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240 Spark Plug Diagnosis

Rusty_ratchet

Rusty_ratchet

Member
Joined
Apr 14, 2015
Location
Southwest
1991 Volvo 240

My mom's car sat for about a year and I drove it in January. It was running a little rough and I checked the spark plugs, shown below.

IMG5682.jpg


The plugs looked ok to me, except for the cylinder 4 plug which was very dirty (shown below)

IMG5683.jpg


I looked up a spark plug diagnosis chart and it looked like a dirty fuel injector. This seemed reasonable since the car sat for some time. I cleaned the fuel injectors in an ultrasonic parts cleaner with 1/3 oil eater and 2/3 distilled water. I also swapped the injectors for cylinders 3 and 4 and replaced the spark plugs.

The car has been driven about 100 miles since then and the spark plug for cylinder 4 still looks dirty compared to the other plugs (see below).


All the plugs (1 on the top through 4 on the bottom)
IMG5934.jpg


Cylinder 4 Plug:
IMG5936.jpg


I'd appreciate any thoughts on what the issue might be.
 
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Rings are not sealing,looks like oil fouled. Changed the injector &, # 4 still the same, do a leak down test. With some driving the #4 cyl might come back.
 
283SD said:
Rings are not sealing,looks like oil fouled. Changed the injector &, # 4 still the same, do a leak down test. With some driving the #4 cyl might come back.
Click to expand...

Sorry, I forgot to add that I did compression and leak down tests in Jan.

Compression Test:
Cylinder 1: 160
Cylinder 2: 155
Cylinder 3: 165
Cylinder 4: 170

Leak Down Test:
Cylinder 1: 10% leakage
Cylinder 2: 10% leakage
Cylinder 3: 10% leakage
Cylinder 4: 15% leakage
 
How old are the wires? How about the distributor cap? If the spark is weaker in that cylinder it could run richer. What did you gap the plugs at? Stock is .028".
 
The photos are kind of small to do a good diagnosis on the condition of the spark plug insulator tips. In the last photo the #4 plug tip and base of the threads almost looks a little shiny suggesting oil fouling rather than mixture fouling. Rich fuel mix tends to leave a flat finish rather than a shiny finish.

The dirty injector diagnosis can swing both ways. If the pintel / disc is dirty it may obstruct fuel flow which results in a lean fuel condition (whitish plugs). If the pintel / disc has debris in the flow area it can hold the injector open resulting in the injector perpetually drooling and the a rich fuel mixture at idle and low engine load (dark colored plugs). You can't clean an injector in an ultrasonic parts cleaner. The injectors need to be cleaned using an aggressive solvent pumped through the injector at high pressure while it is operated at a relatively high pulse rate. Send all the injectors out to a cleaning service and have them flow checked.

Short of really big problems it is hard to make a good diagnosis of fuel mixture on old plugs. Start with a new set of plugs. But, before doing that have the injectors cleaned, clean the MAF and check the fuel pressure if you have access to a pressure gauge. It would not be unusual for a 29 year old fuel pressure regulator to be out of spec. Dirty MAFs and incorrect fuel pressure will influence fuel mix. No point in putting in fresh plugs to diagnose and then having to replace them to repeat the diagnosis. Fix the easy stuff first and then check with new plugs.

Your compression / leakage numbers are not grossly bad for an engine of this vintage (leakage numbers are really subjective and a function of the tester). Have you tried the valve stem seal test (travel at relatively high speed & RPM and then let up on the throttle in gear so you have a high manifold vacuum - have someone check for exhaust smoke) to see if you have a leaking valve stem seal that might be the source of some oi fouling? Blue smoke on cold start-up can also be a sign of leaking. Depending on how bad the leakage is or isn't the smoke might disappear quickly.
 
dl242gt said:
How old are the wires? How about the distributor cap? If the spark is weaker in that cylinder it could run richer. What did you gap the plugs at? Stock is .028".
Click to expand...

The wires, cap, and rotor were replaced about 4 years ago. My mom doesn't drive much so it hasn't been too many miles. The plugs are gapped at 0.028".
 
