Car idles good, then VERY SUDDENLY dies

[Vulpes5.0]

Hey y'all, trying to help a friend of mine who just bought a fox get her up and running right, having some trouble with something I haven't dealt with before, and can't find much online to help me anywhere.
1990 GT, 5.0, Gt40p heads, upper and lower intake, B cam, BBK Longtubes. Previous owner replaced TONS of little things here and there, new plugs, wires, cap, TFI module, MAF sensor, MAP sensor, TPS, fuel pump, and tons more that are great but not really relevant. It all looks very new, and the engine build itself is relatively new. This was a good deal where the guy mostly just got tired of fooling with it despite heaps of new parts, and hardly touched it from what I can gather (even the engine paint looks good!)

Anyway, here are the symptoms. The car idles good. IAC unplugged, spout unplugged, the car surges a bit but mellows out to the proper 750 RPM or so. Got the TPS dialed in, timing seems normal (don't have a timing light on hand but by feel, it seems fine, and was set previously). With everything plugged in, it idles about 1500 on startup then begins to go down to 1000 or so before it suddenly dies on me.

Only thing is, it randomly just shuts off. no surging, no hunting, just dead stops as if someone turned the key off, and then sometimes has trouble getting back started after this happens. The car typically idles for about 15-30 seconds before this occurs.
We made sure it had gas obviously. It was very low, but this didn't fix the issue. Tried raising the idle screw to be sure the car wasn't just bogging down when the computer shut the IAB valve, set the idle slightly smoother but the random shut off still occurred. Tried changing fuel pump relay just because I happened to have two, no change. I'm thinking this is some electrical gremlin, or something to do with ignition, though the ignition itself seems somewhat new. The car runs amazing when it runs. Revs fine, everything, just turns off suddenly.

So far I'm thinking to check engine grounds, the MAF, (despite it being relatively new) ignition components, maybe clean the salt and pepper shakers, possibly check the ECU for some burnt area. Any other clues as to what can cause such a hard shut off like this?

 

[General karthief]

Basics first, since it was bought with a problem, you need some 'stuff' to check system specs, a timing light to verify setting, fuel pressure gauge, and check for codes, this is a must starting point.
We have a checklist that gives you a way to find and resolve starting, stalling issues, stangnet member jrichker put it together with help from others. It works. Just follow the directions.

Help me create the "Surging Idle Checklist"

Updated 05 July 2022 to add rough idle when cold and smooth idle when up to normal operating temperature. See the EGR tech information, section #15 for more help. Many of you are familiar with the "Cranks OK, but No Start Checklist for Fuel Injected Mustangs" checklist and the No Crank...

www.stangnet.com

Got any questions post them in this thread and the members will help you out.

 

[Mustang5L5]

It might be loading up with fuel and becoming flooding and stalling. When it stalls, if you depress the gas pedal to the floor and try to restart, does it have an easier time? Gas pedal down triggers "flood clear" which disables the injectors and helps start a flooded engine.

You'll want to start from beginning and dump codes and see what you get.

 

[AeroCoupe]

Broken record but have you checked for any codes?

 

[Noobz347]

Do what the dude's are suggesting.


I'll go out on a limb tho and say that I think it will come down to the fuel pump needing replaced. Swapping the filter and cleaning the injectors would also be wise.

That aside, just keep it in mind as you're troubleshooting. I take it that the car has been sitting a while. The pump has probably sucked up some stuff and cause the pulling out of hair.

 

[Vulpes5.0]

ALRIGHT! So, sorry for the hiatus there. We're both trying to troubleshoot with minimal tools, and it's cold as all hell here in GA. But I think we may be on to something.
We started by bleeding the brakes so that if this thing does decide it wants to go, we can go ahead and test drive it. All fresh brakes, new ford motorsport springs, SR suspension shocks, subframe connectors, underdrive pulleys, and 90% of the gaskets look FRESH. Even a new heater core that hasn't even been plumbed yet. This car may have been sitting for however long, but whoever was trying to get it going again paid good attention to the drivetrain. Body looks a little rough and mismatched but, for $4500 it was a steal mechanically. Probably $2-3000 in new parts. I'm 99% positive (owner mentioned it) the tank, filter, and the fuel pump are new, visually the tank looks new, fuel pump sounds healthy, and I have pressure at the schrader valve, fuel sending unit works too.

