I finally got around to entering in my gas receipts into my MPG spreadsheet yesterday, only to find that about 2 months ago my MPG dropped from about 24 to 19. It's been 18-19 consistently for the last 4 fill-ups. I replaced the rotor and cap as well as changed the oil about 2 months ago, and foolishly started the engine without the oil cap on. I quickly realized my error, turned off the engine and replaced the cap (and cleaned up some oil). I also (almost) ran out of gas within a week or so of the oil change incident. It started to sputter while I was driving but I was able to get it off the street with the engine still running. Since then the only other thing I did was clean out the flame trap and crank breather box. It still runs about the same and I haven't noticed any significant decreases in performance.

Could the lack of oil pressure for about a minute have caused something to change. I haven't seen any oil spots on the ground and it's not burning any.

Any help would be appreciated!

a-

I finally had the opportunity to put the new pump seal in. The old one looked fine, no tears, dirt, or kinks. The tank opening seemed fine, and I saw no cracks or damage to the pump. I took the time to check the o-rings in the fuel line connections, and they seemed OK too. So far, no leaks, but time will tell.

The only thing I found that *might* have caused teh leakage is that the return line wasn't fully seated onto the pump. Yet why would it only leak when full, and only overnight when it cools off? Tomorrow I will check the the vapor cannister and purge valve.

The oldest B230s I have are a 91 940SE Turbo and a 92 240, therefore I am not sure what makes an 83 tick, but it cannot be too different. A drop in MPGs could be caused by the O2 sensor as stated and even more so by a bad ECT. Common sense items, check vac hoses, including the charcoal canister hoses. If you don’t have a engine temp sensor, I do remember the canister in my son’s ’78. An engine with poor MPG means your are running rich. Too much un-burnt fuel will eventually clog your cat.

Edit, sorry butch, this responce was meant for H4L.

lol, the post above yours under my name (butch), that you answered by mistake or whatever is not my original post at all. I have no idea what is going on.

With no performance drop, if it's an automatic make sure it's shifting into overdrive, not hard to miss if you're not out on the highway. Also check the tire pressure.
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Bruce S. near D.C.

I'm pretty confident that running with the oil fill cap off for a minute or two will only make a mess but not cause damage.

However a gunked up oxygen sensor won't be getting outside air which it does need. If it got oil blown on it that could be your problem. As I recall the '83 oxy sensor is fairly high up on the exhaust downpipe. Do a google search on "testing oxygen sensor" or just go here:
http://www.mr2.com/TEXT/O2_Sensor.html

Other than that, I think it's just a matter of all the usual stuff to check. Pull the air intake hose, examine for holes worn, especially the underside. Check all your vacuum hoses for leaks especially where they go onto their connectors. Change your air filter if appropriate (I think they're rated 30K miles??? but I don't like to go that long). Maybe it's time for a tuneup: plugs, cap and rotor.

Of course using the a/c will drop your fuel economy. So if you are, I think that's the answer right there. Especially on an '83 as I thin it still had the piston type compressor, not rotary. Less efficient if I have it correctly.
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Sven: '89 245 NA, 951 ECU, open-front airbox, E-fan, 205/65-15's, IPD sways, E-Codes, amber front corner reflectors, quad horns, tach, small clock. Wifemobile '89 245 NA stock. 90 244 NA spare, runs.

Thanks for the reply Sven!

I had not considered the O2 Sensor as a possibility. Oil did manage run along the side of the valve cover and drip down onto the exhaust manifold. After I replaced the oil cap, the leaked oil continued to burn off from the manifold for a few minutes. You are correct in the placement of the O2 sensor high up on the manifold. I've also been noticing that it's smells like it's running rich lately.

I read through the linked O2 sensor page and think I'll try testing it to be on the safe side. The page mentions what oil can do to the sensor but there is no mention of cleaning it off (from the outside of the sensor) to fix it. Do you know if this is a possibility? I realize that it may not since the manifold and sensor get so hot.

Until I can get that tested, I had already replaced the rotor and cap and I have new plugs that I should install. As mentioned, I also cleaned the flam trap and crank breather box. Last week I pulled apart the hose from the air box to the throttle body and didn't find any holes or significant obstructions. The AMM was clean but I did notice that it appears to be an aftermarket part. It was also missing the 'anti-tamper plug' that conceals the idle mixture screw. Someday I would like to clean out and adjust the throttle body but it appears to be a sizeable project.

