Boost Codes

[jan5]

I have 99 Suburban 2500 F motor. It would set ses light after long run and brief stop. I suspected a little heatsink problem, because after a few cold starts (5-10)light would go out.
Rather than play around I just went and installed mechanical boost kit.The problem is that it still sets a code for the boost and just can feel some slight loss of performance as if the vacuum system was still hook up. performance returns after cool down and restart, and light goes out after a few cold starts just as before.
I guess ECM is correcting problem that doesnt exist?

[rjwest]

At about 10-12 lbs off boost, A 'hidden '
code ( can not read it ) occurs in the PCM
and goes in to 'reduced power mode ( defuel )
it resets with key off cycle,

You will need a Kennedy boost fooler, or make one
Do a search in forum.....


Note , the code will set very easily if
you wind it up in 2nd and shift to 3rd, big spike in boost.
You do have a boost gage ????

[jan5]

no boost gauge. checked codes and have set 236. 237 was present when checked about two weeks ago but has since disappeared?
this only happens during a hard run at interstate speed. with 4:10s that puts me spooled up at 2300-2400 rpm. guess ecm is not happy with the amount of boost at those speeds?
thanks dave