93 Mustang EFI acceleration stumble

[stretch]

Specs first. 93 Mustang A9L, Ron Francis harness, 98 Explorer 5.0, 4r with UsShift. Been running fantastic for 8-9 months, put some miles on it. Yesterday sitting at a red light, the engine was idling fine, then it stumbled and starting running rough. I could accelerate from the light, but it would stumble at higher RPMs. Headed home ran the codes both KOEO and KOER and nothing out of the ordinary.
Back up a few days earlier, and I noticed that I'm getting an erratic charging volts from the alt. 13.1 to 15.1 at a stop light. This happened once, but now once again at stop with blinkers on, the volts jump up and down .5 volts with each blink. It had never done this before.
So are these related? First place I want to go is the TFI. Its original 93 mustang. If memory serves it is the distributor and tfi are the only used components on the engine. If they are related, I don't see how. Thoughts?

 

[MD]

The TFI and the PIP sensor in the distributor can fail, and sometimes they fail with heat and work again once cooled down, but they are more of the on/off type failures, not intermittent.

Given that the A9L is typically rich at WOT or higher RPM under load, it takes less spark to burn a rich mixture than the leaner or stoich mixture at idle or especially throttle tip in, so spark problems only at high rpm would be far less likely than a fuel problem.

Erratic charging voltage is either a supply side problem (the alternator cant supply enough power), or a demand side problem (something is puling more power at idle than normal). If the alternator wants to produce 14V, but is dropping to 13.5 (for example) when the blinker is on, and it is a new problem, then most likely it is an electrical issue that is unrelated to the spark.
The fuel pump requires a lot of electrical energy especially at high rpm, so it is more likely that the fuel is affected by electrical issues, or even that the fuel pump is drawing a high load. So I would start with checking the current draw of the fuel pump and the current output of the alternator before chasing spark.

 

[73azbronco]

Need to fix the electric voltage problem. But, I'd put a pressure gauge on the fuel rail as step one to EFI diagnosis is always fuel pressure, then fuel flow.

 

[MD]

Just a side note, the Explorer GT40P heads are very efficient for the flame and require much less spark advance at cruise than the 93 Mustang A9L. So with stock A9L, it could be possible to have the base timing on the distributor off, but still run ok at part throttle, but have issues at high rpm. That would not explain the intermittent electrical voltage however.

 

[Broncobowsher]

Everyone always says grounds. This one really sounds like that could be it. You didn't say what charging system you are running? Stable grounds from the engine to the battery and the voltage regulator and ECM. If the ground planes start shifting around you are trying to play ball on a shifting field. I chased a bad ground for a long time that caused a rich condition that was intermittent, then found it was when the headlights were on. Eventually figured there was a weak ground to the body that the ECM was on and the O2 was grounded to the exhaust. Lights on and I got a voltage differential that made an offset voltage on the O2. Kept reading lean and was adding fuel as long as the headlights are on.

Also as mentioned, fuel pressure.

 

[stretch]

I do have a pressure gauge on the fuel rail. 30 at idle, 40ish at cruise. Checked the grounds, these are all new, engine to frame, frame to body, front and back and body to engine. Seems fine.

So during start and warm up, idles fantastic. Once it goes closed loop, falls flat on its face. Idle starts to hunt and runs rough.

 

[Broncobowsher]

Maybe time to rebuild the ECM? Capacitors age out and cause issues.

 

[stretch]

Yep. Starting to wonder. I believe I have a reman in the garage. Unfortunately I can’t remember if it was an auto or manual computer.

 

[stretch]

Two computers, same problem.

 

[lars]

Sort the voltage problem first. Verify that it's real, not an artifact of a mis-reading voltmeter. Etc.

If it's still doing it, try pulling the SPOUT connector, thus fixing the timing. if it can't wander it can't affect idle. Likewise, try pulling the idle air control connector. Both tests when warmed up and closed loop. A dirty or defective MAF could cause problems as well though in that case I would expect a code.

I've had a couple of idle air control valves fail, codes weren't set either time. Symptoms included stumbling idle.

 

[tasker]

mis and stumble not due to a dirty IAC valve is it? used to gave to clean those all the time, really bad with the gas they offer now

 

[stretch]

Closed loop, disconnected the Iac at idle. The idle still surges. I also unplugged the spout, separately, and it still surges at idle.

I cleaned the Maf as well, no change.

 

[blade]

I had a failing alternator on an 02 focus that caused weird idle problems. I would check output and it would be fine. Replaced the battery and that fixed it for a little while until the alternator totally failed.

on ground issues, my uncle had a 460 powered RV that had major fueling issues, it would run rough and on occasion fill the cylinders with fuel to the point of hydro lock. We were working on it in the dark one of the times it acted up and someone noticed a spark when the engine was cranked over. Turned out that the bolt for the ground to the block was bottomed out and wouldn't completely clamp the ground. Fixed that and it was never a problem again.

 

[DirtDonk]

I do have a pressure gauge on the fuel rail. 30 at idle, 40ish at cruise.

Sounds low. Isn’t it supposed to be between 42 and 46 at all times?
I could be wrong, but if I’m right, that 30 psi at idle could be where some of your issue was coming from.

 

[stretch]

It’s been 30-32 constantly. I take the vacuum away and it goes to 40 and holds. Running the explorer fuel rail with return and an intank pump.

 

[EFI Guy]

Figure out the charging issue first. It sounds like the alternator could have a bad diode. When that happens it puts AC voltage into the system and can cause the PCM to behave erratically. The fact that you can pull codes means the PCM is likely fine, but it's always worth checking the capacitors for leakage. Replacing them before failure greatly increases the odds of the PCM surviving.

Fuel pressure should be 40 with vacuum line removed. Look for traces of fuel in the vacuum line when you remove it to be sure the diaphragm hasn't ruptured.
With stumbling you should also check the basics, plugs, wires, cap, rotor, vacuum leaks, grounds, and see if the MAF and IAC are clean.

 

[DirtDonk]

Of course, memory is a terrible thing to waste…
To paraphrase an old college commercial.

But maybe at idle when there’s no load, 30 is OK. But it seems more like 38 to 40 is appropriate, and then when you push on the gas and the vacuum goes down, the regulator lets it go up to 45 or so.
That’s just what I remember so could be off.

 

[DirtDonk]

See? That’s why we have experts on call here at all times.

 

[Broncobowsher]

Figure out the charging issue first. It sounds like the alternator could have a bad diode. When that happens it puts AC voltage into the system and can cause the PCM to behave erratically. The fact that you can pull codes means the PCM is likely fine, but it's always worth checking the capacitors for leakage. Replacing them before failure greatly increases the odds of the PCM surviving.

Fuel pressure should be 40 with vacuum line removed. Look for traces of fuel in the vacuum line when you remove it to be sure the diaphragm hasn't ruptured.
With stumbling you should also check the basics, plugs, wires, cap, rotor, vacuum leaks, grounds, and see if the MAF and IAC are clean.

To that, disabe the alternator and check. Just pull the belt will 100% do it.

 

[stretch]

Alternator disconnected, no change. Once warmed up it starts to stumble.