Other than the obvious loss of economy, is there any other potential damage that could be a result of a failed O2 sensor? I understand that the incorrect readings from the sensor cause the engine management to compensate, which can lead to more damage to the sensor. I probably won't be able to get to testing it until this weekend but I might need to use it for a 300-400 mile trip before then. Would this amount of driving with a (possibily) failed sensor do damage to other systems?

Thanks again for the help!
a-

I just tested the O2 Sensor based on the instructions in the Bentley manual. It says to test it in two stages. One while the O2 sensor is connected and once while it is disconnected.

I used a Fluke 77 that has a nice digital display that includes a little visual meter at the bottom so you can see spikes in your measurements. My results are:

While it is connected, I checked voltage at the connector and find that under a 'fast idle' it jumps back and forth between .50 and .72 volts. When I dropped the throttle to norma idle, the voltage dropped to around .37 and than back into the .5 range for a few seconds and then starts to trail off (I assume because it is not a heated O2 Sensor).

When I disconnect the O2 Sensor and take readings directly from it, It started at around .46 volts and slowly dropped to under .3 volts. When I dropped the throttle to idle it stayed fairly solid at .18 volts decreasing at about .001 volts every 10 seconds. These measurements seem out of spec, however the Bentley doesn't provide any target measurements for this part of the test.

Based on the manual, I can't determine if this is all normal. It only says: "If there is no voltage, replace the O2 Sensor", otherwise I just need to "Adjust the Idle Mixture". However, the section it references for adjusting the Idle Mixture only applies to the CI (K-Jet). I have the EFI (LH-Jet 2.0) and there are sections on adjusting the Idle Mixture but is this something I should try?

I noticed that prior to 85, Volvo recommends to replace the O2 Sensor at 45000 Mi intervals. I'm guessing that it's time to do that, though I have not owned the car more than a year. Are there any differences in the O2 Sensors installed in the older LH-Jetronic (82-85) versus the O2 sensors in the more modern LH Systems (86-93)?

Above all, I am somewhat confused and think I'm getting conflicting information. I tend to think the O2 sensor did get some oil on it which could cause the issues I'm having with lowered economy, but the Bentley doesn't seem to account for something like this. It just says to tweak the Idle Mixture. I'm hesitant to do that since only 2 months ago it was working well and I haven't made any significant changes to the timing or idle mixture since then. But I also understand that throwing new parts at a problem won't necessarly solve it either.

Thanks for all the help so far!

a-

If the O2 sensor has failed and you are running rich it can roast the cat converter ($$). FCPGroton.com has a Bosch generic sensor pretty cheap ($20?), but you'll have to cut the wiring connector off your existing one and splice to the new one to connect it to your harness. If you don't have time for mail order, a good parts counterman should be able to find you that same Bosch unit, but probably a few more $$ than FCP.
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Bob (son's 81-244GL B21F/M46, my 83-244DL B23F/M46 and 89-745(LT1 V8): dtr's 94-944 B230FD; hobbycar 77 MGB, and four old motorcycles)

Honestly I don't know the answers to most of your questions.
We had a case of a clogged O2 sensor on my wife's '89 (located in cat, in lower part of exhaust pipe shortly before the first muffler). Shop fixed it by replacing the sensor. Was clogged by tranny fluid from leaky tranny rear bushing + seal.

The good news is that the '83 sensor should be a lot easier for a driveway mechanic to get out. Get an O2 sensor socket, it has a slot for the wire to go through. I was not able to change the sensor in the '89 working from below as there's no room to get any leverage. With a shop lift it should be a piece of cake to do the '89.

Do some searches to find more economical O2 sensors. Last one I read said you could use one from an Escort. As long as it has the same # of wire leads. I hear they all have the same thread size but you better check. I'd get a Bosch from the nearest decent big box auto parts store.
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Sven: '89 245 NA, 951 ECU, open-front airbox, E-fan, 205/65-15's, IPD sways, E-Codes, amber front corner reflectors, quad horns, tach, small clock. Wifemobile '89 245 NA stock. 90 244 NA spare, runs.