Intermittent timing issue

[skp53]

I have a 93 Chevy p30 stripped chassis (step van) with 5.7 v8 tbi with at. The truck is stock except for egr delete. Sometimes after running a constant speed for 10 minutes or so, I get what I am calling valve rattle (machine gun like noise) when I come to a hill and press the gas pedal to the point of downshifting . I let up immediately and it goes away. If I don’t react quickly enough, I get code 43 knock sensor which I would think is to be expected. I was also getting 42, ignition bypass error, until I routed my spark plug wires away from the connections on the distributor. This engine is a jasper replacement that I have run about 8-10k and it has done this from the beginning. I let up as soon as I here it and downshift manually if need be to avoid it happening again. Sometimes I can drive it 2 or 3 days in a row with no issues. The distributor was put in new with the engine. I have also replaced the tps. Being that this is a stripped chassis, there are no bells and whistles on this one. I have also checked the wiring from the distributor to the ecm and checked the ecm for bad connections and bad solder joints. Doesn’t appear to be anything left but the ecm itself. Has anyone ever had a similar issue? Help is appreciated.
Btw, I have the interface and have downloaded tunerpro. The strange thing is (to me), it will not act up if I have tunerpro recording a file. If tunerpro is connected and up, it will still do it, but once I start recording, it will not repeat the issue.

[MO LS Noobie]

One thing I would try is a couple of tanks premium fuel, the higher octane will add some knock resistance. That's what it sounds like you're having. Another thing to check would be here ignition timing. Point to ponder is that is exactly why the EGR was put on the engines, to fight spark knock

[skp53]

One thing I would try is a couple of tanks premium fuel, the higher octane will add some knock resistance. That's what it sounds like you're having. Another thing to check would be here ignition timing. Point to ponder is that is exactly why the EGR was put on the engines, to fight spark knock

Thanks for the reply.
The timing is set at 0.
Maybe I should just put the egr back on the engine and have my chip flashed.
Seems strange that the problem doesn’t occur with tunerpro recording, but I don’t know how all that works.

[NomakeWan]

I'm not sure if it applies to your ECM, but many pre-94 GM ECMs will actually go into "service mode" if you connect a scan tool to them, which completely changes how the engine runs. I'd wonder if maybe your ECM is one of those that has to go into service mode in order to establish a scantool connection.

[skp53]

I’m not sure either. I can record a file with tuner pro and see the dashboard showing all the different parameters of the engine and speed etc.
Thanks for the reply.

[udidwht]

Always check and confirm fuel pressure when under load first thing with a TBI set up. Also check to make sure your ground cable/s are clean, clean, clean.