78 280z Severe Driving Problems

[Captain Obvious]

I got one basic question to start... Do you think you are running rich, or running lean?

[siteunseen]

He said he has strong exhaust fumes but it pops through the AFM so I'd do what Bob says above, shows us your tips. ?

[Dave WM]

sure sounds like a fuel pressure issue to me. I assume the temp sensor resistance check was done at the ECU?

I don't know why you deleted the CSV, unless you never plan to travel north. those compression figures look too high seems odd. for a stock engine.

I agree with the old school approach for reading the plugs.

Edited August 27, 2018 by Dave WM

[Zed Head]

23 hours ago, kinser86 said:

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.

I think that CO is referring to part of the original problem, the reason for parking it, above.  I saw the same conflict.  The question might be what "rough driving" means.

It's a dilemma because it might have just needed a good tuneup, if it was running well before.  The OP was pondering buying a new AFM, after "calibrating" the existing one.  So the $5 AFM tweak would be a good diagnostic tool.  It might not solve the popping problem, but if it doesn't a new AFM probably won't either.

The basics need to be covered first though, like fuel pressure.  Get it driveable, then worry about gas smell, seems reasonable.  A non-drivable car with clean exhaust isn't very valuable.

There are other ways to get backfiring, like cross-firing plug wires.

[Dave WM]

forgot to ask, how did the plug parts look before deoxit? bad green corrosion can travel up the wire under insulation. Also always a good thing to check is grounds and fuse links for solid connections. If you can make it "run rough" by revving it up, try listening to the injectors with a mech stethoscope. I assume the injectors are the stock ones that came with the car?

[kinser86]

A lot of responses.

On 8/26/2018 at 5:14 PM, siteunseen said:

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

There are a lot of parallels between the driving characteristics described by FastWoman and the car I am working on. I am going to add a potentiometer and tinker accordingly to see if it makes an impact.

20 hours ago, Captain Obvious said:

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.

Awesome. After reading about the Steinhart-Hart equation, I calculated the constants and now have a chart of my own to play with.

20 hours ago, Captain Obvious said:

I got one basic question to start... Do you think you are running rich, or running lean?

Given the symptoms of the engine, lean.

4 hours ago, siteunseen said:

He said he has strong exhaust fumes but it pops through the AFM so I'd do what Bob says above, shows us your tips. ?

I have never been an expert spark plug whisperer but I will add 'Pictures of tips' to my to-do list.

3 hours ago, Dave WM said:

sure sounds like a fuel pressure issue to me. I assume the temp sensor resistance check was done at the ECU?

I don't know why you deleted the CSV, unless you never plan to travel north. those compression figures look too high seems odd. for a stock engine.

I agree with the old school approach for reading the plugs.

Resistances were checked through the harness at the ECU and at the sensor. I agree the compression numbers seem high, the engine was cold. I have not run one with a warm block but I can add it to the to-do list.

3 hours ago, Zed Head said:

I think that CO is referring to part of the original problem, the reason for parking it, above.  I saw the same conflict.  The question might be what "rough driving" means.

It's a dilemma because it might have just needed a good tuneup, if it was running well before.  The OP was pondering buying a new AFM, after "calibrating" the existing one.  So the $5 AFM tweak would be a good diagnostic tool.  It might not solve the popping problem, but if it doesn't a new AFM probably won't either.

The basics need to be covered first though, like fuel pressure.  Get it driveable, then worry about gas smell, seems reasonable.  A non-drivable car with clean exhaust isn't very valuable.

There are other ways to get backfiring, like cross-firing plug wires.

I can't remember how well it ever ran but it definitely was never 100%. Definitely never broke the tires loose, bellow 3500 RPM was unpleasant (flat spots in throttle), above 3500 RPM, the car felt ok. For a while I thought the TPS was a culprit but I tested it both at the ECU and at the component  without issue. Plug wires and firing order are correct. 

3 hours ago, Dave WM said:

forgot to ask, how did the plug parts look before deoxit? bad green corrosion can travel up the wire under insulation. Also always a good thing to check is grounds and fuse links for solid connections. If you can make it "run rough" by revving it up, try listening to the injectors with a mech stethoscope. I assume the injectors are the stock ones that came with the car?

The connectors before the dexoit were actually not bad. I ended up cutting the connectors back about 3 inches when I put in the new connectors. I even checked the AFM carbon trace for wear grooves, also spraying the internals with deoxit. I have not changed the AFM connector. Fuse links were removed and replaced with a maxifuse system.

In reference to the potentiometer, what power has everyone been running? 1/5W? 1/2W? 1W? adafruit has a 1/5W for $1 I can get. Otherwise I would have to go through digikey for some higher power ones.

