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Looks like it's my turn to give tbi swaps a go
- Thread starter az_762_nato
- Start date
Thank you!
If you do plan on programming, when you get there, I can most likely let you borrow my stuff. I can't let it go now unfortunately, as soon as I get the crate motor in I need to check the tune.
With TBI, you just have to get the ECM setup for the newer chips that are used. I never did get into it, but EBL and megasquirt are two options apparently.
@Team208Motorsports isn't local to you, but he does TBI programming mail order. You'll need to do some datalogging with a wideband O2 sensor for him, but he should be able to get it running fairly well.
I put a TBI setup onto my old 77 Stepside with a 350 and had a lot of issues with it. It ran well enough but was down on power and I had issues with it stalling while coasting without the VSS hooked up. I messed with the tuning for a while but never could quite get it right. In the end, I wound up swapping a bone stock TBI engine into the truck with it's stock PROM to match and installed a VSS then it ran like it came from the factory with TBI after that.
The biggest issue wasn't so much with the difference in volumetric efficiency so much as it was with the camshaft profile. The older cam profiles have a fair bit more overlap which allows fresh air to pass right from the intake valve to the exhaust valve while both are open at the same time during the overlap. This causes fuelling issues as the O2 sensor reports a lean condition and the ECM richens the mixture up as much as it can at idle. The result is eye burningly rich exhaust and an engine that just doesn't run right. The TBI ECM just isn't capable of dealing with this kind of an issue like the newer mass air ECMs can.
A couple hundred bucks spent on a computer friendly camshaft would go a very long way in making your engine run like it should, but sometimes it is cheaper and easier to simply swap in a used engine (around here a TBI 350 costs around $3 - 500)
I put a TBI setup onto my old 77 Stepside with a 350 and had a lot of issues with it. It ran well enough but was down on power and I had issues with it stalling while coasting without the VSS hooked up. I messed with the tuning for a while but never could quite get it right. In the end, I wound up swapping a bone stock TBI engine into the truck with it's stock PROM to match and installed a VSS then it ran like it came from the factory with TBI after that.
The biggest issue wasn't so much with the difference in volumetric efficiency so much as it was with the camshaft profile. The older cam profiles have a fair bit more overlap which allows fresh air to pass right from the intake valve to the exhaust valve while both are open at the same time during the overlap. This causes fuelling issues as the O2 sensor reports a lean condition and the ECM richens the mixture up as much as it can at idle. The result is eye burningly rich exhaust and an engine that just doesn't run right. The TBI ECM just isn't capable of dealing with this kind of an issue like the newer mass air ECMs can.
A couple hundred bucks spent on a computer friendly camshaft would go a very long way in making your engine run like it should, but sometimes it is cheaper and easier to simply swap in a used engine (around here a TBI 350 costs around $3 - 500)
Well, a few changes came up. I decided screw it and just sent both of my ECMs to Moates to get socketed (I shake too much from nerve damage to risk soldering them myself). I do plan on running VSS, I have a gauge cluster from an 88 with the green box optical VSS in the back of the speedo. Also decided to just grab an ALDL cable, a burn2, and pulled the wideband o2 out of the Benz for a while while I tune. Got onto tunerpro and started looking at the ECM parameters and decided just to do the tuning myself. I hate (absolutely LOATHE) computers and tuning after doing the tuning on the Benz (E55 AMG) myself, but this TBI setup looks like a cakewalk compared to that thing. Turned minimum coolant temp for EGR activation to 290 degrees, effectively shutting down EGR function, as soon as everything gets here I'll burn the chip, prime the pump, and give it a shot!
Did find an issue with my adapter. I'm using the trans dapt 2206 that rear mounts the throttle body so it's over the qjet secondary bores. One of the bolt holes for the adapter is right underneath the IAC and the bolt holt isn't countersunk so the bolt sticks up in the way. I'll drill that so it's countersunk and out of the way like it should be while I'm waiting for my stuff from Moates
Another question, what park/neutral switch do I need to swap in? The 73 only has 4 wires; the 2 big purple ones for the starter, and the 2 reverse light wires. Just need an idea of what to swap in for the org/blk wire to connect to for the ECM's park/neutral input
Wow, ur, Im not much help there...
If I can't get to the parts yard for a bit, I'll probably end up removing my starter circuit from the original switch and using that circuit to give the ECM its ground in park. I have always kinda liked being able to crank a starter in drive anyways...
I've been spending a little time running through tunerpro rt, the fact that it's not complicated at all is making it overly complicated for me, lmao. After years tuning on our AMGs, I can't wrap my head around how easy this thing is. I think building the TBI harness takes less time than it does to get a Mercedes ecu to communicate with the SDS software!
