95 7.3 surging after oil change.

Unplugging the ICP will default the IPR to regulate at a voltage of 750psi. Its certainly possible that the ICP sensor could just randomly fail. Oil inside the sensor plug can indicate that its dying but mines had oil in it for awhile with no issues. Good ole electrical components.

Did you put the old filter back on, or swap to another new filter?

Yesterday I swapped out the cam sensor with no change. Checked everything over a hundred times. Also put the old filter back on with no change. The bypass valve was still in the filter mount. Took it to my cousins shop and put the computer on it and it miraculously started working just fine. Or at least hardly showed itself. It acted up a little bit with pressure fluctuating, could see it on the icp pressure graph momentarily here and there but ipr duty cycle stayed flat. Icp pressure at wot 3k rpms was 2500 at 32-33 percent duty cycle. Idle ipr duty cycle was low so there isn't a leak somewhere. Only thing I can think of is replacing the ipr and see what happens. On the way home after unplugging everything it started acting up again so could it possibly be IDM related? How flat and steady are the icp pressure on the graph supposed to be? Mine was pretty choppy even when it ran smooth.

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My guess is IPR valve. Maybe switching to the syn broke loose some deposits as they tend to have more souring detergent effects and its gotten in and fouled the IPR.

A failed IDM should show up in a comp test etc I would think and not sure how it would effect IPR values with duty cycle staying in spec.

Why not swap your friends IPR in and see how it does.
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It's been awhile since I've worked on pickup but wanted to give an update for others who may experience similar problems. I have put in a new ipr valve with no change. Swapped pcm with known good one and no change. Watched ipr signal on oscilloscope and looked good. Decided to check for airation in the oil by using port on top of oil reservoir to plumb in a valve and clear section of hose. Brought engine up to temp and RPMs where it starts to surge I opened the ball valve. The oil I ran through looked good until I shut the valve off and then the air bubbles in the oil started to come out and noticed 1/4 of the oil volume was air. Now the engine needs to come out to pull pan to find out what's wrong. Figured I'd share my testing method with everyone for future use. Thanx to everyone for the help along the way.

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