alright the vehicle is a 90 gmc 1500. Had a 305 tbi and installed a late 70s 350 but attached a 350 tbi to it. Tried changing my computer, modules, tps and played around with the map. But the darn thing won't run worth a damn. Has a hard time idleing until I disconnect the tps (I bought a new one and tried it, but nothing changed) If I connect the vacuum hose from the tbi to the map sensor the motor stops dead in its tracks. If I try running the morot without the tps she just bogs out. Now I ran a sanp on scanner on it and it told me the motor was running to lean. What do I need to do??

also does a knock sensor play that much of a vital role? it looks like its in an odd place for the 70's block.


any help to get this beast running would be appreciated.


Ben

 

You would get more help on the TBI forum. I'll let the mods there decide whether it is 3rd gen related enough to let it live.

Not sure what you mean by the knock sensor mounting on the 70's block. It's exactly completely totally identical to the original TBI knock sensor mounting - the cooling jacket drain hole.

 

Steam

Do the basics first:

1) Check for vacuum leaks first. Get some carburetor cleaner and spray around the base of TBI. Make sure that you have plugged all unused ports!

2) Did you check your fuel pressure – it should be around 10 to 13 PSI
3) TPS (throttle position sensor) must be connected for ECM to know what’s going on with the throttle! If your the engine is dying when you connect TPS you may have an open ground wire in the TPS circuit. Under normal conditions, with engine idling Pin C13 (circuit # 416, Dark-Blue wire) or pin B on the TPS sensor connector should read around 0.45 to 0.55 Volts DC when measured with a DVM to electrical ground. At WOT reading should be between 3.5 to 4.7 Vdc. If it reads 5 volts then ground reference wire is open i.e not connected to ground. Check circuit 452, black wire at Pin A of the TPS sensor – with DVM set to measure resistance it should read near zero ohms to ground. If it reads high resistance numbers then sensor ground is not connected to engine ground.
4) MAP sensor takes +5 Volt reference voltage on Pin C (Gray wire, circuit 415), Pin B is MAP output (Light green or green black wire, circuit 432), and Pin A is ground (purple wire, circuit 455). Test the MAP sensor output voltage at the MAP sensor connector terminal B. With the ignition switch ON, and the engine OFF. Output voltage at the back of terminal B should be 4 to 5 volts. To further check functionality of the MAP without engine running a handheld vacuum pump can be used to generate vacuum. Connect Vacuum pump to the MAP, with ignition on engine off measure voltages through the back of the MAP connector. Set vacuum to about 16 inch of vacuum (sensor must hold vacuum!) and measure voltages with DVM with respect to ground at Pin B. Pin C should read 5 Volts, Pin B Output voltages should be between 0.5 and 1.5 volts which indicates a high vacuum condition typical for idling engine (16 to 20 inches).
Output voltages between 1.5 and 3.0 volts indicate a medium level of vacuum typical of a cruise or slight acceleration condition.
Output voltages between 3.0 and 4.5 volts indicate a low vacuum situation such as hard acceleration or a MAP sensor / vacuum line failure.


RF

 

i would, just to get it over with, put the old 305 throttle body computor and all back on,get a jet adjustable fuel pressure reg, put new 350 inj. in and just do a adj. and tune by the o2 %, if you cant take it to a shop with the reading o2 capabilities, have them adj. according to that,,,,,,,,,,,hhhmmmmm?

 

You need a 350 kock sensor and your combo is in dire need of custom chip work. You cannot tune using the stock 02 readings. Your motor will continue to run like death until you are able to burn your own chips (and or get it to a shop that can tune it on a dyno). What are the specs on the 350 you used? There is a good chance it has a non fuel injection friendly cam in it combined with horrible flowing heads and eqauly lame cam. Even at that, your problems are chip related.

 

actually, the cam i used is a crane 2030 grind which is exactly for my fuel inj. i went to this place, i built my motor and and did all the mods my self, i took it to them to tune, w2wpowertrain.com very reputable place or i would not have gone, it runs fine, @ wot, its reading 11, tell me why my car doesnt work? because of a cam your suggesting i dont have, the heads arent the greatest, but new when assembled with new manley valves, just 193's. no biggie , but still my car runs darn good, without a knock sensor change. no bad info was given, no idiot light, nothing, no complaints. whys my car running fine, the o2 readings r fine, nothings changed except needing more fuel for a larger dispacement, no really help me out

 

https://www.thirdgen.org/forums/tbi/...-350-swap.html

You need a 350 specific chip, knock sensor, ESC module and injectors. Otherwise the computer still thinks its got a 305 under the hood and it will run lean.

 

You dont need to change the esc! They are the same on the small block pickups. You should however change the chip and injectors/Kock sensor as mentioned in the last post. I have just finished this exact same swap on the same year pick up. I have a comp xe256h cam though. And a few more goody's. I ordered a prom from the gm dealer to get me started and it runs fairly decent all things considered. Just starting to do some tuning!! Once I get the prom burned and a decent program I'll let you know what I did.

 

What everyone is saying is that anytime you change anything on an engine with TBI you have to retune. You stated that you took the vehicle to a retutable shop for tuning, if the tune is still off I would be going back to the shop to have them fix what ever they didn't get right the first time.

Also as mentioned you need the 350 specific knock sensor and injectors.....although you will need to retune for the bigger injectors, but it doesn't sound like the vehicle is even drivable in it's current state.