Revised to-do list:

• Record/report new fuel pressure numbers
• Record/report vacuum pressure numbers
• Take pictures of the spark plug tips
• Install 1K linear pot and adjust per atlanticZ
• Turn AFM 6 teeth counterclock wise back to previous spot.

Thanks everyone for the help.

Edited August 27, 2018 by kinser86

[kinser86]

Alright reporting back some findings.

• Fuel Pressure: 34 PSI @ 800RPM
• Vacuum:  18 inHg @ 800RPM
• AFM rotated back 6 teeth (original setting)
• 

1K linear potentiometer installed per atlanticz website at 480Ω. 

• Increasing resistance causes the engine to idle lower
• Decreasing resistance causes the engine to idle higher
• There is definitely in audible difference in idle when changing the resistance
• Symptoms do not go away.

Car is still unable to drive, popping and stumbling the second you try to drive off.

Below is a video of the car after warming up with all the previous items performed. Notice the pop in the vacuum gauge. 

 

Edited August 31, 2018 by kinser86
picture

[Dave WM]

fuel pressure to high, with that kind of vacuum you should be close to 29psi at idle. are you sure the vacuum lead is connected to the FPR? is the fuel pressure changing with the vacuum? If those are newish plugs you are too rich, again too high a fuel pressure could account for that.

Edited August 31, 2018 by Dave WM

[Dave WM]

My guess is removing the oil filler cap will have NO effect on the idle. it should make is worse.

Edited August 31, 2018 by Dave WM

[Zed Head]

16 minutes ago, kinser86 said:

• Fuel Pressure: 34 PSI @ 800RPM
• Vacuum:  18 inHg @ 800RPM

1K linear potentiometer installed per atlanticz website at 480Ω. 

• Increasing resistance causes the engine to idle lower
• Decreasing resistance causes the engine to idle higher
• There is definitely in audible difference in idle when changing the resistance
• Symptoms do not go away.

Car is still unable to drive, popping and stumbling the second you try to drive off.

You talk about the idle at different potentiometer settings but don't say anything about what you did while driving.  You want to increase resistance until it's drivable.  A little bit at a time.  Watching your video makes me think that you do things in very large steps.  The resistance changes will be fine steps, not big cranks of the knob.

Your fuel pressure seems high for the vacuum reading.  18 inches of vacuum = 8.8 psi.  34 + 8.8 = 42.8 psi.  It might be that the hose to your FPR has a leak or a split.  Make sure that the FPR is getting a godd vacuum source.  That should drop your fuel pressure, which will clean up the idle smell.

When you open the throttle the FPR doesn't see much vacuum.  That's how you can have a rich idle and a lean driving problem.  The EFI system needs the fine details to be right.

[kinser86]

20 minutes ago, Dave WM said:

fuel pressure to high, with that kind of vacuum you should be close to 29psi at idle. are you sure the vacuum lead is connected to the FPR? is the fuel pressure changing with the vacuum? If those are newish plugs you are too rich, again too high a fuel pressure could account for that.

FPR vacuum lead is connected.

17 minutes ago, Dave WM said:

My guess is removing the oil filler cap will have NO effect on the idle. it should make is worse.

Removing the oil filter cap will make the engine almost die at idle.

17 minutes ago, Zed Head said:

You talk about the idle at different potentiometer settings but don't say anything about what you did while driving.  You want to increase resistance until it's drivable.  A little bit at a time.  Watching your video makes me think that you do things in very large steps.  The resistance changes will be fine steps, not big cranks of the knob.

Your fuel pressure seems high for the vacuum reading.  18 inches of vacuum = 8.8 psi.  34 + 8.8 = 42.8 psi.  It might be that the hose to your FPR has a leak or a split.  Make sure that the FPR is getting a godd vacuum source.  That should drop your fuel pressure, which will clean up the idle smell.

 When you open the throttle the FPR doesn't see much vacuum.  That's how you can have a rich idle and a lean driving problem.  The EFI system needs the fine details to be right.

The reference to the 1K pot swings at idle was stating that it has an impact (it is installed correct). Driving the car is still next to impossible and I have a video I am working on uploading to show it driving. Trying to adjust the pot while driving is still not even an option yet but once it is, then I can start tuning it.

Vacuum reading was taken between the vacuum advance and intake. The hose between the FPR and intake is new and still soft. It sounds like this is leaning towards the FPR being bad.

[Dave WM]

did you see the fuel pressure change with the vacuum? as manifold vacuum decreases (less vacuum, no matter how say it does not seem right) FP should go up. with the engine off (no vacuum) pressure should be about 36 psi, idle should be 29psi, should vary between those with throttle, go even lower than the 29 psi as you snap the throttle closed and the vacuum shoot to 25inhg.