Set the timing to zero (pointer and ball bearing on flywheel match up) Installed the 3.1L computer and left in the 3.1L injectors. Let it idle until it got up to around 190 degrees and actually did better than I expected. Has a slight fluctuating idle but not bad. Idles around 800. The next time I have a chance Im going to experiment a bit more. Plan is to try both the 4.3 and 2.8 injectors with the 3.1 computer and see how it goes. Still wondering about the 261 running better with a 4.3 computer and 5.0 injectors. Maybe I will have the same outcome with the 3.1 computer and 4.3 injectors. The Throttle position sensor checks out fine, the map sensor I'm not quite sure on. I get 5.1 volts across terminals A (sensor return/ground) and C (sensor 5v reference), which seems correct. Across terminals A and B (sensor signal to computer) I get like 4.2 volts. Across terminals C and B I get about .3 volts. All this is with the key ON and engine OFF. From the testing procedure that I got off of a automotive repair site, this is backwards. I have to test the IAC valve yet. More than likely I will just end up purchasing a new MAP sensor anyways and getting a few IAC valves at the local yard. will see!!!
Ignition Timing Ball on pointer is 10° BTDC ~ TDC is triangle on pointer and you certainly don't want that ! .
A bit of a update on this. I have not given up on this, I just recently in the last 3 months started working on my truck again after taking a break for about a year it seems. Othe hobbies took over, almost to the point of complete lost of interest in the truck and going as far as listing the truck for sale. After I listed it for sale I started working on it and decided to keep at it. When I stopped, I had the 3.1L computer, a 4.3L throttle body unit and injectors and was quite happy with how it ran. Truck never seen pavement yet so I can't say much more about that. At startup the truck idled ok, started with a bit of a high idle (about 1000rpm) and as normal would start to drop the idle to about 700rpm. Problem was when the idle dropped and the computer started to lean it out at idle the computer would have to give it a bit of a jult (Idle air valve would open and idle would increase slightly) to keep going. Just recently I picked up a few things to try out. I grabbed a TBI unit off of a 3.1L at the local u-pull-it yard. The 3.1L TBI unit has smaller throttle openings then the 4.3L (1-3/8" compared to 1-11/16") and also a lower flow rating for the injectors (33lb/hr to 40lb/hr). First I tried the 3.1L computer with the 3.1L TBI unit and 3.1 injectors. Result - would not idle at all. Started fine but if throttle left unattended it would die instantly. Guess is too lean of a mixture. Then I tried the 4.3L computer with the 3.1L TBI and 3.1L injectors. Result - same as above but not as bad, but still would not idle. Probably because the 4.3L computer has a longer injecter pulse width then the 3.1L computer so it wasn't as lean. Next I left the 4.3L computer hooked up, but instead used the 4.3L injectors on the 3.1L TBI. Result - much much better, idles very nice, starts at 900rpm and as the engine warms up and the computer starts to lower the idle rpm and lean out the fuel it goes down to about 650rpm. This time around I'm getting technical. Using a ALDL to usb cable and diagnostics program called WinALDL loaded on my laptop so I can monitor the computer and see whats going on. From reading different forums online about tuning I know I can find out if I'm running lean or rich by monitoring the BLM table, a number above 128 means the O2 is seeing a lean mixture and below 128 its seeing a rich mixture. I've also come to realize that the stock computers tune just isn't going to do. So from doing some research on thridgen.org (camaro forum), they have a few computer tuning forums. http://www.thirdgen.org/techboard/diy-prom/ & http://www.thirdgen.org/techboard/dfi-ecm/ I found a few options for tuning. First option (which is what I'm going with) is an adapter from moates.net, since the eprom thats used in the earlier GM computers require expensive equipment write to, this company has came up with an adapter to use a later flashable chip. A little solder work is required but for $135 for all thats required its probably the cheapest option out there. Parts needed: http://www.moates.net/g2-memory-adapter-060-leg-spacing-p-36.html?cPath=64 - adapter gets soldered onto the board after the old 24 pin socket is removed http://www.moates.net/s2-aries-28pin-zif-socket-p-44.html - 28 pin socket http://www.moates.net/c2-sst-27sf512-chip-p-39.html - new flashable chip http://www.moates.net/burn2-chip-programmer-p-197.html?cPath=64 - used to burn or write the program to the new chip The other option, also requires a bit of soldering is the EBL flash. http://www.dynamicefi.com/EBL_Flash.php It replaces the part of the GM ecm where the eprom or memcal and calpak reside with a new board that allows you to flash a new program through a serial data cable, so no need to remove the chip to program. Also includes datalogging and the way I read it the ability to have multiple tunes that you can switch back and forth using the software or a switch. This option was a bit more at $350. I liked this the most but wanted to keep this project as low cost as possible. I have not read any negatives with either route so I shouldn't have a problem. I also came across a program that will take a saved datalog file from WinALDL and make the changes to the bin file(ecm file that is burned/written to the eprom/chip) for you. That program is called ALDL to BIN On top of that I am using another program called TunerCATS to edit the bin file to disable the egr valve and maybe a few others. I can also use this program to burn/write the new bin file to the chip. To also help I purchased a Innovate Motorsports LC-1 wideband O2 sensor kit so I can monitor the air/fuel ratio more closely. The thing I need to figure out is what TBI unit would be better. I'm thinking I should switch back to the 4.3L TBI unit so everything matches. 4.3L computer, TBI unit and injectors then start tuning. When I open the throttle when using the 3.1L TBI unit just the sound of the air rushing in sounds restrictive. I'm going to post a picture soon and ask were would be best to mount the O2 sensor. Im not certain the location I have it at now is the best place for it. And I may end up changing the narrowband O2 sensor to a heated version. I don't know if its OK to always run using the LC-1 wideband kit.
