!!!Exhaust is burning my eyes

[Z_lis]

I don't quite know what to do... my 76 had this problem, sold it, I finally got a 73 240, I love her so much, but just the other day I drove her to work and by the time I got home I was sick! I've replaced the tail light gaskets, the hatch is super tight (I'm going to paper test it again tomorrow) my firend put a new gasket aournd the hatch... the piece of vinyl that is on the upper hatch is loose... I'll fix that up tomorrow, got a muffler. I just don't want to get rid of her. I like the smoke bomnb idea. It's so bad, I know some one has figured out this problem... help!!

[siteunseen]

https://www.google.com/search?q=240z+fumes&rlz=1C1BOFA_enUS494US494&aq=f&oq=240z+fumes&aqs=chrome.0.57j0l3j62l2.3885j0&sourceid=chrome&ie=UTF-8

[EuroDat]

A small leak into the car can be enough to fill the car with fumes. Zeds are known for it. I would start by checking the following:

1: Hatch seal and alignment.

2: Taillight gaskets and the grommet for the numberplate light. (the grommet can be too big for the cable)

3: Fuel tank piping. Especially the small ones that the grommets are good.

4: The frame rails in the car that go forward from the taillights. There is a grommet just behind the frame for the deck. Check all the screws are in the rail. I had this problem and these grommets are what was causing it.

5: Extend the exhaust pipe and check it for leaks.

6: Fit a BRE spoiler.

Dont think things are OK. Check it to be sure.

Chas

[Stanley]

Z_lis my 73 had exhaust leaks from the rusty air galley, that goes from the well-named smog pump to the exhaust manifold, in three places - all where they couldn't be seen. Cut the air galley off inside the manifold and welded it. Better but still had another leak that went away when I had a new tailpipe and muffler installed.

[bryand2]

Well it sounds like you run very, very rich when you coast at high RPM. So rich, in fact, that you're beyond a mixture that will ignite and you're pushing clouds of atomized gasoline mixed with motor oil out the tailpipe. So you should look for things that would add fuel or oil to the party.

Worn rings, valve seals, and maybe a specific kind of head gasket failure could all offer oil.

Non-functioning or improperly adjusted BCDD or AFM could encourage extra fuel. So could a faulty FPR, leaky cold start valve, or injectors.

But of all the items listed above, the BCDD is the one that is supposed to help with exactly that kind of "extra rich mixture at high manifold vacuum" emissions, so that's where I would start.

You familiar with the carbs used on the earlier Z's? If so, think of the BCDD as the fuel injection equivalent of the older throttle opener servo that pulled the throttle open when you coasted. The BCDD essentially does the same thing.

Just to specify, you say I may be pushing clouds of atomized gasoline mixed with oil out the tail pipe, the only problem is if there were worn rings or valve seals there would be smoke, and there is not. There is also no coolant in the oil or vice versa to indicate a head gasket leak. As far as I understand the BCDD, it has nothing to do with mixture at high manifold vacuum, it only prevents the idle from dropping too quickly on coast and between shifts.

[Captain Obvious]

Just to specify, you say I may be pushing clouds of atomized gasoline mixed with oil out the tail pipe, the only problem is if there were worn rings or valve seals there would be smoke, and there is not. There is also no coolant in the oil or vice versa to indicate a head gasket leak. As far as I understand the BCDD, it has nothing to do with mixture at high manifold vacuum, it only prevents the idle from dropping too quickly on coast and between shifts.

A reading from the book of FSM:

"The Boost Controlled Deceleration Device (B.C.D.D.) is employed to reduce HC emissions during coasting."

EC-5 - 1977

As for the smoke... When you are coasting at high RPM, the cylinder vacuum is much higher than it is under other conditions because you are pulling high RPM against a closed throttle plate. Under these intermittently very high vacuum conditions, you'll pull more oil into the cylinders, but you won't see smoke because you're not burning it. You're pumping it out the exhaust without burning it.

I'm just applying theory here trying to help. You asked for it.

[bryand2]

A reading from the book of FSM:

"The Boost Controlled Deceleration Device (B.C.D.D.) is employed to reduce HC emissions during coasting."

