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940 B230FK humping idle after cam change to A

S

sekokupu

Member
Joined
Sep 11, 2006
Location
Finland
I just changed cam T -> A in mine 940 '95 B230FK and it started to idle little rough, checked car for vacuum leaks but everything is fine. Any ideas?

Idles just like this one: Youtube
Sometimes idles fine and sometimes bad.
 
Timing belt on correctly? My B230FT (distributor on back end of the cam) idled very poorly (bumps and spits). Found that in my case (an old timing belt) the cam timing belt had stretched enough so that it was 1 tooth off at the cam. After re-adjusting the tension pulley the cam timing belt was spot on and the car idles very smoothly.

Just thinking out loud - in your case - does adjusting the cam timing also affect the distributor timing?
 
JimG said:
Timing belt on correctly? My B230FT (distributor on back end of the cam) idled very poorly (bumps and spits). Found that in my case (an old timing belt) the cam timing belt had stretched enough so that it was 1 tooth off at the cam. After re-adjusting the tension pulley the cam timing belt was spot on and the car idles very smoothly.

Just thinking out loud - in your case - does adjusting the cam timing also affect the distributor timing?
Click to expand...


I don't have adjustable distributor, so it's on correct position. Timing belt is almost new, and on correct timing. It idles fine sometimes.
 
Nothing wrong with the motor or cam, that's just the way an A cam behaves with LH 2.4/3.1. My '91 245 B230F did the same. The adj timing gear didn't change anything in +/- 5 deg. I took it out for a VX.
A cam, although not a really big or lumpy cam has large overlap and as such can give lower idle vacuum and the CIS hunts for a smooth idle, but cannot cope with the lower vacuum.
If you really want to take advantage of the A cam, advance the timing, raise the idle to ~950 rpm and use an old school coil with wide dwell and big current to ignite cleanly over the larger duration and it will setlte down (a bit). On 2.4/3.1 you can't do anything with it.
 
Jus tdid the exact same swap ( T to A ) on an FK engine. The idle got a little rougher, but not so much that it is a problem.
 
Got now much better idle. That car has EGR, and intake manifold and throttle valve was clogged. Cleaned up everything, adjusted idle and inspected every hose. Still little rough sometimes but something that you can live with :)
 
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