When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
On my '91 245, I'm failing NOx on the CA smog test. I've done a bunch of other work (cleaned IACV and AMM, replaced ECT, replaced EGR temp sensor, cleaned throttle body, flame trap, checked thoroughly for vacuum leaks, new air filter, tune-up, replaced in-tank fuel pump, new fuel filter, etc, etc...) but I'm finding the EGR valve is not opening. The valve itself is functioning properly: It opens when I manually apply vacuum and closes when I release the vacuum. The problem is the vacuum actuator (mounted on the driver's side strut tower) is not kicking on/open. At normal operating temp and part throttle, the actuator should open and allow vacuum to flow to the EGR valve opening it. I tested it multiple times and I don't get any vacuum through it at part or even full throttle (or at idle.) There is good vacuum at the actuator itself so its not that. When I run the test program, the actuator does kick on and off so the circuit and actuator itself is functioning.
QUESTION: What conditions need to be met for the ECU to kick the actuator open? Normal operating temp is one (replaced ECT) and part throttle is another (my TPS tests working.) I thought the EGR temp sensor might be another (so I replaced that) but its still not working. Is there anything else that would cause the actuator to NOT kick on? I guess I'm looking for the ECU code parameters that will allow that circuit to open. Other than this, the car runs really-really well but I want to get this solved before trying to re-smog it because its directly related to NOx. I have no error codes either.
what is the 'egr temp sensor' ? I only know of the engine coolant temp sensor, and the temp gauge sensor.
if the EGR vacuum actuator is working on the DTM3 test, then the other test to do is, with the engine running, disconnect the vacuum hose from the EGR control module, and hook it up to a mityvac. when you pump the mity vac down even a little bit, that should open the EGR valve, and dump exhaust into the intake manifold, stalling the engine. release the vacuum to keep it from stalling. if that works, your EGR system is fine.
tired/dead O2 sensor and a worn-out catalytic converter itself are the other two main reasons to flunk smog from an otherwise fine running engine.
The EGR Temp sensor is mounted on the EGR valve itself just past the internal valve opening to measure temp when the valve is open. Its only on '91 and later 240s (see Bentley).
I have tested the EGR directly using a vacuum pump. It opens and closes as it should and I've verified valve movement by touch and it will idle rough when I open the valve manually as it should. There are no leaks in the vacuum hoses and there is 20psi (at idle) vacuum at the actuator which is more than enough to open the valve when I try it manually with the pump and gauge.
My issue is the actuator is not kicking on/open and that's driven by the ECU (and/or ignition control module.) After warming up the car with a drive, I disconnect the top actuator vacuum hose (going to the EGR valve) and attach a vacuum gauge to the actuator nipple for that hose. When I open the throttle and rev the engine, the actuator should open and the gauge should show vacuum but it doesn't. If the actuator works (confirmed by running the test) why is it not opening?? This is where I'm stuck. Is there a speed condition or something else that needs to be met before the actuator will open? Bentley says the valve should open under my test conditions but it doesn't.
CA smog is a different animal and I won't be passing NOx without a working EGR system. Again, the car is running absolutely great right now which is really enjoyable but I don't want to try to smog it again unless I get this figured out.
Thanks for your help and any further help would be much appreciated. As you can tell, I'm stuck!!
ash, my greenbooks show that temp sensor on the PULSAIR B230FD engines on the 940's I more frequently look at. my only 240 is a 87, no EGR...
and yeah, i see its on the 91 240 california model.
opening the EGR valve should completely stall the engine at idle, not just make it stumble a little. its possible the EGR pipe between the valve and the intake is clogged up.
Right so trying to figure out why the actuator is not opening under normal operation. It does kick on when I run the test program telling me the circuit, wiring, and actuator itself are fine. Any thoughts?
afaik, EGR mostly actuates under deceleration with the throttle closed
Oh gosh no! At closed throttle with the EGR open, the car will stumble (and stall as you say) regardless of what speed the car is moving at. Its part throttle with the engine at normal operating temp--Those conditions I'm certain about for a '91 240 LH2.4. Wondering if there are any other required conditions anyone is aware of.
I tested this again with vacuum applied manually to the supply side of the actuator and when I open the throttle at normal operating temp, the actuator DOES kick open and release the vacuum. No vacuum can but measured on the output side of the actuator though so I concluded the actuator itself must be bad.
