Slant Six Forum
https://slantsix.org/forum/

Gm tbi
https://slantsix.org/forum/viewtopic.php?t=17980		 Page 1 of 2
Author:  74.swinger [ Fri Jun 09, 2006 2:28 pm ]
Post subject:  Gm tbi
I had an article years ago to transplant gm TBI to other cars but I cant find it.
I hate to spend a fortune on holley pro-jection especially(pretty sure it is just a copy of GM stuff) for a beater.
Does anyone have any info or can you point me in the right direction.
________
MARIJUANA TEST
________
Mflb
Author:  Pierre [ Fri Jun 09, 2006 5:22 pm ]
Post subject: 
Do yourself a favor and stay away from the gm computer. Its a pita to program. If you intend to do tbi, the gm parts are fine, but mate it with a megasquirt computer ( www.msefi.com www.megasquirt.info )

Put some thought into going full blown mpfi as well. The price difference as a percentage of total project cost isn't that much more.
Author:  sandy in BC [ Sat Jun 10, 2006 8:09 am ]
Post subject: 
A few notes on GM TBI projects based on my experience (not on slants)

If you want to use a GM ECM....make it the 727 which has large support and is very flexible regarding big cams and other modifications.

The Baud rate on this ECM is so slow that it takes hours for the puter to learn all the tables after even simple mods.

The chips for these are getting harder to find.

You need a good chip guy to work with ( I use Alvin the Chip Monk www.pcmforless.com )

You must have an adjustable fuel pressure regulator to trim. (it took 12 hours to put Vortec heads on my Sub....and 2 weeks to get the fuel pressure right)

ANY exhaust leak will drive you nuts vis a vis O2 sensors

Knock sensors and solid lifters dont work well together.

This is a system governed by speed and Manifold vacuum.....you HAVE to have a VSS . You HAVE to have good manifold vacuum (think sensible cam....less than 270 adv duration....I run 262/270 with 9:1 CR ,,,reg fuel)

I run a Rochester 220 on a spreadbore manifold with a Turbo City adapter.

I run an O2 sensor in the collector of my headers

My chip is custom burnt for no EGR. AIR regular fuel , cam ....etc etc.

Done right you get instant starting at any temp,,,,,WIDE torque band....zero bog or stumbling....infinite altitude compensation(big deal for me)

Mebbe this summer I will do my slant .....sigh.
Author:  Pierre [ Sat Jun 10, 2006 10:56 am ]
Post subject: 
Not all gm computers require a VSS - my howell kit came with a 1227747 computer - sensors were 02, map, clt, mat, and tps.

Swapping chips to fine tune your program is nuts, take the chip out, program it, put it back in, testdrive, come back, rinse and repeat. They do make tools that replace the chip and you can alter the program live but these cost even more. If you want flexibility and performance nothing beats an MS for the $$.
Author:  sandy in BC [ Sat Jun 10, 2006 11:50 am ]
Post subject: 
The fact the Howell system had no VSS underlines its defective approach. In a speed / density system you actually do need to measure the speed....

All 747 puters in stock applications used a VSS.

A good chip burner can usually come close enough (given all the perameters) on the first burn. In 8 years of having a modified GM TBI setup in my work truck I have had 3 chips....each one burnt for a new modification (latest is for Vortec heads with increased CR and bigger cam and bigger TB)
Author:  74.swinger [ Sat Jun 10, 2006 12:34 pm ]
Post subject: 
See what i was hoping for was an early setup that was adaptable withoput custom programming and stuff.
I just want my old pickup to start better in the winter and possibly a slant powered dart for my wifes cruiser.
I was hoping top use an early gm 5.7 setup on the 318 and maybe a 2.8 or 4.3 on the slant.

i know gm guys who took the 4.3's out of their trucks and put in many different small block combos with little mod. I was hoping for something as simple.

im not looking for high performance i just want the thing to start and run reliably in the winter.

Did I mention I hate carburetion.
:lol:
________
HONDA NSR50
________
MARIJUANA
Author:  sandy in BC [ Sat Jun 10, 2006 1:15 pm ]
Post subject: 
It can be simple....I adpted TBI to my 73 Sub in an afternoon....(lotsa pre-thinking went on before that!) It was essentially a wiring swap and an e-mail request to the chip guy. Then I started modifying things....headers , performer intake, cam yada yada. Then you need new chips.

I figure the TBI swap on my Valaint will be relatively simple .....but my simple is not necessarily the next guys simple. The hard part for me is to find the uninterupted time to do it.....the rest is just wiring and Turbo City adapters for VSS and TB.
Author:  Pierre [ Sat Jun 10, 2006 2:22 pm ]
Post subject: 
Quote:
In a speed / density system you actually do need to measure the speed....
There are implementations out there of speed density efi that don't use speed sensors.... MS being one of them. Thousands of these installs working well. Yikes I sound like an MS salesman....

74.swinger - people have had success transplanting gm systems but your mileage may vary. A similarly sized gm v6 may not have same warmup requirments as your engine, etc. I had a poor experience with a "custom" tuned setup and it had nothing to do with a lack of vss, idle quality standing still was poor. (And there are people that run the 1227747 successfully w/o VSS as well....)

