My stock '89 240 failed the emissions test here in Ontario.
Driving test:HC ppm - 41/73CO% - 0.10/0.41NO ppm - 304/836
Idle test:HC ppm - 279/200CO% 0.28/1.00
Looking into it I found the air filter was poorly installed and oil was getting in there that is coming from my front cover. Definite HC sourse especially when the AIV opens. Also de-carbonised combustion chamber and injectors. Feels like idle is smoother, and I had to adjust it down a 100 rpm so all's good.
I should have left it at that, but no...
I test the EGR solenoid and it operates once then sticks partly open. Strange coincidence that it should fail this one time that I am testing it, something else must be wrong. I check the input signal from the ECU and it is faulty. Makes sense if the solenoid never operated for a long time that it would seize.
But if the soleinoid wasn't being powered the EGR would remain open and I should have had a terrible idle and no power. I keep looking and find the pressure line to the BPT is burned through. OK, so that would prevent the EGR from opening, but then how the hell did I pass the NO test??? Also why didn't the ECU throw a EGR code (as it should when the EGR doesn't operate)?
I replace the hose and the solenoid anyways, and expect the engine to die as soon as it's started since the ECU is still sending the wrong signal. But no it purrs like a kitten.
I keep looking and find there is no vacuum coming from the BPT. I trace the source for the vacuum back as best I can to the evaporative canister, which is not generating any vacuum and it fails the test of blowing air into the main purge line. The passage is blocked.
Now I'm sick of this problem snowballing and I want answers.
Is it my faulty carbon canister that caused the high HC reading? How did I pass the NO test with an inoperative EGR? How can I get as good test results as I got with a seized solenoid, burnt BPT hose, faulty ECU and a blocked canister???
Mystery isn't it?
Mech problems don't match emissions failure
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Magnes
- Posts: 101
- Joined: Thu Jan 30, 2003 6:58 pm
- Car: '89 240SX, done up with a chrome-plated ground wire to the engine.
The temp sensor is operating within range. I should test the AIV but I don't have a vacuum pump. The MAF is spotless.
Also I should have said the ECU displayed no codes, and a backup ECU I had performed the same way, not sending any voltage signal to the solenoid at warm idle. Makes me think it's not the ECU but some auxilliary system that is causing the ECU to send a bad signal.
Also I should have said the ECU displayed no codes, and a backup ECU I had performed the same way, not sending any voltage signal to the solenoid at warm idle. Makes me think it's not the ECU but some auxilliary system that is causing the ECU to send a bad signal.
Dude you are so going down the wrong road here. The only thing going wrong here is your diagnostics. The ECM wont send a signal to open the EGR till the hard idle contacts open in the tps switch. Try your test holding the throttle open slightly. You should then see vaccum to the BPT. You will not see vaccum to the EGR till there is enough back pressure in the exhaust to close the BPT vent. This type of pressure is only naturally created under load during accel. This is the reason for DYNO testing. Its the only way to measure true NOx emissions. You can artifically create exhaust back pressure by clamping a 1 inch socket in your tail pipe with a pair of vice grips. Forget about your canister here. the canister is fed vaccum from the same solonoid that feeds your EGR system. It opens and closes the canister purge. But dont chase after the canister here.
240 kid you are right but HC does not mean the car is running rich every time. You need to look at CO in conjunction to determine if the HC is as a result of being rich or not. If you just have high HC and your CO is in normal range[which its not here] you have a lean miss fire condition going on. Simply put,raw fuel is passing through the system without being burnt,either because of plugs,wires or other secondary ignition component. If that were the case the NOx would go through the roof.
In this case the CO is at 1.00% at idle this is likely at or very near threshold. You likely have either a lazy or bias shifted O2 sensor or A fuel injector or seal leaking additional fuel into the intake.
240 kid you are right but HC does not mean the car is running rich every time. You need to look at CO in conjunction to determine if the HC is as a result of being rich or not. If you just have high HC and your CO is in normal range[which its not here] you have a lean miss fire condition going on. Simply put,raw fuel is passing through the system without being burnt,either because of plugs,wires or other secondary ignition component. If that were the case the NOx would go through the roof.
In this case the CO is at 1.00% at idle this is likely at or very near threshold. You likely have either a lazy or bias shifted O2 sensor or A fuel injector or seal leaking additional fuel into the intake.
