Found a 97 Tahoe. Clean body. 160k. New tires. Seller sez it runs rough. Is pretty sure spider injector is issue. Truck will run but poorly. He got truck in trade and wants to sell it vs fix. Or he will fix it and raise price. Is there any way to determine if motor has other serious issues? Or is there a quick way to really prove spider assy is bad?
I bought a '98 model Tahoe with a bad spider assembly. I could tell quite easily it was bad because it was running so rich…I couldn’t stand behind the truck with the engine idling.
Black smoke, P0172, negative fuel trim readings, clean spot next to injector body (which can be seen by removing throttle body) are all signs of a leaking fuel pressure regulator.
Faulty distributor caps are another pattern failure on this model.
The best way to verify that the rough running is not from serious engine problems is to check the compression. Not too many sellers really want you removing and reinstalling parts though - even if it is just spark plugs. In addition to compression, someone who is experienced with a vacuum gauge can also give you a quick snapshot of the engine’s condition. This can be a little tricky with the truck running poorly though. Someone who is very good with a vacuum gauge can actually give you a rough idea of compression, and that doesn’t involve mucking around with much under the hood.
This might be of help.
Here’s what I’d do.
Get a can of SeaFoam Engine Tune-up.
Pour the can in the gas tank.
Fill the tank half full and drive the vehicle.
These spider assemblies have popet valves that rely on the fuel pressure to blow them open to inject fuel into the engine.
Sometimes these popet valve become stuck from gum and varnish from the heat of the engine and don’t open and close like they should. And the engine runs like crap.
Before replacing the spider assembly, I’d see if the SeaFoam provides any benefit.
I agree that the poppet valves can sometimes be freed up
I remember a Jimmy with a stuck poppet that I freed up with injector cleaner hooked up to the test port. I ran the engine off of the cleaner for a few minutes. The poppet got unstuck, and the truck has been fine for several years now.
Back when these stuck poppets were an almost weekly occurrence I often had luck using a MotorVac fuel injector service machine. I’d hook up the machine and a couple of times during the 45 minute flush I’d pinch off the return line at the machine, jacking the fuel pressure up to 90lbs or so. Most of the time the detergent and the high pressure would open them back up.