1977 280z EFI Nightmare

[ckurtz2]

Hey guys thanks for the tips. I found that other adjustment screw and it helped give me lots more range. The firing order, distributor allignment, etc are all correct. I decided to swap the spark plugs, because the old ones were fouled from my AFM "diagnosing". Anyhow, she runs much better, especially when cold.

A few things to note, it takes a long time to start (I am thinking that the fuel pressure bleeds off) and it runs much better when cold. However when warm there is a very clear missfire happening and very, very occasional pops out the intake, but the new spark plugs mostly fixed that. It just sounds like its stumbling. I have done tons of little tricks and tests to rule out spark, which is completely fine. I also believe the timing is almost good, as I have the distributor set where it runs best. Now the missfire and stumbling baffles me, but I have some questions.

First, I reppined the fuel injector connectors for new ones and I am worried that I have every single connector exactly backwards. What I mean by that is that the two wires were swapped potentially. Would this affect how the injector fires. Online has many different opinions as they are just "solenoids" and will work no matter what. Other people say that if they are backwards they may fire out of phase. 

Second, does it matter which injector connector goes where. I remember reading somewhere that it didn't matter on these old z cars.

Last of all, I was wondering if someone could test their own car with the ignition on, and see which port in your injector connector is the switched positive and which is ground. That way I can determine if mine are backwards.

We are so close to correcting all the millions of mistakes I made on this car originally, I see the endzone.

 

[Zed Head]

27 minutes ago, ckurtz2 said:

Online has many different opinions as they are just "solenoids" and will work no matter what.

This is correct.

27 minutes ago, ckurtz2 said:

does it matter which injector connector goes where. I remember reading somewhere that it didn't matter on these old z cars.

The injectors all squirt at the same time in the 280Z's.  Swapping injector plugs is actually an easy way to test for spark or injector problems on a dead cylinder.

[ckurtz2]

Ok, interesting.

Any reasons why when idling it sounds like it's stumbling? When really warm, but still within a good temp range when I press the gas it almost surges. It will go up in rpm, fall, then go up again slowly getting higher, or it will just plain backfire out the intake after idling for a few minutes and pressing the accelerator. Cold though, the engine seems to run really well with way less stumbling. Also when pulling the injectors while the car is running I have noticed some cylinders make more of a difference then others, same with spark. However all cylinders seem to at least make a minute difference. Needs to run longer before I can inspect the plugs and see what secrets they share. 

[Patcon]

I think one of the most helpful tools on the fuel injected cars is a wideband O2 sensor. It make diagnostics much easier

[Reptoid Overlords]

Not to take attention away from the task at hand, but have we verified proper TVS adjustment and checked for any moisture inside the casing?  I'm not entirely sure that these symptoms are a result of that component, but I remember a stumble due to moisture/improper adjustment of my original TVS years ago..

[Zed Head]

2 hours ago, ckurtz2 said:

Needs to run longer before I can inspect the plugs and see what secrets they share. 

Have you taken it out for a drive?  Given it a good thrashing?  These engines like that.

Engine performance with no load only tells you so much.  

[ckurtz2]

1 hour ago, Zed Head said:

Have you taken it out for a drive?  Given it a good thrashing?  These engines like that.

Engine performance with no load only tells you so much.  

Before you commented this I made it up in my mind to try and go give her a rip. No hydraulic brakes, just the good ole handbrake and an empty neighborhood. So i gently drove onto the street and man things went fantastic. My clutch noise went away and I could feel that she wanted to go. So I lightly pressed on the gas and I could hear a faint clanking. Hmmm what could that be. So I listened close and couldn't tell if it was coming from the front or the rear of the car. So I decided either the driveshaft had a weird u-joint problem or the engine had a small ping. Only one way to test it, so I pushed the car to about 3/4 throttle ready to shoot for the moon and all I heard was hell from the engine. Had great torque though. Anyways, the motor is pinging like a mad man, so I think I had a little too much advance:( Fingers crossed no serious damage was done, but man I never want to hear that sound again in 1000 years. I will have to go in with a small camera and check the pistons, valves, and other doo dads out. 

So @Zed Headshould I try that potentiometer trick mentioned earlier? I think that it is not a timing problem anymore, and instead I have been compensating another problem with timing. Vacuum and fuel is solid. New AFM and water temp sensor. Not much else I would be able to try. 

Also the TVS sensor works as it should. 

