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Speed Density vs. Mass Air, opinion as per Chrysler engineer
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Author:  mpgFanatic [ Sat Oct 05, 2013 11:55 pm ]
Post subject:  Speed Density vs. Mass Air, opinion as per Chrysler engineer
I discovered lots of great interviews here on Allpar with various Chrysler engineers, including this guy who helped develop the Slant Six...

At some point after retirement, he was asked about the early days of Fuel Injection, and why it took so long to adopt Multipoint:
Quote:
The thing that always bothered us about our system, you are aware that for probably the first 20 years every single fuel injection system that we released was based on RPM and charge density, not an air flow meter. Air flow meters were expensive. But you could calibrate a whole family of engines with one air flow meter. Those that I worked for were sure that it was cheaper to do a thousand calibrations on TBIs.

Everybody hated it, it was stupid, and it was ridiculous. There had to be a different set of electronics between an A body and a P body of the same engine. There had to be different electronics for every insignificant variation of every engine model, and each had to have its own calibration which took weeks and several people, one engineer and a couple technicians and a dyno operator not to mention car work for drivability. We did it over and over and over, it was just plain stupidity. It was also a lousy way to build fuel injections because what you were doing was you were calculating air flow from the density and the RPM, density being manifold vacuum or pressure in the case of a turbo.

Boy, you really dug up an old pet peeve that I haven’t thought of in years. I’m not sure now if we have all air flow meters but I hope we do.
Thought you might find it interesting. :) No wonder so many hobbyists have spent so long chasing gremlins-- look at the development time required even at the OEM level.

- Erik
Author:  CNC-Dude [ Sun Oct 06, 2013 12:13 am ]
Post subject: 
Its good to finally see an engineer realize that they are sometimes their own worst enemy, that's something that many of us already have known for years. :P
Author:  mpgFanatic [ Sun Oct 06, 2013 12:26 am ]
Post subject: 
Quote:
Its good to finally see an engineer realize that they are sometimes their own worst enemy
I dunno, I thought he was pretty clearly blaming the bean counters or management... 8)

Yes, some engineers are their own worst enemy, but the trouble I've seen more often is with sales people. After all, it's their job to tell the engineer, "OK, that's good enough, we've gotta sell some of 'em. Save your improvements for the next release."

Left to his/her own devices, a perfectionist engineer will never find the end of a project. :lol:

- Erik
Author:  Sam Powell [ Sun Oct 06, 2013 5:03 am ]
Post subject: 
So can mega Squirt use a Mass Air Flow sensor? I have never seen mention of it. Only Alpha N and speed density. MAF sensors are expensive but hobbyists spend a lot of money on their cars. Maybe it would make sense to develop an after market fuel injection system that used one.

Sam
Author:  Reed [ Sun Oct 06, 2013 9:51 am ]
Post subject: 
This logic is exactly why I am skipping the TBI and speed density step and going straight to a Ford MAF based fuel injection system. The system is still fairly cheap (if you scrounge you can get everything you need for under $300), it is completely tunable using aftermarket devices (TWEECER is the one I use on my Ford van), and it is a true MAF based multipoint fuel injection system.
Author:  DusterIdiot [ Sun Oct 06, 2013 10:04 am ]
Post subject:  Maf...
I have a friend who is an ASE Mechanic and works for Ford. He agrees that the MAF system is more efficient than the MAP system, but he also mentioned that if there is an intake manifold leak between the engine and the sensor that the prom will not be able to compensate for this and the engine will just die on the spot (this happened a lot on the old 5.0L when they went from map to maf in late 80's/early 90s). The MAP sensor would register lower intake vacuum and just adjust the fuel per the programmed fuel MAP and keep driving, the MAF would register a section of the fuel map that is non computable (i.e "infinity") and quit. Since our octopus manifold is prone to warping and having the exhaust port blow out the gasket next to it this might create a potential risk situation for having a breakdown on the street that can't be fixed until the car is towed home and a new gasket installed.

