1977 280z possible EFI Problem?

[ckurtz2]

Thanks all for the ideas.

@Captain Obvious I had the original coil, so I swapped it in. No noticeable change. I will get photos next time I am out there.

I agree it acts mechanical, however I have held both the AFM throttle vane steady and the throttle body steady at the same time, and the engine would still burble on and off. This I believe also rules out the sticking AFM vane. I am confident this one is an electrical demon.

This morning started beautifully. After about 30 seconds fell into its rythms again. started popping out intake on acceleration. Turned off car and back on and it started popping (real metallic like clank) out the exhaust again on acceleration and idle. It was running extremely rough at this point. For the hell of it I pulled injector connectors while the engine was running and the pop went away with cylinder #1 disconnected. Reconnected and the pop would return. Very odd. Pulled spark plug and it was carbon fouled, but just barely. Cleaned and reinstalled. Car ran beautifully. I want to state that this injector is brand new. I mean like 50 miles on it new, and so are all the rest. Drove it a few miles after cleaning the spark plug and then randomly when I was back in the neighborhood it started running like crap again (complete loss of engine power, and surging). Not sure really if the engine surging and loss of power was related to cylinder #1 or if whatever the hell has been going on with my engine fouled it.

I have had problems before with this cylinder not firing befire due to the injector not firing (tested with a noid light), but that problem randomly went away a long time ago as it started firing one day just fine. This injector also has new injector connector, as do the rest. I wonder if somehow the ECM is messing up fuel timing/duration for this cylinder. 

CTS sensor tested good for ohms. It is a solid connection, as when I pull it the engine dies completely and immidietly. 

I really am wondering now if it is the ECM. I can't think of anything else that can change the engine mixture so quickly. the popping out the intake and then exhaust just screams to me that the mixture is drastically changing. 

I don't think it could be the AFM, because I held the vane steady and it still was surging. Possibly it was gaining and loosing connection, but I strongly doubt it as the connector to the afm is rock solid. 

I am also going to rule out the distributor cap as being bad, because if it was bad I don't believe I would get periods where the car works perfectly. 

 

 

Edited September 26, 2022 by ckurtz2

[Captain Obvious]

Take a look at the connectors from the injector dropping resistors? That's something that could electrically affect cylinder #1 only. And next time it's screwing up, try swapping #1 and #2 injector connectors. If the bucking now comes and goes with #2 (instead of #1), that could be useful info.

The ECU fires all six injectors at the same time, so other than a bad connection to the box or a broken circuit trace inside the box, I cannot come up with anything else the ECU could do that could affect #1 only.

[jonathanrussell]

Could also swap cylinder 1 injector with another cylinder to see if the problem follows the injector. 

Also, I could be totally off base but it just seems odd that one cylinder misbehaving would cause the severe symptoms you are describing, backfiring, etc. In a healthy engine, you can disable a cylinder and it will run...lower idle speed, lower power, etc...but will run without bucking and backfiring. Just a thought to consider.

 

Edited September 27, 2022 by jonathanrussell

[Captain Obvious]

20 minutes ago, jonathanrussell said:

seems odd that one cylinder misbehaving would cause the severe symptoms you are describing,

Agreed on that. Hearing about the popping followed #1 connected or not seems like a distraction from the bigger picture at this point. But it also seemed like something simple to look into.

[Mark Maras]

Is the "micro crack" in the dist. cap near #1?

[Zed Head]

Could you describe the details of your ignition system?  Do you have two pickups in the distributor?  And the factory ignition module?  Does the distributor vacuum advance work?

Does your engine have the top gear vacuum control solenoid for the distributor?

And do you have the factory EGR system intact and connected?

And, have you checked the throttle valve sensor (aka TPS)?

 

The two pickups might be switching, which would suggest a bad ignition module or a funky temperature switch.  This could cause the rise and fall of idle speed.  You could test this by disconnecting the temperature switch.

The top gear solenoid and switch could be opening and closing the vacuum supply to the distributor.  You could test this just by disconnecting and blocking the supply and driving with no vacuum advance.

The EGR system has its own temperature valve but it also has a vacuum controlled valve.  Might be harder to diagnose.  Vacuum controlled valves can get weird if they cause engine speed to change.  You can get a feedback loop going.

The TVS might just be a sporadic problem.  It's there then it's not there.  If it gets stuck on open throttle it would add 27% more fuel than the rest of the system calls for.  

The distributor pickups are Engine Electrical I think, the TVS is in Engine Fuel, and the EGR is in Emissions.  Read the first few pages of Engine Fuel is you want to get a better idea of how fuel is controlled, without having to read through the whole chapter.  Something might fit your symptoms.

Also, don't overlook just simple loose ground or wire that is causing either an open or shorted circuit.  The temperature switch controlled things are susceptible to that.

Here are a couple of examples from Engine Fuel.

 

[siteunseen]

When I bought my 77 it would hardly run, bucking spitting and sputtering. I tried everything and then ran a mirror under the intake. There was a golf ball size hole rotted out where the egr tube connected to the intake. Under where your block off plate is.

