280zx won't run unless return is restricted

[stevew]

Bought this 82 280zx after a long absence from Z cars. L&S, car has been sitting for a year or two, ran fine for 5 minutes then began sputtering, lost power & etc. I knew it was a fuel issue because I could enrich the intake and it would smooth right out.

Did all the standard things; dropped & cleaned fuel tank, cleaned pickup, blew out all lines, cleaned pump, changed filter, changed fuel pressure regulator, checked & cleaned MAF, fresh gas, but no change. Would crank and barely idle. Pump sounds & runs ok (seems to) & seems to build plenty of pressure, judging from lines being pulled loose & gas flying. The only thing that helps is to restrict the return line coming back off the fuel rail. Car smooths right out and is driveable, although not well. Any ideas?

[sblake01]

Have you connected a guage to it and checked the fuel pressure while it's running? The fact that it runs better when the return line is restricted suggests that there's probably a fuel pressure problem.

[zbane]

In addition to Stephen's suggestion, check your FPR. I know you have a new one, but if it is not working correctly it would allow fuel into the return line before the proper pressure was reached. Additionally, pull off the vacuum line from the FPR to make sure that it has not been breached and flooded with gas.

Check to make sure that all of your fittings/clamps are indeed tight. You may be losing fuel from a bad line/connection.

VERIFY that you have ONLY fuel lines that are rated for FUEL INJECTION ! I very recently had to correct the counterperson at a local parts store when I was presented with non FI lines for purchase.

If you are using the wrong line type, it will bulge (creating a loss of deliverable pressure) and eventually rupture. You may be countering this by building more pressure in the line when you clamp down on the return system...If this is the case, you are heading to a very dangerous situation-burst line while running/driving...

[stevew]

Thanks guys. Any chance I could have put the wires on the fuel pump backwards? Does it matter?

[zbane]

Thanks guys. Any chance I could have put the wires on the fuel pump backwards? Does it matter?

Sure, it's possible, and yes, it would matter. Are you using the original fuel pump (or OEM replacement), or an aftermarket unit (like Wallbro, Beck/Arnley, Masters, etc.)?

However, I don't think that is the case. If you had reversed the wires, you wouldn't be getting any pressure in your lines. These pumps are great at pushing fuel, not so good on the suction part.

Another thought...

Fuel Injectors.

You state that it will run, albeit poorly, when extra pressure is applied to the system. I am thinking that perhaps your injectors are all crudded up inside, and the only way you can get fuel through them is to force it through.

The car had been sitting for a couple years, so methinks you may have some varnish/rust particle/assorted ick clogging those little buggers.

Run a search for Dr. Injector, both on this site and your favorite search engine.

[stevew]

Well, I t'eed a guage into the fuel line right after the filter, and have pressure out the wazoo (which is a bad place to have pressure). 100 lbs with the return restricted, 40 lbs. without restriction. Seems to have adequate flow when the filter is unhooked.

I'm thinking fuel injectors clogged. Any way to clean those things?

[zbane]

Pressure at the rail should be 36.3 (I think-search the site to be sure). As far as cleaning the injectors yourself, I have no idea. I would send them off to the Dr. Injector guy, he seems to have a good reputation, and a couple members have used his services.

Otherwise, there are injector services to be found online, but I wouldn't know of quality of service/value, etc.

http://www.docinjector.com/

on ebay

http://myworld.ebay.com/dr.injector/

[zbane]

Assuming you have the original stock fuel pump, there may be another possibility.

There is a small metal mesh cone filter at the intake side of the pump. I wouldn't be surprised if that has built up a layer of tank sediment in it. If that were the case, your pump is not putting out the required amount of fuel with the required amount of pressure.

When you block the return line, you increase the pressure but not the amount of gas being pumped and that might be another reason why the car is running rough.

Just an idea.

[RogerZ]

injectors have a screen/filter in the injector if they get varnished up this would cause what you are experiencing. Probabaaly someone knows a way to clean them but not I. i have used alchohol to clean varnish in other appliations and worked but????????

[adcvideo]

Hey Gent's

If I might just say thank you all for your valuable experience,patience,and tenacity.

I recently bought a (weekend warrior)a 77' 280Z in brea Ca. The guy kept it in really good OEM condition but did not drive it much in the 30 years he owned it.

Now I am down to the issue posted in this thread, unfortunately the new fuel rail I ordered on Ebay has not yet arrived to gauge the pressure and return line scenario to collect data.I am just resting from doing all the front end bushings,struts,etc but when I find the problem(w/your help I will post here)

At this point I will review the injector hoses to ensure they are FI variety and the FPR it was not Nippon but some local US mfg so I am suspicious.

At present it runs darn good but fades or lacks the "power band" when shifting at 3500- 4000 rpm I think perhaps some adjustments may need optimized EFI tuneup butalso related to this, as soon as I release the return clamp it runs like $^!#!

FYI- My fuel problem through me off because it simulated an almost "cold start condition" it would barely idle until it reached normal temperature and then it would occassionally cough in the intake manifold I retimed it and found that went away when I clamped the return line- idle picked up,engine smoothed out.I think the injectors are fine they are also new plus the fuel and vacumme systems have no leaks- *all have been replaced recently I must have tightened and stared at those$#%@$% 30 times! *Some things the original owner had done to sell and smog the rest I figured what the hell it was a thrty year old car so just did it.

But I did replace the:

FPR

filter

Cold start valve

Thermistime switch

*coolant switch

wiring connectors

air Press. reg. (I had an extra one from my 80 Z that was stolen years ago)

None of which helped the issue above.

I removed the fuel pressure snubber device near the Fuel pump and found no difference, somewhere I read that with modern fuel pumps it is no longer required hence the reason it is not found after 1977. Also the Original owner stated that he changed the pump back in 97' w/oem.

Sheer determination wll prevail

Dave

[sblake01]

The fuel damper, which is what I think you are referring to in your last paragraph was present on all EFI S30s and S130s through 1983 (1984 if you include the 810/RWD Maxima). How did you conclude that it's not found after 1977? I have a 78 280Z and a 79 810 and they both have one.

[zbane]

Re the damper near the pump: My '79 zx has one as well, as Stephen stated, they were stock up through the end of the S130 line, as well as the 810/Maxima.

What it sounds like to me is this: Your pickup screen may be collecting tank sediment (rust). As you drive, the fuel pump sucks up the gas, and with it the assorted crud that is in your tank. As you continue driving, more crud gets sucked up and eventually cuts down on the amount of gas that can get through.

Have you inspected the interior of the gas tank? If not, I would suggest doing so. Since the previous owner didn't do much driving over the past umpteen years, there has been plenty of time for rust to develop.