90 F350 7.3L miss

I have a 90 F350 with a 7.3L diesel. It has about 400,000 miles on the original engine and I use it to pull a horse trailer. Lately I have had a miss at about 1700RPM and a lot of smoke from the exhaust. It ran fine until someone at the body shop sprayed some starting fluid in the intake while trying to get it started. It is a bear to get started sometimes since it will sit idle for weeks on end, but patience has always gotten it started. Now I don't know if the problem is internal or maybe a bad injector. Any insight would be helpful. I was thinking about doing a compression test to check for a bad cylinder, but where would I connect the tester, the glow plugs?

You can use the glow plug hole to check compression. If you dont have a tester, you can fabricate one from an old glow plug. Just cut the ends off, drill a hole thru it, braze whatever fittings you need to adapt to your compression tester. Youll need a gauge that goes to at least 400, preferably 500#. Or you may be able to rent one. Spraying either, or any other kind of starting fluid in one of these is a big no no. I have seen it(either) break pistons, rings, blow gaskets......I use carb cleaner, cause it wont kick back, BUT I DISCONNECT THE GLOW PLUGS, until after i get it running. The hard starting problem after it sets, could be fuel leaking down in the filter, or a cracked fuel line sucking air at the transfer pump. This allows air to get in the system, that has to bleed out before it will start. The screw on bottom of the stock fuel filter, has several places that can leak. The drain, the clogged filter sensor, and a schraeder valve on some. The seats and threads can become damaged from water, overtightening ect... If the bottom of the filter is damp, or wet at all, its leaking down. The best solution ive come up with, without replacing the whole filter assembly, is to replace the stock filter and the bottom of the assembly, with a spin on filter, Wix part # 33417, which is a combination filter/water seperator with drain. Always fill the filter as full as you can get it, then use the schraeder valve on top of the filter housing to bleed the rest of the air out as you turn it over.

Thanks, I will look into making a tester. I hope it's just a gasket and not a piston or ring, although I'm sure the engine could use a complete rebuild.