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Magnes
- Posts: 101
- Joined: Thu Jan 30, 2003 6:58 pm
- Car: '89 240SX, done up with a chrome-plated ground wire to the engine.
Thank you! You don't know how happy I am to hear that.NISTECH wrote:Dude you are so going down the wrong road here.
Quote »In this case the CO is at 1.00% at idle this is likely at or very near threshold.[/quote]I think you misinterpreted my test results. The 1.00% is the threshold value at idle, my test result was 0.28%
I'm going to road test the car now. I did check for vacuum (past the solenoid) off idle. I checked for signal vacuum at idle, since that vacuum should be present or there would be no need for the ECU to cut it off at idle. You've given me confidence that I suck, so I'll keep testing a few more times until I get the result I expect.
Still a mystery that I passed the NO test with an inoperative EGR. Remember the BPT hose was burned through!
re evaluated your readings now that I know how you posted them. Through a set of NGK plugs in it and a distributor cap if its old. Make sure you dont have any vaccum leaks and go have it retested.
The NOx is a suprise to me to in this case but it may just mean you have a good cat still and it is cleaning up enough of it. Your NOx should be a little lower though to fall in an average range.
The NOx is a suprise to me to in this case but it may just mean you have a good cat still and it is cleaning up enough of it. Your NOx should be a little lower though to fall in an average range.
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Magnes
- Posts: 101
- Joined: Thu Jan 30, 2003 6:58 pm
- Car: '89 240SX, done up with a chrome-plated ground wire to the engine.
Back from the road test. EGR is functional! I'll have to assess where my analysis failed tomorrow. I'll get the plugs too, thanks. The distributor is like new.
If it helps in your evaluation there is a weird problem I noticed a while back that I've been 'driving around'.
With the ECU out and analysis mode I or II set, the O2 sensor switches at a good rate up to about 3000rpm (in 5th gear). Then it just turns off above that. It turns off at different speeds in different gears.
5th gear: 70mph (3000rpm)4th gear: 60mph (3400 rpm)3rd gear: 45 mph (3400 rpm)2nd gear: 30mph (3400 rpm)
I keep my speed below 70 for the sake of fuel economy but it seems to me there is a problem that needs to be addressed.
If it helps in your evaluation there is a weird problem I noticed a while back that I've been 'driving around'.
With the ECU out and analysis mode I or II set, the O2 sensor switches at a good rate up to about 3000rpm (in 5th gear). Then it just turns off above that. It turns off at different speeds in different gears.
5th gear: 70mph (3000rpm)4th gear: 60mph (3400 rpm)3rd gear: 45 mph (3400 rpm)2nd gear: 30mph (3400 rpm)
I keep my speed below 70 for the sake of fuel economy but it seems to me there is a problem that needs to be addressed.
under heavy load the system goes out of closed loop. This has nothing to do with speed but engine rpm. This is not abnormal at all. I personally dont rely on the flashing lights of the ECM to determine O2 reliability. I use a tool your average do it yourself does not own. Its called a DSO[digital storage ocilliscope] It is a very expensive peoce of equipment. Unless you have a need to use it often its not worth it to buy one. The test proceedure with one is fairly simple and it is a concrete way to tell if your O2 is good or not. You make sure the O2 will go over .8v when richening up the system(I use propane to do this) then when you pull a vaccum line the voltage should drop below .175 volts. This will tell you weather or not it is bias. That test can be done with a multimeter. To determine if its lazy you need a DSO. When you get the O2 to read below the.175v you snap the throttle very quickly and freeze the screen when the O2 goes from below .175v to above .8v. It should rise from the bttom to the top in less then .100 ms if it is any longer then that the o2 is determined lazy.
But like I said since I now understand your readings in the beginning of the thread I dont believe your running rich I think you either have a secondary igintion system problem. Try the plugs and go from there. Also make sure your ignition timing is right on. or even like 2 degrees retarded.
But like I said since I now understand your readings in the beginning of the thread I dont believe your running rich I think you either have a secondary igintion system problem. Try the plugs and go from there. Also make sure your ignition timing is right on. or even like 2 degrees retarded.
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Magnes
- Posts: 101
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- Car: '89 240SX, done up with a chrome-plated ground wire to the engine.
By 'secondary ignition system' I take that to mean the distributor, wires, and plugs?
