TBI with vortec long block, what to expect?

[71 CREWCAB]

The original 165,000 tbi 350 in my pickup is ready to come out. #1 has 30# compression and a bad exhaust valve and #4 leaks oil between the head and the exhaust manifold. I have a complete vortec 350 out of a 96 suburban about ready to go in. Basic rering, stock vortec roller cam, pocket port and exhaust work on the heads, ebay carb intake with adapter plate for TBI. I highly doubt that it will be a 100% drop in fire it up and go. Any ideas what I should expect? Thanks
Nick

[91chevZ71]

more power

you'll need more FP and a little tuning, but nothing major. maybe some exhaust (headers, duals maybe)

you probably get away with no tune for a while, as long you take it easy
for starters, that is. the rabbit hole runs deep, though

[Pauly]

Should be pretty much drop in a fire it up. You will need a chip.
Exhaust manifolds/headers will fit. You may need to rig up[ some heater/coolant hoses, but nothing major.

peace
Pauly

[71 CREWCAB]

Thanks guys that was what I was hoping to hear. Just out of curiosity, would playing with the temp sender for the ecm have enough affect to be worth messing with? I know if you unplug one the ecm sees -40deg and goes rich to compensate. Just an idea.
Nick

[1BadZ71Tahoe]

Thanks guys that was what I was hoping to hear. Just out of curiosity, would playing with the temp sender for the ecm have enough affect to be worth messing with? I know if you unplug one the ecm sees -40deg and goes rich to compensate. Just an idea.
Nick

Don't trick the computer, feed it what it NEEDS. At least that's the only way to do it right IMHO.

- B

[91chevZ71]

Don't trick the computer, feed it what it NEEDS. At least that's the only way to do it right IMHO.

- B


roger that

[71 CREWCAB]

Ok first off I should have clarified the part about the temp sender. I didnt mean just unplug it and run it that way. Thats redneck tuning. I just meant that the computer changes the fuel curve depending on the engine temp.
Anyway, got the motor in this weekend and running and just as I expected it was not a fire it up and go. I started with the stock tbi with the regulator modded to make it adjustable. We didnt have a low pressure fuel guage, the only one we had was a 120 PSI unit on their motorvac. according to that the regulator was set at 14 to start. timing set at 0 with the connector unhooked. Fired right up with no leaks or bad noises. didnt sound too bad. after it warmed up a little bit any time I would open the throttle it would get a backfire and a big fireball out of the throttle body. in gear under any load it would fall on its face. Got the old snap on red brick scanner out and found out first off that the temp sender isnt reading right. The intake right at the temp sender measured 185 with our IR temp gun, and the ecm was seeing 220. grabbed a used one off an old motor for now(no parts stores open in small towns on sunday) and just plugged it in and let it hang. after letting it run a bit the ecm was seeing 150 and it sounded a lot better. but still a little lean. Pulled the TB and cranked the regulator up 2 turns and tried it again. Better stil. 2 more turns and it sounded real good. Good throttle response and real good power in gear. Took it out and drove it with the scanner hooded up and it ran great. O2 sensor was switching back and forth, everything seemed ok other than the ecm seeing 150 degrees coolant temp(its on my list to fix).
Heres where it goes to crap. Pulled in the shop to check for leaks and check fluid levels. put the scanner away and went to pull the truck out and its lean. Real lean. Right back to backfiring and falling flat. I spent probably an hour messing with it before I figured out the scanner was somehow related. Any time the scanner was hooked up and in data list it would be in a totally different fuel curve. WTF?? With it un hooked I just kept bumping the fuel pressure up and trying it. With the regualtor maxed out and the extra temp sender hanging in the air it still sounded really lean and anything over 1/4 throttle it would slow down. Im taking it in to work tomorrow to check the fuel pressure with a good purpose built TBI guage(the advantage of working in a GM dealership). Personally though I dont think its an issue with the fuel system. All I have to do is hook the scanner up and it pulls hard all the way up to 4500(didnt try any higher than that) and sounds beautiful. Unhook the scanner and its way too lean. And thats with the free air temp sender. If the ecm sees 190 like its actually running its going to be even more lean.
So heres my questions,
Why does it run very different with the scanner hooked up?
And If thats normal and the pump and filter check out ok should I go with the next size bigger injectors?
At this point Im lost. Its not like I made a radical change in engines. Still 350 cid, swirl ports to 906 vortecs, stock tbi cam to stock l31 vortec roller cam.
One last thing, what knock sensor should I be running? I though I read somewhere about the roller and non roller having different knock sensors. Right now the roller knock sensor is on the truck. Sorry bout the long post but wanted to give you guys lots of info to work with. Thanks for anyhelp you can give.
Nick

