Hello everyone,

I recently bought a 1990 240SX with auto trans as a "great daily driver. Driven 60 miles a day on the highway. You need an alignment thats it"... we wont discuss how much I paid for it!

#1

Ok, when it is cold in the morning the car makes a thunk sound, exactly like a bad motor/trans mount... except only on the first to second shift. Once the car gets to the first line on the temp gage, the bump is very small. After the temp hits the second line, the car has no bump left at all.

#2

The idle is rough all the time. Not real bad, the RPMs don't drop, every few seconds they jump very slightly. You have to concentrate on the tach to even see the needle move, but it does, and it jumps, it doesn't fall.

#3

If you just barely tap the gas the RPMs drop severely and the car kind of shudders. It doesn't die, but it seems like it wants to. If you step on the gas normally the engine responds normally.

#4

Ok, I have a confession. I have owned a 240SX for all of 3 days now... I may or may not have broken a few laws, but what is important is that after some spirited throttle I get a backfire, or more accurately an "afterfire" sound from the rear'ish of the car. It happened twice tonight at I would say around 50 to 60 MPH from nearly wide open throttle. All I would do is let off the gas, and it would decelerate normally, but I would get a kind of clunk/clank sound. Im "almost" positive it is from the exhaust, but I'm not 100% sure. (It could be one of those weird sounds you hear inside the car from a completely different place. It "could" still be from the intake. I wont know until the weekend.)

I can do whatever needs to be done. I have all the manuals and FSM's I could find, and I am fairly sure, short of pulling a head, I can do whatever needs to be done with a floor jack and some jack stands. I don't know how to use a multi-meter. I can get one, and if someone would explain how to use it, I can test whatever you need too. I just have no idea how some people just seem to "know" what is wrong... I cant diagnose for ****.

Please help,
A very broke and desperate Nissan lover

ForkliftDude wrote: #1

Ok, when it is cold in the morning the car makes a thunk sound, exactly like a bad motor/trans mount... except only on the first to second shift. Once the car gets to the first line on the temp gage, the bump is very small. After the temp hits the second line, the car has no bump left at all.

Does the "thunk" cause the car to shudder?

ForkliftDude wrote: #2

The idle is rough all the time. Not real bad, the RPMs don't drop, every few seconds they jump very slightly. You have to concentrate on the tach to even see the needle move, but it does, and it jumps, it doesn't fall.

#3

If you just barely tap the gas the RPMs drop severely and the car kind of shudders. It doesn't die, but it seems like it wants to. If you step on the gas normally the engine responds normally.

I'm wanting to guess that these two are related. Do you have any vacuum leaks? Check for any hoses that are disconnected in the engine bay.

ForkliftDude wrote: #4

Ok, I have a confession. I have owned a 240SX for all of 3 days now... I may or may not have broken a few laws, but what is important is that after some spirited throttle I get a backfire, or more accurately an "afterfire" sound from the rear'ish of the car. It happened twice tonight at I would say around 50 to 60 MPH from nearly wide open throttle. All I would do is let off the gas, and it would decelerate normally, but I would get a kind of clunk/clank sound. Im "almost" positive it is from the exhaust, but I'm not 100% sure. (It could be one of those weird sounds you hear inside the car from a completely different place. It "could" still be from the intake. I wont know until the weekend.)

What condition is your exhaust in? Is it an OEM exhaust?

Does the "thunk" cause the car to shudder?

No it doesn't. Its a hard "thunk" sound and feeling, and then the car shifts into second and it kind of launches forward. There is very little to no hesitation before the thunk, and after the car accelerates fine

What condition is your exhaust in? Is it an OEM exhaust?

Its completely stock, but slightly loud. I am thinking there might be a small hole in my muffler. The car has been unmodded its whole life.

you have any vacuum leaks?

I am not sure. I work night shift and by the time I get off work it is too dark and too cold to do anything. I have a date with a pretty girl, a 12 pack, and my car this weekend though, so I will be sure to check and replace all my vacuum lines. They were already on my "needs to be done" list

Thank you for all of your help so far. I love this car, she just needs some TLC

1. 1-2 shift clunk.

Would probably be a good idea to change the transmission fluid since you don't know what the previous owner did. After you do that, you can see if the condition is still there. If it is, might be a good time to do a manual tranny swap if that's something you would like to do.

2. Rough idle.

Change your spark plugs, wires, distributor cap and rotor. Also clean out the IACV and the MAF (use maf cleaner so you don't kill it). Again, don't know what the prev. owner did to the car.

3. Throttle stutter.

Check the TPS adjustment and make sure that the voltage is between 0.45v and 0.55v. Also do a slow sweep through the throttle range and see if there is any jump in the TPS voltage.

4. Exhaust backfire.

Do everything else first and see what happens. Not really something that I would be worried about anyway.

