Hi, all. I posted a while back with questions about what a high level of NOx gasses in the exhaust means. I got many very good ideas, most of which suggested I had vacuum leak leaning out the mixture and heating up the combustion. Well, I inspected the vacuum hoses I could find and they all look like new (thanks to the previous owner who took very good care of this car). I am not familiar with all the locations of vacuum hoses, but I did my best. In general, all the hoses (air and liquid) look like they have been replaced. I am very happy about that. This doesn't mean I don't have a bad house somewhere, just that I could not find one.

What I did find, though, was that spark plugs, though in good shape and stock Volvo units, had the gap approximately twice as big as the spec, which is 0.028-0.032 inches. I could not read the nomenclature off the plugs (a bit of corrosion on the outside), so I am not sure they were the right part number. I did measure the gap with filler gauges and it was about 0.070! I quickly ran out to the local auto parts store and bought some Bosch Platinums that were cross-referenced to this car. I took a gauge to the new plugs and it was smack 0.028 with a bit of sliding room for the gauge. So, my question is this. Can a drastically bigger spark plug gap cause hotter combustion? I have not gone for re-inspection, wanted to get some more wisdom first. I am planning to check the intake manifold bolts also to make sure I am not sucking air there. Any other ideas are welcome.

Oh, and I looked at the graphs that I got from the treadmill test. The CO looks normal, not too low as I reported before. Looks like it's comfortably within the limits, but not down in the mud.

Thanks to all!
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Vladimir. '98 S70 base, 5-speed manual - his, '93 945 - hers,

Bad plugs or improper gaps will affect combustion and can certainly alter the gasses levels. In any event, change the plugs. Use silicone dielectric grease inside the plug wire boots to limit dirt and sparkover and make it easier to get them off next time. If these are the original plug wires, get some new Bougicords (including coil wire) from an online vendor.

Thanks. I already replaced the plugs and I did put some boot grease into the plug boots. As far as wires, they do not look old, though they are a Volvo item. I left them alone.

Thanks.
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Vladimir. '98 S70 base, 5-speed manual - his, '93 945 - hers,

Hi Vladimir, high NOx is caused by non-functional EGR system or too much timing advance. Worn-out plugs might create a misfire which would lead to excessive hydro-carbon (HC) emission failure. I would suggest that you bring the car to a warm idle, then manually open the EGR valve. This should cause the engine to stumble or stall. If it doesn't then the EGR passages are plugged. If the engine does stumble or stall then check that the EGR valve is opening . It should open with a warm engine and part throttle opening. If it doesn't you need to check the electrical and vacuum circuits to the valve. The valve electrical circuit includes a temperature switch in the engine coolant passage; if this switch does not close when the coolant is warm then the EGR will not open when it is supposed to. Also check the base ignition timing. If all these things are ok the problem may be in the catalytic convertor

Thanks for the advice. I will need to check the EGR. I am not familiar with this car all that much. I do have a Haynes manual for 740. Will that point me to the ballpark of the EGR valve?

I'll give it a shot.

Thanks!

P.S. What is a good service/repair manual for this car? I used to have a 240 (loved that thing! Saved my wife and two kids in a bad accident) and bought a Bentley manual for that. It was a very good book. Is there a Bentley for this model?
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Vladimir. '98 S70 base, 5-speed manual - his, '93 945 - hers,

Not all '93 940s have an EGR valve, mine doesn't. I think it may be only California cars which have these.

I bought a Bentley manual when I had all 240 models and I find it does help some on the 940, particularly if your car has the Bosch LH system. Mine has the REx-Regina system so there's no help there. I bought a Mitchell CD on Ebay and it is of some help. The electrical diagrams are good and clear.

The 700/900 FAQ are very helpful.

Sometimes you can get a green Volvo manual on Ebay. I have one on the Rex-Regina system. However, I see the Volvo manuals often going for equal or more than Volvo charges for them.

Unfortunately, I sold the Bentley manual after the 240 got totalled. I do have a Bosch system and would like to check the trouble codes, but I forgot how to do it. I see a lot of CD manuals on ebay, but am very sceptical. I would rather have a good-ole Haynes. I think there is a Haynes for 940 in England, but not in US. If anyone knows how to read and enterpret trouble codes on the 940 (I have to look up the version of the system), please let me know. I will check the FAQ as well.

Thanks!
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Vladimir. '98 S70 base, 5-speed manual - his, '93 945 - hers,

The Volvo manuals make a great reference. I picked up a copy of the LH 2.4 and the Rex/Regina manuals (used but in great shape) for about $20.

P.S. I'd avoid the Bosch Platinum plugs, they generally have a bad reputation. If nothing else they're more expensive than the proper NGK copper plugs that work just great.

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alex

'89 765T, 176,3xx mi

OOps, I wish I knew about the Bosch plugs earlier. I did end up buying th Bosch Platinums. The guy at Advance Autoparts told me Bosch doesn't make coper core plugs any more (at least for this application). They did not cost that much, something like $1.89 vs. $1.69 for NGK copper core. What made me choose Bosch is that the ignition system is Bosch, so I went with Bosch. I have heard about problems with Bosch plugs on the FWD forum (I have an S70 as well), but I think that's a slightly different issue, since the S70s use a plug that is very different in construction (3 ground leads) than a conventional plug. Also, the proper Volvo plugs for S70 cost very little (less than the fancy Platinums for that application) and run better by most accounts. I am not sure if Volvo still sells plugs for the 940 (probably does), but I figured that since the 940's plugs are of the plain vanila type, the off-the-shelf Bosch plugs will do fine.

Anyway, I had the car re-tested after changing the plugs and it passed! That'a a big relief. If I ever start having sprk plug problems I will switch to NGK coppers. I usually do not like to run "fancy" stuff on the cars as well designed as the 940. Usually, the plugs that arecommended are best. One thing is strange, though. The plugs I removed were Volvo plugs (not sure who makes them, but they had blue "VOLVO" on them). These Volvo plugs had way too big a gap, though. Not worn out, but big - possibly wrong plugs. The Bosch plugs I bought at Advance Autoparts were gapped at the lower limit of the range specified in the manual. Not sure if this was the test breaker, but the car now passes smog in Maryland, and there were never drivability issues, so I am happy.

Thanks again,
Vladimir
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Vladimir. '98 S70 base, 5-speed manual - his, '93 945 - hers,

OBD codes are in the FAQ, see here:

http://www.brickboard.com/FAQ/700-900/EngineOBDCodes.htm

Hello Vladimir, the EGR solenoid is round and located on the front of the driver side strut tower. It has 2 vacuum hoses and 2 electrical wires. The electric circuit is dead until the engine coolant temperature rises above 131 F. There should be a steady supply of vacuum on 1 side . By joining the 2 vacuum hoses together at warm idle the engine should stumble or stall. There should be power at 1 electrical terminal with a warm engine. The device is triggered when the throttle switch goes above the idle position.

Ok, I looked and looked and could not find anything resembling what you describe on the driver's side strut tower. I saw a cruise control vacuum thingie, the ignition coil and the OBD boxes. That's all I could find. Might my car not have the EGR valve or it is controlled differently?


Thanks!
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Vladimir. '98 S70 base, 5-speed manual - his, '93 945 - hers,

Thanks for that info. I will look into it. Where is the EGR valve itself? On the exhaust manifold somewhere? Does it require maintanace? Does this solenoid switch go bad? I will look at it tonight. My car did not come from California, so I am not sure if it even has this thing. I'll post an update tomorrow.

Thanks again!
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Vladimir. '98 S70 base, 5-speed manual - his, '93 945 - hers,