A guy named Rick

I need to do some more testing but seems like it might possibly be my charcoal canister valve causing a vacuum leak. It makes sense why when undo the vacuum line for EGR off the carburetor base, it shares line with the smaller line to the canister and runs better unhooked. I was messing around under the hood yesterday and unhooked the line to the canister from the T connection and plugged it with my finger, revved the engine a bit and heard air hissing on driver's side. So I squeezed the bigger line and it stopped. The bigger line is the one going to the fitting on the intake manifold that which is a big port with 2 smaller ports, the bigger one going to the AB valve.

Per FSM if you suck air on either of the 2 ports on the vapor canister, no air should escape. The top one with smaller line a very small amount does. The bottom port with the larger line leaks a good amount (using vacuum hand pump with gauge, can get to -20inHg but leaks out in about 3 seconds to 0.

Yesterday decided to unscrew the mixture screw and shoot some carb cleaner in there. Apparently when I did the carburetor rebuild, I did not clean out that port. The spring was pretty nasty, the needle tip of the screw wasn't really bad. I couldn't get around a driving at last night so I drove at this morning to get some gas and throw some Techron in. It ran great! Until I realize that I had left the line undone that T's into the EGR off the curved port that's on the bottom section of the carb near the mixture screw. So obviously I hooked that back up and then it goes back to stumbling a bit off takeoff. So, EGR opening is giving me the issues!

So, if the EGR is what's giving me problems, the BPT is working... however, is it POSSIBLE that the BPT can be overactive? Hence, plugged catalytic converter?? Or is it possible the BPT is just a bit over sensitive? Maybe, just maybe, I can throw a restriction orifice in it like what a few of the vacuum lines have?? I figure the BPT would be a "it works or it doesn't" type of thing.

5 hours ago, Thomas Perkins said:

Just maybe,like real soon.California will break apart and float out to sea and sink.Then,New York does it to.Then we build a wall around Georgia to make sure we stay red.

And then the we will lose the largest agricultural producer in the US.

5 hours ago, Thomas Perkins said:

Just maybe,like real soon.California will break apart and float out to sea and sink.Then,New York does it to.Then we build a wall around Georgia to make sure we stay red.

Not here to discuss politics.

I can take the top off with it on the carb, and I have 2 spare MC solenoids laying around. If I were to swap out and crimp some spade terminals on, would that work or does it need a good solid butt connector crimp job? I don't have the tool to get the wire out the big connector so I'd probably just cut and figure quick connect terminals would work. Who knows, maybe the solenoid isn't correct for the ECC module on this truck. 

Well I swapped back to the O2 sensor that was in before replacing it, runs better. OK, still stumble and hesitation off idle, not so bad though. Choke flap is gone for now, so choke not on. Idle switch adjusted fine. No vac leaks. Float level brought up a bit. If I have foot light on pedal in say 2nd gear like 15 maybe 20mph you can feel it bucking. At a stop, revving engine can hear rpms up and down a bit, can hear misfiring every now and then. But it runs awesome putting your foot down. Pulls pretty well. It's just the low speed circuit/idle circuit whatever messing me up. 

Datzenmike always says coils don't misfire, they work or don't. How about ignition control module? 

This shit is pissing me off.

18 minutes ago, Stoffregen Motorsports said:

Don't you have a test only station nearby? I wold not have gone all in until you knew it was ready.

Went to a test only. You mean one I can pre-test? Looking into that.

I had one give me shit for having a different VIN on my dash because previous owner swapped it (not the cluster though, judging by my vin history report I had showing mileage at various points through the years) saying I need a vin verification when the door jam and engine bay vin tags both are what's on my registration.

16 minutes ago, datzenmike said:

Open loop means no O₂ control of the mixture ratio solenoid and does not occur during warm up, full throttle, starting and deceleration.

 

 

 

The function of the idle cut is to have a means of shutting off fuel to the idle circuit. The solenoid is on, has to be, at idle. It's generally on all the time but when suddenly decelerating at higher speeds the vacuum switch detects the high intake vacuum and with transmission and clutch switch and other conditions inputs this info to the ECU and it decides if the idle cut is turned off to save wasted fuel. There are a clutch and a transmission switch to defeat this when shifting or if in neutral so the engine does not stall. You can disconnect this vacuum switch and won't notice a thing.

 

The other vacuum switch detects low intake vacuum signaling heavy throttle use such as passing or climbing a steep hill. This turns off the exhaust side spark plugs and advances the timing to compensate for single plug running. Again if disconnected you really won't notice anything much, perhaps a little more engine noise.

 

Neither of these are on or active at idle (or shouldn't be) so can't affect idle. If it runs better disconnected then run disconnected. The pollution test does not check for full throttle or deceleration.

 

Most likely the vacuum switch hoses are miss connected.  Not hard to believe as the under hood looks like a basket of snakes. 

 

 

 

 

 

The inspection lamp only has to flash more than 4 times in 10 seconds.

