I'm not sure what to make of this. Whenever I go up hill in my 98 s70 t5 I get a misfire. I can run the car on flat ground or even a mild hill with my rpms up in 4k+ range and I won't get a misfire, but when I cruise at 70mph and go up a semi steep hill I will get a code probably about 50%-60% of the time. Anyone ever run into this? It seems fairly odd.

 

Have you replaced your plugs lately? How about your wires?

 

Plugs have about 15k on them, wires have about 5k. I have the IPD plug wires if that makes a difference.

 

How about the rotor and cap?

 

Put the front of the car on jack stands, and see if she misfires at 4K in neutral. If so, you have an electrical issue.

If the engine runs smoothly, it's likely a fuel/air issue. My $.02 would be on a badly clogged or failing injector. You can most times tell it's only at the beginning stages of failure because the spray pattern only gets bad under really heavy load, (like going uphill at 70 MPH in top gear).

 

When an engine is running under heavy load, more energy is required to fire the spark plugs than is required at idle. Simply running an unloaded engine at 4k RPM won't reproduce the problem if it's an issue that occurs under load, because the conditions are different- under load, it takes a lot more fuel and air to make the engine run at 4k RPM. And it's this additional compressed fuel and air that increases the voltage necessary to create a spark. So while a fuel issue can cause the symptoms you're having, there would likely be other symptoms present. Especially if the code you're getting is P0300 (which may be accompanied by codes for single cylinder misfire that were set before the computer "figured out" that it was actually a random miss) , which is multiple/ random misfire. Injectors don't fail all at once, and they rarely fail at all, though they can get clogged.

With all of this in mind, the most likely culprit IS the ignition system. You have a '98 S70, which uses a distributor, plug wires, and a single coil (this is for the benefit of folks in here who have 99 and newer cars, which use a totally different, coil- on- plug ignition system) There are 2 things that will cause a misfire under load. High resistance in the system, and low voltage from the coil. High resistance in the system comes from bad plugs, bad wires, and worn cap/ rotor. Even though you changed the wires, pull them off and test them- you could still have one or more bad ones. Using a multimeter on the ohms setting (usually the 20k setting is sufficient) take a spark plug wire off the car and connect the multimeter to the ends. There should be no more than 5,000 ohms of resistance per foot of wire. i.e, if the wire is 2 feet long, no more than 10,000 ohms. If it's 1.5 feet long, no more than 7,500 ohms. If resistance is infinite (no reading) make sure you're touching the terminals themselves with the meter leads, and if so, the wire has a break in it and is bad. If resistance is higher than 5,000 per foot, the wire is "breaking down" internally and needs to be replaced. Check all 5 plug wires and the coil wire that goes from the cap to the coil.

If the wires pass the test, check the coil. It could also be breaking down and unable to produce high enough voltage. To test this, again, use the multimeter. Disconnect the coil- to- cap wire and the 2 wires that go from the ignition module to the coil (they're red and blue, called terminal 1 (where the blue wire goes) and terminal 15 (where the red wire goes) Set the multimeter to the 200 ohms setting, and check the resistance across terminal 1 and terminal 15 (the bolt studs where the wires went.) It should be between 0.5 and 1.5 ohms. Here is where you need to consider any internal resistance in your multimeter leads. Cheap multimeters usually have a few tenths of an ohm of internal resistance that the meter doesn't zero out. Connect the leads to each other and hold them there for a couple seconds. usually, cheap meters will show .2 to .5 ohms. read what the meter says. Subtract that number from any value you get when testing things in the 200 ohms setting.

