76 280Z fuel injected, intake valves stuck open

[poolman]

Hi Z guys, I am friends with 2 guys trying to get a 76 280 out of mothballs. One guy's wife owns the car which sat indoors for about 6 years and was not touched. The other guy is a professional mechanic. Car is in good shape and she has had it since it was new.

Fluids were drained and refilled, valve cover removed top end and timing chain lubricated, fuel lines cleaned, new fuel pump and filter, fresh gas.

Engine would turn over, but not start, injectors tested found to be bad, new injectors installed, ECU and MAS tested and found to be good.

Engine started ran pretty good, slight miss/hesitation at part throttle. Ran engine about an hour, shut off, changed oil and filter.

The next day, tried to start engine and made a banging noise, so stopped. Removed valve cover and found #2 intake valve stuck open.

Removed head, found the valve has been hit by piston and bent, piston ok. Head rebuilt with all new intake valves and new guide in #2 intake. Head looked good, valve endplay good in all guides. Valve springs good condition. Exhaust valves cleaned, lapped, and reused.

Put engine back together, fired right up, ran great except for slight miss/hesitation just at part throttle opening. Engine ran for about 2 hours that day, normal coolant temp, normal oil pressure, timing was set, valves were adjusted after warmup etc. Engine was started 4 or 5 times over about 6 hours with no problems.

Yesterday tried to start engine to move the car to start work on brakes, banging noise again. Removed valve cover, all six intake valve stuck open. Looks like plenty of oil on the head, new valve guide seals were installed, ?

Sorry for the long post, but hopefully someone has a thought or suggestion... or maybe has seen this before.

thanks

Dennis

[FastWoman]

That happened to me once with my '75. After not running the car for a year, I fired it up. Ran a bit poorly, but not bad. Ran a couple of errands, returned home. The next day all my valves were stuck, valve train fell apart, banging and snapping, and the head had to be rebuilt. The mechanic said my gas had gone REALLY bad -- that it drained from the tank like syrup. My theory is that someone had put sugar in my tank (for the gas to be that thick).

[TomoHawk]

I didn't know the '76 had an MAS?

Edited August 17, 2010 by TomoHawk

[sblake01]

I didn't know the '76 had an MAS?

[AZMarty]

Actually it has an air-flow sensor that operates with an air vane (damper flap) and not a MAF as is used in more modern systems. The system in the early Z is a licensed version of the Bosch L-Jetronic.

[TomoHawk]

I think we, or almost all of us with the L28E engines, know that. But occasionally, an MAF or MAS sneaks in as it did here. Hopefully, our OP is updated on that.

One person on another website, asked me to point out where the MAP is, then earnestly claimed that the E.F.I. engine cannot operate without one.

[Nigel1943]

Hi Z guys, I am friends with 2 guys trying to get a 76 280 out of mothballs. One guy's wife owns the car which sat indoors for about 6 years and was not touched. The other guy is a professional mechanic. Car is in good shape and she has had it since it was new.

Fluids were drained and refilled, valve cover removed top end and timing chain lubricated, fuel lines cleaned, new fuel pump and filter, fresh gas.

Engine would turn over, but not start, injectors tested found to be bad, new injectors installed, ECU and MAS tested and found to be good.

Engine started ran pretty good, slight miss/hesitation at part throttle. Ran engine about an hour, shut off, changed oil and filter.

The next day, tried to start engine and made a banging noise, so stopped. Removed valve cover and found #2 intake valve stuck open.

Removed head, found the valve has been hit by piston and bent, piston ok. Head rebuilt with all new intake valves and new guide in #2 intake. Head looked good, valve endplay good in all guides. Valve springs good condition. Exhaust valves cleaned, lapped, and reused.

Put engine back together, fired right up, ran great except for slight miss/hesitation just at part throttle opening. Engine ran for about 2 hours that day, normal coolant temp, normal oil pressure, timing was set, valves were adjusted after warmup etc. Engine was started 4 or 5 times over about 6 hours with no problems.

Yesterday tried to start engine to move the car to start work on brakes, banging noise again. Removed valve cover, all six intake valve stuck open. Looks like plenty of oil on the head, new valve guide seals were installed, ?

Sorry for the long post, but hopefully someone has a thought or suggestion... or maybe has seen this before.

thanks

Dennis

Sounds like a camshaft timing issue. Is the dowel in place on the camshaft sprocket ? Other possibles are a defunct tensioner or a broken key on the crankshaft sprocket.

[poolman]

Sounds like a camshaft timing issue. Is the dowel in place on the camshaft sprocket ? Other possibles are a defunct tensioner or a broken key on the crankshaft sprocket.

Thanks for a place to start, everything looked ok when the head was off and as it was reassembled, but will start with this. Thanks again.

Oh, and the engine does have the vane type air flow meter, not a MAS as I stated previously, used a generic term.

[sblake01]

Oh, and the engine does have the vane type air flow meter, not a MAS as I stated previously, used a generic term.

MAS would not be a generic term for an AFM. Two different things.

[Nazgul280]

I'm thinking the tension on the valves is gone? Buy new springs?

[doradox]

That happened to me once with my '75. After not running the car for a year, I fired it up. Ran a bit poorly, but not bad. Ran a couple of errands, returned home. The next day all my valves were stuck, valve train fell apart, banging and snapping, and the head had to be rebuilt. The mechanic said my gas had gone REALLY bad -- that it drained from the tank like syrup. My theory is that someone had put sugar in my tank (for the gas to be that thick).

http://www.snopes.com/autos/grace/sugar.asp

[FastWoman]

Thanks, Doradox! I feel a bit better knowing that.