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So it's another failure at the Emissions facility with my 95' 3.4L Bird.

In the past 2 weeks I've performed the following to try to pass by lowering my Nox levels:

New CAT (With the new CAT, I'm getting hotter on the inlet and colder on the outlet of the CAT using my infarred temp gauge (Difference of around 135F or slightly greater))

Checked the following sensor readings during driving and fully warmed up:

MAP sensor (1.6v at idle/cruise - 4.25v at almost WOT)

TPS stays consistent to pedal position with no fluctuations

EGR solenoid (under light acceleration, Sol.1 and 2 open. Under WOT all 3 open but during cruising at 1500rpm, all stay closed. Cleaned all passages as well with carb cleaner and nylon brush)

02 Sensors (bosch) replaced last year. Bank 1 and 2 continue to fluctuate between .090-.870v during any acceleration/rpm range and when at a cruising rpm.

Last notes:

At cold, she idles smooth but at full warm up and AF ratio switches to 14.7:1 (holds steady) she has a very slight, slight miss. No one else seems to see it in my family, but I notice it.

When fully warmed up, she hangs for maybe 2 seconds longer than usual before falling back to idle during blimps of the throttle.

Other than this, she runs great, fuel mileage is excellent (21 city, 27 freeway) but I feel she still is running lean.

What do I start checking next? Any suggestions is most appreciated because I'm stumped at this point....
 

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Ramblin' Wreck
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Fred's the guy you need for this. But before he arrives, better get the inspection failure datasheet ready and post it in this topic. He will ask for it for sure.
 
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Discussion Starter · #3 ·
Fred's the guy you need for this. But before he arrives, better get the inspection failure datasheet ready and post it in this topic. He will ask for it for sure.
I have no objections to that. I'll post it as soon as I get off of work (6:30pm)

Thank you
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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Three top reasons - running lean, coolant running hot, EGR failure.

Have your scans turned up any codes?

Need figures for HC, CO and NOx - allowable vs. measured.

When you are cruising in top gear at low load with all three EGR ports closed, what happens when you open the throttle, lugging the engine? That's when EGR is typically needed.
 

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Discussion Starter · #5 ·
I'm sorry for the late response.

I have to run by Ohio E-Check at lunch to pickup another copy of my test. I will post it immediately after work!!

Fred,

My coolant temps are staying within normal and is not cycling too much. At idle standing for more than 10 mins, it'll reach 230 and the fans turn on, but that's just how GM set that. I'd like for them to come on as soon as it reaches 225....

Lugging the car at 1500rpm in 4th going 38mph, I'll apply 1/2 throttle and all 3 ports open according to my scanner/monitor tablet (Autoxray)

as soon as I reach 1800-2200 rpm only egr solenoid number 1 is left open and immediately closes when it goes past 2200rpm (barely any load I assume at that point).
 

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What leads you to believe it is running lean?
 

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What leads you to believe it is running lean?
First off I want to apologize to any one reading this who is having this same issue as I am. I never like to leave threads unanswered. Towards the end of last week, my father was rushed to urgent care. He complained of chest pains and I feared the worst. He's alright but I'm keeping a close eye on him.

Fred,

Sorry for the wait on the Echeck readings. They are as follows:

HC - 22.6ppm Max allowance = 117ppm

CO - 0.17% Max allowance = 0.65%

Nox - 1289.9ppm Max allowance 821ppm (this is where I failed obviously)

Evap system (basically they test my gas cap pressure) 25.50 inH20 Min. allowance 6.00 inH20.

I believe it does run lean because of these numbers and because:

1. The plugs are pure white with a grey tip (granted all newer EFI vehicles run leaner than the 80's vehicles.

2. When the car is fully warmed up, sitting at idle, and I go to free rev it from anywhere above 2k-5k rpm, I get very loud backfires out of the exhaust!

My plugs have only 40k miles on them. The Taylor wires (8mm) have only 35k miles on them. And if my spark was weak, I'd be running rich.

I replaced the check valve on the air pump since it was allowing exhaust gases back into my air pump. I caught it early enough to where it didn't fry the pump or the built in check valve in the pump.

Last night, I did a ohm's check on the fuel injectors. At fully warmed up, they read between 15.4-15.8 ohms. At cold this morning before work, they read 13.2-13.5 ohms.

I'm starting to think they might need replacing...or at minimum they need to be removed and cleaned thoroughly. I saw Accel sells my injectors but they read 14.4 ohms brand new!

My FSM says I should be reading between 11.1-12.8 ohms per injector but doesn't provide me which temp I should be checking them at.

I've never cleaned them but twice a year I run JB brothers cleaner through the tank....I wonder if a good bench cleaning with my fathers injector cleaner would help.

I'm at a loss as to what I should check next. My last day for echeck is up on the 14th (i'm on an extension already). After that, I'm not sure what they'll have for me inorder to get my bird registered.
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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When you replaced the cat, did you get the correct one for the car? I've seen people on eBay selling the older style 2-bed cats, with the intermediate air injection connection, and calling them "universal". Good for a 3rd Gen, but not a 4th Gen with the monolithic 3-way cat, and no diverted intermediate air injection.

