Head Scratcher

[Jacob Williams]

Hey,

I had a long discussion with y'all earlier about my engine running like s***, turned out to be a stuck open injector- and I'm infinitely thankful for the help. But there's something else strange about my car that has irritated me for a long time. About 99 out of every 100 times I drive it, it will start going through these 3-second "cycles" of not accelerating at all with a dull sound from the engine, with another 3 seconds of working perfectly. It will do this for the rest of the day, and after leaving it parked overnight it will drive perfect for the next few weeks like nothing happened. One time and only once, it backfired loudly during this behavior and started driving perfectly again. This behavior seems to always occur during very hot weather, and is especially likely after idling while running the AC for a while. It always seems to happen at the worst times- I can drive a perfect 3 hour trip, only for it to **** the bed on a night out with the girlfriend the next day. Any idea what the hell this is??

 

[koda2000]

A backfire with the symptoms you describe sound like it may be spark related. You can try removing your coil pack and making sure the bottom is rusty. If it's rusty remove the rust as best you can. That could be creating a coil grounding issue.

 

[Jacob Williams]

A backfire with the symptoms you describe sound like it may be spark related. You can try removing your coil pack and making sure the bottom is rusty. If it's rusty remove the rust as best you can. That could be creating a coil grounding issue.

Didn't look rusty when I took it off during the fuel injector fiasco. I might change the wires, they do look pretty beat up. Excessive heat and somehow the AC seem to make the problems show up, so I guess a spark-related answer does make sense.

 

[1998Exp]

A backfire with the symptoms you describe sound like it may be spark related. You can try removing your coil pack and making sure the bottom is rusty. If it's rusty remove the rust as best you can. That could be creating a coil grounding issue.

I also thought that way, until someone corrected me. Turns out that a "waste spark" system does not need a ground connection for the coils at all. The only ground connection is for the capacitor, and that's to reduce the high frequency electrical noise only, with no effect on functionality. If you look at the schematic, you find out that the coil primary (low voltage) winding is supplied with +12V at one end and driven to ground by the PCM at the other. The secondary (high voltage) winding has two terminals; to two plugs on opposite sides of the engine. The secondary current flows through the plug that makes the spark, then through the engine metal, and finally through the plug on exhaust stroke back to the coil. Exhaust gas has low resistance, so the plug on the exhaust stroke is a virtual short circuit to the wire going to the opposite end of the coil.

 

[Runnin'OnEmpty]

The metal strap at the bottom of the coil pack is grounded to the engine with one screw,
if I remember correctly, and is there to dissipate any electrical field that may be generated
as the coils fire. Although there isn't a direct coil connection, if the metal strap isn't grounded
the engine will indeed run rough.

I also remember that Ford had a TSB on faulty MAF connectors at one time. You might try
unplugging the MAF sensor and spraying it with WD-40 and see what that does. Might not
do anything, but is easy and quick to try...

 

[1998Exp]

The metal strap at the bottom of the coil pack is grounded to the engine with one screw,
if I remember correctly, and is there to dissipate any electrical field that may be generated
as the coils fire. Although there isn't a direct coil connection, if the metal strap isn't grounded
the engine will indeed run rough.

No choice, but to test. Shouldn't be too hard to remove that one screw and see what happens. I'll report when I get to it.

 

[swshawaii]

You might try unplugging the MAF sensor and spraying it with WD-40 and see what that does.

I'm CERTAIN you meant MAF sensor cleaner or electrical contact cleaner, yes?

Any type of oil is the last thing you want on MAF wire filaments. K&N air filters come to mind?

EDIT- Thanks Turdle, apologies Runnin'OnEmpty. What happens when people like me don't READ carefully.

 

[Jacob Williams]

No choice, but to test. Shouldn't be too hard to remove that one screw and see what happens. I'll report when I get to it.

Makes sense, but I still can't understand how it only causes a problem 99 out of 100 times I drive. Wouldn't such an issue cause constant trouble, or can excessive heat somehow trigger it?

 

[Turdle]

I'm CERTAIN you meant MAF sensor cleaner or electrical contact cleaner, yes?

Any type of oil is the last thing you want on MAF wire filaments. K&N air filters come to mind?

He meant to spray the electrical connector with wd40 which is a good contact cleaner.

Jacob, if you feel it may be heat related, change the ECT ( engine coolant temperature) sensor. It has 2 wires, ignore the "sender" which only has one.

 

[Runnin'OnEmpty]

Thanks Turdle, I indeed meant the connector and not the sensor itself. I should have made that clearer. Good suggestion on the ECT sensor.

Jacob, assuming there is no MIL or codes present, this is probably something simple such as a poor electrical connection or a sensor getting tired. If a fault is intermittant like yours, it won't always trigger a code. Since you don't get misfire codes, I suspect the MAF or TPS could be involved, or as Turdle said the ECT. You might try unplugging the TPS and spraying it's connector too.

You mentioned 3 second intervals when the problem occurs. There is a 3 second time-out with the fuel pump after the key is turned on but the engine isn't started. I don't see how this is relevant, just something I thought of....maybe reset the pump inertial switch located in the passenger side under dash area. Lift up the carpet and press down on the red button...

 

[Jacob Williams]

Thanks Turdle, I indeed meant the connector and not the sensor itself. I should have made that clearer. Good suggestion on the ECT sensor.

Jacob, assuming there is no MIL or codes present, this is probably something simple such as a poor electrical connection or a sensor getting tired. If a fault is intermittant like yours, it won't always trigger a code. Since you don't get misfire codes, I suspect the MAF or TPS could be involved, or as Turdle said the ECT. You might try unplugging the TPS and spraying it's connector too.

You mentioned 3 second intervals when the problem occurs. There is a 3 second time-out with the fuel pump after the key is turned on but the engine isn't started. I don't see how this is relevant, just something I thought of....maybe reset the pump inertial switch located in the passenger side under dash area. Lift up the carpet and press down on the red button...

I use that switch to let off the fuel pressure, just unplug it and run the car til it dies. I've never had the switch spring up though. I'll try cleaning the connectors and maybe messing with a voltmeter on them. Then again it may be a month or longer before I find out if it's actually fixed. I've done lots of little things that I thought fixed it, only for it to suddenly f*** up again a long time later.