TPS/smog and high CO discussion

[darom]

Greetings,

Before I bore you guys with a lengthy post, here is the question:

can a misadjusted TPS (in an always lean condition) cause high COs? My numbers were at 15 mph - 5.01 (allowed 1.36), and at 25 mph - 5.42.

HC - 113 (max 214) at 15 mph and 86 (max 181) at 25 mph.

The car is 1976 280z, stock + catalytic converter.

My TPS and lousy weak spring linkage wouldn't return the idle back to the far right/middle TPS metal contacts and would stay in the middle position (lean/cruise mode). The dashpot also would be very slow to return the idle.

I searched and found a bunch of threads where TPS was one of the reasons why our cars might run rich. My dilemma is that in their cases the TPS was in the WOT position, which commands ECU to dump more fuel, thus creating the rich condition.

In my case it seems that the TPS was always in the middle/lean position. Would this attribute to my smog problem with high COs? Logically, it should be running lean. Am I wrong?

Here is what has been done:

- FI Bible and fuel injector FSM - all troubleshooting steps returned positive results (thermotime switch, water temp sensor, operation of the CSV, AFM resistance, AFM temp sensor readings, injector operation). The sensor readings were taken with cold/hot engine.

- all vacuum hoses and PCV valve are new

- AFM rubber boot is new

- new intake gasket

- fresh oil change, oil filter, air filter, new NGK spark plugs (gapped at 0.039)

- fuel tank was cleaned, fresh gas and fuel filter.

The car idles at 800, ign. timing is at 10, vacuum is at 17, fuel pressure (not running test - 36 psi), running it stays at 30 psi. The CSV is not leaking. The spark plugs look dark, cylinder 5 - shows some oil/fuel (hard to tell).

I haven't played with AFM yet. This is going to be my last stop (hopefully).

Air regulator is faulty (it doesn't close) and i just pinched the hose. It will be replaced. The car starts with a half-turn of the ignition key. It runs great. It passed smog 2 years ago.

What I haven't done:

- pull the fuel rail with injectors and check for leakage (especially, cylinder number 5)

- attach voltmeter to the CSV while the car is running and check for voltage presence (to isolate CSV dripping during the normal operation).

I have also adjusted the TPS to have proper contact engagement at idle. The contacts break loose as soon as the throttle is applied (how important is 1400 rpms?). It was really hard to aim for 1400 rpms limit to disengage the contacts. The WOT is applied almost at the end of the throttle pedal application. I installed 2 springs to the throttle linkage. It closes and returns to idle fast. The dashpot was adjusted to catch the throttle movement at the end.

My mechanic's smog equipment is getting repaired. I will take my car next week to do a simple tail pipe sniffer test to see how rich the mixture will get. Before I see him, I'd like to cover all my bases. We probably can tinker with the AFM at his shop.

Thanks in advance for your input.

Den

[sblake01]

The smog test in California, both the 15 and 25 mph tests, are done in an area where the TPS would be in that middle position anyway, off-idle and full trhottle both open, which is what you're referring to as 'lean cruise' so I don't think that's your problem. What's the condition of your cat?

[darom]

That was my suspicion about the middle/lean TPS position. The cat was installed by PO 2 years ago - he had to install it to pass smog. I can't tell its condition without removing. It looks like an aftermarket unit (no brand name or CARB numbers). Btw, thanks for reading my essay :-)

I just did the CSV check with voltmeter connected. It is warm here (about 75F) and it never got activated. I restarted the car a few times to double check. CSV is not running. The fuel pressure starts at 30 psi, when warmed up it drops to 28psi (it also might be due to the cheap fluid filled gauge not taking the heat).

The only thing that doesn't work at the moment is the air regulator (or auxiliary air valve). It stays open all the time. I ordered a new one from Nissan. I have 2 junk yards CSVs and none of them worked for me.

After adjusting the TPS/throttle spring the spark plugs look ok, dry and on a lean side.

Spark plugs order:

Left picture: 6-5-4

Right: 3-2-1

Edited April 16, 2011 by darom

[darom]

I found some printed numbers on my catalytic converter and it appears to be CA legal:

94000 0607

CA/CE 99000

It looks clean with an anodized 'cooked' finish.

[darom]

Update: took the car to my mechanic and did the CO test at idle (he doesn't have a dynamometer). The AFM was adjusted too rich. Opened the AFM case, the previous technician (Ed, from 11/2002) didn't even installed the return back/bumper spring. After 12 clicks CW, the CO went down to under 1%.

Took it back to the smog place, the car failed the smog again with almost the same numbers, 15 mph - 5%, 25mph - 6%. At this point I just told him to charge me the $95 'diagnostic fee' and tweak my AFM. After going back and forth, he finally made it pass, but pretty close to failing under 25mps. Besides the set screw in AFM, he opened up more the idle bypass screw.

15 mph - CO 0.00 (max 1.36), HC 6 (max 214), NO 221 (max 1364)

25 mph - CO 0.98 (max 1.16), HC 10 (max 181), NO 28 (max 1224)

The discrepancy between the 15 and 25 mph testing tells me the AFM is about to give up a ghost. What do you guys think?

During all this my "Floor Temp" light went on and the water temp gauge was getting very close to the red zone. Should I bump my ignition timing from 10 BTDC to 14-16? While pulling out of the smog shop, my car died from a very low idle speed. I had to unscrew the idle screw to get back home. I revved the engine at idle and it made a popping noise (too lean?) I feel like adjusting the AFM myself again and make it run a little on a rich side.

I will start looking for a rebuilt AFM (it did pass all the Fuel Inj. Bible tests, and the FSM tests with applying voltage and reading the volt settings at the pins).

Thanks!

[darom]

UPDATE: I finally replaced the PO's fuel pump (it is one of the Autozone replacement pumps, Airtex). This fixed the lean condition finally! What confused me was the fact that the old pump was delivering the "prescribed" by FSM fuel pressure with the key in ON (starter solenoid disabled) position and at idle with the stock FPR. Since I couldn't verify the fuel pressure while driving, it was my last stop.