Tailpipe results are somewhat consistent with a lean A/F ratio. Low HC and CO, high NOx.

On the V8 injectors, GM says to measure the resistance at 70-degF. Lowest acceptable resistance is 11.6 ohms. What page is the V6 injector spec on in the 95 factory manual? Generally I've looked for values in the range of 12-15 ohms on the Multec injectors. The PCM can correct for low injector flow by adding up to 25% extra fuel, in response to O2 sensor feedback. An inability of the PCM to correct a lean condition would possibly set DTC 64. Can your scanner pull the long term fuel corrections? If not, the Scan9495 software for the V6 can. See link in the PCM forum for free download.

Based on reviewing problems like this over more than 17 years, I would personally not recommend the Accel injectors.
 

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Discussion Starter · #10 ·
When you replaced the cat, did you get the correct one for the car? I've seen people on eBay selling the older style 2-bed cats, with the intermediate air injection connection, and calling them "universal". Good for a 3rd Gen, but not a 4th Gen with the monolithic 3-way cat, and no diverted intermediate air injection.

Tailpipe results are somewhat consistent with a lean A/F ratio. Low HC and CO, high NOx.

On the V8 injectors, GM says to measure the resistance at 70-degF. Lowest acceptable resistance is 11.6 ohms. What page is the V6 injector spec on in the 95 factory manual? Generally I've looked for values in the range of 12-15 ohms on the Multec injectors. The PCM can correct for low injector flow by adding up to 25% extra fuel, in response to O2 sensor feedback. An inability of the PCM to correct a lean condition would possibly set DTC 64. Can your scanner pull the long term fuel corrections? If not, the Scan9495 software for the V6 can. See link in the PCM forum for free download.

Based on reviewing problems like this over more than 17 years, I would personally not recommend the Accel injectors.
Unfortunately, I did replace it with a Walker universal. It's the same one I had on my 92' Firebird 3.1L and that car always passed e-check for the 14 years we had it in our family (That cat went on the 8th year of ownership until we sold it). That is the only reason why I went with that.

Can this really be causing the high Nox? It's hard for me to believe this....especially when I'm still getting a hotter inlet and colder outlet on the cat with small backfires in the exhaust system (lean AF ratio indication)

I'll get the pages for you when I get home after work. It's no problem....can't believe how many pages you get with these FSM!

And I too believe my AF ratio is off. Like i said, I tested the MAP sensor on and off the car. My readings read 1.6v at idle and under load 1600rpm in 4th I'm getting 4.6v. Low gear at 3/4 throttle, I'll get 4.7v. This is all live data through my Autoxray.

Bench tested, it fell within the parameters according to the vacuum hg i applied and read through my DVM.

I wonder if the O2's are shot. I just realized they are Bosch and I've been reading bad reviews on them. But they still fluctuate consistently between 100mv-945mv.

I don't have a heated garage and it's around 29F outside. I won't be able to test injector resistance at 70F degrees.

I rescanned the car last night, and still no history or current codes.

I'll see what fuel trim readings I can pull with my Autoxray. At this time, I don't have a connector to go to the OBDII port to a USB connector...if i did, I would take advantage of that free download. Thank you for that link btw.

And yes, I'll stay away from the Accel's. So far, OE injectors is going to cost me $366 at minimum. I'm not sure I can swing that at this time especially since the local parts stores can't get them in until Friday!!!
 

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Up to 92, they used the 2-bed cats. The first bed is to reduce the NOx to N2 and O2. The second bed is to oxidize the unburned HC and CO to CO2 and H2O. There is an air injection pipe in between the beds. The engine drive AIR pump feeds air to the exhaust manifolds on startup, to help burn the overly rich exhaust from cold start, which also generates heat to get the cat working. When the engine warms up, the AIR diverter valve sends the air flow to the pipe on the cat, to assist in the oxidation of the HC and CO. All this piping was deleted on the 93's and up.

The 93 and up cars use a monolithic single-bed cat, that does both the reduction and oxidation processes, as the A/F ratio is toggle from slightly rich (below 14.7:!) to slightly lean (above 14.7:1).

These cats are not interchangeable.

Since you have a pipe on the 2-bed cat, what did you do with it - cap it or leave it open? Are you sure the cat is installed in the correct flow direction? The oxidation process is exothermic, releasing heat. That would cause the outlet end to normally be hot. If your HC and CO is low, something is oxidizing it. A lean mixture would cause the oxidation to occur, which may be explained by the cat being installed in the wrong direction.

I don't think you have an electrical problem with the injectors. Since you apparently have access to a cleaning machine, why not clean them?

MAP sounds fine to me. At idle you should see 30-35 kPa. That corresponds to 1.2-1.5V. WOT MAP shouldbe as high as 95-100 kPa (depending on elevation where you live), which corresponds to 4.5-4.9V.
 

