Need some invice on my 78 280z..

[Shade133]

yesterday i worked on it all day. before today it would miss, spit and sputter and have 0 power while under a load.

this is what i did and the outcome

pulled oil pump and put to TDC and timing was set right.

Found out spark plugs were in the wrong order was set to go 153624 going clockwise not counter clockwise, so i fixed that.

pulled all injectors and replaced with new ones.

pulled all spark plugs (sorta new) and cleaned and re gapped

adjusted TPS sensor,

fixed intake leak between AFM and intake.

set timing with timing light to 10 degrees BTDC

started her up and she idled perfect.

my question now is it has a sputter at partial throttle and no power under a load.

it has somewhat power at half to full throttle but the RPM's hit a wall at 4.5k RPM's

what could cause this and what should i do next? good fuel, good spar, timing right, good air.

whats next?

the one thing im worried about is the position of the butterfly, vs the idle screw. would this effect anything other then idle? because its been messed with quite a bit.

please let me know what i could do so i can get this thing on the road ASAP!

EDIT: made a typo on my subject line. it was supposed to say "advice"

Edited August 23, 2010 by Shade133

[FastWoman]

I think the butterfly closes all the way anyway. The idle screw simply sets the bypass opening, but it shouldn't affect anything other than the idle.

A note about timing: For whatever reason, my '78 engine doesn't seem to like the factory spec of 10 deg BTDC. Nobody has been able to tell me yet whether it is normal for the RPMs to bog quite a bit at this setting, vs. a few degrees more advanced. I run the engine at 10 deg, per spec, but it might run quite a bit better at 13 deg. Dunno. I look forward to reading other people's comments on timing, as I often get no answers to the questions I ask.

Just a guess about your problem: It sounds like your engine might be fuel starved. Check your airflow meter to make sure the vane moves freely, and also open up the black box on its side, so that you can clean the electrical contacts (wipers) with WD-40. I'd almost bet money the problem is something to do with the airflow meter.

And since you have a '78, any idea about my check valve?

[Shade133]

ive read about your check valve and i honestly dont think they pose a performance issue when bad. emissions, maybe but performance i dont think so.

If im thinking about the right thing. the little round thing that is on some of the vacume lines that should allow vacume one way but not the other or something like that?

also i might be totally confused on what your talking about hense my charcol canester is by my fuel filter, but you said something about it being by your fuel pump when my fuel pump is by my gas tank. so i might just be confused on that subject.

and i think your right about the timing. mine always runs better advanced so i might just try advancing it and see what happens. as for it being fuel starved i wasnt able to check my fuel pressure that night but was one of the things i wanted to do.

as for the afm, i wouldnt be suprised if that was the issue. the door on it moves freely but the contacts inside might be nasty. its never been opened so who knows. i got some carb cleaner and wd-40 wich would clean better?

[FastWoman]

I know the WD-40 is safe, as long as you don't go crazy with it and clean up the excess before sealing the box back up. You'd of course need to clean any oil off of the housing to get the sealant to stick. The best stuff to use would be Deoxit.

Fuel starvation could be a fuel pump issue. The fuel pressure is actually regulated in relation to intake manifold vacuum, so the fuel pump has to deliver the highest pressure to the fuel rail when engine vacuum is weak (e.g. engine under load). If it can't deliver that pressure, then the engine would be starved for fuel. Perhaps you could also have a clogged filter that would limit flow rate to the fuel rail, causing fuel supply to choke up under load. Of course a pressure reading would provide that info. I don't think it could be clogged injectors, as they are on/off. The longer they are on, the more fuel they will deliver. If they can deliver a little fuel, they can also deliver a lot of fuel, depending on the pulse duration.

[Shade133]

Ya plus the injectors are new .

as for fuel filter. it looks new and the guy said he replaced it right before he sold it to me, ill replace it again just for kicks and giggles. as the pump. you got a very good point here and i want to check the fuel rail pressure now!

would i want to check the pressure with the engine off and the key on after the pump primes? or should i do it while idling or under a load?

[FastWoman]

Yes, check fuel pressure with the engine stopped. That way there will be no intake vacuum, so the fuel pressure will be at its maximum in relation to atmospheric pressure.

I suppose there's also good reason to check fuel pressure with the engine under load. (Simply revving the engine briefly at WOT should tell you what you need to know.) If the pump output is inadequate, and if you dump fuel from the fuel rail through the injectors, then the pump might not be able to pump enough fuel to keep the pressure up. If you can observe the fuel pressure and manifold vacuum while the engine is sputtering/hesitating, you should have all the info you need to determine whether the fuel pump is at fault.

BTW, the filter isn't any big thing. I think it's $13 at your local auto parts store.

[Shade133]

ya the fuel filter is no biggy i just never replaced it due to it looking new and the guy told me it was new.

ill check the fuel pressure and clean the afm and get back to you!

[Nazgul280]

Shade,

Are you saying the engine won't rev past 4500 RPM? No power is one thing, but not revving to red-line is another.

Honestly, the only thing that keeps an engine from actually revving is airflow (as long as there is fuel and spark and the firing order is correct, wink wink). When I built my engine, I had a custom intake manifold made, and it was made very poorly. It had so many air leaks that the first time I started it up it shot right up to 4500 rpm and stayed there.

I am wondering if the flap is opening correctly, or if your fuel pressure is dropping. If you can see the pressure and it is fine, and the AFM is working correctly.

I would take ohmmeter readings as per the Service Manual on the AFM and make sure they are within specs (there are several). I know a lot of people that had to get another AFM because theirs failed the test.

So, my priorities would be:

Fuel pressure

AFM readings

and if that all checks, find a spare ECU to borrow and hook it up to your Z to see if there is any change. They have proven reliable even after 30 years but it is something to consider.

I have a fuel rail from a 77/78 that still has the pressure regulator on it, so if it turns out your fuel pressure is the problem, just email me and I will mail it to you.

Keep us posted,

-Dana

Edited August 31, 2010 by Nazgul280

[Shade133]

Thanks a lot Dana! i plan to check the fuel pressure asap. and the butterfly in the throttle body is something im concerned about. it has been messed with and i cant find anywhere that tells me how to adjust it or if it is even a big deal to adjust it as long as it idles fine. (which it does) as far as the AFM i do want to check that because seeing whats been done to this thing i doubt it has been left alone.

hopefully this weekend i can check some stuff out and get back to you guys!

thanks for the info!

[Nazgul280]

as far as the AFM i do want to check that because seeing whats been done to this thing i doubt it has been left alone.

Here you go Shade, this is probably the single most useful source in the Z car world for troubleshooting a 280Z:

http://www.atlanticz.ca/zclub/techtips/EFI&fuel.htm

And here is the main page:

http://www.atlanticz.ca/zclub/techtips/

Read it and follow it and you will most likely find the problem this weekend!

PS: as far as the Throttle Body is concerned, all you can do is make sure it's metering the proper amount of air for a smooth idle, and you can take the boot off and have someone work the throttle to see if it is opening and closing correctly. Usually there is years of gunk around the butterfly, so it won't hurt to remove the TB and clean the throat and butterfly with some Seafoam and a fine steel wool.

[Shade133]

will do thanks a bunch!

[draztik280]

I don't know if anyone have this issue on my 77. Whenever I start the car first thing in the morning while the engine is cold, the rpm drops below 500 and shuts off. Then I have to start again. This happens 2 or 3 times until the engine warms up.

Then while at cruising speed, Car sometimes stall at 4th or 5 gear. Then I need to change to a lower gear able to start the engine back up.

The car has no problem revving past 4k or any rpm at all.

I may check the TPS and see if the it's the problem.