Intermittent Loss Of Power-1972 240Z Stock

[gundee]

Your fuel pressure doesn't bother me too much if you have good volume output.

 No way to test that though. Electric one, yes.

[gundee]

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

Don't say that. I have one on the way.

[AWAUDIO]

@lumens  The volume per the FSM is 3.71 quarts @1k rpm per minute.  As I could imagine a "T" hose setup, which would let me run raw fuel out of a running engine into a containment vessel, this would satisfy the test,  but I'm not the gut to try this.  I maybe crazy, but not insane.  I'm sticking with the fuel pressure issue (I really hope my $25 gauge is good).  Volume, as in mixing music, can sometimes be deceptive. As it's getting dark in NorCal I won't get her up today.  But the inspection scope I got actually looks useful.  It focuses very close and the screen is sharp.  Has a variable light source and a right angle lens adapter with a 36" head lead.  Is waterproof to 3 meters, do not use in gas or solvents.  On a really weird tangent, one of the other guys inquiring to buy the fuel pump on EBay lives 3 minutes away.  I thought I knew all the "Z" cars in 94947, but I guess not.  Considering the world is a big place, that's just plain weird. 

[AWAUDIO]

@blue I'm going there after this adventure is resolved.  The posts I've seen and researched have pointed out a tach issue.  Have enuf problems at the moment to not add another.  But did see the thread where the tach needed to be disconnected to make it work.  I'm sure this been done to death on this site.  Back to my own hell……...

Aw

[Zed Head]

With dual carbs and intake manifolds you have essentially two separate engines connected by a common crankshaft.  The fact that it always runs and allows you to get home, and that the plugs don't get wetter and darker with extra fuel, could be from one carb suction piston getting stuck down, blocking the jet.  If I understand how they work.  That would kill or wound (lean out) three cylinders.  The old plug color wouldn't burn off so you wouldn't see it on the plugs.  It would allow idle but act up when more fuel is needed.  From Post # 5 - " It does idle perfectly when this happens, accelerates ok, but under load it's a no go."  The other three cylinders have normal power, so you have half an engine to get home on.

 

You could probably force it to run on three cylinders to see if the symptoms are the same.  Lock a piston down maybe.

[siteunseen]

Are the pistons rising and falling the same? Mine weren't and I loosened the screws holding the dome down until they were then retightened them. No needle bind anymore.

[AZ-240z]

   

    @AZ-240Z I opened dizzy and triple checked the insulators and the 2 wires inside the dizzy.  I replaced one wire (from points to insulator on the inside) a few years ago, as the original was frayed.  The 2nd wire from dizzy ground to plate measures good continuity .01 ohm.  Can't see any cracks, but I may just order the insulator if available.  

   

 

 

Andy, I still can't help but think that the little white plastic terminal insulator mounted on the top edge of the dizzy housing could be the issue.  Have you tried ordering it

from Nissan (part # 22403 - 18005 / Assy terminal) to see if it is available?

 

You may not see a crack in yours, but it doesn't take much for arcing to occur, and it sure stopped the missing, bucking, power loss issues I was having.  My dizzy was

a new factory re-manufactured dizzy and was defective.

 

I hesitate pressing the issue, but, if I am wrong, you are out maybe $5 for trying.

 

Best of luck with a very frustrating issue.

 

Dan

Edited May 5, 2015 by AZ-240z

[AWAUDIO]

@AZ-240Z  I have that insulator on order and am awaiting delivery!  Will replace as soon as I get it.  Along with the correct interior dizzy     wires…the long one and the short one.

@siteunseen  I've done the clunk test and they seem to be ok, and unless I have a bad fuel pressure gauge, I'm hitting fuel delivery issues first

@Zed Head  Unless my fuel pressure gauge is off (I hate it when test gear goes bad) I'm going into the tank and lines and fuel pump.  When it fails big time, it's a lurching drive from hell. When it's just throwing a hissy fit, it'll bobble on hard acceleration, this past Cars and Coffee, was the "I'm just gonna let you know I'm not happy".  And the time it was a lurching spasm from hell it started running fine 2 blocks from home.  Her name is not Christine, Steven King notwithstanding, it was a clear a case of possession as I've seen since the "Exorcist".

