anybody with a cpi engine noticed there cars running way better in open loop then losing a ton of power in closed loop when the coolant temp is anywhere over 120degrees.car has a tons of power cold 60psi at idle 16mpg consistantly every sensor oil pan to intake is brand new on the car no engine codes at all.power loss is noticeable car will go sideways right from idle on a cold engine and barely chirps them at operating temperature.is it the way these things are engineered or what ?

 

I have not noticed this, my 93 with 195k still gets 22-23mpg city/highway combined

 

WOW 22-23 in a jimmy is hard to believe especially from this motor since its only rated at 15mpg in a short box pickup.do you have any modifications and in 195k what have you replaced ?

 

No modifications, all stock, usual maintenance done to it.
And my calculations are not off either, this was done on a 550mile trip.
Filled up before leaving, drove up to the cabin, drove around up there, filled up on the way back, took miles driven for how many gallons it took to fill up.. was I believe 22.4mpg.
Driving in the city its around 17-18mpg.

 

I was/am working on tuning a TBI engine I put together. It's a long process though. Cold loop uses set values for fuel and timing values. During operation in open loop there will be adjustments made with the coolant, air temp, and maybe a cople others. Then when closed loop turs on the fuel and spark are modified by the ECM to make the engine run within target parameters. I would check the O2(s) to make sure they are good.
I don't know if there is a detonate answer to what you want besides having the ECM flashed with changes made to the closed loop target values.
I would start by looking for reasons why timing would be pulled. Adding 3-4 degrees of timing was enough to go from not turning over the tires to leaving 20' lines. This was with a weak 305.

 

spark advance seems to fluctuate between 15-26 at idle and in the 30's at higher speeds.from start up knock sensor noise is always 2.46V and i get knock counts of 177,183,220 only at low rpms but spark advance seems relatively uneffected.what i have noticed is that if i let the car sit for a while even though coolant temp is still above 120degrees the power will be back until i drive it for a while almost like its heat soak.

 

Or does it just run good until it enters closed loop again?
That seems like a lot of knock counts. If I had to guess, you might be right as far as heat soak and it's leaning out to the point of causing detonation to give the large knock counts. I get worried when I have anywhere around 100 at any point.
It sounds like you know what you are doing. Just keep investigating and try to get rid of the knock. I think you should pick up some power then. Maybe do a compression test to rule out a weak cylinder that is throwing off the sensors.

 

it runs great until closed loop kicks in.my engine is modified with valvetrain and headers so its questionable if the noise they are actually picking up is genuine knock.i believe the computer does not pull timing unless it sees something like 255counts in a single cycle which explains why the spark advance seems uneffected.i have had this power loss since the car was stock and at this state it still continues to elude me.

 

Did you have it tuned following the engine mods? I can't imagine it getting any better by increasing the V.E.(volumetric efficiency). It should not be picking up any noise unless you are running solid litters or gear drive instead of a timing chain. You said all sensors were replaced? This is a 4.3 with CPI?

 

its a 95 4.3 CPI SS RCSB it has exhaust and a mild towing cam that is meant to work with the stock tune.like i said all the sensors are new and it has had the closed loop power loss since the truck was bone stock before any mods.