Dj Cutler

I have a 98 Z28 and if I give it anything less then half throttle it will jerk. But WOT it doesn't do it. It's been doing that for years. Recently I replaced the fuel pump and the next day it would fire up then dies or it would crank and crank and when it finally fired I could smell it was really rich.. Cold starts it starts up just fine. Last code (P0141) was a O2 sensor which I replaced yesterday. Fuel pressure is at 58 lbs. Only thing I can think of what it might be is like the coolant temp sensor is faulty and its tricking the computer to do a cold start when its warm. But I haven't noticed any abnormal temp gauge readings on the dash. I haven't checked it with the scan tool yet. Any ideas what it could be? Any help would be appreciated.

RPM WS6

iTrader: (3)

If the starting issues began immediately after the fuel pump swap, then I would suspect something being wrong with the new pump or install (always suspect the newest item(s) if an issue begins immediately after install.)

As for the long term jerking issue, if you aren't getting a misfire code (P0300/P030x) and have proper fuel pressure under load, then I would start with an MAF cleaning/unplugging the MAF and see if it still does this under MAP sensor control only. This is a free and easy check before digging any deeper.

Dj Cutler

I will pull the pump back out and see if I can see anything noticeable wrong with it. I cleaned the MAF yesterday and nothing changed. Unplugged it and drove around and it didn't make a difference in the jerking. When I got back from the drive the scanner read the ECT at 208°F and the dash gauge reads 185°F. When I started it both gauges was more together at 143°F and that's when the hard starting comes up. I can start it 5 minutes after I park when its hot and it'll fire right up, but it will hang around 500rpms for maybe a second then idle normal..

The other night the temps got down in the low 40s and when I was driving it it wouldn't drop below 1500 rpms fully warmed up. It hasn't done it since that night.

Dj Cutler

Driving back to the house and it acted like it had no fuel pressure. Ran back out to my dad's house and grabbed my fuel gauge and hooked it up and its like the fuel pump is kicking itself off. It goes from 60 psi down to 40 psi then back up. It's just idling. Give it throttle and it drops down to 10 psi before it turns back on. This is the first time its ever done anything like this.