Eating Humble Pie in my '78 on I64. Yum! Failing pump? Fuel tank siphon tube leak?

[FastWoman]

So we're headed out I64 to see family in Richmond for Easter, with an almost full tank of 93 octane. I'm feeling pretty confident in my '78, which has run like a top ever since I straightened it out early last September. (My inspection sticker says 9-11, BTW.)

Along about a half hour from our destination, as we're tooling along just as happy as can be, my engine starts sputtering and then dies within a 10 or 15 sec period. As I'm rolling, I try restarting a few times, to no avail. I coast to a stop along the shoulder, and I'm unable to restart. At this point I have about 7/8 of a tank of fuel. I had been checking gauges periodically, because I had noticed my voltage seemed a tad lower than usual at idle. (I was keeping a good eye on the alternator, which was still putting out 14V when the engine died.) I gave all the gauges a fast check as the engine was sputtering, but not quite dead:

Fuel, check

Coolant temp, normal

Oil pressure, normal

Voltage, normal

An additional note: I noticed my tach bouncing quite a bit as the engine was sputtering. It does that when the cylinders are running extremely lean, causing a bit more kickback at the end of the spark's "burn time." My tach has a retrofit Mopar board in it and is very sensitive to misfire this way. Indications were pretty clear this was a fuel starvation issue and not an ignition issue (or else my tach wouldn't be bouncing at all).

Here's the smoking gun: Some of you may know/remember I installed a fuel pump priming switch that lets me manually actuate my fuel pump (e.g. for clearing a vapor lock) or switch it off entirely (e.g. for clearing a flooded condition). So when I hit this switch, I could definitely hear my fuel pump run. However, instead of a soft, low, rubbery rumble, it was a very slightly higher pitched, slightly louder growl. My SO and I both noticed this, so I wasn't alone.

I tried priming the fuel rail with the switch and restarting, and the engine would crank, crank, crank, and maybe go "vroom," then immediately die. I was able to get a few "vrooms," and then couldn't get anything after that. Ordinarily my engine starts immediately with about 1 revolution.

I thought there was an extremely small likelihood my engine might have flooded somehow. So I switched off my fuel pump, cranked for maybe 10 sec to clear the cylinders, re-primed my fuel rail, and gave it another go. Nothing.

At this point I'm thinking I'm somehow pumping air (hence the fuel pump sound). I'm reminded of an earlier time when I owned a '75 Z in the mid 80's. The siphon tube in the gas tank rusted through, and I ran out of gas with a half tank. The symptoms were exactly the same.

There was nothing to do except call AAA for a flat-bed truck. I wasn't about to start working on my car on the shoulder of an interstate highway. A couple hours later, my car was sitting in my driveway back home. I stuck the key in the ignition, fired up my fuel pump (which sounded normal this time), and the engine went "crank, crank, crank, sputter, sputter, vroom" and was running like a top. :tapemouth I had been ready to spend the rest of my free time today diagnosing the problem, but there's no sense in that if I can't replicate the problem.

So here's my thought: Because of the sound I was getting from the fuel pump, I'm betting either the pump is going out, or I was sucking up air in the lines. I saw/smelled no signs of leaking fuel either alongside the insterstate or back at home, so I'm pretty sure the problem, whatever it is, is contained internally.

If the problem was my fuel pump, perhaps it corrected itself once the fuel pump cooled down? Can these pumps fail and then start working again if the motor doesn't fail?

Working with the theory that my pump was drawing up air because of a rusty siphon tube: I saw inside my tank when I removed it, cleaned it out, and reinstalled. (It was surprisingly rust/crud-free, BTW!) The fuel siphon went to a structure in the middle of the tank that looked like a tall coffee can, where I imagine the intake screen was located. I couldn't see any thing inside the can and don't know if the siphon tube goes anywhere high in the tank, where it would have the opportunity to rust and admit air. Does it?

My engine failed when I was cruising at about 70 on flat ground. When I pulled off on the shoulder, the car was sitting on a slight slope towards the righthand side. Perhaps that made an air siphoning problem even worse.

Then my car was loaded onto and unloaded from a flat-bed tow truck, so that its nose was pointed maybe 25 or 30 deg in the air for a few minutes. Perhaps that allowed fuel and air to move in such a way as to get things working again?

Anyway, I'm totally frustrated and confused. Does anyone have a clue what might have happened or what I might check? Can anyone describe how the pump (and not motor) portion of a fuel pump might fail and how it would behave? Can anyone describe the internal plumbing of a 1978 tank? Help!

I'll add what the problem is probably not ("probably" not, because I haven't been given the opportunity to properly diagnose the system): It's not rust in the tank, because that tank is BEAUTIFUL inside. Hard fuel lines were blown out. Rubber fuel lines were replaced. Vent hoses were replaced. New fuel filter. Squeaky clean fuel rail with new injectors. All electrical connectors on engine new. New coolant temp sensor. My air regulator probably needs replacement, but there's no way that killed the engine at highway speeds. Refurbed/cleaned up AFM. EVERYTHING on that engine carefully gone through, checked, cleaned up, brought to specs or replaced. All new ignition components (HEI retrofit) with new wiring. Everything's been working great since September on this daily driver.

Thanks for any help/ideas, y'all!

Edited April 25, 2011 by FastWoman

[Zed Head]

Blocked tank vent? Engine used enough gas to pull a vacuum and the pump couldn't get fuel? Did you take the gas cap off while working on the highway?

I can't determine for sure how that would apply in the closed loop of the "inlet line/pump/regulator/return line/tank" but maybe since the vacuum is pulling against the back of the regulator, the pressure imbalance shuts flow down.