After spending $232 on a new EGR actuator, I get the same test result: At engine warm and part throttle, no vacuum flows through the port/nipple on the actuator that goes to the EGR valve. ???
With everything re-connected, I tested again at the EGR valve by getting my pinky finger in one of the slots on the EGR valve and feeling for the diaphragm. With my finger in there touching the diaphragm I opened the throttle and sure enough, I can feel the EGR valve opening. I'm not sure how that actuator works but there must be some back pressure or something required for it to allow vacuum to flow that the vacuum tester doesn't provide. I have no idea but at least I know its working. If you're going to to try this, a fiber optic camera or something would be better as its really tough to get your finger in there and I got one 2nd degree burn trying it--Those tubes from the exhaust get HOT.
Bad assumptions:
-No vacuum was flowing out of the actuator port that goes to the EGR so the actuator itself is not kicking on
-No vacuum at the output port of the actuator using a vacuum gauge means no vacuum is getting to the EGR
So I guess the moral of the story is to test multiple ways and don't assume any one test is definitive unless its truly scientific with proper controls. If my EGR system was working all along (hopefully not due to a bad ECT that's now replaced) then I don't think my NOx problem will be solved, but the only way I'll know for sure is to re-test smog.
i have recently failed california smog test due to high NOx emissions (592ppm, max allowed is 525ppm) also on a 1993 Volvo 940.
I also replaced a few things, like fuel pumps and fuel pressure regulator. O2 sensor was replaced a couple years ago and seems to fine.
I also did the usual tuneup, spark plugs, wires, cap rotor, oil and air filters, cleaned the throttle body, and MAF/AMM, added fuel injector
cleaner in the gas tank. Check for vacuum leaks, and finally replaced the catalytic converter as last resort, and still failed for high NOx.
I checked my ECT and it seems to be okay despite a small blip in the voltage at the ECU ever 2 seconds where the voltage seems to jump
up and then back down. Not sure what is the cause of that if it even matters. I also checked the EGR Regulator Solenoid valve. It can be
operated using the diagnostic test in mode 3. You will hear various compents clicking and turning on/off, cooling fan, IAC, Injectors, Pulse Air
solenoid, and the EGR Solenoid valve.
I connected a vacuum gauge with a T - Fitting and a long hose and placed the gauge inside my car on the dash. I noticed in park the EGR only
pulsed a vacuum signal very little upon revving the engine. However when driving on the road, and engine under load, the vacuum conditions are
and engine conditions are different. Clearly their is more load on the engine under driving vs in park. Well at light to medium throttle the EGR
vacuum solenoid does open and stays open, and a steady vacuum signal can be seen on the line to the EGR Valve.
The EGR Temp sensor I believe (cannot find wiring diagram for california model yet) I think it goes to the ICU but I am not sure. Anyhow I think this
is used to measure EGR flow. If the ECT were reading incorrectly, the check engine light should come on and have a DTC fault code set for low
EGR flow.
I do notice on the highway cruising about 65mph the EGR vacuum increased to 10inches of mercury. Oddly, if I turn off the Overdrive switch, the
vacuum signal to EGR reduced very much. Also under heavy acceleration full throttle the vacuum to EGR goes away, and on deceleration (closed throttle)
EGR Vacuum goes to 0inches. I think the ICU gets a closed throttle switch signal from the TPS, and so it knows to cut the EGR valve off at closed throttle
so as not to stall the engine. I am nt sure why it cuts the EGR valve off at full throttle acceleration other than opting for better performance and also the
fact that under richer fuel mixtures NOx is usually reduced. I noticed also that fuel pressure is higher at full throttle due to low engine vacuum to the pressure
regulator. So perhaps the drop in manifold vacuum at full throttle explains the drop in EGR valve vacuum as well.
I just wanted to share these observations about the EGR Valve and Vacuum regulator Solenoid, which I have discovered in my process of testing and
troubleshooting.
I honestly still have some doubts about the degree of opening of the EGR valve at the california test speeds of 15mph and 25mph at light throttle because
simulating this myself on the road, I discovered that the vacuum signal drops to as low as 1-2inches of mercury at those steady cruise speeds at light
loads. If I were to be going up a slight hill or press the gas peddle just slightly more, the vacuum increases to about 5inches. But then the car would gain
speed and the test requires maintaining 15mph or 25mph so the technician cannot provide a wider throttle opening.
