Question for the Techs

[tollboothwilley]

My friend has a 2003 350Z 6MT with ~66K miles on it. His car has been acting strange. When the ambient temp is under 45* his car will bog down under heavy acceleration. It is not gear specific and it is not a constant thing. It can happen 10 times in a row and then not again for 10 more.

After driving for 20 mins or so the problem will not occur again until the engine cools down some.

It is almost like he is pushed into limp mode at around 3000rpms at random times. He hasn't kicked any CEL. There are no codes present.

Thought it was the spark plugs and since the mileage we changed them. No change.

He only has an intake mod, nothing else.

Any ideas??

[Poyzinous]

test the fuel delivery system. And run a check with the Air fuel ratio sensors and oxygen sensors.

[tollboothwilley]

Well, unfortunately I dont have the equipment to test the A/F or the O2s.

Wouldn't O2's kick a code though?

Would a MAF sensor cause this to be a problem?

[BrandAidDesignG35]

My car went into limp mode once. It would not engage over 2nd gear.

I felt that it was due to moisture on the ECU, I had it cleaned, as suggested by steve the tech, and it's never happened since.

This seems to be related either to an air filter clogging, or maybe a fouled MAF.

Which intake system is he running? Did he damage his MAF during intake install? If he didn't properly install his air intake, and his filter element is cramped or blocking air flow, this could be the culprit, I don't know the relavence to the ambient temp... It's also hard diagnosing a car half way around the world

[tollboothwilley]

Ambient temp is for some reason a factor. When the temp outside is over 40-45* then there is no noticeable difference.

Thats why its such a weird issue.

[SteveTheTech]

My first inclination would be a MAF related concern. 90% of the fuel and ignition system issues will at least through you a symptom related code, ie fuel system lean, or timing control. The MAF and integrated IAT (intake air temp) really only detects an open or short in the circuit although they can cause all kinds of driveability concerns.

I strongly recommend this scanner that allows you to monitor live data, the 3130 model even records, I bought mine a while back and I think it's the model before that, but it's a great device for running OBDII codes, and getting a rough idea of what the ECM is seeing.

To start this diagnosis the first thing I would do is remove the air filter and check it? If it is not a direct factory replacement (remember that increased air flow means bigger holes the filter median) than I would pull the MAF sensor itself. Once the MAF is out look into the lowermost forward facing hole (where the exposed wires are). I would use something like a computer can of air to blow anything that may be interfering with air flow out. Once it's out check both the male and female ends of the MAF connector.

Check that first and update us and we'll try to point you in the right direction.

[tollboothwilley]

gracias

gonna swap out MAF and maybe intake system completely tonight after the gym

i'll report my findings

[awdjdmtalon]

I would also check the engine coolant temp. sensor. If the car thinks it is colder then what it is, it will add fuel and cause the vech. to loose power due to running too rich.

[tollboothwilley]

Wow. You'll never guess what the solution is..........AFTERMARKET LED Tail Lights. Cause an irregular voltage to the ECU

It treats it as if the brakes are depressed, which also affects the cruise control function

[SteveTheTech]

So how did you manage to get from the engine running rough intermittenantly to aftermarket tails as the route cause?

I'm just curios. What led you to the conclusion.

[G_whizz]

So how did you manage to get from the engine running rough intermittenantly to aftermarket tails as the route cause?

[Tampa G35 Sedan 6MT]

I want to know too!

[kmech_7]

[tollboothwilley]

The only thing that has changed in my friends car was intake, rims, and tail lights.

I know the rims aren't going to cause a problem. The intake he has had for a long time so there was no change from that. He actually paid a shop to replace the MAF already back when this started happening, so that was also out.

Did some searching around and found out that many aftermarket LED tail lights are not prewired with correct voltage in mind. Stock 2006 350Z tails are LED and have no problems, but it would appear that they were constructed with a specific range of resistance.

A simple swap of the lights with some OEM lights...

[tollboothwilley]

He still wants to keep these aftermarket LEDs, so now it will be a game to find resistor values to correct the resistance levels.

My assumptions are that with 20 LEDs there is a greater resistance load and that I will have to find a high-wattage resistor to wire in parallel.

Some people have thought the opposite, and have wired in series with a higher resistor....

This should be fun! LOL

[Sentientbydesign]

I think you should be able to run 5 lines of 4 LEDs and that should work with a small resistor.

Assuming the LEDs have a forward drop of 3.4V (typical of super bright white LEDs). So 3.4V x 4 (in series) = 13.6 which is close to your top end voltage when the car is running.

If the LEDs draw 30 mA, then (I cheated and used an online calculator) a 1/8W 15ohm resistor would make everything peachy.

The problem with all of this is all of the assuming. We don't know what the specs of the LEDs are, so some testing is in order.