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Sorry to keep bringing this problem up again for the third time, but I'm desperate -- the car just flunked again today, and now I've only got two weeks before the car ('84 B23F, LH2.0, automatic, 240K miles) is condemned: running out of time to fix it after failing state inspection (so far retested 4 times). The car's HC emissions are way too high (especially in NJ's new "fast idle" phase of its new test protocol) about 4-5X too high based on the several times I've had retested (although this last time at "slow idle it's a little lower but still in violation), and yet the other gases (CO, CO2) are low.
And this is relatively sudden, as only two years (and only 8.000 miles) ago it passed easily (as it always used to), so there has been some sudden catastrophic change, not something gradual over its life.
QUESTION:Is it possible (or likely, based on the problems described) that I've got a bad ECU (it's original, showing p/n 0 280 000 510)? That, or my distributor (also original, p/n 237 508 003), which shows by timing light a slight variation, about 3 degrees (between 6 and 9 deg) at idle although is steady at higher rpm (maxing out at about 30 deg), are the only two things I haven't replaced yet?
Or is there anything else that can be causing this very high HC that I haven't addressed (see below)?
The idle is admittedly very *rough* compared to my '93s, although the engine pulls very strongly on the highway without any bad spots along the rpm band; but coming off idle for sudden accerations (e.g., from a stoplight), there's sometimes a subtle cough (backfire?).
It's been run on synthetic oil (and doesn't use any between changes), and only on *premium* octane Exxon and AMOCO gas, since I bought it in '86 with only 30K miles on it; and I drive hard, keeping the rpms up by using the shift a lot, so I wouldn't think of carbonization.
To recount my work, and the parts I've thrown at it (without regret) so far:
All vacuum lines (new, silicone, and including those to the fuel-carbon cannister) and PCV hoses (and flame trap) are new and clear, and larger ones are clamped to prevent leaks; also the AMM-to-throttle body ribbed hose is new (and clamped) to preclude any hidden cracks.
The throttle body has been thoroughly cleaned (with new gasket), and the throttle position switch is perfectly positioned.
New fuel pressure regulator (2.5 bar).
I've listened to the fuel injectors (with an electronic "stethoscope") and they all have consistent clicks); and I've checked their individual resistances (all are about 16.6 ohms, compared to 16 ohm specs) as well as their combined (at the ECU plug) of 4.8 (instead of 4.0, but below the 5.6 indicative, per the green manual, of a bad injector).
New O2 Sensor, and new (factory rebuilt) AMM; likewise, new (factory rebuilt) IAC (and new hoses and clamps for them). And I set the base idle to specs (although it isn't a smooth idle whether at base or regular).
Of course, it has new plugs and distributor cap and rotor (and the wires have been checked and have equal resistance).
The temperature sensor checks out perfectly over a range of temperatures (measured at the ECU plug); and I've checked all the other wiring connections (at the ECU plug) spelled out in Bentley's table d (pp 241-12&13) for the LH2.0 system.
The new AMM was factory set to 380 ohms, and I adjusted it further to get swings on the O2 sensor (approx. on a DVM -- it's hard to see swings with the digital display), but it swings up and down mainly at faster rpms (~2,000 and above) -- I don't see such swings at idle, even though the O2 sensor must be really heated up (just moments after a suburban 5 mile drive in 2nd and 3rd gear which happened to be between 2 and 3,000 rpm).
In addition to following Bentley's chapter 241, I've been step by step through Volvo's green manual for the "LH-II" system (model years 1983-4), and haven't found any significant problems (except hard-to-see O2 sensor voltage swings, preceding paragraph). There's little by way of actually testing the ECU; it's almost always be elimination. Likewise, distributor testing is largely on a test bench, not in the car.
I really don't want to have to junk the car -- I'm desperate.
Thanks all (and especially for your tolerance of my repeated inquiries).
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Greetings:
rough idle always makes me think of plug wires, distributor, and vacuum leaks. However, you might consider a different approach. Who is your local state politician? Representative, senator, whatever. This is probably a state matter, not federal except indirectly. Approach one or more, whoever seems friendly, with a concise, well written explanation of ALL THE TIME AND MONEY you have devoted, and the factory correct things you have done, and a picture of your shiney - polish chrome, etc. - not junker - car. See if they can "help". Obviously the problem is NOT with your classic car that you drive for safety reasons. Hopefully you and your family are registered and VOTE. Alternatively, see if there is an inner city inspection station that for $100 will make sure you pass. Approach this circumspectly, no obvious statements. I am quite sure people in the inner city drive junkers they NEED to get to their nursing home job, and they are NOT going to start walking through the ghetto just because of elevated hco.A $100 "tune up" will not cure an old oil burner GM but they can't afford all you did, either.Any hot rod clubs - incl. Nissan, etc. rice burners - that can recommend a friendly inspection station?
bmw john in indy/avon
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A blown intake manifold gasket will produce the symptoms you describe. They are cheap and easy to install. If you wish to test before yanking it apart, spray acetylene or propane, if you have the equipment, around the manifold runners where they meet the head. The engine will pick up immediately when you get to the bad one. If it does, then you are $15.00 away from a repair.
