Hi people!

This is actually a continuation of this thread: https://www.brickboard.com/RWD/index.htm?id=1641092&show_all=2

I'm making a new thread so as to present the case concisely. My engine is running very poorly, and I can't make heads or tails of it. Here's the history:

*** Current Symptoms:
Starts up OK, then after about 30 seconds, RPM starts to seek, oscillating from stumbling low to high, and then settling on a rough stumbling low speed around 500RPM, and shaking like it's on just three cylinders.

When driving on the freeway, I can feel it surging slightly, even with no change to my pedal input. Surges last between 3 and 10 seconds, and come seemingly randomly. Engine seems to purr normally.

When driving on back roads, it sometimes fails to give any power when I ask for it. Coming up a hill it was around 2000RPM, and I wanted to accelerate, so I floored it. Aside from sounding like the throttle was open, there was no change. It didn't develop any extra power.

When driving in a parking lot, it alternates between purring normally and sounding like it's on three cylinders - like all the "old" cars in the movies sound. Very embarrassing when a nice young lady driving a 940 comments on my car! Haven't seen her since :( Accelerating seems to send it into "three cylinder mode".

Engine has 250k miles on it. It has been well maintained throughout it's life, according to the records.

*** Work done as part of fixing this:
Oil flush, oil and filter change (Napa Gold filter)
Fuel Filter change
MAF swap with known good
Complete intake clean, reset, lubricate as necessary, including PCV, EGR, IAC, TPS
O2 sensor replace (it had the 02 code, changing the sensor got rid of the code and the CEL, and for a few miles, it seemed to perform well, so I thought the issues were gone).
Checked for vacuum leaks with a Mityvac - nothing
Checked FPR, no leaks, even with pump on and pulling on it with mityvac.
Visually inspected for vacuum leaks - nothing.

*** Possible Clues:
When I changed the O2 Sensor, the old one was clogged with white ash.
When seeking RPMs, the tachometer sometimes moves erratically, The erratic movement does not seem to be connected with poor performance.
I pulled all the spark plugs today to inspect. The plugs seem quite new; no corrosion or heavy buildup. What I saw:
#1: black carbon "dry" fouling.
#2-4: black carbon "wet" fouling, oil in plug threads, central electrode had white deposits on it.
I pulled the fuel rail off to look at the injectors. The flat tip of the injector was clean, but there was carbon build up around the sides of it.
When I cleaned the intake components, I found standing oil in the intake bellows, TPS was full of oil, PCV was clear and clean, EGR pipe where it entered the manifold was crudded up, but not clogged, IAC was dirty, but not clogged.
Since the oil change I've driven almost 100 miles with these symptoms, and the oil is still a beautiful clear gold color on the dip stick.
Probably unrelated: the rear muffler (I think the correct term is resonator) is somewhere on the roads; I don't know when it disappeared, but it was during those 100 miles. It sounds faster now!
Usually idling in neutral or park it will purr happily. Putting it in Drive or Reverse will knock it down to the three cylinder sound. THis is not a rule though; sometimes it sounds funny in park, sometimes it drives just fine (though this seems to be increasingly rare).
If I rev it up a bit (say to 3k or 4k), then let it drop, I'll hear some mild pops in the exhaust.


Your expert opinions welcome! At this point, I'm leaning towards the following:
Injectors blocked?
Fuel pump going bad slowly?
ECU going bad?
I'm not quite sure how to test those items.

Update:
Today I checked comprehensively for vacuum leaks with the Mityvac, with propane, and with carburettor cleaner. Nothing.

I also checked the flow through each injector; each has an identical cone pattern and flow rate.

My suspicion now shifts to the ignition system. I cannot find anything wrong with air system, nor with the fuel system (unless the fuel pump is having intermittent issues which does not seem to be the case), so it must be ignition?

I took off the valve cover to check the valve clearance, but the gasket broke, so I have to wait for a new gasket before I turn it on again. Clearance seems fine. Timing belt was replaced just under 20k miles ago.

