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ficke ficke is offline
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Join Date: Nov 2004
Location: Tucson, Az.
Posts: 2,344
This post was on another thread, thanks Scarseller, this is why I do not want EFI.... Tuning
Many times people with EFI say how wonderful it is, after it is tuned which can take years to get right for all occasions.

"I own a modified euro 3.2L and it has custom cams, extrude honed port polished intake, light flywheel, SSIs with 2in2out M&K pipe. Runs the stock Motronic DME. I bought the car like this and it ran like hell at WOT and very hi-loads but was very un-drivable, stalled easily bad idle quality, failed emissions, terrible cold start, list goes on.

Mechanically it was very well built solid engine, cost the prior owner $15K to build the motor but ran so poorly on the street he sold it and I bought the entire car for 18K! He could not sell it for over a year. Bought it back in 2006 and then my journey began, I'm a EE with a computer science degree so I opened up the DME and saw the processor and as luck would have it I actually programmed that exact same processor back in the 80s at IBM we used it for real time embedded factory control systems.

I immediately disassembled the program code and spent the next 4 years (on and off in spare time) understanding the entire stack of code not just the maps. Once I knew how it worked and what all the maps did I then fine tuned the issues, re-tuned the maps and the car drove far better. One other complication was that someone prior to me decided that increased fuel pressure is a good thing so they crushed the FP regulator in a vise and increase FP from 2.5bar (stock) to 3.0bar, not a good idea!

After I got the car running better I then really decided to start making more changes to the old EFI components. I removed the AFM and replaced it with a modern day Lab grade Hot Film MAF and then I re-wrote the entire Air Fuel portion of the software in the DME to properly process the MAF signal. You can NOT make a MAF pretend to be a AFM for a lot of reasons but one big reason is that the MAF response to air flow changes in about 10ms while the AFM takes 100-200ms and the Acel Enrichment must be done differently.

So 8 years later I have a great driving 3.2L that pushes about 270HP at the crank at 5800RPMs. But it still has a slight drivability issue that I can't tune around completely. This engine surges at very light loads in the 2600-3200RPM range, like foot on the gas very very slightly at lower speeds, parking lot crawl or slow traffic in 2nd gear the engine can sort of kangaroo/bucking the car. I've spoke to several experts and some tips have helped a lot but you just can't dial this out. It's most likely cam related as even other builds that use carbs have had these issues.

Would I trade the experience over the pat 8 years, no way, loved every minute of it. Developed new products for these cars and have a few local cars running some of what I've learned. But the point is this experience is not for everyone, the prior owner hated the car and lost his shirt on this car!"
Author is Sal
and I am not even close to his level of expertise, tuning flat scares me.
Old 10-17-2014, 08:18 AM
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