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Hi friends,
My 92 740T started misfiring slightly. It only misfires once warm, and only seems to misfire while warm at idle.
3-4 weeks ago we found a spark plug wire boot that was burned and cracked. All of the spark plug wires and boots were replaced. When they were replaced, the misfire disappeared. But this week it returned.
On a seemingly separate note, every once in a while while driving the car will randomly go into overdrive (by which I mean the same effect as if I pushed the little button on the shifter, also it's an automatic). When I try to push the button to turn off the overdrive, it usually doesn't work. I frantically push the button until it turns off ~1min later. From my research, this seems to be an overdrive relay than needs to be re-soldered, correct? Where can that be found?
Any suggestions are greatly appreciated!
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The easiest test for your wires and whether or not they're shorting out is to run the car at night (in the dark) until it starts to miss, then use a spray bottle and mist the wires. If you have tiny cracks allowing shorts, you'll get a pretty lightshow. You can also pull the plugs and check their condition, and that would be a good idea just to be sure.
To check for airleaks, spray a flammable solvent (carb cleaner works best) around all the joints in the intake system - where the throttle body meets the manifold, where the manifold meets the head, where the IAC connectors are, and so on. This can be done warm or cold, but don't spray anything flammable on the exhaust side. You could start a fire that way. Most people prefer propane because it's not a mist, but that's not always an affordable option when carb cleaner is $4 a can.
You should also at some point replace ALL of your vacuum lines (1 at a time). They degrade and leak.
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Hi friends,
I would like to focus on the misfire issue. Again as a reminder, the car only misfires when warm and at idle (in drive). Because there are no misfires while driving or while cold idle or while in park, I don't believe the problem is related to the spark plugs, spark plug wires or distributor. If the problems were related to any of those parts, it should misfire always, correct?
Since we last spoke, I performed the spray test on the intake manifold to test the intake manifold gasket, fuel injectors, throttle body, and surrounding areas for vacuum leaks. The engine passed the test with flying colors, never sputtering or hesitating no matter how much carb cleaner was sprayed from whichever angle. I also removed the throttle body, cleaned it thoroughly and replaced its gasket. I opted not to change the intake manifold gasket because it didn't seem to be the problem, and I didn't want to risk breaking the studs on which it is mounted.
Next, I removed and thoroughly cleaned the idle air control valve (IAC), located just below the throttle body. Before cleaning the IAC valve it seemed much cleaner already than the throttle body, for example. But I cleaned the IAC valve anyway. I sprayed it with WD40 and while turning it on in order to ensure the WD40 completely penetrated the valve.
I am running out of ideas for places to look for the problem. I have already changed the spark plug wires recently. I have not changed the spark plugs, distributor cap and rotor. I am willing to, however, I'm not convinced that any of them is the problem because as I mentioned if one of them were the issue, there would be a CONSTANT misfire rather than the very specialized and intermittent misfire I experience. It's also worth noting that while the misfire only occurs at warm idle in drive, occasionally it doesn't misfire under those conditions. It misfires under those conditions more than not, but it doesn't always misfire while warm idle in drive. So, my next thought is that it may be a computer component like the ECU?
Any help or advice you can offer is greatly appreciated.
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Welcome to the frustrated 700 Club! (see my past posts...)
In first post, a spark plug wire/boot was found fried. That raises a flag, but I'm sorry to say I don't know what it means exactly. However, I do think that spark plug from the fried wired should should be replaced. If the wire is fried, what happened to the poor plug?? Replace all four plugs, not one, that seems like a cheap way to go next.
Also, old plugs can be "read" for engine burning lean, rich, etc...
--
I own a Volvo or Does Volvo Own Me? Try the easy to search Expanded Style FAQ Index http://40mph.com/Brickboard_700-900_FAQ_Expanded_Index_Version/
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Misfire - How old are the cap, rotor, plugs, and wires? What kind of condition are they in? Clean the connections to the coil just for good measure (and because it's easy). If one wire was dead, it's a good bet the others are not far behind.