[91chevZ71]

That's weird. Are you using a 7747 ecm?
couldbe something with ALDL mode in the ECM or something like that.
Anyway, If you have a 7747 I can send you my old 7747 to see if it is a bad ECM.

[Fast305]

Make sure that you have all the grounds in place for both the ECM and the engine. A loose or corroded ground will cause several of the issues you are seeing, especially the coolant temp sensor problem. You should have a ground on the front of the intake manifold near the thermostat, a second ECM ground is located on the back of the passenger side head, then you have the body to head ground strap also on the passenger side head.

Second the TBI ECM is a Speed Density ECM, even major exhaust system changes will throw the stock tune off badly. It needs to be programmed to accomidate the increased head flow. The Vortec cam is smaller than the TBI cam and the Vortec heads flow better which increases vacuum at part-throttle, leaning out the mixture further.

Furthermore, I recomeend a Vacuum Compensated fuel pressure regulator for the TBI unit. The 350 vortec needs about the same fuel as the TBI 350 at idle, but much more fuel under load. That is the grace of the VAFPR

http://www.turbocity.com/product_info.php?cPath=16_24_52&products_id=602

[71 CREWCAB]

right now there are two grounds at the front of the motor. one went the the t-stat housing and the other went to one of the intake bolts. each one had two wires crimped onto a single factory eyelet. The ground at the back of the head to the firewall is hooked up as is the big one front the block to the frame. The exhaust is the same as it has been for 3 years now with the old motor. Id have to look up the specs but Im pretty sure the vortec cam is slightly bigger than the tbi cam. plus with it being a roller the lobes are real fat compered to the tbi one. Im going to pull it in in a bit and check the grounds and fuel pressure. Hopefully I can come up with something.
Nick

[71 CREWCAB]

Ok figured this much out today. First off its not lean. Got the old tech one out over lunch and took it for a drive. When its falling on its face the o2 sensor is up around 800 and stays rich. There is also no no knock signal. Pulled it in after work and realized the hard way that I had never put a fuel filter on. 45 min later I had the filter changed and the shops fuel pressure guage installed. with the regulator maxed out its at 18 psi. I backed it down to 15 for now. I also bumped the timing up to 15 degrees with the connector unhooked. That alone made a huge difference. I also cleaned both grounds and bolted them straight to the intake. still not right but closer than it was. Still need to figure out why it needs to see a cold temp sensor and why im not getting any advance. Keep the replies coming.
Nick

[71 CREWCAB]

Was kindof hoping for some ideas by now. Last night I tried 2 defferent modules, two coils, and a different ecm tonight. I checked all 4 wires between the ecm and the dist. They are all fine. With a meter on the wire that sends the advance signal to the module its at 1.6 volts at idle. close to 3 at 3000. 195 engine temp on scanner half throttle in gear stopped is around 2 volts. If I give it more throttle the voltage drops and it backfires out the tb and almost dies. If I umplug the temp sensor and plug in the extra one and just let it hang so the ecm sees 80-100 and do the same test half throttle is still around 2.0 volts but if I lean into it more the voltage goes up over 2.5 close to 3 and it starts spinning the tires(which says a lot in a truck with 265s 3.42s and 500 pounds of racing gear in the back.) I thought maybe it was something in the ecm so I tried a different one tonight with no luck. Really need some help on this.
Nick