Intermittent Loss Of Power-1972 240Z Stock

[AWAUDIO]

No rear fuel pumps.  BUT  Just fired it up after 3 hours of sitting, and she screamed.  Purrfect.  Fuel pressure back to 3.5 lbs.  Mounting  full blown attack on the tank and connections.  Am still planning on 5 gallon ext supply test.  Really need a scope for tank, wish one of the maker folks had one I could make.  AW

[Stanley]

At least you've ruled out electrical. Rule out lack of venting of tank since it happened with the cap off. Probably rule out air coming into fuel lines since it wouldn't be intermittent. Maybe something in tank. Rule out vapor lock since it happened cold.

If it was me, I'd be off to the store for a new fuel pump, but I have a record of installing an unnecessary fuel pump (at least now I have an extra good one). Also I don't know if it's possible for a mechanical fuel pump to have an intermittent problem.

Don't like the new pressed-steel fuel pumps. Don't look right in my opinion, they're "globally sourced" and you can't adapt them to AN fittings. Old style can be rebuilt, though.

[siteunseen]

Be extra careful with the external fuel tank, I wasn't at first and gas sloshed out.  Too full and didn't stuff a shop rag around the mouth of the jug.  Bungee cord it somehow between the radiator and the front lip where the horns are.

 

The sending unit comes off and out easy enough it's those nail head connectors and their old dried out rubber covers that are a pain.  If you put a flashlight in the filler hole then a camera in the sending unit hole you should get a decent picture.

 

Good luck and have fun, I did! 

[AWAUDIO]

@Stanley  I agree, those new pumps look cheesy.  Used to be able to get pump rebuild kits.  NOS pumps are around $350  ouch  I don't think pumps go intermittent. Someone correct me if I'm wrong.  I checked screws on mine, all fine.  Couldn't detect air leak at the pump gaskets, thought of that.  

@siteunseen  Will have to wait till this weekend, and I will be careful.  If I didn't have to work for a living, working on the car would be a lot easier.  BTW, started it up a few hours later and fuel pressure was back to normal.  At least I have something to go by now.  I was actually pleased to see the low fuel pressure reading.  I now have a target to attack.  Will report back in a few days.  Thanks to all for the suggestions.  Andy

[bartsscooterservice]

+1 on ztherapy - they have a specific high-silicone hose for this application, which will hold its shape and not put stress on the nozzles.

 

I would not use silicone, but only rubber hoses that are fuel rated.

[Stanley]

How about these hoses? http://www.mcmaster.com/#standard-plastic-and-rubber-tubing/=wybjii

I like the bend radius and temperature range, and they get an "A" grade for gasoline.

Edit: that link goes to the general area. I meant to refer to "Fuel-resistant Blue Fluorosilicone tubing"

Edited April 29, 2015 by Stanley

[240260280z]

This one? http://www.mcmaster.com/#standard-plastic-and-rubber-tubing/=wycgza

[240260280z]

MC's web site sucks for hyperlinks...

[bartsscooterservice]

I'm thinking this is a "hot sink" problem…….until one morning after a cold start it did the same thing.  Just wouldn't go.  Really pissed me off, so I drove it humping and bucking for 20 minutes.  Stopped, pulled cap/rotor  checked gap, put it back together and YES voila…. she pulls perfectly again.  I can't jiggle any wires to make it happen.  And finally today, after the usual great run for an hour, stop, start up, soon complete bucking and bouncing starts, I nurse it towards home.  Within 2 blocks of home she's running perfectly again.  So it happens under both "hot sink" and "cold start" conditions, and now between those extremes.   Any thoughts?  Coil?  Fuel pump?  It's driving me nuts.  Totally intermittent.  Sigh  AW

 

Problem seems in the ignition. I think it's in the distributor, because after you adjusted the point gap it runs good again for a short while, like you describe above.

Edited April 29, 2015 by bartsscooterservice

[gundee]

If you are still having problems and have not done this, I would next pull the distributer.

On the bench remove the breaker plate that the points attach to.

You now have access to the weights and springs. See if you have any broken parts floating

around in there. Such as a broken spring. Make sure the weights are not dry and move freeely.

Reassemble. Then you can eliminate another item.

[AWAUDIO]

Hello All,  thanks for staying with me.   I have a day off, so I'm putting her on the stands and checking the tank.  First I'm going to Harbor Freight for an inspection camera ($79) and looking into the tank.  Also checking flex fuel line from the tank.  In the meantime I've ordered the fuel pump rebuild kit from Canada and downloaded the excellent rebuild procedure from WoodWorkerB http://woodworkerb.com/home/datsun-240z-rebuild/datsun-240z-mechanical-fuel-pump-rebuild/  as a number of folks have told me the fuel pump could behave erratically.  I'm also trying to buy an NOS fuel pump off Ebay (spares are gold in my book), but seller is "out of town" -first time I've seen that on EBay with a "Buy It Now".  Please don't ace me out if you need one.  As a third backup, I've got the gaskets coming from MSA with a cheap non factory OEM pump on the way.  So attacking the fuel lines and tank will be first task.  Will access tank thru sender unit as I have nut and "O" ring.  Took it to Cars and Coffee this weekend, and as usual she started, ran and pulled fine, got there, sat, started fine, and then started acting up on the way home.  At least she's predictable.  Fuel pressure was again low when I got home.  If I didn't have work get in the way, I could solve this and end the suspense.  

 

@lumens  I know that there are 3 ball bearings in there and that if you have 2 in there you're lucky.  If it didn't just scream when normal, I'd be all over that solution (along with a Petronix pointless system), but with my pressure gauge between pump and manifold, I think I'll pursue fuel pressure issues first.  Thanks for the thought.

[240260280z]

FYI I have a friend who just installed a Pertronix points conversion. It lasted ~ 30min.