4.3l 1990 different sound and it feels more light

hello..
so here's my new problem.
1990 blazer 2wd 4.3L
everything is ok with the truck...
but... when i push the accelerator pedal to the floor the truck run very very good!!... but after that.. the sound of the engine sounds like i have a 4 cil. engine(less noise).. and it feel more soft(less weight) like when you advance the timing.. but have less power..
so, when i turn it off, and wait 10minutes the truck feels normal again..
but this happen each time that i press the peddal to the floor..
i don't know what's happen now..
the mechanic guy say that my timing chain is going bad..
but i have my doubt..
everything is ok.. engine oil.plugs, cap, rotor,air filter etc..
before feel this change, the "check engine "light comes on.
but i already scann for codes. so the only code that is storaged in the ECM is the 24 vss sensor. but this sensor always been faulty.. and after that everything was normal, nothing change..

so please help me..

Nalgman

ok.. this is weird .
my timing is like 20degree,so if i retard the timing ,the engine starts to knock a little.
so i always have to use too much degrees.
is there anything related to the ESC or other sensor?

thanks :( :banghead:

i will replace the timing chain because my mechanic says that the chain is goin'bad....

i don't know!!!!

Nalgman

Check your fuel filter and pump . The pressure may be dropping as the flow gets higher . Which FI system do you have TBI or CPI ?

Check your fuel filter and pump . The pressure may be dropping as the flow gets higher . Which FI system do you have TBI or CPI ?

TBI , the pressure for this models are 15 pounds max. and mine is 13, the lower in the range specifications is 9

i already change the filter. the only thing that donde is slow down the RPM. but was fine ... :S

so, i dont really know what is the problem :S

thanks anyway

Nalgman

When you are checking your timing, are you checking it in bypass mode, with the connector disconected under the dash on the passenger side? Thats the only way to check the timing, any other time, it is controlled by your computer/ESC. Also, to check your base idle, ground the diagonistic port under the dash(like when you do to get the codes read), turn the key to the on position, and let it read the codes, wait for about 30 seconds, go under the hood, and disconnect you IAC valve. Pull the code reader out, or stop grounding it. Start the truck. The truck should start and get to idle right away. If it doesn't idle, (assuming you have no vaccum leaks, and your engine is alright)get to your idle screw on the TBI and set the base idle. It would also be very advisable to check your TPS reading at idle, because if its way off, like to high, it will give you a high idle too. You have to also do this when your engine is warm.