Engine missing badly

[bogey]

I have suddenly developed a problem. The car has run fine this morning and at lunch, but on the way home started to badly miss.

Check engine light came on and I limped it home. No oil or temp problems, no smoke, just running on 2 or 3 cylinders.

Checked all the connections and all seemed fine. No obvious problems.

I will be going through the FSM diagnostics tests, but that takes a while. Is there a "most likely" cause to check first?

[Griff]

Obvious suspects are plugs and wires.

[chuckerants]

Does the 96 have OBD2?

[bogey]

I have spare wires and I will pull the plugs to eyeball them. The plugs are new and the wires only hage about 5K on them.

But the problem came on suddenly. I suspect a fuel injector, or possibly a sensor problem (MAF?).

[bogey]

Yes a 96 has ODBII, but my reader does not work on this car. (I don't know why) I think it will show random misfire, or perhaps indicate a specific cylinder.

[Banshee]

Check 5th injector for leakage, or any injector for that matter.

When I developed this problem, it turned out to be my water injector. It was leaking in alcohol at idle, causing misfire. But excess fuel will do the same.

[Tom @ Fast Forward]

Pull the four spark plugs. Should be able to make some diagnosis from that. Check the wires from the PC and SS to the ECU harness. Could be one disconnected?

[bogey]

Tomorrow... I am too tired to work on it tonight.

I was also thinking about the ECU connections and wondering if they would affect it.

[bogey]

OK - I finally got a chance to pull the plugs. #1 and #4 looked new. #2 and #3 are black as coal! A heavy layer of soot on them.

Based on this, I would assume the coils are fine because 2 & 3 share the 1 & 4 output. (This is my understanding of it.)

Is this caused by too much fuel or not enough fuel?

What else should I look at?

[bogey]

Correction! 2 & 3 share a side of the coil. Since both 2 & 3 are fouled together, is it that half of the coil pack that has failed?

[bogey]

Checked the secondary coil resistance. 1/4 is 9.6Kohm, 2/3 is 9.5Kohm - within spec. Plug wires resistance is correct at 2-4Kohms depending on length.

Question: on the passenger side of the coil pack is a 4 pin connector (grey outside, orange inside). Not the oxygen sensor or CAS connection on the drivers side. This connector "may" not have been seated all the way. ( I am not sure, but it did not feel fully engaged.)

Is this the signal connector for the coils? I suspect it is, but have not found is documented in the FSM. Can someone confirm this?

If so, I will clean up the plugs and reinstall, ensuring the connection is on right. Then retest.

[Tom @ Fast Forward]

I don't know if that is the coil plug or not but that sounds like the right problem. The one coil does feed 2/3 and the other 1/4. So it sounds like an ignition problem.

[bogey]

OK - I cleaned off the plugs and got the car put back together. Double checked all connections and installed my gauges today. The AF indicates it is running VERY rich.

The boost is not showing any vacuum or pressure. I assume that there is a leak somewhere, and I need to locate the connection problem.

If the boost is not connected to the JRPC or the SS, would they cause it to run so rich?

Also, what kind of connections are best for making T-connections to the hard vacuum line. Apparently I have not had much luck getting a good seal.

[Tom @ Fast Forward]

They wont go rich if they don't see boost. The fuel injectors work by having one side tied to 12VDC and the ECU pulls the other side to ground to turn it on. The PC looks at the grounded signal and simply holds it to ground for an extended period of time based on boost. If it doesn't see boost, it does nothing.

The SS runs the 5th injector also by grounding one side of the injector. If it doesn't see boost, it doesn't turn on. Easy way to see if it is the culprit is to unplug the 5th injector.

Is it rich off boost as well?

[bogey]

It is rich all the time. It barely idles now. I think cylinder 2&3 are getting flooded with fuel.

I don't know what happened. It was running fine, then suddenly stopped running fine.

I am trying to determine if it is too much fuel, or unburned fuel from lack of ignition.

[Tom @ Fast Forward]

As you said earlier, the one thing that is common to 2/3 is ignition.

[bogey]

OK - I got the car running well again. I really don't know what the problem was, but I checked/rechecked all connections.

The air/fuel meter is doing a nice dance between lean and rich, so I am buring fuel again, and the engine is running smooth again.

These are the possible scenarios I came up with to explain the misfire on cylinders 2/3.

- the ECU connection to the coil pack may not have been making good contact. Connection 4R controls the firing of the 2/3 coil pack. Remove/reconnected all the ECU plugs.

- the plug to the 2/3 coil pack was removed/reconnected

- possible cracked coil housing causing loss of charge (working fine now, but the sun may come up again tomorrow and problem could start again)

- JRPC connection to the fuel injectors for 2 and 3 could have been a problem. I know it should not add fuel, but I checked all the connections.

I still have not ruled out a bad coil pack, but I will wait to see if the problem happens again.

[Tom @ Fast Forward]

All right. Back on track again. Awesome.

[Kyp J]

"Possible cracked coil housing"????

I don't know about coil packs but old style distributer caps with cracks or even dirt and oil residue will short out with humidity or moisture (washing engine or big rain puddles) and create carbon tracks that continue to short out even after it dries out.

[bogey]

My understanding is the plastic insulating housing of the coil pack can get hairline cracks that become conductive, enough to bleed off significant charge.

I don't think I have this problem.

[Kyp J]

Sorry, I thought you actually saw cracks. But I guess you would have to have x-ray vision to do that.