Hello Everyone,

I purchased a '93 940 Turbo Wagon back in 1999. I carried both of my newborn children home from the hospital in it. I taught those same children how to drive it, and now we all drive it everyday. I change the oil religiously. And other than brakes and exhaust and one fuel pump relay, the car has never let us down. We had the timing belt changed about 30,000 miles ago. I also changed the plugs and wires about 3 years ago.

Lately the engine is missing. It vibrates at idle, It misses under heavy acceleration. It still starts on a dime and will get us home - but the journey is nerve racking. Mileage is just under 200,000.

I understand enough about the engine to know that this problem could originate from a number of sources. My family and I would like to drive this car for years to come and even pass it on to a third generation some day. So, I'm thinking I might take this opportunity to update several systems on the car.

I write to ask if anyone thinks I might be missing something from this list. Here is what I plan to do. Hopefully one of these will address the engine miss.

New distributor cap and rotor (still factory)
New fuel injectors and fuel filter (never done)
Valve adjustment (never done)
Replace air intake hoses? Or maybe just inspect?
Maybe a new timing belt and water pump while I'm at it.

The turbo doesn't push us the way it used to. Maybe not a problem because I am not in a rush much anymore. But if the Turbo can be serviced, then I'm all ears

I grew up working on air cooled VWs from the '60s and '70s (and still have a few as hobbies). Thus I am mechanically capable, but honestly my knowledge of the various sensors on the "modern" Volvo is nada. Do these need to be serviced or replaced? Or do they last forever? Can anyone list the sensors on the '93 to help me to get my mind oriented in the right direction? Could these sensors be responsible for the engine missing? Sensors are a big black box to me.

Thanks so much for chiming in if you can.

 

I am not one for replacing things just because... if it ain't broke, you know. Especially today, the parts you get are usually not as good as the original OEM so you may be worsening rather than improving.
I'd fix the misfire, do scheduled maintenance, leave things that don't need replacing alone.

From your list. Inspect the air hoses, a leak there would cause problems, especially the big intercooler hoses, this may be the turbo problem. Change the fuel filter. Do the cap, rotor, plugs--OEM, copper NGK plugs. No point doing any of the rest as it can't be causing the misfire.
I assume no check engine light? Run the OBD codes anyway.
If this doesn't fix the miss, do a compression test, you may be a candidate for a head gasket or have a burned valve in worst case.

 

Good advice - especially about holding on the factory components. I have learned a few new things. First, the codes come back 1-1-1. Nothing to report. Second, the compression test came back 102, 138, 142, 143 ( in order). #4 is a problem. I used an old VW trick and poured a teaspoon of engine oil into the plug hole and repeated the test on #4 to get 145. So #4 needs attention - either the exhaust valve or probably the rings. But probably not the cause of the engine miss. But a big sigh over the inevitable future of this engine - getting old like me. I re-gapped the plugs - only tiny adjustments were needed. No change. I also inspected the hoses under idle - all look good there but one can never be 100% sure. I did notice an unexpected rhythmic spark bolt between the coil wire and the AC accumulator. I moved the coil wire over a little to end that. Still no change though. New plug and coil wires have been ordered. I also ordered a cap and rotor. I'll hold off on the fuel filter for now. This problem seems ignition related. Though I will add injector solvent at my next full tank.

 

If oil helped the #1 compression, it's a ring which is unusual in these engines unless super high miles, and under 200k yours is not that high. That spark leak may be your problem...

 

Probably useless thought - fuel sending unit?

 

You mean, pump/sender in the tank? Why mess with it if working, not a maintenance item.

 

With great disappointment, I write to share the news that a new rotor, cap and wires did not solve the poor engine performance. The problem persists - lot's of vibration under idle, missing during initial acceleration, less noticeable at high speeds (almost normal performance at 65mph). . I'm thinking my next step is to inspect the timing belt for cracks and wear. Any other diagnostic steps to take? I didn't mind replacing the ignition components as the originals were very old, but I would also prefer not to keep throwing parts at the problem either. I'm also thinking the low compression in #4 could be a contributing factor. I am a sponge for advice if anyone has any to share!

 

Did you use quality parts? Bougicord wires, NGK copper plugs, Bosch cap? Not that those would be the cause but these cars don't like some aftermarket parts...

The compression, yeah, that might be it, and that would be bad! You'd have to get another motor which is not as expensive as you'd think and depending on where you are motors are available but a major event under the best of scenarios. Because if oil upped the compression it'd mean that it's not a valve. Weird though to have a ring problem with less than 200K...

