98 Z28 won't take any throttle
Thread Starter
Joined: Nov 2005
Posts: 2,149
Likes: 4
From: Gainesville, GA
98 Z28 won't take any throttle Alrighty. I've had this 98 Z28 M6 for 21 years and she was bone stock when I got her. Been trying to drive her more (156K) and now I've got an issue. I had a CEL that indicated knock sensors, so I ordered GM parts (with harness) and put them to the side until I felt like pulling the intake. One day she wouldn't hardly run at all. She'd start and idle, but when you tip in she wants to die. As long as you're feathering the throttle then you can get the rpms to climb enough to get it to move, but anything above 10-15% throttle and she wants to die. If I rev to about 2k and then go WOT it will die for at least a full second, then stumble back real hard and try to rev with a backfire or two.
I pulled the intake, swapped my knock sensors, and got her all buttoned up and no change. No more CELs - at all. Here's what I've done so far:
-Took the TPS off and put my multimeter on it and seem satisfied that the resistance changes smoothly across the sweep.
-No melted O2 wires that I can see. No melted wires that I can see period. Plugs and plug wires have about a thousand miles after new headers. Ran strong after headers/plugs/wires, no issues and don't think my issue is related to that. I just replaced my old pacesetters with Speed Engineering. Straight forward.
-I unplugged the MAF and immediately got a CEL; no material changes in how it operates. Still strong stumble on tip in and won't hardly rev. Plugged MAF back in and cleared code. No change.
-Thinking there might be a vacuum leak, I sprayed carb cleaner around the brake booster hose, near firewall (back of intake), along edges of intake manifold, along each injector. No change in idle.
-Infrared thermometer shows consistent ~300° temp on each header primary, so I think all 8 are firing about the same.
AI is telling me to replace my crank position and maybe cam position sensors. Argh. I'm about 99% sure it's a sensor issue but don't have any CEL's (even after letting it come to temperature and all kinds of attempts to rev it).
I have not checked fuel pressure.
I'm stumped. Before I start buying parts I figured I'd inquire with ACTUAL intelligence instead of trying to rely on the artificial kind. Any ideas?
I pulled the intake, swapped my knock sensors, and got her all buttoned up and no change. No more CELs - at all. Here's what I've done so far:
-Took the TPS off and put my multimeter on it and seem satisfied that the resistance changes smoothly across the sweep.
-No melted O2 wires that I can see. No melted wires that I can see period. Plugs and plug wires have about a thousand miles after new headers. Ran strong after headers/plugs/wires, no issues and don't think my issue is related to that. I just replaced my old pacesetters with Speed Engineering. Straight forward.
-I unplugged the MAF and immediately got a CEL; no material changes in how it operates. Still strong stumble on tip in and won't hardly rev. Plugged MAF back in and cleared code. No change.
-Thinking there might be a vacuum leak, I sprayed carb cleaner around the brake booster hose, near firewall (back of intake), along edges of intake manifold, along each injector. No change in idle.
-Infrared thermometer shows consistent ~300° temp on each header primary, so I think all 8 are firing about the same.
AI is telling me to replace my crank position and maybe cam position sensors. Argh. I'm about 99% sure it's a sensor issue but don't have any CEL's (even after letting it come to temperature and all kinds of attempts to rev it).
I have not checked fuel pressure.
I'm stumped. Before I start buying parts I figured I'd inquire with ACTUAL intelligence instead of trying to rely on the artificial kind. Any ideas?
