Engine runs a LOT worse with high HUMIDITY !

[sage691]

Hi folks,

 

  It's been a while since I have been here ! My 1985 720 (2WD, Automatic, 2.4L Z24) has been having this problem for a while that gets a LOT worse whenever the humidity is at a high level. I live in New Orleans and so the weather is now starting to get tropical again, with humidity levels near 100%.

 

 Anyway, the problem starts to happen once I reach about 30mph. The truck starts locking down and sputtering. If you try to give it gas to go faster it can lock up completely. Going up an exit ramp is virtually impossibe and makes it a LOT worse, and running on the highway is also out of the question because you can't get it over 35mph without it bucking and sputtering. I have been having these type issues with the truck for a while, but now it has become a lot more noticeable and to the point where I am afraid to drive it. What is REALLY weird is that on days where the humidity is 30-60% it runs a LOT better and can even go on the highway. Heck, I had her up to 70mph last week on the highway when the humidity was at 40%. But last night with 85% humidity I was lucky to make it home staying under 30mph the whole way. Like I said, if you try to go faster then it will lock up and kill out. Also, I have noticed that when turning the engine off it will make this weird sputtering sound for a few seconds before it turns off completely.

 

THINGS I HAVE HAD DONE: 1) changed all spark plugs, wires, cap and rotor

                                                  2) new battery, new terminals

                                                  3) tightened the alternator belt to spec and confirmed it is                                                       charging properly

                                                  4) siliconed the valve cover gasket (oil was leaking out before)

                                                  5) replaced fuel filter with a brand new one (weeks ago)

                                                  6) new air filter

 

 The only thing I haven't had done yet is replace the valve cover gasket and the 2 semi-circle rubber plugs. I have those parts now, but i just haven't gotten around to it yet.

 

WHAT DO YOU GUYS THINK IT COULD BE ? I have a mechanic buddy who keeps mentioning O rings, but in my Chilton Manual I don't see and such O rings in the Z24 engine diagram blow-up. He thinks that moisture is getting into the spark plug area and causing these problems, and that is why the humidity makes it so much worse. Before I fixed the oil leak the plugs were getting oil fouled up pretty bad, but now they just get carbon fouled. I had the spark plugs changed just 1 month ago, so I can't see how they could already be going bad.

 

 Man this SUCKS and I am really at my wits end trying to figure this out ! And the COVID 19 situation makes the situation 100X wosse because I need the truck to survive right now. Any advice from you guys would be greatly appreciated.

 

 DO I NEED TO CLEAN THE CARB MAYBE ? I remember using a wire years back to make the choke stay fully open all the time, so I don't think the choke is making this happen. Maybe I need to give it a good deep cleaning, but not too sure how to go about doing that. A mechanic told me 2 years ago I should replace the carb.

[bottomwatcher]

Is this the feedback carb with o2 sensor?

[datzenmike]

 

Manifold on lower right has a green wire to the O₂ sensor. There will be a round electrical plug at right rear of carburetor and a mystery electrical box under the driver's seat if you have the ECC (electrical controlled carburetor.) If there is a failure with the ECC system it goes into limp mode, an over rich condition that moves it away from any chance of an over lean condition that could harm the engine. Mileage and performance are terrible and it's assumed that the owner will notice and correct. I can't imagine how  humidity would affect this. The 6 wire plug at the rear of the carburetor is problematic. The short wires tend to break contact when disturbed taking the air filter off. While it's running wiggle this connector and the wires and see if the engine idle changes.

 

If your '85 was built in April or later it will be a Z24i engine with throttle body injection and the air filter will have 2 wing nuts holding it on. The throttle body has two injectors that have O rings.  You say you wired the choke open so it won't be this.

[sage691]

Hi datzenmike,

 

  Man, thanks a MILLION for the quick response. This forum is truly awesome !!

 

 YES, my mechanic friend had mentioned "sensors" as possibly being the culprit. I just assumed (wrongly) that my truck probably didn't have one ! So I went digging after reading your reply and I found what you are talking about, and also a SKETCHY looking splice job of the wire that runs from the carb to that sensor. There was some old dry rot electrical tape around the splice section that just crumbled off when I squeezed it, exposing BARE silver looking stranded wires.