My truck is California emissions so I don't have the switch that turns off exhaust side coil. That's done through the distributor icm. I have 2 switches on passenger side connected by a T off the intake port that has 2 nipples, the other going to the AB valve. Through the FSM I gather the ECC control module gets signal of low intake vacuum, decides which switch to go based on engine temp and goes open loop, so if I leave it disconnected like I did it failed horribly on emissions. 

Basically the computer thought the engine was under WOT because of the low vacuum signal. The first 2 times I had this connected, I failed because the spring on the idle switch arm. The second time was my TVV drawing air warmed up, destroying vac signal to the EGR. This third time I failed because was rich worse than the first time (different carb, different MC solenoid) and only thing different was plugged the line going to vacuum switches A and B because it ran way better.

I understand the light has to blink 4 times or more in 10 seconds, but I'm curious if it is an indicator of either rich or lean state? The pulse changed having switched back to the old 02 sensor and taking off from idle improved somewhat. So I'm wondering if my new O2 (sane brand and part # Bosch) was defective. 

What does the green light flashing on the ECC control unit mean? I went back to old O2 sensor and it's more of a consistent flash vs new one which was more rapid but more time green light on.

I attempted smog again and my truck is now classified as a gross polluter. It ran severely rich, worse than the first time. Second time was lean once I realized the idle switch wasn't activated because the little spring came off. This time I tried another carburetor I rebuilt but I forgot Vac switches A and B were plugged. I believe this caused it to run in open loop, and the mixture solenoid jet is larger on this carburetor resulting in an even richer mixture than before.

I need some help understanding Vac switches A and B. When connected is when the idle will go up and down a tiny bit, which is not a problem, it's not by much at all. The problem is taking off and when around town I let the gas pedal go and start accelerating again it's often jerky in the lower ram's until the idle switch is off above 1500. I understand there is a fuel cut function for the idle circuit, why is it doing something when still on the idle circuit? 🤔 it runs fine in the running circuit. I'm wondering if the idle cut solenoid is partially activated at idle? My understanding is if I leave it plugged, the computer thinks it's under WOT and will be in open-circuit, per the FSM. If I have it connected, it's very annoying around town. My next guess is float level, but this doesn't make sense to me because in open-circuit it idles and runs perfect. Just that it's insanely rich. I'm out of ideas 💡 

11 minutes ago, 720_Jeff said:

 

 

Just asking, what I suspect datzenmike might ask in a conversation like this.

I second that

16 hours ago, 720axr said:

Hey all I'm having issues with my z24 idling high and stuttering in park. I've been scouring the internet to see if anyone else has had the same issue and I've had no luck. I've recently performed a vacuum delete and I've capped the EGR valve. I have no A/C solenoid either. Any and all input would help!

Been trying to get some help with some stuttering too, I have a manual though. It's when Vac switch A and B (you only have 1 of these) is hooked up, it stutters around town especially taking off. Runs amazing otherwise 👌 and the switches test OK. Idk if I have too high vacuum at idle or neutral switch not working or something not communicating with the fuel management. Idle also a bit up and down too when connected. I know it will run OK without but will save me a bit of gas around town and will switch to open loop under wot if the idle cut is working properly. 

Loose red wire, thick jacket like the black wire that goes to the distributor, which is grounded near or on the vacuum advance. Where does the red wire go or is it extra?? 

And one more thing: is it possible the LED inspection light on the ECC control unit has burned out after all these years? No light flashing 4 times in 10 seconds like it says in the FSM that it should.

So made a breakthrough. I mentioned that my anti-dieseling solenoid had to be grounded through the 2 wires that are grounded on the intake below the carburetor. Previous owner must have known there was a ground issue because one of those ground wires' coat is stripped and twisted with the truck side of the black wire on the 6 wire connector. Without this connection, the anyi-diesel solenoid doesn't work. I found a ground wire near the battery that is loose, not screwed down so I secured it and guess what? Have ground to the solenoid now. I want to see what effect this has with vac switch A and B, I'm thinking possibly I don't have a working neutral switch so need to test that theory, possibly check my temp sensor (seems it may be going closed-loop when it's cold and shouldn't be).

5 minutes ago, datzenmike said:

 It will run fine even if both these functions don't work. Separate them. Find out which one when connected is causing the bad idle.

Oh yeah no doubt it runs fine. Just bugging me not knowing what's going on.

Can't wait for Datslocos tomorrow, Manteca CA. Just wish my 720 was looking good enough to not just sit in the parking lot. 

Also while at idle I've tried this with both gauges: drawing vacuum to where they would be engaged. Timing light on exhaust side. Rev engine and still getting timing light flash from exhaust side plugs. 

1 minute ago, datzenmike said:

 

It's who we are. It's what we do.

 

What switches? There is a vacuum switch to turn the exhaust side plugs off, but only under full throttle conditions and another shuts off the idle cut solenoid when decelerating. Neither should affect any vacuum they are closed systems so if they affect the idle. Look for vacuum leaks on the hoses to them. Pinch off the hoses to them one at a time. If you can isolate the leak to the switch then the switch is the fault.

