June 02, 2014 02:52PM
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Registered: 9 years ago
Posts: 6 |
'86 M20- cold start- fine, but when warmed the engine dies when clutch is let out in gear; it idles rough but if it doesn't stall, can be sometimes be teased to reving in neutral; when the revs are high enough slipping the clutch can get it moving and keeping the revs high (running in the lower gears) it seems normal, stopping at a light I have to play with it again to get it moving; when idling often it will die or nearly die when the accelerator is pressed; often when I get it moving by slipping the clutch it will accelerate, then die.
It has a new AFM, new throttle position sensor, new temp sensors; new spark coil, ignition wires are fine; just checked the cold start valve hot, it's tight; the vacuum line to the fuel regulator is fine; there seems no diagnostic check list in Bently's.. .. any suggestions..? |
June 02, 2014 03:33PM
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Registered: 15 years ago
Posts: 87 : Rigaud Quebec |
June 02, 2014 04:23PM
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Registered: 9 years ago
Posts: 6 |
June 03, 2014 10:49AM
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Registered: 15 years ago
Posts: 797 : Ottawa |
Manifold vacuum is highest at closed throttle, lowest at wide open throttle. The pressure regulator, via the vacuum line, responds to alter the fuel pressure as required. less fuel pressure at idle, higher fuel pressure at open throttle.
My 1990 325i had similar symptoms, occasionally running way too rich, stumbling and belching black smoke. That was diagnosed as a faulty fuel pressure regulator. Regulator and vacuum line was changed. Made no difference. Bummer. It turned out to be the Bosch Motronic ECU. A previous owner had installed a cheap performance chip and that apparently kacked out. I found a used ECU for $100, swapped that in, and the car runs like new again. Eureka! |
June 03, 2014 11:20AM
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Registered: 9 years ago
Posts: 136 |
But the '86 M20 with a cold start valve could be a 320i with L-Jetronic.
Anyway, my guess is that the engine is breathing non metered air. That means air bypassing the AFM somewhere. Search by spraying start gas on various parts of the engine while it is running, and listen for idle increase. It could be as simple as the oil filler cap not being properly on, or the dip stick not properly in, but usually the problem is a leaking air hose. The rubber cracks up when it gets old. |
June 03, 2014 05:55PM
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Registered: 15 years ago
Posts: 1,538 |
That would be my guess as well. There are half a dozen or more places where unmetered air can leak in. The flex hose between the throttle body and the AFM, the manifold vacuum hose that feeds back to the ICV, oil dipstick, the oil filler cap, the intake manifold gasket, the throttle body gasket, etc. One additional thing to check out is the wiring to the fuel injectors. The connector under the diagnostic connector is a known trouble spot. If one set of injectors are not firing, the car will idle fine but stumble or stall when a load is applied along with throttle. |
June 03, 2014 06:38PM
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Admin
Registered: 15 years ago
Posts: 584 : Vermont, USA |
Sounds like a likely reason. If this is the case, then I think the check engine light should be on. On North American E30s, we can do the stomp test (e.g. https://www.youtube.com/watch?v=5GlBsrOSefg). An intake leak would give a code 1215. I had this happen on my E30, and I never did find the source of the leak until I removed and reinstalled the intake manifold for an unrelated problem. __________ Dave '91 325iX |
June 03, 2014 06:45PM
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Admin
Registered: 15 years ago
Posts: 584 : Vermont, USA |
The OP didn't say where he's from, but if it's North America, it's probably a 325. I don't think I've ever even seen a 320 here. Were they even sold in North America? If so, they're very rare compared to the 325. __________ Dave '91 325iX |
June 03, 2014 10:28PM
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Registered: 9 years ago
Posts: 136 |
June 08, 2014 09:00PM
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Registered: 15 years ago
Posts: 1,869 : Amagansett, New York |
June 09, 2014 09:05PM
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Admin
Registered: 15 years ago
Posts: 944 : Lake Havasu City, Arizona |
June 12, 2014 08:09PM
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Registered: 15 years ago
Posts: 1,869 : Amagansett, New York |
Yes, I like this guys design. The glow plug seems like a good idea. With all these vacume leaks on todays (and yesterdays) motors this seems like a needed tool in my shop... youtube [www.youtube.com] |
June 12, 2014 09:09PM
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Registered: 15 years ago
Posts: 1,538 |
June 12, 2014 09:58PM
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Admin
Registered: 15 years ago
Posts: 944 : Lake Havasu City, Arizona |
Checking for vacuum leaks might be easier to do with a propane torch. Just turn on the gas and do not light it. direct the gas to areas of interest that might have a leak. The engine should be running of course. a marked change to the idle speed would indicate leaking air was also drawing in propane fuel with the air.
Bob in Lake Havasu |
June 13, 2014 06:05PM
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Registered: 15 years ago
Posts: 1,538 |
June 14, 2014 11:54AM
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Admin
Registered: 15 years ago
Posts: 944 : Lake Havasu City, Arizona |
Well, if the plug leads are arcing, that could explain the trouble with stalling on acceleration. But to answer your question, yes if the propane were to be ignited by the arcing wires, it would quickly indicate what to fix next. Might singe some eyebrows. I think the risk is low because the vacuum leak detection is on the opposite side of the engine compartment.
Bob in Lake Havasu |
June 16, 2014 03:43AM
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Registered: 14 years ago
Posts: 799 : O Porto |
June 18, 2014 07:46PM
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Registered: 15 years ago
Posts: 1,869 : Amagansett, New York |
There's a youtube with a guy using a butt to blow smoke into the system but a steady stream is needed to really source out hidden leaks, cracked T fittings and such. |
June 23, 2014 07:18AM
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Admin
Registered: 15 years ago
Posts: 584 : Vermont, USA |
I finally watched this video and really like this. This kind of thing is fun to build, and I could really use this to track down an elusive vacuum leak in my wife's Mazda. It's been defeating me for months. I think I might just try to build one of these. __________ Dave '91 325iX |