[Zed Head]

On 3/28/2021 at 2:58 PM, ckurtz2 said:

rebuilt head

You had so much new stuff from the beginning and odd problems that it might be worthwhile to just go back and fill in some details.  Who rebuilt the head?  What did they do to it?  Is the engine 1977 stock with dished pistons?  Etc.

Pinging is usually caused by advanced timing and/or high compression ratio.  Seems like you set your timing on how it runs with no load.  You didn't give a number though, for timing at idle.  A number from your timing light would be good to have, plus verification that the advance mechanisms work as designed.

Seems like you're close.  If it's drivable that's a pretty good sign.  Might be worthwhile to get back under the valve cover and recheck valve lash since it's a "new" head".  Things wear in.

It might be just me, but I tend to create a big circle of things I check when I have engine problems.  Lots of verification of things I've already looked at before.

[ckurtz2]

@Zed Head You are right, it won't take too long for me to verify and readjust a few things. When I said a rebuilt head I meant that I took it off and removed the cam and cam towers. Sent it to a machine shop where the cleaned it, shaved a little of the bottom to flatten it, and then did a valve job with new valve seals. I then re installed the cam and so on. I can get you officially timing readings later this week, but I am likely to change where it is at knowing that the car has a stock shortblock so the compression ratio isn't causing the issue.  A simple question I have is which way turning the distributor advances or retards the timing. I had mine turned as far as it could go clockwise on both adjustment points. 

it does have the stock dished pistons and they looked good as new once I wiped all the carbon off.

How do I check the advance mechanisms to see if they work properly? 

Also to see if the potentiometer trick would work without doing it, should I adjust the AFM idle mixture to test and see how much better it would run at idle with a slightly richer or leaner mixture?

[siteunseen]

For me to do the coolant temp tweak my car ran like crap up to 2,500 rpm then ran good. It would buck and spit and sputter starting off then when I got it over 2,500 it did good with that much load I guess?

A trained Nissan guy from the 80s I know worked on it but couldn't figure it out. He didn't know about the coolant temp tweak but he did clamp off the return line coming off the FPR and said it ran much better. Talked about a rising rate pressure regulator, $200. I started reading on here and found Blue's Tech Tip. Went to Radio Shack when they still existed and bought a volume knob for $5. Installed it like Blue showed and bam! new car. Still have that volume knob in the passenger's floor board. It's fun playing with as I drive down the interstate. I can control the engine's temp gauge, get it lean and improve the MPGs or flood it out and stall the car.

Try clamping off the return line. Not completely just almost. 

[Zed Head]

11 hours ago, ckurtz2 said:

A simple question I have is which way turning the distributor advances or retards the timing.

 

11 hours ago, ckurtz2 said:

How do I check the advance mechanisms to see if they work properly?

You can do a lot with a timing light.  Connect the light, start the engine, watch the light move as you turn the distributor.

Disconnect the vacuum advance hose and rev the engine.  Timing should advance (more degrees on the damper pulley as you watch the light) as RPM increase.

Let the engine run at a speed slightly above idle (so that the ported vacuum will be applied) and reconnect the vacuum advance hose.  Timing should advance considerably once vacuum is applied and drop when the hose is disconnected.

Basically, you'll be leaning over a hot noisy engine watching the timing light flashes on the damper pulley while you work the throttle and disconnect/reconnect hoses.  It's fun.

Edited May 18, 2021 by Zed Head

[ckurtz2]

Thank you for all the advice, I just got outside and gave everything a try.

To confirm, when I pinch the return line it definetly likes more fuel. I accentuated this when I lowered the idle rpm and could really notice the stumble and chop from the motor and exhaust. I then pinched the line about 4/5 of the way and it smoothed out significantly. However, it did still have a small stumble.

Regarding timing, my light says that it is firing 18deg advanced. Interesting thing is at idle the timing read the same with or without vac advance. In addition without the vac advance plugged in when i revved the car the timing advanced further anyways and then came back. What could that mean? Essentially, the vac advance connected or disconnected made no difference. Even more interestingly when I put my finger over the hose that should be holding the vacuum against the dizzy vac advance I feel almost no suction. I tried other vacuum ports around the engine and I do feel suction there. Also removing and connecting the hose made no difference in how the engine ran. 

I tuned the advance to about 10btdc to prevent pinging for now. 

At this setting it seems to idle just a tad smoother but surges when initially revving.

Another thing I noticed is that the rotor has slop. Not the rotor itself but the shaft it is connected to. It is radial slop, so I can twist it about 1/4 in each way. I also can pull it further one way which I assume is the vac advance function. 

Here are some photos of inside the dizzy

I am lost here on what is going on with the vac advance and dizzy.