Sorry to add fuel to the fire, but my friend brought it up when he asked if I was going to go EFI at some point.

-D.Idiot
Author:  Reed [ Sun Oct 06, 2013 10:29 am ]
Post subject: 
Interesting. I am using the MAF fuel injection system that was installed on late 80s and early 90s Mustangs (mine is off of a 93 Mustang 5.0) n my van. The van has a 1984 351W motor and was originally carbureted. I swapped it over to the MAF FI system pretty easily. It has taken me a while to get it running almost perfectly, but most of that has been a result of my having to teach myself about the system, troubleshoot the swap, and replace components that I should have bought new instead of used to begin with.

I had several vacuum leaks when I first completed the swap but none of them caused a stalling condition. There was poor running, but the engine never left me stranded. I did use a special set of durable intake manifold gaskets since the felpro ones were known to get sucked into the heads, but that is all. I don't think there is any need for worry or concern about using the Ford MAF system on the slant so long as correct manifold installation procedures are followed.

One would want to use a different exhaust manifold than stock since one would not want the carb heat provisions provided by the stock exhaust manifolds on a fuel injected motor. Dual exhaust would actually be ideal since the Mustang injection system uses one O2 sensor for each bank of the engine.
Author:  mpgFanatic [ Sun Oct 06, 2013 12:16 pm ]
Post subject: 
Quote:
and replace components that I should have bought new instead of used to begin with.
tell us more...? :D

In my memory of 15 years enjoying a stock '89 5.0, it required very few EFI part replacements. At least one and maybe two EGR Position Sensors (the potentiometer wiper gets noisy and feeds intermittent false answers which illuminate the Check Engine light). And one new pair of plastic vacuum switches for the air pump and thermactor control, since they were mounted only about a foot above the exhaust manifold and couldn't take the heat. (That might have been 2 new pairs, come to think of it, because in one of the replacements I discovered that Ford had molded the incorrect part number into it and therefore put it in the wrong box.)

Overall, not a horrendous track record for 250k miles. Worked pretty darn well, too.

One thing I can tell you... which might be taking this off-topic... if you install the EEC-IV system in a different vehicle, install as much of it as you can. If you miss something that the computer is expecting, or ignore inputs you think you don't need (i.e. clutch switch sensor, or a VSS from the transmission), the computer "knows" there's a hard fault and it refuses to engage the diagnostic test mode (the one where it tests all inputs and outputs while the engine is running, including a cylinder balance test if Sequential.) I'm still fixing the frankenstein project that someone else began for me... wish I'd done it all myself.

- Erik
Author:  Reed [ Sun Oct 06, 2013 12:28 pm ]
Post subject: 
I bought the initial bunch of components I used in my swap off of Craigslist. The computer, wiring harness, and sensors mostly came from a $200 bulk purchase I did of someone else's abandoned project (retrofitting fuel injection to a 302 powered Mercury Marauder from the early 60s). Other "hard parts" (manifolds, EGR valve, serpentine belt setup, timing chain cover, water pump, etc...) came from a 351W motor pulled from an 89 Bronco that had sat outside for a year before I bought it.

I ended up having to replace the EGR position sensor, the EGR valve, the AIR injection pump, the coolant temp sensor, the TPS sensor, and a few other sensors because I tried to use the used parts. Maybe if one were to pull these form a vehicle that had been freshly running instead of sitting outside for a year then there wouldn't be a problem.

The beauty of the TWEECER tuning system is that you can tune literally every single programming parameter of the EFI computer. You can turn off the EGR system, turn off the AIR injection system, modify all aspects of the spark map and fuel map, use the computer to turn an electric radiator an on and off as set temperatures, everything you could ever want to do. It allows real-time datalogging and reprogramming, there is an active Yahoo group and mailing list for support, and it has a five position switch that lets you run the car with the TWEECER off (running on the stock factory calibration in the computer) and four other programmed profiles that can be modified and updated as you drive. I can't say enough good things about it.