Now test the coil. Is the reading, after correction, between 0.5 and 1.5 ohms? Then your primary winding in the coil is good. Now to check the secondary winding. Set the meter to the 20,000 ohm range. connect the leads to terminal 15 on the coil (the stud where the red wire normally goes) and the high tension terminal (where the wire that goes to the cap plugs in) Resistance should be between 8,000 and 9,000 ohms. If it passes, move on to the cap and rotor. This is a subjective test- you're using your judgement on this one. Take off the cap, and look at the rotor. Does it look badly burned? (some carbon deposits and burning is normal. Look to see if a significant amount of material is burned off of the metal rotor tip after you clean it with a small, fine file- parts stores sell ignition files for this purpose. Then, check the cap. There will be a bunch of buildup on the terminals around the diameter of the inside of the cap. Again, this normal. Clean it off with the file- is there a lot of missing material? Look at the cap for cracks and for "carbon tracking" on the sides between terminals. Also, check the spring- loaded carbon rod in the center- does it protrude enough to make contact with the button on the rotor? does it look broken, or is it smooth like it should be? Can you push it into its hole, and it springs back? If there's any doubt, replace it, and use a high quality replacement- Bosch is a good one to get- these cars can be finicky about ignition parts, and poor quality parts sometimes aren't made right. The distributor cap is actually a precision part.

Finally, the spark plugs. Make sure the gap is within specification, and that they are clean and there's no damage to the ceramic insulator. What brand are they? are they the correct plugs for the car? Again, these vehicles are kind of finicky about plugs. Genuine Volvo plugs, or Denso plugs are good, so are NGK V- power. Autolite plugs, especially the double platinum plugs, are bad news in these engines- I have seen misfiring at load with them on a number of vehicles. So are standard Bosch platinum plugs. Champion plugs, though many people have some personal bias against them, are actually okay in these engines. I'm one of those who mentally has a bias against them, so I don't use them myself, but I've seen them work well.

If everything checks out on the ignition side of things, move on to the fuel system. Change the fuel filter, test fuel pressure, clean the MAF with MAF cleaner, and as a last resort, you can take the injectors out and have them flow checked, cleaned, and rechecked- there's places online that you can send them to- but this is usually not a cause, like I said earlier. I'll bet you're going to find something wrong on the ignition side.

 

Thanks for the details Carrots. Appreciate your input.

 

Jesus, Carrots... I'm in a '99. Didn't even dawn on me...

To be fair though, I only thought 1 injector was altering pattern under load.

 

Sorry if it sounded like I was saying you were wrong... you offered a good suggestion. In fact, if his problem isn't in ignition, your route is the next step. But yes... the '98s have conventional ignition systems with a distributor and plug wires. The 99 and up models sometimes have coils fail, though, and that can also cause similar symptoms early on, though usually when a coil goes on the coil- on- plug systems, it usually fails completely and you lose that one cylinder.

Anyways... you didn't give bad advice. I'm sorry if I made it seem that way.

 

++1 to everything Carrots said in post #6!!

I also agree that i would look for an ignition system fault given these symptoms. I remember i fixed my brother's truck (years ago); it ran fine everywhere except when pulling a hill. I pulled off the dist cap, and sure enough, you could see the slight carbon tracks. New cap and rotor fixed it.

But would add one more thing about cking the spark plug wires. Usually when these high tension wires fail it's because the insulation breaks down and they short circuit (again, most likely under a load as Carrots pointed out). So continuity ck won't expose the issue. I've found the best test is to spray/mist the wires w/water while the engine is running/idling. Nothing like some H2O vapor to expose a carbon track...

Same thing with coils; never seen a coil fail a continuity test, again they usually fail by arcing externally. From my experience FWIW.

 

Carrots, thanks a lot for the write up. I'll be checking all this stuff when I get home from work. The car does indeed throw a p0300 code which is why I was skeptical on the injectors as well. I'm almost certain the car is due for a new cap and rotor, so I hope that's the issue. I also seem to think the car started doing these misfires after the wires were installed. Can't wait to get home and get this checked out. I hope these ipd wires have a warranty if they are indeed the problem. Thanks again guys. I will keep you posted.

 

Finally got a chance to pull off the cap and rotor this weekend. The cap had a ton of carbon build up on the contacts and the rotor was worn down 1/16 to 1/8 of an inch. Installed a new Bosch Cap + rotor and 2 days of no misfires. WOOT! Thanks for the help fellas, I appreciate it.

 

Thank you for the sound advice Carrots. This kind of well thought out advice helps long after the original response. I have my game plan for my Wifes Volvo now, hopefully its as easy as cap and rotor too.