Hello and good day to everyone here,

My name is Jason and I've been having problems passing emissions the last few weeks. I can't really think of anything else so I thought I would ask the masters here for a little guidance. ;-)

Here is what the car has installed:

Stock motor.
K&N FIPK
New cat. converter 2 years ago (aftermarket)
160 Thermostat (Hypertech)
Madz28.com performance tune (chip)
SLP mid-length headers
SLP Loutmouth catback
Richmond 4.10:1's
Hurst billet plus shifter
MSD coil


Here is what I have tried and replaced:

PCV valve
re-oiled the K&N air filter
NEW AC-Delco O2 sensors
Seafoam'd the motor
New high octane gasoline
Ran the car for about an hour before the test

I had problems passing two years ago and I replaced a bunch of parts then too:

Taylor Spiro pros 8mm wires
AC delco platinum spark plugs
New Cat. converter (aftermarket)
New EGR valve
New air pump

The car shows no codes and the service engine light is not on. What I am failing on is the HC's. The allowed HC's for my year is 1.5 and I test at 3.65. The CO came in ok at 9.9 with an allowed 15 and the Nox came in ok at 2.8 with an allowed 3.5.

I have a few questions...

1. I 'upgraded' to an MSD coil this year. Could the coil be bad and the car not miss? The car runs and drives great with no problems. Sure wish I would have kept the stocker to test lol...

2. Should I pass with the Madz28.com tune installed? (I did select the power tuning package.) Do people pass with a 160 degree tstat installed?

3. How many cycles does it take the computer to re-learn the air/fuel curve? I disconnected the battery today before I installed new O2 sensors. I did start it a few times and drive it around but perhaps it needs more cycles to lean out the air/fuel curve more? I drove to the emissions test a few hours afterwords having driven the car for 2 hours or so.

The thing that is frustrating is last emission test (last week) I almost passed! My HC's came in at 1.59 with an allowed 1.5! I got worse lol...

Any thoughts are appreciated,

Jason

 

I wouldn't think the 160* thermostat would make that big of a difference. It is possible with the new 02 sensors that it needs some more time to learn. makes it tricky with the SES off though. I've never had any problem as long as my SES was off with my 87 (even though it smells rich it still passed). EGR valves can be a bitch sometimes. I know it was on my 96 for a while there. I can't remember if there's any way you can pull data or not. If so i would suggest pulling the data and finding out the fuel mixture. I would also check vacuum, fuel injectors, AIR system, and ignition system. All that can cause high HCs. Other people on here will be able to help you more than I will though.

 

Under what conditions are your tests run - idle, low load/low RPM, moderate load/moderate RPM? If more than one set of conditions, which specific test is it failing?

A rich mix will elevate both HC and CO, and depress NOx. Appears that only the HC is high, others within spec. Have you considered the possibility that you have a leaking injector (or injectors)?

The PCM "learns" within minutes. Problem is that there are 16 different "sets" (or Cells) of long term fuel corrections, and each Cell has to be learned. The boundaries of the Cells are defined by the engine's RPM and load (as indicated by MAP). This requires that you operate the engine over a very wide range of RPM and engine load, varying the throttle position frequently.

How many and which of the Cells you need to stabilze will be determined to some extent on the conditions under which they do the testing... hence my first question, above.

 

I had significant problems passing the Penna IM240 test when I first modded my car with a 160 F thermostat. I had a tune from Hypertech but it still seemed that HC readings were high. I changed a lot of things that didn't make a difference. Switching to a 180 F thermostat for the test actually got me through it. I theorized that the power program from Hypertech was adding timing throughout the range but it wasn't enough to overcome the losses in thermodynamic efficiency from the lower coolant temps at lower engine loading and speeds. The IM240 test is a dyno test with a test speed of 25 mph.
Ok so theories are worth about what you pay for them without proof but....

Interestingly enough, my carbon monoxide readings were in spec too....but it dropped with the hydrocarbons when the coolant was a bit warmer.

Check for a leaky injector as Injuneer stated and if that doesn't do the trick you might want to spend the $20 to see if higher engine temps will help.

 

Hello,

Thanks for the quick reply! :-)

The actual test is a 4 minute test (Colorado) where they run the car up to sixty mph varying the loads at all times. There is no specific data other than a graph they gave me but the HC levels are ok when the car is at idle. The graph spikes when the car accelerates.

I suppose a leaking injector could be the problem. I'll have to have them tested. Anything else I should try before I get them tested?