I have said it before in other posts but the only part of the Ford MAF EFI system that is difficult to adapt to the slant six is the Hall effect sensor mounted in the distributor. This sensor not only controls the timing but also the firing order of the injectors. I believe the easiest way to adapt this part to the slant is to get a Ford 300/4.9 distributor from a fuel injected motor and machine the base and shaft to fit into the slant six block. I have spoken to a couple guys who have done this, so it shouldn't be too hard. I just have stalled on my efforts to adapt this system to the slant six.

Honestly, I think adapting the 89-93 Mustang MAF fuel injection system is the way to go if you are going to make the effort to swap to fuel injection. MAF, MPFI, fully tune-able, able to be retrofitted with only minimal machine work (manifold, injector rail, distributor), able to run all modern emissions controls for minimal pollution and maximum economy.
Author:  Matt Cramer [ Tue Oct 08, 2013 2:08 pm ]
Post subject: 
Quote:
So can mega Squirt use a Mass Air Flow sensor? I have never seen mention of it. Only Alpha N and speed density. MAF sensors are expensive but hobbyists spend a lot of money on their cars. Maybe it would make sense to develop an after market fuel injection system that used one.

Sam
It can; most users don't run it as much of the information from other users is based around speed density tuning though. It does take a couple hardware mods, and you'll need the transfer curve for the MAF you intend to use.
Author:  Reed [ Tue Oct 08, 2013 3:09 pm ]
Post subject: 
Not to be a broken record, but again the Ford MAF system has widely and cheaply available MAF sensors and the TWEECER has pre-defined MAF curves for a variety of applications and fine-tuning the MAF curve for your particular engine is quick and easy to do. Just an FYI.
Author:  Sam Powell [ Fri Oct 11, 2013 5:33 am ]
Post subject: 
Hmmmm............
Author:  CNC-Dude [ Fri Oct 11, 2013 10:15 am ]
Post subject: 
From what I saw with this system during the 5.0 Mustang days, I often thought it would be neat if you could apply this system to other engines because it was so performance friendly and seemed to be self adapting to whatever mods you did to your engine.
Author:  WagonsRcool [ Fri Oct 11, 2013 8:43 pm ]
Post subject: 
MAF & MAP systems both have their own pro's & con's. I see both types on a daily basis.

MAP: the hardware is cheap & easy to install. However, as stated earlier, the software has to be calibrated for the particulars of any given engine. ANYTHING that alters engine vacuum will throw off the ecu calculations. Minor vac leaks will only change idle speed. Large leaks= lower vacuum which is interpreted by ecu as high load= rich run condition. You can end up with the "flushing toilet" syndrom-a fault causes low vac which causes the ecu to dump in more fuel which causes the engine to run WORSE- etc. Chrysler is the only company AFAIK that still only uses MAP systems (even Honda gave in some years back).

MAF: the sensor is pricey, & ALL air going into the engine must go thru the MAF- so plumbing & ducting to the throttle body is more involved. Any leaks downstream of the MAF ("false" air) causes a lean condition- how bad depends on size & location. On the plus side the system is generally self correcting for changes to the engine (X amount of air will always need Y amount of fuel). On the minus side most MAF sensors are somewhat fragile & sensitive to dirt or PCV goo contamination. Most bad sensors that I see are on Fords, Nissan, VW's (heck, EVERYBODY has problems with MAF's)
Author:  wintermute [ Tue Dec 17, 2013 1:49 pm ]
Post subject: 
I'm new to the slant-6, and I definitely want to convert to a MPFI setup. Reed, I like what I'm seeing here in regards to the Ford MAF setup. I still have plenty to read, though!

The '05 Impala I used to have had the PCV plumbed into the plenum just behind the throttle body. It also had a MAP sensor, probably as a check against system vacuum draws from the plenum.
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