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BMW 2.8 straight 6 petrol.
Runs fine when cold.
After about 10-15 minutes it starts spluttering about 2,500rpm and then will not rev and hold steady at 2,500rpm or higher.
This is recorded with the camera held under the bonnet while the car initially idles and then tries to rev to 2,500rpm
Not really but I'll take a guess. Inlet manifold leak or vacuum advance leak ( if it has one 🙂 ) or advance / retard failure
I had a loose boost pipe that would do that. it wold blow as the revs get higher then it would drop and close.
but the bigger clue was victorian levels of smog out the back and the lack of ability to take on anything over dead flat.
Air leak?
My guess too. Just got to find the bugger
Doesn’t sound great idling either, as if it’s perhaps only using 5 of the 6 maybe…
Spray something flammable around the engine bay on all the pipework - if the revs rise then thats where the leak is
Oh hang on - its WCA - do not take this advice 🙂
Can’t see the video. My starters for 10 (depending on which engine it is) are either VANOS related or the crank position sensor.
Is it throwing an EML or restricted performance message via the iDrive?
What you need is the fault code(s).
Witness WCA taking a swig of petrol to blow into the engine bay
1997 engine but no error codes. New plugs and coils.
I suspect the air intake as I had it apart before doing the plugs to fix a different problem plus it is a home made bodge to connect the 2.8 engine to the better breathing 2.5 intake so lots of silicone and jubilee clips unfortunately
advance / retard failure
WCA’s login in a parallel universe
Throttle position sensor/switch.
It thinks it’s still in idle.
Wild guess really rather than proper diagnosis.
BMW straight six ? Sounds like a briggs and Stratton lawnmower engine.
Doesn’t sound well at all.
Phone held in the engine bay just above the modified air intake. Sounds quite normal from outside or sat in the car. I just wanted to capture the funny rise and fall more clearly.
Throttle position seems less critical than revs. It does the same thing in every gear at 2,500rpm but that is different points of throttle travel. Also, only happens when hot.
Poor running when hot is usually a sign of a failing HT lead but I'm guessing this engine has coil-on-plug instead?
Manifold /vacuum leak tends to be worse at idle, and youd get lots of popping and banging on the overrun as the lean mixture doesn't ignite in the cylinders. Not wanting to rev is usually an ignition problem IME.
Poor running when hot is usually a sign of a failing HT lead but I’m guessing this engine has coil-on-plug instead?
+1
I had it apart before doing the plugs to fix a different problem
My guess would be either the replacement parts are faulty or you've messed something up in putting them back on.
I will double check the coils and plugs in the morning. Thanks
When driving and accelerating from 2000rpm upwards, everything starts fine and then the spluttery revs and a bit of woofly pop from the exhaust but not in a nice or sporty sound, more like engine has over eaten something and it trying to cough it back up
do the engine revs rise high with minimal throttle opening? IMO you want to figure out if its lots of air (wide throttle * high revs) causing the issue or just high revs. if its lots of air (so it happens when you are using WOT at lower revs) then it might be maf.
you might be able to get a diagnostics tool with a live feed of sensor readings on it - that'll help identify anything that looks strange
Plug in a code reader? Not all errors throw a light
Sounds a bit like lean surges. Mine (not a BMW) sounded similar when the intake air temperature compensation was incorrect.
Basically fine on cold start but as the engine Temperature increased Vs the intake temperature it would go lean when not under load. Under load the MAP sensor would sort it out.
Most apparent on hot starts in cold weather, once the afterstart enrichment cuts out.
When I was first fitting the 2.5 inlet manifold to the 2.8 engine there was one pipe I needed to connect which was impossible to get at without removing most the ancillaries from one side of the engine bay. The simple solution was to cut the pipe where I could reach it and then attach the new pipe. That worked fine for 7 years but now that last little bit of the pipe has perished so I stripped the friking car down to get to it. Just before realising it is Sunday and the replacement hose shop is shut 🙁
Can't edit the last post but this is the culprit. Removed along with half the friggin engine it feels like.
