Hey all.
So for a while now we have had our 280z running with an MS2 v3 board. Last week we were doing some street tuning and pushing 10psi the car was running great up until about 5200rpm where I noticed the injectors were starting to max out. I saw the duty cycle hitting 92% or so and decided that we aught to bump up the fuel pressure to keep from running the injectors static.
Bumped the base fuel pressure from 40psi to 45psi.
Problem is, since last week the ambient air temps have dropped nearly 20 degrees F. During that run last week, at 10psi and 5000rpm or less, A/F ratios were in perfectly safe levels around high 11.8:1 with intake air temps around 98 degrees. Today IATs were around 78 degrees.
Today we took the car out after bumping up the fuel pressure and as we boosted the car to the same level, A/F ratios were getting dangerously lean, up in the high 13's. I realize that some IAT corrections are in order and intake charge temps have quite a bit to do with overall mass of air entering the engine, but can a 20 degree drop in IAT account for at least 2 points leaner A/F ratio?
IAT corrections for colder weather
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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). For tuning/troubleshooting questions, please attached a datalog and your MSQ file to your post.
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.
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Random Hero
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DonTZ125
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Re: IAT corrections for colder weather
Hiya, Random.
A temperature drop from 98F to 78F will result in a 3.7% denser charge. A fuel pressure increase from 40 to 45psig will increase fuel flow through the injector orifices by 4.4%, so this is a bit of a wash. I think part of your problem is that you are into the non-linear range of your injectors, and you have unfortunately no real way of determining what flow you'll get with any changing conditions.
I would suggest your best bet is to swap injectors to at least 20% bigger, and try again.
A temperature drop from 98F to 78F will result in a 3.7% denser charge. A fuel pressure increase from 40 to 45psig will increase fuel flow through the injector orifices by 4.4%, so this is a bit of a wash. I think part of your problem is that you are into the non-linear range of your injectors, and you have unfortunately no real way of determining what flow you'll get with any changing conditions.
I would suggest your best bet is to swap injectors to at least 20% bigger, and try again.
