99 Taurus not running right

[DavidL]

I have a 99 Taurus with 3.0 Vulcan engine, 110,000 miles. I have started noticing a slight, but very perceptible "jerking" when I accelerate or go up a grade (and need more power). When I'm driving at a steady speed it runs fine. It also idles fine when sitting still. I only notice this when I have to push on the gas pedal to get more power. It's not due to the tranmission shifting because it stays in the same gear when this is happening. There is also no change to the RPMs on the tachometer. One other thing I have noticed is that it seems to be worse when the A/C is on.

I started with the easy things. I have checked the transmission fluid, replaced the fuel filter and added a can of Seafoam to the gas tank. Any suggestions on what I should try next?

[shorod]

Sounds like you might be experiencing a misfire under load. You're probably due for new spark plug wires and spark plugs. I don't recommend going the route of performance aftermarket spark plugs, but rather an OEM-style replacement. Often the performance plugs don't agree with modern computerized engines for some reason from what I've experienced as well as others. The coil packs could also be the source of a misfire in the event spark plugs and wires have been recently replaced or they do not fix the issue.

If you have access to a scan tool that can access the component parameters, you can see if a cylinder or two are reporting misfires, even if the misfire counts are not high enough to trigger a diagnostic trouble code.

And please post back with what you find to be the solution to this issue.

-Rod

[DavidL]

The plugs and wires have about 40-42,000 miles on them. How many miles should I get out of the average set of plugs and wires?

[shorod]

If the plugs and wires were of good quality, there are probably still a few thousand miles left on those plugs and wires. Your issue still sounds like a misfire though.

You may want to verify that all connections from the plug wires to the plugs and coils are secure. Also make sure the air intake tubing is secure and there's not unmetered air entering the intake. I would expect a loose air intake hose to cause a misfire all the time though, not just when the engine is under load. An intermittant MAF sensor could act like a misfire, but often that would act up when you hit bumps in the road.

-Rod

[DavidL]

I went ahead and changed the plugs and wires this morning. I took it for a test drive but no improvement.

[shorod]

Any chance you can find a scan tool that has a datastream mode so you can attempt to determine if the misfire is air or fuel induced?

You could also try cleaning the MAF sensor to see if that helps. If it's cleaned properly, it won't hurt anything and probably will, at a minimum, improve your fuel economy a bit. It may be the source of your misfire, but if it's dirty enough to cause a misfire under load, I'd expect it would also trip a code.

Depending on how much money you want to spend shotgunning parts, you might end up saving yourself some time and money in the long run by having a professional diagnose this issue in person.

-Rod

[DavidL]

I don't have access to a scan tool. If I go to a garage to have it checked, would I look for one that advertises computer analysis? I haven't gotten into this kind of issue before.

In the meantime I went ahead and cleaned the MAF sensor but no improvement. I also checked out the ignition coil pack to the extent that I can. The primary resistance was within the spec of 0.5 ohm both when the engine was cold and hot. The secondary resistance was also in spec at around 13,600 ohms when I checked with a cold engine. I later checked it when the engine was hot and the resistance on each coil had increased to the range of 15,800 to 16,000 ohms. Not sure if that is a problem.

One other thing I tried was using an ignition spark tester that I picked up at Advance Auto (see below). The guy said that a normal spark should be blue or white, and a yellow spark would be abnormal. I tried it on each spark plug wire and did see a yellow spark on the no. 3 wire. Does anyone know if this is an accurate test?

[shorod]

Well, I suppose one thing you could try would be to swap wires between cylinder #3 and a cylinder with a similar length wire to see if the yellow spark follows the wire or the coil tower. If it follows the wire, and if you bought the wires at Advance Auto, you could talk to them and inform them that the spark tester they sold you says the wires they also sold you are no good. Explain that you moved the wire and the weak spark followed the wire. If the yellow spark follows the coil tower, then swap the wires back to the original locations and leave the wire for cylinder #3 disconnected and take it for a drive. If it seems to have about the same weak power, then you likely have determined that the coil pack for cylinder 3 and whichever pair (maybe 1) is bad. You might be able to buy just the coil for that pair of cylinders, or you may need to buy the entire coil pack for all 6 cylinders. That will probably take care of your misfire.

Does the plug for cylinder #3 look different from the rest?

-Rod

[DavidL]

I'm still trying to figure things out on my own because I have a feeling that it could turn into an expensive "wild goose chase" if I have a mechanic look at it. As I have searched the forum I noticed that the engine RPMs should increase when the A/C is turned on while idling. Mine actually decreases slightly when I turn the A/C on. Also, the RPMs don't increase when I turn the steering all the way in one direction. Is it possible that the IAC could affect my engine when I'm driving at highway speeds?

[shorod]

The IAC should not affect the engine when you are off idle (hence the name "Idle Air Control"). If the IAC were stuck part way open, it could effect the engine early into the fault, but it should be at any engine speed until the engine recognizes the lean condition and adjusts the fuel trim to compensate. That would probably require so much fuel trim adjustment that it may trigger a diagnostic code, I'm not sure.

Ideally, when the IAC is operating properly, you wouldn't notice an increase in idle speed when a load is placed on the engine, it would compensate to keep the idle at the desired speed. What you don't want to experience is a drop in idle speed when a load is placed on the the engine at idle.

Have you tried moving wires around to see if the apparently weak spark follows the wire or stays at the coil yet?

-Rod

[jarreg02]

Was reading did you try a differnt wire in place or disconnect it all together on the #3 wire? have you checked you air filter? sounds like it is a coil pack but thats just a guess you could take the coil pack off and switch it with another pack and test it that way if you change its location and you are still getting weak spark from the one side than you could bet that theres your problem hope this helps.

[Scrapper]

i agree on taking wires back if you bought them at the zone? and with your car if it cuts out under a load i'd be checking into those wires and your plugs,coils you never cracked one did you? a small crack will do them in. and you checked all vaccum hose or did you?

[DavidL]

I checked the sparking again and didn't really see a noticeable difference in the spark on the #3 cylinder, so I decided that just looking at the color of the spark was probably not a good indicator. Obviously, if there were no spark at all, that would be a problem, but that's not the case.

I have tried a different ignition coil pack with no improvement.

Also, a guy at Advance Auto hooked up his scanner to the car and it didn't show any pending codes or problems with the various diagnostic tests (it was an Actron Autoscanner Plus). He suggested it might be something in the fuel system or a vacuum leak. His suggestion for checking for leaks was to spray WD-40 on the vacuum lines with the engine running and listen for an increase in engine speed. I tried that but didn't notice anything.

Is it possible that there is a leak that isn't bad enough to let air in at idle speed, but leaks when the engine is under load?

As far as the fuel system is concerned, I have changed the fuel filter. I guess the next thing to check would be the fuel injectors.

[shorod]

So the Actron scan tool did not show any current codes for your car? Is your scan tool maybe displaying history codes for you rather than pending or current codes, so you're seening the recent codes that the scan tool has recorded for your car?

I would be more suspect of a plug wire causing problems under increased load/higher engine speed, than of a vacuum leak that only appears when under load.

Is it a tremendous problem to try swapping the #3 plug wire with another wire of similar length? Are you sure the plug and wire you're looking at is #3? On your transverse Ford V6, cylinder #3 should be the one on the driver's side of the engine, rear cylinder bank (near firewall).

-Rod

[Scrapper]

one question is the spark blue or yellow? it should be blue.