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OK, I know it's a 90 degree block but I could REALLY use some help. I've got a s-10 with a 4.3 that is running terrible and I can't figure out what the problem is. The truck has always had a little "wandering" under a load at about 2k, but I didn't really worry about it but now it's gotten way worse. Pretty soon it start and idle bad at a warm start but then after driven a few minutes it would smooth out, but still run pretty bad at full throttle. Then it progressed to run horrible at all rpms, especially at full throttle or under load. At full throttle it was almost like the whole engine would cut out for a few seconds and then come back. I checked the truck on a scan tool and the map sensor readings appeared to be high, especially under load. I plugged off the vacuum ports on the intake one at a time and found no difference. this led me to believe it was either the plenum or intake leaking. The intake was leaking coolant anyway so I replaced it. Now the truck runs a little better but the problem is still there. Here is a list of the other things replaced:
Fuel filter, air filter, pcv, cap, rotor, plugs, wires, coil, pick-up coil, ignition module (checked with another one with no change) distributor gear, map sensor, intake gaskets.
On the scan tool I noticed that on a warm start when the truck runs bad my spark advance is all over the board, jumping from high values (30 degrees) to low values (-17 degrees) as the spark advance balances out so does the idle. Fuel pressure is about 57 psi and goes up when I give it throttle, to about 60. O2 sensor switches often but I did notice when the engine "cuts out" at full throttle the O2 sensor drops to next to nothing (83mv for example) meaning I have a lean condition. When the engine comes back it goes back up to the 900mv range. CTS reads fine. EGR is cleaned and working fine. TPS and IAC also check out. I'm unsure of my map sensor ground... and the engine grounds. Does anybody know where to find them? Basically if there is any help somebody could give me it would be very appreciated. Thanks in advance.
Fuel filter, air filter, pcv, cap, rotor, plugs, wires, coil, pick-up coil, ignition module (checked with another one with no change) distributor gear, map sensor, intake gaskets.
On the scan tool I noticed that on a warm start when the truck runs bad my spark advance is all over the board, jumping from high values (30 degrees) to low values (-17 degrees) as the spark advance balances out so does the idle. Fuel pressure is about 57 psi and goes up when I give it throttle, to about 60. O2 sensor switches often but I did notice when the engine "cuts out" at full throttle the O2 sensor drops to next to nothing (83mv for example) meaning I have a lean condition. When the engine comes back it goes back up to the 900mv range. CTS reads fine. EGR is cleaned and working fine. TPS and IAC also check out. I'm unsure of my map sensor ground... and the engine grounds. Does anybody know where to find them? Basically if there is any help somebody could give me it would be very appreciated. Thanks in advance.
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