do I need an electric fuel pump?

[ta240]

whenever it gets to over the low 70s and I spend any time in traffic my Z starts cutting out something awful. It isn't so much a sputtering as it is half seconds of no power at all. No real coughing just jerking along where it pulls then doesn't for a second or less then pulls again for a second or two and then repeats.

It will rev freely if it isn't in gear but as soon as I put a load on it it goes back to the cutting out. Generally once I get out of traffic and start moving again it goes back more to normal.

It will idle pretty much normally at that time too. It slows a bit like it is bogged down if it sits idling at a light for too long but doesn't cough or sputter there.

It just has the stock mechanical fuel pump on it and it is likely original. It also has the SUs off a 72 on it.

What all should I check? It almost feels like it is an electrical issue with the ignition as it cuts in and out so completely. I have a petronix ignition with MSD 6 on it (the MSD box is inside the car).

I know these are prone to fuel overheating problems but didn't want to go throwing money and time into adding an electric fuel pump if it might be something else.

It is a bit hard to diagnose as even if it is still cutting out as I pull into the garage it will rev fine in neutral.

thanks for any help.

Trevor

240z.me

Edited March 26, 2013 by ta240

[Jarvo2]

I experienced very similar issues with my '72. First thing is I'd suggest making sure your fuel filter(s) are clean, including the 'last chance' filters in each of the carbs. Once I upgraded to an electric pump my issues went away. Most likely was the 40 year old diaphram in the manual pump.

Feel free to check out my write-up on how I installed the electric pump: Dave's 1972 Datsun 240z: Electric Fuel Pump Installation

[ta240]

wow, great writeup on the electric fuel pump install. How is that one for noise level?

Trevor

http://240z.me

Edited March 26, 2013 by ta240

[GeoJoe]

+1 on fuel filter. I already replaced mine once and only a few weeks later (after a fill up) I have some lagging as described above. I think I stirred up some sediment on the fill up. I need to have my entire tank drained.

[Jarvo2]

The type of pump I have is silent. You can search for it at Rock Auto, its listed as an RX7 replacement pump (Airtex E8016S). The advantage of going with one of these little pumps is that you don't need a fuel pressure regulator like you do with the bigger pumps.

[Wade Nelson]

Trevor almost sounds to me like you're vapor locking. That's rare when the engine is actually running, but not impossible. What i would do is seek out ethanol-free gasoline, and run a few tankfuls. See if the problem is reduced. I know all sorts of classic car owners, carburetor cars, that have trouble with "oxygenated" fuels containing ethanol. Corvettes, MGB's, you name it. Altitude makes it worse.

Higher fuel pressure will prevent vapor locking in the lines, but will NOT prevent boiling of fuel in the float bowls.

Good luck and let everyone know what works/didn't work for you.

[ta240]

I wondered about the gas some as the problem does fluctuate but right now the weather fluctuates a lot too so I wasn't able to nail it down completely. A 72 degree day with a breeze makes it a lot less likely to act up than a still 72 degree day. So I keep wondering if it is just a bit cooler so it is doing better and some days I don't hit every stoplight red like others.

I only do Exxon, Texaco or Shell for fill ups. I'm not sure how to find ethanol-free gas around here. I checked one site but there wasn't anything for 90+ miles on it.

I thought I read one place where having the tank fuller helps as the gas that recirculates back cools before coming back up again so I'm trying that too.

I ordered a new mechanical fuel pump to try that. I guess an electric fuel pump isn't that much work (and it allows for really a really fun hidden kill switch). I've had an aversion to them since my old Z had one. But I didn't have Dave's writeup back then and had one of those little box style ones that go thump,thump,thump no matter how much you isolate them and then tried a different style one that kinda screamed so that was always fun.

[Travel'n Man]

Are you running a return line? Is your current line vented?

[FastWoman]

I agree with Wade. Even '77/'78 vented hood compartments are quite stuffy and get very hot. The earlier ones are doubly stuffy and hot. There's lots of room to the side of the engine, but the top of the engine is quite close to the hood, and there's very little circulation. I think you Californians are still on the more highly volatile winter formulation gas. That formulation, combined with warming weather, near-zero fuel pressure (engines aren't carbureted anymore), and poor hood compartment ventilation, could well be a recipe for boiling gas.

[ta240]

Are you running a return line? Is your current line vented?

There is a return line ( I should check it tonight to make sure it isn't plugged or restricted ). The tank is vented.

I've got a basic infrared thermometer, I think I'll put it in the car and the next time it acts up I can pull off and kinda scan things to see what the temps are on the different components.

I've got a couple electric fans from my old Z and thought about either trying one in front of the radiator that I could turn on when moving slower on hot days to try to force some more air through the engine compartment. Or figured it wouldn't look great but also thought maybe the smaller one I could mount facing upward somewhere on the passenger side of the engine to force air up and around the engine and push some of the super hot air coming up from the exhaust manifold in the other direction.

I also seem to remember something about the ZX injector fan being used by some people to help cool the carb area. Might look a little cleaner than an oddly mounted fan on the other side of the engine.

Changed the fuel filter last night but they said chance of rain today so I didn't drive it, new mechanical fuel pump should be here by Saturday.

Edited March 28, 2013 by ta240

[Travel'n Man]

Engine venting and fuel venting - I would check them off my list first - process of elimination.

[olzed]

Loose or dirty ignition wire.

Check all the connections to and from the coil and dizzy.

Give any spade connectors a gentle squeeze with some pliers, and shove them back on.