Join Date: Sep 2003
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Re: 1997 tahoe, shuddering at highways speeds
Ok man.. Do yourself a favor and get a fuel pressure tester and tell me what your trucks fuel pressure is running at idle. Also, check it cold first thing in the morning. All of GM's modular fuel pump assemblies (of which you should have since you have the first year they used a modular assembly in these trucks) have a problem getting enough pressure to the poppet valves if your charging system is not supplying enough voltage to the pump. This is especially prominent in trucks in cold weather, as your battery doesnt put out enough voltage (in some cases) to start the truck. This would also apply to you if your pump is defective and just not supplying enough pressure to force open all 8 poppets. Poppets need 52+ pounds of constant operating pressure to STAY open. If it drops ANYWHERE below that, they will close and you will have a rough idle condition.
On another note. Lets assume you have enough fuel pressure at the schrader valve on the line there... This could be the pressure regulator is not keeping enough of the fuel pressure at the meter head. Unfortunately due to the placement of the regulator, testing the fuel pressure at the schrader valve will only give you pump pressure, not line pressure. Your pressure regulator regulates fuel on the return side of the line, not pressure (amazingly). So the fuel meter body and or injectors could still be the cause of issue for you. Two sticking poppets could very well make your truck not run correct as you are stating.
Finally... if you want GOOD parts to put back in your truck, call me at Brown and Sons Automotive in Flint MI. My number there is 1-800-852-6933. Ask for Mike. I will even give you the GM employee discount on anything you need to fix this truck of yours. I keep the pump, fuel meter assembly, pressure regulator, poppet injectors and anything else that you can imagine needing for the job right in my store.
I want to see you get your truck working to its fullest again. I hate to see someone with a problem they cant figure out, fix it by not buying Chevy again. So let me know if I can help you anymore, ok? Later!