The plugs happen to be NGK. They were bought from Nissan less than a year ago and their part number matches the one listed in NGKs parts catalogue. They look healthy too. The wires were donated from a scrapped 240. I measured their resistance at 3-4K ohms. Is this too low? The cap and rotor are healthy and the timing mark doesn't waver under the timing gun.
On Monday I will replace the AIV solenoid (I used it to get the EGR to work) and adjust timing as you recommended. I will get it re-tested and post the results.
The plugs happen to be NGK. They were bought from Nissan less than a year ago and their part number matches the one listed in NGKs parts catalogue. They look healthy too. The wires were donated from a scrapped 240. I measured their resistance at 3-4K ohms. Is this too low? The cap and rotor are healthy and the timing mark doesn't waver under the timing gun.
On Monday I will replace the AIV solenoid (I used it to get the EGR to work) and adjust timing as you recommended. I will get it re-tested and post the results.
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Magnes
- Posts: 101
- Joined: Thu Jan 30, 2003 6:58 pm
- Car: '89 240SX, done up with a chrome-plated ground wire to the engine.
Passed!
Driving test:HC ppm - 32/73CO% - 0.02/0.41NO ppm - 439/836
Idle test:HC ppm - 43/200CO% - 0.02/1.00
Oddly enough my NO went up a bit after fixing the EGR. Oh well whatever.
To sum up the fixes I did:- Ran some fuel injector cleaner and some combustion chamber cleaner.- Replaced EGR solenoid and BPT pressure hose.- Replaced air cleaner (and made sure it was properly installed)- Set soft idle switch, it was a bit 'on the edge' and might have been bumped off idle by engine vibrations.- Set idle and ignition timing.- Tested temp sensor, O2 sensor, AIV system, compression, checked all vacuum lines. All are good
So now I have some safety margin for my next test when the limits will be lowered 11.5%. Big thanks to NISTECH!
Driving test:HC ppm - 32/73CO% - 0.02/0.41NO ppm - 439/836
Idle test:HC ppm - 43/200CO% - 0.02/1.00
Oddly enough my NO went up a bit after fixing the EGR. Oh well whatever.
To sum up the fixes I did:- Ran some fuel injector cleaner and some combustion chamber cleaner.- Replaced EGR solenoid and BPT pressure hose.- Replaced air cleaner (and made sure it was properly installed)- Set soft idle switch, it was a bit 'on the edge' and might have been bumped off idle by engine vibrations.- Set idle and ignition timing.- Tested temp sensor, O2 sensor, AIV system, compression, checked all vacuum lines. All are good
So now I have some safety margin for my next test when the limits will be lowered 11.5%. Big thanks to NISTECH!
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Magnes
- Posts: 101
- Joined: Thu Jan 30, 2003 6:58 pm
- Car: '89 240SX, done up with a chrome-plated ground wire to the engine.
The saga continues... I'm convinced my ECU is in fact shot.
On the way back from work the engine was stumbling at steady throttle when cold. It occurred to me this might happen if the EGR was allowed to operate before the engine has warmed up. From the tests I did on my ECU that is very likely the case, since it never sends the signal to shut off the EGR. (Which is partly it's function).
I also noticed while my car was being tested that it idled poorly, listening from behind the car. I remember walking up to the garage door thinking "I hope that's not my car idling!". With the EGR being allowed to operate the only thing preventing it from stalling would be the low backpressure at idle, which is too weak to fully activate the EGR. If my EGR was partially open at idle it would account for my relatively good emissions result at idle.
I'll have to remember that for my next emissions test, but in the meantime I need to get a lock on what's making my ECUs (both of them) act bezerk.
On the way back from work the engine was stumbling at steady throttle when cold. It occurred to me this might happen if the EGR was allowed to operate before the engine has warmed up. From the tests I did on my ECU that is very likely the case, since it never sends the signal to shut off the EGR. (Which is partly it's function).
I also noticed while my car was being tested that it idled poorly, listening from behind the car. I remember walking up to the garage door thinking "I hope that's not my car idling!". With the EGR being allowed to operate the only thing preventing it from stalling would be the low backpressure at idle, which is too weak to fully activate the EGR. If my EGR was partially open at idle it would account for my relatively good emissions result at idle.
I'll have to remember that for my next emissions test, but in the meantime I need to get a lock on what's making my ECUs (both of them) act bezerk.
