MFI troubleshooting - high idle, pops and bucks at part throttle

[Arne]

Good tips. I'm going to look into cleaning the bypass passages, as the air screws don't seem to change things much.

Also noted this warning in the C-M-A document. Giving this a bit of thought, as while I did add about 6 gallons of 87 the other day, I don't know what fuel the seller put in prior to shipping the car to me. I wonder if this is really a significant possibility, especially in combination with the slightly colder plugs. I think I'll pick up a set of BPR6ES-6 later today.

[G69]

Somewhere I read- "I lean left". Being a leftie myself that works fore me.

[G69]

Remember the fantastic NGK spark plugs heat range numbers are reversed compared to what many are used to.

[Scott72]

When tuning ours we also used one of the below which helped map the whole mess. Really need to weld in a bung for the sensor though as the tailpipe readers don't work well.

https://www.innovatemotorsports.com/products/lm2.php

[Arne]

Not a lot of progress today. I installed a fresh set of plugs (just because), and used some B12 injection cleaner to make sure the bypass passages were clear. Verified the passages by shining a light down the air screw holes and looking for the spot of light inside when I open the butterflies. All 6 passages are clear.

Still don't seem to see a lot of difference in idle speed when adjusting the air screws, though. Perhaps I'm simply not opening them far enough, but the idle speed is still barely above stalling. A bit of black smokiness to the exhaust, too. So still rich at idle.

Warmed it up, then went to richen the main rack again. Promptly dropped the Allen head plug, and it -- with unerring accuracy -- fell straight through the hole in the shroud used for idle adjustments. Tried using my inspection scope and magnet on a stick to get it back out, ended up having to remove the left heater duct so I could get in there to retrieve it.

So with the time I had today, I only had time for one adjustment to the main rack. Might be a little better once off the t'stat. But still not even close to right. Hope to have time to run through a couple of tweaks and checks tomorrow.

When tuning ours we also used one of the below which helped map the whole mess. Really need to weld in a bung for the sensor though as the tailpipe readers don't work well.

https://www.innovatemotorsports.com/products/lm2.php

If I thought I was going to be doing this very often, I'd get one, Scott. But my plan all along has been to get it close by trial and error, and then take it to my local shop for fine tuning with AFR. Then once it is set, NEVER MESS WITH IT AGAIN!!

I will be replacing the heat exchangers at some point, I will probably have a bung welded in the new ones at that time, just for future ease of use.

[Arne]

Ed, Arne, The idle mixture adjustment your talking about will go "Richer Clockwise". Leaner is CCW. Now the main rack adjustment is the opposite, CCW for richer and CW for leaner.

Mark, you are a lot closer to Eugene than Ed is. Do you do house calls?

Sure would be good to have someone who is familiar with this stuff peek at it, if only to tell me I'm on the right path (or not).

[2.5MFI]

Arne, If I wasn't so friggen busy and behind schedule, I'd be glad to take a fun drive over the Cascades down to Eugene to help figure out the problem.

[Arne]

Arne, If I wasn't so friggen busy and behind schedule, I'd be glad to take a fun drive over the Cascades down to Eugene to help figure out the problem.

While it would be great if you did, I wasn't serious about that. I hope to get it handled eventually. I'll have to drive it over the hill for a visit someday, when it's better.

Should have some time to work on it this afternoon. Y'all wish me luck.

[Arne]

Further MFI adjustments on hold as of now. I made another adjustment to the main rack (richer) and then leaned the idle a bit as well, then took it for a drive. And things felt pretty good, for a while.

Then it suddenly went bad. Popping, cutting out, backfires, no power, and even died once. Struggled a bit but got it back home.

The thing is, it came on so sudden and so hard, I don't think it's the injection. I suspect ignition.

This was not like with what I've felt (or thought I've felt) with it coming off the thermostat, this was like "I'm going to have to call AAA to have it towed home" sudden failure.

Which doesn't mean I haven't been experiencing this all along, to some degree.

So now to look into the ignition. Still seems to be temperature related, so the likeliest culprits would seem to be the coil and CDI boxes.

Swapping a different coil won't be hard, but how can you test or bypass CDI? I tried a search here, and the forum seems to ignore 'cdi' as a keyword. Any suggestions on testing or bypassing the CDI?

[mobius911]

My car showed similar problems after the CDI box heated up- it was so bad that a sheriff stopped where I was pulled over, saying he had reports of gunfire... Changed the CDI and the problem was solved. Try swapping in a known good CDI. If that's the problem, there are shops that rebuild them with new electronics but maintain the original appearance.