Any help greatly appreciated! I can't afford to take this to the mechanic, nor to play "swap it and see".

Thanks!

Report from today's tinkering

I replaced the ignition coil with a known good one from my 240; no improvement, so I switched back. I also used contact spray and a wire brush on all the connections, just in case.

I cleaned up the engine ground connections.

I checked valve clearance; all good (0.4mm cold).

I checked the records: distributor, plug wires, and spark plugs were replaced only 20k miles ago. It may still be the distributor or the rotor, I will investigate this, but the symptoms are curious.

I did the "Flood engine with seafoam" treatment... it was fun, but I don't think it had any real effect. The only good thing about the seafoam treatment is that I found out that there must be some holes in the exhaust header: I had smoke coming out from somewhere along the header, I think down near the convergence, before the O2 sensor. Could a pre-O2 sensor exhaust leak cause my symptoms?

I took the car for a 15 mile jaunt, some freeway, some city, some hills. Here are the results: (Note: when I say "running rough" I mean, it makes that zhitty sound that every old jalopy in the movies makes. I can't tell if it's rich or lean; I've heard conflicting advice on either side).

Park or Neutral: Engine purrs ok, occasionally has short spats of running rough.
Drive or Reverse, standstill: Engine purrs ok, but has more often and longer spats of running rough (due to load?)
Accelerating from stop: Engine runs rough, not much power, until above 1800RPM, then it starts to purr normally.
Flooring it to get up to speed on the freeway: I tried a few times, with varying results. Some times, it works fine (all the way up to 75mph). Some times it accelerates well but has obvious misses on the way up.
Cruising on the freeway around 65mph: Engine runs OK but has misses; feels like the engine is dropping every few seconds.


At this point, I'm suspecting the dizzy rotor. The salient evidence seems to be the wet carbon fouling on plugs 2, 3, 4.

Very frustrating! Any additional points of note are welcome. Thanks!

Well, I've had some time to work on this despite the bad weather, and here's the results.

High on my suspect list was a slipped timing belt. The belt had been changed just before I got it, and I'm guessing that it was overdue for it's tensioner adjustment. The car did have an incident where it was flipped into reverse going down hill, so I thought maybe that caused the timing belt to jump.

Dug down, inspected seals (all new and good!) belt is also new, re-seated it to be sure of timing, and replaced the harmonic balancer (the rubber gasket had a pretty severe bulge and many deep cracks). I also replaced all of the drive belts with new NAPA ones - they were all due for it anyhow.

After doing that, I now had symptoms that I could reliably demonstrate and duplicate: on moderate to heavy acceleration, I have the engine running shitty, like a typical "old-timer" engine.

One dark night while jump-starting another car from Wilma (the Volvo in question), I noticed blue arcing everywhere. Steady arcing across all three terminals on the coil, random arcing from the main spark line between coil and dizzy, and arcing at the boot of the #4 plug on the dizzy.

This got me thinking:
*Spark is strong, so IPS is probably not the issue. Likewise with the coil.
*Could be cracks in the coil housing, or bad plug wires, or bad plugs.

I coated the coil housing liberally with vaseline to seal off any cracks. Now it's still running shitty until the engine warms up, then it seems to run fine at any loads.

Inspecting the spark wires showed no degradation of the insulation except at one spot where it rubbed against the engine hoist hook, but that's not where the spark was.

So that tells me it must be the plugs. I pulled all the plugs and they were all wet carbon fouled: either it's running rich, or it's not burning fully. I'm wagering the latter.

Now I've replaced the Bosch Platinum plugs with NGK platinum ones (the best I could get at the local store), and all seems to be fixed.

I have a new set of wires, dizzy rotor and dizzy cap on the way from RockAuto, and will likely put the wires on when they arrive, but until then, this seems to be fixed!

