Cylinder #4 to dreaded random misfire..

[Missy]

Allright , got a 2007 gmc Yukon 5.3 with the afm . Randomly one day I was driving low speed , vibration cel went off along with the tc and stabilitrak. Code read misfire in cylinder #4. Replaced all plugs and wires , apparently they were never changed in this truck with a 178k miles on it . Checked the codes still misfire #4. Replaced ignition coil on #4 ,then came the random misfire code . Clean oil change ,pressure is good .I've always had issues with the fuel pressure sensor even after getting a new one . I can't get it in til next week .But I'm trtrying to do a process of elimination in the meantime .Shifts hard, rough idle, knocks once hitting 10mph but then drives smoothe .Any ideas ?

 

[Kraig]

My guess is AFM lifter collapses or spun in it’s tray

 

[swathdiver]

So once the coil was replaced, #4 code disappeared and went to random? Do you have access to a bi-directional scan tool like the Tech-2? You can find out in moments what the problem is with one.

 

[Missy]

So once the coil was replaced, #4 code disappeared and went to random? Do you have access to a bi-directional scan tool like the Tech-2? You can find out in moments what the problem is with one.

No decent scan tool at this point .It's going in tommorow .But it's actually back to the cylinder misfire #4. Occasionally it'll show fuel pressure code.

 

[swathdiver]

No decent scan tool at this point .It's going in tommorow .But it's actually back to the cylinder misfire #4. Occasionally it'll show fuel pressure code.

Ok Missy. Which fuel pressure code? Keep us posted on what the mechanics say.

 

[Missy]

Ok Missy. Which fuel pressure code? Keep us posted on what the mechanics say.

P0521. The rough idle has definitely improved since changing out the sparks and plugs at least.

 

[swathdiver]

P0521. The rough idle has definitely improved since changing out the sparks and plugs at least.

That's not fuel pressure, that's for the oil pressure sensor. That code is telling us that the sensor is not reading the oil pressure right, it's become inaccurate. If you decide to replace it (GM OE or ACDelco only for best reults) have them clean and or replace the little screen (about $7) underneath it too.

 

[Missy]

That's not fuel pressure, that's for the oil pressure sensor. That code is telling us that the sensor is not reading the oil pressure right, it's become inaccurate. If you decide to replace it (GM OE or ACDelco only for best reults) have them clean and or replace the little screen (about $7) underneath it too.

Yes ,your right .Sorry that is what I ment .The sensor and screen were both replaced 6 months ago.That's what throws me off

 

[Kraig]

Was it replaced with OE-quality parts or parts store parts?

 

[Missy]

Was it replaced with OE-quality parts or parts store parts?

Original