s/w AFAIK, TAs were replaced just a couple of months before I bought the car!  . Although that was 5 1/2 yrs ago now, they are rebuild.org TAs and the car's only done about 12k miles since then.
I also very recently lubed the throttle linkage pivots/bearings with dry PTFE.
Did the ITB test and got a 'not ok' on 1 of bank 2's test, but still no error codes. Not had the chance to find out what this results means.
Checked inlet man. pressure sensor plausibility, that's good.
Turns out these don't have a MAF, lol.
I wondered if anyone else has had this, and what cured it for them? |
Well, I am going to say some stupid things to try and help lol. But with My car with a SC and being living at 6000+ feet I can definitely say fuel/air ratios are important.
My immediate response would be the TAs, but with them "fixed" I don't think it is them.
When my engine is cold (below freezing is worse), the engine almost refuses to rev. I think the mechanical limitations from the blower and it being cold where I think the ECU might step in to stop fuel flow, you have to convince the car to rev with several presses of the throttle. This is all happening in neutral.
However, once the car is warm, I have no issue and it's happy to scream.
My car is also way happier and easier to drive (6MT) at Power or Power+ throttle mode.
Before anything else, I would try driving the car in power and/or power+. I know it makes a world of difference on my car for what the peddle does. I really think BMW did some weird things with the throttle peddle when in normal mode. There feels like a lot of dead space where nothing happens. Very poor modulation in what the throttle does in terms of 0-15 vs. 20-30 vs 60-80 (MPH)
This is tune dependent but if I am launching my car and I go from 100% throttle 1st gear, and I accidentally (I have done this a lot
) let off the throttle to 80% at around 6500 RPM the car will almost stop increasing in revs and even once I go back to 100% the car will still behave the same.
I would seriously try the car with power and/or power+ even when cold. It might at least help narrow down the issue. As we all are familiar tune re-flashing, your throttle might simply need to be tuned.
My examples which are just like yours, either go away or are in angry driving. So, for it to still occur even when the car has been fully warmed up is odd.
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.
I'm gonna say something stupid. Are you ready? Are you sure?
Your octane is too high? Hear me out.
My VF-595 supercharged s65 runs on 91 octane even at sea-level. We are talking about weird, freaky, gremlins that are not leaving. I would think anything is possible. I am not familiar with what modifications you have but if it is mostly stock, maybe try a tank of 93 octane if you are comfortable with it.
All I am going to say is octane can be too high. Not familiar with where this engine is at in particular. If others have had no problem running SUL 99, then please ignore me for my absolutely outrageous reasoning.