I kind of feel like a fool going from A through Z to B, but at least I know that the engine is in good shape. It needed the overhaul anyhow.

I'll post back here after a week or so of driving to verify that this, indeed, is the issue.

Glad to know the problem went away after changing the spark plugs. IME its better to use copper core though. Yes I've used NGK platinum tip before but nothing beats the normal copper core. With NGK platinum tip the spark is concentrated to a fine stream but with copper core you get a big fat spark. Seems to me that a big fat spark is well suited to our engines. I guess our Bosch EV1 fuel injectors don't atomize the fuel as fine as modern injectors thus a big fat spark is needed. Anyhow it could be different in your experience.

Regards,
Amarin.

Dear Swiftarrow9,

Hope you're well. I recall a post (or posts), wherein it was reported that Bosch platinum plugs created problems: the platinum electrode was so narrow, that the slightest amount of dirt caused malfunctions.

I use Volvo brand resistor-type plugs (#270746). They work reliably.

Hope this helps.

Yours faithfully,

Spook

Spook and Amarin,

Thanks for your replies, and tips on fixing the exhaust. The pipes are all a little rusty, but I don't think it's too bad... that said, the previous owner had a new muffler put on shortly before I got it, and I recently noticed that the muffler is missing, LOL!

I've been driving it around a bit, flooring it up hills, etc, trying to find a repeatable pattern of problem. I had an interesting issue today: started it up and instantly noticed something was very wrong: definitely running on three cylinders and smelling very rich. After about a mile, it didn't go away, so I pulled the plug wires one by one, and cylinder 4 was the culprit. I pulled the injector cable (no point wasting the gas) and kept on going. Got to the dump about 6 miles away, pulled #4 plug, and saw that it had a large gop of grease/gunk bridging the spark gap. I cleaned it off and put it back, and we're back to where I was before.

Well, now that I know what three cylinders really sounds and feels like, I can say that what I was earlier describing as three cylinders was only about half way there. It's more like a stumble. This makes me suspect that it is actually a lean condition, but it still could be the distributor. I'm going to call it "running rough".


Immediately after cleaning and putting #4 back, I noticed that moderate (normal driving) loads on the engine caused the rough running. This happened when accelerating, when starting from stop, when sitting in drive or reverse, when going up a hill, etc. It did NOT happen when accelerating very gradually, when accelerating down hill, or when sitting in neutral, which leads me to believe that it is only when the engine is loaded.

Over the course of driving about, the behaviour gradually improved.

By about 20 miles later, on my way back home, I found that the stumbling only happened in heavy loading: jumping out of a stop, flooring it up a steep hill, etc.

So, condition improved, still not resolved. Next step is to check the distributor. Why oh why did they move it to the back of the head!

Spook: yes, I have checked the Ignition Power Stage, or Ignition Coil. I swapped it with a known-good from my project 240, but the symptoms persisted.

When it is dark outside. Open hood start engine let it idle. Keep loose clothing and hair from moving components. Look very closely at ignition wires. Look for a blue arcing spark to metal ground. My car was idling rough and the coil wire was touching the power steering hose metal clamp (close enough to arc) I relocated wire and rough idle disappeared. GENUIS !!!!

For the distributor cap I would use a small 8mm spanner to loosen the 3 screws (unless you could find a very short stub screwdriver for the purpose). After the screws are loose I would just spin them off by fingers till the cap is free. This way is faster than using a spanner.

You then have to maneuver the cap backwards and upwards to free it off the back of the engine. Remember to first disconnect that ONE ignition wire (this from the coil) at bottom of the cap. Examine the insides of the cap for any oil or carbon tracks. If its just oil you could use carb spray to clean them off and reuse the cap. Worthwhile also to check the rotor contacts. Pull the rotor out just like Spook mentioned. Some wear (appear as rough surface) on those 4 internal cap contacts is normal but you don't want to see any "deep groove" kind of wear on any contacts. If thats the case you'd need to replace the cap.

