92 240sx : not maintaining speed

[worangejuice]

1992 240sx 5 speed 120,000 miles aem intake fresh oil changeHi,On smog test, my car will not maintain 15 mph during the testing. So my 240 can't be tested. Any theories.Thanks *First post, I searched and found no relevance to this question.

[onosqv]

What happens exactly? Does it go up or down or fluctuates?

Have you tried getting it to hold 15mph in gear 2?

Checked the throttle cables and throttle body plate for gooey/looseness?

[NISTECH]

Yes more info. What is it doing when its on the dyno that it wont stay in the 1 mph window?

[worangejuice]

Wow, thanks for replying guys!

Yeah the speedometer count on the "smog" machine goes up to 15 then drops to no less than 14mph (14.3,14.7,etc.) The tester runs it in 2nd gear. So the tester says it can't be tested. I cleaned out the throttle body, far as I could reach in. There was some grimeyness;blackstuff. A problem was also that my 240 would be sluggish from 2k-3k, then it screams through the rest of the RPM's. I just got some new tools and I'm going to change the spark plugs and the wires. I hope it's that simple. I would like to 'test' the fuel injector's, but lack the knowledge. I also changed out the fuel filter to a z32 one. It still acted the same. I also read up on some "seafoam". Still need to read more into that. The car still runs like a little beast, but still feels like it could run better. Thanksworangejuice

[NISTECH]

I run smog tests all the time. I am trying to understand what is happening. When he trys to maintain 15mph. Is it staying in the window but jumping around more then .4mph in 2 secs? That too will kick it out of the test. The window is 1 mph up or down almost. You cant go below 14.1 mph or over 15.9 mph and you have to hold it for up to 90 secs. At 25 mph same window but only 60 secs.

[worangejuice]

I passed smog with no problems!!!!!!!!!It turns out it was my o2 sensor. I changed out my spark plugs with new NGK's. I seafoamed the gastank, crankcase, and intake. A sh_tload of whitesmoke came out when I took it for a test run after I seafoamed my coupe! It was pretty funny. I replaced my old o2 sensor with a new bosch from napa. I also got a oil change with castrol for a sweet hook-up price! I'm still waiting on aurora plugwires, then I'll be set. My car also doesn't 'choke' between 2k & 3k.

Mind you I have minimal mechanic experience, and had to buy new tools, cause I didn't have any. You can do it too!

NGK plugs: $833 piece tool set: $30Bosch o2 sensor: $32o2 sensor remover tool: $153/8-1/2 wratchet head adapter: $5Castrl oil: $15/5 qts.bosch oil filter: $5Seafoam: $12/ 2 bottlesZ32oem fuel filter upgrade: $12New tank of gas: $40 CaliforniaNumerous trips to autozone and club240/nicoclub.

Fixing my car and passing smog myself: priceless

Thanks for all your help guys!

[matt4pl]

nice dude, we need more people liek you, that actually go out and do things instead of thinking about them and asking endless questions, congrats on the test