Dan Baldwin Posted May 11, 2001 Share Posted May 11, 2001 Hi all. My 3.1 liter '71 (as always a work in progress) currently has an overheating problem due to too small an aftermarket electric fan. That is not the main subject of this post, however. A few weeks back, I took the Z to the dyno, and suffered some higher rpm power loss, a succession of downward spikes in the torque curve above 5000 generally, which got worse with each successive run. Don't know if this is ignition or fuel delivery related, but I suspect the former. Anyway, I had to drive the Z to Boston yesterday evening, and of course got stuck in traffic a few times (had to pull off once to cool 'er down). I noticed that as the temperature rose, I developed a serious misfire (at least that's what it felt like), and as the temp cooled back down, the misfire went away. So, I believe this is the same problem I was running into at the dyno. That is, something's breaking down directly related to engine temp. What does that sound like to you guys? Here's what I got: Fuel system: Carter fuel pump (could feed three 3.1 liters) mounted near the fuel tank Purolator fuel pressure regulator set to 3 psi Stock fuel lines, including return line 2" Jag carburetors Ignition system: Stock distributor w/ Pertronix Ignitor replacing points Jacob's Energy coil Jacob's helically wound wires NGK BP6ET plugs Just got my MSD-6AL today, along with a new Blaster 2 coil. Will install Sun. or Mon. Might solve the problem? Might get new plugs and wires, too. All informed ideas welcomed and appreciated. Thanks, Dan Baldwin '71 240Z 3.1 COMSCC #7 SPB Quote Link to comment Share on other sites More sharing options...
DavyZ Posted May 11, 2001 Share Posted May 11, 2001 Dan, if you've owned the Jacob's stuff since new, that would be my choice. I have never heard of Jacob's stuff being the cause of such a problem; that sounds too strange and I don't think the MSD 6AL will solve your problem; but, if you bought it used from a flea market, then who knows? I'm assuming the fuel pressure (3psi) is actually line pressure, not pump pressure? If it's line pressure, kicking it up a notch to 4psi or even 5psi. Your radiator and cooling system is definitely a problem. If the car can't get through traffic w/o heating up like that, then there's your menace. What radiator are you running? Are you using a fan shroud? What kind/brand of fan do you have? Shoot, when was the last time you flushed the system? Are you using straight coolant or a 50/50 mixture? Water cools better than coolant alone. I would not yank the Jacobs stuff yet, without addressing the cooliing system on your car FIRST. Hope this helps! David Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted May 15, 2001 Author Share Posted May 15, 2001 Thanks for the reply, David. Only one! I replaced the Jacob's coil (I didn't have their whole system, just a regular coil) with a Blaster2 and still had the problem. Will install the MSD 6AL tonight (been meaning to get one for a while anyway, so it's not really specifically for this prob). Tried to reproduce the problem yesterday (let the coolant temp go up by leaving the fan off), but couldn't. Outside temp was much hotter when I had the problem. 3psi was/is the regulated line pressure. Will try increasing it. Car never ran hot in traffic with the stock fan. When the fan clutch siezed, I installed a too-low-cfm electric. Whoops. BTW, I'm talking about Boston traffic, which is worst have had to deal with. Stop-and-go, all day, every day. I have a 3-row 260Z radiator, no shroud, Tripac 11" 880 cfm fan. Flushed the system last year. Usually run 25/75 antifreeze/water with Water Wetter, but I think it's more like 50/50 now. Will likely change it before going to the track next Mon/Tue. I'm going to get a header blanket to keep the carbs cooler, and reroute the fuel lines to keep them cooler, and replace the lousy Puralator fuel press. regulator with a Holley before I go to the track. In the future, I'll get a more serious fan and/or a more serious radiator. Dan Quote Link to comment Share on other sites More sharing options...
spotfitz Posted May 16, 2001 Share Posted May 16, 2001 quote: Originally posted by Dan Baldwin: Thanks for the reply, David. Only one! I'm going to get a header blanket to keep the carbs cooler, and reroute the fuel lines to keep them cooler, and replace the lousy Puralator fuel press. regulator with a Holley before I go to the track. In the future, I'll get a more serious fan and/or a more serious radiator. Dan I have been having a similiar problem. When sitting at a drive through to long the rpm's would drop 2-300 and when trying to pull away it would stumble and once I got going it would "even out". I have noticed one thing about the Purolator FPR. The pressure fluctuates. Mine has been known to fluctuate from 3-6 psi when the FPR is set at 3.5 psi. I've suspected this for sometime as I didn't have this problem prior to installing it. With a guage just behind it I think I have found the problem. I wouldn't think that when idling you can build up this pressure between the FPR and the carbs. I thought I may have been getting pirculation of the fuel in the lines/bowls from the heat from the ceramic coated headers, but after making a heat shield I can put my hand on the bottom of the carbs and hold them there, after I've been idling at operating temp for about 15 minutes. The domes are even cold to the touch. The FPR and guage are mounted on the pass. fender so heat soak of them shouldn't be the case. Fuel rail(which is also ceramic coated) insulation didn't help with the problem. I feel it's the FPR. Is yours the dial type like mine? I feel with the fluctuation it is allowing higher pressure on the gross jets, which inturn load up the carb causing the stumble. Sound like a theory? I have yet to replace my FPR, but plan to once I get her painted. Hope it helps. Quote Link to comment Share on other sites More sharing options...
240Z Turbo Posted May 16, 2001 Share Posted May 16, 2001 It is possible to confuse detonation with the engine missing or getting spikes. If your timing is already on the edge from high compression then the added heat will only worsen the problem as additional heat in the engine will increase cylinder pressures and possibly cause detonation. Just check your plugs for signs of detonation. Small metal slivers on the plugs or the porcelin shows signs of being peppered. That is the only thing I can imagin would cause such a problem and have a direct relationship to your engine temps. Adding fuel will probably kill power more than backing down the timing a degree or two. Timing is the correct fix if you are having this problem. I could be way off, hard to diagnose from a message, but definitely something to look at. BTW, what is the engines static compression? Quote Link to comment Share on other sites More sharing options...
240Z Turbo Posted May 16, 2001 Share Posted May 16, 2001 One last thing, if your motor were in Houston traffic you would really be screwed because of the humidity. An 850cfm fan will not cut the mustard, nor will a 1600cfm fan. You will need atleast 2000cfm to properly cool the motor in all driving conditions(Houston weather). Spal makes a nice 16" fan that flows 2350cfm and costs under $100. Quote Link to comment Share on other sites More sharing options...
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