 

 Here are some dropbox links photos that I just took of all this:

https://www.dropbox.com/s/pq2t5oyoza1tzt0/DSC00618.JPG?dl=0

https://www.dropbox.com/s/x2iwrlobc78sj1a/DSC00620.JPG?dl=0

https://www.dropbox.com/s/w4aw8stpzl2l80b/DSC00621.JPG?dl=0

 

 Sorry, but I could not figure out how to attach pics here, so I used my dropbox account. Just click on each link and a photo should come right up. In the 1st photo you can see that sketchy looking splice with EXPOSED wires !! I can't imagine that is anything good. In the 2nd and 3rd photo you can see that O2 sensor from two different angles. It looks just like what you (datzenmike) posted to me. The 3rd photo has my finger pointing at it.

 

 So now I am wondering if that sketchy splice with exposed wires is the culprit causing the engine to lock down when giving it gas ? It seems that might explain WHY when it is crazy HUMID that the problem gets a lot worse; those exposed wires likely get very moist and may start shorting the sensor out ? What do you guys think of that ?

 

 Also, is it possible to simply CUT that wire and disengage the O2 sensor completely until I get a new one ? I was hoping I could at least use the truck for a little while in the meantime.

 

 OR, should I just try to clean that splice area up really good and then thoroughly seal it off with some electrical tape so moisture cannot get to the wires ? Maybe THAT will solve the problem temporarily ?

[datzenmike]

So one or two wing nuts holding the air filter on????

 

This will tell me if you have a ECC carb or a Z24i with throttle body fuel injection. Both have O² sensors.

 

 

 

 

Yes that's an O² sensor but wait to see if it's bad or not. The wire appears to be co-axial or shielded with an outer woven wire cover. This is to prevent any outside RF from messing with the signal inside. Unless the cable is broken wait on replacing it for now.

 

 

[sage691]

Thanks Mike !!

 

  Yes, it is indeed the ECC version. It has 1 wing nut in the center of the air filter cover, and I also noticed that "mystery electrical box" under the seat.

 

 Today I cleaned and taped up that sketchy part of the cable and gained a false sense of confidence. So I took her for a ride from my house to my studio downtown -- BIG mistake ! What is weird is that from a cold start (after being off for several hours) the truck will run sorta OK for the first 5-7 minutes or so. The total distance of that trip was about 10 miles, and for the first 3-4 miles (cruising at about 25-35mph on side streets) she was able to handle that OK with just a little locking up when trying to go faster. But man oh man, after about 10 minutes she started locking up BIG TIME and I barely made it to my studio.  So I let the truck sit for about 6 hours and then decided to try and make it back home -- another BIG MISTAKE ! And the same thing happened again. She ran OK at 25-35mph for the first 7 minutes/4 miles and then started acting up the worst I have seen her do yet. It felt like a MIRACLE that I actually made it home. I had to keep going back and forth with small movements of my foot on the gas pedal just to keep her going, and my speed went from 25mph down to about 15-10 mph by the end of the trip. The thing is, if you try to give it gas to go any faster it locks up right away and will kill on you. So I had to keep lightly (and quickly) pumping the pedal just to putter along at 15mph to avoid killing out.

 

 WHAT DO YOU GUYS THINK ? I am REALLY praying that it can be fixed because I need the truck pretty badly right now. I never imagined that a faulty sensor could make a truck run this bad, but I am truly glad I made this post as I am gaining an education for sure ! I was thinking about looking at the 1 month old plugs to see if maybe they are carbon fouled already. Maybe the "over rich" condition is causing them to foul up quickly ? But I just can't believe that alone would be causing the truck to run this bad. Honestly, this is the worst she has ever run in the 13 years that I have had her.

 

 So it seems the wire is probably not the problem, but instead the 02 sensor or something inside that "mystery box" under the seat ? You are right that the wire is hard and seems to be a co-axial type, so it is probably just fine because it is not broken or severed anywhere.

 

Oh yeah, and I did jiggle those 6 wires (round electrical plug) in back of the carb while the truck was running and it did nothing to change the idle -- so I assume those are OK as well.

