Question: 88 Coupe - Emissions Test Failure

[WTS]

Emission Test Results

2500 RPM
HC (ppm) Limit 200 - Reading 208, CO% Limit 1.00 - Reading 7.17

Idle
HC (ppm) Limit 200 - Reading 508, CO% Limit 1.00 - Reading 7.56

Has anyone seen this magnitude of failure before and if so what was the cause?

According to my OBD-1 program the car is running rich all the time.

I am thinking that this radical failure is likely due to a failure of the Air Injection Valve Solenoids. I will be looking at the engine cold condition
and the warm condition to see if the Air Pump output is being switched correctly. I am thinking that the exhaust is being fed continuously
with air causing the O2 sensor to think the engine is running on the lean side forcing the ECM to add more fuel.

Anyone have and thoughts or experience that may help?

Thanks WTS

 

[Hib Halverson]

How many miles are on the car?
Have you run the fuel pressure tests in the Service Manual? If so, what were the results.

 

[WTS]

How many miles are on the car?
Have you run the fuel pressure tests in the Service Manual? If so, what were the results.

The car has approximately 260,000 kilometers on the odometer.
I have not run the fuel pressure tests this year.

WTS

 

[WTS]

Hib

Finally managed to measure fuel pressure !

Engine Stopped - Ignition ON - 42 Psig
Engine Running at Idle - 37 Psig

Code 45 set - O2 Sensor Rich
O2 Output - .729 Volts
BLM 108

MAF at Idle 9.02 gm/sec
This according to the Manual is high which quotes 4 to 7 gm/sec

Disconnected the AIR Control Valve output to the exhaust - no change in BLM, still maintained rich condition.

Any thoughts

WTS

 

[89Z51]

ECM data

Hib

Finally managed to measure fuel pressure !

Engine Stopped - Ignition ON - 42 Psig
Engine Running at Idle - 37 Psig

Code 45 set - O2 Sensor Rich
O2 Output - .729 Volts
BLM 108

MAF at Idle 9.02 gm/sec
This according to the Manual is high which quotes 4 to 7 gm/sec

Disconnected the AIR Control Valve output to the exhaust - no change in BLM, still maintained rich condition.

Any thoughts

WTS

Out of curiosity, have you run through the procedure to set "minimum air"? Do the throttle plates move freely? Is the idle higher than normal? The reason I ask is that if the MAF sensor is showing more air through the throttle plates than there should be - almost like the throttle plates are stuck partly open or the minimum air setting is wrong. This all assumes that the sensor is reading accurately, but absent any evidence that it is faulty, you must assume it is accurate and work from there.

 

[WTS]

Hi

I have checked the minimum air setting but I will.

Thanks

WTS

 

[Hib Halverson]

Hib

Finally managed to measure fuel pressure !

Engine Stopped - Ignition ON - 42 Psig
Engine Running at Idle - 37 Psig

(snip)

Any thoughts

WTS

During the fuel pressure test, key-on/engine-off was 42-psi but what happended when you turned the key off? Did the pressure drop slightly then hold, did it drop slightly then drop more very slowly or did it drop steadily and rather quickly?

Do you have the Factory Service Manual?

 

[WTS]

I believe that the pressure dropped off relatively fast once the ignition was turned off.
If memory serves me correctly I believe it dropped to about 20 Psig within 10 seconds or so.

The fuel injectors were all replaced with Accel 24's in late 2009. However, I suppose it is
possible that one or more have partially failed.

WTS

 

[c4c5specialist]

HI there,

Accel injectors, while very good, still function off the same kind of principle as the OEM.

YOU REQUIRE 16.5 ohms resistance at EACH injector with a tolerance of plus or minus 1 ohm. This measurement is on a cold engine.


Please measure resistance and we can assist further.

Allthebest, Paul

 

[WTS]

Paul

I will have a look at the injector coil resistance again to confirm.

thanks for the input.

Regards WTS

 

[WTS]

Injector Coil Resistance is normal.

Any further thoughts ?

