farhorizons

I've got multiple smog test failures on my (apparently) stock '87.

My car has been dyno'd by everybody from a friend of mine who teaches smog technicians, the state smog referee, the Gold Shield smog shop, and even an inspector from the Bureau of Automotive Repairs. Every sensor works properly, every acutator functions as it should, and yet I fail rather miserably for Carbon Monoxide. Help me! Please!

When all is said and done, the computer is choosing to inject 15% more fuel than ideal. Is it possible that somebody has reprogrammed the chip? If so, how can I tell? What will it cost me to go back to stock, if only to pass the test? All input is welcome!

Alvin

Take it out an look at it. If it has a silver foil sticker over the chip in the memcal with 3-4 letters on it than its stock.

farhorizons

How can I tell if it's programming has been altered? This car has been spending a lot of time on the scope lately. Is there any place that I should be looking to tell the difference for sure?

Alvin

What I said will tell you if you have had the programming altered. If it has been altered that sticker would have had to be removed in order to erase and replaced with something else.

farhorizons

Thanks for the tip! So then, I guess the stock chip can be reprogrammed, but the foil sticker can't be reused. That helps.

Alvin

it can be reused if they are extremely carefull.. but how likely is that.. its bascially a low tech tampered if broken seal

65Z01

When I used to burn EPROMs I would just cut a piece of black tape and stick it over the quartz window to keep UV light (we had fluorescent lighting) from erasing any of the data.

If I were custom burning chips I surely would not even try to reuse the factory seal.

formul89

SLP chips are stock blanks with their programming.

farhorizons

Thanks again for all the helpful input. This forum can be quite educational.

I've never played with performance programming. While I've understood the basics of changing fuel injection parameters in the quest for better performance, I've never dived in to this stuff before. Slapping in a Holley Trick Kit this ain't.

So correct me if I'm wrong: the stock chip is actually an EPROM that is erased by ultraviolet light. A stock GM chip can be reprogrammed, but it is not unheard of for aftermarket performance chips to look completely stock to the uninitiated.

My problem here is that Carbon Monoxide is reaching the tailpipe sniffer in quantities that the state of California disapproves of. I'm trying to sort out whether or not aftermarket code might be the cause of my smog test failures. Is there any way that I can verify if this is really what is going on?

Every expert who examines the car says that every sensor and actuator functions just like they should, yet the computer is deliberately injecting 15% more fuel than it was programmed to. Can anybody recommend a southern California shop that might be able to reinstall the original GM programming so I can get my '87 registered again? Unless I can pass smog, I've got a freshly restored $14,000 driveway ornament. I'm getting a little desperate here!

Mike_88Z51

IF the O2 sensor is working correctly the ECM should lean out the mix in closed loop to the point where you pass emmissions. Since you are 15% too high in CO, there are 2 distinct possibilities I would consider:

1) The original ECM has been replaced or reprogrammed. The easiest way to fix that is to buy a new stock chip for your 87 or have the current one reprogrammed to stock 87 specs. Since it requires no "tuning" I'd guess that there are a couple of guys on the Forum who frequent the Scan & Tune section who could load a stock 87 bin into a new chip for you for a very reasonable price. They would need to know if you have an Auto or manual tranny and the rear gear ratio at a minimum. This info is available in the RPO codes printed under the center console lid.

2) Since you have had a lot of experts look at the car already, I am assuming that they did some ECM scans and that they say nothing appears wrong in the closed loop operational values of the ECM. On an 87 this can lead one to "assume" incorrectly that closed loop operation is working correctly. There is a flaw to that thinking. Like my 88, your 87 has only one O2 sensor and it is mounted in the exhaust pipe just below the exhaust manifold on the driver's side. The single O2 sensor is only giving closed loop feedback to the ECM based upon the burn results of the 4 odd numbered cylinders on the driver's side of the engine. Any one or more of the injectors in cylinders 2,4,6,8, could be something funky and you wouldn't necessarily know.

Do the scans show the ECM Integrator and BLM readings to be in the correct range or on the limit of what the ECM can do to compensate for a too rich condition? The ECM/O2 sensor readings can be fooled if one of the even numbered cylinders is having a problem in an early C4. Later models used more O2 sensors to avoid this potential problem.

Redeasysport

Just a thought but why are you looking at the chip? There are overthings that could cause this First thought is O2 second is the FPR.Youcan get a free download of data master for your laptop and you will need a cable(ALDLCable.com) and you can log what is really happening.Watch your longterm(BLM) and O2 but my guess is you need O2 sensor.Even if your are not inclined to do this you should be able to take it to a shop to verify this. Just my .02

waynesTPI

2) Since you have had a lot of experts look at the car already, I am assuming that they did some ECM scans and that they say nothing appears wrong in the closed loop operational values of the ECM. On an 87 this can lead one to "assume" incorrectly that closed loop operation is working correctly. There is a flaw to that thinking. Like my 88, your 87 has only one O2 sensor and it is mounted in the exhaust pipe just below the exhaust manifold on the driver's side. The single O2 sensor is only giving closed loop feedback to the ECM based upon the burn results of the 4 odd numbered cylinders on the driver's side of the engine. Any one or more of the injectors in cylinders 2,4,6,8, could be something funky and you wouldn't necessarily know.

