I'm having a problem with fuel starvation on my '78 280-Z. I had been running the car on 5 year old gas and it was rather hard starting so I drained the tank and replaced the gas with fresh stuff and a shot of Texron. When test driving after changing the gas I found I couldn't accelerate in first gear over around 2500 RPM.

I changed out the fuel filter this morning and found it to be full of rusty fuel. I test drove the car after changing the filter and now can't run higher than an idle. It will pick up rpm after idling for a while but craps out as soon as I try to accelerate in first gear.

My question is this...is there a gas filter of some kind on the end of the pickup tube in the gas tank in this car? I am wondering if it is clogged with the same kind of junk that was in the filter.

I have had the car for 25 years and have only put around 1700 miles on it [maintenance driving].

Any ideas or comments would be appreciated.

Thanks, Guy

Rusty fuel tanks are a Z car phenomenon which few of us escape. A whole series of tank ventilation tubes and a vapor "kidney tank" in the wall panel behind the passenger, *almost* control it in most cars.

The main cause of rust in the tank is leaving the car sitting with less than a full tank of fuel. Condensation forms all along the inside of the tank above the fuel line (as temperatures change) and cause surface rust. That rust causes pinhole leaks in the upper chambers of the tank and drops rust flakes into the fuel. Suspended rust flakes get sucked up into the fuel pickup and clog fuel filters and lines.

Yes, every Z has a form of fuel filter inside the tank, in the form of the fuel pickup. The 280s had combination fuel filters/electric fuel pumps atop the tank, just behind the passenger. Either or both could be clogged.

But try this first: some of our 280z and ZX owners have reported clogging of some of the fuel tank air vents atop the tank, which prevent air from entering the tank as fuel is used. That means as the fuel level drops, a slight vacuum occurs atop the remaining fuel as the electric fuel pump tries to suck fuel out of the tank against this vacuum. As the fuel level drops lower and the vacuum above the fuel line increases, less fuel gets pumped out and the engine can soon starve for fuel until it eventually is only capable of idle. Some owners have actually seen their tanks collapse under the vacuum, making the tank appear as if it was driven over a large rock which caved in the bottom of the tank.

Reported clogs have been found to be insect nests (mud daubers) in the vapor vent tubes, which prevent vent air from entering the tank as the fuel level drops.

Because you drive your car so little (70 miles a year for a quarter-century), there is a fair chance this vacuum issue may have developed in your tank, and you seldom have to open the fuel filler to add fuel. Open the gas cap and listen for a tell-tale "whoosh". That would be a sure sign of the vacuum problem. Some owners even reported the vacuum was so strong, it was a struggle to get the gas cap off.

If your RPM return after venting the tank by opening the gas cap, that's the acid test for clogged vent tubes. Once vented by the open gas cap, the engine will run again until the vacuum rebuilds.

Your tank might require draining and dropping, acid etching and sealing the inside, and removing the clog if there is one. Replacement of all the vent tubes is an excellent preventive maintenance job since the tank is off, anyway.

With only 17,000 miles on it, your car should not smoke at all. If you get any black smoke out the exhaust pipe, you should expect a clog somewhere in your air intake. Make sure there are no mouse nests in the induction track, and that your summer/winter air valve on the air cleaner box is fully open.

Frank

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1970 240Z

Hi Frank
Thanks for the info. We dropped the tank yesterday and found both the outlet tube [the one that goes to the pump] and return tube clogged. I tried to blow through them and couldn't. All other openings were clear. I'm going to try reaming them with guitar strings today. I'm also trying to rig up a light that can be inserted into the tank so I can make a visual inspection through the sender hole. I have already replaced the engine compartment gas filter. I found that to be totally clogged [I couldn't blow through it].

If I am unsuccessful in reaming out the above mentioned tubes I am considering replacing them. Do you know if anyone has ever done this?

The factory manual refers to a fuel line screen in the tank but makes no mention of it in the fuel section. So far as I can make out the only filter is the one in the engine compartment. It is quite possible that the previous owner of my car had the tank replaced. I know that they had done extensive work because I found body repairs done with lots of bondo that had been laid over rusted areas. I dug all of that stuff out and replaced it with metal. The tank I took out yesterday looks almost pristine on the exterior.