WTS

 

[WTS]

I believe that the pressure dropped off relatively fast once the ignition was turned off.
If memory serves me correctly I believe it dropped to about 20 Psig within 10 seconds or so.

The fuel injectors were all replaced with Accel 24's in late 2009. However, I suppose it is
possible that one or more have partially failed.

WTS

Further Testing as follows;

Fuel pressure Engine off, Ignition on 42 psig
Fuel pressure Engine off, Ignition off 41 psig and holds for longer than 5 minutes.
Fuel pressure regulator reduces rail pressure with vacuum applied.

BLM 108 with O2 sensor connected to ECM
BLM 128 with O2 sensor disconnected
Engine stable at 925 RPM
TPS stable at at .51 volts

Any thoughts

WTS

 

[tmkassin]

Nobody mentioned cleaning the electrical connections. Make sure you have good clean grounds especially the bell housing connection. You could be sending the ECU all kinds of bad info if the juice isn't flowing properly. And it doesn't cost any money to do, just a little time.

 

[WTS]

Thanks for the input, I am gradually completing all of the electrical checks.

WTS

 

[ecss]

Appears your base idle speed is high at 925.

My 89 has a superram intake and Accel 74219 cam, idles at 850 and the maf
gps is around 10 so I don't think you have a MAF problem.

I'd suspect a leaking injector on the driver side because the O2 sensor
is monitoring cylinders 1,3,5 and 7.

Pull the plugs and see if one of them has carbon build up or a wet look to it.

 

[WTS]

Subsequent testing has revealed a normal output from the MAF for the engine idle.

Fuel pressure holds for a considerable time after the ignition is shut off, so I do not think I have any leaking fuel injectors.

I have looked at all engine sensors including MAT and Coolant sensors and all have outputs consistent with the shop manual.

I have not yet looked at the ECM in terms of connectors or wiring condition but this will be next.

Plugs, wires, distributor cap and rotor have now been replaced but no improvement in BLM as it is still sitting at 108.

There appears to be nothing obvious causing the rich condition.
Fuel pressure is normal with a corresponding change in output with the application of vacuum.

When the O2 sensor is disconnected BLM goes to 128 which indicates a normal condition.

The O2 sensor was replaced two years ago but it seems in theory to be working based upon testing conducted. When the O2 wire to the ECM is open the O2 output is approximately 0.44 volts, and when the O2 line to the ECM is shorted in accordance with the shop manual the SCAN indicates a very low output of approximately 0.04 volts.

From my perspective the only check left is to examine the electrical interface and grounds for any abnormalities.

Thanks for your input !

Regards WTS

 

[Hib Halverson]

(snip)

I'd suspect a leaking injector on the driver side because the O2 sensor
is monitoring cylinders 1,3,5 and 7.

Pull the plugs and see if one of them has carbon build up or a wet look to it.

I'd say it's unlikely to be a leaking injector as the fuel pressure held at 41 psi for five minutes. If there was a leaking injector, the fuel pressure would have dropped quickly.

 

[Hib Halverson]

Have you verified the MAP sensor is working properly and there are no leaks in its hose?

Is the TPS functioning properly and is it adjusted per the FSM?

When you disconnect the O2S, do not assume the system is operating normally. With no O2S, BLM will go to mid-scale because the system is in open loop and, thus, BLM is disabled.

For the BLM to be 108 at idle, the engine will be rich in open loop. When you reconnect the O2S, the system goes closed loop and dials the fuel back 20 points to bring the AFR to stoich.

 

[WTS]

I agree that it is unlikely I have any leaking injectors based on the test results.

My 88 does not have a MAP sensor.

The TPS is set to 0.56 Volts and is stable.

This one is truly a mystery.

WTS

 

[ecss]

I agree that it is unlikely I have any leaking injectors based on the test results.

You've never posted what the electrode of each spark plug looks like.
Are they all tan color which is normal.
Are they all carbon fouled?
If only one plug/cylinder is carbon fouled it would indicate a bad injector
or spark problem for that cylinder.