I have noticed the EGR valve diaphragn has some kind of locknut and threaded rod on the top of its frame. in line with the center of the valve shaft. It is painted
with some white paint perhaps after it was factory calibrated. I wonder if perhaps I could adjust this preload to make the EGR open a little more easily. But being
careful not to make it so easy that it opens excessively under exhaust pressure. But I haven't found any discussion of this yet online.
Newer OBDii cars have EGR flow plus EGR Position Feedback signal to the ECU in many instances. and this allows the computer to target an exact EGR valve
opening percentage. Usually those are contolled by an electrically controlled valve or a pulse width/duty cycle modulated square wave to a vacuum regulator solenoid
as we have on our vehicles. Our obd1 Volvos only have the EGR Temp sensor to monitor EGR Flow, but I would imagine a well designed system would use that as
feedback to determine if more or less vacuum is needed and adjust PWM signal accordingly. However this system could be very rudimentary and simple uses hard
coded PWM signal levels based on RPM, engine load, throttle position, and EGR Temp. A hard coded system will not be self tuning and so if somethin is a little out
of adjustment/calibration, the EGR flow will not be correct.
I wonder if you eventually figured out the problem and could post your findings here. I'm going to check more for vacuum leaks, exhaust leaks, and possibly change the
o2 Sensor. One thing I noticed is my ignition timing at idle is about 15degrees and I heard its supposed to be 10 degrees. Advanced timing is known to increase NOx.
Wanted to add this detail that I feel is important to consider when trying to solve high NOx emissiosn problems:
However walker exhaust website says the following
SLIGHTLY LEAN CONDITIONS ARE THE MAIN REASON FOR HIGH NOX READINGS
EXHAUST LEAK PREVENTS CONVERTER FROM REDUCING NOX EFFICIENTLY
NOX IS NORMALLY TESTED ON A DYNO WITH ENGINE AT PARTIAL LOAD
02 READING SHOULD BE CLOSE TO BUT OFTEN SLIGHTLY LOWER THAN CO READING (WELL WITHIN .1% OF CO)
HIGH READINGS INDICATE A LEAN CONDITION THAT CAN RESULT IN A FALSE P0420 CODE
I can hear some tiny exhaust leak near the front of the car so perhaps I need to replace some gaskets or look for holes in the pipes.
Someone else mentioned the O2 sensor if it is reading on the rich side would fool the computer into a leaner mixture. But also I do believe
that o2 leaks upstream of o2 sensor could cause the o2 sensor to read leaner which would cause the computer to add more fuel.
I think this is part of the problem in that the engine AFR is not as lean as the ECU actually believes, so its not achieving the true lean
condition that is required for proper catalytic converter operation.
More from Walker Exhaust website:
HIGH HC READING CAN RESULT IN EXCESSIVE CARBON RESTRICTING THE CONVERTER
IF HIGH HC READINGS EXIST ALONG WITH O2 READINGS, A MISFIRE OR CYLINDER IMBALANCE MAY BE INFERRED - THIS MAY CAUSE THE CONVERTER TO OVERHEAT AND THE SHELL TO GLOW RED AND DISCOLOR, RESULTING IN SUBSTRATE MELTDOWN
LOWER HC READINGS ARE ALWAYS BETTER FOR ENGINE AND CONVERTER EFFICIENCY
Regarding the Volvo 940 EGR Valve components, I found this diagram on google images I believe is correct:
A little more insightful information about the particular Catalytic Converters used on 1993 Volvo 940 and similar models and years.
I believe these models have a 3 Way Catalyst without Air system. The earlier generations of cars may have had an air tube on
the middle of the Catalytic converter to admit addtional air for the second substrate, but our models use the o2 sensor to cycle
the fuel mixture between lean and rich conditions and Oxygen storage inside the catalyst during lean conditions to provide the
extra O2 needed to reduce HC and CO into H20 and C02.
