low grill gas pressure

Look for a spider web or nest in your grill's burner. Or, maybe a pinched line under the RV from hitting a rock or something.
Do your other RV appliances work fine on propane or is there a pressure problem with the whole RV?

Look for a spider web or nest in your grill's burner. Or, maybe a pinched line under the RV from hitting a rock or something.
Do your other RV appliances work fine on propane or is there a pressure problem with the whole RV?

Often the rig connector is for low pressure. Connecting a grill with a regulator can cause the problem you've encountered. In this case remove the grill regulator.

I installed a high pressure connection and use the grill's regulator.

I already made sure there is no obstruction in the grill and all my devices other than the grill work fine. The grill was made for the trailer, came with it from the factory, and worked the first three years, so it not working now is probably a line blocked, but somewhere between the distribution in the trailer and the valve (no regulator on the grill) but how do I test for that?

You need to find a propane dealer that has a pressure gauge to test for pressure. I have a hard time believing that the line could be plugged in the middle. The quick connector could be plugged though at the point where you plug the grill in.

Are you sure that something in the grill itself is not plugged. I know that you said that you checked but, that would be the easiest thing to fix. There has to be a valve on the grill to control flame height. Are you sure the knob on the valve is turning the shaft that it is connected to ??? Could there be a chunk of dirt that fell into the grill line and got stuck at the valve ???

Hope you get it fixed easily. Have a nice day

We had a quick connect fitting under the trailer that went bad. There's a little o-ring there and I think that got messed up. Some days there'd be no gas and some days it would be fine. If you look inside your fitting you might be able to see if it's okay or not.

The RV quick connect fittings are 1/4", are RV specific and cost a lot at an RV dealer. I find the valves on them are a nuisance and have been pondering switching to a 3/8" natural gas quick connect like below ($15 on Amazon). We have a 20' 3/8" dia. hose for our Weber Q. Not sure if it's much better than a typical 1/4" hose but we never have a flow problem.

So, I checked the fitting by ordering another a matched set of male and female, plugged the male in to allow gas to flow free to the atmosphere and nothing happened. I then followed the one suggestion I got to check the o-ring, and in doing so noticed it was darker than it should be, turned out to be a nest of some bug. Cleaned that out and viola! got gas, grill worked perfect.

There is a regulator on the tanks. Many of the plug in BBQs also have a regulator. That is two regulators on the gas line.
Don't work.
Take the regulator off the BBQ, and hook it up direct to the already regulated gas line.

As Dave said, you are likely dealing with the double regulator problem. You have one on the trailer and you have one on your grill.