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 attempt to tweak GM 454 TBI or go with carb? 
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Joined: Sat Aug 24, 2013 7:57 pm
Posts: 152
Location: Frostburg, MD
Hello All,

I just bought a decent '88 C3500 single wheel ton truck. All stock dog 454. I've seen where one can piggyback a WB on and fool the ECU. I'm not sure that I have the spirit required though. Can I come close for economy with a carb? I'd rather have gas smell on me that pull my hair with the ecu fight.


p.s. - the truck's stock TH400 has elec speedo output. Anyone know if the speedo output on a 4L80E would run the '88 speedo? [4L80E control issues aside]

Sat Dec 19, 2015 4:32 pm

Joined: Wed Jan 29, 2014 12:00 am
Posts: 60
Hi Dave,
I am in the same boat... I have a 1991 Chevrolet 3500... I rebuilt the engine (454), ported the (peanut port) heads, edelbrock tbi intake, and throttle body.
The engine runs better, but still lacks the torque I was anticipating,... I am also thinking of replacing the tbi with a carburetor... Just not sure if I should go with a quadrajet or holley...
I am going to need a transmission controller for the 4l80e...
Curious to see what others suggest..

Sat Dec 19, 2015 4:52 pm

Joined: Thu Mar 28, 2013 6:09 am
Posts: 726
Im in the process of doing this but i have stalled as having issues with the motor that's in the truck at this time. Running a 5.7 in a C2500 and it hurt so building a 383 for it now so it's going to be a wile.. But lots of good info here..With the E trans your going to need another ECM to control the trans..

Sun Dec 20, 2015 9:06 am

Joined: Sat Aug 24, 2013 7:57 pm
Posts: 152
Location: Frostburg, MD
From 1st post;

I said: "I'd rather have gas smell on me that pull my hair with the ecu fight"

Should read"

I'd rather have gas smell on me THAN pull my hair with the ecu fight

Sorry for getting off topic here;


> .With the E trans your going to need another ECM to control the trans..

Understood there, if I wanted fully auto. There is a $200 manual shift option, and afaik, the lockup can be controlled w/o an ecu too. I just need to know if I can make the speedo work w/o a trans ecu. I was surprised to see an elec drive on the TH400 in the '88 truck.

Sun Dec 20, 2015 11:29 am

Joined: Sat Aug 24, 2013 7:57 pm
Posts: 152
Location: Frostburg, MD
Here is a ST post from tuner on piggybacking a WB onto the TBI

Postby Tuner » Sat Nov 21, 2009 10:36 pm

Before you dive headlong into all the drama and expense of changing large and expensive hard parts, consider this.

Replace the original O2 sensor with an Innovate LC-1 programmed to mimic the original sensor signal but set to run at 16.5/1 instead of the so-called "stoichiometric" AFR it is commonly misunderstood to be running at now. In reality, the system on that engine is bouncing between rich (approx. 13) and lean (approx. 17) to average stoich.

Because you are a shop you undoubtedly know these things, but......

In that vehicle, the original ECU and O2 sensor operate in a feedback loop when the TPS is less than 50%. When the TPS is over 50%, that system switches to a programmed fuel strategy that gives near 12.5/1 AFR for power and to prevent engine damage at high load.

The feed-back loop only averages an AFR of 14.7/1 (stoichiometric). In actuality, the OEM narrow-band O2 system on that engine is bouncing between rich (approx. 13) and lean (approx. 17) to average stoich.

Depending on several factors, sensor temperature, ECU programming, etc. the extremes can be very rich (12-13) and very lean (17+). The ECU only maintains an average target of stoichiometric. This means half of the cylinder firings are much richer than an economy mixture. (Have you ever noticed spark plugs out of some ECU controlled engines are black and rich on the metal shell and white and lean on the ceramic, as if it was running rich and lean at the same time?)

As you see in a scope waveform of a narrow-band O2 sensor, the voltage oscillates between nearly 1V and nearly 0V.

The ECU expects to see the voltage swings or it will flag a code. With the LC-1 you mimic the voltage swings by setting the analog output voltage to a rich limit of 16.3 at .9V and a lean limit of 16.7 at .1V with a delay of 1/12 sec. The ECU thinks all is normal and it will control the engine to run at the LC-1's programmed average, which is 16.5/1 (or whatever AFR you choose).

