My '87 Z52 was hit 9 months ago by an unlicensed and uninsured illegal alien in a Honda. My registration expired while it was in the shop, so upon completion of the repairs, I ran it through a "Test Only" shop and failed for excessive carbon monoxide. I've got a friend who teaches at a school that trains smog mechanics, so I figured it wouldn't be a problem to get this sorted out. How wrong I was!

In the last month I've:

Given this thing a fresh tune up with new components, including plug wires.

Replaced a non pumping smog pump, plus burned out non functioning diverter valve and all three air injection check valves.

Replaced an EGR valve that was giving me a Code 32.

Replaced an evap circuit purge solenoid that was purging continuously.

Replaced bad vacuum lines, and cured a plenum to runner manifold leak that was caused by the mechanic reusing old gaskets when he did the EGR valve.

Replaced all three cats, since none of them were lighting off.

Replaced the MAF, since it was reading low.


The vitals have been scoped so many times that I know the numbers by heart:

The Block Learn (Short Term Fuel Trim) is running 140-142 (when it should be 128). The computer is choosing to hold the injectors open longer.

Free Oxygen - O2 is 0.00%.

Unburned Hydrocarbons - HC measures 84 ppm at 15 mph (Max allowable is 112) and it reads 83 ppm at 25 mph (Max allowable 86).

Oxides of Nitrogen - NO measures 18 ppm at 15 mph (Max allowable is 778) and it reads 15 at 25 mph (Max allowable is 717).

Carbon Monoxide - CO measures 1.50% at 15 mph (Max allowable is 0.72%) and it reads 1.54% at 25 mph (Max allowable is 0.60%) Carbon Monoxide is killing me!


The Smog Referee sent me to a Gold Shield smog shop. Those guys had the car for 3 days. An inspector from the Bureau of Automotive Repairs stopped by while my car was on the dyno, and he spent an hour on it. They checked for:

Proper sensor function. Everything reads perfect.

Fuel pressure. Spot on.

Performance chip. They found the computer had a stock chip.

Cracked exhaust pumbling. They found everything intact.

Bad cylinder. They performed a cylinder balance test, killing one cylinder at a time, and saw an equal rpm drop each time.


We're grasping at straws now. Here are some of the theories:

Vavle adjustment. The Gold Shield guys say that with the car on the dyno, it's possible to zero lash the valves and watch the tailpipe sniffer numbers change. This seems like a longshot.

Fuel injectors. Is it possible that larger injectors were installed? Is it possible, if this is the case, to pull back on fuel pressure (with an aftermarker regulator) to compensate?

Cam timing. Is it possible that a stretched timing chain is doing this to me? But if incomplete combustion were the issue, why do I pass on HC and fail so miserably on CO?

Computer chip. Is it possible to reburn the stock chip? Can it look original and not be? Why does it dump 15% more fuel than it should?


Has anybody got any ideas? I could sure use the help. I just spent $14,000 restoring the car, and was looking forward to a long and happy life behind the wheel of this beauty. There is a smog waiver offered to cars that won't pass, but it's a one time only thing. I'm not going to let the state of California tell me that I have to junk the car in 2 years.

 

[QUOTE=farhorizons]

The vitals have been scoped so many times that I know the numbers by heart:

The Block Learn (Short Term Fuel Trim) is running 140-142 (when it should be 128). The computer is choosing to hold the injectors open longer.

Free Oxygen - O2 is 0.00%.

Unburned Hydrocarbons - HC measures 84 ppm at 15 mph (Max allowable is 112) and it reads 83 ppm at 25 mph (Max allowable 86).

Oxides of Nitrogen - NO measures 18 ppm at 15 mph (Max allowable is 778) and it reads 15 at 25 mph (Max allowable is 717).

Carbon Monoxide - CO measures 1.50% at 15 mph (Max allowable is 0.72%) and it reads 1.54% at 25 mph (Max allowable is 0.60%) Carbon Monoxide is killing me!

QUOTE]

To me it seems that you are passing everywhere except the CO. Also what concerns me a little is the fact that the fuel trims are running in the 140's. This means that the ECM thinks the engine is running lean due to its feedback from the O2 sensors. Have they replaced the O2 sensor? It could be fouled or just lazy. This is one sensor I would replace before doing anything else. It is the final control element in the system and it has the final say when the ECM is controlling in closed loop. Or another cause for this problem maybe in the MAF sensor, if it isn't giving the correct information as far as incoming air mass the ECM maybe fueling for less air than is actually entering the engine. In that case this could also cause a high fuel trim number because the O2 sensor sees a lean condition.

Otherwise your actual emissions is not that far off. But because of the EFI sytem there are really no external adjustments that one can make to offset what they are seeing. You could retard the timing a little which may get it to squeak by, especially if the timing is advanced.

