From: Jeff Fraisure
Sent: Friday, July 20, 2012
To: Bob Musgrove
Subject: Junkyard TBI
Hi Bob. We got it done! Two of us worked 4 days to put it together but that included a new aluminum manifold and removing and cleaning up and painting the valve covers. Noble has about $400 in the whole system (not counting the manifold). We tested it yesterday and it runs perfect, as good as mine. His engine has about 95,000 miles on it. We used Swartzendruber's schematic from the Eastern states website with the exception of the oil pressure switch. Your chip must provide fuel a pump drive signal any time there are ignition pulses?
Noble had pulled a couple of appropriate wiring harnesses in a junkyard for a total of $14 from old trucks so I was able to build a custom harness in place from premade pigtails to the sensors routed up through the floor under the passenger seat and stay true to the color coding. The ECM is under the pass seat. Splices were all soldered for reliability. The tbi was from a 95 truck with a 454 that he got for $40. The problem with that year was it used 45 lb/hr injectors at 30 psi. I would rather not run that high a pressure. I had tested the tbi on my coach and it ran fine but it makes my butt pucker. We found a set of 80 lb/hr injectors on ebay for $60 and used a 15 psi pressure regulator from a junk 350 tbi. A tbi rebuild kit was $25 from O'Reilly. All of the sensors were from the junkyard except the O2 and knock sensor which he got new on ebay for about $20 each. The 1227747 ECM was from a junkyard for $30 and the distributor was junkyard for $30. The fuel pump was a new aftermarket Ford style from ebay for $40 and we used a new Ford style high flow filter like Howell uses. He still has to figure out how to make an intake plenum and filter system.
Bottom line, if a guy has the skills to do this, is not rushed for time, your chip, and is willing to scrounge the junkyard and knows what he needs, you can do a quality job for little money. While I was doing it and my back was aching and my legs were going to sleep while soldering the wires to the ecm harness I kept thinking this is crazy, I'll NEVER do this again. But when we hit the ignition and it started right up you kind of forget that part. All we had to do was set the timing and adjust the throttle position sensor and the throttle idle stop. We took it out on the freeway, up and down hills and all over town and it never hesitated. He said it has never ran so good. My feeling is that if you can test your parts on a friends known good coach with the same system, use your chip and do an accurate job of wiring to Swartzendruber's schematic, it will work. The other alternative is to buy a premade harness from Howell. (When my legs were paralyzed from kneeling we came real close to getting one overnighted). The problem with the new Howell harnesses is they are more generic and have a lot of plugs and pigtails that we don't need. Plus it is $350 which kind of kills the economy of it all. Ours was essentially $14 but a lot of planning and work. It is my understanding that they don't make a specific GMC harness like they used to. If you have the ability to custom make one it will be a better fit.
I still think a 350 tbi will work on a 455 and probably for sure on a 403. I have one but I have to find another set of 80 lb/hr injectors. The stock ones are 45 lb/hr. The 350 tbi is more plentiful, easier to find and cheaper than a 454. The engine just does not rev high enough on a motor home to warrant 600 cfm. I'll let you know when I get a chance to test it on my coach.
I'm going to advise Noble to get a spare chip from you. We all try to carry spares for the whole system for troubleshooting if needed on the road. He is a good guy. He spent 6 days helping me remove and replace my engine last year.
Thanks for your help on this. Without your chip it wouldn't be possible.