Fuel pressure and detonation


New Member
May 26, 2001
A friend has an 84 GN with recent stock rebult engine. I think it has a slight amount of detonation. The fuel pressue is at 36 lbs., line off. This seems low to me but I'm more fimilar with the 87 GNs. Can someone tell me if this is an exceptable FP setting and where you might look on an 84 for detonation.

I have 87's, so the static fp may be different. I set my static fp, vac line off, at around 42 to 45 lb. The main problem with detonation at WOT is fuel starvation. My car with the stock fuel pump has this problem at WOT over about 60 mph.

If your static fp is set at 40 and you have 15 lb boost, then the pump needs to produce 55 lb at WOT. My stock pump only puts out about 50 lb at WOT, so you see that the car leans out on the high end, which is very dangerous for the engine, you get knock. So if you have not replaced your stock fuel pump, get a Walbro 307 or 340 and hot wire it. This is one of the best safety upgrades for the cars.

I have read that 3 or 4 counts of knock are acceptable at shift points, just be sure you do not have run away knock-it would keep increasing. Also do you have an aftermarket boost guage and what is the boost set at? Too high of boost will cause knock. Seems simple but a lot of people are not aware what boost they are running.
Can you log the O2 mV and the fuel pressure under WOT?
This will help you determine the problem.
Stock hotairs don't like alot of fuel pressure. If he has the stock fuel pump most likely that is the probelm. What boost is he running?