Are my plug wires bad and if so would that cause stalling after the car is hot? - Page 6 - Alfa Romeo Bulletin Board & Forums
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post #76 of 302 (permalink) Old 03-27-2017, 08:46 AM
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Frankly, I think you already did the bench test. With any conventional pressure regulator of this type, you have to have connected and operational fluid flow, fluid pressure, a demand on the outlet, and a pilot signal (vacuum) to the diaphragm. Your results are displayed by the gauge behavior.

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post #77 of 302 (permalink) Old 03-27-2017, 09:09 AM Thread Starter
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Would I necessarily be seeing gas in the vacuum line if it's faulty? I can always hook up a clear hose to test that.
Short of that giving me any definitive results and/or the new filter improving the situation, I should probably see about a new regulator, huh?

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post #78 of 302 (permalink) Old 03-27-2017, 09:59 AM
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If the diaphragm is leaking, yes you'd likely see gas into the vacuum line, although if it would be enough to be visible is anybody's guess. I'll attach a cutaway of a typical regulator. Stupid question-- is the vacuum tube connected to where it should be on the intake plenum?
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post #79 of 302 (permalink) Old 03-27-2017, 10:08 AM Thread Starter
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Uh, I think so... I mean, I just swapped the hoses. Same ports.
Where is it supposed to go, just in case something's ALWAYS been awry (remember I've had this issue for ages)? Digging through my service manuals now...

EDIT: Yeah, according to the manual it's correct. The port closest to the front on the passenger side of the plenum.
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post #80 of 302 (permalink) Old 03-27-2017, 09:53 PM
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So I finally got a decent fuel pressure gauge installed with no leaks and was able to monitor until it stalled and died. This is after I went ahead and pulled out the tank, which I've been meaning to do for years anyway. No rust, varnish or sludge, although the return banjo had some gunk lodged in the outlet. Checked all of the fittings, hoses, relief valve, etc. Purged the hard lines with carb cleaner and a few blasts of dry shop air. Tested current to the fuel pump, which was right at 12.8 volts continuously. All good.

After a couple of hard starts to get the gas flowing back into the engine, the car idled fine for a while with fuel pressure right at ~35psi. Then it started to drop rather quickly, maybe over about 30 seconds, to around 20 psi, whereupon it stalled and died. So I started it again, and the pressure would only increase if I pulled the throttle, before dropping again. I tried pinching off the return hose from the regulator with a pair of vice grips, with no noticeable change. Stall.

The fuel pump is new, after the original one seized after a prolonged stay in the garage. But what else could it be? I swapped three different combo-relays with no difference. Spark is strong. Battery is new. Current to the pump is full strength and consistent. Fuel filter is new but I'm going to swap one from the parts shelf, just to see what happens. Maybe it's waterlogged.
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I could be wrong, but I think this is classic pressure regulator malfunction, either from a leaking diaphragm, broken spring, or some other internal problem. Because if you give it throttle like you did, it will demand more fuel, which will drop the pressure on the regulator outlet momentarily. It should catch up quickly though, if it's ok. Pinching off the return hose may not have any effect in this case... depends on how the regulator is failing.

So what's the story on the pressure regulator? Is there reason to suspect it in your opinion? You could have a bad pump... we've seen defective new parts before, but it's not my primary suspect at this point.
Good job on getting a proper fuel pressure gauge hooked up and checking inside the fuel tank. I take it that the in-tank strainer was clear, then? A gradually clogging strainer or filter could cause your symptoms, so a quick filter replacement is a good idea to eliminate that variable . . . .

However, based on your description, your symptoms smack of a failing fuel pump, not a bad fuel pressure regulator. Did you pinch off the fuel return line as the engine was stumbling, or during normal running with good fuel pressure? With a healthy fuel pump, completely pinching off the return line should cause the fuel pressure to go sky-high (like 80+ PSI; this is known as "dead-heading" the fuel pump and is a good stress test).

The fuel pressure regulator is designed to vary the fuel pressure in relation to intake manifold vacuum to maintain uniform fuel delivery volume at the injector tips (which are of course inside the intake manifold) regardless of throttle position. Increased vacuum at the fuel pressure regulator pulls the diaphragm against spring pressure, which opens up the internal chamber and allows more fuel to return to the tank, thus decreasing fuel pressure in the rail.