Simple stuff first.
Rhys
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Thanks for responding.
Actually, I thought of the intake manifold (and I even bought the gasket just in case), but then I've tested it with my propane torch (as you suggested) with a long hose on the burner pipe to direct the gas closer to nooks and crannies underneath as well, and didn't find any response.
I did think that maybe it was too subtle for me to notice (given the rough idle), but you just wrote that the engine "would pick up immediately", making me think that it would be very noticeable had I had a leak.
But thanks, and please don't stop thinking of this. You're help is appreciated.
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"...the O2 sensor .... swings up and down mainly at faster rpms (~2,000 and above) -- I don't see such swings at idle..."
They may not test at idle speed, but that doesn't sound right.
What voltage is the DVM reading when the sensor is stuck (not swinging) at idle?
--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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Thanks for answering.
At idle, voltages are way too low. I only get voltages at hundredths, e.g., 0.03 v. -- not even a tenth of a volt (using the 2 volt scale). But when I rev it up, I'll get swings from, say 0.87 down to .15 volts at the current AMM's pot's setting.
Again, thanks.
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I just read Rhys' post. That's the answer, I'm sure, if you haven't already done that gasket.
--
Art Benstein near Baltimore
A truly happy person is one who can enjoy the scenery on a detour.
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Thanks again.
You guys are convincing -- I'm going to retest it again with my propane torch as soon as I get off this computer, just be certain. That, and the temperature of my cat; and tonight, in the dark, for stray sparks (shorting from the secondary wiring) under the hood.
I didn't get a chance to also answer your kind offer about the ECU. I know that this one doesn't have the awful rep of the ECU for the later cars, but I'll write back this weekend if I want to try it out. Much appreciated. And I'm answering your other questions next.
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Ken, rather than re-test, just replace the gasket. Using propane to find vacuum leaks in an environment under constant idle engine management may be a more subtle skill than you and I have. If you've never replaced one, you'll be surprised how easy it is to do, and how brittle the old one is.
--
Art Benstein near Baltimore
If speed counted, rabbits would rule the world.
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Ken, I can send you a 510 to try, but I doubt very much the ECU will make any difference, based on your observation of oxygen sensor output. When that sensor is switching, the system is in closed loop and should be passing HC spec.
The trouble is the sensor looks at all four cylinders and adjusts injector time based on the aggregate mixture (oxygen level) so a problem with just one cylinder could force the system to compensate. What do the plugs look like? Any clues that one cylinder isn't right? Compression readings? I'm thinking a burned exhaust valve or a leaky (or clogged) injector affecting only one cylinder. Any exhaust leaks, especially at the manifold?
What is the cooling system doing? Does the car come up to temp quickly? A broken thermostat is what I'm hinting at. Plug wires only checked but not replaced don't give evidence of insulation failure -- the more common cause of misfiring as compared to broken conductors. Low CO along with high HC reminds me of raw fuel more than incomplete combustion due to insufficient air (filter).
If the state gives you no leeway on this, you might want to find an emissions specialist to diagnose the rich idling. In my state, a waiver will be available once a certain dollar threshold is met attempting to cure the problem - usually just past the price of one cat. The specialist will have the tools we don't - mainly an exhaust gas analyzer, and of course, experience.
Let me know if you want to try a known good 510. benstein at cleanflametrap dot com
--
Art Benstein near Baltimore
Nobody cares if you can't dance well. Just get up and dance.
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Hi again.
When I changed the plugs (at the start of all this a couple of weeks ago), I noted that all the plugs looked identical: same gap (a bit too big), same color, and no deposits.
I did note in other responses that I'm rechecking for the intake gasket leak, and I'm thinking of buying a leak-down compression test kit, too.
My cooling system is really good; never any leaks (in fact, in its life, it never overheated, although 20 years ago the thermostat did stick open on a vacation and I had to run it for a few hundred miles running a bit too cool -- that's why I've changed the t-stat every 2 years from then on); and the gauge is really good, not showing any behavior that hasn't been typical throughout its life.
BTW, thermostat (87 deg) and coolant (M-B's glysantin-type, because I prefer the yellow over Volvo's darker blue glysantin, mixed 50:50 with distilled water) is changed every two years like clockwork.
Thanks again.
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Ken, I haven't followed this saga closely. Have you pulled plug wires one at a time while idling to try and find a deadbeat cylinder?
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Hi. Thank you for responding. Yes, I did report (but left that out in this latest message) that I pulled each plug wire (and grounded it through another old plug so it won't harm the ignition computer, as warned in the Green manual), and the engine's rpm dropped equal amounts -- I'm figuring that each cylinder is able to contribute the same amount.
