TBI Conversion

[Jason915]

My TBI Conversion

My 70 K5 had a real tired 350 in it that maybe put 100 HP down so I decided to start thinking of replacing the engine. My goals were to build a daily driver that would have adequate power for light towing up mountain passes and some off roading and most importantly get better than 10MPG. I decided to do a TBI conversion and I picked this set up because it is a real simple EFI with just a handful of sensors and nothing real complicated about it. I first started off at the local junk yard and got a TBI intake, with TB and all the intake sensors, CPU, distributor, and knock sensor off of a 1989 K2500 Suburban with a 350. Then I started looking for an engine, I was just going to order a longblock for an 87-95 (L05) Chevy truck so I was sure that everything would work as it should. But then I decided to put my own engine together in an effort to build an engine that had a bit more power than a stock L05. I ended up getting some rebuilt cylinder heads that are 083 castings GM used these in Z28 TPI 350’s through the 90ies as well as factory 285-300 HP GM crate engines, and HP Marine engines basically they are Iron versions of the Vette L98 cylinder heads. They flow better than the L05 swirlports and they have traditional combustion chambers. But most importantly they have the center intake holes angled at 72* so the TBI manifold bolts right to them. I also picked a CPU friendly CompCam CCA-12-249-4 and bought a rebuilt 4blt main 350 short block. I planed on using the headers already in the Blazer so I welded in a bung for the 02 sensor. Because the 02 sensor is located further than 12” from original intended location I used a 02 sensor for a 1995 S-10 4.3 V6 because it is a 3 wire sensor or what is also referred to as a “heated” 02 sensor. I had to also get the GM pig tail for the sensor it has 3 wires a green a black and a white the green goes to the ECM the black to ground and the white to a fused ignition hot wire. From painless wiring I bought a stand alone TBI wire harness, a vehicle speed sensor, and a park/neutral wire kit. I intended to use the EGR for better efficiency on the Highway so a VSS is required to keep this functional. The park neutral kit just lets the ECM know when the vehicle is in gear or neutral. I also bought a Walbro inline fuel pump that will supply the required supply to the TBI; this is the pump that Holley sells as for their aftermarket TBI set up. It is silent in operation and that was a surprise to me because everyone told me that inline fuel pumps are real noisy. I also had to run a return line to the gas tank and that was easy all I did was run the line to the frame on the drivers side to the filler tube then I made a pipe with a tube that turns down into the tank and connected the return to that, I didn’t even have to drop the tank. Because I used different cylinder heads, headers, and cam then a stock L05 that my ECM was programmed for I ordered a custom chip from tbichips.com. Everything was straight forward and only a few snags like the kick down detent cable had to be replaced. I just fired it up last weekend 4th of July so I haven’t driven it enough to record my MPG but throttle response is great and power is very adequate. My EGR vacuum solenoid has a different connection than the painless wire harness has so I need to change the solenoid out before my EGR is functional. Also when its cold it surges at idle and will die but once warm it’s just fine. So I have just a few bugs to work out of it but overall I am very happy. Total cost for me was about $900 for this conversion and I didn’t think that that is too bad because if I was going to a carb set up I would have spent 300+ on a carb 130 on an intake and 180 on a distributor.


10/20/06 Update I have been working out the bugs when I have time, just got my chip reworked and put an open element air filter on it and now it runs real strong!

This is an older picture when I was still finding minor wiring problems and stuff, now all the wires are neatly re routed and covered and I have a new air cleaner


http://www.tbichips.com A great GM Chip tuner

http://www.advanceautoparts.com/engl...0001001fi.html a good TBI conversion Article

http://www.fullsizechevy.com/forums/index.php Late model Chevy truck fourm this board has a lot of good info about late model EFI stuff.

[BIGRIG]

I'm doing this swap right now. I pulled the complete motor and trans from a 93 caprice. I'm wondering if you had problems with the main line on the truck being 5/16" and the supply line to the tbi being 3/8"? any help is appreciated.

Chris

[Jason915]

No fuel line problems at all I just installed a filter inline before the fuel pump and one before the injectors.

[culookn]

if I pulled the entire harness along with the ecm I will be able to almost "bolt the entire thing in? what about a vent for the gas tank?

[ol' truck]

interesting.. does anyone have a list of sensors.. what I need/not need.. I wanna convert mine when I build the engine in my 71..

[Jason915]

Sensors are

Knock sensor
Map Sensor
CTS (coolant temp sensor)
02 sensor
oil pressure sensor

I think that's it, simple set up

[clay68c10]

As far as wiring it in, you'll have to work out the different power circuits and also figure out what isn't needed on the old harness. I bought a factory wiring diagram for the donor truck so I can figure that stuff out. It may be time consuming, but I'm trying to save that $300. The used GM wiring manual cost $35 off ebay and I enjoy the challenge of figuring this stuff out.
You shouldn't have to worry about the TBI charcoal cannister/purge venting stuff. You could just get rid of it all or incorporate it into your truck's factory charcoal can (69-72?). Or, you can use the vent line on your tank for your fuel return line.