OKay guys here's the deal. I have swapped a 350 into my originl 305 car. the 350 is simply a stock 350 from a 1987 iroc, rebuilt. SO probably a 355. The problem is at idle the spark advance will jump from 19 (where it overs) to 37 and drop to 10 and all that stuff over and over and over again. I have no knock counts nor knock retards. I am unsure what is going on. I've checked all my sensors and they appear to be working fine. I've recently upped my fuel pressure to 50 psi and now I run slightly lean at idle and while driving it variates between rich and lean just like it should. I'm unsure what to check next. any suggestions sure would be helpful! What could cause the timing to jump around? Thanks!

 

Thats pretty normal for a GM ECM to do that with the timing at idle. Don't worry abou it unless you're actually having some kind of problem.

 

I am. When it odes this the car tries to die and surges really bad. It also surges at constant throttle though not as bad sinceI bumped up the FP and cleane the injectors. When I mean try, I mean it dies more often than not.

 

Have you checked for vacuum leaks?

 

Yup I sure have. None that I can find. All hoses are in good shape. All routing where they're supposed to.

 

Anymore Ideas?

 

Did you keep the original injectors and ECM from the 305?
Stock 350s have 22lb injectors at 'around' 45psi. If you have 19lb injectors at 50psi you're only putting out 20.3lbs/hr so you are probably running lean. The timing problem you posted about is completely normal and shows that the O2 sensor is working.
Be sure to clean/check your IAC for your surging idle trouble.

 

How much fuel pressure can the stock pump handle? Also is it possible you could post your formula for figuring out injector flow at a certain psi so I can use it for reference? Yes, they are the stock 19# injectors and also the stock 305 Memcal. The IAC is acting normally and I did check/clean it and put it back so that's not my problem unfortunatly. I've checked just about every sensor I can think of. My TPS, MAF, MAT, IAC, 02, Knock, temp sensors, is there any I may have missed? Also how would I know if the maf burnoff relay is bad? What are some systems/tests? Thanks guys I appreciate the help!

 

I dug this up from a search:

new flow rate (#/hr) = SQRT[new fuel pressure/rated pressure] * rated fuel flow

example: flow rating of 24# SVO injectors at 48psi

new rating = SQRT[48.0/39.6] * 24.0 #/hr

new rating = 1.101 * 24.0 #/hr

new rating = 26.42 #/hr

Now this is an estimate, but is fairly close, close enough for our purposes.

Stock injectors are rated at 43.5psi (Ford SVO are rated at 39.5psi)

For your setup:

square root(50/43.5) * 19#/hr
1.0721125 * 19#/hr = 20.370138#/hr


Not sure what the stock FP can handle.
A bad MAF relay would more than likely set an SES code. (Heck a good one will set one too sometimes! )