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!!!

Street Lethal

iTrader: (16)

This part got to me. Listen to me, a larger cam will introduce more air into the combustion chambers, but at different RPM's depending on its' specs. In your case with no chip to compensate, what you will want to do is bring your idle as close to stoich as possible so the car is at least drive-able, but remember this does not mean the other areas will be tuned correctly, so a chip will obviously be in your future if you want to pass smog. This goes for the stock camshaft as well, because even the slightest of changes will affect your VE. Have the engine reach operating temperature, then find out what your air/fuel ratio is with the new cam during that temperature. Get yourself an adjustable fuel regulator, and either pull or increase fueling to get that air/fuel as close to stoich as possible. The way it works is like this, the ECM is already programmed to have O2 correction during Closed Loop, meaning the ECM is told what the air/fuel is and it will either add or remove fuel to bring it to its' programmed stoich value. It's imperative to keep those values within the shortest ranges possible and not allow them to deviate too far, as this will not only cause the ECM to hunt, but it will greatly throw off your Open Loop fueling because Open Loop uses the Closed Loop VE fuel table. Meaning, if your Closed Loop air/fuel is precisely 14:7 stoich, and your Open Loop is programmed for 13.5 during warm up, it will calculate the exact amount needed to hit that target. In your case, that cam threw everything off. Tuning with fuel pressure is a very prehistoric method but it will get you on the road, but again the bottom line is that all you want to do is bring O2 correction to it's shortest swing possible, you want it as close to stoich as possiblefrom the getgo, so the correction itself will be more fluent and quick, and not hunting and surging. Again though, you will want a chip in the near future to dial in your timing, as well as your other tables if you expect to pass smog with flying colors, but the adjustable regulator will at least get the engine running decently and on the road. Just get the idle as close to stoich as possible with the engine fully warmed up while listening to the smoothness of the combustion and watching your air/fuel, then adjust the fast idle screw to help the engine breath if need be...

Best of luck.

- Rob

MrWillys

If you put Bosch type 3 yellow injectors that do not flow 22 lbs that is your problem.

TTOP350

iTrader: (8)

Are the valves adjusted correctly? Fuel PSI regulator ok? No raw fuel in the vac line? Timing set correctly? MAF working correctly?

It should run ok with that cam.
I'm running a big inch sbc with 245 afr heads, mini ram and a large solid roller on a stock tune right now.. no drivability issues, drove it all over this weekend.
It will be tuned soon.

ULTM8Z

Agreed 100%. I looked at that L31R cam just now and with only 191 deg intake duration at .050, there is no way a mass air TPI system can't adapt to that on its own. Its about the same size as a stock TPI cam. Even a speed density system could handle it.

Of course this is assuming there is no other malfunction.

BTW you swapped the heads but did you verify the combustion chamber size? How do you know what compression ratio you have?


12530283 - Chevrolet
Specs:
1986-2000 style block, 1pc rear seal 4 bolt mains -(No mechanical Fuel Pump Provision)
Nodular Iron Crankshaft
Powdered Metal Connecting Rods
Hypereutectic Pistons
9.4:1 Compression Ratio
Roller Camshaft-
Specs-
Intake Lift- .414"
Exhaust Lift-.428"
Intake Duration @.050"- 191
Exhaust Duration @ .050-196
Lobe Centerline-111

midias

You say you did not put on vortec heads but you also say use used the casting #10239906. Those are the vortec heads. The cam is the L31 is similar enough to the l98 so that is not your issue. What did you hope to gain with this swap we can help you out?