With the engine idling normally and with good fuel pressure, snap the throttle open several times---snapping the throttle causes intake manifold vacuum to momentarily increase, which with a properly functioning fuel pressure regulator will result in a commensurate decrease in fuel pressure before returning to normal. Slowly opening the throttle to WOT will cause the fuel pressure to slowly increase (up to a point), as the open throttle plate will decrease intake manifold vacuum accordingly. Manipulate the throttle in different ways while watching the fuel pressure gauge---if it reacts as described, then your fuel pressure regulator is probably OK.

Also, you mention that "current" to the fuel pump is good at 12.8V. This is not an accurate statement as "current" refers to electrical flow, which is measured in amps, not volts ("voltage" is electrical pressure). When a fuel pump fails, it typically draws an increasing amount of current (due to increased internal resistance) while voltage to the pump (which is what it sounds like you are measuring) remains constant. You would really need an inductive amp clamp and a scope to accurately measure current to the pump, which is usually not available to the average DIYer . . . .

Repeat the fuel pump "dead head" test and re-check the fuel pressure vs throttle position and check back with us.

Chris

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post #81 of 302 (permalink) Old 03-28-2017, 06:46 AM Thread Starter
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Thanks for the lesson. I'm still learning this stuff, and there's maybe no better car to learn on than one that's always broken!

SO I can tell you that I dead-headed the line and the pressure continued to decrease until it stalled. Opening the throttle brought it up a bit, but it never reached 36psi even under WOT. However, the fuel pressure being reported is generally so low that I don't have much opportunity to do any extended tests. I'll go through this battery of tests again later this evening though, just to confirm.

I should mention the problem has been getting worse. A few weeks ago the car would run reliably for a while, with intermittent hard starts or stalls at idle. Lately I can barely keep it running for more than a few seconds.

As for the electrical test, I was really just ensuring there was power making it to the pump. I've read MANY instances of a bad ground or power connection being the culprit.

And at least I know my injectors aren't leaking - it's held 20psi for 2 days now, according to the gauge.
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post #82 of 302 (permalink) Old 03-28-2017, 09:24 PM
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Thanks for the lesson. I'm still learning this stuff, and there's maybe no better car to learn on than one that's always broken!

SO I can tell you that I dead-headed the line and the pressure continued to decrease until it stalled. Opening the throttle brought it up a bit, but it never reached 36psi even under WOT. However, the fuel pressure being reported is generally so low that I don't have much opportunity to do any extended tests. I'll go through this battery of tests again later this evening though, just to confirm.

I should mention the problem has been getting worse. A few weeks ago the car would run reliably for a while, with intermittent hard starts or stalls at idle. Lately I can barely keep it running for more than a few seconds.

As for the electrical test, I was really just ensuring there was power making it to the pump. I've read MANY instances of a bad ground or power connection being the culprit.

And at least I know my injectors aren't leaking - it's held 20psi for 2 days now, according to the gauge.
Haha, thank goodness for small victories---at least the system holds residual fuel pressure!

OK, so you are sure that the fuel pump is getting full battery voltage, even as the engine is stumbling and ready to stall? That will be a key factor in determining whether the issue is with the pump itself or it is an electrical issue. This could be tricky to determine just as the engine is dying, because the airflow meter flap will be moving back and forth as the engine stumbles, possibly to the point where the airflow contact switch within the AFM will open momentarily. If this occurs and the engine stalls and won't restart, simply open the airflow meter flap manually with the ignition switched on and check if the fuel pump is getting full voltage.

I assume that you have checked the inertia switch in the engine compartment? This is extremely easy to check, as you can bypass it by simply shorting the two wires together.

If the electrical supply is OK, try to perform the fuel pressure tests previously outlined, and hopefully you will find the culprit! This must be very frustrating----I do this for a living (on Porsches and BMWs, not Alfas) and I know what it is like to stare into a black hole and be out of ideas. Keep at it and hopefully you will be able to track down the issue and then drive and enjoy your GTV6!