There's an extra step in your case in that you must test the internal conductors of the cap. This to explain why #4 cylinder have poor ignition. Use a voltmeter to test the resistance between each internal contact to each ignition wire plug points outside the cap. Although it is very rare to have such internal breakdown (I always use Bosch OE cap) check it nevertheless. Resistance should be zero i.e. it is conducting well. Check the resistance of the rotor too between centre contact and the tip. Bosch rotor for 940 (that I know of) doesn't use any internal resistor but aftermarket rotor may have. If rotor indeed has internal resistor it is marked on the rotor itself. Usual resistance should not be above 1000 ohm or 1k ohm.

Regards,
Amarin.

Dear swiftarrow9,

Hope you're well. The Ignition Power Stage and the Ignition coil are two separate items.

The Ignition Coil is cylindrical, mounted on the passenger's side strut tower. The Ignition Power Stage (IPS) is a "flat" item mounted on the inner fender well on the driver's side, just to the rear of the headlight.

This said, based on your most-recent comments, the problem seems more likely to be with the distributor. The cap is most easily removed with an 8mm ratcheting box wrench.

The distributor's rotor is finger-pressed onto the end of the distributor's shaft. Grasp the rotor firmly and pull rearwards (towards the firewall). The rotor will come loose.

Since the problem seems to be with one cylinder, I'd guess the distributor cap has failed, so be ready to replace it.

Hope this helps.

Yours faithfully,

Spook

Good thing that the Seafoam treatment has revealed the exhaust leak. I use the "smoke effect" of Marvel Mystery Oil or Seafoam once in a while just to check for any leaks. However I don't think that may have caused your symptoms. Patching that leak might help the engine to run smoother but that doesn't explain your intermittent rough running. Another likely culprit is oil leaks into the distributor contaminating the internal contacts and rotor (this caused by worn distributor oil seal). Just check yours and see.

Regards,
Amarin.

Dear swiftarrow9,

Hope you're well. Perhaps I overlooked it, but I see no reference to the ignition power stage (IPS). A failing IPS could produce the symptoms you report.

This said, if the distributor cap was changed - but not the rotor - the benefits of a new cap will be lost. A distributor rotor should not cost much more than $10.

The header pipe (downpipe) can crack at "the convergence". If the header pipe is otherwise sound, an exhaust shop can weld-up the crack. Even if the metal at the break is thin, beads of weld metal can be applied to adjacent sound metal. Then, more weld metal beads can be applied to the sides of the initial beads. In effect, the cracked area can be "bridged" with weld metal. This makes a durable repair and the cost will be far less than replacing the entire pipe.

Hope this helps.

Yours faithfully,

Spook

So your intake gasket is ok. Still troubleshooting on "3 cylinders running".

Check your ignition leads/cables. When your engine exhibits that symptom pull each ignition lead (to the spark plugs) in turn. The one you pull out without making idle worse could be the culprit. You could also check each lead's resistance with voltmeter. Typical resistance should read between 3.5k ohm for shortest lead to 10k ohm for the longest lead. Wriggle the leads while checking to look for intermittent discontinuity.

Are you using standard ignition leads (Bougicord) with Volvo plugs? Bougicord is the only recommended ignition leads for our engine. Regarding plugs, Bosch Platinum are known to cause trouble in our B230 engines as the small platinum electrode is embedded flush within the porcelain tip. Slight carbon deposit/fouling on the tip may produce weak spark. In case you're using them revert back to normal standard copper core plugs.

Regards,
Amarin.

Dear swiftarrow9,

Hope you're well. To save time and money, clean electrical connectors: (a) coil; (b) ignition power stage; (c) grounds.

An invisibly thin layer of corrosion - sometimes only a few molecules thick - can disrupt a circuit. Corrosion can contribute to intermittent power flow: as a connector warms - and the metal expands - power can sometimes be lost.