The ecm looks at the TPS to determine if it should send vaccum to the BPT for egr operation. if it sees the hard idle switch in the tps open at idle it will send a signal to the solonoid to send vaccum. It will however not open the egr if the bpt is venting to atmoshere due to lack of back pressure in the exhuast. If your egr was open at idle you would fail for high HC's. When the egr opens it is like a hurrendous vaccum leak except it lacks oxygen because it comes from the exhaust which is already burnt. The egr process is designed to help cool the combustion chamber with out adding the burning properties that could increase the temp. It allows more volume in the cylinder for compresson reasons.The lack of oxygen in exhuast IS the lack of burning properties.
I seriously doubt you have 2 ECMs with the exact same failure. I would take a look at your TPS settings.
I seriously doubt you have 2 ECMs with the exact same failure. I would take a look at your TPS settings.
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Magnes
- Posts: 101
- Joined: Thu Jan 30, 2003 6:58 pm
- Car: '89 240SX, done up with a chrome-plated ground wire to the engine.
You're right to suspect the idle switch, but let me tell you how the ECU failed...
The ECU signal to the EGR solenoid does in fact switch in response to idle position, starting at 0.5V at idle and going to 0V off idle. This is insufficient voltage. It should be switching between 12V and 0V!
Also, there is a tiny bit of vacuum that can bypass the BPT valve to the EGR and open it just slightly at idle, because the BPT never actually blocks the vacuum signal to the EGR, it just opens it to ambient air, like putting a hole in a vacuum hose. But some vacuum is still present in the hose leading to the EGR by virtue of the venturi effect, which may work to open the EGR just enough to allow a bit of exhaust by. If there wasn't enough vacuum at idle to open the EGR there wouldn't be any need for the EGR solenoid to cut off the vacuum (at idle).
That is consistent with the fact that the bad idle is barely noticeable, but the poor driveability when cold is very noticeable, and it just wasn't present before I fixed the EGR.
I also agree with you about the 2 ECUs not likely exhibiting the same problem. The only answer I have for that is that there is an electrical problem elsewhere in my car (like a short) which is causing the ECU to misreport voltage. That's just a theory though.
In my head it all adds up, all I have to do is find the electrical fault that is causing my ECUs to report the wrong voltage. Fat chance right? You have any clues?
The ECU signal to the EGR solenoid does in fact switch in response to idle position, starting at 0.5V at idle and going to 0V off idle. This is insufficient voltage. It should be switching between 12V and 0V!
Also, there is a tiny bit of vacuum that can bypass the BPT valve to the EGR and open it just slightly at idle, because the BPT never actually blocks the vacuum signal to the EGR, it just opens it to ambient air, like putting a hole in a vacuum hose. But some vacuum is still present in the hose leading to the EGR by virtue of the venturi effect, which may work to open the EGR just enough to allow a bit of exhaust by. If there wasn't enough vacuum at idle to open the EGR there wouldn't be any need for the EGR solenoid to cut off the vacuum (at idle).
That is consistent with the fact that the bad idle is barely noticeable, but the poor driveability when cold is very noticeable, and it just wasn't present before I fixed the EGR.
I also agree with you about the 2 ECUs not likely exhibiting the same problem. The only answer I have for that is that there is an electrical problem elsewhere in my car (like a short) which is causing the ECU to misreport voltage. That's just a theory though.
In my head it all adds up, all I have to do is find the electrical fault that is causing my ECUs to report the wrong voltage. Fat chance right? You have any clues?
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Magnes
- Posts: 101
- Joined: Thu Jan 30, 2003 6:58 pm
- Car: '89 240SX, done up with a chrome-plated ground wire to the engine.
I should try that trick I've seen you mention of clamping a large socket onto the end of the tailpipe (or maybe just closing 1 of the 2 tailpipes off altogether).
I can compare how much I have to block the exhaust with the EGR vacuum connected then disconnected. If no exhaust is getting by the EGR at idle it will take the same amount of blockage to stumble/stall the engine. My suspicion is the engine will stall much more easily with the EGR vacuum connected.
I can compare how much I have to block the exhaust with the EGR vacuum connected then disconnected. If no exhaust is getting by the EGR at idle it will take the same amount of blockage to stumble/stall the engine. My suspicion is the engine will stall much more easily with the EGR vacuum connected.