Tbi swap build thread

[glock35ipsc]

Great thread! I have two quick questions, if I may:

1) I might be getting a 91 dually with a TBI 454. Is the TBI harness that is needed for a swap a stand-alone harness, or are the parts of the harness needed part of a larger harness?

2) The 85 I am getting (avatar pic) already has had a 350 TBI swapped in with donor parts from an 87. If I put the 454 TBI motor in the 85, will the existing harness suffice? I am guessing I will need to replace the ECM with the one from the 454 truck though.

Thanks in advance!

[rfmaster]

Originally Posted by glock35ipsc

Great thread! I have two quick questions, if I may:

1) I might be getting a 91 dually with a TBI 454. Is the TBI harness that is needed for a swap a stand-alone harness, or are the parts of the harness needed part of a larger harness?

2) The 85 I am getting (avatar pic) already has had a 350 TBI swapped in with donor parts from an 87. If I put the 454 TBI motor in the 85, will the existing harness suffice? I am guessing I will need to replace the ECM with the one from the 454 truck though.

Thanks in advance!

1) The early OE TBI harnesses, up to about '94, were more or less stand alone across most GM products. In later years additional functionality, notably AC vacuum controls, was integrated along with TBI harness in passenger cars. For the most part trucks used stand alone harness. The biggest hick up with OE harness retrofit can be with the under dash interface - ALDL connector, DRAC I/O (or VSS) and power. Engine compartment difficulties are usually are around Fuel Pump wiring, but this is an easy fix.

2) SBC and BBC harnesses are nearly identical with few exceptions:
a) BBC used different IAC motor and connector is different - four wires.
b) TPS may be different, early BBC used lever style TPS adjustable, while later used throttle shaft style - similiar to cars. Different connector.
c) Some HD BBC did not use knock sensor (KS) and ESC modules - these engines used 1228747 ECM and can be positively identified by broadcast code printed on ECM label (four letter code).

2-1) You'll have to use 454 TBI ECM with your swap to keep things easy.

In general 1227747 ECM (when loaded with appropriate BCC EPROM) was used with V6 (4.3L) and 305/350 SBC V8 and some 454 BBC. The 1228747 ECM has identical harness interface minus KS functionality for HD application. You can swap out your SBC 7747 ECM for 8747 when you perform the swap. Other than aforementioned points 2a and 2b SBC harness is good to go.

//RF

[glock35ipsc]

Originally Posted by rfmaster

2) SBC and BBC harnesses are nearly identical with few exceptions:
a) BBC used different IAC motor and connector is different - four wires.
b) TPS may be different, early BBC used lever style TPS adjustable, while later used throttle shaft style - similiar to cars. Different connector.

So if I were to install the 454 into the 85 truck, would I be able to take the TB that is currently on the 350 and use it on the 454 to avoid these two connector issues?

Thanks for the help!

[rfmaster]

Originally Posted by glock35ipsc

So if I were to install the 454 into the 85 truck, would I be able to take the TB that is currently on the 350 and use it on the 454 to avoid these two connector issues?

Thanks for the help!

Not advisable....

The reason being that the BBC TB has 50mm bores and 80 or 90 lb injectors vs. SBC TB 46mm with 40/55/64 lb injectors depending on engine size. You may be able to get 454 started, but the moment you ask that 454 to deliver power it will lean out and fall on its face. IMHO the swapping harness connector ends is straight forward, except for IAC which may require pin swapping. I believe that I have a set of notes related to this issue. To me revamping harness to mach sensors (2x) is not that difficult.

Take a look at two TBI (SBC/BBC) setups first before jumping to any conclusions.

//RF

[glock35ipsc]

Thanks for the info! I know getting a little ahead of myself here, as I haven't taken possession of either truck yet. Just trying to refresh my knowledge of these TBI's after not messing with them for 20-some years.

[rfmaster]

Originally Posted by glock35ipsc

Thanks for the info! I know getting a little ahead of myself here, as I haven't taken possession of either truck yet. Just trying to refresh my knowledge of these TBI's after not messing with them for 20-some years.

I have both TB types in my collection (and photos) - perhaps posting a side by side comparison, pointing out the differences would be of interest.