Granted there could of been other factors but thats besides the point I'm trying to make here. Regardless of what system you get, and how similarly matched your engine is to the car it came out of, you need to plan on tuning it yourself if you want to have it 100% spot on. People can use formulas and try to tailor chips to your engine but theres no way someone x miles away can predict how your enigne will react to a particular tune unles they have made chips for similar combos before.
Author:  Joshie225 [ Sat Jun 10, 2006 4:23 pm ]
Post subject: 
Speed density engine management is in reference to engine speed not vehicle speed. Vehicle speed sensors are good for different emissions devices, transmission control, etc, but do nothing for engine load sensing.
Author:  sandy in BC [ Sat Jun 10, 2006 8:54 pm ]
Post subject: 
On a 747 the IAC will not be set until the VSS reads 30mph at least once. If you skip the VSS you also skip IAC which is one of the most useful parts of GM TBI systems regarding driveability. If you wish to skip VSS you need to program for it.

When I first swapped a TBI system I had no speedo cable,,,,the darn thing threw codes and refused to run right till I installed a speedo cable (my VSS was in the instrument panel at the speedo as per early GM truck spec)

If you want to use a 747 ECM from a 4.3 Astro van (my choice for a slant) make sure you use all the stuff including a VSS attached to a drive gear appropriate to your final drive ratio.
Author:  Joshie225 [ Sat Jun 10, 2006 9:04 pm ]
Post subject: 
Quote:
On a 747 the IAC will not be set until the VSS reads 30mph at least once. If you skip the VSS you also skip IAC which is one of the most useful parts of GM TBI systems regarding driveability. If you wish to skip VSS you need to program for it.

When I first swapped a TBI system I had no speedo cable,,,,the darn thing threw codes and refused to run right till I installed a speedo cable (my VSS was in the instrument panel at the speedo as per early GM truck spec)

If you want to use a 747 ECM from a 4.3 Astro van (my choice for a slant) make sure you use all the stuff including a VSS attached to a drive gear appropriate to your final drive ratio.
That's all fine and good, but the VSS has nothing whatsoever to do with engine load sensing. Speed density is an engine load sensing strategy.
Author:  sandy in BC [ Sat Jun 10, 2006 9:14 pm ]
Post subject: 
OK....fine. That is great book stuff.

The reality is it doesn t run worth a $hit without a VSS. It wont idle well.....your ECM will think you are not moving and throw a code when your MAP sensor reads low vacuum at 70mph climbing a grade.

GM went to a lot of trouble to get TBI right. The biggest drawback is the slow (yet very flexible) baud rate ECM.....the sensors are stellar . The VSS and the other sensors are all important parts of the system...I like to use them all.
Author:  Pierre [ Sat Jun 10, 2006 9:33 pm ]
Post subject: 
The IAC on the 1227747 is functional without a VSS - I should say, the chip can be made so that the IAC functions without it. My howell kit had a functioning iac. Never threw any codes for me. (edit: not map related codes, one it did consistently set was too rich)

If you want to experiment with GM stuffs I got about 8 different howell chips and 2 1227747 and the harness sitting collecting dust.

I don't think any of howell kits use vss's and theres a crowd of jeep folks that are happy with their kits.

More power to you Sandy if you want to use the VSS, but its not necessary for good operation of the 1227747.
Author:  Joshie225 [ Sat Jun 10, 2006 11:29 pm ]
Post subject: 
Quote:
OK....fine. That is great book stuff.

The reality is it doesn t run worth a $hit without a VSS. It wont idle well.....your ECM will think you are not moving and throw a code when your MAP sensor reads low vacuum at 70mph climbing a grade.

GM went to a lot of trouble to get TBI right. The biggest drawback is the slow (yet very flexible) baud rate ECM.....the sensors are stellar . The VSS and the other sensors are all important parts of the system...I like to use them all.
Excuse me, but speed density is an engine load sensing strategy that your ECM uses. Your ECM happens to need a VSS with it's original programming. I'm not debating that your GM TBI system needs the VSS to be "happy". Engine load sensing using the speed density method is not dependant upon the VSS. Speed density is dependant upon engine speed and air density measurements derived primarily from manifold pressure with corrections for air temperature.
Author:  sandy in BC [ Sun Jun 11, 2006 7:27 am ]
Post subject: 
One of the facts about 747 is that it does not have an Inlet Air temp (IAT) function.

I hear (and understand) what you are saying Josh . Im sure many rock crawler Jeeps do not need VSS (our mudbogger: Twin TBI :wont have it) but for real world driveability it is a big help. I know....I tried TBI without one.

I now have 415,000km on a modified TBI setup in my work truck. I have stepped up the torque output 3 different times via cam changes, exhaust changes, throttle body changes, cylinder head changes and manifold changes. I am on my 3rd chip.

I have 125000km on a less modified vehicle (no EGR, AIR, Comp 252 cam, increased displacement, bigger valves) 1 chip

I can tell you this requires the following things:

1) A good chip man: www.pcmforless.com

2) ALL the sensors ECT, O2, VSS, TPS, MAP, and knock

3) desensitizing the knock sensor(part of chip burning) especially for a solid lifter motor

4) adjustable fuel pressure regulator

5) A structured tune procedure (throttle position, fuel pressure, idle and full throttle O2 readings with digital voltmeter)....a cheap code reader

6) programming for deleted components (EGR, AIR , AC) also part of chip burning.

7) ABSOLUTLY no vacuum or exhaust leaks ( Including the right size PCV and EVAP hoses and valves)


All in all still easier to get right than a 600 Holley on a mild slant.
Page 1 of 2 All times are UTC-08:00
Powered by phpBB® Forum Software © phpBB Limited
https://www.phpbb.com/