Engine rough running - at wits end

[the_tool_man]

10 hours ago, Zed Head said:

Went back through the previous pages and searched for "pressure".  I don't see a verified fuel pressure reading.  You have a lean plug, a rough running engine, in a car that might have sat for a while.  You've replaced some parts but haven't verified that specs. are right.  I'd get a fuel pressure reading before spending too much time on anything else.  You need to know the number.

Your dilemma is typical.  You're working on the easy surface items, but you really need to verify the essentials.  Fuel pressure is critical for electronic fuel injection systems.

It's detailed in my intro thread linked in post #1.  But the fuel system has been gone through from the filter outward.  Fuel pressure was verified.  44psi dead headed to test check valve.  35psi with engine off.  32psi with engine at idle.  New FPR.  New injectors.  New hoses.  I haven't replaced the CSV.  But I'll check it.

[the_tool_man]

I have tried to identify the mysterious black plastic thing that is screwed to the driver side inner fender forward of the coil.  See yellow circle in photo.  I haven't found it through searching, since I don't know what to call it.  I tried to open it last night while working on the car, thinking it might be a junction box of some sort (trying to avoid having to unplug all of the injectors).  I figured out it's potted, and can't be opened.  But what is it?  If it has something to do with the fuel pump, it might explain why mine quit working.  Unfortunately, during the compression testing, I paid no attention to the fuel pressure.  So I don't know exactly when it quit.

 

[siteunseen]

It is a junction type box I guess.  The green and red wires from the distributor connect with the green and red coming out of the wiring harness.  It can be opened from the top, it's hinged at the bottom, by pushing in this little clip you'll see.

here you go, I had it backwards above ^^^^^^.

 

Edited March 1, 2017 by siteunseen

[Zed Head]

1 hour ago, the_tool_man said:

 I tried to open it last night while working on the car, thinking it might be a junction box of some sort (trying to avoid having to unplug all of the injectors). 

I figured out it's potted, and can't be opened.  But what is it?  

 Unfortunately, during the compression testing, I paid no attention to the fuel pressure.  So I don't know exactly when it quit.

Are you sure that you're not actually enjoying working on the car more than having it run well?  Are there wires attached to the mysterious box?  You didn't mention them.  And if you can't get it open, then how can you know it's potted?  Just saying.

There's a simple test of fuel pump operation that get's mentioned about ten times a month.  Remove the starter solenoid wire and turn the key to Start.  Although, you say that you've lost pressure but haven't mentioned if the fuel pump is operating.

You have a lot of good information in your threads.  If you could just get them in order the cause of the problem would probably show up.  You're jumping around from thing to thing, and some of them don't really fit a good diagnostic method.  Like why would you be unplugging all of the injectors?  Seriously, once you've tried the obvious things and haven't found a solution, it works best to go through the basics, in an orderly fashion.  The car looks very clean and original (unless that's a car from the internet).  Doesn't seem like there is much wire hacking, you even have the original rubber cap on the coil, so the basics should work to solve the problem.

[the_tool_man]

1 hour ago, Zed Head said:

Are you sure that you're not actually enjoying working on the car more than having it run well?  Are there wires attached to the mysterious box?  You didn't mention them.  And if you can't get it open, then how can you know it's potted?  Just saying.

There's a simple test of fuel pump operation that get's mentioned about ten times a month.  Remove the starter solenoid wire and turn the key to Start.  Although, you say that you've lost pressure but haven't mentioned if the fuel pump is operating.

You have a lot of good information in your threads.  If you could just get them in order the cause of the problem would probably show up.  You're jumping around from thing to thing, and some of them don't really fit a good diagnostic method.  Like why would you be unplugging all of the injectors?  Seriously, once you've tried the obvious things and haven't found a solution, it works best to go through the basics, in an orderly fashion.  The car looks very clean and original (unless that's a car from the internet).  Doesn't seem like there is much wire hacking, you even have the original rubber cap on the coil, so the basics should work to solve the problem.

I'm not sure whether to find this line of discussion funny or insulting.

I assumed a photo of the mysterious box was sufficient.  For the sake of brevity, I didn't develop an elaborate verbal description.  Again, knowing what to call it would have been helpful.  But I didn't have that information.

I have every intention to resolve the fuel pressure issue at the earliest possible opportunity.  I am quite familiar with the fuel pump test you mentioned, and will certainly perform it.  But in the event the fuel pump doesn't operate, I will be looking for possible causes, starting with most likely ones.  For example, what electrical connections might I have disturbed?  Since I touched the junction box, I wanted to know what it does, so that I can assess whether or not it might be related to the issue.  The time to ask is now, while there is time for someone to answer, not at 8:30 this evening when I need the answer at hand.

I can see how my questions might appear random or spontaneous if they don't correspond with your paradigm of a logical troubleshooting method.  But there is an underlying reasoning, nonetheless.