142 guy said:
The photos are kind of small to do a good diagnosis on the condition of the spark plug insulator tips. In the last photo the #4 plug tip and base of the threads almost looks a little shiny suggesting oil fouling rather than mixture fouling. Rich fuel mix tends to leave a flat finish rather than a shiny finish.

The dirty injector diagnosis can swing both ways. If the pintel / disc is dirty it may obstruct fuel flow which results in a lean fuel condition (whitish plugs). If the pintel / disc has debris in the flow area it can hold the injector open resulting in the injector perpetually drooling and the a rich fuel mixture at idle and low engine load (dark colored plugs). You can't clean an injector in an ultrasonic parts cleaner. The injectors need to be cleaned using an aggressive solvent pumped through the injector at high pressure while it is operated at a relatively high pulse rate. Send all the injectors out to a cleaning service and have them flow checked.

Short of really big problems it is hard to make a good diagnosis of fuel mixture on old plugs. Start with a new set of plugs. But, before doing that have the injectors cleaned, clean the MAF and check the fuel pressure if you have access to a pressure gauge. It would not be unusual for a 29 year old fuel pressure regulator to be out of spec. Dirty MAFs and incorrect fuel pressure will influence fuel mix. No point in putting in fresh plugs to diagnose and then having to replace them to repeat the diagnosis. Fix the easy stuff first and then check with new plugs.

Your compression / leakage numbers are not grossly bad for an engine of this vintage (leakage numbers are really subjective and a function of the tester). Have you tried the valve stem seal test (travel at relatively high speed & RPM and then let up on the throttle in gear so you have a high manifold vacuum - have someone check for exhaust smoke) to see if you have a leaking valve stem seal that might be the source of some oi fouling? Blue smoke on cold start-up can also be a sign of leaking. Depending on how bad the leakage is or isn't the smoke might disappear quickly.
Click to expand...

I have attached some larger photos below:

dbIMG5936.jpg


8a3IMG5683.jpg


I am certainly not an expert, but in my opinion the 4th plug looks like i has a shiny oilily appearance rather than a flat appearance.

I also have one of the tools below to clean injectors with carb cleaner. I also have an electronic "box" that sends pulses to the injectors. What are your thoughts on cleaning with it vs. sending them out?

6absl1600.jpg


I cleaned the MAF a couple years ago. I replace the FPR about 4 years ago. I could double check, but I don't think she has driven more than 20k miles in that time.

There is a little bit of smoke at the exhaust for a few min after starting the car. I can try to take a video if that would help. I will also try the valve stem seal test that you mentioned (travel at relatively high speed & RPM and then let up on the throttle in gear so you have a high manifold vacuum - have someone check for exhaust smoke).

Thanks!
 
That plug is looking on the oily side rather than rich. I might focus on oil consumption issues rather than mixture; however, oil consumption does not necessarily equate to rough running unless it results in an very fouled plug which causes misfires.

I am not exactly sure what that home injector cleaning thing is; but, my reaction is I wouldn't. When I said aggressive solvents I was thinking of things like toluene, xylene and MEK. Some of those will dissolve certain plastics. If you spray them into free air (like in the picture) without some capture mechanism you risk killing yourself either due to VOC inhalation or self immolation because in aerosol form these things can light up with one hell of a spectacular explosion. Cleaning is one of those things best left to the commercial outfits that are set up to deal with nasty chemicals. I flow tested my injectors using a 'pulse generator'; but, I used Stoddard's solvent tinted with ATF for the test fluid and sprayed it into an enclosed container. Stoddards solvent has a much, much lower flashpoint than those nasty solvents.

I would not bother with a video. If you say there is smoke on start-up I believe you. Short of the close the throttle at high RPM test, I cannot think of a definitive way to confirm a leaky valve stem seal. A failed valve stem seal will not show up in a leak down test if the valve is sealing beteween the valve and the seat.
 
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Engines need to be worked. On old sticky stuff, I like to add ATF or MMO to the oil (not too much! It will thin the oil). Then drive it hard for a while. Varying RPMs and loads can free things up if you have a sticky ring. I have also had success on other cars with piston soaks.
 
Cleaning plugs is a waste of time. If they are fouled, fuel or oil, only sand/media blasting will clean them. And they are cheap, so start with a new set.
 
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