Jump to content

marcuspoccia

'78 280z Running Lean?, lack of power

Recommended Posts

After sitting for about 20 yrs in a no-start condition, we have finally gotten our z running once again. In terms of the fuel injection system, the fuel pump(dead) and air flow meter(glue holding it together let go and let in lots of unmeasured air) have been replaced so far. After getting it started and letting it run well a few times, we decided to take it up and down our flat road, with less than a mile of driving. As the engine comes to operating temp, it loses power under load. In neutral/with the clutch in, it seems to healthily rev without stalling out. However, in gear, if more than about a quarter throttle is applied, the engine gives out, eventually coming to a point where it has no power to drive the car back in the garage, but still revs out fairly normal. After cooling, it can be taken out the next day to do the same, and progressively lose power as the engine warms. 

 

From pulling the plugs, it seems the engine runs lean. I have seen that it could possibly be the water temp sensor? How can I test this(does anyone have a link to a step by step guide? I can't seem to find it in the manuals that I have)? Does the new air flow meter need to be adjusted? Also, I have not gotten a fuel pressure reading yet, but it is a new pump. 

 

In summary, runs great while parked, has no power to drive after coming up to temp. I am a beginner, so I am struggling with diagnosing this, looking for some guidance! Thanks!

Share this post


Link to post
Share on other sites

http://www.atlanticz.ca/zclub/techtips/efisystem/280zfuelinjectionbook.pdf

Has the fuel tank been drained, look for signs of rust particles in old fuel?  Fuel filer replaced?  Afm to throttle body boot replaced?  Clean all efi connections & grounds in engine bay.    A manifold vacuum test & fuel pressure test would tell you alot.

Good luck with going thru system.  It is simple, just be methodical going thru it.

 

Share this post


Link to post
Share on other sites
2 hours ago, marcuspoccia said:

 As the engine comes to operating temp, it loses power under load. In neutral/with the clutch in, it seems to healthily rev without stalling out. However, in gear, if more than about a quarter throttle is applied, the engine gives out, eventually coming to a point where it has no power to drive the car back in the garage, but still revs out fairly normal. After cooling, it can be taken out the next day to do the same, and progressively lose power as the engine warms. 

From pulling the plugs, it seems the engine runs lean.

Also, I have not gotten a fuel pressure reading yet, but it is a new pump. 

If the plugs are new you can't really tell if it's running lean.  EFI engines are designed to run clean, the plugs don't brown up like an old carb'ed engine might.

Could be several things.  You need to know fuel pressure at the rail while the problem happens.  Leave a gauge on and check it when it loses power.  Take the black cover off of the side of the AFM and make sure the counterweight is moving with air flow.  It might be stuck.  Usually when these engines run lean you get popping back through the intake manifold.  Popping and bucking, very annoying.  Just a lack of power sounds more like air flow.

You can check the coolant temperature sensor with an ohm-meter, at the ECU connection.  There's a chart in the FSM.

Don't forget the EGR system.  I think that it is actuated after the engine warms up.

Share this post


Link to post
Share on other sites

How old is the fuel filter? It does good after cooling? OR the sediment in the filter falls down.

I went through that with mine. Ran good for 5 mintues then I walk home to get another car and tool bag. Get back and it fires right up, 5 minutes later "wash rinse and repeat".

Share this post


Link to post
Share on other sites

fuel tank has been drained, brand new filter, lines were blown through with compressed air when the tank was emptied, along with again today. all connections in the engine bay have been cleaned. Working on renting a kit to test fuel pressure and vacuum from the parts store. I have gone through every test starting on page 45 of the fuel injection bible, but was unable to complete the test on p53. Pin 20 does not have a connection, does the 1978 have a different circuit? It is the air flow meter fuel pump contact circuit. As far as removing the black cover on the AFM, it is newly refurbished from thezstore.com, and looks like its glued on. Do I just pry it off? I really dont want to break it. And what should I use to glue it back on? Finally, according to the tests I did from the bible, the water temp sensor works fine. Probably could use a new afm-throttle body boot, its got a big crack but I didn't see any that went fully through. 

