UVA3rdGen

this is a two part question, both which i am majorly in the dark about.

first: how does cadillac's fuel injection systems work, the ones that they have used for the past 20 or so years which allow the car to run on, 4, 6, or 8 cyclinders according to engine load, they got incredable gas mileage out of bigs engines becuase of it.

second: does anyone make an aftermaket system like that for sb-chevies. I know accels TPI systems give you the ability to adjust the fuel to each cyclinder, but you could not just cut off half the cyclinders could you? (i know to anyone who really knows what they are talking about that is a totally stupid question) Are all after market TPI systems batch firing or are any sequential?
Thanks for the info in advance.

The Rusty Trombone

well i dont really have your info, but i do remember seeing that engine on the "top 10 v8's of all time"... along with the 4.3L turbo trans am of the early 80's.... pooor... poor engines....lol

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1987 Midnight Blue Camaro IROC-Z, 350 TPI out of an '88, Accel 8.8 wires, hypertech air foil, flowmaster american thunder 3" dual outlet cat-back... slipping tranny!! (T5 swap next spring!!)

Grim Reaper

Ok...let's assume you CAN get sequential fuel injection to meter each injector individually. So what? Are you prepared to put an O2 sensor on each individual sensor? Because without that, how would you know if an individual cylinder was rich or lean?

Are you able to monitor your existing motor to determine if your fuel calibrations are too rich or too lean? Are you able to change those calibrations now?

If not, then how in the hell are you going to do that with your sequential fuel injection?

FWIW, sequential fuel injection offers a little better fuel economy, but minimal performance gains. You would be far better off to learn how to burn your own eprom and take advantage of what you already have. You'd be surprised on the fuel savings and performance increase JUST from getting your eprom optimal.. and this does not mean buying a custom chip.

So, if you are truly interested in sequential injection, I suggest learn how to burn your own prom, optimize what you already have and then, if you think the expense is worth it, investigate SFI.

Personally, I think I can get better performance by spending my money elsewhere.

UVA3rdGen

that is what i figured. What i really wanted to know was how does the cadillac system work and if anything like that could be applied to a tpi system for optimal fuel economy.

Grim Reaper

In a word...no. You might be better to look at the SFI system from a 4th Gen, but I've already seen the discussion on that, and it basically concluded that the amount of money and effort was not worth the minimal gains that you would get with SFI over the batch fire system. You would get better (and cheaper results) just by optimizing your existing eprom on the TPI.

Also, I don't believe the Cadillac Northstar employs the 4-6-8 fuel injection system. They dumped that whole concept in the early 80s when Cadillac was flooded with a ton of warranty claims. One of my ex's father had one of those in the early 80s and it was a pain in the butt. He eventually got rid of the car.

FYI, the SD TPI actually has a hidden table that GM never enabled called "Highway Mode" (or Lean Cruise on other ecms). Basically, Highway Mode allows the engine to run at a higher AF ratio than 14.6:1 when cruising on the highway. This greatly cuts down on gas mileage. But it was nixed by the EPA because it increased NOx emissions. The neat thing about Highway Mode, is you can set the speed that it comes on, so if you are subject to a dyno test, you make the speed high enough that it will never kick in while on the dyno.

When I was subject to dyno/emission testing, it was done at 40 Km/h (about 25 mph), so you just set the Highway Mode not to kick in at that low of a speed (which you shouldn't anyways...45-50 mph is more reasonable).

UVA3rdGen

I gotcha, will the computer switch out of highway mode once the engine is underload or will it perminetly run lean after that speed? Also what system does cadillac use now that allows them to get 35-40 mpg highway? I drove from virginia to the middle of ohio on one tank of gas. Is it that highway mode preset?

RMK

I have the manual from a 98 Deville that I was driving and it specifically says that thwe car will indeed shut off cylinders when they are not required.

Also, should you drain every drop of coolant from it the car will still run by shutting off 4 cylinders and pumping cool air through them. Then when they heat up too much they change them round with the other 4. Very clever system indeed.

Hope this helps. If you need any more let me know and I'll look it up for you.


Rob

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1987 IROC-Z Auto (LB9)
Black/grey with the stance of a streetfighter

Mods
Custom exhaust. 4 Inch pipe from the headders all the way back to a single muffler at the rear. No Cat.

Future mods:
K&Ns
RAM Air
New Underdrive pulleys-either March performance pulleys or Auto Specialties Performance
Air foil

Grim Reaper

RMK, thanks for the info on the new Caddilacs.

UVA, Highway Mode is something you must enable. The stock GM eprom for our cars have it disabled by requiring the car to do a minimum vehicle speed of 255.

The controlling of Highway Mode on the SD TPI 730 ecm is accomplished by setting the minimum coolant temperature, maximum MAP in Kpa and minimum vehicle speed. With the maximum MAP, you can adjust it so it returns to 14.6 when a certain load is present on your engine. I currently am using 65 KPA, which will cause it turn off on most grades or part throttle passing conditions at a vehicle speed of 60 mph. At 60 mph, I generally run at about 40-45 kpa on a flat level road in OD.

UVA3rdGen

Thanks RMK, i was almost certain they still did that. It is a great system, and I really wish it was applied to more cars. I long time ago I e-mailed edelbrock about the idea of incorperating a similar system into their FI systems and they wrote me back saying it was a good idea but never saw anything happen with it. Would SB-chevies cam profile not allow for such a system? would the exhuast not give enough backpressure at low rpms? Why has no other car adopted this technology?

Glenn91L98GTA, thanks for that tip, it has really motivated me to look into prom burning. What system are you using to modify your chips?


[This message has been edited by UVA3rdGen (edited January 09, 2001).]

Grim Reaper

I use Xtronics Pocket Programmer to read/modify the eprom. I went with that unit because it works off my parallel port on my notebook. An ISA card based burner just wouldn't work. The cost is $129.00

For a UV Eraser, I went with the Datarase II for $39.00. It doesn't have a timer, but I have plenty of clocks at home.

I also chose to read/burn directly to the GM Calpak/memcal. It only required me to get a cheap "header" so I could hook it up directly to the eprom burner. I got a good deal on a second memcal so it seemed better than modifying my GM Calpak with a ZIF socket and a 27C256 eprom chip. I had to modify the lid of my UV Eraser with a dremel so I could put the GM Calpak into the eraser.

For an Editor, I went with TunerCat ($69). It is one of the easiest to use, works with Windows and has the 8D eprom used on the SD TPI very well hacked. For other ecms, you are best to ask others what they prefer, but for the SD TPI 730 ecm, I highly recommend TunerCat.

I also have a Scan Tool (Diacom+)to help me quantify the changes I make to my eprom. But it isn't really necessary, and I feel it is more useful for the faster baud rate ecms than the slower ecms. I think a person should still use good old fashion tools (like reading your spark plugs, timing yourself and listening to your engine) regardless if you have a Scan Tool or not.

Also, a scan tool is really more useful for part-throttle adjustments. It isn't that useful @ WOT as you go into "WOT mode" and cannot see your BLM/INT values. Some people are very successfully burning eproms without using any scan tool, while other are using it exclusively. I prefer to use as many "tools" as I can and not rely on any method exclusively. But whether or not a scan tool will be useful depends a lot on the type of ecm you have. I wouldn't buy one if I had a tbi car because the information is very limited and the speed is really slow. I consider a scan tool a "nice to have, but not necessary".

Thats about all you need to read/burn an eprom. If is surprisingly easy. What takes time is learning to tweak and play with it.