Re: Tbi swap build thread
 

Got it thanks!Didn't have power under cranking.

Re: Tbi swap build thread
 

Hi Guys,

I'm hoping to start on this project the first part of June. Until then I've been gathering parts - got the DRAC problem solved by a couple of fellow forum members (thanks guys!) and I picked up an electric speedo that's supposed to be off of a '91 Suburban and it arrived today. Got a couple hundred thousand on it but that's OK, I don't care what the mileage displayed is as long as the speed displays correctly. The trip metter even still has the stem and it reset the meter back to zero so I'm assuming it works.

I wish I could find the camera but alas my wife and daughter are gone and I can't find it (I can't find stuff in the fridge either!). It has a cut mylar ribbon cable going to a connector that slides onto the speedo pcb. The ribbon cable and pcb have three leads. I'm assuming soldering to that mylar ribbon cable isn't going to happen so using the connector probably isn't an option (though I haven't taken it apart to see if it is or not yet). I'm sure that's no mountain to climb though, one could probably just solder leads onto the pcb traces where the connector slid on.

Do I take it the three leads are power, ground and signal?

Can anyone clue me in on which is which?

Thanks!

Steve

Re: Tbi swap build thread
 

Found the camera!

Here's the electrical connector I'm talking about. It appears in this pic only two leads have traces on the pcb but the third trace is on the other side of the pcb.

/Steve

Re: Tbi swap build thread
 

Ahhh the joy of reverse engineering old circuits. Take look on component side of the PCB - there should be a 8 PIN DIP IC (I guess) - it is in upper right portion of PCB when viewed from the back. It should have mfg part numbers printed on it. By the looks of it, depending on IC orientation, either Pin 1 or 5 tied to trace that is also connected to the lower trace of I/O connector. Lets start there.

If there are any electrolytic caps - find negative terminal which are usually tied to chassis ground. Use DVM to find which of the three pins (if any) are ground connected by checking continuity from cap neg terminal.

//RF

Re: Tbi swap build thread
 

Ok had a few minutes . . .

I held the speedo in it's normal position and then rotated it so I could see the back. When I do that the connector is on my left side and the three connections are as follows:

Pin 1 ===>
Pin 2 ===>
<gap>
Pin 3 ===>

When viewing the back of the speedo there is a 16 pin dip in the upper right hand side of the pcb with a paper tag and a part number printed on it. I didn't get the part # written down, though I thought I did. It has pins 1 & 5 tied together but where it goes from there I lose as it as the tracegpes under the chip.

There is another 16 pin dip chip below that, It's a Texas Instruments chip and has the following printed on it:

<TI symbol> 022 CB
AC SPARK
980 6535H

There is an 8 pin dip chip in the lower right and on top of it it says:
1681B
CS9035H
Pins 5 & 8 of it are tied together. They run to a 15K resistor and it runs to Pin 1 of the connector

Pin 2 of the connector indeed runs to the negative side of a polarized cap.

Pin 3 of the connector runs to a diode oriented like this: -->l-- and then a resistor and then I lost it.

Sooo, we have:

Pin 1 ===> 15k resistor, 8 pin dip pins 5 & 8
Pin 2 ===> negative side of polarized capacitor
<gap>
Pin 3 ===> diode -->l-- , a resistor and more.

I tried looking the chip part numbers up to see if I could get a clue as to what they do but I didn't have any luck. The 16pin dip in the upper right with the paper printed part # seems to have a crystal hooked to a couple pins if that helps.

Thanks!

Steve

Re: Tbi swap build thread
 

Steve

AC-Delco (GM) is notorious for using custom part numbers of commonly available parts. When you buy a million of anything in electronic industry putting a custom part number is an unquestionable ritual. Makes reverse engineering just a little bit more difficult. Let me take a look at my 94 FSM see if it offers anything worth of note worthy.

//RF

Re: Tbi swap build thread
 

Hey rfmaster, I have been playing with my ride and well it runs awesome expect at idle it just wont idle its too low. I don't have any leaks I have checked ! I thought I read some where something about resetting something?

Re: Tbi swap build thread
 

Well I went and bought a TBI gasket kit including the pressure regulator put everything together and now idles in park and in gear at 250 on the tack, but when its warmed up and idling in gear and I get on it she spits and sputters a little. I am sitting at about 4* with the timing.

Re: Tbi swap build thread
 

Yes, IAC reset - search thread for IAC reset (perhaps we should make it sticky how to do it). The alternative is to increase minimum idle with adjustment set screw (covered by the temper resistant plug )

//RF

Re: Tbi swap build thread
 

IRC you have a 283 of unknown origin! IE, it would be nice to know what cam and compression that motor has. One thing that you should do is to get the cast number of your heads. This way some timing adjustments can be made. Since the 283 was never offered with EFI there are no OE chips, but DIY tune can be done if you are willing to invest in your setup (money and time).

250 on the tach ??? That's a bit low??

//RF

Re: Tbi swap build thread
 

Iam sorry I failed to tell you I found out the vacuum on the 283 was to low to run the TBI so I ended up swapping in a 350.
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Re: Tbi swap build thread
 

Ok I got to take my truck out on the road.... Hope you can help, I ease into the pedal Iam fine on take off, but if I get into it she spits sputters back fires through the TBI and if I stay in it it will die. when Iam running at about 45mph and I kick it down she studders and then goes. When Iam sitting their Idling in park I can rev and their is no problems.?.?.

Re: Tbi swap build thread
 

I'll need additional details about your ride to provide any troubleshooting recommendations worth your time.

