78 280z Severe Driving Problems

[kinser86]

Hey everyone, I have been a long time lurker on many forums and I have decided to post some questions because I am at the point where I believe I need guidance on next steps and want to make the right decision. The car I am working on is a 78 280z California Car. It is not my car, it is my parents car that I bought them as a gift 10 years ago. It has been a long time since I have driven the car so I don’t recall its characteristics but it always had a presence of fuel smell in the exhaust. The car was parked because the fuel smell and rough driving started getting worse. The car then sat for a year and a half and now its time to get it back up and running. All the items addressed have been done within the past four months.

Disclaimer: There is a lot of information here and if I am unclear on anything please let me know. I am trying to get some conversations going and wanted to put my best foot forward.

Symptoms

• Bogging/hesitation/stuttering under any load to the point where the car can’t be driven, can’t emphasize this enough.

• Car idles immaculately

• Backfiring through the AFM

• Fuel smell through exhaust

Current State

• Timing: 10° BTDC

• Idle: 800 RPM

• Aftermarket exhaust header and muffler

• EGR deleted

• Air regulator removed

• Coldstart injector still on rail but disconnected electronically

• Thermotime switch disconnected electronically

Items that have been addressed

• Spark:

  • New Plugs (NGK at .039in gap)

  • New Wires (NGK)

  • New Coil (MSD Blaster)

  • Rebuilt ZX distributor (RockAuto)

    • Vacuum advance confirmed working

    • New Cap

    • New Rotor

• Fuel:

  • New fuel injector connectors

  • Injectors reconditioned from Fuel Injection Services (confirmed working)

  • New Walbro 255 fuel pump

  • Tank removed and checked for rust

  • Fuel hard lines cleared with compressed air

  • New fuel filters (pre and post pump)

  • Inline gauge added between filter and rail

• Air:

  • AFM has been calibrated per atlanticZcar site rebuild guide

    • Bench tested for smooth sweep (open to close)

    • Calibrated spring force with water weights

  • New PCV valve

• Engine:

  • Valves adjusted to:

    • Intake: .008in

    • Exhaust: .010in

  • TDC mark confirmed correct on main pulley

  • Distributer shaft confirmed 11:25 position

  • Leakdown test performed

  • Compression test performed

• Electrical:

  • New coolant sensor

  • New coolant sensor connector

  • New TPS wiring connector

  • Contacts cleaned with deoxit

  • ECU Harness tested in car to EFI Bible specifications

Results

Leak down and compression test performed cold because the vehicle was not running at the time.

The AFM sweep was performed using a 9VDC battery and an arduino. I did two sweeps of the door by hand as smooth and slow as possible. The third sweep I intentionally pulsed the door through the sweep motion by hand to see if something else would happen. I did not see any signs of a bad circuit.

The FSM provides a table relating resistance to temperature for the air temperature sensor and coolant temperature sensor. I generated a chart using this data in both °C(Blue) and °F(Orange). The trend is not linear so a polynomial trend(Thin Orange) was generated so I could plug in a measured value to determine a temperature. The table also provides acceptable ranges within specific temperatures so I added error bars to show this acceptable range. The test environment(Green and Yellow circle) was what the temperature should be and the measured (pink) value was within the error bar at that condition.

I went through the circuit testing per the FSM and found nothing alarming.

Observations

Advancing the timing beyond the timing marks helps but doesn’t resolve the overall issue. Timing at 10° makes the car impossible to drive. Timing at 25°-30° makes it bearable but only above 30% throttle.

Future State

I have worked through what I believe to be the cheapest items to inspect and now believe it is time to find a new AFM and ECU set. Everything appears to be correct and by the book. Should I try to find a 78 280z ECU/AFM for a CA car, or should I find one for any 280z car (non CA). I have toyed with going standalone because at this point I am tired of poking around in the dark trying to troubleshoot this car. I need some assistance from people who have experience with the FI systems on these cars and I don't know anyone locally to reach out to. If I am unclear on something, please ask and I will provide.

[siteunseen]

I'll let the smart members read all the charts but when my '77 had very similar problems I was able to fix it for a $5 volume knob from Radio Shack.  Mine ran like crap up to about 2,500RPM then pull really good.  Here's where i got the idea.  Many have done this so hopefully they can offer better advice.

http://atlanticz.ca/zclub/techtips/tempsensorpot/index.html

I think you'll need the thermotine sensor to function.  That could be the reason for the rich exhaust fumes.

 

[Zed Head]

39 minutes ago, kinser86 said:

78 280z California Car.

Symptoms

• Bogging/hesitation/stuttering under any load to the point where the car can’t be driven, can’t emphasize this enough.

• Car idles immaculately

• Backfiring through the AFM

• Fuel smell through exhaust

 

• Fuel:

  Inline gauge added between filter and rail

• Air:

  • AFM has been calibrated per atlanticZcar site rebuild guide

    • Bench tested for smooth sweep (open to close)

    • Calibrated spring force with water weights

  •  

O. Should I try to find a 78 280z ECU/AFM for a CA car, or should I find one for any 280z car (non CA). I have toyed with going standalone because at this point I am tired of poking around in the dark trying to troubleshoot this car. I need some assistance from people who have experience with the FI systems on these cars and I don't know anyone locally to reach out to. If I am unclear on something, please ask and I will provide.

