Z left me stranded, any help appreciated

[janaka]

Hello all;

Unfortunately I don't like posting things like this but my Z left me stranded down in Niagara Falls two weeks ago and I had to have it towed home to Cambridge.

anyway here's what happened.

I was cruising on the QEW Niagara and merging onto the 402 to NOTL. I hit a nice deep crease in the highway and then all of a sudden my RPM jumped to ~5000rpm I thought it poped out of gear but it didn't. the car then proceeded to drop to ~1500rpm and bog, total loss of power. All of this in a span of a second or so with my accelerator at the same position. when it dipped i tried to accelerate through it but it just pulsated at me and no power. I downshifted and it caught 4th gear and was ok for a few seconds till i hit the next bump and it did it in 4th gear, jump of rpm then bog... scary as all hell at 70-80mph

anyway i limped to the BBQ i was going to and then got it towed home.

Since then I have had the Z started and was able to get it to opperating temps with no issues (big cam needs to be idled at 2k or more to get to opperating temps to idle on its own). I can rev through the RPM range to 5000rpm in nuetral NO issues at all. I thought today was my lucky day, threw it in first and rolled down the driveway, eased off the clutch and it caught gear ok and idled in gear at 5kph, as soon as i accelerated it bogged and wanted to stall as it did the day it was towed. so much for my lucky day.

I've pulled the plugs, front 3 are great, rear three are whitish, carb running a bit lean, wires are fine, distributor looks ok no loose wires/connections. I haven't had time to go much further indepth at this point.

I really will appreciate any help in this as it drives me nuts not knowing whats wrong more than having the car not running. I just want to drive it again

1976 280Z

Mod LIST

Engine/Drivetrain

L28 #F54 engine block, flattop pistons, siamesed cylinders The block was professionally boiled and cylinders honed. New- piston rings, crankshaft bearings, oil pump, timing gear and chain kit, water pump, freeze plugs, gaskets and seals, hoses and belt.

P79 cylinder head. Performance rebuild including- resurfaced head, 3 angle valve grind, rocker arms, lash pads, springs and retainers, seals.

Schneider cam- .460 valve lift, 270 intake duration, 280 exhaust duration.

Dual domed top 4 screw SU carbs- rebuilt, performance needles and nozzles.

N33 carb intake manifolds.

K&N air filter.

MSA 6 into 1 header.

MSA 2.5 inch aluminized performance exhaust with super turbo muffler.

Holley “RED” fuel pump with adjustable pressure regulator. running at 7psi

Inline fuel filter.

Fuel tank cleaned and sealed (POR-15).

Late model “close ratio” 5-speed transmission.

2+2 flywheel mated to a Perfection brand performance clutch.

R-200 differential with 3.90 gears, new u-joints, rebuilt half shafts, solid diff mount.

Nissan electronic distributor with a E12-80 ignition module, Standard Plus UC15 12V coil, NKG BPR6ES-11 spark plugs, Standard Plus silicone core A-5 spark plug wires, new fusible links and covers.

New Autocraft Silver 585 CCA battery

I'm located in cambridge and any help as mentioned is appreciated. if someone has a shop they recommend to diagnose/fix this i would love to know so i can get my baby back on the road.

if email is easier my personal email is jason_anaka@rogers.blackberry.net

thank you

Jason

[Darrel]

Check the easy things first. intake and AFM hoses for cracks or loose clamps.

[Marty Rogan]

When it died, did you check to see if you were getting gas? Spark?

What kind of fuel regulator are you using? IF it's the type with a movable dial on the top, I have heard they can sometimes stick. Move the dial min to max a couple of times. Also 7 PSI is way too high for carbs. You only need about 3 PSI, and never more than 5 PSI.

Sounds like the carbs need adjusting too. You want to see a nice tan color on the plugs.

Just some thoughts.

Marty

[Darrel]

I guess I should have read that he had carbs huh?

[=Enigma=]

I'm guessing this is electrical. Poor connection, high resistance, preventing any strong flow of current while under load. Check all your coil connections, as well as the connections to your battery, alternator and starter and fuses and fusible links. Clean em up and tighten them all.

As to why your engine revved to 5000 rpm while you were driving, either you pushed in the clutch, the clutch slipped, or your tire(s) spun. I think this is something we'll never know.

[Chris'sZ]

My '76 quit running after taking off the positive battery cable to test the alternator. I suppose this meens I have a bad alternator, however she won't start now??? The engine turns over just fine and I am getting gas to the injectors. Any suggestions on where to look first???

Thanks,

Chris'Z

[KDMatt]

-to the original poster-

Have you had your clutch/tranny looked at recently? The only way the engine could suddenly 'leap' to 5k Rpm without changing gears or changing speeds is for the clutch to slip (assuming it's in gear, which you said it was). I've never heard of this randomly happening on a bump before, but I suppose anything is possible... from my point of view that's the most likely explanation for the RPM jump.

Did the bottom of the car 'scrape' on this 'crease?' ... maybe the suspension bottomed out and some part of tranny or clutch slave cylinder knicked the ground?

-To second poster (Chris)-

If you're getting fuel and the starter will crank, see if there's spark.

[JimmyZ]

It is remotely possible that your POR15 detached and is blocking your pickup tube in the gas tank during movement. (Kind of like a floating garbage bag) Another fuel pincher is a possible grain of sand/etc in your return line from your SU's. There is a restrictive opening in the return end of the fuel rail. (about the size of a pin)

I wouldn't even want to imagine a safe way to test fuel flow under operating conditions. A pressure guage could be rigged to where you could read it perhaps. (Drive with hood open to read guage possibly.)

2c

Jim

[JimmyZ]

After re-reading the origninal post...

I'm not sure I understand the bit about the RPM jump. The car was in gear with no actual acceleration and decided to rev freely right? Might have a broken/bent shift fork in the tranny??? (Gear might be engaging and disengaging) Any noises/vibes from the tranny during this loss of power. Could it rev freely with the clutch depressed?

If you isolate the tranny from the engine which is causing things to bog down?

Curious

Jim

[JimmyZ]

Check tranny fluid level/drain fluid and check for crunchies.

Once hit half a truck tire at 700 miles on a 3000 mile trip. By the time I was at the halfway point my tranny had pumped enough oil out to damage the bearings and cause the thing to become an efficient metal grinder. As I limped it into Oklahoma City to visit a junkyard it was popping out of gear and I had completely lost the use of 5th gear.

It was beggining to bog down as I reached a realtive's house where I could do the swap. Laughter, amazement ensued when the dead tranny was shook and sounded like a hardware scrap bin inside. It was incredible that it still turned.. A testament to the durability of the 5 speed. Maybe you ran low on tranny fluid too?

[geezer]

It might be a good idea to check and make sure your motor mounts and trans mount are intact. I can't think of anything other than bad mounts causing a sudden rise in RPM's. Coming down hard on a dip in the road with bad mounts could have caused a combination of clutch slippage and a sudden rise in RPM's as you describe. When you find the answer to this mystery make sure you post what you found. Welcome to the forum. Cambridge Custom Chrome is where I get my plating done.

[=Enigma=]

Ron what r u smoking? How in the world could a broken/bad mount cause a sudden rise in RPMs? unless the whole motor or tranny spun around several times at high velocity. I think you'd notice this.