Fuel mixture problem...fpr???

[Darbji280z]

I've got a '76 280z. My car has been sleeping for four years until I bought her and woke her up. Now she ran great when I bought her (three days ago) but I've been driving her. Mainly showing her off to all my friends and family. Well I notice the car ran increasingly rough. First I noticed just a little loss of horse power. Then she started to hesitate when accelerating. Now she's running like garbage and sounds terrible. The engine bay smells bad of gasoline and the milage is horrible. I've even stopped driving it. What it seems like to me is that the car is getting way too much fuel. I haven't yet tried that little trick of pulling the vacuum line off the fpr but that's where I'm going to start. If that doesn't end up being my issue, what do you guys think it could be? Any ideas? Thanks.

[Chris'sZ]

I start with the little stuff cause usually that's what it is. Have you changed all of your filters? Checked plugs, wires etc...

That's where I would start, but trust me, you will get more and better input.

Chris...

[=Enigma=]

Since the engine compartment smells of raw fuel, I'd start buy looking for leaks on the fuel rail and hoses. While in there I'd check the fuel filter to see if it's clogged with rust from the tank. Rust tends to form in the tank when vehicles sit for long periods of time, especially when exposed to the elements. This could lead to clogged injectors causing them to spill fuel into the cylinders which can be checked by puling the plugs to see if they're wet and smell like raw fuel. Aside from that, I'm not very familiar with diagnosing FI on these cars so I'll stop there.

[KDMatt]

Since the engine compartment smells of raw fuel, I'd start buy looking for leaks on the fuel rail and hoses. While in there I'd check the fuel filter to see if it's clogged with rust from the tank. Rust tends to form in the tank when vehicles sit for long periods of time, especially when exposed to the elements. This could lead to clogged injectors causing them to spill fuel into the cylinders which can be checked by puling the plugs to see if they're wet and smell like raw fuel. Aside from that, I'm not very familiar with diagnosing FI on these cars so I'll stop there.

Hrm, perhaps I'll chime in now, being an FI-guy. What Enigma says is true, if there's a lot of garbage in the fuel and it passes the filter, it can clog up the injectors and keep them from closing properly, thus discharging all of the built up fuel pressure into the cylinders while the car is off.

However, let's not get too far ahead and jump to conclusions.

First, are you seeing any smoke from the exhaust? Grayish/Blackish smoke indicates a rich condition in the engine, that's one way you could tell. The other way is by pulling the plugs. If you see dried-up, black deposits on them (the plugs will usually just be covered in the soot), then it's almost certain the fuel mixture is off as a result of a bad sensor or clogged/leaky injectors (this is my Z's chronic problem).

Also, you say that the engine bay smells like gasoline... I had this happen as well, it turned out to be a leaky hose on the fuel-rail (and that little tiny leak was robbing away enough fuel PSI to make the car run and drive like crap too, I was thrilled when I finally figured it out). So what you should do is, with the car running, inspect all of the fuel hoses. Rev up the engine a few times (this should increase the pressure if there's a leak), and see if you can pin down where it's coming from. Just follow your nooooooose...!

Check it out and report back.

[76Datsun280z]

If that doesn't work, also check your thermotime switch.

Here's a link to the EFI "bible". It's very easy to read and follow, you may want to check it out!

http://www.atlanticz.ca/zclub/techtips/efisystem/280zfuelinjectionbook.pdf

[Darbji280z]

If the injectors are clogged due to the build up in the tank, what is the best way to go about cleaning them? Or should I just test and replace them? Air filter is new. Plugs, wires, cap and rotor are new. I suppose I will check the fuel filter. I might as well replace it. It's old anyway. Most of those cute little hoses leading to each injector are worn and starting to fray. I plan on replacing those, too. I have the day off tomorrow so I am certian I'll spend it working on the car. I am determined to get her running well again. She's far too pretty to sit in my garage all the time.

Now... please explain to me what a thermotime switch is. I sell auto parts for a living and have never heard of such a thing. What is it's primary purpose?

Well, I'll check a couple things and get back to you. Thanks so much for your help.

[76Datsun280z]

If the injectors are clogged due to the build up in the tank, what is the best way to go about cleaning them? Or should I just test and replace them? Air filter is new. Plugs, wires, cap and rotor are new. I suppose I will check the fuel filter. I might as well replace it. It's old anyway. Most of those cute little hoses leading to each injector are worn and starting to fray. I plan on replacing those, too. I have the day off tomorrow so I am certian I'll spend it working on the car. I am determined to get her running well again. She's far too pretty to sit in my garage all the time.

Now... please explain to me what a thermotime switch is. I sell auto parts for a living and have never heard of such a thing. What is it's primary purpose?

Well, I'll check a couple things and get back to you. Thanks so much for your help.