Another trick to get her to squeak by is by adding a bit of "Denatured Alcohol" to the fuel system. Its about a 10% mix by volume, 1 gallon of alky to 10 gallons of gasoline. Doing this would drop the numbers way down, just don't tell them you added something, and it is undetectable, at least by the smog ****'s The only way anyone could know its there is by taking a sample of your fuel and using a hydrometer on it.

I think the first thing to do is to figure out why the fuel trims are so high. That alone could be the cause of the high CO number. Did they get an actual AFR reading? If they did what was it?

 

Since you didn't mention it, I guess you aren't getting any SES error code, right?

I'd first make sure that all the sensors are reading within spec. It would be helpful if you would post the numbers.

What kind of 02 readings are you getting; min/max, activity and cross-counts?

What is the TPS voltage setting?

What is the IAC count at closed loop idle?

What is the base ignition timing?

What is the airflow rate and filtered load?

Is the gas in the car also 9 months old?

BLM - Block Learn Memory, is long term fuel, not short term. Short term is called Intergrator. So with that in mind, what are the BLM and Intergrator values?

Any of those numbers could tell the tale.

Jake

 

Your ECM is trying to add fuel because the O2 sensor readings show that the A/F is too lean.

You state that you have no intake nor exhaust leaks so the problem is likely to be with fuel delivery, assuming the O2 sensor is ok and that the ECM is going into closed loop and staying there.

Since the ECM is trying to add fuel, install an AFPR and bump fuel pressure from stock setting of 45psi to 50psi and look at the BLM cell & INT numbers. If the problem is simply that the ECM cannot add enough fuel you will see these numbers move toward the quiescent values 128.

If the problem is due to partially clogged injectors you can replace them with the Ford types or send the OEM set to Rich at Cruzin Performance to have them rebuilt. His shop time is 48hrs with a cost of $10-$12/injector, including the cold start injector.

What mods have been done to the engine??

 

Interesting. So if you apply for that repair waiver in Cali, they junk the car in 2 years?

Where do you buy denatured alky?

 

One trick that I've heard works on some of the close ones is to do an oil/filter change right before the test. Must help with rich conditions that have allowed fuel to pollute the oil. Regards

 

Most any paint store sells it. You can find it as Shellac Thinner as well. Just be sure that it is 100% Denatured Alcohol.

 

Thanks for all of the suggestions. Let me respond to the questions you've all raised:

tjwong - The O2 sensor was replaced about 2 years ago when I had a miss showing up under acceleration. I've considered the possibility that having the fouled cats not lighting off properly may have fouled the sensor, but it checks out OK when scoped on the dyno. I've watched the readouts bounce between rich and lean. My friend the smog instructor says it is not lazy.

The MAF was changed by the Gold Shield guys 2 days ago after my friend noted that the reading was every so slightly low. It made a difference, but not enough to clean up the CO problem. I've checked for unmetered air leaks and found none.

The timing issue is something I've wondered about. Are you suggesting adjustments to spark or valve timing?

I don't know about Oregon, but Southern California fuel formerly used alcohol as an oxygenate, now it's MTBE. I'll ask my friend about this one. I don't remember the AFR, but since I'm showing 0% free oxygen, I would tend to think that just a touch more in the pipe would burn off the CO to CO2. The question is "How can I achieve that?"


JAKE - The only code I got was 32, an EGR problem that I've dealt with. My NO score is the only one that really shines, so I'm considering that one handled.

The experts all consider the O2 sensor readings in the correct range, although I don't have anything printed out to quote specific activity numbers. I'll pay closer attention to this the next time I've got it on the scope. The same goes for the TPS readings.

The IAC started acting up about halfway through the smog saga, but since California smog tests are not done at idle, I thought that it would make no difference. I pointed out the IAC problem to the Gold Shield guys. They did change the MAF when it consistently read slightly low.

I've put about 700 miles on the car while trying to sort this out, so old gas is not part of the issue.


65Z01 - I show 0% free oxygen in closed loop operation, and the O2 sensor reacts quickly on the scope, so the experts feel that it is working correctly.

Since the ECM is running the injectors rich already, wouldn't upping the fuel pump pressure be counterproductive? I've asked the experts about adding an adjustable regulator as a way to reduce fuel delivery, but I've been told that driveability issues would appear if I cut back on the fuel pressure.

The engine is, as far as I know, a stocker with roller valve gear and first generation aluminum heads. I will look into rebuilding the injectors. Thanks for the tip on Cruzin Performance.


cuisinartvette - The California Smog Waiver is a back door method for the state to take older cars off the road. If you spend $450 in a valiant, but unsuccessful, attempt to pass, the state will give you the waiver. But (and there's always a BUT), the waiver is allowed one time only. You have 2 years to bring it into compliance, and after that they will not allow the vehicle to be registered ever again. I'm not going there. Incidentally, denatured alcohol can be purchased in any drug store. If that's what it takes to pass, I'll dump a quart or so in an almost empty tank, just enough to fuel it during the dyno test.


KAZ2 - Thanks for the tip, but I failed with a fresh crankcase of Mobil 1.