They are apparently quite basic compared to the more modern stuff. Haven't spend much time on the TBI side of the house, but with TPI the issue I don't like is that you will change fueling (through MAF gms/sec) but you then have to go back and work on open loop tune, enrichment, etc. It doesn't extrapolate any of the known data and calculate what other settings should be based on that. I suppose a limitation of the earlier software, but as with cold start tuning, there is no way around getting it right, except to start it up cold and see if your adjustments worked. If they didn't, have to wait until it cools completely off and try again. I believe this is some of what the "self tuning" ECM's out there try and resolve. Or did, as GM OBD1 tuning seems all but dead.
I've been doing a little to it here and there as I get time. Pump is dropped in, TBI is bolted up, dissy is stabbed, throttle and detent cable are hooked up, sensors installed, all wiring done, ECM on the floor, and chip #1 burned. Hopefully tomorrow I'll be pulling the new fuel lines and starting her up. The one thing I haven't done yet is swap out my 73 speedo for the newer one that has the VVS buffer dingleberry hanging off it. I have an entire cluster from the speedo donor, anyone know how difficult it is to swap from the 73 cluster (with mech oil pressure and broken ammeter) to the 88 cluster? I have the oil pressure sender from the 88, that part should be easy.
If there is any at all I'll be very happy. My timing and qjet were tuned about as good as it was going to get. I got great mpg and on the secondaries I had plenty of power too. TBI bores being bigger than the qjet primaries, I'm assuming I'll have some gains. Big upsides for me are the cold starting and that remote start for the winter, and definitely NOT having to play with the qjet every few thousand feet in elevation. My driveway is at 6209ft, where I park at our main mine is just over 13200ft.
Any chance you can take and post a picture of the back of that cluster? I'd like to see what the circuit traces look like...on the '90-91 clusters GM got smart and greatly simplified the layout, if they did it before that, maybe you got lucky.
It's not hard, like everything else on the rig, it's all 12V, ground, and the input from a sending unit (temp, oil pressure, fuel gauge). The 12V and ground can be shared amongst all the gauges, but when you start getting into the idiot lights (brake, CEL, seatbelt, 4WD) they aren't quite so simple, but still not difficult when dissected into the individual component you are dealing with.
When I was messing with mine, I just wrote on the flex circuit copper traces what each trace did as I followed the copper from the gauge/light towards the IP connector, so I wasn't confused when I got to the instrument panel (IP) connector. Then it's just a matter of matching those wires up to what is coming into the IP from the truck. Being a '73, I assume you have no use for the 4WD light, seat belt, etc., so those could be ignored. I assume you know you can move the wires around on the IP connector quite easily, just have to de-pin each terminal from the connector, and move it to the right spot.
Or you can spend a few weeks gathering parts, and hard wire the cluster, and eliminate the IP connector as the failure point it is.
I figured I could repin it pretty easily like most gm stuff as long as I can figure out what goes to what. I'll post a few pics of the back of it first thing in the morning, it's from an 88 GMC burb
Well, it's in and running. BLMs are high 130-160 so it's time to rework the ve table and burn it again. So far the idle quality is stellar!
I'd honestly forgotten how easy these trucks are to work on too. Found a new sender and in tank pump that swaps directly into the 31g k5 tank too, 94 or so 1500 pickup. I can grab the exact model next time I'm at the yard for anyone who needs it, but it's the same depth tank. Pump sock sits right at the bottom and the locating tabs line up perfectly, fuel level seems to be dead on to my original sender.
I did find pinouts for the instrument clusters on the various years, but haven't done the whole swap yet, just dropped the 88 burb speedo and buffer into my 73 cluster. A little more work and she'll be set as soon as my remote starter kit gets here. On a side note, it was rewarding to use a timing light for something again after all these years. With the qjet and hei I just timed it by vacuum. Now if I could just seal up the damn th350 that is constantly in the process of changing its oil all over my driveway....
I did find pinouts for the instrument clusters on the various years, but haven't done the whole swap yet, just dropped the 88 burb speedo and buffer into my 73 cluster. A little more work and she'll be set as soon as my remote starter kit gets here. On a side note, it was rewarding to use a timing light for something again after all these years. With the qjet and hei I just timed it by vacuum. Now if I could just seal up the damn th350 that is constantly in the process of changing its oil all over my driveway....
So far this thing drives like a dream, only issue I've has is a malfunctioning tank vent that is closing up and making my tank pressurize, then the gas cap starts squealing as it releases the build up. It does still like to idle a bit high, and in open loop for some reason today. Here is the log from this afternoon's drive if anyone who knows these wants to take a look and offer any advice they may have.
https://drive.google.com/file/d/0B4TWX8OROOmQODQzTUJ4bmZTWTg/view?usp=sharing
https://drive.google.com/file/d/0B4TWX8OROOmQODQzTUJ4bmZTWTg/view?usp=sharing
