: Can someone help me with this?

02-21-05, 07:30 PM
My 91 FWB is starting to give me some probs Put a 350 inplace of the 305 a few weeks ago and all is going well but its doing some weird stuff now. When I start it in the morning and leave the house it bucks, it stalls and runs awful. The "check engine" light comes on and it starts shifting all messed up (feels like the trans is gonna fall out). Park it somewhere, leave it alone for an hour or two, start it again and it runs like a new car. This has been going on all week and I cant figure it out. I changed the 02 sensor but that didn't work, no vaccuum leaks detected and honestly I have no idea what is going on. If any of you have experienced anything like this and know how to fix it, please share.

02-22-05, 01:04 AM
Sorry for the dumb question, carb'd or EFI?

O2 won't cause drivability problems like that, look elsewhere.

My first questions for drivability always are:
1. It is good cold and then bad hot?
2. Is it good hot and bad cold?
3. Is it always bad?

These narrow down the computer inputs/outputs.

As for the swap, if the cam is mild like the factory 305 cam, this should be a non issue for the computer. Big cams (like over 210 degrees at 0.050) are too much for a stock computer unless you compensate for it in the programming. Check the Integrator if you can (not sure if you can on these cars) Low vacuum, especially from a large cam, tends to get the computers undies in a bunch. Check simple things like vacuum lines, ensure they are all 100% in the correct place, none plugged off (unless you know exactly what they are and what the ECM will interpret them if they are missing).

Does it run better at low RPM or higher? (please don't damage it trying, it it won't rev, don't force it to).

With what little I know, here is a shot.
Are you getting sufficient fuel pressure? Any plug wires reversed? Check 5 and 7, they are easy to reverse. My 455 Pontiac was good for mid 14's with 5 and 7 reversed. Just had to stay on the 2 bbls, hit the 4bbls and she backfired. But on 2bbls, ran like a bat. Fixed em and had even more fun. PCV in place? Hoses good? Does it idle at all? Did the PCV line get loose? Is the master cyl vacuum line loose or broken?

Any backfiring? Through the intake or the exhuast?

Is the cam phased properly? Is the distributor timed properly with a timing light? Earballing it doesn't count for beans. Get a light. Do it right....

Feed us more and we can give you some pointers.

Many of these I have learned from experience. It was the best way to learn!


02-22-05, 06:50 AM
Thanks for the response bro. The car is EFI, I used the stock TBI setup from the 305. I was told I needed 350 injectors and computer but two auto parts stores said the injectors and computer for the 305 and 350 are the same.

As far as driveability goes, it is good hot and bad cold. Its really pretty weird. It drives like crap the whole time you are driving after its first start up. When you turn it off and let it sit for a little while and start it again, it runs great, all day.

Cam: The motor is an 87 L98 from an 87 Iroc 5.7. The motor has the stock cam for an Iroc 350 as far as I know. I dont have the specs on the cam but I am inclined to believe an Iroc had a bit more lift than a Caddy.

I've checked and replaced all the vacuum lines but in all honesty I'm not 100% as to their placement after I put the motor back in. I'll have to get some kind of diagram. I've driven the car about 1500 miles since the swap and this problem started about 200 miles ago.

When warm after the first startup it runs good in all rpm ranges. The wires are not reversed. I will check on the other things you mentioned when I have the time. I appreciate the help, thanks :coolgleam

02-22-05, 07:21 AM
You said the CEL comes on. Have you checked for codes? That should at least point you in the right direction.