However, an intake (air) leak is much more likely the cause of a stumble/miss at idle. the airflow reading is much more precise at idle and so smaller variations in the air flowing into the engine have more effect. Check your vacuum lines for age, hardness, and cracks, and spray starting fluid or carb cleaner NOT BRAKE CLEANER (propane is best actually) around the intake to find intake leaks. Most things you can spray will drop the idle. You can even use soapy water, but aerosols work better.
Overdrive - Arrow on = overdrive DISabled. Arrow off = overdrive enabled. the button on the shifter does not enable the overdrive, it moves a solenoid to prevent the transmission from shifting into overdrive (which serves as 4th gear on planetary transmissions).
Find a wiring diagram and verify if the relay is normally open or closed. When the overdrive is engaged (4th gear allowed), power flows from the relay to the overdrive solenoid through a wire. Pressing the switch on the shifter removes the power from the wire to the solenoid (maybe shunting it to the dash-light, again, check on a diagram).
Either way, pressing the switch disables the overdrive. If the wiring to the solenoid is damaged, the overdrive will not work ("4th gear" always locked out).
The most likely culprit IS the relay. The switches and wiring almost never fail. The bulbs rarely fail. It's also pretty easy to reflow and add solder to the relay if you're decent with a soldering iron. Used ones are no more likely to be good than bad.
The relay is located behind the fuses. It makes it much easier to see if you remove the 5-band equalizer (or little empty book-holder). There is a diagram in the FAQ of where the relay is and instructions for opening the relay and reflowing the solder.
Good Luck!
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I can think of one scenario for a warm misfire, Thinking out of the box.
If your car has a ballast resistor this could happen. Cars with ignition points almost always have them.
A ballast resistor is a large resistor that is in line with the primary feed to the ignition system,
When you turn the key to start, this resistor is by-passed and full voltage is fed to the ignition system.
After the key is released, the current then goes through the ballast resistor (which usually looks like a toaster heater wire attached to a ceramic block) As the resistor wire heats up, its resistance increases, lowering the voltage going to the ignition system to some lowered level.
Under this process, weaknesses in the ignition system could show up as misfires.
The computer may do this in place of a ballast resistor - I really don't know.
Perhaps, your power stage has a bad connection or ground.
See this site for some ignition help -
http://www.vlvworld.com/indexframe.html?VolvoRepairManual/700_2_9.htm
There is a green book (Volvo service manual) here -
http://www.ohio.edu/people/ridgely/Volvo_docs/Volvo%20TP%2031397-1%20Ignition-OCR.pdf
When I had some ignition issues with our '90 744 TI a Volvo tech (and 740 buff) suggested that I check and clean all connections in the engine compartment, including grounds - add dielectric grease and zip tie any connectors together if I could.
I did one each week so that I could find a problem if one popped up.
Keep in mind that if a device has no ground wire, it gets its ground through its mounting to the engine or body.
I think that your engine has at least two copper ground straps, one on the top and possibly one on the bottom. You may find a copper terminal on the body or engine, but no strap.
Have you tried fuel injector cleaner? I use Techron twice a year.
BTW - you wont believe how much a teaspoon full in my snow blower and lawn mower smoothed them out. I do that at the beginning of the season now.
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How does your air cleaner look?
Did you look at your plugs? A bad boot could foul its pluug.
Are you up on stage I?
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What do you mean by Stage 1?
Apologies for all of my questions to your questions; I'm learning! :)
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We had a '90 740 that had a bad switch in the shifter.
Does it always go back to normal after you shut the car off?
I also had a 740 that had a rip in the coil wire insulation where it clipped to the firewall. Did you install a new coil wire?
Do you still have all the looms for the plug wires, including the ones under the rocker cover bolts?
If any of the wires touch each other, or any other part of the engine, that can lead to a misfire - if any touch, examine them carefully for marks of any kind and move them in the looms until they are separate.
A crossfire can burn a hole in short order.
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Yes, the overdrive always goes back to normal when I turn the car off. Less frequently, when I turn the car on, the overdrive will be on (even if it wasn't on the last time I used the car).
