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How far will GM TBI self adjust?

vandelay industries

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How far can/will GM TBI self-adjust or learn if changing things from stock?

For example, stock 5.7 tbi engine's cam is around 191/202 ish @.050". If we change the cam to say, 222/222 @ .050", then will the ECM self-adjust to it? Or would we need a new chip made?


Same with, what about going to 383 inches from 350?


2) Is the ECM the same between 4.3, 5.7 and big block? Although i ASSume the proms are different?
 

HankScorpio

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I was wondering this for my 454 swap, it has a cam and .030 bore. From what I have read not very far, TBI likes to be stock. Decided to go to ProFlo4 before fighting the TBI. Lots of guys have had a chip burnt but it seems very few were actually totally happy with the results.
 

Bent77

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At one point I was told 5%. There are cams ground that will play nice with a factory chip. Going to 383” is an optimistic stretch
 

sweetk30

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i had a stock 350 with a tiny rv cam and it didnt like it . ran great with a carb but swapped on tbi and NOPE . loopy idle and little crank .

i swapped the engine for a good tbi 350 and she was back to normal . i sold the other one .
 

dyeager535

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In reality the answer is none, and some. Lol

Where it really counts, none. When the O2 sensor is in play, it can basically compensate until the injectors can't supply enough fuel at the pressure they are running at, assuming vacuum is still good. With BBC and SBC running the same fuel pump IIRC (talking the early TBI, not later high pressure), the SBC theoretically should have plenty of fuel capacity.

The problem is under heavy throttle and cold engine/open loop idle. The O2 sensor is not used to calculate fuel delivery. Fuel delivery is preprogrammed (hard coded if you will) so if the engine needs more fuel, it runs lean. This would be even worse if displacement is increased.

This is why you can sometimes get away with bumping up fuel pressure alone. It's a very crude way to do it, but it can work. Since the ECM will use the O2 sensor under most conditions, dialing back fuel when not needed, is something it will do. Generally however, an engine doesn't need x% of fuel across the board, which is what bumping fuel pressure up, without tuning the ECM parameters, does.

FWIW, I've used the example quite often, but my dad's 454 was rebuilt fairly stock except a mild cam, Edelbrock performer intake, and headers. It didn't run right. Needed tuning and more fuel pressure to get it even close, and still really needed a higher pressure pump, but with dual tanks and new pumps installed, didn't want to deal with replacing them. Tuning "fixed" it, but there was essentially no margin for error towards going lean. Fuel pressure being maxed out, nothing to do to fix that but swap pumps. Lose pressure, run lean.
 
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scouthead

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360 cubic inch

Roller cam from a cop car- cant remember specs but with the roller tipped rockers (different ratio than stock) was supposed to be similar cam specs to the vortec 5.7 truck engine... but its a roller
-cut most of the swirl bump out of the heads
-port matched everything to the gaskets i was using
-edlebrock tbi manifold with runners gasket matched to gasket/head
-bored /shaved throttle body
-bored throttle body spacer
-stock injectors, map, and icm
-correct knock sensor for the roller cam
-flat top pistons- just over 9 to one compression
-stock exhaust manifolds because i need the air injection for emissions.
-Custom air cleaner with 2 snorkels and both have the wax pellet valve/cold air blend valve things for cold weather
-taller air cleaner lid with the tall filter element.
-stock chip that came in it (manual trans though)

The thing ran GOOD. Passed emissions here in CA 3-4 times over 6-7 years. I broke something around 60,000miles. Just pulled the motor a week ago. Have a stock motor swapped in for now- dang it feels like there is half the power. Im running 3:73 gears in the diffs with 35 inch tires. 1st gear hurts now- slipping the clutch sometimes now.
Even on 7 cylinders my old engine had a noticeable more amount of power than the stock one i just seapped in.
 

gonefishin

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As far as I recall from working with my tbi stuff 10-15 years ago it never self adjusted anything other than idle and light throttle cruising.

I think I still have the adjutable fuel pressure regulator and I think I have the tuning cord for the prom chip.

i ran a basically stock 350 with a 212/218 cam and long tube headers. I turned up the fuel pressure and also adjusted the timing up 4 degrees from stock. It ran pretty good. But not as good as when i put a performer intake and carb.
 

SnackPack

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Your open loop will never be right, and TBIs do run in open loop quite a bit. If you can't adjust by simply adding fuel pressure, then you'll need to tune the chip.
 

1-ton

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I am curently running a pair of AC/DELCO EP381 fuel pumps in my saddle tanks that are capable of 60-PSI max on my 1991 V3500 with a TBI 350. The original TBI was bored out 1/8 of an inch with ultimate mods, and adjustable fuel pressure regulator by Vic Morse machine. The fuel pressure is currently set at 12-PSI (it was only 9-1/2 PSI stock). I am running a mild Comp Cam Computer Control cam that is 262/262 duration, .444/.444 lift, and 111 degrees of lobe seperation with AC/DELCO lifters. Timing is set at 0-degrees. This engine runs OK, but is still too under powered for such a heavy truck.