I have isolated it there. When the line is capped off, it's fine. I can pinch the line, but then I have to undo one hose to the switch to release the vacuum from the switch. I've tested them with a vacuum hand pump with gage and they operate fine it seems per FSM spec. Vac lines are new.

It should be noted when my hand pump vac gauge is connected to that port to manifold at idle is about 20ish and rapidly bouncing up and down a few in/hg. but that could be the gauge bouncing since it is a brake bleeder hand pump after all.

29 minutes ago, datzenmike said:

The idle cut solenoid helps reduce run on or dieseling after hot shut down. On Z24 engines there is a fuel cut feature on deceleration. Remember that when foot is off the gas when slowing down the carburetor is at idle and fuel is still being sucked into the intake. This fuel is completely wasted out the exhaust. This feature actually saves you gas and reduces HC emissions.

 

 

What are vacuum switches A and B??? Where are they?

They are the 2 round ones on passenger inner fender. It's California model, does one control the fuel cut and the other controls spark plug switching? Or does the Cali model even switch plugs? I have no 3rd round vacuum switch on driver's side which in the FSM is for spark switching.

I get the concept of reducing the wasted fuel, but it seems active at idle and should not be if throttle is closed with an idle switch adjusted properly, transmission in neutral and the clutch released, there should be no reason it would make the truck go from a smooth idle to a noticeable miss and slightly fluctuating idle. Also jerky when rolling between idle and when it becomes closed circuit. 

7 minutes ago, Stoffregen Motorsports said:

Yes, I've cheated here and there on other vehicles (small ball bearings inside of vacuum hoses), but again, if it passes the pipe, he/she probably won't care.

😉 😉

With Vacuum switch A and B hooked up, the idle is a bit rough and a bit up and down. With the line plugged off, it's fine. I know my throttle switch works and is adjusted to come on like 1400rpm, temp sensor works, why on earth would my idle be affected by the vacuum switch? It stumbles a bit off idle too with it hooked up. Without then, it runs amazing. Thoughts?? 

JB welded a penny there, don't like the hesitation I sometimes feel taking off. Adjusted idle mixture a bit.

Do I really need the fuel cut feature?? Am I better off without the vac switches?? Will it affect smog at all?? Someone let me know please.

On 5/16/2023 at 6:04 AM, datzenmike said:

They all fire all the time and together normally. Apparently under heavy load the engine makes excessive noise* so Nissan changed the distributor to 4 wires and a vacuum switch to sense the load condition. The exhaust side is deactivated while under extreme loads.

 

* This could be the two flame fronts colliding inside the combustion chamber. Might make clacking sound like a diesel? I had a Z24 in my 620 and it had a three wire distributor and I never noticed any extra noise under load.

 

If that separate wire is unplugged or the vacuum switch removed then the exhaust side CAN'T be shut off.

 

I believe the four terminal distributor began with the introduction of the Z24 engine in Nov. '82 the start of the '83 model year. The '81-'82 Z22 had the three wire distributor.

 

I couldn't guess which wires go to which terminals

I'm curious, I see in the FSM about vacuum switch C and I have a California model Z24 but I don't have vac switch C. And I have the 4 terminals. Does A or B control it also in addition to the fuel cutoff? 

1 hour ago, NC85ST said:

You can use just about anything to cover the hole, think bolt or glue a penny over it. As long as it contacts the switch, you’re good. I had that happen with the brake switch. The little rubber? piece deteriorated and the brake lights would stay on. Unfortunately I don’t remember what I used to fix it and my truck is about 2 hours away.

I have some JB weld if it comes down to that! 🤣 I was thinking something along that line, a bolt, but I like the penny idea. 

It runs so much better with the switches bypassed. I just wish I could feel the secondary kick in a bit better and I'd be happy. It's amazing, I've been chasing a vacuum leak for a month almost just to find out it's been that switch the whole time!! The rpms would flutter up and down +/- about 15-20 rpm with a slightly rough/misfire but not so bad. And when you take off the EGR opens a bit and was causing a lean effect because the fuel was cutting too. It idles so smooth now 😎 glad I don't have a crusty leaking EGR internally. 

The secondary spring that holds the flap closed, can I put a softer one on it? Maybe that will help it open by needing less vacuum? 🤔 🤔

Anybody know what I can rig up on my pedal to hit my clutch switch? The pin it's supposed to press just goes through a hole. Never had anything there, just a hole so now everything is hooked up right but the truck thinks it's got the clutch pressed in and messes with the fuel cut taking off from a stop or releasing the gas pedal slightly after having been accelerating makes it act all jerky. I have the port capped for now but I need to smog this thing this week. 

Is there a way to measure backpressure to the BPT to determine if I have too much, i.e. a clogged cat? If cat is clogged, I'm assuming would signal BPT to open EGR too early, causing a stumbling premature lean condition. 

I also noticed I had to adjust the BCDD because when shifting I think it was going rich on deceleration, so coming into the next gear you can feel it lagging out a second like the ecm is playing catch up going lean to cancel out. Turning the screw clockwise on the BCDD helped remedy this, and with a muffler that's not stock I can hear some nice pops in the exhaust now. Thoughts??