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Trying to understand my exhaust test results on my 1998 C1500 5.7 the first 5 seconds are 750 RPM the next 5 seconds are 2000 RPM and the last 5 seconds are 3000 RPM. I don't understand the high vacuum on the 2000 RPM is this normal for a late 90's Chevy Pickup.
What are your thoughts?
Hopefully the link will show in this post.
How do I display a You Tube link of my test results?
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Last edit: 4 years 3 months ago by Dinos55. Reason: You Tube link not showing in post.
As Jürgen posted it all depends where you measure the pressure.
At close to the tail pipe end by definition the mean pressure is atmospheric but it will pulse above and below atmospheric pressure.
Same is true on the induction side of the engine you get pulses of reverse flow from a carburettor.
When high exhaust back pressure.is suspected it is best to work from from to back of the exhaust unless there is access problems or on some vehicles that have known issues with secondary cat breaking up.
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
That particular test test was in front of the Cat. However I did one after the Cat. and a test with muffler disconnected, I did those test on both banks and all were the same results. So that being the case what would be your thoughts on the most likely cause of that reading. " The reason for doing this test" the tuck runs perfect in all conditions except under a load like pulling a hill" after about a Min. of pulling the hill truck starts missing and shaking, if I let off the gas for about 10~15 seconds the engine goes back to running normal again.
I didn't do a volume test, but what I did do was with a fuel pressure gauge attached I ran it up a hill to see if the pressures dropped off when there was a greater demand, it pretty much stayed the same around 55~60 PSI on the gauge.
To confirm or discard a fuel delivery issue watch the front O2 sensors while the car is under full throttle (best up-hill). They should stay rich all the time while at WOT, 800+ mV!
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