Re: Tbi swap build thread
 

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

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

http://www.lightningmotorsports.com/...lbro_chart.gif

and another

http://www.expressfuelpumps.com/images/gsl391-psi.jpg

But you get the idea...

Re: Tbi swap build thread
 

Very nice....

Re: Tbi swap build thread
 

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?

Re: Tbi swap build thread
 

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

Re: Tbi swap build thread
 

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!!!

Re: Tbi swap build thread
 

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.

Re: Tbi swap build thread
 

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

Re: Tbi swap build thread
 

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?

Re: Tbi swap build thread
 

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

Re: Tbi swap build thread
 

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?

Re: Tbi swap build thread
 

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.

Re: Tbi swap build thread
 

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.

Re: Tbi swap build thread
 

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 :lol:.

Re: Tbi swap build thread
 

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. :metal:

Re: Tbi swap build thread
 

I am running the vss just not hooked to anything..... As far as the adapter I used one and just put the sensors close to where they were stock.... I ran a stock coil so I cant help ya there....

Re: Tbi swap build thread
 

Thanks CJ ;)

Pancake - you can mount coil on the fire wall (or in its original location). If you do so make sure to run a ground strap (braid) between intake and coil mounting bracket. Low resistance ground return path is required between EST and coil.

I have seen third gen boys mount monster sized coils (lots money) on the firewall. Generally, performance coils can be saver and trouble all rolled into one. The problem stems from current requirement that these coils place on EST module (inside dizzy). To get HV coil to deliver joules of spark energy (at 40 - 50kV) requires more current flowing through the primary (12 volt winding). EST module operates as a switch which turns on & off current flowing through the coils primary windings. More current = more heat. Semiconductor devices do not like heat and fail over time if subjected to operation beyond rated limits. For our trucks, with engines spending most of their lives below 3000 RPMs use of 'monster' coils is not necessary.

One of these days I'll setup experiment in my lab to measure primary coil winding current and publish my results. I have factory coils, but I do not have any 'monsters' for obvious reasons.

As to recommendation on coil - I have never used anything but stock, hence I can not recommend one.

Sensor placement. I prefer to mount my sensors away from heat sources for the aforementioned reasons. I mounted my MAP on the firewall, ESC module is mounted on fender skirt. All my relays are mounted away from engine. GM mounted the same sensors on a bracket bolted to intake manifold.

//RF

Re: Tbi swap build thread
 

SEEEE I told Ya.
I knew RF would have a very good answer.

Re: Tbi swap build thread
 

It has taken a bit longer that expected to get this TBI swap done.

After going 4 wheeling to a hard t rail here in Colorado I was motivated again to get this TBI swap done. The blazer would die and be hard to start and would not run on its side. This was a huge hassel and made the trails harder.

So needless to say I am going to get this swap done.

Ordered the VSS and the 4 wire O2 sensor. I will pick up a KS and I should have everything.

I decided to use the stock intake and just drill/machine out the 4 center holes. This solves the issue of coil mouint and sensor mounts.

I will have a question when I wire the O2 sensor when I get it. I have the relays but do not know what color O2 wires go to what parts of the relay? I bought the AC delco AFS75 O2 sensor and the relays are off a 83 ish caddy.

I am hoping to start wrenching on it next weekwend.

Thanks again for all your help and all the great information in this thread.:lol:

Re: Tbi swap build thread
 

I understand what you mean about taking longer than you think it will to do this swap. It took me about two months longer than I thought it would take. What takes longer than anything is the little things you just thik of untill...

Good luck and if you have any questions just ask. We all will try to help ya out.