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Discussion Starter · #12 ·
Up to 92, they used the 2-bed cats. The first bed is to reduce the NOx to N2 and O2. The second bed is to oxidize the unburned HC and CO to CO2 and H2O. There is an air injection pipe in between the beds. The engine drive AIR pump feeds air to the exhaust manifolds on startup, to help burn the overly rich exhaust from cold start, which also generates heat to get the cat working. When the engine warms up, the AIR diverter valve sends the air flow to the pipe on the cat, to assist in the oxidation of the HC and CO. All this piping was deleted on the 93's and up.

The 93 and up cars use a monolithic single-bed cat, that does both the reduction and oxidation processes, as the A/F ratio is toggle from slightly rich (below 14.7:!) to slightly lean (above 14.7:1).

These cats are not interchangeable.

Since you have a pipe on the 2-bed cat, what did you do with it - cap it or leave it open? Are you sure the cat is installed in the correct flow direction? The oxidation process is exothermic, releasing heat. That would cause the outlet end to normally be hot. If your HC and CO is low, something is oxidizing it. A lean mixture would cause the oxidation to occur, which may be explained by the cat being installed in the wrong direction.

I don't think you have an electrical problem with the injectors. Since you apparently have access to a cleaning machine, why not clean them?

MAP sounds fine to me. At idle you should see 30-35 kPa. That corresponds to 1.2-1.5V. WOT MAP shouldbe as high as 95-100 kPa (depending on elevation where you live), which corresponds to 4.5-4.9V.
I brazed welded the cap they had on the air pipe. I learned with my other Firebird, their tack welds will eventually fail on that little cap.

When I called about the direction of flow, they said it can be installed in either direction. Even when I had my magnaflow universal cat on prior.

I never liked that answer, but they would have changed that if others were experiencing this issue.

My father's setup is homemade. It's not shabby (Plastic box with a glass window, backlight, etc.)

I can see the spray patterns, but that's as far as it goes. Since it's idling good and revving up fine, I skipped the cleaning.

Also, I rechecked my vacuum at idle. It's sitting at 32.25 and holding steady by about .50kpa of swing.

I wondering if my CTS is not reading right back to the ECU even though I'm registering temps between my Autoxray and infrared temp gun, at about a difference of 2-3 degrees....??
 

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The scanner shows you exactly what the CLT sensor is sending to it. The gauge is driven off a different sensor. What does the scanner indicate when the dash gauge reads 230*F? Stock programming fan on temp is 228*F, fan off temp is 208*F.

Test sensor:

http://shbox.com/1/4th_gen_tech2.html#ect
 

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Discussion Starter · #14 ·
The scanner shows you exactly what the CLT sensor is sending to it. The gauge is driven off a different sensor. What does the scanner indicate when the dash gauge reads 230*F? Stock programming fan on temp is 228*F, fan off temp is 208*F.

Test sensor:

http://shbox.com/1/4th_gen_tech2.html#ect
Oh yeah, I knew that one a few years ago. I had to replace the gauge temp sensor due to the plastic housing cracking.

When the dash reads 230F, my Programmer & infrared temp gun read 232F.

I might double check the CTS with the DVM just to be on the safe side. Thank you for the link.

Anything else I could/should be checking for this Lean condition?
 

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I've given you my opinion of what the problem is. I've told you how to check if the PCM is correcting for a lean condition. I think at this point you are tilting at windmills.

Nothing more to add.
 

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Discussion Starter · #16 ·
I will search for another CAT. I'll have to find a direct replacement and modify it to fit.

My intermediate pipe rotted years ago and i only have a mandrel bent pipe the PO put on. This was another reason why I opted for universal. I didn't need direct fit connections.

I'll also try to see if my programmer can pick up the long term fuel corrections. I wish I had a better understanding of these readings and how they apply. I'm still learning about these things.

For instance, when you were referring to the CAT and it's internal design, it was going over my head. But at lunch, I was able to study up on it a bit.

It kinda upsets me that a company would sell something specifically for my vehicle, call it universal fit (as in connections), and not care to make sure it works properly with my engine/setup.

last bit, before I let you go Fred. If I'm able to determine that my PCM is not correcting for a lean condition, and a new PCM does not solve the issue still, where does one go from there?

Selling the car is out of the question.
 

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You are overthinking this. PCM failure is EXTREMELY rare. Why are you chasing that?

Run a data log with the V6 version of Scan9495. I can tell from the log if the PCM is working.

What I'm going to attach is V8 specific, and the V8 is a "mass air flow" air measurement, vs. your "speed-density" air measurement system. Where an MAF sensor can directly provide the PCM with data to indicate the mass air flow, your speed density does some complex calculations involving the perfect gas law, calculating the density of the air entering the cylinders using the inlet air temp (IAT) reading, and the manifold absolute pressure (MAP) reading. Then is has to calculate the volume of air entering the cylinders using the volume of the cylinder, RPM/2 and the table of volumetric efficiency that is programmed into the PCM. Density X Volume = Mass

Other than the mass air determination method, everything else will be similar. The "cell" numbers for the V8 and V6 are different, but read the section on A/F control and you should be able to get a basic understanding of how this all works, including long term fuel trims (also known as block learn multipliers, or "BLM") and the short term fuel corrections (also know as integrators, or "INT").
 

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