The coil wire is the wire that connects the ignition coil to the distributor, correct? Yes, I replaced that wire along with the spark plug wires. However, it is worth noting that there were some wires included with the kit which I could not figure out. So, I have some new wires that seem to go somewhere, I'm just not sure where.
"Do you still have all the looms for the plug wires, including the ones under the rocker cover bolts?"
This question confuses me a little. By looms, I assume you mean some kind of rigging that holds the wires separate from the block and from each other? I do have the old wires, so I'll inspect them for any 'looms'. What do you mean by "rocker cover bolts"?
Also, about your point that any contact between wires or the block will cause a misfire: while I understand this in theory, it would not seem to be my problem because the misfire only occurs when the engine is warm, correct? What could possibly make it misfire when warm but not cold? Contacting wires would seem to always misfire, no?
I'm leaning toward a distributor, rotor, spark plug problem. What do you think?
Thanks for your help!
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Have you read the FAQ? It contains a wealth of information.
I mention the switch (and wiring) in the shift lever because the relay needs a signal to operate.
If the relay were bad, the arrow would never light and the transmission would never lock out.
When you shut off the car, the relay loses power and reverts to normal.
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I have read through some of the FAQ.
This misfire is a bit odd because of how specific it is (only when warm and at idle).
As far as maintenance of the car, I would say it's close to stage I. I have had the car for about 1.5 years and have replaced many parts like radiator, waterpump, fuel pumps, rpm sensor, thermostat, three exterior belts, air filter, regular oil changes etc. About 6 months ago I had an issue where the car would almost stall and choke along home (much worse than this misfire). I cleaned the MAF sensor and the problem disappeared.
I'll look at the throttle bottle and clean it. Your idea about an air leak also sounds good. Any idea how and where to start checking for one?
Also, you asked about the looms and wire separators. Mine didn't have any, so I bought some. Though I haven't yet installed the loom, I did install the separator clips and ensured that the wires don't touch each other or the block. Didn't solve the misfire though.
Thanks again for your help.
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Almost everyone gets the overdrive backwards.
Under normal conditions, the overdrive works whenever appropriate.
If you push the button, the arrow lights, the transmission will not operate normally and the overdrive is locked out - this feature is provided for situations under heavy load, like pulling a trailer or very hilly country when you do not want the overdrive to shift in and out on every hill. This avoids bogging the engine down.
I may not be completely correct, but I think that there are two plastic clips that have four slots to hold the spark plug wires apart and two or three nylon clips under the right hand rocker cover bolts to hold the wires away from the engine.
The four wire clips float up in the wires and are only attached to the wires, these can get lost over time, The cover bolt clips get brittle and break - many people never see these clips as they are gone before they buy their car. The rocker cover is the black cover on top of the engine - rocker cover is not the correct term - cam cover would be more accurate - sorry.
All the clips and looms are important as you can position the wires through the clips and looms so that none of the wires come near each other, or touch the engine. The wires should never be closer together than they are in the looms.
I ask about stage I - this means are all the maintenance measures up to date? Many people forgo Volvo's schedule of maintenance because dealer work is expensive, Stage I is a fully tuned standard engine stages II,III, IV, and V are various levels of modifications for more power, V being a full race car engine.
Stage I means good spark plugs, good ignition parts, clean oil and air cleaner, no worn or damaged parts, etc. A well maintained engine.
Having a burned plug boot tells me that the plug wires were older than Volvo's schedule would dictate. And, probably other matters may not be up to snuff.
Things like a dirty air cleaner, valves that have never been adjusted, a dirty throttle body, an old rotor and distributor cap, old spark plugs, etc., etc. can cause misfires.
Volvo's engine management system can compensate for a lot of things and the engine can run pretty well despite neglect.
Your misfiring may not be related to the wires, but some of the other potential problems.
Misfires cold vs warm - it is normal for an engine to misfire mire cold than warm. A warm misfire could be an air leak that lets in too much air - under cold conditions, extra fuel masks the problem.
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