My 87 Brougham keeps failing emissions tests for NOx. I have a new cat converter and ox. sensor. I did notice today that the egr valve isnt getting vacuum. Maybe the solinoid is out.
Would no egr cause high NOx numbers.
Any thoughts would be appreciated.
307's are notorious for plugging up the EGR tube extensions under the carb. The valve isn't the common probem, the tubes are.
Best fix, remove carb, and run a drill bit down each tube and clean. If you can, remove valve and run a piano wire through all passeges. That is best to fix up. Then you can run 87 octane fuel again. A sign of these plugged is not able to run stock timing or slightly higher with 87 octane fuel. ALL 307's can do if these are clean.
DO NOT remove the tubes! There is a high risk of dropping them in, or a weak floor on the intake may leave you looking for a new intake.
The "Olds" ECM back in the 80's didn't have any checks for EGR, so you won't get a code for it not working.
Hmm, would higher octane fuel help? Higher octane burns slower and won't ping in higher combustion temps/pressures. It has more oil per gallon than lower octane. So the potential for slightly higher emissions of HC and/or CO.
A bump in timing down a degree or 2 might also help if the EGR system is working properly.
Actually it will. EGR is so refined into the AFR, Air Fuel Ratio that missing it is a critical component, and the engine runs lean with too much timing. So adding it actually makes the AFR correct, which will boost power and fuel economy. That is why the 307's also aren't too thrilled with high flow exhaust. The EGR valve is a positive backpressure EGR, so it works at the wrong time, if not at all, so your AFR is just wrong. It boosts power at WOT yes, but part throttle can hurt.
I did one on my 350 Olds with a 307 PCM (85 Cutlass transplant) and had to go to a ported EGR and get rid of the postive backpressure EGR.
Enjoy! Mine went from 93 octane to 87 when the EGR was unplugged. With power increase to boot!