I deleted the egr system. The one vacuum line that was left after the thermal vacuum switch, TVS, I hooked to a nipple below the TPS box I think. Somewhere down there around the bcdd.

Just a little story of my 77's problems. I've got the pictures on my laptop I can post when I can. You might find a recall sticker under the hood on the passenger's side if your's was fixed. Mine was not and that egr tube got loose and exhaust gas ate up my damn intake.

 

[siteunseen]

 

[kickstand80]

Do you have a spare distributor you could swap in? Are you running the stock distributor or upgraded to a matchbox? Is your distributor ground hooked up?

[zeeboost]

Judging off the last video uploaded, definitely doesn’t sound like an ignition fault such as loss of spark, typically those cause an abrupt stall…this one sounds like the engine stays running during the problem, but seems it’s starving for fuel. I would be inspecting the fuel control inputs (afm voltage, coolant temp voltage, throttle valve switch continuity in spec, etc.)

if you could get a meter to measure injector pulsewidth, you could compare all inputs to the pulsewidth and see if they stay constant while the pw changes (bad ecu or ground / power / poor connection) or if you have one of the inputs that fluctuates with the problem, you could inspect that circuit. If pulsewidth doesn’t change during problem then possible cause could be unmetered air, such as the egr valve potentially hanging open…though that mostly had an effect at idle and not partial throttle situations. 

[kickstand80]

A long time ago I owned a 1967 Oldsmobile and the capacitor inside the distributor went bad and man that car ran like S--T. Spark was jumping all over the place except for where it was supposed to go. Dont rule anything out. . Do you have a timing light that you can hookup to each plug wire and watch the light flash to see if things are consistent with each plug? 

Edited September 28, 2022 by kickstand80

[ckurtz2]

Thanks guys for the replies! I will try to get through everything.

@Zed Head My ignition system is bone stock. I am running  about 6 month old spark plug wires, about a year old cap, rebuilt stock dizzy, original and transistor ignition unit. The distributor I believe has a single pickup? I provided a photo.

Ok. I am assuming by the vacuum control solinoid you mean vac advance. Yes I am running it. It is connected directly to manifold vacuum as I am running the Comp Cams 260s on stock injection. I know it's a debated topic, but I got great advice from @Chickenman and I pretty much had it running near perfect for a few weeks before this stupid issue.

I am running 6 to 1 headers so I deleted the entire EGR system. Capped it at the top of the intake. TPS has not been checked yet, tommorow is the big day for running through FSM things, but because things are so erratic I doubt I will find anything wrong. If it is the TPS it is something like bad wires to the connectors or something. I have had the cap off of it for diagnostics and all the contacts are adjusted just right.  When I get the surging again I will try disconnecting vac advance and see if that helps. 

@siteunseen That sounded like quite the issue! Now I am not sure exactly what you mean by where the intake had rotted through, but I took photos. While the engine was running though I covered both the opening under the intake and the one on the side with my finger and noticed no change in runability or RPM. Thus I am assuming it is fine. I also got a mirror underneath the intake and when looking through the hole I see the shiny block off plate.

Arrow on top shows side opening in intake. Curved arrow represents the opening underneath the intake at the EGR.

@kickstand80 No I don't have a spare distributor unfortunately. Also to expensive for me to buy one:( Really trying to limit myself on buying uneeded things. Yes ground is hooked up and good. I will check continuity tommorow. 

        So I actually ran some tests, but couldn't come to a viable conclusion. I am 100% confident something is amiss with cylinder #1 at the very least. Popping out exhaust at idle goes away when removing injector connector/plug wire. I cleaned spark plug and the popping went away for a few minutes then came back. Makes me think the injector is bad/sticking, but I just don't believe that yet at all given how new it is and clean my fuel is. Popping does not follow injector wires or spark plug wires.

        Ok, so I pulled plug wire and put against valve cover. sporadic spark. I took a video. Every other cylinder maybe had a miss every once and a while, but not as consistent. I also put a timing light on each wire and it confirmed that the spark was sporadic on cylinder 1. However, I almost wonder if my timing light was wrong, as it seemed to be different every time I disconnected and reconnected my timing light. However, I put the plug wire against the valve cover and then hooked up my timing light, and the timing light looked consistent with the plug wire zapping the valve cover. Once again the car has confused the hell out of me. Sometimes cylinder number 2 looked sporadic was well, but not nearly as often. The loss of spark was not dependent on RPM, I revved it up and at higher RPM from time to time the spark would dissapear. This is super frustrating as it isn't consistent enough for me to tell if it is a bad timing light, only related to cylinder number 1, or following plug wires. It seemed like it kept changing from loosing spark, to sometimes loosing spark, to being consistent, etc. Here is a vid.

 

@zeeboost could you send a link to the type of tool that you mean? I don't have any fancy diagnostics tools besides my dandy multimeter. If I had an oscilloscope I would already have gone through the entire ignition side of the FSM. Unfortunately they are super expensive, makes diagnosing ignition circuit hard as hell. 

The idle RPM wasn't surging violently today, so I don't know if I am chasing rabits or if this cylinder issue is a clue. I was able to replicate the RPM surging by holding the AFM to be more rich. Odd stuff. This car gives me a headache.