Results 1 to 23 of 23

Thread: four cylinders not firing, oil in each; stock 240z

  1. #1
    Registered User
    Member ID
    CZCC-29573
    Join Date
    Aug 2013
    Location
    Montana
    Posts
    16

    Default four cylinders not firing, oil in each; stock 240z

    I don't really know where to start, so please bare with me.

    About three months ago, I sent my carburetors off to Ztherapy to re manufacture them because the rear three cylinders quit firing, and my float bowl was overflowing. I finally got them back (2 months later), installed them, did all the necessary tuning that I could without the car running (including float level), and it will only fire up if I've got both carbs fully choked. It'll run at high rpms until I unchoke it, and then it just sputters out. Turns out, (from the front) the 4th, 5th, and 6th cylinders are for sure not firing, and I think the 1st isn't because its exhaust channel on the exhaust header is the same temp as 4, 5, and 6. When I pull 4, 5, and 6 spark plugs, the tips are drenched in oil, but they're still sparking. Could it be that my cylinders are full of oil, and it's not sparking? I adjusted the timing, distributor gap, and valve clearance properly about 800 miles before I had to send off the carbs, so I don't think it's any of those. I just don't get why those cylinders aren't firing.

    Please feel free to bombard me with questions and help me figure this out!
    Last edited by jwilliams905; 08-30-2013 at 09:51 PM.

  2. #2
    Rust Free'ish zKars's Avatar
    Member ID
    CZCC-12190
    Join Date
    Jul 2006
    Location
    Calgary, AB Canada
    Posts
    1,256

    Default

    Not good. Sorry to have your first experience here be related to a problem.

    Do a compression test on all six cylinders and see what's up. Combustion requires fuel, spark and compression.
    Also test your fuel pressure and volume. Disconnect the fuel line to one carb, crank the engine and let it pump fuel into a bottle. See how much you get. Do each carb fuel line separately. replace your fuel filter too.

    Let us know what you find.
    -----------------------------------------
    Jim
    73 240Z HLS30 149331
    69 510 PL510 77603

    www.zKars.com
    www.calgaryzclub.ca
    Reference materials
    www.xenonS30.com

  3. #3
    Registered User
    Member ID
    CZCC-29573
    Join Date
    Aug 2013
    Location
    Montana
    Posts
    16

    Default

    Haha, it's a learning experience, and I'm eager to work out the kinks, so I'm pretty thankful to even have a forum to post questions on! Before this, I was pretty well capable of figuring out the minor problems, but this one's had me baffled.

    I'll see if I can't get a hold of a compression tester from somebody. And I never thought of checking the fuel pump that way. I'll get back to you with the results and hopefully a conclusion!

    Thanks a lot, Jim!

  4. #4
    Registered User rcb280z's Avatar
    Member ID
    CZCC-21454
    Join Date
    Apr 2010
    Location
    Ventura Ca.
    Age
    58
    Posts
    873

    Default

    You can usually rent a compression tester from your local parts house.

  5. #5
    Registered User madkaw's Avatar
    Member ID
    CZCC-7622
    Join Date
    Dec 2004
    Location
    bloomington IN
    Age
    58
    Posts
    2,288

    Default

    If you were dumping fuel into the cylinders before you could have done several things. You have washed down the cylinder walls with fuel and the rings are not doing their job keeping the oil out. There's the possibility of hydraulic damaged from fuel in the cylinder also.
    I would turn over the motor with the plugs out for a while.
    I would also make sure to clean plugs well or replace oiled plugs before restarting and do compression test
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

  6. #6
    Registered User
    Member ID
    CZCC-29573
    Join Date
    Aug 2013
    Location
    Montana
    Posts
    16

    Default

    So I spent about ten hours on trial and error. I first found a friend who'd let me borrow his compression tester. So I tested each cylinder and found that all were running (dry) about 165 psi except for the rearmost which was at 175. Didn't make much sense to me, but I don't think it's a major issue. So I pulled the valve cover and adjusted my valve gaps again, hoping that might even out each cylinder, but it didn't change much. Still wouldn't crank and hold unless I was choking it, and every time I'd hit the throttle, there'd be a delay in it revving up. Spent a lot of time pondering, tinkering with my air flow and mixture nuts, and finally decided I might have adjusted the floats wrong. I originally adjusted them according to the Ztherapy video which was .55 inches (approximately 13.97 mm), but I've seen some say between 12 and 13 millimeters. So I re-adjusted them to 12.5 mm (float to float bowl lid). It made a slight difference, but not enough. Still the same issues, still pretty sure those three cylinders weren't firing. I knew fuel was pumping, I just didn't know how to measure the fuel quantity, and how much I should be getting, so my brother recommended pulling and plugging the fuel line to the front carb to see if the vehicle would start and run off of the rear (the cylinders that aren't firing up). Sure enough, fired right up, ran the same way just different cylinders. I'm pretty sure there must be a blockage in the fuel line, because I'm getting fuel, it's just going to the first carb. The filter is still good (by visual inspection), and the fuel pump is brand new (installed by the previous owner maybe 4 months ago).