EC-5 - 1977

As for the smoke... When you are coasting at high RPM, the cylinder vacuum is much higher than it is under other conditions because you are pulling high RPM against a closed throttle plate. Under these intermittently very high vacuum conditions, you'll pull more oil into the cylinders, but you won't see smoke because you're not burning it. You're pumping it out the exhaust without burning it.

I'm just applying theory here trying to help. You asked for it.

Thank you captain, but remember that I am only experiencing this while decelerating in gear, If I am coasting in neutral I do not experience the burning eyes

[bryand2]

Does anyone have any more ideas as to why I am experiencing this only while decelerating in gear?

[Zed Head]

What RPM are you talking about while decelerating?

The ECU also has a fuel cut function, from 3200 to 2800 RPM on the way down. Page EF-12.

The BCDD's purpose is HC reduction (EC-5). Not idle control. It's not clear how though, the FSM just says it's for "maintaining manifold vacuum at the proper operating pressure". Maybe to provide extra air to allow proper burning of any fuel injected. Implied by the word "operating" in the FSM description.

I'm glad this came up because I've been catching one sharp whiff of unburned fuel right as I stop. Noticeable since it's warm now and the windows are down.

Off to check the BCDD...

Edit - just realized what that one connector with the plug in it is for, up by the coil. It's the BCDD, and maybe other, "function test connector". Looks like a pain.

Edit 2 - the instructions in the FSM for checking the BCDD are confusing. Check resistance and voltage on the same circuit at the same time. Might take more thinking.

Edit 3 - I think that instructions in the FSM for the BCDD are incorrect up to 1978 (says that 0 volts is good for everything - incorrect). The 1979 FSM has a whole new test procedure with new diagrams and a chart. That makes sense.

Edited May 14, 2013 by Zed Head

[Captain Obvious]

Thank you captain, but remember that I am only experiencing this while decelerating in gear, If I am coasting in neutral I do not experience the burning eyes

I didn't say anything about coasting in neutral, and neither did the FSM.

In the FSM, when they say "The Boost Controlled Deceleration Device (B.C.D.D.) is employed to reduce HC emissions during coasting." They aren't talking about coasting in neutral. By "coasting" what they mean is "moving down the road with your foot not on the gas pedal". In other words, "Letting the wheels drive the engine instead of vice-versa."

Question - What's the difference between "coasting in neutral" and "idle"?

Answer - Nothing.

No Duh, you don't get the problem coasting in neutral. That's because you're "idling". You happen to be "idling while your car is moving", but your engine doesn't know it's moving... As far as it's concerned, it's at idle.

Does anyone have any more ideas as to why I am experiencing this only while decelerating in gear?

I've got an idea... How about you vigorously investigate the suggestions that have been made so far and let us know what you find.

[Captain Obvious]

The ECU also has a fuel cut function, from 3200 to 2800 RPM on the way down. Page EF-12.

Hey Zed, I'm sure you know this, but just wanted to make sure it was clear to everyone else.

The fuel cut function kicks in anytime the RPM's are above 3200 and the idle switch portion of the TPS is closed. This can occur at 3200, 4000, 5500... Anything above 3200.

And once the fuel cut function HAS kicked in there is some hysteresis such that it will not kick out until either a) the idle switch is opened or the RPM's drop below 2800.

Maybe it's just me, but I found your description misleading. Made it sound like the fuel cut was only active in the band between 3200 and 2800, and that's not the case. It's anywhere above 3200.

[Zed Head]

My mistake, thanks for the correction.

I wish they had extended the fuel cut to a lower RPM. I think that's a big part of why these cars tend to be gassy smelling. 3200 RPM is pretty high, even 2800 is. Regualr driving gives no fuel cut most of the time. My 95 Pathfinder, apparently, cuts fuel when the throttle is shut at any RPM if moving. They learned.

p.s. to my other post - My BCDD and TPS both check out. I think that my AFM is a little bit funky and has an uneven enrichment curve. Not super relevant to the OP's problem. Enough about my car...