//RF

[rfmaster]

Originally Posted by rfmaster

I have both TB types in my collection (and photos) - perhaps posting a side by side comparison, pointing out the differences would be of interest.

//RF

Freshly pulled TB units from my local JY. Note the differences in IAC and TPS. Additionally, the 454 (that I see) were not setup for 700R4 TV cable

454 BBC (87-89) OE# 17087021



350 SBC (93-94) OE# 17093030

[glock35ipsc]

Excellent, thanks for your time and effort in this thread! And cjracing15 too!

[FRENCHBLUE72]

Hey guys I put on a summit brand fuel fuel pump that is rated at a free flow rate of 43 gph and a max pressure of 85 psi will this work as is or should I regulate it somehow?

[rfmaster]

Originally Posted by FRENCHBLUE72

Hey guys I put on a summit brand fuel fuel pump that is rated at a free flow rate of 43 gph and a max pressure of 85 psi will this work as is or should I regulate it somehow?

As long as you have 5/16 or 3/8" return line built-in FPR should be able to handle it. When manufactures specify fuel pressure they usually publish "deadhead" pressure. Typical FP has a two dimensional performance curve - Y axis GPH and X axis working fuel pressure. Most marketing data published is very incomplete! So at near zero fuel pressure this pump is capable of delivering 43 GPH, but as fuel pressure increase the volume decreases (usually non linear curve) until deadhead pressure is reached.

//RF

[FRENCHBLUE72]

I have 3/8 return line so I should be ok then sweet..

[rfmaster]

Originally Posted by rfmaster

As long as you have 5/16 or 3/8" return line built-in FPR should be able to handle it. When manufactures specify fuel pressure they usually publish "deadhead" pressure. Typical FP has a two dimensional performance curve - Y axis GPH and X axis working fuel pressure. Most marketing data published is very incomplete! So at near zero fuel pressure this pump is capable of delivering 43 GPH, but as fuel pressure increase the volume decreases (usually non linear curve) until deadhead pressure is reached.

//RF

Correction - Y axis is Flow (GPH), X axis is pressure (PSI)

Walbro is one of the few mfg that publish their performance curves.



and another



But you get the idea...

[FRENCHBLUE72]

Very nice....

[FRENCHBLUE72]

Ok guys heres an update I got her running but not very well Im in the process of tracking down the check engine light and varrious odds and ends.. Can anyone tell me where this green box goes? And whats the deal with the light at then end of it?

[brontotx]

Originally Posted by FRENCHBLUE72

Can anyone tell me where this green box goes? And whats the deal with the light at then end of it?

Sorry for not responding sooner... I got caught up working at work and on the truck and hadn't looked at this thread in awhile.

The green box and light you asked about are the VSS signal from the speedometer to the ECM. The light hooks into the back of the instrument cluster at the speedo drive and a gear in the cluster (a reluctor I think it is called) causes the light to pulse at a speed/frequency that is proportional to the vehicle speed and the green box converts that light pulse into a 2000 pulses per mile square wave DC signal to tell the ECM how fast you are going. rfmaster discusses the importance of VSS in post #46 of this thread (I also use the JTR VSS signal generator hooked up at the tranny due to speedo cable wind-up).

Mark

[smogdave]

Great project. I am just about done with my TBI transplant myself. I have a 1976 1/2 ton fleetseide that had a 250 I-6 in it. I installed a 1988 GMC 454 TBI with a TH400. I used the 1988 wiring and computer and I modified all of the interior and exterior wiring to work with my original equip. Very healthy set up. just need more traction!!!

[smogdave]

I had to use a 1987 RV fuel tank and fuel sender assembly for the fuel injection. Works great. I just have to figure out how to use a speedo cable in ther TH 400 with the speed sensor. If you have any ideas let me know.

[brontotx]

Originally Posted by smogdave

I just have to figure out how to use a speedo cable in ther TH 400 with the speed sensor. If you have any ideas let me know.

There is only one option for your '76 that I am aware of: get an "2PRS" adapter from JTR. You can mount this anywhere along the speedo cable as it has the same male and female connections as the speedo cable. Wiring is dead simple as the 2PRS has only two wires: one side is grounded and the other wire connects to the VSS signal wire to the ECM.