Guys, help me out. Please keep those tips coming! All suggestions are appreciated. Help me keep a beautiful C4 on the road!

 

Trt running this past JSAAUTO (may be jsauto). He's a member here and good with vettes. We had similar problems with mine. You can usually find him in the C5 sec. Doesn't post much, but shoot him a pm anyway. Knows his smog stuff.
Thanks for the tip...Is this the same alky you hear (I know its not Nitro! ) guys talking about on this and the FBody boards? Does it pick up hp or is it just for smog?

 

How about this? Since your NOx low and NOx is created when the combustion is nice and hot and efficient could it be that the engine is running too cool or that the egr which is used to reduce NOx by cooling combustion is working too well? Maybe if you run the hottest 'stat you can find that will help lean things out. I realize that that seems counterintuitive because cooler temps in the intake are denser but the low NOx seems to be pointing to a colder combustion chamber.

 

Can anybody tell me if a stock '87 chip can be reprogrammed? And, is there any way to tell by the readings on a scope?

I'm thinking that my fuel trim numbers tending to the low 140s with all sensors and acutuators performing properly could be due to a past owner swapping in a power chip.

My friend at the smog school said that the lack of a serial number would tend to indicate an aftermarket chip. The Gold Shield smog experts tore the computer out to investigate this possibility, but they found what appeared to be a stock GM chip.

How can I tell if it has been reprogrammed? Is it even possible? How do I cut back on the extra fuel if it has been changed from the factory settings?

Does anybody have a stock '87 chip that they would like to sell? If I'm offered one, how can I be sure that it will work? We all know how easily chips can be damaged by static, etc. Please help me out!

 

Since the ECM is adding fuel it is detecting a too lean condition.

A Wide Band O2 sensor will show if the A/F is truely 14.7:1. If it shows too rich something is causing the ECM to see an incorrect A/F from the stock sensor; if it shows too lean the ECM cannot add enough fuel so the problem could be with the chip, the injectors or fuel pressure.

I think the next step should be to get the actual A/F value in closed loop at several steady RPMs.

 

Is the computer staying in Closed Loop after warmed up? Does the scanned water temp match the guage? I would look into the oxygen sensors and the temp senders/sensors. Tuned Port 350s like a bit more fuel pressure than the stock setting. Maybe clean and check the injectors and get an adjustable regulator and play with your fuel pressure. I don't think timing is an issue, but you should be able to move it around some and it's the one thing that won't cost you anything. So much for narrowing it down, huh?!

 

damn... I am not sure the cause of this...

A thought - get some Seafoam and run that through the engine. It will clean carbon off of valves and pistons. You might get a smoke screen!

I like the idea of Dry-gas (alky) to get through. A point of reference, the alcohol won't add performance when added to gas. It will lower economy, tho, if you add enough. Alky does not contain enough bang to be as powerful as gas, so it takes about twice as much alky to make the same power as gas.

Another thing, if you can, drive this car around for a few days and exersize it. It sounds to me as if it's been sitting and might just need the fire run out of it.

Injectors? It is possible, but they would have to be huge... check the fuel pressure regulator, you might find it is leaking gas past the diaphram. remove the vacuum line and see if fuel is coming out. I see that the fuel pressure is ok, but you can not be 100% sure of those stupid things...

 

Somethings not working right, but a few tweaks will get you past.

Dry gas, retard timing 1 or 2 degrees. Is your egr temp switch closing? Mine never threw a code, but caused the CO to run high.

The easy way to test it, is to remove it, and check for continuity while holding a lighter under it. When it heats up, it closes.

 

I bet there is an issue with the newly replaced air injection. I've seen faulty divertor valves that allow some pumped air into the headers. This throws off the o2 sensor forcing it lean, thus causing the ECM to bring things back into what it thinks is inline. Pinch off the air hoses at the headers and see what happens to your fuel trims.

 

Agree that the smog pump circuit is a likely culprit. Air should be diverted to the cat in closed loop. Make sure you haven't got the wires switched on the Divertor solenoid. If so, air will go to the cat first, then the headers. Should be the other way around.

 

Thanks for the tips! Looks like there is a consensus on the use of alcohol as an oxygenate. The air injection circuit suggestions will all get investigated, too, especially the divertor valve wiring.

Can anybody provide any answers to my questions about the chipprogramming?

 

It looks like excess fuel is being dumped into the system.

My suggestion is something that has been over-looked: The cold start injector! I've seen various cold start injectors stick on over the years. This causes a very rich condition that is hard to pinpoint. That is my guess. E-mail me if I'm correct.

It's the only thing that makes sense assuming that wiring isn't damaged/pinched from that idiot hitting you.

 

Except that a leaking cold start injector would cause the fuel trims to be below 128 as the ecm would be seeing this unexpceted fuel and attempt to lean things out. He's seeing fuel trims on the positive side, indicating the ecm is adding fuel due to a percieved lean condition.