Detonating 318i M40
Posted by Flyboy
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Hi Guys
Need your wisdom with regards to my little 318i M40, all of a sudden, out of the blue it has started to detonate under moderate load, WTF???? Isn't there supposed yo be a knock sensor to stop misbehaviour like this? So here is the low down, motor has 400K on it, and is getting tired now, uses quite a bit of oil, of which I have no doubt it is drinking a fair amount of it, although it is not smoking per se, only a nice big blue puff if you step on the gas after an extended period of trailing throttle, such as coasting down hill, which would indicate valve guides more than rings, the rest is escaping through a dodgy front main crank seal, which can stay as it is until the next cam belt change or engine overhaul, whichever comes first. Compression is on the low side, specs state service limit between 1000 -1100 Kpa, all four pots range between 925 - 975 Kpa, when measured about 3 months ago, note, there was no detonation at the time. It does not require a heavy throttle load to detonate, a moderate throttle load will get it pinging and detonating, it does not detonate when the motor is cold, only once it is up to running temp, fuel consumption is normal and has not changed, so I don't see a lean condition being the problem. She runs fine otherwise, just down on power. I use the same grade of fuel, as always, and put in at he same garages, so I assume fuel quality can be ruled out. My thinking is that there may be a build up of carbon due to the oil consumption, that is creating a red hot glowing hot spot, causing the trouble, seeing as that Bosch takes care of the fuelling and the timing. I am thinking a jug of cold water through the airflow meter to give the internals a bath and get rid of the carbon might sort the problem out, or am I missing something here?? Any ideas on this guys, I really would appreciate your input, I would like to sort the problem before it knocks unwanted ventilation holes in the top of my pistons. ---------------------------------------------------------------------------------------------------------------------------------- E30'S AREN'T BUILT, THEY'RE CAUGHT IN THE WILD!!! 
When in doubt, use full throttle, it may not improve the situation, but it will end the suspence. |
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Thanks Bob, I really needed that,,,hahahaha
 one more electronic gremlin and it is getting a set of 40DCOE Webers, whether it likes it or not.
No Idea how to access codes or interpret them, so strike out there, I would give a kingdom for a case of Seafoam, you lot sure are blessed over that side of the pond. But I hear what you are saying, any idea which sensor would have timing input. TPS or coolant sensor, maybe? Been kicking the idea around that it may be the head gasket starting to go bad, mainly because in the morning when the car is cold, it does not do it, bt starts once it has heated up to running temp and been driving a while, sort of like something is opening up on expansion as it gets hot, like a failing spot on the head gasket, no water in the oil or vice versa and no coolant loss, so probably between two cylinders, any thoughts on that? No Al, been through more than one batch of gas from different garages, no change. ---------------------------------------------------------------------------------------------------------------------------------- E30'S AREN'T BUILT, THEY'RE CAUGHT IN THE WILD!!!
When in doubt, use full throttle, it may not improve the situation, but it will end the suspence. |
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I never used that sea foam you mention.
My old beat-up Citroen has a carburetor, and shows several symptoms as your BMW, so don't go blaming BOSH for your trouble... I guess the oil use inside the cylinders is the main cause of all trouble. Knowing you need the BMW and money shortage (aren't we all?!), do you have access to the electric schematics and can you check all the connectors and sensors on the engine by yourself? Anything further will need specific equipment, professional help and some money... 
Good luck, keep us posted! |
I've got a question about seafoam, what's the consensus on that? I've heard it both ways, "YOU'RE GONNA KILL YOUR E30" and "YOU'RE GONNA REVITALIZE YOUR DYING E30". Which is it? I've got a can in my garage, never used. |
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Bam, we don't have it here, so like Jose, I have never used it, but I am on a few forums for cars and bikes and I have heard nothing but good things about it, not once have I heard any negative comment, but I am sure the guys will jump in with thier personal experiences.
Jose, all the electrics are good, like your Citroen, she is just getting old and showing her age now. ---------------------------------------------------------------------------------------------------------------------------------- E30'S AREN'T BUILT, THEY'RE CAUGHT IN THE WILD!!!
When in doubt, use full throttle, it may not improve the situation, but it will end the suspence. |
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Hi All
Been a while, between computer issues and general life getting in the way, as well as spending all my spare time and cash, rebuilding my faithful Suzuki GS1000G, so I can relieve my faithful 318 from her duty as daily driver and spend some much needed time on her giving her the love she deserves, to bring her back to her former glory. Her 470 000Km and daily duties with minimal maintenance have taken their toll on her and she is showing it, but now that I can afford to take her off the road for extended periods, work shall begin. That said, she has been fantastic, never missing a beat. The misfire turned out to be a worn cam and lifters, once replaced, she ran strong again. My Suzuki GS1000G "Jennifer" before and after 
The offending cam and rockers that caused the misfire. 
 ---------------------------------------------------------------------------------------------------------------------------------- E30'S AREN'T BUILT, THEY'RE CAUGHT IN THE WILD!!!
When in doubt, use full throttle, it may not improve the situation, but it will end the suspence. |
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