69L48Z27

I posted this in another thread and I didn’t get any responses there, let me try here.

89 IROC 5.7 - all stock

I’m in the process of trying to determine if my fuel pump is weak:

“So it looks like a fuel pump is in my future. Check my thinking and see if missed anything.

- Changed fuel filter.
- With the car priming itself from zero, the two second thing, I get about 30lb. Bump it over and it goes up to about 38 and fires on the third bump cold. Shut the car down and it goes up to about 41. Pressure will hold for several hours.
- Next I ran a jumper to the relay harness and sent power straight to the pump. It gets to about 40 and that’s it.
- Next I pinched off the return line and I still only get 40 psi.

This is tells me this pump is only ever gonna do 40 psi no matter what the load. I’m a few psi below where I should be.

Would you you change the pump or run it? The car falls flat at high rpm but I haven’t driven it yet since I change the timing. So, it’s either running out of fuel or the timing was that far off.”

ploegi

Would be interesting to see what fuel pressure was doing under load.

69L48Z27

My guess is it will drop. The hose on the fuel pressure gauge isn’t that long, not sure I can tape it to the windshield while I drive.

Drew

iTrader: (58)

Have you put a pump in it? Do you have any first hand knowledge of a pump ever being installed? Because after 30 years, I'd pretty much put changing the pump on the preventive maintenance list right below changing all the fluids. It's a mild pain in the rear, but it beats having Big Cletus come out and hook up the Big Rig WRECKER! and drag it home when it kicks the bucket.

69L48Z27

Drew,

No, no new pump yet, that’s what I’m trying to confirm through the diagnostic. While I don’t disagree with you at all, this is likely the original pump and it will eventually need replaced.

I would like to confirm that I have this diagnosed as a weak fuel pump and not some other problem. Nothing worse than throwing parts at something to find you still have the same problem as when you started.

69L48Z27

I had an opportunity to drive the car today with a fuel pressure gauge. At idle I was around 38 and under load, no vacuum, I had about 42. When I would run it hard it would dip to 35 and ping. Not sure how old the fuel is or what grade, it smells a little off.

Setting the timing helped out a lot for drivability. But, looks like I’ll be pulling the tank. The fuel pressure should always be above 42-43psi from what I read.

Drew

iTrader: (58)

You'd probably be surprised how low the fuel pressure can be and the engine still runs. The fuel pressure regulator goes off of engine vacuum. More vacuum/less pressure, less vacuum/more pressure.

If the pressure doesn't stay consistent, and doesn't keep up with demand under load, there's probably something cutting the pressure. Doesn't necessarily have to be the pump. It could be the pulsator or the short rubber hose between the pump and the sender, or a clogged filter, etc. Now it's just a matter of narrowing the problem down. You could try replacing the filter, unhook the vacuum line from the fuel pressure regulator and see if gas pours out, etc before dropping the tank. But really, if you've never changed the pump, I'd change it just for the peace of mind. That said I've been meaning to change mine, but I've got a few things to take care of before it's a high priority. A driveability issue would move it right to the top of the to-do list.

GeneralDisorder

iTrader: (1)

Look at your O2 voltage, and your BLM/INT data. Is it trimming for a lean condition (BLM/INT above 128)? Is the O2 voltage pegged lean (consistently low voltage and not switching) at medium throttle under load?

These are the symptoms of a fuel delivery issue.

Your pressure seems low. But it's borderline and gauges are never 100% accurate so you need corroborating data.

GD

69L48Z27

I don’t have a scan tool, I’m looking for something the I can use with a Chromebook. Everything seems to be an Android only solution for Bluetooth ALDL plugins.

69L48Z27

Fuel pressure always needs to be consistent and in range, at least with LS engines they do. This is my first TPI car but from what I’ve read it’s just as important. It may still run, just not well.

Fuel regulator does not smell of gas and responds to engine vacuum. Pinching the return line does not raise pressure either.

Fuel filter is new. I’ll check the pulsator when I drop the tank.

Thx

ploegi

You aren't going to find anything for a chromebook, you can't install software on it in any event.

69L48Z27

Thx. I’m not finding any for iOS either. Really didn’t want to buy a cheap tablet just for this.

69L48Z27

I have the tank pulled and the new pump showed up today. Everything was bone stock in the tank. I had no idea the pulsator just slid over the hose barbs and really has no clamping. I wonder if this is where my pressure was going.

Im going to eliminate the pulsator. Let me know if that’s a bad idea for some reason. From searching it appears it’s common to leave them out.

I’ll report back tomorrow with hopefully good test results.

69L48Z27

New pump is installed and working great. Straight 12V to pump I get 44psi and when I crimp of the return line the gauge jumps up. That would be a PASS. Pulsator was not reinstalled and I think this pump is quieter than the stock pump. I put some 93 in the tank, when I hammer on it I get just a little ping now at the 1-2 shift. Other than that, this thing runs strong now. Seems to start quicker too but time will tell.

Now on to some other tweaks...