    Tomorrow, I'm going to blow the fuel back into the fuel tank from the filter, hopefully clearing the blockage, and then I'll just drop the fuel tank and clean it.

    Feels like I wasted a lot of time, but I learned every damn inch of my carburetors, and much more. Thank you all for your help! I wouldn't have known where to start without your advice!
    Last edited by jwilliams905; 08-31-2013 at 11:53 PM.

  7. #7
    Registered User madkaw's Avatar
    Member ID
    CZCC-7622
    Join Date
    Dec 2004
    Location
    bloomington IN
    Age
    58
    Posts
    2,288

    Default

    Why would you pull the fuel tank if you are getting fuel to the carb. So you think that there is only enough fuel coming up to operate 1 carb? That doesn't seem to make sense. What About the fuel rail-have you checked it? Have you visually verified how much fuel is coming from the fuel rail?
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

  8. #8
    Registered User beermanpete's Avatar
    Member ID
    CZCC-21519
    Join Date
    Apr 2010
    Location
    Northridge, California, U.S.A.
    Age
    57
    Posts
    631

    Default

    You should measure the fuel pressure and delivery rate. The factory service manual explains how to do this and provides the performance specifications.

    Will the car run (at idle) on ether (starting fluid)?
    Did you replace the plugs when you installed the freshly rebuild carbs?
    How long did you let the car run before turning off the choke? If the preheat water in the manifolds is not flowing (disconnected or plugged up) the car takes a long time (about 10 minutes) to warm up enough to idle correctly and drive without stumbling a bit on acceleration.

  9. #9
    Registered User
    Member ID
    CZCC-29573
    Join Date
    Aug 2013
    Location
    Montana
    Posts
    16

    Default

    Quote Originally Posted by madkaw View Post
    Why would you pull the fuel tank if you are getting fuel to the carb. So you think that there is only enough fuel coming up to operate 1 carb? That doesn't seem to make sense. What About the fuel rail-have you checked it? Have you visually verified how much fuel is coming from the fuel rail?
    Doesn't make too much sense to me either, but If the rear three cylinders aren't firing while the front three are, and I can unplug and block the fuel line to the first carb and all of the sudden the rear three are firing up just fine, then that's the only explanation. I figured the tank was probably in need of cleaning anyway, but it seems I'd have to cut the thing open just to clean it and then get it re-welded when I'm done, so I don't know what I'll do there. I'm afraid if I just blow out the fuel line, and it clears the blockage into the fuel tank, then it'll just get clogged again. I'm assuming that the reason why there's a delay in it reving up when I open the throttle is because it's taking longer for that float bowl to fill up. the float level is to spec, and it runs fine if it's the only carb that's hooked up, so I'm assuming there is either a blockage or just not enough fuel pressure.

    Could it be something to do with the return line?

  10. #10
    Registered User
    Member ID
    CZCC-29573
    Join Date
    Aug 2013
    Location
    Montana
    Posts
    16

    Default

    Quote Originally Posted by beermanpete View Post
    You should measure the fuel pressure and delivery rate. The factory service manual explains how to do this and provides the performance specifications.

    Will the car run (at idle) on ether (starting fluid)?
    Did you replace the plugs when you installed the freshly rebuild carbs?
    How long did you let the car run before turning off the choke? If the preheat water in the manifolds is not flowing (disconnected or plugged up) the car takes a long time (about 10 minutes) to warm up enough to idle correctly and drive without stumbling a bit on acceleration.
    I've just managed to get it to hold at idle off of only 3 cylinders (I unplugged the rear three plug wires and it didn't affect the way the engine was running).

    I put brand new NGK Plugs in before I even tried to start it (they're just nickel).

    I ran it choked for about 10 minutes and still when un-choked it, it sputtered out. I think resetting the float level is what caused it to finally hold at idle.

    I'll look into running a fuel pressure and delivery rate test, like you said, before doing anything else.

