Now at sea level and car runs terrible.......

[RacerX]

I just purchased a 73T in Denver and drove it back to Seattle. Car has a rebuilt 2.7 MFI motor w/ GE 40 cam. It ran superbly until I got back to sea level, so today, I took the car to Chris Powell to have the MFI adjusted to increase the fuel richness. While in the shop, it was also discovered that two plug wire connectors were bad. They were replaced. This BERU plug wire set was brand new. Just purchased last week.

I drove the car home tonight and while it runs without the constant stammering and hesitation that it had before, it now runs very rough and power flattens out badly as you rev through 6,000 RPM. Also, it is creating alot of emmissions/hydrocarbon fumes.

It never ran like this while at altitude.
I am concerned and wonder if something other than MFI adjustment is needed.

Any ideas appreciated....Thanks

[kenikh]

Take it back to Chris; he'll figure it out. If it was running badly and he knew it, he wouldn't have let it leave. (Edit) ahve you checked the plug wires? Perhaps the new plug wires got crossed.

[Eric911S]

Hello; I would check the fuel mixture. I would also have the altitude correction diaphram checked as well. Hope this helps. Thanks Eric

[RacerX]

Thank you for the suggestions.
I took the car back to Chris this morning. He tried several combinations and road tested the car about 5 times. Ultimately the car required 3 additional clicks of richness, and a leaning of the idle rack. Still not optimized, but closer to how it ran in the mountains. I just drove the car from Denver CO, through Vail to Steamboat, to Jackson WY, Missoula MT, then Idaho- Spokane to I90 - home and will be very happy to get it back to how it was. One of the best times I have ever had alone with a machine.
There wasn't enough time today to go through the A to Z work up of correcting this problem fully, but will address it in the near term. For now, much improved.

[kenikh]

Now we need photos...

[LeafGreen]

Hi,

Check the following:

Plugs from every cylinder; make sure they are the same color either showing rich or lean.

Balance the cylinder to cylinder airflow.

Ignition system. Previously mentioned plug wires, and while you're in there, the dwell angle - I believe 38 deg.

Someone said the altitude comp., maybe it's stuck in the wrong position? This is very important for proper fuel mixture. DO NOT LOOSE THE SHIMS, as these adjust the ratio of rack movement vs. throttle movement.

Cold start thermostat just to make sure it's expanding smoothly and repeatedly when heated. Is the hose hooked up to the heat source? Also changes the ratio of rack movement vs. throttle movement.

Auxiliary cold start circuit. Extra fuel is supplied to the stacks by little hoses all tied together, and they are fed from the top of the fuel filter mount/distribution block by a little solenoid. The solenoid is controlled by a thermo time switch and is only supposed to come on below a certain temp (I don't remember what, but here in CA it probably rarely kicks in if at all). Pinching off the supply hose will take that out of the picture.

The pump may be out of whack and needs to be calibrated. Send it on a CA or NY vacation and get used to running some old Zeniths until it returns.

Good luck.

[Jeff Higgins]

It can be all too easy to miss-diagnose these kinds of problems when you go in with any assumptions. In this case, a change in altitude appears to be an obvious influence, but is it really? A friend just bought a car and drove it cross-country home, through the desert, and had it start acting up. With temps approaching 120 degrees in the desert, the obvious problem was vapor lock on the carbs, right? It turned out to be a bad coil and miss-adjusted points that just happened to give out in the desert.

I relate that story to point out that the altitude change may not have anything to do with it. The barometric sensor on top of the pump compensates for these altitude changes; it is a pretty fool-proof setup. Have you looked elswhere?

What does it run for ignition? I had my original Bosch CD box fail, and symptoms were as you describe. Does it still have points? It seems you can't buy a quality set anymore (I switched to the Pertronix Ignitor out of frustration with modern point quality). Maybe the fuel filter finally clogged after the long drive. How about plugs? Most of us are now running a heat range or two hotter than original recommendations to try to keep fouling at bay.

I guess what I'm trying to say are there are lots of other things to check when it appears to be running rich and losing power. If the MFI was working properly when you left Denver, that would actually be one of the last places I would look. Poke around a bit and look at the other systems as well; something may have just given up about the time you arrived home, fooling you into thinking it was the altitude change. These little cars like to do that to us; they are mischevious little beasts...

[rs911t]

My 2.8 lived in Denver most of its life. When I converted it from carbs back to MFI, Grady Clay suggested I shim the barometer to fool the pump into running richer. It's a long shot, but I wonder if this was done to these cars to get a rich mixture at high altitude.

[Jeff Higgins]

That's an interesting trick, Greg. I've never heard of that one before. I guess the obvious question would be why not just use the high speed and low speed mixture screws? I wonder what shimming the barometric sensor accomplishes that adjusting the mixture in the normal manner would not.

[rs911t]

That's an interesting trick, Greg. I've never heard of that one before. I guess the obvious question would be why not just use the high speed and low speed mixture screws? I wonder what shimming the barometric sensor accomplishes that adjusting the mixture in the normal manner would not.

Maybe Grady will chime in here. Apparently they did this with other 2.8S MFI engines they built.