[Charlie69]

I run the Weber DGEV 3236 on all my Datsuns/Nissans.  Where are you located?  Do you have to emission test you truck?

I would unplug the six wire plug first and see if there is any change in the way it runs. getting correct good parts for these ECC carbs is difficult.

 

Please report back what happens with the 6 wire carb plug disconnected.  This could be a carb problem or the ECM (mystery box under the drivers seat.  I have had 2 trucks that had bad ECMs.   My 86 ECC truck runs great and passes emissions in Phoenix AZ every 2 year.s  I have to emission test it again this year.  I will most likely have to replace the catalytic converter to pass emissions.  I use the cheap $30 cats and have to replace them every 2 to 3 years depending on how many miles I drive.

 

With the Weber I keep the oxygen sensor, the cat, and the EGR in good working order.  I on the Weber there is one wire for the electric choke and (optional) one wire for the fuel cut solenoid.  The fuel cut solenoid is a optional part only needed id when you shut your engine off it diesels.  Webers are simple carbs.

 

Have you run any kind of cleaner through your fuel system?  I use Seafoam once or twice a year.our a can in my tank and fill it up.  just drive normally.

[Charlie69]

What is the mileage of this truck?  Has it set for a long time not being used?  Did changing the fuel filter have any change.  Are you using the stock electric fuel pump on the side of the frame rail under the fuel door?  Start the truck and put your hand by the outlet of the exhaust and feel how much flow the exhaust has.  have some one rev the engine up while still having your hand by the exhaust.  You should feel much more exhaust when the engine is revved up.  What your are testing for is a plugged cat.  this will cause a vehicle to not be able to be driven properly.  If the exhaust flow seems normal I would start by cleaning the carb and the tank and fuel lines.  If you have a bad gas cap you could be getting moister in your tank from the high humidity.  Do all the simple things first.  I am willing to bet that mechanic 2 years ago was correct with the diagnoses the carb needs replaced.

[bottomwatcher]

Got a voltmeter? YouTube how to test an O2 sensor.

[datzenmike]

 

You keep saying 'lock up'.

 

 

 You say 'lock up' but I'm guessing it acts like turning the ignition off and on? The truck may lurch forward and stall, forward and stall??? Would this describe what happens?

 

If yes this is more like it's not getting enough gas. Next time drive it hard enough for it to quit. Then as quickly as possible get the ignition OFF and clutch in and pull over. Do this is a safe location. The intent is to preserve evidence of how much gas is in the carburetor and to do this we need to shut the electric fuel pump off ASAP or it will refill the carburetor while pulling over.

 

On the front of the carburetor is a small round glass window with a dot on it. Gas level should be close to the middle or on the dot. Go and have a look at it now and then try driving it around the block till is quits or 'falls on it's face' while driving. What I'm expecting is that the carburetor will not show any gas.

 

IF this is what's happening it's a fuel delivery problem and that can be fixed. If it stays full then delivery is not the problem.

[sage691]

OK,

 

 Thanks again Charlie69 and Datzenmike !

 

 I am going to do all of what you both recommended and report back the results ASAP. I will do what Datzenmike recommended first as he described very well what the truck is doing -- lurching forward when giving gas, then stalling. Yep, "lurch and stall, lurch and stall" !!

 

Btw Datzenmike, the truck has an automatic transmission. Checked the trans fluid and it is nice and healthy.

 

 And a question for Charlie69: Any tips on how to remove those 6 wires without ruining anything ? Are there any "tricks" to it ? If the problem is the ECC system I was hoping I could just disconnect it for a little while and use the truck to survive in the meantime.

[sage691]

Hi guys !

 

 OK, I ran all of those tests today you guys recommended.

 

 Datsenmike: I found that little glass with the dot in the middle on the carb. Before I started the truck up toady I noticed it was empty. So I started it and let it warm up for 10 minutes before taking it on a nearby street where the speed limit is 40mph. Once I got up to about 25mph she started acting up again, and so I did what you told me and gave it more gas attempting to accelerate. Then she sputtered out and stalled (making some popping sounds), and I immediately turned off the ignition and pulled over. When I looked at the carb glass there was VERY little gas in it -- nowhere near the dot in the middle. The gas level was pretty much to the bottom of the glass, hard to even see it really.