Wow, that is some diagnostic work.  Did you mark the starting points on your AFM "calibration".  I love the atlanticz site but some of the things on there are not actual factory procedures, but things extrapolated from educated guesses.  The calibration procedure was developed by examining a "known good" AFM and assuming that all AFM's should be like that one.  It might not be right.

I don't see fuel pressure readings although you do have a gauge.

Your symptoms, the popping through the AFM,  have been solved by many of us by adding the "AFM tweak", or potentiometer, to the coolant temperature sensor circuit.  It's described n the atlanticz site also.  I would set your AFM back to the starting point and try the potentiometer.  Something about today's fuel or a general degradation of the AFM circuitry causes much popping and backfiring with 280Z's.

Welcome to the forum.

I see that siteunseen has replied, He mighht be suggesting the smae.

[kinser86]

1 hour ago, siteunseen said:

I'll let the smart members read all the charts but when my '77 had very similar problems I was able to fix it for a $5 volume knob from Radio Shack.  Mine ran like crap up to about 2,500RPM then pull really good.  Here's where i got the idea.  Many have done this so hopefully they can offer better advice.

http://atlanticz.ca/zclub/techtips/tempsensorpot/index.html

I think you'll need the thermotine sensor to function.  That could be the reason for the rich exhaust fumes.

The charts might be overkill, but just trying to throw what I have learned up there to see if anyone else has seen the same thing.

From what I read about the thermotime switch is that it is just an open/close type switch that closes the circuit to the cold start valve. After start, it should not impact the enrichment.

1 hour ago, Zed Head said:

Wow, that is some diagnostic work.  Did you mark the starting points on your AFM "calibration".  I love the atlanticz site but some of the things on there are not actual factory procedures, but things extrapolated from educated guesses.  The calibration procedure was developed by examining a "known good" AFM and assuming that all AFM's should be like that one.  It might not be right.

Thanks, I have been trying to cover my bases and I have seen countless of FI threads with no data supporting any decisions and people ultimately getting pointed back to the EFI bible. I did mark the AFM, ended up adjusting 6 teeth clockwise to achieve 145mL water weights. I can always move it back but the car is acting exactly the same prior to adjustments.

1 hour ago, Zed Head said:

I don't see fuel pressure readings although you do have a gauge.

I need to get the numbers again now that the reconditioned injectors are in the car. They were within spec and even evaluated with the FPR off but I will get numbers next time I am next to the car for diagnostic record purposes.

1 hour ago, Zed Head said:

Your symptoms, the popping through the AFM,  have been solved by many of us by adding the "AFM tweak", or potentiometer, to the coolant temperature sensor circuit.  It's described n the atlanticz site also.  I would set your AFM back to the starting point and try the potentiometer.  Something about today's fuel or a general degradation of the AFM circuitry causes much popping and backfiring with 280Z's.

I have read about this tweak but have always felt it is a band aid to another problem. I ultimately tried taking the car back to zero without any modifications other than some components to see if anything would go away.

1 hour ago, Zed Head said:

Welcome to the forum.

Thanks, I hope to bring more to the forum than my pain and suffering... eventually. ? 

I really want to learn from others experience so I appreciate all the help. If I am wrong about something please correct me! I enjoy how easy it is to support replies with images in this forum, it has made things a lot easier for me. ? 

Edited August 26, 2018 by kinser86
typo

[Zed Head]

1 hour ago, Zed Head said:

Your symptoms, the popping through the AFM,  have been solved by many of us by adding the "AFM tweak", or potentiometer, to the coolant temperature sensor circuit.  It's described n the atlanticz site also.  I would set your AFM back to the starting point and try the potentiometer.  Something about today's fuel or a general degradation of the AFM circuitry causes much popping and backfiring with 280Z's.

All I can do is repeat the above.  I don't think you can get back to "zero" without going back to 1978 and using 1978 fuel formulations with a new 1978 AFM.  One without 40 years of age.  I bought a new MSA AFM and it does run richer than any of the old AFM's I tried.  So, that might be a "back to zero" option, if you want to spend the money.  But the AFM tweak will tell you more about if it's going to work.  Think of the AFM tweak as a diagnostic tool.  Adjusting your AFM would be considered a band-aid by many members.  It was glued to where the factory set it, wasn't it?  Did you break the glue blobs?

You can get your fuel pressure by just running the fuel pump without the engine running.

Generally, though, your popping symptoms are signs of a lean mixture.  So fuel pressure, AFM, and vacuum leaks are where you want to look.  Good luck.

[siteunseen]

And from all I've read the fuel tweak corrects the ECU's OHMZ or resistance? to the coolant sensor. 

