Hubby's 240Z is at the mechanic's. He drove it to work and it ran like a top. When he tried driving home, the engine died and when he started it, it ran rough. Sparks were coming from the muffler as well as black smoke so he limped it around the block and back to the parking lot. The muffler was incredibly hot and an odd burning smell (not like oil though) filled the car. When I got to the lot to pick him up, he started the car up. It sounded fine to me but Hubby said it wasn't running right and that odd smell started in the car again, but I couldn't smell it outside. No smoke from the tail pipe either.

We had a cat converter installed a couple months ago as a last-ditch effort to get the car to pass emissions.

Any idea what the problem is?

I don't think you can run a cat on an early Z. There is too much raw fuel for the cat to deal with. I imagine that the cat was clogged.

If you have an exhaust leak it's possible to have flames come out of the tail pipe when downshifting. (air mixes with unburnt fuel on decel and exits as flame) It's pretty neat actually. The driver just hears a muffled pop but others can see fireballs coming from the tailpipe.

"Sparks" like little embers could mean that the cat is/has broken up a bit or you have a vandal or mice making a nest. ??

Have you guys looked into the smog pump system and had the carbs tuned? I hope the odd smell is not the cat burning the underside/inside parts adjacent to it. Cats tend to get pretty hot.

I'm sure if you search the threads for emissions you will find some helpful ways to pass.

2c

Jim

Edited October 24, 200915 yr by JimmyZ

OK, that doesn't sound bad Not exactly good, but I could definitely handle that.

OK, that doesn't sound bad Not exactly good, but I could definitely handle that.

Does your 240Z need to pass emission testing? And if so what is the criteria that they use ?

I have a 82 ZX engine in my 240Z with zero emissions equipment and running SU carbs , no cat or anything.

I am not required to test for emissions but I took it to the State testing any way, and it passed. My Z is a '73.

Gary

Gary, unfortunately we have to test anything built from '67 up. I'll have to find exactly what they test, it's two elements; one is CO and I believe the other is hydrocarbon, both at idle and at load. My 260Z has a stock engine, running home-rebuilt SUs (about 6 years ago) and no emissions. It's passed for several years, last year was the first it failed. The 240Z original engine has been rebuilt and overbored, has professionally rebuilt SUs (about 3 years ago) and also no emissions. This is the one that fails every year, and each year it's a little worse. I don't know if the county is tightening the requirements (entirely possible) or if it is a function of wear of the carbs.

I'm wondering if the needles could be causing the problem? I assume they DO wear.

Lean it out as much as you can and still get good power. It will run hotter so I would do it about a block before the station....

HC and CO tells me you should try to lean it out to see if it helps. Where the load test takes place, the mixture adjustment does very little IIRC. The needles really take over when the vacuum pots rise. Also check the condition of your spark plugs/gap, cap, rotor, and wires. Your smog pump would help with your HC levels. Playing with your timing/advance may help too but I can't really say which direction you should go. They obviously aren't checking visual if everything is removed so there may be no spec they are checking.

Too much fuel will destroy a cat in short order. The internals of the cat overheat when they try to catalyze the unburned fuel. This is why owner's manuals in newer cars tell you to pull off the road if your check engine light starts blinking at you. It is essentially telling you there is a fault severe enough to damage the cats.

A hotter spark may also help but too much may raise the NOx levels a small amount.

It's a good thing you don't have a visual test there... hope this helps you a little bit