 

I have to ask all your indulgence, I'm freelance and the phones been ringing, and I didn't get a chance to use my new inspection scope today.  So she's not on jackstands yet, but my fuel pump parts are on the the way from Canada, a new cheap fuel pump and gaskets are on the way from MSA,  and the dizzy insulator and wires are also in the mail and on the way.  When I'm done, I think I'll have a few spare parts to let go.  

 

Thank you all again for your thoughts, I won't be able to work on her again till this weekend.   Andy

[AWAUDIO]

Ok folks, getting there inch by inch.  Put in a new fuel pump from MSA. My old one looked way better, but new one did put out higher numbers on the in line gauge.  BUT  guess what, problem remains, so I have it isolated to a pick up problem in the lines to the tank, from the tank.  That inspection scope is gonna pay for itself.  It's on to the jackstands and into the tank………..again.   It's gotta be there. I have no where else to go.  

[AWAUDIO]

OK sports fans, the results are in….I think.   After replacing fuel pump, and noticing that there were air bubbles coming out of the top of the fuel filter, I thought it had to be the line into the tank.  WRONG  That main line was fine, vent line was fine, no leakage at the rear tank float (it looked perfect) no wetness anywhere.  OK, drain the tank again.  A word of caution and advice.  You will get gas on you, it will be messy, and please be safe.  Tank drained, and out came my Harbor Freight inspection scope.  At this point I will issue a disclaimer.  As I was using this scope inside my gas tank, and talking to my brother at the same time, (who also has a 240Z) and who is a certified moon suit safety engineer, he inquired:  "Is that device you're using certified to work in explosive environments?"  DUH  Well  guess not…….Ok I'm still here, but that is not an endorsement.  Those fumes in the tank can and will explode if exposed to a stray spark.  So, fool that I am,  I'm practicing being a proctologist in my gas tank, trying to decipher the imaging, and after about an hour I get it.  My fuel float is perfect, I can read the info on the side, the tank looks clean, rusts spots here and there, no particles drained.  Top, bottom, sides, all look ok.  I mean, rust spots, nothing looking scary.  Eventually I stumble on the fuel inlet tube which enters high next to the vent line and goes toward the bottom of the tank.  I couldn't examine the bottom of the tank, as I was using the drain outlet for my inspection insert.  So, I bumbled along until I could examine the fuel intake tube inside the tank.  Not as easy as it sounds.  I spent 2 hours listening to good music while I manipulated the probe end.  Finally I got a view of the tube.  I wasn't sure I was certain of what I was seeing, but after multiple pulls and retries, I was pretty sure I found the problem.  My fuel pick tube inside the tank has a hole in it.  When the fuel tank is super full it runs great.  When the fuel level drops below the hole, the engine starts sucking air.  If the tank is super pressurized, on a hot day, pickup isn't a big problem.  The time it happened cold, it was a cold morning.  Got hot outside later in the day, pressure in tank builds, not so much a problem.  Full tank, super full, it was never a problem.  I think the hole in the line has gotten larger and the problem has gotten worse.  It was a gradual failure.  I never correlated fuel tank fullness till now.  On the scope,  I could only ID the "apparent" hole once.  It's impossible to snap a pic while probing.  Will hook up video recorder next.  And I'll run motor on jacksatands off external fuel supply.  I'm going to return my original pump to service, as it's beautiful and rebuilt.  But, first, double verify hole in fuel pick up tube in tank.  No easy way to pressure test it.  I just have to be sure using scope.  Any and all thoughts accepted and appreciated!  Thanks for staying with me, it's been a long haul……...

 

Andy

Edited May 18, 2015 by AWAUDIO

[AWAUDIO]

BTW  If I verify internal tank pick up tube problem, does this mean a new tank?  Can you separate and repair tank? This is uncharted territory for me. I actually bought ALL the tank replacement hoses 3 years ago, just because I thought it was a good idea and they were available.  Yes, the OEM ones.  Wasn't so expensive back then. But now it seems like cheap insurance.   So what are my tank options?  I've already started looking for replacements, but repair would be nice.  aw

[Zed Head]

People cut open tanks to install baffles and internal pumps.  Pretty sure it's doable, not uncommon.