  11. #11
    Registered User madkaw's Avatar
    Member ID
    CZCC-7622
    Join Date
    Dec 2004
    Location
    bloomington IN
    Age
    58
    Posts
    2,288

    Default

    I would remove or blow out the fuel rail first and check the return orifice
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

  12. #12
    Registered User
    Member ID
    CZCC-23125
    Join Date
    Dec 2010
    Location
    Spartanburg, SC
    Age
    51
    Posts
    468

    Default

    Check the screens in the banjo bolts, replace the fuel filter and do a flow test. The rear screen may be clogged and with the front line blanked off enough pressure can be built up to feed the rear carb. Cutting on a gas tank and welding for that matter is a very bad idea. The tank has to be absolutely clean and your welding has to be very good to not have pinhole leaks. I weld a lot for a hobbyist and I wouldn't try it. There are kits that can be used for cleaning the tank and resealing. Clean with acid, neutralize and coat with tank sealant. A much easier and safer idea...
    Charles

  13. #13
    Registered User
    Member ID
    CZCC-29573
    Join Date
    Aug 2013
    Location
    Montana
    Posts
    16

    Default

    Quote Originally Posted by Patcon View Post
    Check the screens in the banjo bolts, replace the fuel filter and do a flow test. The rear screen may be clogged and with the front line blanked off enough pressure can be built up to feed the rear carb. Cutting on a gas tank and welding for that matter is a very bad idea. The tank has to be absolutely clean and your welding has to be very good to not have pinhole leaks. I weld a lot for a hobbyist and I wouldn't try it. There are kits that can be used for cleaning the tank and resealing. Clean with acid, neutralize and coat with tank sealant. A much easier and safer idea...
    Charles
    Yeah, it didn't take long to give up on that idea. I'm assuming banjo bolts are the two nozzles on the sides of my fuel pump?

    (circled here in faint red)

    Click image for larger version. 

Name:	IMG_20130901_183827_4401.jpg 
Views:	89 
Size:	89.0 KB 
ID:	65750
    Last edited by jwilliams905; 09-01-2013 at 06:06 PM.

  14. #14
    Boat Anchor Repairman Captain Obvious's Avatar
    Member ID
    CZCC-24608
    Join Date
    Jul 2011
    Location
    Philadelphia, PA
    Posts
    1,845

    Default

    I may be completely off base here, but I think you're off in the weeds...

    I think what you're calling oil on the rear three plugs is actually gas and not oil, and I think that when you disconnected and plugged the fuel supply to the front carb you were still running off the front carb and were simply consuming the fuel that was in the front float bowl. (The engine will run for at least thirty seconds with the fuel line disconnected.)

    So... When you disconnected the front carb supply and the engine started suddenly running on the rear three cylinders, how did you verify that it was the rear three? Did you suddenly discover that the rear three exhaust tubes were now hot and the front three were now cold? Or were you just assuming that since you had the fuel line to the front carb disconnected, the engine must be running on the rear carb?

    If your rear three plugs are wet, I think your rear carb is running too rich. So rich, in fact, that those three cylinders won't fire and the plugs are drenched with unburned fuel, not oil.

    I don't think you ruined your rings. I don't think you're having a problem with the restrictor orifice... I think you're dumping in too much fuel through your rear carb. I think you're overcomplicating this. Like I said, I may be off base, but that's my read.

  15. #15
    Registered User Stanley's Avatar
    Member ID
    CZCC-24191
    Join Date
    Apr 2011
    Location
    Redondo beach
    Posts
    641

    Default

    Might be time to give it a rest. I'd just sit back with a cold beer and some chips, and try again tomorrow.

  16. #16
    Registered User
    Member ID
    CZCC-23125
    Join Date
    Dec 2010
    Location
    Spartanburg, SC
    Age
    51
    Posts
    468

    Default

    Captain Obvious may be right on this. He nailed an earlier diagnosis. Banjo bolts are at the intake to the SU float bowls. The intake tube has a bolt that goes thru it, fuel goes thru the intake port, then thru a small screen around the bolt, then thru the bolt and into the float bowls. Google "SU Banjo bolt"...
    C

  17. #17
    Registered User
    Member ID
    CZCC-29573
    Join Date
    Aug 2013
    Location
    Montana
    Posts
    16

    Default

    Quote Originally Posted by Captain Obvious View Post
    I may be completely off base here, but I think you're off in the weeds...

    I think what you're calling oil on the rear three plugs is actually gas and not oil, and I think that when you disconnected and plugged the fuel supply to the front carb you were still running off the front carb and were simply consuming the fuel that was in the front float bowl. (The engine will run for at least thirty seconds with the fuel line disconnected.)

    So... When you disconnected the front carb supply and the engine started suddenly running on the rear three cylinders, how did you verify that it was the rear three? Did you suddenly discover that the rear three exhaust tubes were now hot and the front three were now cold? Or were you just assuming that since you had the fuel line to the front carb disconnected, the engine must be running on the rear carb?

    If your rear three plugs are wet, I think your rear carb is running too rich. So rich, in fact, that those three cylinders won't fire and the plugs are drenched with unburned fuel, not oil.