So far - you have 350 CID motor (I assume it is stock??) - details please it is very important to know what we are trying to work on.
Trany - THM-350??
VSS = Yes or no.
Verified fuel pressure 13 PSI with engine idling???
ECM 1227747 with BCC code (ASDU or ???)
Do you have functional SES light?
Do you have functional P/N switch??
MAP sensor connected to back port of TB (only MAP sensor can be connected to that part nothing else),

//RF

Re: Tbi swap build thread
 

So far - you have 350 CID motor (I assume it is stock??) Yes


Trany - THM-350?? Yes
VSS = Yes or no. NO
Verified fuel pressure 13 PSI with engine idling??? Unsure on how to check
ECM 1227747 with BCC code (ASDU or ???) where do I find the BCC ?
Do you have functional SES light? YES
Do you have functional P/N switch?? Whats this?
MAP sensor connected to back port of TB (only MAP sensor can be connected to that part nothing else), MMM I have it on the front left port and the trans is hooked on the rear port.

Re: Tbi swap build thread
 

Take a look at your TB, in the back. Between inlet and outlet fuel ports there should be 1/4" vacuum port. Connect MAP sensor vacuum line to it. Nothing else can be connected to this port! For transmission vacuum modulator use intake vacuum port - there is usually one port available tapped into #8 cylinder intake runner. It usually used for power brakes booster and transmission vacuum modulator. Front vacuum ports are not suitable vacuum ports for MAP sensor.

BCC is printed on the ECM service label along with service part number - 1227747. If this label is missing you can remove EPROM cover plate (2x 1/4" sheet metal screws) and read BCC from EPROM label. However, this is not critical at this time.

P/N switch stands for Park/Neutral switch and tells ECM if trany is in Park/ Neutral or in Drive - ECM will increase idle RPM when gear selector is moved into drive to prevent engine stall.

Since you have 350 CID engine - you better have 62 lb injectors - right???

Do you have EGR??

//RF

Re: Tbi swap build thread
 

I used the search feature and found this thread, man is it awesome! I started at the beginning and made it to page 9 before skipping to the last page praying that this thread was still alive. I have an 85 k20 suburban with a 350 and swapping out the manual trans for a rebuilt 700r4, was going yo do the 5.3 swap but it's just not for me right now. Anyways I'm going to pick up a 91 1500 suburban parts truck after work and going to start my swap this weekend hopefully. I'm going to go back and read over the 21 pages I just skipped but I'm sure I will have a few questions for you guys along the way and were just wondering if you guys were still here
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Re: Tbi swap build thread
 

With a square body to square body swap with both being Suburbans your swap should go fairly smooth.

Good luck and keep us updated.

Re: Tbi swap build thread
 

Thread is still alive - we just enjoy driving our trucks during nice weather!

Since you have a 91 donor for your swap it will make conversion easier. Couple of issues that I see for you - are you planning to keep 4 wheel drive system in your 85 K20? How much of the 91 drive train are going to swap into 85???.

//RF

Re: Tbi swap build thread
 

I'm keeping my entire drivetrain just using all of the tbi stuff of of the donor truck, was gonna take the heads and intake but this truck has blown head gaskets so I may just use an adapter plate on my intake. What problems did you forsee with my swap ? I do know that the donor truck is 4x4 but I'm not sure if it has a 700r4 in it or not but I just assumed that a 91 would
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Re: Tbi swap build thread
 

Your 91 V1500 should be a 700R4/4L60 with an electronic speedo NP241C transfer case. You will need to swap in both the trans & transfer case along with the gauge cluster as the speedo is electronic and not cable like your 85.

The computer may not like the cam in your 85 very much so you will probably need to do some tuning once you get it running. The VE of the older heads and intake are bound to be quite different than the TBI parts too. Nothing a little quality time with TunerPro RT won't fix.

Re: Tbi swap build thread
 

How do I go about keeping my older 700r4 in it ? It's freshly rebuilt with 0 miles on it
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Re: Tbi swap build thread
 

Is the spline count different on a newer 700 and 241 transfer case
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Re: Tbi swap build thread
 

I don't think so. The 208 and 241 transfer case are pretty similar, save for the speedometer drive.

If you don't want to swap those out, JTR sells a VSS that is driven by the speedometer cable. I went that way on my swap; the part is $75.

Re: Tbi swap build thread
 

Thanks guys. Look at me flooding you guys with questions and I haven't even picked up the doner truck yet, man 4:00 is taking forever to come I feel like a kid on Christmas eve !
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Re: Tbi swap build thread
 

Did you already do the manual trans to auto trans conversion?

If not then the transfer case of the 85 manual trans in the K20 should be a large fine spline that won't allow the older small fine spline 700R4 / 4L60 to bolt up to it. It could also be a large 10-spline setup if somebody retrofit an older SM465 & transfer case into it some time in the past but neither will fit the 700R4.

You will have the small fine spline transfer case you need to do the 700R4 / 4L60 conversion with the 91 V1500 parts truck. The NP241 in it is an upgrade over the NP208 as well with a stronger chain design and a few other upgrades.

Your older 700R4 will bolt right up to the transfer case in the 91 and the driveshafts should be close to the right size for you too. You will have some differences in the rear section of the rear driveshaft with the 14-bolt vs. the 10-bolt rear axles. You should be able to put the back half of the 85 driveshaft onto the front half of the 91 rear driveshaft to make a hybrid length version to bolt the 700R4 / NP241 to the 14-bolt in the 85.

It will simplify your TBI conversion too as all the wiring and ECM is set up for the non-mechanical speedo pieces in the 91.