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special k
Member
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Posted: Wednesday November 21st, 2007 02:07 pm |
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Been reading on this and other forums about always checking the integrity of the vac pipe when experiencing running probs.
Can someone enlighten me on what a vac pipe does, where is it and what does it do/stop happening when it has a hole/split/not seated correctly.
Thanks in advance of what i am sure seems an easy question to most, but not to someone who is just learning
Steve
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DaveShreeve
Administrator
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Posted: Wednesday November 21st, 2007 10:33 pm |
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Ahhh, the pipe! If you've run earlier minis it's the same plastic pipe as the inlet manifold to distributor pipe and is used to supply the ECU with similar information, ie manifold vacuum. PS not too early or it would have been a metal pipe.
These days most systems use a sensor in the manifold wired to the ECU. For the Spi, and others around the same date, Lucas mounted the sensor in the ECU and ran a pipe manifold-sensor.
The pipe runs from the rear centre of the manifold, via a fuel separator on the bulkhead between manifold and clutch master cylinder, to a port in the base of the ECU next to the wiring connector. If you're trying to trace the pipe: remove the air filter, presuming it's in its original case, and you should then be able to see the fuel separator and the ECU port. Most of the rest usually turns into a check by feel exercise, especially the connector at the rear of the manifold. The pipe isn't usually a problem unless it's been disturbed and touched the exhaust manifold. The problem is the right angled rubber connectors, *4, that connect everything together; they harden and can crack which can cause all sorts of problems especially if the crack only opens up when the engine moves in use.
The easiest place to start checking is the fuel separator, check also that this is not blocked, then the ECU, and finally the one you can't see, have difficulty feeling, and is a pain to get off, at the rear of the manifold. If you have extra strong, super slim, double jointed fingers, you may like to try this one first and use it to check for vacuum leaks down the line.
Numerous faults have been attributed to this pipe, very often linked to tickover speed, cutting out at tickover, and similar.
Remember, other pipes can cause vacuum problems. It gets into a chicken and egg situation - is the fault in the pipe, or is the fault elsewhere so that there's no vacuum to pass on to the sensor via the pipe? An obvious culprit would be the pipe from the charcoal canister under the nearside wing.
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special k
Member
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Posted: Thursday November 22nd, 2007 09:47 am |
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| Right!!!!....lol
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hawaiianblue
Member
| Joined: | Saturday June 2nd, 2007 |
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| Posts: | 214 |
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Posted: Saturday March 22nd, 2008 12:28 pm |
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basically it does the same as on the carb cars.
When the engine is under load it advances the ignition to give more pulling power, when its idling it retards again it to make it run smoother.
If split it sucks air, so makes for rough running at idle, and with no auto advance it makes the car gutless.
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