 

Have you considered that a fuel injector might be clogged or have a poor connection? It's not much work to pull the rail and test the injectors. (my .02)

 

Thanks so much for the advice guys. So here is my plan
1] Check the compression again. #4 is the most difficult to measure owing to its angle against the firewall. Adding oil during my last test may have lubricated the threads allowing the compression tester to screw in further. Maybe the higher reading is a function of the better test fitting. A long shot, I know. But spark plug #4 wasn't covered with oil, which would be true with a bad ring. #4 is on the left in the pic below.
2] Clean the injectors - can't hurt at this point. They've never been cleaned in the 21 years I've owned the car.
3] Inspect the timing belt - turn the engine as I check each length for cracks or stretches. Check the timing marks. The engine *feels* mis-timed to me based on my experience with air cooled VWs. This could be a red herring of course.
4] If nothing changes, then, haha, I'll be back here for more advice.


.

 

Good news and bad. First, I measured again the compression in #4 and it was as high as the others. The oily measurement last time was likely a function of getting the gauge better seated with the oil (and not sealing the rings with oil). I seated the gauge this time without oil and got about 145.

The bad news is that after cleaning the injectors and spraying the MAF sensor, the problem still persists. I also carefully inspected the intake and exhaust for air leaks - nothing arose.

Here is another clue, when pulling the #4 plug again, I noticed carbon build up on about half of the tip of the plug - this is new. I'm not getting black smoke out of the exhaust yet, but I'm guessing that might be next.

Any clues on why I'm running rich? There is a popular Youtube video that says that if you unplug your MAF sensor at idle, then the car should stop running, and that if it doesn't stop running, then the MAF sensor is bad. So I tried that easy trick - unplugging the MAF sensor did not kill the engine. Hmm.

 

Actually, very good news! A bad ring eliminated as a cause is great news, and quite in line with these engines' lives.
That MAFS test is useless, as is cleaning it, neither works! Your problems may well be caused by a bad MAFS. Lately many of our posts are about seemingly hard to diagnose problems ending up due to bad MAFS--it's a complicated, hard to figure gadget impossible to test, causing various issues. Best way to know is to swap with a good known MAFS, and you will know immediately, all problems disappear! That of course is hard to do if you don't have a good spare one, but here you are. I went through that a year ago with a 240. I was told all things by all the gurus, several trusted shops, some swearing it was the computer (always convenient culprit when clueless) until I finally swapped all possible parts until I got to the MAFS and immediately it was all good! Unfortunately, acquiring a good MAFS is not easy, many "new" ones are bad, rebuilt ones also. Best is to have one to swap knowing it's good before you spend.

 

Good advice - lev - I hope I can follow it. Looking now for a period Volvo owner in rural central PA. Anyone out there nearby? The legit MAFS is $250 - yikes.

 

When spraying the MAFS (with the appropriate stuff), I noticed little trigger wires passing across the tunnel.. Are there supposed to be three wires making a triangle? Or only 2? Mine had only 2 trigger wires.

EDIT: THERE ARE SUPPOSED TO BE 2 IN A V SHAPE

 

Hard to say, that's just a probe. Looks, shapes, number of wires doesn't matter.

 

I removed the top timing cover today. The belt itself looked good - no cracks or missing teeth or anything. But I also notices a *lot* of belt slack to the right of the cam pulley - it *easily* moves at least an inch or more with just my pinky. The left side of the cam pulley looked taut. I'm guessing this is not normal, but I would like to hear a "second" before I dive in and inspect the tensioner. Thanks for any feedback on the timing belts on these cars ('93 940).

 

You can adjust that with the tensioner. Just loosen the tensioner bolt, then retighten it, it is spring loaded and takes up the slack as it is loosened.

 

Thanks, Lev. I did just that. Loosened the tensioner and the belt tightened up nicely. Then I tightened the tensioner nut. Wondering if the loose belt might have skipped a tooth, I checked the timing. I lined up the blue marks on/behind the cam pulley and then examined the timing mark on the crank pulley. Pictured below is what I found. To these amateur eyes, things look poorly timed (and maybe the source of my engine woes). But I would appreciate feedback from someone who has been around this block before. Thanks.

 

It's not off by much... I don't think that's a skipped tooth.
How many miles on that belt?
Still the same driveability issues?

 

Yes - the car still stumbles at idle, misses during acceleration, and runs fair but not good at top speeds. Starts right up though. I'll go ahead and move the timing belt over one tooth tooth just to see. I found a "known good" used original MAFS sensor on ebay for $70 currently being shipped. If it's not the timing or the MAFS sensor, then it's back to the drawing board for the next idea.