    I don't think you ruined your rings. I don't think you're having a problem with the restrictor orifice... I think you're dumping in too much fuel through your rear carb. I think you're overcomplicating this. Like I said, I may be off base, but that's my read.
    I agree about the oil actually being fuel. I know the rear three were running at that point because I used a wet rag to compare the temperatures at the header, and I also pulled the 6 and 5 plug wires and it quit running. Before then, I had it running with all three of the rear plug wires unplugged. I haven't got the tools and means at the moment to run a fuel pressure test, so tomorrow, I'll get the proper equipment.

    Is that fuel pump in the picture I posted the stock fuel pump? It looked that clean when I bought the car, so I don't know if the original owner put some crappy aftermarket pump in.

  18. #18
    Registered User
    Member ID
    CZCC-23125
    Join Date
    Dec 2010
    Location
    Spartanburg, SC
    Age
    51
    Posts
    468

    Default

    That is a stock fuel pump, and if you buy one from a parts store it may not even look like that. Some of the newer cheaper pumps don't have that type cover. whether that is the original pump or not who knows, but I doubt it.
    C

  19. #19
    Boat Anchor Repairman Captain Obvious's Avatar
    Member ID
    CZCC-24608
    Join Date
    Jul 2011
    Location
    Philadelphia, PA
    Posts
    1,845

    Default

    Well if you're convinced that it's a fuel delivery issue it should run on all six cylinders if both carbs are getting the right amount of fuel...

    Pull and plug the fuel supply tubes off both carbs and fill the float bowls with a funnel and a short piece of tubing while checking the float bowl level with a clear piece of tubing on the outlet nipple on the bottom of the bowls. Once you're convinced that both carbs are filling to the correct level, then start the car.

    If you're right, then it should run well on all six cylinders for at least thirty seconds until the float bowls are sucked dry. If not, then it will still run like crap.

  20. #20
    Registered User beermanpete's Avatar
    Member ID
    CZCC-21519
    Join Date
    Apr 2010
    Location
    Northridge, California, U.S.A.
    Age
    57
    Posts
    631

    Default

    Quote Originally Posted by Captain Obvious View Post
    Well if you're convinced that it's a fuel delivery issue it should run on all six cylinders if both carbs are getting the right amount of fuel...

    Pull and plug the fuel supply tubes off both carbs and fill the float bowls with a funnel and a short piece of tubing while checking the float bowl level with a clear piece of tubing on the outlet nipple on the bottom of the bowls. Once you're convinced that both carbs are filling to the correct level, then start the car.

    If you're right, then it should run well on all six cylinders for at least thirty seconds until the float bowls are sucked dry. If not, then it will still run like crap.
    Good idea. Divide and conquer!

  21. #21
    Registered User
    Member ID
    CZCC-29573
    Join Date
    Aug 2013
    Location
    Montana
    Posts
    16

    Default

    Yeah man, that sounds like a plan. Sadly, it'll be friday before I can touch the car again, so I'll get a few parts ordered and perhaps an electric fuel pump just in case. Does anybody have a reccomendation for an electric fuel pump? There's a lot to choose from, but I wanna go ahead and get the best one I can get.

  22. #22
    Registered User madkaw's Avatar
    Member ID
    CZCC-7622
    Join Date
    Dec 2004
    Location
    bloomington IN
    Age
    58
    Posts
    2,288

    Default

    RX-7 carbed pump

    Check that fuel rail
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

  23. #23
    Registered User
    Member ID
    CZCC-29573
    Join Date
    Aug 2013
    Location
    Montana
    Posts
    16

    Default

    Quote Originally Posted by madkaw View Post
    RX-7 carbed pump

    Check that fuel rail
    I have already blown the rail through from both the fuel line and the return line end and it blew through fine (according to my innexperienced perspective). Somebody mentioned that there could be a pin hole or something in the diaphragm of the fuel pump. Now that they mention it, I recall when I pulled it apart that there was fuel under the diaphragm. By my understanding, that should not be.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. firing order 1971 auto 240z
    By pantherf9f in forum Help Me !!
    Replies: 3
    Last Post: 11-05-2012, 07:51 AM
  2. Turning over but not firing up 1973 240z
    By branham76 in forum Help Me !!
    Replies: 1
    Last Post: 06-26-2012, 06:42 PM
  3. 240z not starting, low compression in 2 cylinders
    By airbornealex in forum Help Me !!
    Replies: 3
    Last Post: 02-06-2012, 08:43 PM
  4. Having Trouble Installing a 240z Stock Radio in '71 240z
    By lonetreesteve in forum Help Me !!
    Replies: 1
    Last Post: 01-10-2006, 09:05 PM
  5. FI's may not be firing
    By lance75_280z in forum Help Me !!
    Replies: 3
    Last Post: 03-16-2003, 07:10 AM

Tags for this Thread

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •