[fordtech]

I am looking for some info to try to help out a friend in need....

His 94 HB with the 2.4 failed NOX test standard is 3.0 he failed at 5.6
it had a horrible misfire and we replaced plugs, wires, cap and rotor, it also had a cooolant leak causing it to overheat, that was repaird and now runs at a steady 180-185 degrees. After these repairs it is still at 5.6 and failing. I am not very farmilliar with nissan's EGR system, but from what i can tell it is operating fine, when idleing I apply 5-6 inches of vacuum directly to the EGR valve and it stalls the engine which tells me the EGR system is flowing. When driving it is getting up to 4 inches of vacuum to the EGR valve which seems that should be enough to flow enough EGR to control NOX output.....Am i missing something?
Any help/advice or experience with this issue would be appretiated

 

[zanegrey]

read the codes...

 

[fordtech]

already did, no codes, no cel .................................

 

[zanegrey]

test o2 sensor and check cat for damage and proper function...

 

[Skinny G]

NOx is controlled by the EGR. High combustion chamber temperatures cause NOx.

The BPT valve (back pressure transducer) controls the application of the EGR, and is connected to a wee metal tube that threads into the manifold at the back of the block (intake side) - a wee hole in the tube often carbons up stopping the EGR from working. Remove the wee tube, poke the hole clear again, and repair/replace the probably rotten section of rubber hose.

The BPT valve itself is quite expensive, but the plugged tube is far more common.

There is also a solenoid that connects vacuum to the rest of the EGR system. I've forgotten the tests for it. The tube... the tube...