Replaced module in distributor. No change. Tested coolant temp and throttle position sensors. Good. Checked computer. Service number ending in 7747. Checked injector spray. Looks good. Nice cone shape. Checked vacuum at idle about 17. That is low according to most accounts. Just off idle goes to 20. We installed a mild "rv" cam. Do I need a programmed chip for the ecm? Should using the v6 TB unit with the V8 injectors be a problem?
Have you located the esc module yet? About 3x3x.5" thick, wide flat plug. Should have been mounted to intake. V8 and v6 units are different. I may have a v8 one kicking around
There is a parts mismatch somewhere.. what parts did you use off the V6, and what from the V8 donor?
I'm thinking the cam is the root of the problem. What are the specs of your "rv cam"- lift, duration, etc? How was it installed- straight up, advanced, retarded? How did you adjust the valves?
Try throwing more timing at it- my experience with Chevy TBI motors is that they really wake up and run better in every way with 10 degrees or more of initial timing.
I'll second that, +10 degrees of base timing advance was good for mine as well.
TBI is known for not playing well with bigger cams, so the cam could potentially be an issue if the computer is expecting more vacuum. If the vacuum signal oscillates a lot, it can also cause issues, and either a small orifice or a chamber to dampen the signal in the tube can help with this.
Yep. Missed the cam. The low vacuum signal will mess with the timing.
I can loan you the chip burning stuff and aldl cable if you want. Just let me know.
patgizz wrote: Have you located the esc module yet? About 3x3x.5" thick, wide flat plug. Should have been mounted to intake. V8 and v6 units are different. I may have a v8 one kicking around
Pat, I'm confused. I thought the ESC was in the distributor. What you're saying is a different item altogether. I believe I know what you are talking about. It's mounted on the same bracket as the MAP. I did not get from the v8. Will hit salvage yard today. Fingers crossed.
Got a picture of one for reference if that will help 
Here's the location on a C1500 
It's a good idea to grab the MAP sensor if you can, it's behind the TBI on the left next to the distributor if your are facing the engine. New aftermarket ones usually suck, I've got a bunch of factory ones for spares as they rarely die.
Got the ESC. Still poor idle, low vacuum. Got the cam specs this morning. @ .050, 204/214. Harris performance puts that at level 4 or stage four and not compatible with the stock prom. Waiting to hear back from him for chip suggestion.
Just drove it. Anything over half throttle with a load (going up slight incline) causes loading up and backfire.
Just looking over the website for Harris Performance tbichips.com he seems to be pretty adamant about having adequate fuel pressure, the stock 12-13 psi won't make much power and if your pump is old you may not be getting even that. I may look into getting one of his 18 psi regulator springs for my truck, lots of good info there for TBI setups.
06HHR wrote: Just looking over the website for Harris Performance tbichips.com he seems to be pretty adamant about having adequate fuel pressure, the stock 12-13 psi won't make much power and if your pump is old you may not be getting even that. I may look into getting one of his 18 psi regulator springs for my truck, lots of good info there for TBI setups.
Waiting to hear back from him.
Fuel pressure does help (I had mine at about 18 psi using the ghetto adjustable regulator mod) but I don't think that is necessarily the problem. May just be too much cam... it may see the low vacuum signal and think you're getting close to WOT independent of the TPS...I'm not sure how that computer prioritizes those signals. Hopefully there is a chip solution.
So SIZE does matter! Need to get 350 injectors and 350 eprom. I did not pay attention to 305 versus 350 parts. Back to the salvage yard.
Did not realize that you were running a 305 setup....
Dusterbd13 wrote: Did not realize that you were running a 305 setup....
Yeah, me neither.
Offer still stands if you need my obd1 gm tuning stuff.
Dusterbd13 wrote: Offer still stands if you need my obd1 gm tuning stuff.
How tough is that? I have a netbook not being used I could download software onto.
Not too bad, but I never really figured it out. But I also didn't put a hell of a lot of effort into it either. I'm finding megasquirt much more intuitive.
So with the right parts it runs and idles. I was always taught that any mechanic can put on the right parts, but it takes a special mechanic to put on the wrong ones and make them work.
Just a small lean condition (I think) under load at rpm.
FYI you can make an adjustable fuel pressure regulator. I drilled the center out of one, tapped for a 3/8 stud with an allen head, and it pretty much is what you buy from the store. Costs just the 89 cents or whatever a stud is now
I did it to get a stock computer to make a 330hp vortec head engine work. It was rich at idle and great above or great at idle and had a lean stumble. I gather you are at less power than that, and just another psi or two of fuel pressure might get you just right
In reply to patgizz:
Well, I still need to change the fuel filter to make sure that's not causing any issues with the fuel pressure. After that we'll see. Thanks to you and the rest of those who have contributed to helping me solve the issues with JCDV. This is the best place on the web by far.
Replaced the fuel filter. It was plugged but not the worst I've ever removed from a car. Drove it today. Ran extremely well. Still backfires, but only while moving, under light load (part throttle) when I try to bury the throttle. If I ease into it I can go full throttle where it sounds like it's sucking all the air out of the neighborhood. 
(No air cleaner housing on it yet).
Currently at 12 psi with adjustable FPR. Need to put in longer screw though as I've run out of adjustment. Hoping to solve rapid throttle tip in backfire with more psi.
Want to avoid a chip through the mail. Read of issues getting a good one from a variety of sources.
Dusterbd13 what would I need beyond what I could borrow from you?
An adapter board, zif socket, and blank eprom. All available from moates.
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