evlbeak

Hello all! This is my first time posting so I'll try to make this as clear and detailed as possible. I have spent hours, days, weeks, months, and years searching this site and have managed to make it this far with all my search results but right now I'm a little stumped and was hoping all you third gen geniuses could help me!

I have a 1987 Trans Am GTA 5.7L 350 TPI with a brand new GM L31R engine from Summit I just finished putting in but it is still not running 100%! I did NOT use the vortec heads it came with and took those off and put on the regular stock cast iron heads (casting #10239906) so I didn't have to track down a discontinued/expensive vortec TPI intake manifold. I did leave the L31R cam in there though and I'm starting to think I should have removed it and put in the stock L98 cam from my old block because it is idling rough and will stall at stop signs/stop lights and I'm getting a lot of unburned fuel dumped into the exhaust and it will not pass California smog and I cannot get my registration tags until I get this fixed and running properly. I was hoping it would all be done and this would be my new daily driver for now but apparently I'm missing something!

My first question is: After much more research I learned that I probably need the chip to be reprogrammed with the different cam but is this the correct fix? Or should I make more work for myself and take out this L31R cam and put in the old L98 cam?

My second question is: are there other parts that might help this run better like different spark plugs maybe? Right now I have new AC Delco R43TS plugs in there that I think are for the L98 but not sure if they are the right ones for this L31R engine, or if it doesn't make a difference since I don't have the vortec heads on there.

Any help is GREATLY appreciated! I've been out of work for both my jobs for a couple weeks now since I'm car-less and this car is losing me tons of money! Just need it to pass smog so I can think about selling it already so I can consider a newer daily driver (anyone interested in buying? lol) Along with the swap I have new plugs, plug wires, Bosch 22lb fuel injectors, distributor, EGR valve, starter, alternator, battery, pretty much everything so it's a little frustrating that I need to dump more money into it and it's still not finished but that has been my entire relationship with this car: it's always something else! I'm hoping a chip reprogram is all it needs. Please let me know what you think and thanks for all the incredible info this website has provided me! I cannot tell you how many screen shots and diagrams and part numbers and member comments have helped me out so much along the way! Thank you again TGO!!!

arrg

Are you sure about the heads? The 906 casting is a vortec head along with the 062 casting. Sounds like you swapped one set of vortec heads for another. Please verify the casting number of the heads you currently have on the engine.

midias

Second that if you put on vortec heads then you manifold is not sealing and you will get all sorts of issues. BTW the vortec heads are the best part of the L31. The cam is nothing special very similar tot he l98 cam IRIIC so that should not be an issue. Why did you do this swap? Was the old motor blown? Without the vortec heads you are basically putting in another stock motor.

Manifold here
http://sdparts.com/i-23896057-sdpc-s...baseplate.html

redneckjoe

can you hook up a vacuum gauge and report your vacuum reading at idle?

what is your ignition timing set at? did you set timing with the EST wire disconnected?

can you do a compression test also? perhaps your valves are adjusted too tight?

dont give up yet. sounds like you need to get everything dialed in and tuned.

cosmick

The L31 cam is milder than the L98 grinds, so is not causing any rough idling. My first thought was vacuum leak, even before I saw the other replies.