I need a set of gears more than more power. I have a set of 5.13:1 gears for this truck, but have no time to install them because of all the hours of work I have to do, in order to make up for all the people that do not have to work for a living anymore.

full
 

vandelay industries

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I am curently running a pair of AC/DELCO EP381 fuel pumps in my saddle tanks that are capable of 60-PSI max on my 1991 V3500 with a TBI 350. The original TBI was bored out 1/8 of an inch with ultimate mods, and adjustable fuel pressure regulator by Vic Morse machine. The fuel pressure is currently set at 12-PSI (it was only 9-1/2 PSI stock). I am running a mild Comp Cam Computer Control cam that is 262/262 duration, .444/.444 lift, and 111 degrees of lobe seperation with AC/DELCO lifters. Timing is set at 0-degrees. This engine runs OK, but is still too under powered for such a heavy truck.

I need a set of gears more than more power. I have a set of 5.13:1 gears for this truck, but have no time to install them because of all the hours of work I have to do, in order to make up for all the people that do not have to work for a living anymore.

full

So, the engine itself runs good, just no power? Sort of like if you put a 4.3 in a suburban? (something i would do.....)
 

1-ton

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So, the engine itself runs good, just no power? Sort of like if you put a 4.3 in a suburban? (something i would do.....)
My crew cab came stock with a small block. Not sure why GM thought a small block in a crew cab like mine was a good idea. I was thinking of going with a 383 stroker, but like has been posted before an OBDI/ECM with a TBI could burn up a 383 stroker under hard acceleration when it went into fixed fuel mode and went lean. I might just take the original 4-bolt main small block and build a .30 over (355 cubic inch) small block for it.
 

bp71k5

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Tuning the GM TBI isn't all that. If you modify the ECM to take removable chips, it can be done with a moates burner. I still have my setup and its been running well for a few years even though I went from a 350 to a 454 with a larger throttle body and aftermarket injectors. But I haven't had to tune around a big CAM, so that might be harder to do, but not impossible.
 

1-ton

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Tuning the GM TBI isn't all that. If you modify the ECM to take removable chips, it can be done with a moates burner. I still have my setup and its been running well for a few years even though I went from a 350 to a 454 with a larger throttle body and aftermarket injectors. But I haven't had to tune around a big CAM, so that might be harder to do, but not impossible.
Can the wide open throttle fixed fuel program be modified on an OBDI/ECM? I know that Moats offers a service where they will solder in a removable ROM socket. One of my main worries is that I have a rare OBDI/ECM/PCM (7060) that was only available for a few years. This ECM has a PCM that controls my 4L80E trans. If somehow this ECM/PCM got screwed up modifying it...it would be hell ever trying to get my hands on another (7060) ECM/PCM like it.
 
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bp71k5

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Can the wide open throttle fixed fuel program be modified on an OBDI/ECM? I know that Moats offers a service where they will solder in a removable ROM socket. One of my main worries is that I have a rare OBDI/ECM/PCM (7060) that was only available for a few years. This ECM has a PCM that controls my 4L80E trans. If somehow this ECM/PCM got screwed up modifying it...it would be hell ever trying to get my hands on another (7060) ECM/PCM like it.
If I remember correctly, on a 7747 computer that table is the same as the open loop table so it can be modified. I think there was also a couple settings where you can boost the AFR relative to throttle position.
I don’t know about the 7060 ECM but I can take a look. I would suspect it has more capabilities not less. Soldering in the new socket is pretty easy but obviously if you can’t replace the ECM that’s a concern.
 

SnackPack

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Not sure about the 7060, but a popular mod is to swap to a 7427 ECM. They're cheap and they can control these automatic transmissions. I've done the swap and it does make the engine run a lot smoother (IIRC, the frequency of the computer is about 10x, so there's a lot more fine adjustment in the ECU).

Like I mentioned above, you could simply bump up your fuel pressure a bit to help out those fixed table modes (open loop). The ECU doesn't measure out fuel itself, but just pulse widths of the injectors. More FP with the same pulse width = more fuel, and probably a close match throughout the fuel table.
 

bp71k5

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More FP with the same pulse width = more fuel, and probably a close match throughout the fuel table.

I dunno about a close match if making significant changes or changing motors from a 350 to 383 but increasing fuel pressure for small mods can get you by ok if it was running well before the change.
 

1-ton

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Not sure about the 7060, but a popular mod is to swap to a 7427 ECM. They're cheap and they can control these automatic transmissions. I've done the swap and it does make the engine run a lot smoother (IIRC, the frequency of the computer is about 10x, so there's a lot more fine adjustment in the ECU).

Like I mentioned above, you could simply bump up your fuel pressure a bit to help out those fixed table modes (open loop). The ECU doesn't measure out fuel itself, but just pulse widths of the injectors. More FP with the same pulse width = more fuel, and probably a close match throughout the fuel table.
I did some research on using the 7427 ECM, and apparently those only work on 1994 and up 4L80E transmissions because the motor pulse width comunication is different. My 4L80E is the original early model 1991 that my truck came with, and has had the valve body updated to 1993 version, wich fixes many of the known problems the first year 4L80E trans where known to have. I have done some data logging with TunerPro, and my BLM's where too rich at 13-PSI when under 2600 RPM. The BLM's where great at 13-PSI and over 2600 RPM, but with an overdrive transmission I rarely run over 2600 RPM. When I turned down my fuel pressure regulator to 12-PSI my BLM's got much better at average cruising speed RPM's.
 

DB Cooper

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* edit to remove link

yikes, I had no idea about their rep changing for the worse.
 
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dyeager535

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TBI chips started to get a bad rep a few years back. Others come more highly recommended now.

Howell I believe is one that seems to be doing quality work for TBI guys now.
 
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