1992 240SX detonating or stumbling - Timing can't seem to find the happy median.

[qat727]

From the top - 1992 240SX 5 speed base model, I just rebuilt the KA24DE and have put approximately 400 miles on it since the rebuild. First tank I filled with 91 octane, second tank with 93 octane.

Internal mods - KA24E pistons, crankshaft, and rods. Complete new timing chain set including cam and crank sprockets from eBay. Upper timing chain guide removed. Still has stock 240/248 cams. I matched up the cam and crank sprockets according to the FSM during initial assembly, so unless they jumped, they should still be in the correct locations.

External mods - S14 upper intake runners installed and SCV delete performed. Most emissions parts were removed prior to purchase and engine rebuild. EGR has no vacuum attached and block-off plate install is planned. Flowmaster muffler installed in place of fart can, but exhaust is otherwise stock. As of now, the only vacuum line hooked up (with the exception of the IACV and related components) is the one to the fuel pressure regulator. It was running horribly when I first got it started (about 2 or 3 months ago). I replaced the fuel pressure regulator with an extra one I had around and it started running better.

Symptoms - I just got it to idle a couple of days ago, so I'll base my observations off of what I've seen since then. It runs quite rich. When you adjust the distributor completely counterclockwise, the idle goes down to approximately 800 RPM when warm. However when you try to accelerate, it starts stumbling and choking. I had it die on me when I was pulling out for a left hand turn. It just acted like the fuel shut off to it and would not start again. I managed to get it turned around and was able to roll start it when going down a hill. That was yesterday night and I didn't drive it today.

I tried advancing the timing a bit to see if I could reduce the hesitation problems. As soon as I move the distributor clockwise even a few degrees and try to drive it, the engine starts detonating under even slight loads. It still stumbles, just not nearly as bad.

I put a timing light on it tonight to try to see where the timing was at. I got it started and heard a metal tapping sound from under the valve cover which seems to be isolated to the area of the timing chain. I'm not sure what the problem is with that, but I didn't let the engine warm up until I can figure out what it is from. I did check the timing with the TPS unplugged and the engine at ambient temperature (around 85*F today) and with the distributor completely counterclockwise, the timing was in the middle of the 6 grooves as I was looking from above.

Does anyone have any idea what might be wrong with the timing to cause it to detonate like it has been? By the research I did on NICO, the KA24E pistons are supposed to work with Premium gas and yield 11.1:1 compression. This isn't working. If I advance it enough to where it isn't stumbling, it starts detonating all the time. Anyone have any idea what the tapping sound might be from and if I should worry about it? Any help would be appreciated. I want this car to make it to Import Alliance, and if I can't get it fixed, I won't be able to go.

[MaximA32]

I would pull the valve cover and see if you left anything loose. Any noise such as you described is never good especially when coming from within the engine.