Using the Innovate devices, LC-1, LM-1 or LM-2, gives you laptop control of any ECU that uses a NBO2 in feedback.
Tuner Guru
Guru Posts: 1330Joined: Sun Apr 01, 2007 5:26 am

Sun Dec 20, 2015 11:36 am

Joined: Sat Aug 24, 2013 7:57 pm
Posts: 152
Location: Frostburg, MD
FWIW, I hope not too far off topic:

Most would say cams with TBI should be wide. I'm a vizard groupy [groupie?] when it comes to LSA, and I suspect that a cam for 454 with 106* lsa and .050" duration in the 2teens would run best for towing, albeit possibly a narrow power range. The question is if that would be too much overlap for the tbi ecu. I bet so, although some would say you could tune ecu to be ok.

Cam thread on ST; ... 13#p581478
Note that cam guru camking has twice recommended something on 111-112 lsa range for towing. Once in above thread and once in thread linked. Big Joe [Sherman] likes 108*, specifically isky 256 super cam, 212/212, .525", still made, but I'm sure he used it with carb.

Sun Dec 20, 2015 12:08 pm

Joined: Thu Nov 13, 2014 3:11 pm
Posts: 8
I bought a 91 CC dually 2wd new...and totally upset with its ability to pull my 26' enclosed down the hiway at hiway speeds

In 97-98 I did the Edelebrock TBI conversion that they made, converting it to 8 injectors...I installed the kit as described 100% by their directions...the truck was a whole different animal...MPG was not effected but the ability to tow 70mph now was finally had. No more 15-25mph losses going up hills on hiways any longer

kit was straight forward to install

it did not change the system to sequential. It was either bank or batch..I dont remember which

was the best $1100 I spent in a long time and beat buying another new truck at the time

Wed Feb 03, 2016 4:45 pm

Joined: Thu Mar 28, 2013 6:09 am
Posts: 726
SC3283, Buddy has that set up on a PU with a 454 and it runs great!! Hes also got some spare parts. To bad its not available
anymore as I would consider it for my truck..

Thu Feb 04, 2016 7:16 am

Joined: Sun May 12, 2013 5:21 am
Posts: 319
Location: Michigan
Buddy of mine that has had a lot of problems with his 454 Silverado sensors n cats(I forget yr maybe 93) I was gonna suggest using the $800 Fitech 400hp n an old style HEI. Also considered doing the same for my TPI car and I thought you could just leave the stock ecm hooked up and it would deal with the trans.

Sometimes you ask the wrong question, but it still leads to the right answer.

Tue Apr 26, 2016 11:25 am

Joined: Thu May 08, 2014 7:47 pm
Posts: 206
I am going to reply to this old thread too.

The tbi fuel injection was very far off in those transition years from carb to fuel injection. The were retarding everything, as well as removing any and all compression, the early years of the great fuel injection emission fight.

Cams do not work well unless you plan to adjust the fuel table that bases everything off map vs. ect vs. rpm.

Now. you can tune fuel injection with out a chip, its just different. and you kinds go at it like a carb, but with a fuel injection mindset.

1st think to do, check the codes, and fix any and all issues, until the light is off.
If you can't get the light off, you got to fix the problem.

fuel pump and pressure

The biggest issue is very little fuel flow, and any change kills hp fast. I put at least a 255lph pump in the tank. good for 550 to the ground. when this pump wears out or the filter becomes restricted, its still flowing enough fuel, unlike the stock pump that is just hardly big enough to begin with.

Pressure. The have different springs, I put the 454 spring in the 350 tbi all the time, and chevy has a few different ones available for fuel pressure adjustment in TBI. You can also shim the spring, but you got to get the flow up, and the pressure up to around 15-20 psi The injector flows more, better, and has more control, instead of just full enrichment all the time. it will actually flow more fuel with higher volume and pressure. The injectors are more precise, better spray pattern, flow more volume. and the computer will have more refined control over the fuel correction this way.

This is the biggest part. no fuel no fire.

GOOD ECT SENSOR A MUST! if its not accurate, the fuel is going to be righ or lean, depending on the sensor!

once you got all the lights off, good fuel flow, throw a set of colder plugs in I like ngk 7's, then un plug the timing spout, to check timing, and then add 10-15* and blug the spout back up.

reset the battery, and enjoy what chevrolet should have done along time ago. You will hardly believe the difference.

Go tow something!

I am currently setting up a 454 TBI throttle body to hold the 350 tbi injectors. so i can step up the 350 performance. I got a marine 350 roller in the tow truck, its got the marine Heads and roller set up, full exhaust, 454 pump & spring. the 350 tb is only good for 350 cfm i believe, and the 454 throttle body is good for 500+cfm. It should wake up pretty good with bigger air flow. and the injectors should have plenty of flow and pressure to cover it.

If it sets a lean code for enrichment, i will put the 454 injectors on, and burn a chip then.

Wed Oct 05, 2016 2:00 pm
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