[FastWoman]

Hmmmmmm...... Hadn't thought of that, Zed! And no, I didn't remove the gas cap alongside the highway. I did notice when I previously filled up that there was a pretty strong "whoosh" when I opened the gas cap. I didn't notice in which direction. That's definitely on my "to check" list now! Thanks!

The thing is, though, do you think a vacuum in the tank could kill the engine that suddenly? It was literally within the span of 10-15 sec.

EDIT: Oh, and I get what you're saying about the return vacuum pulling against the back of the regulator. Hmmmmm.... To the FSM to think about this one!

Edited April 25, 2011 by FastWoman

[olzed]

Wow thats a darn Sarah. Don't know about these new fangled fuel injected Zeds:) but on a carbed engine, the clattering fuel pump you describe would point to fuel starvation,as you would know.

Zed might have 'hit the nail on the head.'

Brian.

[FastWoman]

Update: NOT a blocked vent. I sucked air through the gas cap, per the FSM. It vented freely.

I ran a few short distances today in the Z. It started and ran each time. I primed the fuel pump each time to listen to the tone of the pump. Before one of my starts, the pump made the slightly higher pitched, slightly louder, more growly sound for a couple of seconds, and then it settled into a lower pitch, softer, more rubbery rumble (its normal tone). This seemed to be the difference between no-load and load. So when I was stranded by the side of the road, I would presume my pump sound was telling me no-load -- no pressure, no fuel supply, but running pump motor.

I suppose another possibility is a failed fuel pressure regulator that got stuck open and dumped all the fuel pressure. However, the engine sputtering yesterday would seem more symptomatic of air bubbles than of fuel pressure going south.

Any other thoughts, anyone?

Thanks!

[ZCurves]

Sarah, How old is your fuel pump? I have noticed that my pump will lower in tone as it builds pressure (when first starting), but I am not convinced that it is not working very well either. It is an NOS pump - but that doesn't mean anything. Did you notice a distinct pitch or tone when the pump was no worky?? Low or High, Oscillating or Surging?? The pressure regulator is ~$40, so it might be time to change then check the fuel pressure? I hope I am not rambling, just throwing ideas out.

[FastWoman]

Didn't see your post, Brian! Yes, I know the clattery carb pump sound from our boat! The sound I'm getting isn't a clatter, so much as a growl -- a bit like it's not doing anything.

Andrew, that confirms what I thought, that the pump tone lowers (and mellows??) as pressure builds.

I have no idea how old the pump is. It came with the car. I think I can say it's older than 1994 (when the PO purchased the car, and where my more detailed service history begins). I see a 1982 fuel filter change in the warranty book, but it appears to be part of a 120k mile scheduled service. I'm assuming the pump is original to the car.

But yes, in answer to your question, when the pump seems not to be pumping, it makes a slightly higher pitched, slightly louder growl, rather than the usual soft, rubbery, lower-pitched rumble.

I have an idea for a way to recreate the problem in my driveway -- maybe. It will take a trip to the hardware store to purchase my test apparatus and will probably take a lot of patience to do the test. I'll hook up a couple of "T" fittings off of the fuel rail line. One will go to my pressure gauge. The second will go to a small valve and then to a piece of clear tubing that I can put in the gas tank filler neck or into a gas can. I'll put my battery on a charger and jumper the fuel pump relay to run the fuel pump continuously for a very long time. I'll adjust the valve to simulate different rates of fuel consumption and will dump the "consumed" fuel right back in the tank. Optionally, I can drain down the fuel level in the tank by dumping "consumed" fuel into some gas cans. I figure I can just keep running the pump and circulating fuel until something breaks. Then I can figure out what's broken.

Sound like a plan?

[ZCurves]

I believe that you have become a mad scientist . I have read many of your problem solving techniques (my favorite being the Yogurt cup) and I am convinced that you are a mad scientist or a distant relation to Rube Goldberg. What is fun is that they all work! Great Ingenuity!! Please post pics.

[madkaw]

Sarah,

I had a similiar issue happen with my daughter's 280ZXT. It was really random, but the car would studder, then die pretty quickly. I went thru all the same steps as you and had a squeaky clean gas tank. I had also installed, what looked like a new fuel sending unit in the tank from another Z. I replaced my stock pump with a performance pump, but still acted up. Ome thing that did change with the other pump was the noise. I could hear the pump cavitating, or what i thought was a cavitating noise-so I broke down and bought a fuel pressure guage. WOW-I was showing 100psi on the return line. So I dived back in to find the blockage. It turned out that my brand new looking fuel sending unit had something clogged on the return side.

I'd said something is causing your pump to cavitate. I believe there is a screen on the end of those pumps too.

[FastWoman]

Scientist, yes (or used to be). Mad... well... (mhuahahahah...) well, depends on who you ask. But never evil!

I'm afraid I overcomplicated my apparatus. All I really need is a clear return line that I can stick in the filler neck or in a gas can.

Against my better judgment, I started to drive my Z a couple of blocks from one house to another. It started to stumble, so I did a U-turn and headed back to the driveway. My car might just cooperate for me.

Steve, I assume cavitation would only occur if there is some restriction in flow from the tank to the pump, right? Is it possible that ethanol gas might have clogged my pickup screen by corroding it (i.e. with the corrosion coming from the screen itself)? I suppose if this is the case I should see reduced gasoline flow out the return line. What would the normal flow rate be for these pumps at full pressure?

Hey, thanks for scratching heads with me, guys!

[cozye]

What's your fuel pressure readings when this is happening? This should tell you everything !

[madkaw]

My thoughts too! A fuel pressure guage will tell all.

Another thing that suprised me with my ZXT was the amount of heat around the diff on these cars after being on the highway. I found the diff to be HOT to the touch-like you can't hold your hand on it. Now consider a rubber fuel line close to that heat, or even touching the diff like mine was, it gets really soft and could collapse.