I originally installed a 2PRS at the end of the speedo cable that hooks into my cruise control transducer because it was easy to get to and install, but my speedo cable is pretty long (or worn) and the speedo cable wind-up resulted in wildly fluctuating signals to the ECM at low speeds. By wind-up, I mean when the friction in the speedo cable builds/twists up and releases the tension at low speeds - if your speedometer needle swings back and forth (especially at low speeds), you have wind-up. To get a good low-speed signal, I ended up mounting the 2PRS at the speedo cable output on the transmission itself.

If you had a later model truck (which I do, but didn't go this route), you could also get an '87-'89 instrument cluster with the VSS optical sensor built in. This option also requires the green box thing and light pickup mentioned a few posts back.

Good luck,

Mark

[FRENCHBLUE72]

Do I really need the vss hooked up to the speedo? As I have no speedo just a tach... Also any tips on what wire is for the check engine light? I assume it plugs into the back of the cluster?

[brontotx]

Originally Posted by FRENCHBLUE72

Do I really need the vss hooked up to the speedo? As I have no speedo just a tach... Also any tips on what wire is for the check engine light? I assume it plugs into the back of the cluster?

Opinions vary on the need for VSS - see rfmaster's post #46 for the reasons why and DirtyLarry's post #48 for another opinion. My opinion is that GM put it in, so I needed to replicate it. My reason is partially driven by my also swapping in an electronically/ECM-controlled 700R4 from an '87 and I am pretty sure VSS is needed for proper torque converter lock-up by the ECM. My point here is that your use of a manual tranny (like DirtLarry) may minimize (eliminate?) the need for VSS.

If you decide to replicate a VSS signal, you do not need a speedo. The JTR 2PRS signal generator can hook to the side of your tranny (or wherever the speedo cable normally hooks to in your truck).

As for the check engine light wire, it is normally the brown w/ white stripe wire going to terminal A5 of the 1227477 ECM. Since my '82 instrument cluster did not have a check engine light, I pushed a stripped wire end into the choke light terminal on the back of my cluster. This made my choke light (which wasn't being used anyway) into a check engine/SES light. Another option is to install and wire any 12V light as your check engine/SES light. Please note that this light has 12V+ with ignition on and the brown and white stripe wire from the ECM switches the ground.

Hope this helps and good luck,

Mark

[FRENCHBLUE72]

So basically I just need the wire from A-5 on the brain wired to the ground side of a light of some sort with power going to the positive side of the light when the ignition is on??? correct?

[brontotx]

Originally Posted by FRENCHBLUE72

So basically I just need the wire from A-5 on the brain wired to the ground side of a light of some sort with power going to the positive side of the light when the ignition is on??? correct?

Correct... see rfmaster's circuit diagram in post #108. The only caveat is that the light you use should not be a grounded internally to its mount or it will be on whenever IGN is on.

[pancake]

Hello again, I have a quick question.

If I use a adapter plate to bolt the TBI to a carb intake:

1) are there rules on whereto mount the sensors that were mounted to the TBI intake.

2) can I use a diffrent coil mounted to the firewall? what kind of coil do I need?

Thanks again.

[cjracing15]

Originally Posted by brontotx

Correct... see rfmaster's circuit diagram in post #108. The only caveat is that the light you use should not be a grounded internally to its mount or it will be on whenever IGN is on.

THe computer turns on the ground for the light so you can have a full time 12 volts to the light but it will not come on untill the computer turns on the ground for A-5. This is how I have mine run. I also used the place for the choke light because that is where GM put the check engine lite from the factory. (except ofcourse it says check engine soon not choke)

As for the vss you will keep getting a ses light untill you install one. Ask me how I know .

[cjracing15]

Originally Posted by pancake

Hello again, I have a quick question.

If I use a adapter plate to bolt the TBI to a carb intake:

1) are there rules on whereto mount the sensors that were mounted to the TBI intake.

2) can I use a diffrent coil mounted to the firewall? what kind of coil do I need?

Thanks again.

1) I would put the sensors as close as I could as the factory did it.

2) As for the coil I am not sure. I am sure RF will chime in on it. He rocks on the wiring diagrams.