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In Reply to: Hmmmmmmm posted by ian M635 Uk on June 15, 2002 at 23:20:31:
Your symptoms do seem related to fuel delivery. My car also will stall out during hard acceleration if the tank is under a quarter full. This seems common (I've seen this mentioned in posts a bunch), it is probably just a case of the fuel rushing to the back of the tank and causing air to get into the aux. fuel pump. But unlike your situation, my car pulls strong as hell all the way to red line (well, it did before my valve issue cropped up) when I'm above a 1/4 tank.
I would change the filter, check the pickup screen, and replace the regulator. Then think about replacing your fuel pumps, before I would suspect cams. Unless the top end has suffered from oil starvation, the cams would be the last things to look at. If you really think it's the cams, open the valve cover and measure the lobes with a micrometer. Tell me the results and then I'll measure mine to compare.
Are all of your plugs the same color? A nice golden brown? If not, maybe you've got some funky injectors.
If this were my old MGB we were talking about, I'd check the distributor to make sure the timing was advancing properly. But, we have Herr Motronic doing that for us. Have you checked your timing?
Anyhow, it sounds like either fuel or ignition is your foe. Make friends with the culprit and he'll buy you a pint.
Cheers,
Ethan
P.s. I had a long day of rehearsal with too much beer. I hope all that makes sense : - )
Ethan - funny you should mention fuel delivery!
When my tank runs low I can get drastic fuel starvation under heavy acceleration in 2nd gear.
The car practically stalls above 4500rpm. Full tank no problem. I was going to strip the pumps, fit a new fuel filter and clean the strainers.
CAT is not the issue as I don't have one thank God. So I should have 286 hairy brake horse monsters under the bonnet. Just doesn't feel like it above 4500rpm. Runs out of puff and will not scream to the redline. I have been in another M6 with a very strong engine so I know what to expect. Torque from 1000rpm to 4000rpm seems very strong though. New air flow meter made things a lot smoother as well.
Cheers
Ian
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After I did a leak down test I found that cylinder 1, exhaust valve 2 is burnt or cracked.
My engine has 180K miles and was running great.
Could your problem be a clogged cat? or maybe fuel delivery?
Regards,
Ethan
OK chaps did the compression test for a second time with a more accurate guage and got the following results
Engine warm, throttle fully open, fuel pumps disabled.
Cranked engine over 7 times on each cylinder until max pressure reached.
No1 194 PSI
No2 197 PSI
N03 195 PSI
N04 200 PSI
N05 195 PSI
N06 197 PSI
Repeated test with a little oil down the bores and got about an extra 5 PSI on each cylinder.
Engine has 156k miles and was rebuilt (new rings no rebore) at 77k miles.
With a compression ratio of 10.5-1 I would have expected around 150-160 PSI. The results I have seen good?
My problem is that if these are OK then it does not explain why I have a power drop off above 4500rpm. Top end is a little noisy and the cam lobes seem worn (ridge can be felt on some of the lobes. I'm thinking that just a change to new cams would bring back the lost power. I have been offered Schrick cams in the UK for £1200 for a pair (272 degree vs origonal at 264 degree). These require no machining of the head but it is recommended that new valve springs are used due to the increase in valve lift.
New origonal cams cost £1000 per pair from BMW.
Which way do I go? will schrick cams need a remap? Can I get the old cams reprofiled and save £100's
Let me know what you think.
Regards
Ian
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