I just got done swapping my L03 for a vortec headed 350 with a Comp XE262 cam. It starts up fine and idles kinda rough(which I expected from a cam with 110 lobe seration) for about 10 seconds and will then just die. If I give it gas, its seem to want to stay alive. I have the Hypertech Thermomaster chip that I had with the L03 still in it and just a stock TBI with the Ulitimate TBI mods and the FPR made adjustable. I've played with the timing a little just by turning the distributer but can't seem to find anything that it likes. Any help would be great

 

stock or holley tbi? what manifold?
if you still have stock intake that would be your problem right there is my guess, but then again I'm only a backyard mechanic.

 

From what I've read on these boards, and if you feel it's the chip, you're supposed to use a L05 Caprice chip, and change your injectors to those off of a 350, which I believe are 65 lbs/hr (don't quote me). Your best bet as far as chips go, would be to have a custom one burned, or learn how to do it yourself. I would guess that Hypertech probably makes a Thermomaster for the caprice as well.

 

Your engine is running like crap for two reasons, one is timing the other is fuel. Both are caused by running a stock speed-density EFI chip in a motor with a big cam.

The car is idling at a higher manifold pressure (less vacuum) with the big cam. Stock was probably somewhere around 17" and you may be down around the 11" area. This makes the computer go to a portion of the fuel table that used to be used for a load condition like going up hill at a low rpm... lots of fuel. Same goes for spark... you are probably in that high load area so I bet its pulling spark out in that detonation sensitive area for a stock motor.

Big cams like lots of timing at idle. Don't be suprised if it wants 20 degrees base with your current chip. There is no way to fully tune this with a stock chip. You will just chase your tail. Take out fuel in the bottom and you will be lean up top. Add spark down low and you will knock on top.

Better go with a Custom chip, programable EFI system or carb... whatever you have the money and skills to tune.

 

If I were go try to locate an L05 Caprice chip, what years applications would I be able to use?

 

Honestly, I'm not sure what years would match. But, I'm sure if you do a search on it you could find it. Keywords would probably be: L05 and caprice TBI. Goodluck!

 

isnt jprevost using a 350 vortec engine maybe you should look for him

 

what is your base timing set at? remeber, you have to run more initial timing to compensate for the bigger cam.


later
tim

 

I haven't had a chance to hook up the brake vacuum yet. When I do this, will it help bring down the manifold pressure thus making it run a litte better? And I did get it to idle now, and you were right, it looks like its over 20 advanced but hard to tell. I also had to crank down the full pressure a bit which seemed kinda odd to me cause it kept wanted to back fire out the top of the TBI which is a symptom of running lean right? Is it possbile that too much pressure on the 305 injectors was making the not function properly? Plus it also looks like it get a much better cone with the lower FP.

 

It's never going to run right without a custom chip. Jump over the DIY-PROM page and read up. If not, park the car and get a daily driver.

Once of my friends thought he could cheat the custom chip by using both feet. One foot to keep the car in place and one to make it idle. To make a long story short he crapped up the ENTIRE $5000 motor he bought. The rings got washed down, the oil got crapped up and turned the inside into black goo.

 

What did you mean when you stated this?

"I haven't had a chance to hook up the brake vacuum yet. When I do this, will it help bring down the manifold pressure thus making it run a litte better? "

If you are using your stock manifold with out the brake vacume line hooked up then you must have a large vacume leak. That would make it idle horrible and also die. Or did I miss something in your post?

 

Its a Performer RPM Vortec intake and the place where I'm gonna hook up the brake vacuum is just plugged for now.

 

Usually an intake backfire is due to too much timing... plugs fire while the intake valve is still open. Do you have a timing light or let me guess you don't have an adjustable one. If this is the case, you need to get a timing tape so you know how much timing you are running.

re-read my first reply for the answer to why it wanted less fuel.

How much vacuum are you seeing? Do you have a vacuum gauge?

All this is really moot. You can not tune your car through whole operating range with fuel pressure and timing changes. You must choose a different path to tune it. I know this isnt what you want to hear. If you want it to run right, you absolutly must start programing your efi system or swap to a carb.

This has nothing to do with your idle problem but make sure you have a large enough throttle body, injector and fuel pump to support your power levels if you spend the money on a custom chip. You are probably in the 300 - 350hp range... Stock injectors only support about 200 hp. A holley 2" unit with 85# injectors or a GM 454 TBI unit will do the trick. Custom chip absolutly required to run these big injectors.