Share this post


Link to post
Share on other sites

Good job.   Yes, the 78 fuel pump circuit was moved to the oil pressure sender, likely working correctly if car starts & runs.  I would leave the afm cover alone, probably ok and may void warranty if tampered with.   There is a later 1980 efi bible which covers some of the subtle changes since 75 or the 78 factory shop manual.

Use some starter fluid or similar and with car idling, spray around afm rubber boot & listen for idle rpm change.  If leaking & allowing in unmetered air, idle will speed up.  Also spray around injector seals & vacuum lines listening for change.

Fuel pressure should be about 28 lbs at idle,  vacuum about 18"

Share this post


Link to post
Share on other sites
4 minutes ago, S30Driver said:

Good job.   Yes, the 78 fuel pump circuit was moved to the oil pressure sender, likely working correctly if car starts & runs.  I would leave the afm cover alone, probably ok and may void warranty if tampered with.   There is a later 1980 efi bible which covers some of the subtle changes since 75 or the 78 factory shop manual.

Use some starter fluid or similar and with car idling, spray around afm rubber boot & listen for idle rpm change.  If leaking & allowing in unmetered air, idle will speed up.  Also spray around injector seals & vacuum lines listening for change.

Fuel pressure should be about 28 lbs at idle,  vacuum about 18"

haha. as you were typing this i took off the afm boot. theres a pretty good hole in it at the bend that i can stick my finger through. this wasnt there when I replaced the AFM itself, so I figured i would deal with it later if it broke since it was not in great shape. Going to order a new one. Should I continue to diagnose or should this be the fix? I really hope this does it. Got a week and a half before I go back to college! 

Share this post


Link to post
Share on other sites

hole in AFM to TB boot will cause lean run, so don't mess with it until that is fixed. Make sure you have the spring wire inner support inside the boot, keeps it from crimping shut. It looks like a wire hoop that fits INSIDE the boot.

Edited by Dave WM

Share this post


Link to post
Share on other sites
15 minutes ago, Dave WM said:

hole in AFM to TB boot will cause lean run, so don't mess with it until that is fixed. Make sure you have the spring wire inner support inside the boot, keeps it from crimping shut. It looks like a wire hoop that fits INSIDE the boot.

wow. good call, THANK YOU! I had noticed that inside there, but would not have thought to switch it over. Thanks to everyone here, this was really helpful and learned a ton. 

  • Like 1

Share this post


Link to post
Share on other sites
26 minutes ago, marcuspoccia said:

 Should I continue to diagnose or should this be the fix? I really hope this does it. Got a week and a half before I go back to college! 

Just complete the fp and vacuum tests and go from there.    Dave is right, replace that boot...

Share this post


Link to post
Share on other sites

Hi again. Since my last update, I received and replaced the afm-throttle body boot, and tested vacuum/ fuel pressure. The boot did not fix the problem, and the testing showed no signs of an issue there. I have spent time cleaning connections, like grounds, and the connections to the sensors on the thermostat housing. 

 

let the car idle for a long time the other night, and could rev it out with no stumble or hesitation. 

Last night took it back out onto my road, and proceeded to become undrivable once again once it warmed up. 

Im not sure what to do

Share this post


Link to post
Share on other sites
1 hour ago, marcuspoccia said:

Last night took it back out onto my road, and proceeded to become undrivable once again once it warmed up. 

Im not sure what to do

What was the measured fuel pressure when the problem happened?  Does the engine have EGR?

It's hard to solve problems with the EFI system unless you're very methodical, or lucky.

 

Share this post


Link to post
Share on other sites

Looks like I got lucky. After cleaning many electrical connections, along with fiddling with vacuum hose line connections, i have got the car running pretty good. over the last three days, ive put a few hours of driving around the neighborhood and cant get it to die. Still experiencing a slight skip under heavy heavy acceleration, but i am glad it is much better than it was. Now its time to pack up and head to college, returning to the project over winter break. thank you all for the help

  • Like 2

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.