350 to 305 {I didn't do it} - Third Generation F-Body Message Boards

steelhorse96 · 09-10-2009, 12:07 PM

89 Chevy 1500 5.7
Like I said I did not do it, but someone else did so it has come to me to finish.
From what I am told and can see the block code is CDD, after some research I found that is a 85 305 carb. Bad 350 motor was pulled from truck and 305 block and heads put in its place. I was told it spit and sputtered, I noticed some issues with the TB {rebuilt it} and the EGR was trash so I tended to the obvious first. Now I started it after those repairs with EST disconnected cause I still have to check base timing and it ran okay I guess, hard to tell as most of the exhaust is gone. But what issues am I going to run into other than my injectors are a little bigger. I checked with the parts store on the distributor and it is the same so that rules out the module. Is the knock sensor going to be a issue. So it should run rich, if so can I put a set of headers and a cold air intake and balance it out? And yes I know I will have to tend to the O2 sensor with the headers. I am told it will be a work truck so I am trying to keep the cost down.

I'm guessing when I hook the EST up is when its going to slap me.

But anyway you guys seem to have all the information on GM TB vehicles so any info you can give me will be less time this thing is in my driveway

Thanks,

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five7kid · 09-10-2009, 02:25 PM

Not to be a wet blanket in welcoming you to thirdgen.org, but we need topics to be "relatable" to 3rd gen f-bodies. In this case, TBI specifics is the closest we can get to that (not really an 3rd gen f-body engine swap relatable topic).

steelhorse96 · 09-10-2009, 02:49 PM

I know its not F-Body, but you guys and tbichips.com seem to be the only resource for information...Like I said any help would be greatly appreciated.

I did connect the EST and start it, without checking timing and it does run a little rough. Check engine light on with code 15, looks like they did not install a t-stat but that was it other than a normal code 12. My miss could be the injectors not spraying properly, the throttle body was so bad you could not turn the throttle linkage. I was worried they be clogged. So I find me a used 305 TB and that hopefully takes care of that.

Knock sensor and ECM is what I am worried about... Are these compatable

Fast355 · 09-10-2009, 10:40 PM

Here is my experience running the SAME 305 engine you have in that truck on a 1992 TBI 350 ECM and TBI. It will run but it will run WAY RICH. You need to swap the Prom Chip, Injectors, and Knock sensor for the 305 equivalent pieces. Mine ran fine after doing that. The non-swirl 305 heads liked running best at 6-8* BTDC on the base timing without the timing wire connected. It also liked about 14-14.25 PSI of fuel pressure. The 85 305 has signifigantly more HP/TQ than the TBI version of the same engine.

steelhorse96 · 09-11-2009, 03:01 AM

That's what I was looking for, I am already in the process of chasing down some injectors and I don't think it will be hard finding a used prom then a new knock sensor.

Many thanks for the info Fast355. Looks like we are neighbors {kinda}, I am in Allen

This truck needs a lot of parts, alternator, p\s pump, radiator, seat, door panels and a window motor for now so if you have any local suggestions on parts that would be great also. The truck was acquired by a friend of mine at no cost so at that price its well worth fixing.

Thanks again....