+1 on vacuum leaks, tranny fluid check/replace (with filter), possible TPS issue, and cleaning the IACV. You also might want to try seafoaming the engine (if you don't know what that is, try doing a NICO search, or Google search if that fails).

Thank you for all of the suggestions so far. I just ordered a silicone vacuum hose kit off Ebay, and I will go get a can of some MAF cleaner this weekend.

Supposedly the guy I bought the car from had just done a tune-up minus fuel filter and plug wires. He said he "didn't have the right wrench" to replace the fuel filter (flare nut wrench?) and the plug wires "were fine and didn't need to be replaced" But now that I am thinking about it, I wonder if the tune-up is part of the problem. I have worked on Honda's before that simply refused to run right unless you used NGK (Honda OEM) plugs and Honda OEM distributors. Maybe my car received some DuraCrap from Autozone and just doesn't like it? Ill pull the plugs this weekend and see if they were gapped right and such.

I will also do a drain and fill on the trans. I would prefer to wait for a filter change since it is COLD outside and preferably I wouldn't want to lay on the ground for an hour to pull the trans pan. If I have black sludge come out, I will have no choice but to pull the pan and replace the filter though.

I am kind of afraid to SeaFoam my engine. I have heard horror stories about bending rods/blown engines using SeaFoam and this is my daily driver, with no second car, and no money for a new engine (I just bought a horribly overpriced car after all )

One less question. How do I run electrical tests? I can get a multi-meter from my friend, and I have all the wire diagrams in my Nissan FSM... but how do you know what to test? I have seen people say things like "check pins 8 and 37" ... what exactly does that mean? And how do you know what pins to test?

Thank you again for all of this help. I look forward to many years of owning my 240 and to contributing to the forums once I learn a bit more.

I never trust anyone when buying a car. When I got my Maxima, I had the coolant, oil, tranny fluid, brake, and clutch fluid changed within the first week. That was also a perfectly running car. As long as you don't let the engine suck in an entire can of seafoam, you shouldn't have any issues with it. Here's a good article on seafoaming a car. how-to-seafoam-your-engine-the-right-wa ... 26583.html

You should be able to find similar articles for everything that you need by either searching the site, or looking in the articles section.

A small update. I got off early from work tonight and went to the parts store. When I started the car, it idled ok (by its standards at least) but after I pressed the gas the idle was all over the place. It would drop to 300 RPM and sometimes lower. It also died 3 times, but starts right back up. Now the car will basically not idle for more than a few minutes at a time without dieing.

At least I made it to the store to get oil, oil filter, MAF cleaner (can I also clean the throttle body with this?) trans filter and gasket, SeaFoam, and fuel filter. Tomorrow is going to be a long day

MAF cleaner is essentially electrical parts cleaner and is pretty weak. When I'm taking parts off to clean I like to use carb cleaner because it cuts through anything. If you are cleaning things while they are still on the car, use throttle body cleaner because it won't mess up sensors.

Good luck with everything.

Well I have bad news. My landlord is an old school mechanic and I bought him a case of beer to help me.

Long story short, My MAF sensor was ghetto "fixed"... there must have been something wrong with it, and they gutted it. As in, they literally broke off all the internal parts, so it is nothing except an open tube connector with no electronics. Actually right now, the MAF sensor is sitting on my kitchen counter, and the car runs exactly like it did before.

MAF Sensor - $455 from Courtesy

I also have 2 injectors that are leaking badly (remember that backfire I mentioned? I have tons of unburned fuel dumping into my exhaust) And the other 2 are sticking open every once in awhile. What makes this slightly better is that I have a rust hole in one of the exhaust pipe, right before the CAT... because of the hole raw fuel drips out. If it didn't slowly leak and drip out, the car would backfire every few seconds

4 fuel injectors installed - $700 from his buddy's shop

Throttle body was black with oil and fuel, the fuel filter was so rusted it looked original, and the timing was very very off.

Long story short, I am looking at well over 1000 dollars in parts and labor, and we aren't positive that is the end of it... the 240 dream car and project is basically dead in the water and is going to need to be sold. I need a reliable daily driver for now... unfortunately I got a badly abused, neglected, and highly unreliable car.

I will be taking 3 buses, a train, and walking a mile, each way, to work until I can sell it... god I hope it sells semi quickly

And now that I feel bad, I will let you guys know how much I paid for it... it was 1800 cash. I am hoping to get 800 back out of it, but probably not

Go to a junk yard man. Hell, I have a spare 240 MAF if you want it... its for a dual over head cam instead of a single over head cam, but you might want to see if it will work anyway (do research before you take it from me). An entire fuel rail (with injectors) can probably be had for under $100.

Definitely jump over to the classified section of the forum and you should be able to find everything you are looking for MUCH cheaper. The sohc and dohc mafs are different, so make sure that you get the right one.