When you've got an extra hour this thread is a good read and might light a bulb in your head.

https://www.classiczcars.com/forums/topic/37549-purs-like-a-kitten/

 

[zeeboost]

Check your fuel pressure inline with a gauge between the filter and the rail, verify that it can maintain 35+ psi when loaded up. I've had your same symptom before with 0 psi in the rail. I had no clue how it was idling (possibly secondary source through the charcoal canister...?), but it would sound healthy as a horse until you tried to drive it, then fall flat on its face. To make sure the gauge wasnt broken I used clear vinyl tubing on both sides and sure enough, the air bubbles in there would remain stagnant, yet it would idle until I shut it off.

And of course check for vacuum leaks, etc

[siteunseen]

Was it a bad pump or fuel regulator, maybe a cruddy tank? Your fix can help us all in  the future.

[kinser86]

1 hour ago, Zed Head said:

All I can do is repeat the above.  I don't think you can get back to "zero" without going back to 1978 and using 1978 fuel formulations with a new 1978 AFM.  One without 40 years of age.  I bought a new MSA AFM and it does run richer than any of the old AFM's I tried.  So, that might be a "back to zero" option, if you want to spend the money.  But the AFM tweak will tell you more about if it's going to work.  Think of the AFM tweak as a diagnostic tool.  Adjusting your AFM would be considered a band-aid by many members.  It was glued to where the factory set it, wasn't it?  Did you break the glue blobs?

You can get your fuel pressure by just running the fuel pump without the engine running.

 Generally, though, your popping symptoms are signs of a lean mixture.  So fuel pressure, AFM, and vacuum leaks are where you want to look.  Good luck.

Correct. Since the cars history is unknown, I never knew who's hands were where. The glue blob on the AFM was already off and the cover had a different adhesive on it when removed. I had to assume someone had been in there tweaking something prior to me so given that, I adjusted per the atlanticz car site. Again, I can move it back to the previous setting no problem.

44 minutes ago, siteunseen said:

And from all I've read the fuel tweak corrects the ECU's OHMZ or resistance? to the coolant sensor. 

When you've got an extra hour this thread is a good read and might light a bulb in your head.

 https://www.classiczcars.com/forums/topic/37549-purs-like-a-kitten/

 

Excellent! I will take the dive!

30 minutes ago, zeeboost said:

Check your fuel pressure inline with a gauge between the filter and the rail, verify that it can maintain 35+ psi when loaded up. I've had your same symptom before with 0 psi in the rail. I had no clue how it was idling (possibly secondary source through the charcoal canister...?), but it would sound healthy as a horse until you tried to drive it, then fall flat on its face. To make sure the gauge wasnt broken I used clear vinyl tubing on both sides and sure enough, the air bubbles in there would remain stagnant, yet it would idle until I shut it off.

And of course check for vacuum leaks, etc

I will get some fuel pressure numbers this week. The car is not at my house so I make plans of what I want to measure and test then go out there and go through those steps. If I pull the breather line off the valve cover, the car idle takes a heavy dive and almost dies but I will get better numbers once my vacuum gauge comes in. The healthy as a horse and falling flat comment represents this car very well with a lot of timing on the car.

2 minutes ago, siteunseen said:

Was it a bad pump or fuel regulator, maybe a cruddy tank? Your fix can help us all in  the future.

The tank wasn't bad at all. There was already filter between the tank and filter that was replaced. There was no filter inside the fuel pump inlet when removed from the car. At this point I was chasing potential bad fuel having the car sit for a while so I opted to change it out just in case. This is when I also blew all the fuel lines out from the back of the car up to the engine bay using compressed air thinking there was crud in the lines. There were no visible signs of debris in the lines when cleared out.

I have a vacuum gauge on order and my next plan is to record the following data points:

• Fuel Pressure
• Vacuum Pressure

I can always add more items to the list ? 

[Zed Head]

8 minutes ago, kinser86 said:

the car idle takes a heavy dive and almost dies but I will get better numbers once my vacuum gauge comes in. The healthy as a horse and falling flat comment represents this car very well with a lot of timing on the car.

The engines are very sensitive to even small vacuum leaks.  Removing the PCV hose is a huge one and lets umetered air in.  The engine leans out when that happens.  The vacuum gauge might find large leaks.

One test for vacuum leaks that I use is to run the idle speed screw all the way down.  The engine should die from lack of air.  If it doesn't there's a vacuum leak.  If it does, any leaks are probably very small.

Good luck.

Edited August 26, 2018 by Zed Head

[rcb280z]

I would definitely put the AFM back to where it was when you bought it. And then install the potentiometer. Play with that and see if you can get her to run better.

Like everyone is saying, check fuel pressure and look for vacuum leaks. I like Zed Heads test of running the idle screw all the down. But if you do have vacuum leaks they may be hard to find if you can't keep her running. I've been known to unscrew and lift the oil fill cap just a little to test for vacuum leaks. If there is no change or very little change you may have vacuum leaks.

I didn't see this anywhere but have you pulled the plugs to see how they are burning? That will also tell you a lot.

Edited August 27, 2018 by rcb280z

[Captain Obvious]

Nice work so far. Taking the bull by the horns and not wanting to be simply referred back to the FSM.

Here's a chart I whipped up a while back to evaluate the resistance measurements from the air and water temp sensors:

*This chart was created using the Stienhart-Hart Equation with coefficients derived from data points in the manual.