Valve Rattle

[GIXJ90]

I have a Golen 4.6 on a '90 model Renix system with the following aftermarket componets: 21 lb/hr injectors (IIRC), Hesco adjustable fuel pressure regulator & 61MM(?) TB, Borla Header & downtube and MSD capacitive disch ingnition (the "Off Road 6" i beleive), all other engine components (intake manifold, Golen "internals" are either stock or as Golen installed).

In general, the engine is strong, runs great and I have no complaints, it has about 2,500 miles on it - Great Engine! Anyway, i have noticed a valve rattle at "cruise" speeds (30-80 MPH), the rattle is barely discernable or non-existant while applying an even "cruising" throttle, but if i press it lightly to accelerate, i get a pretty bad vavle rattle; however, if I go all the way to WOT the valves do not rattle - or well it does for a brief moment, then once the RPM start climbing, it goes away - or ican't hear it - either way the "light throttle pressure" makes a horrible rattle. I run only premium fuel and even supplement with Octane booster, but it dosen't really help.

I figure this is a lean/rich issue, but I really don't know all that much about engine tweaking for maximizing performance or if I lean it out is that worse or better for valve rattle. I figure I can trial and error, but would really like someone more knowledgable than me to to offer a little guidance.

Of Course if anyone thinks it is something other than what i think, Please speak up and let me know, I really don't want to damage my new engine.

[Mgardiner1]

What weight oil do you use? Does it do it equally hot and cold?

My non stroker renix had a terrible rattle/knock when at cruising speed, if you would float the pedal just enough to make like no load on the engine (no accel, no decel). The warmer it got, the worse it got. I knew the bottom end of the engine was pretty badly worn out, so i contributed it to a piston pin slap, or some other kind of high tollerance knock, which is why i think it got worse with thinner oil.

[dwg86]

It might be running lean with the 21# injectors. You might want to get 24# injectors and an air/fuel gauge.

[1bolt]

It's part throttle ping. Which is the sound of gas exploding instead of burning making a diesel like combustion noise, it can be quite harmful to your engine if you let it go on without fixing the problem that is causing it.

If you are using less than high octane then stop using low or mid grade and go to 93 octane (this is the best way to fix the problem, as your ping is most likely due to higher than stock compression, and the factory ECU's tendency to keep timing on the bleeding edge. Those two factors are the exact reason that high octane pump gas exists, and it is absolutely the most efficient and desirable solution to ping that is compression and timing related.

Ping Can also be caused by excessively lean mixture, during cruise leading to ping until you hit WOT.
Solve by increasing fuel pressure with an adjustable regulator. Going up one size in injectors may help (or may not help at all, this is more likely to help if you have ping AT WOT and not part throttle)

Realize that Mustang 5.0's came with 19lb injectors not every (or even most) 4.0 strokers REALLY need larger Injectors. Still there's no real harm in them. As long at they are modern designs that still have good spray patterns at lower pressures, they will work basically identical to a smaller injector, as your ECU and O2 sensor have more to do with your fuel mixture at normal throttle openings, than the maximum fuel your injectors can flow at a given pressure.

Improving your rear end gearing, especially if you have stock gears but larger than stock tires will also help your problem specifically.

Getting cooler air into your intake will often help ping dramatically, as heat in the combustion chamber will contribute to ping. If you ever get ping after yo idled at a store for instance, it will be due to the heat in the intake and air charge.

If you have replaced the factory air box with a cone filter hanging there sucking hot engine air, then you're just costing yourself power and contributing to heat related ping.