Hi my name is Joerg from Germany.
I have a problem with my new build 455.
It runs like crap at idle stalling and sound like one cylinder is missing.
Have double checked spark plugs and wires. Initial timing is set to 10° BTDC.
There are 2 options my engine builder messed up cam dial (can this be checked some how) in or there is an leak at intake gasket (have checked this from outside with brake cleaner, but could be inside)
Can somebody give me an advice what could it be.

I made 2 approaches one with carb and one with EFI.

Please see movie.

THX very much Jörg

 

Do you have a vacuum guage, tac, and a compression tester
Do you know your cam specs.

Start with a vacuum reading at the correct idle speed. Then a cpmpression test on all cylinders to possibly identify a weak cylinder or valves hanging open.

What distributor are you using.

 

Hi cam specs are lobe sep 110 /Ex.closes 4 ATDC / Ex.opens 50 AADC/ In.opens at 8 BTDC / In.closes at 42 ABDC / lift in. .565 / lift ex. .552 / duration at .050 - 230 in / 234 ex
Pertronics Igniter 3 with pertronics billet bistributor and matching coil.
no compression tester but can buy one

 

 

X2. Vacuum, compression and also leak down readings are good indicators of base
engine health. Nothing else matters until these readings are taken. If these check good, then you move on to ignition and fuel.

 

You mentioned the 455 is recently rebuilt. Did you install a new harmonic balancer? I ask because the Olds harmonic balancers have been known to slip. If this is the case you could try to set your timing all day long and never get it right. You can check the condition of your harmonic balancer by moving the #1 cylinder to TDC of the compression stroke. Your timing mark should be right at 0* on the timing tab.

 

Hi Jesse,

good point i never thought about, but balancer is brand new and also balanced to specification.

I ordered compression and vacuum gauge.

But I'm pretty sure intake gasket is inside engine not sealing,

because i can't get with carb on engine the engine to die with idle screws full in.

Even with idle mix screws full in engine was running (bad)

I have the pan style gasket one now in place, but I will switch to 2/4 piece Felpro or Edelbrock one EDL-7284


Regards Joerg

 

Joerg, you can double check for a vacuum leak using an old trick:


Of course, carburetor cleaner sprayed at the base of the intake manifold works too, but this is a disaster waiting to happen.

 

Have done my homework
compression on all 8 cylinders 130-150 PSI
Intake vacuum is only 5-10 in Hg Vac
If I am correct seems like intake leak right ?

 

I cant answer your engine vacuum question, other than to say maybe you need more timing. 16-18 intial is not unheard of, although you will need to map mechanical and vacuum advances to work that.

i can say ive had more than 1 brand new pertronix ignition not run or not run right fresh out of the box.

if you have another distributor i would give that a go as its easy to try.

 

If you aren't a smoker and don't want to try the trick I posted in the video above, here is a thread detailing how to make your own smoke machine using a can, air compressor and WD-40/vaseline. Unfortunately, the pics don't work for me. Really, this is the BEST way to ID a vacuum leak because it emulates the tool professional technicians use to find vacuum leaks.

http://www.fiero.nl/forum/Archives/A...-1-081547.html

 

Your vacuum is far too low. You should easily be able to pull a vacuum of 17" Hg. You have essentially 1/2 to 3/4 less amount of vacuum you should have. Why you have such a low vacuum I do not know. But your vacuum is far too low. Your vacuum range should be a within the range of 17" Hg - 22" Hg. Have you made attempts to adjust the carburetor air/fuel mixture screws to achieve the highest vacuum possible? Is the vacuum gauge needle widely deflecting up & down? It doesn't sound like it's steady if it's between 5 - 10. What does the vacuum gauge needle do - bounce all around? Did you simply hookup some vacuum lines wrong or have several open manifold ports you forgot to close off?

EDIT: Did you use real vacuum line hoses and not some cheap thin-wall hoses which can collapse?

 

We don’t know what piston is in it but I’ll guess no more than 9.5:1 with that cam and cranking compression. I get 180+ with 10.0:1 and a cam with 5 or 6* more intake duration. So given that scenario there’s no way he’ll get 17” of vacuum out of this, MAYBE 15 tops.
The first give away there’s a problem is you can hear the IAC open up to try to hit the target idle rpm. That’s your first indication you have either a vacuum leak or it’s starving for fuel.

 

I just thought with the compression he achieved of 130-150 psi & the numbers he posted he'd be able to achieve 17" Hg. You're right, I don't know piston size, any milling and/or gasket type used. Gosh, it does make some sense I guess. When I listen to the video it sounds like it's pulling a terrible vacuum and starving for fuel based upon A/F mixture out of adjustment.