1992 300ZX CAR TROUBLE IN NEED OF HELP!!

[WimboZ32]

Hey everyone,

So I am new to the forums and I just bought a 1992 Automatic N/A 300zx from a friend of mine that has been sitting in his garage for 8 years due to some problems with the transmission. With only 79,000 miles on it I thought this thing was a steal and I new I could fix it up over time (and lots of money). I have already had a lot of work done on it (general upkeep and repair) and it has done really well for the short time that I have had it. The previous owners of the car didn't take good care of it and it has some body damage as well as interior damage that I have not yet taken care of.

My biggest problem as of late is I recently replaced the stock air filter with a cool air intake system and I don't know if I did more bad than good. Driving in the city is really good but when driving on the interstate for 30 minutes or so it starts to bog down on RPMs. To give a better description, I'll give you a scenario of what happens.

EX: Driving on the interstate going 80 mph. Slower vehicles ahead of me gives me no other choice but to slow down and wait until I have enough room to get past them. When given the chance to get past them and speed back up to my original speed of 80 mph the car will not do it even if I floor the gas peddle. I am completely unsure of what the problem is... To make things more confusing, the situation goes away if I pull off on the side of the interstate, turn off the car and wait a few minutes, turn it back on and go down the road for 20 minutes more only to have the car go through the same issue again.

I have to take regular trips on the interstate so I need to figure this out and I would love any input from you guys, THANKS!!

[AZhitman]

Sounds like either an issue with the MAF sensor or a disconnected vacuum line.

The original Z intake was not a bad design - You won't get enough benefit from it to justify the other issues that come along with it, especially if you are trying to return it to its 'as new' glory.

Welcome aboard!

[MarkerZ32]

Could be a clogged catalytic converter. These don't fair well in vehicles that have been sitting. If you let off the throttle, does it momentarily get power back?

[WimboZ32]

MarkerZ32 it does get a little power back but not much and not for long.

AZhitman I have been reading where most people say the same thing about it not being much help. I'll be putting the stock filter system back in

[MarkerZ32]

Sounds like the typical symptom of a clogged cat(s). Exhaust pressure is building up as well as heat in your manifolds and that's not good. Have a shop with an optical scope look down both pipes. There are two, three bolt flanges with 14mm bolts. These bolts will break if heat is not applied to the flanges first (this will cost a diag fee). If they have a temperature scanner "Temp Gun" they can measure the temps before and after the cats and some shops might even waive the fee if you have them replace it. or Or OR a shade tree mechanic will hollow them out for you

A note on engine performance: you will not see any gains from improving your intake with out also improving your exhaust flow. As far as flow is concerned; bigger is not always better. If you increase exhaust volume too much, you will lose velocity.

[WimboZ32]

Thanks for the info MarkerZ32! I hope I can figure this out soon

[MrFeesLaw]

You have an intake currently installed on your car (which I imagine wasn't free), so if you find that the cats are bad, a good suggestion might be to replace them with a straight piece of pipe the same diameter as the rest of the pipe. This will give you greater exhaust flow without losing much velocity (as previously stated) and it will give your intake enough extra flow to actually be useful! You have a 92 model, which means there is no sensor after the cat so your car will not even notice that anything has changed, aside from the fact that it can suddenly breathe better.

Good luck with the project!!! I recently did a manual trans swap and custom welded my own full exhaust system so if you have any question feel free to pm me.

I also have my working auto trans and every auto trans part (except some of the wiring) for sale in the classifieds section of the 300zx forum. Let me know of there's anything u need from that.

[MarkerZ32]

^^^^^^^^^ yes. So much yes!

After my last emissions test, my car became exempt as the next test date fell after the car hits 25 yrs. So what did I do? Headers, x-pipe, a pair of megans and sold the cats! Talk about a noticeable difference!!!

[MrFeesLaw]

I still need an x-pipe for mine. But I have race-style headers and 2-1/2 inch pipe all the way back to dual magnaflow mufflers. Sounds really angry and I love it! We have no emission testing where I live, so I can pretty much do what I want.

[WimboZ32]

One quick question about the cats. Because there is no sensor on my 92, would I have to have a tune up on the car once I put straight pipes on AND can this project be done at home with common tools or would I need to go to a shop and have this done?

[MarkerZ32]

You should have only 2 heated oxygen sensors (three-wire type) before the cats, one on each (they will be on the manifolds, upstream from those three-bolt flanges I told you about). Since your '92, like my '92, does not monitor exhaust gasses after the cats you do not need a tune. The stock ECU will compensate for the faster flow and advance the timing and adapt injection pulse as necessary without throwing a check engine light. However, if you have to test your emissions it will most certainly fail without cats. If you fall into that category, I would have any exhaust shop weld in a pair of test pipes (two lengths of pipe with two or three-bolt flanges on both ends) this way you can "wait until you have the money for cats". If you got a welder I'd say have at it. But, if your not a serious wrench you should leave this sort of work to a professional.

Note: someday down the line you might want to delete your EGR as this is also part of the power-robbing BS the government would like you to believe is gonna save the planet. I would do this in conjunction with a pair of headers. An oil catch can (to retrofit the PCV system) is also a really good way to extend engine life.

[MarkerZ32]

Oh, and you need to give your Z a tune up every 60k miles. Timing belt, spark plugs, fuel filter, air filter, clean idle air controls, clean MAF (gently and with the right cleaner). Then there's a 120k mile service which is all of the above plus water pump, oil pump (optional), timing idlers and studs, timing belt tensioner and pulley, coolant change, thermostat and VTC sprockets (you will hear them when they start s*** the bed).

Following this maintenance schedule along with diligent oil changes will keep your N/A motor running for a very, very long time.