Hi,
Just thought I'd post the results of my search to fix some engine problems. Might help someone else if they have similar.
At the end of January I bought a 1990 318i 4-door. Low miles (79k) and the current owner had bought it off the original owner 12 months ago. Looked clean (especially inside) and was a good price, so I snapped it up. During the test drive noticed it was a little sluggish. I figured with the low mileage it might just need a good service and hard run to clear out the cobwebs.
Once I’d bought it I noticed it had a lumpy idle (for a BMW ”“ I've driven plenty of Suzukis and Daihatsus with worse but I also had another E30 318i Touring and also a E36 318iS which both seemed better for idle vibration). Not a big problem, but suspicious.
I also noticed how down on power it was. Up to about a throttle the response was ok and power didn’t seem too bad, but from a to WOT there wasn’t any improvement in performance. The engine noticeable picked up from about 3500rpm (the normal on-cam point?) but again there didn’t seem to be any benefit from using full-throttle. This was a real pain on the motorway, constantly having to downshift to re-accelerate from 60-70mph in traffic. It was so bad on a slight hill in 4th at 40mph there was almost no acceleration possible.
The day after I bought it, whilst reversing off my driveway it stalled and it wouldn’t restart. After a call to the previous owner he said he’d had the same and it needed a bit of extra throttle just after cold-starting, and if it stalled it would flood and needed the plugs drying out. So I did that, and following his tips I was able to keep it going. You still had to be careful and have a 10mm spark-plug socket handy. But I found this suspicious, and combined with some of the other problems and a slightly ”arich”a smell while stationary I did think it was generally over-fuelling. Also the fuel economy wasn't great (on a mostly motorway tank of fuel it averaged 29mpg) - much worse than my old E30 touring.
The last problem I only noticed once I’d started using it regularly. At constant-throttle at constant-speed on a flat surface (low throttle, less than a), there appeared to be a misfire. What you felt is a sharp shock to the car, the car actually sped up slightly, and the ”aswingometer”a fuel economy gauge diped down. It appeared to be slightly worse the longer you ran at constant throttle.
So, in summary the 3 problems were :
1. Lumpy idle
2. Down on power, especially at full-throttle
3. Hesitation/misfire at low-throttle constant-speed
I’d already bought some service parts anyway, so I changed those during February. That’s sparkplugs, HT leads, distributor cap (but not rotor arm as I couldn't get the hex-screws out - the hexes were rounded-off!), air filter and fuel filter. I read on here that the blue engine temperature sensor which sends to the ECU goes it makes it over-fuel, so I changed that ”“ but it didn't improve it.
I had replacement oil & oil filter ready, but didn’t want to do that change until I’d sorted out the other issues, since if it was over-fuelling it’d just be contaminating the oil.
My next steps were going to be to check the compression, timing, check the spark on each HT lead, somehow check that the mass-airflow meter is working (but I didn’t have the resistance values to check), and then start looking at the throttle/idle-control-valve assembly.
But instead I gave it to my local BMW specialist (M-Tek of Northampton - I highly recommend them). Almost immediately they found the timing was out by 2 teeth (how it got that way I don't know). They also found the idle-speed-adjust screw had been turned all the way in, so effectively the car was never actually idling. They set the idle-screw properly and changed the timing belt and now it is sweet-as-a-nut! Idle is still a little bit shaky, but it sounds much cleaner at idle and through the rev-range, and the fuel economy appears to have immediately improved. They also cleared a cylinder-head oil-feed while they were there, which has cured the extreme tappet-noise the car had.
Now I'm going to flush the engine with some cheap diesel oil (as recommended on here) and get on with some minor cosmetic jobs.
I just thought this might be useful if someone else has M40-engine problems, as it might get them to check something like this before looking at the MAF or ECU.
Cheers,
-J
M40 Engine Problems Fixed
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