I am the 'proud' new owner of a 3000GT/SL and we are having difficulty getting the car to pass emmissions test. At first the car waqs failing all tests, now after some $$ and some time, it passes only on NOx gases. CAr has 117,000 miles on it and it may have never been serviced before our purchase. The var is failing on the 25 and 15 MPH tests, engine is expelling about 3 times the allowed limit for CO and HC.

The following has been done:

1. Running 2% fuel mixture when measured at the exhaust manifold before the CAT. Tapped a probe port on the front manifold and checked gases before CAT.
2. Complete tune up including NGK platinum plugs straight from the dealer
3. Replace Oxygen sensor (OEM Bosh)
4. Oil & Filter
5. Fuel filter
6. Air filter
7. Waterpump (bearing noisy when purchased)
8. Timing belt tensioner (worn out and rattles after about 100K miles I guess)
9. Replaced upper intake manifold, it's the only way to get the variable intake stepper motor and sensor, this causes fault code '62'. Fault code went away immediately after replacing
10. No fault codes
11. Temp guage indicates engine warms up
12. Resistance at coolant temp sensor is correct
13. Throttle Position switch is functional
14. Replaced CAT converter (now passes on NOx still fails on CO and HC)
15. Coils ohm to correct value
16. No vacuum leaks can be found.


The only other symptom that I have, that may be unrelated is that the car stumbles a bit till the engine warms up, that takes about 2-4 minutes. At times you can feel the car stumbling at about 1/2 throttle...then something really seems to kick in and the car launches forward like you took your foot off the brake. This problem goes completely away after the engine warms up.

What makes these cars run fat and can you adjust the fuel mixture?

 

umm, ya got me.............. try a combustion chamber cleaning, complete fuel system flush............ other than that i got no clue.......

 

OK so how would you go about cleaning the combustion chambers?

We use to blast the inside of the intake manifold and back of the intake valves with crushed pecan shells and compressed air...but that was a long time ago. I am currently running through a can of 'G2P' (Guaranteed to pass) with hopes that I might have an injector or two with a partially clogged pintel. I dont think this is the case because the car holds fuel pressure when not running and no black smoke from flooded cyls when started or parked for brief periods.

I know for sure the top side intake manifold is squeeky clean, it was just replaced, and when replaced I also cleaned as far down the lower manifold as possible...as far up as to the base of the intake valve. I cant say how clean or dirty the back of the intakes could be...but again the G2P (a strong fuel addative) I hope will help in that regards.

I am measuring voltages at the engine control module also and so far they have all been spot on. I do need to confirm that not only is the O2 sensor attached (it's new as well) but also need to confirm the proper signal is getting to the engine control module.

All I can say for sure is that I am getting too much unburned fuel in the emmissions which could be caused by an over rich condition (adjustable fuel/air ratio anyone?), cam timing is not right (just replaced the tensioner right?), or anything else that might cause a miss-fire. I know it's unburned fuel but can't for the life of me explain for sure if it's just too rich, or a mechanical or electronic.

No fault codes and all sensors are checking out correct EXCEPT for the air mass sensor. from 32F to 180F the ohm range should be something like 400 ohm to 6K ohms. The lowest reading I could get (ice on the thermistor) was 600 Ohms and the highest was just a hair over 4K. The reading at 68F should be 2.7K I am getting 1.7K. I previous (Stealth) I owned had a cold running problem (turned out to be a fuel pump) and the air mass sensors were almost exactly the same as this car so I feel somewhat sure it's not the air mass meter...but could be wrong.

 

well, im not to familiar with the 3kgt but if you think it might be the MAF you might try opening the intake up a little..... if they are anything like the eclipse then they have honeycombs in front of the resistor, leave the one in front of the resistor there, but you might try pulling the other ones out one at a time and see if that helps your readings at all, cause if your not gettin enough air in then it would cause the engine to run rich....... ill try and find that link for the combustion chamber cleaning for ya....... hope this helps..........