If you take the fuel rail off to get the injectors out, you can take them down and have them cleaned by Napa Auto Parts and they will clean them for you. We had this done on my car. It was pretty expensive, so I would start out with the small things first such as checking your themotime switch for continuity. If you do a search on this site under "thermotime switch", you'll learn just about everything you ever wanted to know about them and how they work and the other "ins and outs" of how the efi works on these cars and the problems they can have and such. Basically what the thermotime switch does is control cold start (which is essentially a 7th injector) to add more fuel (about 10seconds) when the car is completely cold for easier starting and will then ground it out thus cutting fuel to the coldstart valve. If the thermotime switch is getting a bad connection or needs to replaced and not working correctly, the cold start valve could be on all the time which would account for the rich bad running. If you've got a volt. meter, you can check for continuity which there shouldn't be but for 10 seconds or so right after you started it when it was cold. Since it sat for so long too, if you haven't already done it, drain the old stale gas out of the tank. Even better, if you check out and read the efi bible, you can learn even more and you'll learn where all this stuff is and how it all works together and how you can test it if you've got the right equipment.

[KDMatt]

Actually, to my knowledge, that little bit about the thermotime switch isn't true.

The thermotime switch is only active when the circuit powering the starter is active. As soon as your key returns from the "Start" position to the "On" position, the thermotime/cold-start circuit is dead. So I highly, highly doubt a bad thermotime switch could be giving you any grief. Sorry '76, not tryin' to steal your thunder bro.

Anyway, just start by checking the hoses with the engine running and looking for gas. However, frayed hoses aren't necessarily 'leaky' hoses. I have plenty of old hoses under the hood of my Z that look like crap, but still hold up every day.

You could theoretically spend over $100 getting the injectors professionally cleaned/rebuilt, but I would not worry about that right now. If the injectors got clogged, then they got clogged for a reason, and it would be in your best interest to find out why before you go down that road, otherwise, what's to keep it from happening again?

Anyway, check simple stuff first... Find a copy of the EFI bible (I could probably send you the PDF for it tomorrow if you want, plus the full '76 Service Manual) ... for all we know it could just be a faulty temperature sensor... and that's a very simple fix.

[76Datsun280z]

Yup, you're right about the cold start valve being opperated only when the key is turned. Big mistake of mine. I also forgot to mention how the temperature of the engine effects the length of time the cold start valve stays open.

So, since the thermotime switch grounds the cold start valve from flooding the engine from when it's warmed up since it does not need the extra fuel, wouldn't that be something to check to see if it is opperating correctly? In other words if the thermotime switch is getting a bad connection or the heating eliment inside the switch is not working correctly (bi-metal not opening) wouldn't that be causing the car to run rich?

[KDMatt]

So, since the thermotime switch grounds the cold start valve from flooding the engine from when it's warmed up since it does not need the extra fuel, wouldn't that be something to check to see if it is opperating correctly? In other words if the thermotime switch is getting a bad connection or the heating eliment inside the switch is not working correctly (bi-metal not opening) wouldn't that be causing the car to run rich?

My hunch is it can't cause the car to run rich. The thermotime switch breaks the ground connection with the cold-start valve, but in order for the circuit to be complete (even if there were a shrot to ground in the tt switch), a positive charge has to be supplied as well, and that can only happen when the key is in the "start" position... unless the wiring is totally messed up and there's a short on the + side of things, but if that were the case the cold-start would be stuck open even with the engine off! ... but I don't think that's very likely at all.

Now as far as I remember from the EFI guide, there are four components that impact the fuel-mixture as far as the ECU is concerned.

AFM (Air-flow-meter)

Air-temp sensor (inside the AFM)

Coolant temp sensor (inside the thermostat housing)

O2 Sensor (in the exhaust manifold ... my Z doesn't have one, does yours?)

oh, and I suppose the Throttle Position Sensor (TPS) also.

What that doesn't take into account is the possibility for leaky hoses, leaky injectors (including a leaky cold-start)... basically anything mechanically faulty.

... and I'm sorry about hijacking your thread Darb, we just both really want to make sure you get this taken care of before Z-withdrawal kicks in.

[sblake01]

280Z's don't have oxygen sensors. They didn't show up until the ZX in 79.

[Darbji280z]

Well, just for kicks and giggles, I checked the injectors with am ohm meter and they're all okay. Which I expected. I found a hose with a little tiny leak on the fuel rail, which would account for the smell of gasoline in the engine. I fixed that hose and the problem still remains of the car running bad. Today I'm just going to go through everything I can think of and see what I can find. This may not even be a fuel problem at all... This engine is still a little foriegn to me. I'm used to working on little and newer four cylinders and the V-6 in our DeLorean. This engine is new and I've got to learn my way around it. Anyway, I am going to go over her with a fine-tooth comb today and get back to you with what I find if anything. I really appreciate all you help with this. I can admit that I am very frustrated. I just got the car and can't really drive it. It's the most terrible circumstance having a new toy and not being able to play with it. I love her though and I am confident I'll find the issue and get it resolved.

Thanks again, guys and I'll get back to you soon.