I have not checked codes - I have an OBD1 checker but I couldn't seem to get it to read anything, I was probably plugging it in wrong but it was getting late so I had to pack it up by that point. I'll work on that next!

Previous owner had videos of it running and idling for 2+ minutes but then claims he messed with the timing or something and it started acting up.

Bought a timing light and set it at about 12 degrees, car seems to do good around there. Also checked virtually all vacuum hose locations to rule that out. had to reseal the PCV valve (behind intake) as well as replace some of the nipples on the Exploder intake that had cracked up. Set the idle as best as I could between the car dying and got it to around 800-900 RPM which I'm happy with for the time being.
The car seems to run alright, when it does run. We got it to idle for a period of about a minute, maybe more, until it succumbed to whatever issue is at hand.
I think Noobz347 / Mustang5L5 may be right and I may have narrowed it down to the fuel delivery. The injectors are one of the FEW things on the engine that appear factory 19 lbs. They look like they've seen better days, but what makes me suspicious of them is this sound I keep hearing.

1 - When you turn key, obviously you hear fuel pump prime in the back, but you also hear a HISS from what I believe is one or more of the injectors letting off pressure straight into the cylinders. It doesn't happen every time, but it is repeatable, and it's something that I don't think I hear on my fox that runs great.
Could this just be the sound of the return line? I was under the impression that it stayed pretty pressurized. It also seems to do it more after cranking rather than just priming the pump.
2 - After the engine dies, sometimes it practically refuses to light up from that point. Sometimes it cranks right up, others it cranks and cranks with no fire at all.

Could I theoretically test this by removing the upper intake and fuel injectors/rail, and turning the key to see if they spray fuel out with out cranking?

 

[Mustang5L5]

The rail should hold pressure for a little bit. Usually they bleed down eventually due to the check valve/nipple in the fuel pump.

But if you lift the rail up off the lower and pressurize it, you may shoot a few injectors out of the rail at 39psi.

However if you pull the upper off, the noise should be pretty loud in the port of the injector is just spraying off. If you have a gauge on the rail you can see if the sound matches the pressure falling off. You should also be able to smell it.

 

[Vulpes5.0]

The rail should hold pressure for a little bit. Usually they bleed down eventually due to the check valve/nipple in the fuel pump.

But if you lift the rail up off the lower and pressurize it, you may shoot a few injectors out of the rail at 39psi.

However if you pull the upper off, the noise should be pretty loud in the port of the injector is just spraying off. If you have a gauge on the rail you can see if the sound matches the pressure falling off. You should also be able to smell it.

here’s a pic of the engine bay just for attention, or if there’s something obvious I’m missing!
So we checked the fuel pump at the rail, stays at a pretty solid 30 PSI and goes up to 40 when pump is first engaged. Stays at a good pressure while (shortly) running too. At least that confirms the pump is good, and that it isn’t leaking down.
Trying to run through the surging idle checklist and eliminate things. Not sure if i should be there or at the cranks but no start, because it does crank no start sometimes

 

[Vulpes5.0]

here’s a pic of the engine bay just for attention, or if there’s something obvious I’m missing!
So we checked the fuel pump at the rail, stays at a pretty solid 30 PSI and goes up to 40 when pump is first engaged. Stays at a good pressure while (shortly) running too. At least that confirms the pump is good, and that it isn’t leaking down.
Trying to run through the surging idle checklist and eliminate things. Not sure if i should be there or at the cranks but no start, because it does crank no start sometimes

Had to fix the throttle cable, couldn’t actually press the pedal down 100% since the cable was stretched. Threw a homemade plastic “bushing” on there i made from a door lock knob cut into a C-shape with a dremel, along with some zip ties, so now I can do the flood clear. That under dash throttle cable area is a pain….

Flood clear seemed to help on the times that it would crank no start. Popped cold air intake off and it smells of fuel at the butterfly, AND smells like fuel at the oil cap as well. I’m pretty convinced that this is something to do with injectors, but didn’t get a chance to pull intake off tonight. Check engine light did not come on when we got the car to idle for a period of about a minute. Do these cars blink only when you dump codes or blink every time you get a fault?

 

[Mustang5L5]

There can be codes stored without blinking the CEL. It’s really quite primitive compared to modern obd2. You really just need to dump the codes.

 

[AeroCoupe]

Pressure on the fuel rail should be 39 psig when running, with the vacuum line disconnected from the fuel pressure regulator. Be sure to cap the vacuum line when you check this. Also, if the vacuum line has gas in it the fuel pressure regulator is bad and should be changed.

