Diagnose my 91 EB

[sd_iconoclast]

Too late. I used my smoke machine.
It works great. Turns out there was a hose disconnected from the "octopus".
So there was a pretty big leak. I reconnected the hose and verified no leaks after that.
I went for a drive and the car seemed abnormally smooth and quiet. Idle was smooth.
Then, just about when the car reached 200 degrees or so, I got major jerkiness.
When I got home, I noticed a strong sulfur smell. I had noticed it before, but never thought about it until I saw a YouTube video that mentioned it as a symptom of a bad O2 sensor.
I have also verified that my gas mileage has gone to hell.
I usually get about 17.5 MPG. This time I got 13.3.
Now I did not disconnect the battery after fixing the vacuum leak, so maybe the car had learned to be rich all the time?
Or maybe I screwed up the O2 sensor by running with the vacuum leak?

 

[1991 sploder]

U need to do idle relearn procedure ..
Just disconnect the battery for a while and re connect let it idle for a couple minutes. Yea I bet it was running super lean increasing mpg hahaha

 

[1991 sploder]

Check the vaccum diaphram off the airbox that little 2 vaccum lines is a little thermostat opening and closing the "thermostatic air cleaner" to shudder open a little door that draws in air off the exhaust...vaccum diaphram is probably blown there too after it reaches temp..

 

[410Fortune]

strong sulfur smell is usually un burnt fuel going through the cat converter
Clear the code
check fuel pressure

 

[sd_iconoclast]

Check the vaccum diaphram off the airbox that little 2 vaccum lines is a little thermostat opening and closing the "thermostatic air cleaner" to shudder open a little door that draws in air off the exhaust...vaccum diaphram is probably blown there too after it reaches temp..

Wow, you are right on top of this Sploder. The vacuum diaphragm you describe is where the disconnected hose was going.

 

[sd_iconoclast]

Today, I checked vacuum. It looks good. 18 in HG at idle.
I put a fuel pressure gauge on the fuel rail and saw this:
When I put the key in the ignition and I hear the fuel pump run, the gauge shows 39 psi.
As soon as the fuel pump stops, the pressure drops to 30 psi.
When I start the engine, fuel pressure stays at 30 psi during idle.
When I step on the gas, fuel pressure goes down slightly. Maybe gets as low as 28 psi.
I used my mechanics stethoscope to listing to all the injectors. I can hear all of them clicking at the same rate although the clicks sound more sharp on some injectors. That might be a function of where I put the stethoscope probe on the injector.
So Do I need an fuel pressure regulator?

 

[Mbrooks420]

Or a pump.

 

[Roadrunner777]

As I understand it, the fuel system spec is 38-45 PSI, with 38 PSI at idle and 45 PSI at WOT. The amount between 38-45 PSI is managed by the fuel pressure regulator, based on manifold vacuum.

So, to begin with, you are not attaining a high enough pressure on KEY-ON. Next, there should be zero pressure drop after the pump cycles. Finally, the pressure is going the wrong way at WOT.

I would do the following in order until you get better results:
1) A system restriction could cause this, so my first step would be to replace the fuel filter. It's cheap and not hard to do unless the connectors are nasty.
2) To me, the odds of this being the pump vs regulator are about even, and I can't think of a diagnostic that would help decide. So, I would replace the pressure regulator next, simply based on cost and labor.
3) If the first two steps fail, I'd go after the fuel pump. Could be a weak pump, could be a clogged up filter sock on the pump.

I can't quite make a connection from this to a bad injector. But, I'm comfortable in suggesting these other steps first because these parts have known failure rates, where an injector could last the life of an engine. I could be wrong!

I'm writing this to address only the fuel pressure symptoms. I don't know if this relates to your original issue. But, you will not get optimum performance from the engine until the fuel pressures are correct.

 

[410Fortune]

pump is weak you never saw 38 psi let alone 42-45 psi
30 at idle is toooooo low it will not run well with this pressure as the fuel is not being atomized properly, not enough pressure behind it and when you have a high demand for fuel that pump will not keep up giving you a lean condition

You can remove the vacuum line from the regulator and check for fuel
any fuel in the line = ruptured regulator diaphragm

Also what happens to fuel pressure when you pull the vacuum line off the regulator? (while running)

I would suggest you need a new Bosch pump and fuel pump screen as well as a new Wix or Motorcraft fuel filter
That is AFTER you verify battery power is being sent to the pump at the fuel tank (low voltage issue can cause low pressure too)
Check for corrosion on the fuel pump fuse and relay blades, clean battery terminals, etc

 

[sd_iconoclast]

I replaced the pressure regulator and found that the pressures did not change except that the pressure no longer drops after the fuel pump stops. But then we pulled the plugs and found that the #6 plug was completely melted and the electrode was missing. I did a compression test and found zero compression on #6.
Surprisingly, it starts just fine and does not seem to lack power. Except for the occasional shudder and obvious (from outside the car) miss, and other symptoms I mentioned, it seems to run OK.
So next I will pull the head I guess.

 

[sd_iconoclast]

So my theory is that my massive vacuum leak on the octopus caused #6 to run way lean until it melted the spark plug. The electrode then fell off and was crushed in the cylinder (probably the POP my son heard). The question now is whether the damage is limited to just the head

 

[Mbrooks420]

I’ve melted holes in the tops of pistons, but never melted a plug.

 

[sd_iconoclast]

So I pulled the head and the #6 exhaust valve had about 1/4 of it missing.
I got a new head with valve job and now the car runs pretty well.
I am still having oil pressure at idle issues though. I think I will start another threda.