Since the tank is out I am looking into sealing it. Have you had any experience with the products that are available?

I don't understand your last comment with regard to the mileage and smoking.

I wrote up a method sheet on how to get the tank out of the car but need to proof read it. I'll send it off in a day or so.

Best, Guy

Guy ~

["If I am unsuccessful in reaming out the above mentioned tubes I am considering replacing them. Do you know if anyone has ever done this?"]

Yes, probably everyone who has completely restored a Z has had to do this. MSA (and Previously Black Dragon and Victoria British) all sold pre-shaped braided replacement tube kits. Know your car's Month/Year 'birthdate' [ on the driver's door build plate] when ordering the replacement kit because the tank vent hoses changed some over the years. If you fail to locate a kit, contact another known 280Z restorer (maybe Vinny Bedini 860-355-1829) to see if he has a set or knows a source. On the early cars those vent hoses were different diameters, sometimes only slightly, which made the correct replacement a bit of a challenge. Don't stick the wrong hose on the wrong vent.

But I think some really hot water poured into the tube might dissolve whatever insect nests might be blocking it. I keep a dirty old turkey baster in the garage for such jobs; boil hot water and baste it into the clogged tube (which is held in a vice) and repeat until the nest dissolves.

As long as you have your tank out of the car and empty, test it for pinhole leaks above the fuel line. In total dark, insert a strong flashlight into the filler neck. Check for any tiny "light leaks" around the top or sides of the tank. Mark them with a marker or even a crayon so you can find them in the light, and repair them.

Several companies make good tank sealers; POR-15, Gold-Standard, Red Kote and my favorite Caswell are known to me. If you know you have rust issues inside, you will want to acid-etch the interior before sealing it. Those same companies sell all that's needed to do that.

Sorry for not being clear about the black smoke. I mentioned the black exhaust just in case your rpm problem was not in fact a fuel starvation problem, but an air starvation problem (which would have almost of the same symptoms and results). You'd be amaZed at how many Z owners drive around in the summer with their air cleaner's winter air flap closed (set for winter driving), and I've seen cars with mouse nests in the intake ducting after sitting over winter. Pulling any spark plug will tell you if you have an air starvation problem; black flaky carbon soot on the plug would mean not enough air is getting to the engine but fuel is; brilliant white "baked" spark plug electrodes and center insulator may indicate too lean mixture (plenty of air but not enough fuel).

Did you say your 280 did NOT have an electric fuel pump at the tank?

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1970 240Z

Hi Frank
The bass guitar strings worked quite well. I started with a single string, then two and then four which I twisted together. I rotated the twisted set while pushing and pulling. I can now blow through both tubes.

I don't believe I have any pin hole leaks because the car is parked in our garage which has become the main entry to our house with a lot of foot traffic. We would smell any gas leakage immediately. I am keeping the tank which has been filled once with water and then emptied to drive as much gas fumes out as possible in the garage. I can smell residual fumes now when I walk through so I think a pin hole leak would have been readily apparent. Just to be on the safe side I will check with a light tonight. I mounted a 12 volt light bulb on a two foot dowel and powered it with a 12 V. DC transformer I had laying around [one of those black cube energy vampires]. I poke it through the filler hole in the side of the tank and can light up the inside.

Happily I have no blockages due to insect nests probably due to the fact that the car has been stored in a tight garage. All vent holes easily pass air. I haven't blown through the vent tubes yet but will do so just in case.

The way my car is set up is there is a gas pick up tube at the lower right side of the tank with a hose attached which goes to the electric fuel pump which is mounted forward of the rear axle on the passenger side underside of the car. From there it makes a home run forward to the engine compartment fuel filter. I looked into the tank with my light and couldn't see any filter in there although the factory put a small baffle plate over the fuel pick up and what is behind it is a mystery. I have to presume that the only filter is in the engine compartment.

The fuel gauge sender is mounted on top of my tank. It is through this hole that I peek at the inside. I attempted to include a photo but I don't think it worked.

