98 Suburban Injector testing - spray pattern?

James Howell · August 29, 2020

I have taken the fuel injectors (spider assembly) out of my suburban 5.7 vortec. Luckly I have a 12v 1A power supply with test leads that I can engage the fuel injectors with. So I got the upper intake manifold off and removed all the injectors, and I had my girlfriend sitting in the truck turning the key off and on for me. Well I started with the first injector. Had her turn the key on and could hear the pump kick on for a few secs. Then engaged the fuel injector and it has a fine stream coming out.

I thought that it should be cone shaped or at least a mist or something. Seems to me that a fine stream of gas like that wouldn't atomize properly and would result in either misfires or fouled plugs etc. I repeated the above procedure for the remaining 7 cylinders and all of them sprayed a very thin fine stream of gas.

Am I going crazy or is it suppose to be like that? I thought it was suppose to atomize the gas so it could combust it properly and efficiently. One other thing I thought about is maybe that I do not have good fuel pressure. Sad thing is I do not have a fuel pressure tester gauge thingy so I can't test that right yet.

The symptom I was originally getting is a miss through the complete rpm range. There is no codes being throw for it but I can feel that it doesn't have the power it should have. I did a complete tuen up, new distributor cap and rotor and new coil and new plugs and wires. Am getting spark on all cylinders, but it is missing on one cylinder. Almost like a dead cylinder. I also removed the valve covery and there is no extra play in any of the rocker arms so I think all the valves are seating properly, but that does not mean that one exhaust valve isn't burnt out.

But mainly I just want to know if the injector (MPFI STYLE) should shoot a steady fine stream or should it be releasing an atomized cone of gas for the intake valve? Will get a fuel pressure gage asap and test that as well. Thanks in advance and if there is anything information you need then please just let me know.

Edited August 29, 2020 by James Howell

KINGENGINEMAINTENANCE · September 1, 2020

Yo, I have had a situation where I was trying to track down an issue in a (direct injection) car and I took the fuel rail off the intake with the injectors still clipped to the rail and pointed the rail toward the front of the car (so I could crank it and see the gas) and tested them one at a time by unplugging electrical to all but one injector. They all sprayed a straight stream and did not atomize to a mist. I don't remember what issue I was tracking down this was a couple years ago but the injectors were all good. Maybe check compression on all cylinders, or if you know which cylinder is missing check compression on it. Spark gap should be at 0.060 right? Check that. Good luck! Peace