CIS problems

[Aren D.]

Hi, I have a 78 sc, with the 3.0l motor I am having some issues with it and I am hoping some one with a bit of experience can help me out.

when the car starts, it idles very rough like its only on 4 cylinders, then it warms up and idles at 1000rpm but the engines surges to 2000rpm and back to 1000 it will do this until the car is shut down.

the car has a MSD 6A ignition installed, otherwise its all stock. I replaced all the seals in the CIS manifold - fuel injectors seals, throttle body seals, cold start injector seal ext ext... I also searched for vac leaks and replaced all the vac lines. No change.

Any help would be greatly appreciated.

[Two Rivers]

Make sure you have the proper vacuum at the deceleration valve and I believe there is a egr valve as well on that year. If you have manifold vacuum at the egr valve it will hunt and run poorly. There should be vacuum at the egr valve only after the throttle is opened. It may be the egr valve is stuck open or leaking ditto with the deceleration valve.

[MBruns]

First thing to do is put the proper pressure guages on between the fuel dist and WUR to test system press. and pump press. after cooling back down check cold control press and as it warms up to temp see what the warm control press is, all the values are in the small spec book with a graph to account for ambient temp. then watch your rest press after you shut it down, with what you describe it may have a leak in the accumulator or the injectors or the check valve at the fuel pump outlet. What happens with a leak is it bleeds down and has to purge and fill the system when you restart, thats why it is picking up cylinders as it runs. If you have some injectors that are sloppy it could also "flood" a cyl or so to give a simular rough running til it clears out. the accumulator is the easiest to test and confirm the rest are a bit more work.

Mike Bruns JBRacing.com