 

 Charlie69: I tried your suggestion of letting a friend rev the engine while feeling the exhaust pipe output. What I noticed is that when the engine was reving higher the heat increased but the air pressure output seemed to drop. In other words, at normal idle I could feel some air pressure on my hand at about 4" from the exhaust pipe hole; BUT when my friend started pressing the gas pedal and reving the engine higher the pressure output seemed to drop but got significantly hotter. Heck, I was afraid my hand might get burned if it was too close -- that's how HOT it would get !

  I haven't tried disconnecting the 6 wires at the back of the carb yet because I wanted to wait and see what you guys say about these tests first. Btw, the truck has 285,000 miles on it and has had this issue for a while, but now it is a LOT worse. No it has never been sitting up and I have been using it everyday for 13 years ! I just don't drive it much (about 15 miles a day), but she has always run GREAT for the most part and been very reliable. Changing the fuel filter didn't really make any difference, and I am not really sure what fuel pump I have.

 

 Well, I hope you guys can give me some more insights now as to what the culprit may be ?

 

 And thanks again SO MUCH for your help -- it is sincerely appreciated !!! We are in New Orleans where the Covid 19 is pretty bad, and so we really need the truck working to get thru this.

[sage691]

Question for Charlie69: I was trying to locate the fuel pump and was wondering is it somewhere near the carb or under the chassis ? Any clues on what to look for ?

 

 Since the carb had almost no fuel level in that little glass when it killed out, I was wondering if the fuel pump might be going bad. A mechanic told me they start leaking fuel when malfunctioning. I can't remember if I ever changed the fuel pump in the 13 years I have owned the truck.

[datzenmike]

Outside of the frame just forward of the right rear wheel. May have a 3 sided metal box around it for protection.

 

The bottom of the pump has a magnet and twists off to access the filter. The filter is 16404-28530 if they have it.

 

Pull hose off and direct into a suitable container. Pump should produce 1.4 liters per min or less, so if it does even close to this there's no sense replacing it with something that's of a lesser quality.

[sage691]

46 minutes ago, datzenmike said:

Outside of the frame just forward of the right rear wheel. May have a 3 sided metal box around it for protection.

 

The bottom of the pump has a magnet and twists off to access the filter. The filter is 16404-28530 if they have it.

 

Pull hose off and direct into a suitable container. Pump should produce 1.4 liters per min or less, so if it does even close to this there's no sense replacing it with something that's of a lesser quality.

 OK, and thanks !

 

 So I guess since there was almost no fuel in that little glass when the truck stalled/killed, that means we can rule out the ECC system being faulty ?

[Charlie69]

It sounds to me that your catalytic converter is plugged.  Is it a flanged converter or is it welded into the exhaust pipe.

when you rev the engine you should have more flow out the exhaust the fact that it is increasingly hotter is also a sign of a clogged converter.  The exhaust gasses do get some what hotter when more exhaust moves through the converter put you should feel a higher volume of exhaust moving out the tail pipe. If it is a flanged cat then disconect it and see if this makes any difference.

 

Edited April 26, 2020 by Charlie69

[datzenmike]

Well low fuel is not the same as no fuel. Although it does act like it's running out of fuel. Perhaps using it up faster than it can be kept refilled. I was expecting to not see any fuel. The trick is to get the fuel pump turned off as soon as possible or it will quickly fill the carb while you pull over giving a false test..

 

The float may be set wrong. The primary jet is actually a solenoid that is constantly opening and closing, the pulse set by the ECC's control unit under the driver's seat using feedback from the 0²sensor to tailor the mixture to stoichiometric. The exception is during warm up and at full throttle.

[Charlie69]

Here is the stock 720 fuel pump on my 66 520.

 

 

Mike might be on the right track with fuel starvation. 

 

[sage691]

37 minutes ago, datzenmike said:

Well low fuel is not the same as no fuel. Although it does act like it's running out of fuel. Perhaps using it up faster than it can be kept refilled. I was expecting to not see any fuel. The trick is to get the fuel pump turned off as soon as possible or it will quickly fill the carb while you pull over giving a false test..