If there is no gas in the vacuum line and the pressure is low then I’d suspect the filter needs to be changed and/or there is a pump issue.

 

[General karthief]

Flooding, stalling
I think there are more than one issue effecting this ride. Needs fresh plugs, plug wire, cap and rotor inspection, also I'd be looking at that ignition switch under the dash.
Just my 2 cents worth.

 

[Vulpes5.0]

Pressure on the fuel rail should be 39 psig when running, with the vacuum line disconnected from the fuel pressure regulator. Be sure to cap the vacuum line when you check this. Also, if the vacuum line has gas in it the fuel pressure regulator is bad and should be changed.

If there is no gas in the vacuum line and the pressure is low then I’d suspect the filter needs to be changed and/or there is a pump issue.

Plugs are fresh, wires are new, cap and rotor is fresh, fuel pump and filter have just been changed. I think the distributor is old, but TFI is new as well. Could this be a TFI issue? I did look for fuel at the pressure regulator but it was dry, didn’t try checking the pressure without the regulator on though. So if I check pressure with it disconnected and it holds about 40 PSI it’s fine?
It very well could be an ignition switch issue. As usual of these cars, I’ve seen a bit of questionable wiring so far but haven’t checked the column. But at least this guy used quality crimps instead of wire nuts!

 

[Noobz347]

Stays at a good pressure while (shortly) running too. At least that confirms the pump is good, and that it isn’t leaking down.

Not necessarily. There are two things to consider with fuel-flow: Pressure and Volume. You can achieve the pressure and still not maintain adequate volume and it can lead to fuel starvation.

As with many of these cars, I’ve seen a bit of questionable wiring but haven’t checked the column. But at least this guy used quality crimps instead of wire nuts!

How are your solder and shrink tube skills?

 

[Vulpes5.0]

Not necessarily. There are two things to consider with fuel-flow: Pressure and Volume. You can achieve the pressure and still not maintain adequate volume and it can lead to fuel starvation.



How are your solder and shrink tube skills?

You’re right, Is there any way to adequately check it?

I don’t have a soldering iron where I’m at (away for college) but I can definitely shrink tube lol.
Any connection I saw that looked suspicious I made sure to tug firmly on. It’s not the most kosher but almost every connector has shrink tube integrated into the connector, and looks like it was done with a bit of care
Edit- Is the fuel smell at intake and oil filler cap normal? I know these cars are port injection instead of direct but it still seems off.

 

[Noobz347]

Is the fuel smell at intake and oil filler cap normal?

Normal? No. Things that come to mind are excessive blow-by and/or bad or not operational PCV system.

 

[Noobz347]

Also... These things work pretty good:

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Not an emergency, I understand. It's good that you're checking them as you go.

You’re right, Is there any way to adequately check it?

It wouldn't hurt to disconnect the fuel line at the rail and run a hose down to a gas can. You would at least be able to get a visual on the stream of gas being pumped. It is significant, even with a stock 85 L/hr pump.

 

[Vulpes5.0]

Normal? No. Things that come to mind are excessive blow-by and/or bad or not operational PCV system.

Hmm… that’s odd. I had to RTV the valve behind the intake and got it to seal good (old RTV was oil soaked and i could pull it out easily)
And the tube going from throttle body to oil filler is on there. The valve seemed okay but hard to say. Could be blow by, my other car’s oil has a similar smell but it also blackens the oil within a 1000 miles because my engine is an old dog.
I’ll see if i can try the fuel line here soon. I already probed the schrader valve just to check and it seemed to spray pretty healthy but I’ll double check. Like I said, most of this stuff is new so it’s throwing me for a loop.

 

[Vulpes5.0]

The previous owner is really kind and answers every question we have even after we bought it off of him. Seemed adamant that he wanted to hear about it running and doing some burnouts again.
He says that it sounds to him like injectors, or potentially the distributor being bad, those seem to me (and mentioned by him) to be some of the few things that have yet to be replaced on this car. I checked for spark and it's shooting out huge ones for sure, so I don't know if dizzy would really be the problem there.

 

[Noobz347]

Call around to some shops in your area and find an injector cleaning and flow testing service.

You can clean and rebuild them yourself if you have a mi nd to but you would be hard pressed to flow test them yourself.

The "suddenly dies" thing can def be a bad distributor/ bad PiP inside the distributor. Worse, it can be intermittent.