But I'm still thinking about the rough idle, and that (in addition to the ECU) maybe it's the distributor's erratic timing????
Thanks again.
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Have you checked the TPS with a meter or just listening for a click. It could click but not close.
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Ken,
I see you are satisfied that the TPS is adjusted correctly, but the stumble off idle kind of sounds like a TPS. On my 945, I was adjusting the TPS by ear, listening for the click. It turned out that something else in the throttle or cable system was clicking. It fooled me into getting the adjustment way off. So, if you haven't already, you might want to check its operation with a multimeter.
It sounded like you weren't 100% sure that your O2 sensor was responding correctly. Below is a clip from a Bosch service sheet on testing the O2 sensor so that you can see if you are doing the procedure according to Hoyle.
Charley
Simplified Test Procedure
Locate the oxygen sensor and determine the wiring layout. On heated sensors check for heater element continuity, adequate 12 volt supply to heater and correct ground when the engine is running.
Note - Many late model vehicles have the ground circuit of the oxygen sensor heating element controlled by the engine management ECU for sensor temperature control purposes. Do not supply direct voltage or external ground to these circuits.
With engine speed at ~ 2000 RPM the sensor voltage should be seen to cycle smoothly between 100 – 900 mV (0.1 – 0.9 Volts) approximately eight times or more every ten seconds as shown. [Graph not included here]
A contaminated or tired sensor will be slow to cycle between the sensor voltage limits and may not generate the full potential of 900 mV. It may also be noticed that the lean swing may drop to zero voltage.
Remember!! – The oxygen sensor is a battery, a sensor that generates 900 mV constantly is generally not faulty. Faulty sensors, like a failing battery, will be slow to cycle between the control limits and be generally slower to react to mixture changes.
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Thanks for responding.
My sensor is not the heated kind -- it's only a single wire. And it's new.
But I have followed the shop manual's advice and test it after a long run on a suburban road, coming back to my driveway; and then actually testing it with my meter attached, each time giving it a two-minute rev at 2-3,000 rpm for two minutes (as called for in the shop manual), so it should be hot enough.
Thanks again. It's appreciated.
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I get the impression from your posts, that you are obsessively meticulous, so this must be driving you crazy. Your 84-240 must be in great shape and must be rescued.
Could high HC indicate raw fuel making it through the system unburned? Have you checked for actual spark at the plugs? (Pull plug with wire and ground it.) You did mention that the idle is rough.
Maybe it's not the car. Are you using the same shop to test? Maybe defective test equipment?
As a last resort you could take it to a dealer. Or before that replace the cat, which I think you haven't done yet.
In Ontario, Canada, cars over 20 years old aren't tested. Where are you located?
--
1980 245 Canadian B21A with SU carb but electronic ignition and M46 trans in Brampton, Ont.
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Thank you for responding.
re "...Or before that replace the cat, which I think you haven't done yet...."
No, I haven't yet. I asked that on my first post, but someone mentioned that since the CO levels were very low, it seemed that the cat was working, and I've sort of forgotten about that possibility in subsequent posts.
But maybe I should recheck that -- maybe I'll take my IR thermometer and check the cat's temperature -- if it's working, I'd expect that it should be much hotter than the pipe in front of it, right?
Is it possible that the cat is still good for one gas, e.g. CO, and not for another, HC?
I'll post back after I make a temperature measurement.
re "...Maybe it's not the car. Are you using the same shop to test? Maybe defective test equipment?..."
Funny you should mention that ... I thought so, too, and for this last test on Friday (which showed slightly lower "slow idle" HC levels), I did take it to another station about 20 miles farther way. But the "fast idle" level was the same.
And my plug wires are only two years old Bougicord-brand. But I'll check them along their length when it gets dark -- easier to see arcing in pitch dark (some years ago, I found the coil wire that way, shorting against the power steering that it laid against).
And thank you again.
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I'm not so familiar with the 240 series but I would suggest the following:
1. Compression check. I know you pulled wires to get a feel for cylinder balance, but a smaller compression leak might not show up that way. Wear in the valvetrain?
2. Fuel pressure and volume (I'm not sure if the 240 has an easy test point?)
3. Try running a can of injector cleaner through (perhaps one injector is leaking?) and also try running sea foam through the intake (as per directions on the can).
4. Try checking for intake leaks as mentioned before.
5. Check the ignition wires not only in the dark, but use a squirt bottle with a "spray" or "mist" to help any arcing show up better.
The O2 sensor switching seems fairly normal but I might also suggest checking voltages at the connector to the ECU (actually, for all sensors). This lets you know if there is a problem in the sensor wiring.
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thank you for responding.
I have checked for intake leak, but I'm doing it again in a little while.
I also checked all the wiring at the ECU's plug (resistance and voltages) and are all OK following Bentley's table (pp 241-12 and -13) for the LH2.0 system.
I don't have the equipment for a leak-down compression test, though. I may have to get that!
Thanks again very much.
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