Tbi swap build thread

[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]

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

[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.

[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 .

[FRENCHBLUE72]

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....

[pancake]

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.

[cjracing15]

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

[cjracing15]

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.

[cjracing15]

Originally Posted by D13

I'll be following along for ideas on my TBI 250 conversion! What trans do you have? And do you have cruise with VSS like the 1990?

I have the stock 700 in it. I will probablly hook the cruise up later down the road but not this time. And I am going to use a vss sensor from jag that run.
Stay tuned.

[rfmaster]

Part numbers of interest
Part Description Part #
TBI ECM 1227747 BCC ASDU: 1227747
Heated O-Sensor 4-wire: 25312184; AFS75
TBI Overhall Kit: CK1081
Injectors (350) Orange Black: 17112493; 217-344; 5235206
Coolant Temperature Sensor (CTS): 12146312; 25036979
Throttle Position Sensor (TPS): 12116257; 17111787; 17111471
Manifold Absolute Pressure (MAP): 16137039; 2131545; 16017460; PS10076
Idle Air Control Valve (IAC): 17111460; 25527077; AC102
EGR Control Solenoid: 1997111?; EVS30; 17112193
VSS (from JTR): 2PRS
Knock Sensor (350): 10456288; SU154
Engine Spark Control Module (ESC): 16128261; 16131231

[cjracing15]

Ok here we go I got all the pins labeled today was able to take two pics before the camera batt's played out (got new ones tonite), will show the labeled harness tomarow. Here are the two I got off today. It's the engine after I striped all the top-end off. I am rather proud of how clean my rebuilt engine is after a year of daily driving (and a little off road stuff).

[cjracing15]

Originally Posted by Damien

It helps to have a wiring diagram for the donor vehicle. It will take about half a day to sort out and remove all the unneeded circuits. The harness on the newer style trucks comes through the fire wall on the passenger side near the heater box, so some of the wires may be too long or short for a factory appearing installation. Good luck. This should be helpful for a lot of people.

The harness I am using came from a 87 truck (thanks beater c-10), I also had a 90 suburban I bought for parts and I have that harness also to save for anouther project. Anyway I will show everybody tomarow where the stock suburban harness came out of the truck. It is in the same location on this 86 truck because it had the esc distribitor from the factory. I am going to use this hole.( It's on the pass side also)

I looked at a 92 today and they would probably have a little extra wire if you use that harness but not so much that you could not make it look factory if you wanted to.

[cjracing15]

Well I did not get to my truck till late today. But I did get rid of all the wires I do not need on the harness. What you see in the first pic is the harness all labeled and sorted out. As you can see it is kind of in two parts. Tomarrow I am going to take apart all the tie points in the harness and that will untangle the last of the wires and then i will recrimp all the tie points like the factory but hopefully a little less of a spaghetti mess. I will take pics of before and after i do this.

The second pic is where i am going to run my wires in the cab. It is the rubber grommet for the esc brain. It is the same size hole that was in the 90 suburban, so it should work real nice.

In the third pic you see the factory oil presure unit and switch adapter, in the last pic is the one out of the suburban that I will have to use because the tbi oil switch adapter has a different thread size than the carb model. I think I will just drill and tap the 90 model adapter for for the stock gage sending unit. You have to use this stock tbi switch to tell the ecm that the engine has oil press. because the fuel pump wire is run through this switch.

I will try and post here again tomarow. stay tuned.

[rfmaster]

You may want to temporarily drop dizzy back in to check for interference between dizzy body and oil pressure switch. I have a spare SB sitting on engine stand - this gave me ample opportunity to check interference.

[cjracing15]

Originally Posted by 68c10owner

Can anyone tell me if there is a single external fuel pump that will work wit hthe TBI? I have dual tanks so i would need 2 fuel pumps if I went with internal pumps right? Would I have to change my tanks or just the sending units?

If you use in tank pumps you will have to get a FI tank. The fuel injected tanks have baffels in them to control fuel slosh so the pump will not suck air if the tank is low of gas. Plus you will have to get the sending unit and pump.

I am just going with one tank right now because that is what i have. I will get both tanks working in the futrue.

I have talked with "Dirtylarry" about what he did and it sounds real good.

He swap the one primary tank on his truck with the in tank pump, and then monted a transfer pump so he can just pump gas out of the spare tank when he needs it. It will be cheaper I think than making every thing work like stock. (unless I can find a donor parts truck cheap)

[cjracing15]

Well I got to work on the old truck today. Got a little done before I had to quit.

First I untangeled the harness a litle more. I cut all the tie points on the harness and re soldered them so they are all untangeled, and i can route the harness some time this week hopefully. THe first pic is what you will find with a stock tbi harness with all the tie points. They are crimped and covered with tape from the factory. The pic has a sample of both.

Second I got the oil sending unit and switch fixed. I went to the parts store and got an brass adapter to adapt my oil switch to the tee threads. Problem sloved.

Third I instaled the intake on the motor I to use anouther intake than the one in the pic above because I found a crack in on of the back bolt holes. So I was thankfull that I had a spare. You can see in the last pic of the oil switch and sending unit instaled on the block. Stay tuned.