Chris
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post #83 of 302 (permalink) Old 03-28-2017, 11:58 PM
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OK, so you are sure that the fuel pump is getting full battery voltage, even as the engine is stumbling and ready to stall?
Or during your testing you could just connect the fuel pump directly to a battery or any reasonable 12V source and not worry about the AFM switch, the inertia switch or any other parts of the car's wiring. Make sure you get the polarity right!
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post #84 of 302 (permalink) Old 03-29-2017, 03:41 AM
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Question Oops? Did we assume too much?

Forgive an old man who no longer has any car such as yours. But I have had two in the past, and several Alfetta models. I know your pain.

After reading this thread over I noticed comment that reminded me of once when I had an Alfetta die twenty miles from home and I had no cell phone with me to call my son. After a couple hours a fellow Alfisti stopped, and after I told him I had done everything. He said: "Have you checked the inertia switch?" I said I didn't even know what that was, so he had me reopen the hood, and then poked the button down and said "Try it now." It worked perfectly. So, here is the comment I saw:

"I ASSUME that you have checked the inertia switch in the engine compartment? This is extremely easy to check, as you can bypass it by simply shorting the two wires together."

I apologize, but you might merely have a defective inertia switch. It can partially short. Why not by pass it and try again? Sometimes the worst and most nagging problems have very simple solutions. You would be surprised how many Alfetta and GTV-6 cars run around with the inertia switch bypassed.
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post #85 of 302 (permalink) Old 03-29-2017, 07:39 AM Thread Starter
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I do know the pump is getting full voltage, consistently. Tested at the terminals with the car running and with the AFM flap jammed open, key to accessory.

What I've noticed is that from a cold start, fuel pressure might max around 28 psi, then drop to about 21 or 22 before the car stalls. But it'll hold there indefinitely. It's been three days and it's still at 21 psi (again, I'm extremely happy to know I have no injector or hose leaks). But when I restart after a stall, slightly warm, the pressure will actually jump up to 35-ish and it'll run fine for a bit before it begins to dwindle. Sometimes that dwindling happens within seconds, sometimes it takes MANY minutes. It's not consistent, although it does seem that more often lately it'll begin to die fairly quickly, whereas weeks ago it would take much longer or maybe not at all.

Opening the throttle slowly but consistently, revving from idle to about 3500 rpm, the pressure will hold where it was, but not necessarily rise. As soon as I release there's an immediate drop and stumble. Sometimes it'll recover a bit, but often it'll immediately begin to stall. It does not like throttle snaps AT ALL. Immediate choking.

The inertia switch is bypassed. I did rebuild it a few years ago, but realized the copper contacts need to be de-oxidized about every six months, the springs for the ball bearing re-tensioned, the connectors cleaned... it's just too finicky. The pink wires are now butt spliced.

No fuel present in the clear vacuum line. I'm really leaning toward the fuel pump. That new fuel pump. That highly suspect $50 eBay fuel pump...
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post #86 of 302 (permalink) Old 03-29-2017, 07:54 AM
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ok-- Remove the vacuum hose from the pressure regulator with the car running, make sure you have strong vacuum. Put a vacuum gauge on the plenum or past the throttle plate, you should read around 15-19" hg at normal idle.

We're running out of answers, but that also means you're zeroing in on the culprit!

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post #87 of 302 (permalink) Old 03-29-2017, 08:41 AM
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One thing to bear in mind is that fuel pressure should not be constant. The regulator maintains a constant ~36 psi pressure difference between the fuel rail and plenum. So if there's 5 psi plenum vacuum, the fuel pressure will be 5 psi lower than spec (i.e., 31 psi).

That's why you're seeing the fuel pressure drop when you snap the throttle closed: you get a spike in plenum vacuum and the fuel pressure goes down to match.

This wouldn't explain your fuel pressure steadily going down at idle, though. If I'm understanding your description that doesn't sound normal at all.

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post #88 of 302 (permalink) Old 03-29-2017, 08:56 AM Thread Starter
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I'll try to get a video tonight, if that'll help illustrate. And I don't have a vacuum tester so I'll either need to see if the parts store has one in their loaner stockpile or just hunt up my Harbor Freight super coupon...

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post #89 of 302 (permalink) Old 03-29-2017, 09:04 AM
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Oh yeah.. always have a vacuum gauge! That's a direct readout of your motor's health, along with compression psi.

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post #90 of 302 (permalink) Old 03-29-2017, 04:14 PM
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I feel for you - you can't seem to catch a break with this car!

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