I have about 7 feet of rubber vacuum hose connecting my intake to the MAP potentiometer on my ECU. At idle, my car gives about 64kPa, which seems high.
If I connect a 3ml syringe to the vacuum line as per the test in the MS manual, I can get 84kPa of vacuum. If I connect the same syringe to a 6-inch piece of the same hose, I can get 42kPa. I don't understand this, since the manual also says there should be no issues regarding the length of the hose.
Therefore I presume my engine is actually idling a lot lower 64kPa, and I would like to get a more accurate reading. Would using a solid vacuum line (for example, copper brake line, or some plastic vacuum hose) give a more accurate reading, or is the issue with the length of the pipe? I could remote-mount my pot inside the engine bay, but I'd rather avoid this as it would be a lot more work.
Advice much appreciated!
James
MAP vacuum hose problem
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Read the manual to see if your question is answered there before posting. Many users will not reply if the answer is already available in the manual.
If your question is about troubleshooting, configuration, or tuning, you MUST include your processor type (MS-I or MS-II) and code version in your post. If your question is about PCB assembly or modifications, you must also include the main board version number (1.01, 2.2 or 3.0).
If you have questions about MS1/Extra or MS2/Extra code configuration or tuning, please post them at www.msextra.com Such questions posted here will be moved to: a temporary MSextra sub-forum, where they will be removed after 7 days
The full forum rules are here: Forum Rules, be sure to read them all regularly.
Re: MAP vacuum hose problem
I have spent so long thinking about this and you just explained it in two sentences - thanks!
Still don't understand why my engine only produces a vacuum of 64kPa at idle though... If I shortened the hose, would I see a lower reading (in the same way it is easier to suck through a short straw as opposed to a long one)? And if so, would I get a better tuning map by having a broader range of MAP pressure?
Still don't understand why my engine only produces a vacuum of 64kPa at idle though... If I shortened the hose, would I see a lower reading (in the same way it is easier to suck through a short straw as opposed to a long one)? And if so, would I get a better tuning map by having a broader range of MAP pressure?
Re: MAP vacuum hose problem
It's a 36 year old 911 - maybe that has something to do with it! 60-ish is the best I could get with any tuning.
Thanks for your help - much appreciated.
Thanks for your help - much appreciated.