98-LS1Z28

I have a 1998 Z28 stock. Over the last couple of weeks the performance has dropped when hot. Now it will stall or have no power leaving from a stop. But when it's cold it runs great, for the first 15 minutes or so. No DTCs. Has 58 psi for fuel when it's not acting up. When it acts up the pressure jumps around. Almost like it's not pumping. I've cleaned the MAF, the fuel filter isn't clogged, the low coolant light is on, but it is full. Thinking that there might be crude on the sensor itself. Only thing I've noticed is that the scanner and the temp gauge isn't reading the same. The scanner reads 15-25 degrees hotter. I don't know if the ECT is going out or if I have another sensor going out like the crank or cam sensors. Any ideas on what to look at or try doing?

Injuneer

Low coolant light is a problem with the sensor. Usual problem is a corroded printed circuit board in the sensor due to coolant penetrating the sensor housing. You could try cleaning the sensor, but the often does not help.

What are the coolant temp readings you are getting from the scanner? When you cold start in the morning, does the scanner reading approximate the current ambient temp?

How much does the fuel pressure vary, when it "jumps around"? What are the maximum and minimum values? I'm assuming you checked the pressure and established the 58 psi value with the engine under a real load, not just idling.

98-LS1Z28

The current temp when I was going to work the gauge read about 170 and the scanner read 150. When I got to work it read 212 and the gauge was still below the 185 mark. I haven't really checked it when it's cold but will do when I get off work tonight.
The fuel pressure drops from 58psi down to 10psi or less before it kicks back in. Does it with the new pump i installed today and with the old pump. Under a load it only drops couple of pounds when it runs good.

98-LS1Z28

After letting it sit for 6½ hours yesterday it was still reading low 100s so I decided to just let it sit over night and check it. The ect sensor is not the problem. It was close to the actual temp outside.

98-LS1Z28

https://youtu.be/1wslf0DndkQ
This is what it's doing when it acts up.

Injuneer

Erratic/cyclic pressure - Possibly an overheating fuel pump losing pressure, a fuel pressure regulator problem, or a hole in the flex pipe between the fuel pump and the sending unit.

The LS1 fuel system has a "tee" at the fuel filter, and returns fuel to the sending unit from that tee. The fuel pressure regulator is inside the tank, attached to the sending unit. The spring loaded diaphragm returns excess fuel to the tank, opening and closing to control the pressure - essentially a "bypass" system. I haven't worked on an LS1 fuel system, and the LT1 system that I am fairly familiar with is totally different ("recirculated"). Since the return line is at the fuel filter, I'm wondering if damage fuel filter media could cause the problem. Has the filter ever been changed?

98-LS1Z28

Yes the fuel filter has been changed back in Jan 2013 when I replaced the fuel pump. It got drove for a month after that and sat with fuel stabilizer until the beginning of this month. So the old pump had maybe 1000 miles on it. The new pump has 17 miles on it before it acted up. The inside of the tank looks clean. But I'll buy a new fuel filter and see what that does.

98-LS1Z28

Well its not a fuel filter issue because it still acts up. I did notice when I was parking it wouldn't stay running long enough to move. Got out and checked the fuel filler neck to see if it was hot. And unscrewed the cap and alot of pressure was released. I've never run it under 3/8 of a tank of gas. This time it has a half of a tank of fuel. So it should theoretically have enough gas to keep the pump cool. Any ideas on what to do or look for that might cause the pump to be overheating? And the fuel relay was warm to the touch.

GaryDoug

Try swapping the fuel pump relay with one of the others, like the A/C compressor relay.

98-LS1Z28

I have tried 3 different relays and it still does it. I have also tried a jumper wire to bypass the relay itself and it still does it. Orignal when I seen the fuel pressure jumping around I thought maybe the relay was going out. Tomorrow I'm going to check all the fuel lines for any kinks, unhook them all and blow compressed air through them to make sure it's not the lines. Pull the pump back out and inspect the bottom of the tank for crap in it that might be causing it. It only seems to act up when it's hot outside. I can't get it to act up at night, but that could just be from not driving it long enough. I don't know if it's any relevance but since I've owned this car (8 years) I've had #7 injector plug up on me. But the last time had to be summer of 2012. It has done it every time a fuel pump went out.

Can a defective part in the evap system or as a whole, can cause the issues I'm having?

98-LS1Z28

Update. I didn't find any issues with the wiring, or lines. I did notice that the LTFT for bank 2 is usually around -14 and for bank 1 is within +-5. But at times I've seen them both be at -14. The O2 difference is bank 1 is 300-700 mv on the graph and just looking at the number, it reads on the lean side more. But looks normal on the graph. Bank 2 is on the rich side 800 mv. Graph shows it switching normal but at times it just flat lines rich. As soon as the issue happened both O2s flat line lean. Today has been the first time its acted up since I last posted. And the current outside temp is 78°F.

Injuneer

Not sure if the fuel pressure regulator itself can be temperature sensitive. If it's sticking open, all the fuel is going to recycle back to the tank and the pressure is going to drop.

98-LS1Z28

The last 2 pumps I've put in are Precision fuel pump part #A43014 from O'Reilly. Has anyone else have had issues or know people who have had issues with these pumps?

JakeRobb

Not specific to that part, but I've had issues with EVERY non-OEM electrical part I've ever bought. High end upgrades excluded -- I'm talking about the stuff you get from AutoZone, etc. Sensors, pumps, motors, everything. They're never as good as the factory parts. My advice is that if you suspect the pump, get on RockAuto and try an original ACDelco pump.

Or, if you have plans for more power someday, you could plan ahead and get a Racetronix.

98-LS1Z28

If I would of known it would of been this much of a pain, I would of bought the racetronix. I do plan on getting work done to it. It just involves more money and my ol' lady would probably kill me for spending that much money.