An aerosol corrosion-remover, e.g., DeOxit, can reach corrosion otherwise inaccessible. Separate connectors and spray each side, according to the instructions.

If removing corrosion doesn't help, then it may be time to replace the ignition power stage and/or coil.

Hope this helps.

Yours faithfully,

Spook

Yes I've read your previous threads.

*** Current Symptoms:
Starts up OK, then after about 30 seconds, RPM starts to seek, oscillating from stumbling low to high, and then settling on a rough stumbling low speed around 500RPM, and shaking like it's on just three cylinders.

Does idle/engine running improve a bit after the engine has warmed up? If so I suspect the intake manifold gasket. The intake gasket is known to disintegrate in long milage engines. A hairline crack in the gasket lets more air in while engine is still cold and seals itself when engine parts expand with heat. A small test to do is to spray carb cleaner around the intake gasket (including hard to reach areas) while engine is RUNNING. If idle becomes worse then the gasket needs replacing. The commonly affected gasket area is at intake 1/runner 1 at frontmost of engine. Thus this might produce your "three cylinders" symptom.

I think one of the reasons for this deterioration is the way the fuel injectors fire diagonally down towards the gasket. Long mileage dirty injectors could scatter their spray thus wet the gasket more. Vibration and heat cause more deterioration and there you have it. If indeed it is your intake gasket then manually clean your injectors too. There are many videos on youtube.


A few more checks you could do. Your symptoms could be due to more than one maintenance aspect need checking:

1. Check your timing. Dismantle the upper timing belt cover, first may need to dismantle the water pump pulley and belt, set timing to top dead centre and make sure all the timing marks are spot on. For 1994 to 1995 940 the timing belt is of the round cog type (earlier years was square cog). Round cogs are less susceptible to cog jump but check it nevertheless.

2. Check your valve clearances. Intake/exhaust 0.40mm both on stone cold engine. The clearances would increase 0.05mm more when engine is hot. Yes the recommended clearance is 0.45mm when hot. Easier to do on cold engine I think.

3. Use a contact cleaner, spray and clean your Neutral Safety Switch at the gear lever. For automatic cars the NSS also play other roles than just preventing the starter turning at other gear positions than P and N. It also turns on the reverse light when in R and increases the baseline idle speed when in D, 2 and 1. NSS is the one that tells the ECU that the transmission is engaged or not. NSS failure might cause very low idle while in gear.

Regards,
Amarin.

Amarin,

Thank you for your reply.

I will do the carb cleaner test for leaks; oh if only it's as simple as the intake gasket!

I have done timing belt jobs before. The previous owner had just changed it, and I've driven it up to Canada and back before this issue started, so I doubt that it's the timing. Still, I'll put that on the list to check.

I'll also check the valve clearances. While I have the valve cover off, I guess that it's a good time to also check whether there is much gases coming up the valve stem - would indicate a valve seat regrind. However, I don't think that will be, as I have done the "loose oil filler cap" test, and it sucks right down quite well.

Will keep everyone appraised.

Dear swiftarrow9,

Hope you're well. This problem likely is electrical, i.e., a randomly- intermittent connection. Corrosion on connectors can cause this as can failure of ignition components.

Have engine bay grounds been cleaned? If not, do so.

Further has the ignition power stage (IPS) been replaced? If it is factory-original, it is past the end of its service life. On cars with Bosch ignition/fuel management, the IPS is mounted on the driver's side inner fender wall, to the rear of the headlight, behind the wiring harness. The IPS has a flat gray cap and bears Bosch #0 227 100 124.

At 250K miles, it's possible that the coil - a cylindrical device mounted on the passenger's side strut tower - is failing, or that the coil contacts are corroded. I'd clean them, and see if that ends "three-cylinder" shakes.

Hope this helps.

Yours faithfully,

Spook

Spook,

Thanks for the tip! I will check on that coil; I'm sure it has been replaced before now, but will check.

The grounds are an easy thing to clean; I'll do those as well.