The following is from the walker exhause technical articles but similar info will likely be found many sources on the net:
THREE-WAY CATALYTIC CONVERTERS
Allows reduction of NOx (nitrogen oxides) to N2 (nitrogen) and O2 (oxygen)
Allows oxidation of CO (carbon monoxide) to less-harmful CO2 (carbon dioxide)
Allows oxidation of HC (unburned hydrocarbons) to CO2 (carbon dioxide) and H2O (water)
THREE-WAY CONVERTERS have been used in vehicle emissions control systems in North America - and many other countries - since 1981.
The three-way converter without air uses advanced catalyst chemistry to store and release O2, in conjunction with an O2 monitoring and control system.
This system utilizes one or more O2 sensors to oscillate the fuel mixture between lean and rich conditions. This oscillation, combined with the O2 storage and release on the catalyst surface, allows for optimum reduction of all three emissions.
I want to add 1 more thought to this... I just realized that I had a crack in the 3 way hose (#8 in image below) on my Pulse Air Injection system. This is downstream of the Vacuum Valve that opens during cold startup. I notice this Vacuum valve is only open when engine is cold and after it warms up the pulse air system shuts off. However. if there is a leak after the vacuum control valve(#13 in diagram below), then this would admit air into the exhaust which could lead to a high NOx reading...
I am going to check over the connections there again. Its something worth looking at if you are having high NOx and solely focused on the EGR valve O2 sensor and Catalytic converter as I have been.
Here is a diagram of the Pulse Air system on volvo 940: Volvo 940 B230F Pulse Air Injection system diagram, I believe similar on 240 260 and 740 models
Photo of Volvo B230F Pulse Air Vacuum Control Valve, and Hoses/Lines
The silver hose to exhaust manifold cover is for hot air, not exhaust. In really cold weather the cold air will hinder mixing of fuel and air and the hose was to give warm air to counteract this. The hot air being available with warm freash air temp will send NOx up drastically.
Your 93 240 has the B230FD engine with Pulsair. Those hoses are used for cold start oxygenation of exhaust to lower cold start hydrocarbon (raw fuel) emissions. The hoses get air from the air cleaner and it is sucked into exhaust through the two check valves. The pressure drop at exhaust valve closing creates enough suction to get the job done without an air pump. No NOx reduction from Pulsair. The hoses have the vacuum shut off to stop the Pulsair function on a warmed up engine.
You have a heated O2 sensor so it will give a reading. Exhaust temp will be great enough for function regardless. Anything you do to cool combustion temp reduces NOx. EGR reduces NOx by making the combustion richer with exhaust encapsulated oxygen removed from availability during combustion, effectively richer but that oxygen is freed post combustion and is available for catalyst function and will be part of the exhaust gas sensed by O2 sensor.
The person says to check that thermostatic heated air intake valve on the airbox is closed, when engine warms up. It can fail open and circulate hot air into the intake at all times, increasing NOx emissions by raising combustion temperatures/counteracting the function of EGR which is to lower combustion temps(thus reducing NOx)
Also be sure your air cleaner housing thermostat is not stuck open. The hose that leads back over to the cover over exhaust manifold goes into chamber in air cleaner box where a door controlled by a thermostat closes fresh air opening and opens the hot air hose side. These are notorious for sticking. Remove the thermostat and use a screw to lock door closed to the hot air hose fitting.
The OP, mentioned he replaced his CAT with a California Unit, but was told by the smog technicians that due to cars having EGR, the california cats, lacked NOx reduction capabilities, which is unfortunate and explains why a new Calif. CARB Approved CAT does not help reduct NOx emissions...
number of remedies recommended and executed including a new CA cat, cleaning the TB, new oxygen sensor, replacing a few very old vacuum lines. After these fixes all readings were excellent EXCEPT NOx. It was still off the charts. It was explained to me that the CA cat doesn't reduce NOx because Volvos sold in CA during that period had an EGR system
Unfortunate news and very disappointing as California Air Resources Board and Bureau of Automotive Repairs regulates the approval of Catalytic converters that can be sold and installed on every vehicle in the state. They failed to realize that NOx emissions standards are stricter here and for older vehicles the CATs if they are going to cost 3x - 5x more than EPA federal CATS, should at least include additional NOx reduction chemistry in the substrates. Otherwise California motorists are being cheated out of their money on Calif. Approved Catalytic converters!
03-04-2014, 08:01 PM
EGR Valve Actuator Conditions
You misunderstood how the EGR valve functions...
