My 79/auto just died like I turned the key off

[globalwad]

Hi everyone. I'm in the middle of troubleshooting my 79 and could use some direction from the experts here. My lady and I were on a drive down the highway at 75mph when the engine just stopped like I had turned the key off. No stumbling or shuddering ahead of time, just off. Made it safely to the side of the highway and got a tow home.

Since I started digging into it, I have checked a few things so far, but none have solved the issue. I have had my 928 for about 2 years now, and it is driven often and doesn't sit for long periods since I've owned it. It has 89k miles

It cranks fine, but will not even attempt to start.
It has a full tank of new fuel
I checked fuel pump fuse #22, and it tested good.
Pulled the fuel pump relay and bridged 30-87, fuel pump is confirmed running.
Pulled the air filter off and sprayed starter fluid down the intake, starts immediately and then dies (even did this while fuel pump relay is bridged, no change)
Replaced fuel filter with new
Traced out the green wire to the distributor, looks fine without damage or crumbling.

Not sure where to go next here. Will be trying to track down the ground points and confirm my grounds are solid next. The only other info I can provide is that I did notice that for about a week before this, my starts were not happening as quickly and would take 3-4 attempts. Meaning, that the first cold start would fire immediately and then die for 3-4 attempts before it fired up and ran normally. I had assumed it was time for a new fuel filter, but obviously it was more than that!

Thank you for any guidance on where to go next,
Mark

[stepson]

Okay, you jumpered the fuel pump relay (XVII) and the fuel pump worked. Did you try to start it at that point?

The old adage is "Relay, Relay, relay". In other words, replace the fuel pump relay with a correct relay (928.615.113.01)

[GrayM]

1984 928 mine ended up being the fuel pump relay. NAPA had one, I couldn't believe it.

[globalwad]

Originally Posted by stepson

Okay, you jumpered the fuel pump relay (XVII) and the fuel pump worked. Did you try to start it at that point?

Yes, the pump is running fine with the jumper. No change. Does the accumulator do anything other than maintain pressure in the line when the pump shuts off? Will it prevent fuel from flowing if it has gone bad?

[stepson]

So even though the fuel pump is pumping, the cylinders are not getting fuel?

[globalwad]

Originally Posted by stepson

So even though the fuel pump is pumping, the cylinders are not getting fuel?

Well, up until tonight, I thought the answer was no. But I took off one of the fuel lines coming from the fuel distributor down at the injector, and with the fuel pump running, I am getting fuel out of the line when I press down on the diaphragm plate.
So now I am thoroughly confused. It still cranks fine, but absolutely doesn't even attempt to start unless I squirt starter fluid in the intake. And then it starts immediately, then dies.

[GrayM]

I also have a 1989 Corvette and I had a similar problem. What it ended up being was a bad injector that was shorting out the injector system. Take your injectors off one at a time and try starting it after you remove each one. If you have a bad one it should start when you remove it.

[stepson]

Originally Posted by globalwad

Well, up until tonight, I thought the answer was no. But I took off one of the fuel lines coming from the fuel distributor down at the injector, and with the fuel pump running, I am getting fuel out of the line when I press down on the diaphragm plate.
So now I am thoroughly confused. It still cranks fine, but absolutely doesn't even attempt to start unless I squirt starter fluid in the intake. And then it starts immediately, then dies.

So what happens if you push down on the diaphragm plate and hold it down while the engine is being cranked? Will it start?

[globalwad]

Originally Posted by stepson

So what happens if you push down on the diaphragm plate and hold it down while the engine is being cranked? Will it start?

I should have my son here tomorrow to help be my second set of hands to find that out!

But in the meantime, I had a thought. I picked up a Chilton's service manual that covers my 79, and it says that all 1979 928s have two fuel pumps. One internal and one external. I have only found one, the one located at the rear cover plate. (which is working)
Now I'm wondering if my internal pump went out, but my external pump is buzzing along, but not pumping anything due to the internal pump not pushing any fuel to it?
Or am I not understanding how the 2 pumps work together?

[stepson]

If you have an internal pump, it will have a second set of wires attached to the terminals at the tank end of the rubber hose that is attached from the fuel tank to the fuel pump. The internal pump slightly pressurizes the fuel (@5 lbs)to the external pump to help prevent hydrolocking in hot weather.

I have a different year 928 from yours, but I have replaced the internal pump on mine with an internal strainer. Replacing the internal pump requires that the hose connecting the tank to the external fuel pump be replaced since the strainer opening is 1 1/2 times the size of the original hose. I have NEVER had a hydrolocking issue with any of my 928s. If and when you do remove your internal pump, just separate and insulate the extra wires so they don't try to connect to anything on their own.

When my internal pump went bad on my GTS, the external pump was pulling fuel through the seized internal pump. It functionally worked at lower RPMs, but at higher RPMs, the engine was pinging (ie not getting enough fuel).

Good Luck

[globalwad]

*SOLVED*

Got it sorted out!
It ended up being a bad fuel pump after all. Even though the pump was audibly running, something happened internally, and it wasn't actually pumping fuel to the engine. I verified this by removing the fuel line from the bottom of the fuel filter in the rear passenger wheel well and then jumpering the fuel pump relay socket to make the pump run. No fuel at all was leaving the new fuel filter. Once I installed the new pump, it was flowing immediately out of that same line.
Just got back from an hour long test drive, it runs better than ever now

[stepson]

Glad to hear you got it figured out. Drive it like you stole it !