 

The float may be set wrong. The primary jet is actually a solenoid that is constantly opening and closing, the pulse set by the ECC's control unit under the driver's seat using feedback from the 0²sensor to tailor the mixture to stoichiometric. The exception is during warm up and at full throttle.

Well, to be honest when I did that test I am not sure that I turned off the ignition in a nanosecond, so maybe a little fuel got in there post stalling. Also,  I REALLY had to get my eye right up on that little glass just to make out that line which seemed to be 1/32" of an inch to from the bottom. So yeah, there was virtually nothing in it from my memory of that moment.

 

 I will run the fuel pump test tomorrow to see if it is putting 1.4 liters per minute and report back my findings.

 

 

[datzenmike]

Oh, I thought you could see it up near the bottom of the glass.

 

Appears to be a delivery problem. Check the filter is not clogged. If it is throw away and put an inline fuel filter between tank and the pump. Make sure you do it protects the pump from crap.

[sage691]

1 hour ago, Charlie69 said:

It sounds to me that your catalytic converter is plugged.  Is it a flanged converter or is it welded into the exhaust pipe.

when you rev the engine you should have more flow out the exhaust the fact that it is increasingly hotter is also a sign of a clogged converter.  The exhaust gasses do get some what hotter when more exhaust moves through the converter put you should feel a higher volume of exhaust moving out the tail pipe. If it is a flanged cat then disconect it and see if this makes any difference.

 

Thanks Charlie !

 

 Yeah, I think it is definitely clogged up. I started up the truck today and let it idle for about 5 minutes, and when I walked by the exhaust pipe in the rear I felt some mist with dirt on my bare leg. Stuck my hand there and got some more of this wet mist with brownish dirt mixed in. And then the same thing again -- when you rev the engine the air pressure output from the exhaust pipe goes down and gets really hot. BTW, I am 99% sure the cat is welded on the pipes. I need to check again, but when I had my head under there (for a few seconds) it looked like it was welded. This is REALLY hard for me to do because I recently had spinal surgery to my neck, and so I need to lay down on my back so as not to trigger bad neck/arm pains. But I am determined to get this baby moving again.

 

 I think I may have the Double Whammy going here: 1) a clogged cat on the exhaust side and 2) a starved carb.

 

I know it may sound crazy, but I was thinking about getting somebody to cut the exhaust pipe right before it reaches the cat. Is that feasible ? Here in New Orleans we don't have to worry about yearly emissions tests. I'm just not sure if I could run the truck like that before having somebody weld a new pipe in there to connect to the exhaust pipe in the rear.

[sage691]

27 minutes ago, datzenmike said:

Oh, I thought you could see it up near the bottom of the glass.

 

Appears to be a delivery problem. Check the filter is not clogged. If it is throw away and put an inline fuel filter between tank and the pump. Make sure you do it protects the pump from crap.

That fuel filter was changed about 1 month ago. But I'll go ahead and get another new one put in there since they are so cheap !

[NC85ST]

Also if it’s a fuel delivery problem and you change the filter inside the pump, make sure you order the rubber gasket that goes with the filter. It doesn’t come with the filter. (Ask me how I know) The bottom twists off the pump to access the filter. You can see where in Charlie’s picture.

[sage691]

3 minutes ago, NC85ST said:

Also if it’s a fuel delivery problem and you change the filter inside the pump, make sure you order the rubber gasket that goes with the filter. It doesn’t come with the filter. (Ask me how I know) The bottom twists off the pump to access the filter. You can see where in Charlie’s picture.

Wow, I must have a different pump altogether as mine does not look like Charlie's picture. And my fuel filter is separate from the pump -- it is housed in a clamp and has a hose coming out of it that attaches to the fuel pump.

[datzenmike]

Can you post a picture of it? If after market it could have failed or be incapable of providing the quantity you need.

 

Well that leaves a volume test at the carburetor.  If over 1 liter per minute then the problem is perhaps at the carburetor inlet. There is a banjo fitting with a brass screen to catch dirt right at the carburetor inlet that could be part plugged. Then maybe the needle valve or float set way too low.

 

If not, a volume test at the pump. It's even possible that the fuel line is partly plugged or pinched between pump and carburetor.