: 86 brougham pre ignition after warmup



cadmat
12-19-07, 10:56 PM
I've noticed this a few times, i can only hear it if the windows are open.. This car is not driven but a few times a month, but I always make sure part of the trip is a few minutes to an hour of freeway speeds. always starts right up, choke drops down properly after warm I bump it, the engine is so smooth that I can't tell if it's on at stop lights, but after it's driven awhile, I notice a little pre ignition gergle under load at low speeds ( under 25 ish) what should I check first?
car has about 140000 miles, and was tuned up about 2500 miles ago ( a year and a half ago) , plugs, wires etc.. not sure if the carb was serviced any further then simple adjustments.. passed an emmissions test at about the same time with flying colors.. I've wondered if a sea foam treatment may be in order.. never did it, but it always seemed like a good idea.. What do you think?

Thanks, Matt

joe_padavano
12-20-07, 04:20 PM
The 307 Olds motor is famous for this if the EGR passages get clogged. Start by verifying that the EGR valve is working. If it is, then pull the valve and check the passages in the intake. Also, pull the carb. You'll see two vertical tubes stickup up from the floor of the intake under the carb. Be sure these are not carbon clogged.

N0DIH
12-21-07, 09:29 PM
Also do not forget a frozen EFE valve will also do the same, and do it very bad.

Check for proper EFE valve operation.

But agreed, after dealing with my 85 Cutlass and the EGR Jet Extensions being plugged, yeah, that is a crap design

What I did was remove the tubes (GM DOES NOT RECOMMEND!!!) as they are screw in and then replace with a brass plug with a hole drilled into it with same size as GM had on the OEM tubes. Increases intake flow (yeah, like the 307 can use it... I had a 350 though) and does reduce the disruption in the intake just under the very sensitive area under the carbie.