Dee Posted August 5, 2012 Share Posted August 5, 2012 Yesterday I swap on a N47 head on my F54 block set timing for 10* and filled up with 91octane -- other than a 3-2 header to straight exhaust & MSD Coil the car is bone stock. On the test drive I found an open stretch and eased on to WOT felt really good on the low end but around 5,500+ rpm the motor drops on it's face and sputters. Driving around normal at part-to-half throttle it's fine but sounds like I hit an ignition cut or something when I go flat out? What does this sound like? time to upgrade stock ignition? For reference on my other combo(F54/P79) it did the same thing just not as bad. Thanks Quote Link to comment Share on other sites More sharing options...
BluDestiny Posted August 5, 2012 Share Posted August 5, 2012 Is this with carbs or stock EFI? I know its a 280z, but just want to make sure. Quote Link to comment Share on other sites More sharing options...
Dee Posted August 6, 2012 Author Share Posted August 6, 2012 Is this with carbs or stock EFI? I know its a 280z, but just want to make sure. Stock EFI right now. I have a complete SU carbs setup that I could put on but just haven't gotten to it. Quote Link to comment Share on other sites More sharing options...
josh817 Posted August 6, 2012 Share Posted August 6, 2012 I had the same thing with mine. P90 head/F54 block with 40mm Webers. Right at the same RPM too! For the three years that I daily drove it, I could never get it past maybe 6500RPM because of the problem. One day I decided to see if the problem persisted if instead I didn't floor it but just slowly went through the RPM's in first. Got up to 7000 and then it chucked a rocker. Leads me to believe maybe the cam, valves, rockers, etc. were having stability issues and maybe a floating valve? I was running a "Stage 3" MSA cam with proper springs (.490" lift 290º duration I think). Even with stock springs, I don't think stability issues would occur unless if they were REALLY used for a long time. Stock springs should get you past 6500... I remember JohnC I think it was talking about the ITS Z's saying that one race weekend you may be able to bring it up to 8000RPM, the next maybe only 7500 without valve float, progressively getting worse as they're used. Another thing I would note. My Z had a persistent belt stretch. What would happen is one day, I never really noted the weather so maybe it was dependent on humidity or heat, I would be driving along and then all of a sudden at a random RPM, it would fall flat and then sputter. Pretty much exactly like a rev limiter, it would not go above that RPM. I eventually widdled it down to a stretching belt because one day I peaked under the hood and I could turn my alternator with my bare hands. I would tighten up the belt, problem went away. Maybe a few months later it would come back. And when I say random RPM's, it happened at 3500RPM once, just pulling away from a stop light. I don't remember it happening at night time so I can't comment on whether the lights were dimming or anything like that. The belt never squeaked when it did it either so... maybe it was just a quiet belt. All I know is that when I tightened it up, the problem went away. Anyway, I know exactly what you are talking about. I always thought it was either my belt slipping, valve float, or not enough air. I guess ignition too. I was running an electronic dizzy from a '77 Z I think. The one that doesn't have the black box, and you use it with an HEI module. Stock '83 turbo coil. Quote Link to comment Share on other sites More sharing options...
Pyro Posted August 6, 2012 Share Posted August 6, 2012 (edited) Could be detonation since you have high compression and a stock cam. Lower the timing 10 degrees and try it again. If that fixes it, then reduce the amount of timing in the advance curve. Also, check to make sure the spark plugs are tight. I recently had the same issues and loose plugs was the problem. Edited August 6, 2012 by Pyro Quote Link to comment Share on other sites More sharing options...
NewZed Posted August 6, 2012 Share Posted August 6, 2012 For reference on my other combo(F54/P79) it did the same thing just not as bad. Sounds like a part that is common to both setups. Fuel system - pump, filter, FPR - or ignition. Fuel pressure when it happens would tell you something. Quote Link to comment Share on other sites More sharing options...
madkaw Posted August 6, 2012 Share Posted August 6, 2012 What about under load going up a hill or something- does it sputter or anything even in the lower rpms? Almost sounds ignition related- like a weak coil Quote Link to comment Share on other sites More sharing options...
Leon Posted August 6, 2012 Share Posted August 6, 2012 (edited) Sounds like a part that is common to both setups. Fuel system - pump, filter, FPR - or ignition. Fuel pressure when it happens would tell you something. I'm with Zed, sounds like a lack of fuel in both cases. Check fuel pressure while driving. Just make sure that everything is tightly secured. FWIW, I had an issue that only popped up on the freeway. I'd be driving along just fine until I got to a hill. It would start misfiring and loosing power. It was tough to tell whether it was ignition or fuel related, since it appeared to coincide with warmer weather. However, the problem continued to get worse so I attached a fuel pressure gauge to my windshield and confirmed that pressure was dropping to zero right before the condition appeared! I replaced the filter by the tank and deleted the factory helper pump (260Z) and all was good again. Edited August 6, 2012 by Leon Quote Link to comment Share on other sites More sharing options...