This is currently where I have the narrowband O2 sensor. Just a stock GM replacement that goes to the ecu. http://i175.photobucket.com/albums/w124/rockfan1815/final tbi conversion pics/100_0862.jpg I was wondering if it would be better to mount it closer to the header or in the header at the collector. http://i175.photobucket.com/albums/w124/rockfan1815/engine/100_0094.jpg
Chris good to see you back at getting that 54 engine to work as you want it to. Just wish I had the time and energy to do that also to my 54 engine. Keep up the great work. Also are those headers off the shelf at cliffords?
Thanks Yes they are clifford headers. I bought them and the intake for I think $500 total from a guy on another forum a couple years ago. I just recently pulled the headers off, brought them down to bare metal and sprayed them with cast blast and used the heat from the exhaust to bake them. Came out nice.
Good to hear you are back into this. I still believe when you get this figured out, you could package it and sell it.
I was thinking of that, or at least writing up a good tech article once I'm 100% satisfied with how it runs. Once I get a tune that works I can upload it to one of the tuning sites so others can use it.
What I'd really like to know is if a 1 barrel TBI unit/injector could be used on a stock manifold (with possibly an adapter) and run correclty, with a computer tune of course. Could probably use a 4.3L 1227747 ecu. Though its used with a 2 injector tbi setup, that pulses the injectors one then the other, not both at the same time, I can't see why you couldn't wire both injector outputs to 1 injector. Might need some type of diode in both injector output wires to prevent 1 output from feeding back into the ecu through the other output wire. Someday I'll have to print the following list and take a walk through the local u-pull-it yard. Anyone know the distance of the 2 bolts on a stock 235 manifold. Also the bore/diameter of the stock carb. Like I said an adapter would probably be needed. http://www.championparts.com/tbi_applications.pdf also a interesting writeup by someone http://www.rowand.net/shop/tech/SlantSixTBISwap.htm
Wow ~ This is SO comprehensive ! . You're doing a bang up job here , thank you for sharing all your thoughts and information .
I have bought at least 4 of those $6.00 Universal Ignition switches, they all are bad out of the box or go bad in a few months. I have an original 54-57 switch in my 53' from our sponsor. Pretty good Quality but the Stainless Outer tightening ring doesn't lay down right on our 47-53's dashes with 12v key start ignitions. If anyone knows of a good quality Ignition switch for key starters, that will mount correctly please let me know. Flashlight
Drumming52 I'm not 100 % but I was thinking you may overload the no 1 circuit trying to run 2 injectors off it. Jus my 2 bob
No I was thinking of doing the complete opposite of that, run 1 injector using 2 output circuits. The TBI systems alternate the injector firing so if using a single barrel throttle body unit that only has the 1 injector both injector outputs would be wired to the single injector. If I still had the stock intake manifold for my 235 I probably would have pursued this route and found a way to mount a single barrel tbi unit on the stock manifold. Of course the injector probably would be a bit undersized because as far as I can tell the only engines that used a single barrel throttle body unit were 4 cylinders. Might have been able to find a higher flow injector that would of worked but it probably wouldn't be cheap.
6 injectors Wonder if you could screw 6 injectors into the manifold and let the TBI control the air flow? The new cars have injectors close to the valves/heads. It seems to work by magic, smoke & mirrows.
Injectors Sorry, missread your post, if you were to wire 2 signals to the one injector you could get overlap on the signal or get too close to the injectors pulse limit at higher revs, I'm not sure one injector would supply enough fuel, it's asking a lot for one injector to do an old long stroke lump, I noticed you said you wasn't going to use the knock sensor but (and I'm the first to admit I know not a lot) I thought they had to be used, even though you can't hear a knock the sensor is giving feedback to the ecu about the state of the combustion and without it it's a bit blind, Please don't think I'm being critical, I'm just interested, I once fitted a merc (European not the US one) injected v8 into an late 60' merc and got it working, but that was many moons ago
Probably why most people that do a tbi conversion go with a 2 barrel setup whether a 2bbl tbi unit on a 2/4bbl manifold or 1bbl tbi units on a multiple carb manifold. I did end up using the knock sensor, one from a 4.3L and from what I can see it works fine. Mounted it on the driver side where the coolant drain was. The way I read it on a tuning forum, using the diagnostic program on my laptop which shows the knock count, if the knock count increases any more than it did at startup there is excessive knocking. It can be removed just by wiring the input to a 5v reference signal.
That would be a multi-port injection system. These systems are a bit more complex then a TBI system as they usually use a cam and/or crank position sensor because it only fires the injectors 1 at a time. There are a few systems that do fire all the injectors at once, a batch fire system. Like what this guy used http://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=437492#Post437492 The TBI systems just use an input from the distributor to fire the injectors. Every time a spark plug fires, the computer gets an input to fire an injector.
Is there any reason you could not use a 1bbl to 2bbl adaptor and then adapt from the 2bbl to the 4.3 tbi? The 2bbl to the TBI is what Jeep users do on their 258s, so why couldn't we just adapt to the 2 bbl and then go from there? Or, you could machine an adaptor from the 1bbl mount to the 4.3l tbi body, then you only have the one adaptor. Would that be possible, or am I missing something?