I am going to try to clean up the tank interior by introducing a bunch of nuts with water and shaking it around. In You Tube a lot of people do that. That will give me a better idea of what I have to work with.

Frank, Would you take a look at the method sheet I created on tank removal to see if it looks understandable prior to my sending it to the Forum? I could PM it to you.

Guy

Glad your clever trick resolved your problem! If it wasn't insect nests plugging your hoses, what was it? What came out?

Here's an excellent example of what I was describing above:

http://www.zcar.com/forum/10-70-83-tech ... -tank.html

This writer is our esteemed member and Club officer Uncle Phil, and you can see the damage the vacuum did to his tank. His car is a ZXTurbo and so the tank is different than yours, but the principle is the same issue. His vent tubes were blocked, and the fuel pump kept pulling fuel out of a sealed tank until the vacuum above the fuel was as strong as the vacuum of the pump, so fuel stopped running in sufficient quantity to keep his engine running above an idle.

Pinholes above the fuel line aren't necessarily noticeable until you take a hard corner and slosh the fuel up to reach them, or when you fill the tank to capacity. Interior rust causes these tiny little holes and if your tank is rusty inside, there is an excellent chance you have a few pinholes you may not be aware of. Many of us have. That's why, as long as you have the tank out anyway, you should take advantage of the accessibility and do the light test. A usual place for these holes is around the juncture of the two halves of the tank; around the 'waist band', if you will, so be sure to look all around the sides too.
A single drop of silver solder on each pinhole should stop the leaks, but if you are going to seal the inside that will stop them up as well.

Ironically, the good side of pinhole leaks is they allow air into the tank even when the vent tubes are blocked! Not quite the way we want to do it, but it helps, anyway.

Yes, please do send me the rough of your plan; I'd like to read it.

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1970 240Z

Hi Frank
My problem was with the metal fuel pickup and return tubes that the hoses attach to on the side of the tank. There was no problem with the vent tubes. When I ran the guitar wire in and pulled it out it was coated with rust which must have pooled around the pick up inside of the tank. I had no problem with fuel starvation until I tried to siphon the old fuel out of the tank [at least five years old].
That old fuel was causing hard starting. Once warmed up the engine ran fine.

For some reason I couldn't pick up fuel with the siphon hose but with my shoving it around in the tank I must have stirred up a lot of rust. After giving up on siphoning I looked under the car and discovered the drain bolt. If I hadn't been so lazy and bent over in the first place I would have located it earlier.

After adding fresh gas and running the car my problem started with lack of gas flow [the car did start easily though].

Now that the tank is out I will add a bunch of steel nuts and water and shake it all around the clean things up as much as I can. After flushing I will search for pin holes as you suggest.

I don't remember whether it was me or a friend that put a non vented cap on a tank that relied on a vented cap and had it collapse back in the 60's. At that time most cars had mechanical fuel pumps.



Any idea why I can't include a photo? I hit browse and it went into download mode but wasn't included in my email.

Also...how do I send a PM?

I received and read your excellent PM so I know you've figured out how to do that.

Your instructions sound good and allow me to visualiZe about 95% of what you describe. I will highlight the few parts which I feel might use some more detailed description and send it back to you.

Immediate suggestion is for you to add two cellphones and a bag of cat litter to your preparation items. In case of a fire you don't want one guy fighting it while his helper waits till he's done to borrow his phone and call for help. Kitty litter will soak up most of a fuel spill quickly. Clean towels and eyedrops for the accidental eye splash (happened to me just two summers ago, after we thought we had drained the entire tank). Other minor suggestions listed in my PM but overall that's an excellent plan outline. No beer and no smoking should probably be added to the precautions list.

No, I have been unable to figure out how to post pictures on this new website for about 2 years. It got changed and now I can only post pictures which I take off the internet, but can't post anything from my computer library. Very frustrating; welcome to my life.

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1970 240Z

Thanks for reviewing that for me Frank. You are right about the safety aspect. We should add a paragraph about that. I worked outside the garage and away from the house when draining the tank. I was also working on top of cardboard to minimize the chance of sparking from gravel rubbing together. I also tried to stay still while the gas was flowing.

I will watch for your reply with your suggestions.

Best, Guy