Fuel or Exhaust issue - not sure

[bhermes]

I have not had time to run any additional tests but will do so in the next couple days if not on the weekend. Extremely hot here. I did check out most of the hoses and did not find anything at least that I could see. Ok other than the boot between the AFM and TPS. I am attaching a photo which may be a little hard to see but the right end of the boot is taped with black electrical tape. Appears to be taped well but probably is covering a leak point. How significant could this be if at all? In addition could someone please tell me what the part is called and what it does in the second photo. There are a few small lines that are not connected and or damaged. Just a reminder I am learning.

[madkaw]

I would think any leaks between the AFM and the throttle body would be of signifigance. Your AFM is measuring the amount of air going to the TB and you are sucking more air past the AFM that is NOT metered. You could try the old propane test and see if you are sucking air in that area. Some guys use carb cleaner to spray around possible leaks also. If you note any change then I would suspect that the tape is not holding or other cracks have formed.

Not sure what the second pic is

[grantf]

the second picture is for the heater controls, I forget there name. When power is supplied they open to allow vacuum to the vacuum selector behind the heat and fan controls. I believe there is a check valve somewhere in line before the vacuum canister.

[bhermes]

The small lines running to the bottom of this part are bad. Will this have any impact on how the car performs?

[FastWoman]

The intake boots usually crack inside those accordian-like folds, so I'm skeptical the tape is covering a crack. But you never know. Pull off the tape and have a look!

The little doodads in the second photo are called "magnet valves." One of them turns the vacuum on and off to your HVAC control systems. It sometimes goes bad, so people just bypass it without any ill effects. The other one switches vacuum on and off to the high idle actuator on your throttle linkage assembly. It's the thing mounted to your intake manifold with the hook on the end of it, which pulls against the tab on the side of the throttle linkage. This system is actuated along with the compressor when your A/C kicks in. Mine is fussy as hell, and it's almost impossible to adjust well. If yours doesn't work, I wouldn't worry about it too much. The engine can pull the compressor at a normal idle just fine. There's a diagram of how all the HVAC control tubing is connected in the heating/AC section of the FSM.

[bhermes]

Ok back from being gone for 2 weeks. I am just ablout convinced that I am running lean and will be making some minor adjustment to the AFM and probably to TPS as well. I will adjust slowly and just check things out as I go along. I will also be replacing the boot that has the tape on it. Not worth worring about in the future.

A couple other things if you don't mind.

1) A little background so you can understand what happened. I drove the car from Louisville to Lexington 4 times in the last 2 weeks (about 120 miles round trip x 4). This is the most I have put on the car in a short period of time. Normally drive 6 miles per day during the week and normally top off the fuel each weekend. Basically the tank usually runs no more than 2-3 gallons below full. My fuel gage does not work (on the list for fixing in the future). The car drove fine minus the kick back and little exhaust fumes. The day after I returned the car stalled on me. It appeared to be kind of like running out of gas but maybe a little more abrupt with just a couple spurts before dying. I am getting 24-25 mpg and based on the fuel I added while on the trip I suspect I was down to less than 2 gallons left in the tank. Cant be completely sure. Question, I am suspecting either rust in the gas tank or a hole in the pick up line. I really not that familiar with the gas delivery. I added about 1 gallon of gas 10 minutes after dying and the car would not start. Wanted to but acting like no gas. I waited about 2 hours and added 2 gallons of gas and the car started but was struggling. Tried to drive the car home but died about 1 mile later. Added another 2 gallons the next morning and the car seemed to drive fine. Sorry for the lengthy explanation.

2) This should probably be another post and I need to search but how do you lossen the idler pulley to put on the AC belt. I have lossened the screw going up and down and not sure if I need to loosen the screw going directly through the pulley.

Thanks in advance.

[bhermes]

Got idler pulley to move and belt is on. Still would like feedback on the rust in tank or hole in pick up line.

[FastWoman]

I onced had a '75 that developed a rust hole in the pickup tube. It "ran out of gas" at about a half tank. It only took until 1984 (?) to develop this problem. I believe the '76 and '75 tanks are probably similarly constructed, but I don't know for sure.

That said, your fuel pump might be dying. The pump in my '78 recently died (faded away, really), and it had symptoms similar to yours. The only difference was that I didn't add gas before trying to start my car again. Simply letting the car cool down and rest was enough to resurrect the fuel pump for another 10-20 min, before pressure and delivery volume went south.

If you are persuaded it might be the pump, please don't just replace it to see what happens. Again, parts are disappearing, and someone else might really need that pump. Throwing away a functional antique part is very bad karma, so please test the old pump first.

Here's how you can test both the hose and the fuel pickup line: Buy a long, clear vinyl hose to connect from the fuel return fitting of your fuel rail. The hose should be long enough to drop the other end into your fuel tank filler neck. Start your engine, and let your car idle in the driveway. Watch how fast fuel flows out of the end of the tube and back into the tank. If your fuel pump has a heat-related failure, the return flow will diminish over time. Mine took about 20 min for return flow to stop altogether. If you have a hole in your pickup tube, with a gasoline level low enough to draw air, you will see air bubbles flowing through the vinyl return line.

[bhermes]

Just a quick note. The fuel pump was bad and replaced about 6 months ago. Does not mean that it still could not be out again but more than likely something else. I will try the clear tube test and see what happens. Also replaced the fuel filter.

If air is getting into the fuel line through a hole in the pick up tube, and I fill the tank above the hole, would it take some time for the air to escape the system? If not I would lean toward rust. Can the pick up tube be replaced or inspected or is it part of the gas tank assembly?

[FastWoman]

Air should clear the system pretty fast. The tank can be repaired by a radiator shop. It will take some cutting and welding -- probably not cheap.

[Datsun Clark]

If your still having problems with your idle speed coming down before a stop or when you press down on your clutch (assuming your car is a manuel that is), then I might be able to help. I own a 77 Datsun 280z that had the same problem. Called a guy in california that works on them and all he told me to do was to tighten the nut up on the bottom of the BCDD, which is underneath the throttle body. Try to just tighten up the nut on the bottom and see if it works.

[johnny haywire]

I know we are jumping from topic to topic here, but one thing that madkaw/fastwoman mentioned above - before adjusting your TPS and AFM - if that boot between the AFM/TB has a crack/leak in it, replace that before adjusting anything else especially if you think the car is running lean.

Also, if you haven't done it recently, changing the fuel filter in the engine bay is a cheap and easy place to start when experiencing fuel delivery issues. If the issue subsides for a bit, it may be a sign of sediment in the tank. Did the car sit for a while before you took ownership?

Keep us posted!