Disconnecting the fuel injectors was so that I didn't get sprayed by fuel while performing the compression test.  Because I wanted to minimize cooling down during the test, I took out all of the plugs at the same time to get compression readings quickly.

Edited March 1, 2017 by the_tool_man

[JSM]

Don't sweat the small stuff. Remember it's just the internet and tone doesn't come across. Folks are just trying to help. 

[Zed Head]

Sorry to be blunt.  I'm just trying to figure out what you're really trying to do.  There are actually people on the forum who have been working on their cars for years, and have never driven them.  Because they like the work more than the driving.  They're building something.

My bluntness is also an attempt to break through, and make the point that there is a basic logic level to work from, starting with how the basic elements of the system work.  For example, on the injectors, you could just disconnect the coil's power wire.  No spark, no injection.  And the fuel pump power system is also described, so you don't have to guess there either.  

Just trying to help.  You have the "searching where the light is" problem.  Now that's a funny joke.  I Googled it and it's even been Wikipediaized  - the streetlight effect.

[Dave WM]

fyi easy way to compression test, get a momentary push switch, get a few feet of 2 conductor hookup wire attach one end to switch, the other end put a alligator type clip and a female spade connector. with car in neutral , disconnect the starter solenoid wire and use the swiched wire to activate the starter (female end to starter solenoid spade, alligator to a positive supply (right there on the starter if you like).

now you can turn the engine over with the key in the off position. I use this sometimes when adj the valves as well to bump the cam shaft around.

 

[the_tool_man]

12 minutes ago, Dave WM said:

fyi easy way to compression test, get a momentary push switch, get a few feet of 2 conductor hookup wire attach one end to switch, the other end put a alligator type clip and a female spade connector. with car in neutral , disconnect the starter solenoid wire and use the swiched wire to activate the starter (female end to starter solenoid spade, alligator to a positive supply (right there on the starter if you like).

now you can turn the engine over with the key in the off position. I use this sometimes when adj the valves as well to bump the cam shaft around.

 

Thanks for that.

I went to Harbor Freight and bought a ready-made remote start switch for $8 (with coupon).  Worked great for re-starting while diagnosing running issues, looking for leaks, etc.  I also used it for compression testing.  But it never occurred to me that I could have left the key off to disable fuel, saving me the trouble of disconnecting the injectors. I was in the habit of turning the key on every time.  I guess I deserve to be treated like an idiot, when I act like one.

[the_tool_man]

Tonight I pulled the plugs, cleaned them and gapped them to .038". I pulled the valve cover and checked the valve lash. All were in spec. While I had it open, I rotated it to put #1 at TDC and verified the cam timing was correct. I checked the torque on the head bolts. They were all tight.

Does the red on the camshaft mean anything?

Then I buttoned it all back up and started the engine. I pulled each plug wire in succession to see if the idle changed. The idle is so rough that it was hard to tell. But it seemed as though #2, #4 and #5 made a difference and the others didn't. I confirmed with a timing light that all plugs are getting spark. Fuel pressure is good. That leaves injectors and vacuum, right?

I don't have a stethoscope (I'll pick one up this weekend). And my hearing is shot. So I've decided to just replace all the injector connectors. I already have new ones, since I'd planned on swapping them anyway (boots are disintegrated). As I said, the injectors are brand new. I practiced connector pin removal tonight at the kitchen table.

I also borrowed a fog machine to test for vacuum leaks. I'll play with that this weekend.

 

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[Zed Head]

Hey, I was wrong in my post about your 1977 ignition system.  Nissan was setting plugs at .040 by then, not the low end like my 76.  But .038" is fine for what you're doing, not worth going back.

Here's a test you can do to see if you have a vacuum leak that maybe somebody tuned around in the past - loosen the oil filler cap and slowly remove it.  See if the idle speed gets faster or slower, and if the engine dies when it's fully removed.  It's a simple test, similar to moving the AFM vane, except it makes the mixture leaner.

The other test you can do is to either remove the hose from the AFM and push the vane open, or remove the black cover on the side of the AFM and move the weight to open the vane.  The black cover pops off with a flat blade screwdriver, but is sometimes sealed with silicone.  If it has a large amount of silicone then somebody has already been in there and may have messed up your AFM tuning.  Opening the vane tells the ECU that more air is entering and it supplies more fuel, making the mixture rich.  The amount of air is controlled by the throttle blade so don't think that you're allowing more air in, you're just fooling the ECU.

Since you've confirmed all of the timing events and compression and the engine should run right if the fueling is right, these two tests might tell you if you're running lean or rich.  If you can get it to run better by changing the fuel-air ratio then you'll have a target to shoot at, making the mixture leaner or richer, or fixing vacuum leaks.  Good luck.

[the_tool_man]

Hey, I was wrong in my post about your 1977 ignition system.  Nissan was setting plugs at .040 by then, not the low end like my 76.  But .038" is fine for what you're doing, not worth going back.

FSM spec is .037-.041 for a '77. Five of the new ones I bought were at .038. so I gapped the sixth one the same.

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