Tbi 350 swap problems?

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JamesRednour

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Alright go easy on me this is my first post and my first engine swap, only 18 lol anyways I have a 87 r10 which had a tbi 305 I just got done swapping a 350 from a 78 caprice, has a decently choppy cam in it but running my heads and intake for the time being, i got it running and took it for a little drive, made it about a mile and died at a stop wouldn’t start, got it home and the new plugs where fouled, got it idling again and it wants to idle super low to the point it kills itself, I was wondering if running a choppy cam on tbi could be the problem or it’s something else. Appreciate any ideas


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1987 GMC Jimmy

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If that choppiness translates to a vacuum level that’s low and unstable, absolutely. The MAP sensor needs good, reliable vacuum to work properly, not to mention the gaggle of other vacuum accessories. Did you hear it run beforehand? That would be a good reference point from an auditory perspective. The 305 TBI also has different injectors, 6 lb/hr/injector less, and you need a 350 PROM, knock sensor, and ESC module.
 

JamesRednour

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If that choppiness translates to a vacuum level that’s low and unstable, absolutely. The MAP sensor needs good, reliable vacuum to work properly, not to mention the gaggle of other vacuum accessories. Did you hear it run beforehand? That would be a good reference point from an auditory perspective. The 305 TBI also has different injectors, 6 lb/hr/injector less, and you need a 350 PROM, knock sensor, and ESC module.
Thank you very much, I’ve been completely stumped, and yes it sounded really healthy and since I swapped it from carb to tbi it sounds terrible, I ran the timing light on it and it would bounce all over the place then get consistent. Would it be cheaper/easier to get a carb intake and a carb and go from there?


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yevgenievich

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All depends on the specs of the cam. Tbi does not work with cams that have a lot of overlap
 

1987 GMC Jimmy

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Thank you very much, I’ve been completely stumped, and yes it sounded really healthy and since I swapped it from carb to tbi it sounds terrible, I ran the timing light on it and it would bounce all over the place then get consistent. Would it be cheaper/easier to get a carb intake and a carb and go from there?


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Well, you have to unplug the advance bypass wire on the firewall when you check the timing otherwise it’ll be all over the place like that. To someone who knows TBI, it’s not a big deal, maybe a half a day job, and if you can find a 1987-91 TBI vehicle with a 350 being parted out, probably not expensive either.

But yeah, then you still have the cam issue. A carb setup will play nicely with a lopier cam, but you’ll still have unreliable or inoperative vac accessories, namely cruise control, brake booster, and emissions devices if that’s important to you, and you’ll need to figure out how you’re gonna get the fuel pressure down to make it work with carb, either going to a mechanical pump and deleting the tank pumps or regulating the electric fuel pump down to half or a little less than half of the pressure it has now and supplying fuel pump relay pin D with independent voltage since the ECM’s gone.

I don’t know what the actual cam specs are so it’s hard to definitely say that it will or won’t work, but if it’s me, I make the TBI work with some different electrical components instead of rocking the boat even more, and if I have to put a more appropriate cam and lifter set in to finish the job right, so be it. I prefer not to make radical changes to engine control components if it can be avoided.

Others will say go the other route, and they have good reasons to say that, but at the end of the day, you have to make the executive decision.
 

Ricko1966

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IMHO you need to put a very mild cam in it and get all your TBI 350 components.Remember when everything came brand new carburated, and everything was worn out and burning oil by 100,000. Fuel control on injected engines is better.Longer engine life,better fuel milage, better driveability in all temps. And you don't have to rig anything bypass anything delete stuff add stuff etc.
 

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