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1996 G-20 Express Van surging in Drive

OK I am stumped. This is a 1996 Conversion van with a remanufactured 5.7 V-8. There is less than 500 miles on it since install. Once it warmes up, the engine surges (RPMS flux up and down) when in drive. Almost sounds as if it is breathing. Put it in park, and no more surging. Back into drive, and about 30-60 seconds later it surges again. Been over it with the scanner and it tells nothing. No check engine light.

I thought it may be a bad install of the intake manifold gasket (vacuum leak). I changed it again. Still no luck...

I am at wits end with this thing and do not know where else to check.

Here are some thoughts.....wrong engine application? Bad cam lobe? (I did pressurize the oil system) Intake not seating to the heads? Tranny problem??

I dunno, I have reached the end of my expertice on this one.....

Eightupman

Reply to
Eightupman
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mis-placed vacuum hose sending intake vacuum to EGR valve ?

can you watch idle air-speed motor data with the scan tool to see if it's being commanded to do this ?

Reply to
TranSurgeon

EGR valve electronically controlled. No vacuum there. I will have to get a hold of the scanner again (I borrowed it last time)

There is one vacuum line that goes from a sensor on the maifold to what appears to be the vacuum line for the vents under the dash. It disappears under the AC unit. The only other line goes between two sensors on the passenger side of the manifold.

Reply to
Eightupman

make sure that line goes to the proper place

that's the MAP sensor, line should go to manifold source

Reply to
TranSurgeon

So the map sensor is somewhere under the AC unit??? The other end plugs into a sensor on the left side of the manifold. I'll try anything at this point...

Reply to
Eightupman

no, the MAP sensor should be on a bracket above the RH valve cover

little black rectangular thing about 1-1/2" by 3 " by half inch thick

three-wire electrical connector and a vacuum hose going to intake source

remanufactured

Reply to
TranSurgeon

Pressure sensor PN 16187556 plugs directly into the manifold. I sprayed it with carb cleaner to see if the seal was leaking. No joy.

This is a FI Vortec engine...forgot to mention that.

Reply to
Eightupman

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