MFI and altitude

[rowingone]

So just finishing my 1972 2.4 MFI and admittedly I have spent a fair amount of time in the garage at under 2k rpms as I work thru CMA and noticed that the plugs become black and the car won't start easily. The MFI pump was just tested, cleaned , calibrated by Mark Jung so I am good there . . my question is the plug I run is the NKG 7es and I am at 5280 feet of altitude .. should I try a hotter plug or will my problems disappear when I start to drive it on the street? The car runs great until it doesn't and then a quick clean of the plugs will bring it back to normal.

[NorthernThrux]

MFI always runs best rich, and if you don’t get into the high rpm range, odds are you will foul your plugs. So try exercising the car first and see what happens with the plugs before you go to a hotter plug.

You cannot truely calibrate the pump,without it being on an engine dyno. Mark would have set it up for the “average” 2.4. That should get you close, but ideally put an AFR onto one of the heat exchangers and see where you actually stand. If running rich, in combination with your 2k limit, upu could really be fouling the plugs.

Lee Rice has a quick test for richness in his MFI primer, available in pdf form on this forum. Just disconnect the MFI pump linkage and push it slightly (throttle valves at idle) and watch the rpms go up and then down as he says.

Ravi

[rowingone]

Thanks Ravi . . good info for me to proceed!

[nigel911]

When I first relocated to CO I took my 72 2.4 Targa to Eisenbuds down in Denver - he leaned out the MFi for the emissions test and then I took it back to him and he adjusted the system to better suit the elevation - car runs like a champ and I've had no plug issues.

Mine also came from FL but is Signal Yellow - I'm just down the road from you in Lyons.

[rowingone]

Thanks Nigel . . I will contact Eisenbuds if I don't figure it out on my own.

[gled49]

The MFI pump will adjust for altitude, but have the mixture adjusted for the altitude you will be spending most of your time in. This fuel system needs to be driven hard and heat cycled. A heat cycle is an hour not 10 minutes.

[Jeff Higgins]

There is a barometric cell located on top of the pump (small CAD plated canister) that is supposed to provide for altitude (or other barometric change) compensation. I am not entirely sure what its range of compensation might be. On my car, tuned at sea level, it appears to be well outside whatever that range might be when I drive the car at high altitude.

I made about a 4,500 mile loop down to Sante Fe (I'm just north of Seattle) last May for our annual club Treffen. We travelled over three mountain passes of roughly 10,000 feet elevation. My car ran extremely rich at that altitude, with little power. The affects were felt at lower (5,000-6,000 foot) elevations along the way as well, but I kept thinking this was a temporary situation anyway. In retrospect I should have leaned out the main rack a few clicks, then just reset it when I got home.

At home, with our passes running more in the 3,000-4,000 foot range, I can get over them just fine with my sea level tune. I wonder if that might be about the limit of the altitude compensation offered by the barometric cell.

So, yeah, living at higher elevation, I bet this is as simple as leaning your pump out to a different "nominal". If you ever travel to, and plan on spending any time at lower elevations, it would be worthwhile to richen it up for such a trip. In my case, going from lower to higher, it just goes blubbery rich and robs power and mileage. In your case, going from higher to lower, it could wind up dangerously lean.

This is a very easy adjustment to make. It's worth getting comfortable doing it yourself, if you travel across widely varying altitudes. Just make note of what you did, and return it to your "nominal" when you get back home.

[rowingone]

Thanks Jeff . . great information . .sounds like a simple adjustment is needed. And Nigel .. what plugs are you running since you live near me?

[nickelplated5s]

Way back when they had supercharged MFI motors in planes. Think the late 30's into 45. Those would have run into the 20K altitude at least.

[Jonny042]

I do the odd calibration/test/repair/rebuild on MFI pumps and always recommend the owner add a wideband O2 sensor and gauge if they haven't already.

I would not own an MFI car without also having a WBO2 system. There simply isn't enough downside not to. Otherwise you are guessing. And not just for initial setup, for tuning along the way, and diagnosis of issues.

IMO if it's fouling plugs it's over-rich but you'll never know by how much!

[targa72e]

I second the wide band O2 as a required tool.
Remember all the special tools and procedures for setup in check, measure, adjust manual were because they had no ability to see what the actual mixture was. They also assume everything is like new and stock. If you search there is more tunning you can do outside of the standard adjustments.
If you have changed anything on the engine, pistons, cams or exhaust you are outside of the standard calibration. I general tuning MFI (like a carburetor) is a series of compromises. You are limited by the fuel curve on the space cam and can only tweak it a little here or there. The baro cell can only adjust for so much. All of these variables and mile high plus elevation are what make a wide band O2 the best tool for tunning.

john

[nigel911]

Can check my plugs later today if it helps, pretty sure I'm running BP7ES - will say though, I try not to use the car for short trips, mainly mountain drives.

[tobluforu]

Get that car out on the road, tuning it in your garage is only going to get you so far. Those plugs are fine. There are shims under the cell, do a search on how they work, but since your pump was just setup, should be fine???? There is dry/wet fouling of plugs. My car has dry fouling, and I live with it. It has no effect on starting, for me. Wet fouling, I get that on my 2-stroke bike, at times. Usually when I let it idle too long after starting. Out they come, in go new ones until I clean wet ones.
Drive your car.

[rowingone]

So I purchased a cheap Amazon wideband O2 sensor and mounted it in the tail pipe yesterday . . 10.5 to 11 on part throttle . . . thats rich!! So today I will lean the pump out 2 clicks and see if that gets me in the zone. And yes it is dry fouling and I will be driving the car on the road finally! It will be interesting to see how much 2 clicks changes the readings and the drivability.

[Jonny042]

Let us know how you make out!

One thing to keep in mind is for whatever reason MFI likes to be rich, and you're unlikely to ever get it to cruise anywhere near stoich without felling like a stumbly mess.

[tobluforu]

I run 11 at wot, but the reading changes as you know depending on where your foot is, and I don't race the car. Don't let the wideband drive you nuts. I had one in my car for a few weeks, once I got it right, out it came. I did the same on a moded turbo car I had, but the gauge was digital so I could turn the damn thing off. Same with a car I had with a SC on it.
Like stated, these cars like to run rich.
One last thing, make sure you get the pump timing correct. Once you drive the piss out of the car, check the pump timing just to make sure.
Good luck and have fun.

[rowingone]

two clicks lean on the pump was the magic formula for this altitude as mentioned on here previously. I learned much about how to properly read a spark plug . . more than just color . . many great videos on YouTube about accurate reading of plugs. Also went a click hotter on the NKGs at least for the winter. Runs fantastic