BluDestiny Posted August 6, 2012 Share Posted August 6, 2012 +1 for ingenuity leon. I would be afraid of murphy's law with that setup. Quote Link to comment Share on other sites More sharing options...
Leon Posted August 6, 2012 Share Posted August 6, 2012 +1 for ingenuity leon. I would be afraid of murphy's law with that setup. Hey, it was about as safe as I could make it! Quote Link to comment Share on other sites More sharing options...
Dee Posted August 7, 2012 Author Share Posted August 7, 2012 (edited) Thanks for the replies, Think I'm going to be swapping over to a set of SU Carbs I refreshed, so while I'm at it I'll have to spend a day checking out wear on my ignition components. What about under load going up a hill or something- does it sputter or anything even in the lower rpms? Almost sounds ignition related- like a weak coil It does it every time I go WOT no matter downhill or uphill, it has never done it in the lower rpms; always around 5,500. I notice the other day some wires over by the main relay area were extremely brittle, the two blue wires that connect near the battery....I'm going to start there and work my way to the distributor/coil. I do have a MSD Blaster 2 coil that I forgot to mention but everything else is factory..... Edited August 7, 2012 by Dee Quote Link to comment Share on other sites More sharing options...
Dee Posted August 8, 2012 Author Share Posted August 8, 2012 (edited) Ok so I finished up swapping to the SU carburetors and got them somewhat dailed in. The problem is gone now; it pulls hard all the way through the power-band without a single hiccup and idles smoother than ever. Only other thing I did was replace the spark plugs which I found out the old ones were gapped way out @ .054, so upon installing the new ones I gapped them @ .044 & reset timing @ 10*. So it was either the plugs or something in the tons of EFI crap I pulled off. My only problem now is that it smokes like crazy, at little at idle and lots @ light/hard acceleration. I'm hoping it isn't my rings, and it's just the valve seals coming back to bite me in the ass for not changing them during the head swap. Edited August 8, 2012 by Dee Quote Link to comment Share on other sites More sharing options...
NewZed Posted August 8, 2012 Share Posted August 8, 2012 EFI crap Gave up? Bummer. No Megasquirt for you. Quote Link to comment Share on other sites More sharing options...
Dee Posted August 8, 2012 Author Share Posted August 8, 2012 Gave up? Bummer. No Megasquirt for you. hah, When the speed bug bites and my pockets are a little fatter....RB25DET. Quote Link to comment Share on other sites More sharing options...
Pyro Posted August 8, 2012 Share Posted August 8, 2012 What color smoke? White or black? Quote Link to comment Share on other sites More sharing options...
Dee Posted August 8, 2012 Author Share Posted August 8, 2012 (edited) What color smoke? White or black? Mostly white, and depending on how I adjust the carbs I get a little black puffs mixed in, coolant? EDIT: just took it for a 15 mile drive and it's definitely blueish, gonna run a compression test before I bother with the seals. Edited August 8, 2012 by Dee Quote Link to comment Share on other sites More sharing options...
Dee Posted August 9, 2012 Author Share Posted August 9, 2012 Just ran a compression test, slightly warm engine(cooled off for about an hour and a half). Results: Cyl #1 = 190 Cyl #2 = 200 Cyl #3 = 200 Cyl #4 = 200 Cyl #5 = 200 Cyl #6 = 205 These seem pretty normal? I've read that a newly rebuilt motor should get around 170 but I'm well above that which comes as a shock as I have beat the dogsh*t out of this motor for some time. I'm going to run another test soon as the car gets up to operating temps and record. Quote Link to comment Share on other sites More sharing options...
Leon Posted August 9, 2012 Share Posted August 9, 2012 Those results are great. If you're burning oil, it's the valve stem seals. They won't show up in a compression check (obviously). Quote Link to comment Share on other sites More sharing options...
Dee Posted August 9, 2012 Author Share Posted August 9, 2012 Those results are great. If you're burning oil, it's the valve stem seals. They won't show up in a compression check (obviously). Sweet! Ran comp again while warm and #1 went up to 205 but the rest were the same. Definitely good news....I'll have to get to the stems sometime this week. Quote Link to comment Share on other sites More sharing options...
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