I am curious if I just drive the car for a week (instead of a day) and let the new O2 sensors and computer re-learn everything for all the cells if anything would be different?

Thanks so much Injuneer and Supplysgt for all you help!

Jason

 

Excellent! I will have to try that... After all $20 would be excellent to get the car to pass lol. Thanks! bw_hunter!

 

If you can drive it under every condition that you'll see on the test it's possible. Is there any indication that it's running rich? if so then that would point towards the leaky injectors along with the high HCs. Y'all do it way different than we do here in TN. they take the readings at idle and then have you rev it up to approx 2500 rpm. If it's not too much trouble, easiest way i can think of is to take the fuel rail off and have someone turn the key to "on." if fuel leaks out of any of the injectors then that's your culprit. I need to do that myself on my V6 I just haven't had the time to do it (or the help to turn the key while i'm looking at the rail for that matter). Injuneer knows a lot more than I do; I've learned a lot from him the last year and a half or so that i've been on here. But that's what I'd check as far as injectors go. even if that's not it we can cross that one off the list and narrow it down further.

 

Leaking injectors will also cause the fuel pressure to drop rapidly when you shut the engine down. Might want to check the fuel pressure first.

 

Injuneer, you never fail me lol. Learned something new yet again. What's the best way to check that fuel pressure? I'm sure i'm gonna need some sort of tool that i don't have but i can see if i can borrow from someone i know.

 

You probably do need more PCM learning. Since you don't know the actual conditions that they tested HC under you need to make sure it's learned across the board.

I would think that an aftermarket tune would have less HC under WOT compared to stock.

How many miles on the car? On the distributor?

When's the last time you inspected the plugs?

Getting a scanner (like datamaster) on it would help reduce the amount of guessing.

 

Hi Steve,

The car has 140k but the motor has less than 100k. It does have the original optispark.

I replaced the plugs less than 20k miles ago with AC delco platinums. I suppose I could definitely pull one out and see what's going on in there lol...

I have driven the car around for a few days now and it most definitely does smell like gas! It is pretty strong.

I'll do the fuel pressure test and see but I did replace the fuel pressure regulator exactly two years ago (20k miles ago). Hopefully it's something simple lol...

Are there any online write-ups on how to replace an injector and how to test them?

Thanks so much guys!

 

You buy a fuel pressure "test gauge", and it comes with a short hose with a -4AN fitting on it, and a valve stem depresser. Screws onto the Schrader valve on the fuel hard line at the back of the passenger side head. Courtesy of Shoebox:

http://shbox.com/1/fp_reg.jpg

To pull up the fuel rails, release the metal clip that holds the two fuel hard lines to the bracket on the bolt, drivers side rear corner of the intake manifold. Then you remove the 4 bolts that hold the rails on the top of the manifold. Blow any dirt out from around the bottom of the injectors with compressed air. Reach across the manifold from the opposite side and pull up on the fuel rail. The 4 injectors should pop out of the manifold. If they have never been removed, might take a bit of leverage to pull them loose. Do the same with the opposite side rail. Make sure the O-rings came out on the tips of each injector. If you don't see an O-ring, fish it out of the manifold.

Testing the injectors to make sure they are pulsing requires a set of "noid" lights. They plug in between the harness connectors and the injectorsl, and flash as the injectors fire. To determine if the injectors are leaking, first check for rapid pressure loss from the fuel system. If you have rapid loss of pressure, pull the rails as described above, and turn the key to "on" to pressure the system, and watch for drips from the injectors. Do not try and start it .

Running rich can be the result of exhaust leaks before the O2 sensors, or misfires. The scanner would show elevated long term fuel corrections (BLM's) if that is happening.

 

'93 Z28:
Have you tried inspection with the original, stock tune back in the ECU?

 

Hi NJ,

I did and I failed worse but I didn't give the computer a chance to learn either. I disconnected the battery, removed the chip, put the stocker in by itself, drove for an hour, than took the test and failed on both HC and CO.

I'll try the fuel pressure and/or test for the leaking injectors this weekend.

Could the EVAP canister (system) be causing the problem of the gas smell? I need to check into that too. :-)

Many thanks and please keep any and all ideas coming!

Jason

 

AC-D platinums have been known to lose pucks in a couple thousand miles.

However, my guesses were based on your car barely failing HC at WOT, which could just be minor missing that you don't notice when driving.

Since you now say it smells like gas all the time, that implies a bigger problem. Start with injectors.

Regardless, scanning it would be helpful.