MS Tuning & Fuel Pressure

68dime · Post by **68dime** » Mon Jan 17, 2005 10:32 am

I have a question about my overall setup, and wondered if you guys had any advice for me.

I'm running MS on a 155 HP, 2.2L Nissan motor that I've installed into a Datsun 510. This car uses a custom manifold that's got Ford Mustang injectors on it (19 lb/hr). The fuel map that I've been playing with was set up by the person that owned the MS previously, on the same motor.

The motor has a big, torquey cam in it and it's been hard to find a fuel map that works. I need some advice on where, exactly, I should start the process of trying to improve my setup.

The car has running rich since I installed this engine and the Megasquirt, even though the power and overall 'feel' of the motor is very good, and I'm driving myself crazy trying to figure out why. Bear with me, because I'm new to fuel injection...but I'm trying hard to learn this stuff.

Okay. So I'm fouling plugs like crazy, and the exhaust smells like fuel. So the first thing I did was start checking the values in MS. The REQ_FUEL number is a ways off, in my calculation....the previous owner of the MS had set it to a value of 13, and the value that I get when I calculate is 11.7. Dialing that number back and scaling back the VE table that I have seems to help, but isn't solving my problem.

The guy who owned the car before seemed to know what he was doing...if I show you guys a VE table, would that be enough information to figure out whether it's a reasonably valid map or not?

Also, his RPM bins start at 1300 and go up to 6000, and jump at one point from 2800 to 4300. Is this a valid way of setting up a fuel map? The visual version of the VE table shows a very sharp plateau between those RPM's. It seems like a more stable curve would be desirable. The car also doesn't want to idle very smoothly, and I'm wondering whether the fuel map starting at 1300 RPM might be part of the problem there.....

The strange thing is, when I do my own VE table from scratch, using what the web calculator gives me, the motor runs in a manner that is not as rich, but lacks power at nearly all RPMs.

The last thing is, I may be using a fuel pump that is rated for a pressure that is higher than I need. I am using a fuel pressure regulator that I think should dial it back to within reason, but if all the tuning that I'm doing is going to be defeated by this fuel pump situation, please let me know.

I'll get you all some better numbers to look at, but in the short term I am wondering whether I should attempt to 'fix' the map that I have, since it seems to work reasonably well, or whether I should start over from scratch. Also, what is the best guess as to what is causing me to run so rich?

Any responses would be appreciated....thanks....

Bernard Fife · Post by **Bernard Fife** » Mon Jan 17, 2005 10:48 am

68dime,

I think this is one of those stuations that illustrate that different people come to different tunes on the same engines, depending on their driving style and preferences.

If only the idle is rich, lower the VE table entries at the rpm(s) and kpa(s) where you engine idles to lean it out. However, if the opening time is too long, (and/or the injectors are too big - yours aren't) this will only help to a point. Check that your opening time is ~1.0 millisecond.

I think you are on the right track; keeping things smooth, relatively evenly spaced, and covering the entire range is a good way to start, you can always chenge them later to solve specific problems if you have to. The original owner propbably did this for a resons, but unless you know that reason, I would work towards it independently.

Do you have an O2 sensor? If so, you should use it, datalogs, and MS Tweak to fill in the lower load areas of the VE table.

You could also attach your settings file and a datalog or two to a note in these forums so we could have a look.

The fuel pump is fine, the regulator reduces it to the desired level. (Make sure it has a vacuum line attached if this is port injection.)

Lance.

68dime · Post by **68dime** » Mon Jan 17, 2005 12:23 pm

Those are 30 lb/hr injectors that I'm using....sorry. But I still don't think those are too big for this application, correct?

I'm going to go back to the VE tables, and start from scratch, then. I'll spend some time testing that, and then I'll check back in. Thanks, Lance!

Post by **efahl** » Mon Jan 17, 2005 1:14 pm

68dime wrote:

> Okay. So I'm fouling plugs like crazy, and the exhaust smells like fuel.

This combined with the fact that the power is good when you get on it seems to indicate that the upper right part of the VE table is ok, but that the cruise and idle (middle and lower left) are too rich.

> Also, his RPM bins start at 1300 and go up to 6000, and jump at one
> point from 2800 to 4300. Is this a valid way of setting up a fuel map?

Well, it sounds a little strange to me. I'd have at least one bin well below idle, say at 500, then try to narrow that gap in the middle a bit.

> The visual version of the VE table shows a very sharp plateau between
> those RPM's. It seems like a more stable curve would be desirable.

Yup, I think you and I agree on that:

http://www.not2fast.com/efi/spacing.shtml

> car also doesn't want to idle very smoothly, and I'm wondering whether
> the fuel map starting at 1300 RPM might be part of the problem there.....

Seems likely.

> pressure that is higher than I need. I am using a fuel pressure
> regulator that I think should dial it back to within reason, but if all
> the tuning that I'm doing is going to be defeated by this fuel pump
> situation, please let me know.

Changing the fuel pressure will indeed require a retune, but don't worry about it, as soon as you've tuned it once, you'll get engrossed in tuning and want to do it again anyhow.

--
Eric Fahlgren http://www.not2fast.com/

(posted by email)