Do the scans show the ECM Integrator and BLM readings to be in the correct range or on the limit of what the ECM can do to compensate for a too rich condition? The ECM/O2 sensor readings can be fooled if one of the even numbered cylinders is having a problem in an early C4. Later models used more O2 sensors to avoid this potential problem.[/QUOTE]

The first time I hooked up the Diacom (bought it for the 89) on my son's 95 9C1 police package LT1 I was shocked to see the amount of data, includeing the twin O2 sensors. Compression check / injector check on 2 4 6 8 maybe needed?

Salt is for steaks, not roads!

94blue6spd

hey i have a stock chip from an 87 auto vette. let me know if your interested

farhorizons

Mike_88Z51 - My fuel trim numbers are about 15% above ideal. I'm seeing 140-142 on the scope when I should see 128. My Carbon Monoxide reading from the tailpipe sniffer on the dyno is 1.50-1.54 ppm, which is 2 to 2.5 times the maximum allowable. I found old paperwork that showed this car pegged as a Gross Polluter 5 or 6 years ago with a Carbon Monoxide reading of 5.50!!!

I'm looking into replacing the chip with something that has verifiable stock GM programming.

Since L-98s are a batch fire set up, aren't all the injectors seeing the same signals from the ECM? Even if the O2 sensor is in the drivers side pipe, isn't the stock computer incapable of sending a separate signal to the passenger side cylinder bank?


Redeasysport - The experts who've scoped this for me all say that the O2 sensor is showing proper voltage. We can watch it switch between rich and lean with enough frequency that it is not thought to be "lazy".

I wish I had a laptop, but even if I did, I can't do any better than putting it on the scope while running it on the dyno. I've got a friend who is head instructor at a school for smog techs. We've run every diagnostic known to man, and we still can't get this thing to clean up enough to pass.


waynesTPI - The Gold Shield smog shop guys spent 3 days on this car, and among the myriad of things they tried, they did a power balance test. Every single cylinder is working just as hard as any other. They thought that I might have a flat cam lobe or a collapsed lifter that might be causing one cylinder to pass incompletely burned gasses down the pipe, but the cylinder balance test shot that theory down.

I am looking into having the injectors rebuilt, but if the computer is choosing to run the fuel trims in the low 140 range, even brand new injectors won't change that. I keep coming back to thinking that the chip has been altered to deliberately run the injectors rich.


94blue6spd - Im eager pursue this option. My car is a Z-52, with A4 and a 2.59 ratio.

Morley

If the computer is seeing a lean condition (140+ BLM) then replacing or getting the injectors cleaned and flow matched could absolutely help. If there is a cylinder that has a bad injector (bad spray pattern, partialy plugged) the O2 sensor will see the lean condition caused by it and try to fatten up the fuel trims to get it right.
Next thing to do is ohm out all of the injectors. You are looking for 14-17 ohms 16 being ideal. If any of them are out of that range it should be considered bad.
If they pass that test have the shop or whoever perform an "Injector Balance Test". This will spot any leaking or plugged injector(s).

94blue6spd

same as my car

formul89

IIRC, California uses a different chip than the rest of the 49 states.

Try to locate a CA calibrated PROM and go from there.

_twisted_

Is it an auto or stick, you could probably get a stock memcal for 20-30 bucks.

Is there an adjustable fuel pressure regulator on it?

Mike_88Z51

If the ECM is reporting 140-142, then it is assuming that there is excess oxygen in the exhaust (i.e. a lean condition) and is compensating. There are several things that can fool the ECM into seeing a rich mix that isn't there. One of those is a dead cylinder. You already said that the Gold Shield smog shop guys did a test and found no dead cylinders, so that isn't a factor.

Here are some other things that could be the cause of your readings in the 140 range: vacuum leak, restricted injector(s), cracked exhaust manifold, defective air pump upstream-downstream switching valve, low fuel pressure.


Yes, to both questions. That is the inherent problem with a batch fire setup and only one O2 sensor that isn't centrally located. The ECM is firing the passenger side injectors based on the results it sees from only the driver side exhaust. Even though the capability exists to fire the two sides differently, the feedback capability isn't there with only one O2 sensor on the driver side. If an injector is working incorrectly on the passenger side, the ECM has NO WAY to know. Conversely, if the ECM sees too much oxygen in the driver side exhaust it "assumes" that BOTH sides have too much oxygen and increases the pulse width of BOTH driver and passenger side injectors to compensate. Now that I know your ECM is showing BLM of 140, my view is that there is a probably problem on the driver side bank.

If the driver side cylinders have a problem runnnig a touch lean and the passenger side is normal, then the ECM will see the driver side lean condition and adjust BOTH banks the same. This brings the driver side into compliance and the passenger side becomes a touch too rich. Possibly the source of your 15%?

Morley has valuable advice here: "Next thing to do is ohm out all of the injectors. You are looking for 14-17 ohms 16 being ideal. If any of them are out of that range it should be considered bad.
If they pass that test have the shop or whoever perform an "Injector Balance Test". This will spot any leaking or plugged injector(s).