1989 MPFI 2.8L Automatic.
I had a misfire under acceleration. It started so suddenly I thought it was a bad tank of gas at first. It only happens under heavy load. After some research, I suspect something with my ignition system. I had just replaced plugs/wires about 6 months ago, and bought the cap/rotor but didn't put them in yet.

Since I already had the parts, I started there. New cap/rotor with brass terminals. No change. I can't tell at idle, or at any non-moving throttle position because it works perfectly then, and pulling any wire off at the cap causes the motor to stumble a bit. It's only while under moderate-severe accelleration or load (up a hill).

I bought an Advance auto coil. Got a GP Sorenson part that looked exactly like my coil. I found the original to be riveted in, (see other thread), so I plugged it in, and laid it in the engine compartment. Now a week later, the same misfire is back.

Does the coil need to be grounded? I thought it was just a transformer? Maybe so, not sure if I broke the new coil or not. Any other reason why this coil would go bad? Next place to look?

 

So the new coil definitely worked well for a week (i.e solved the misfire completely) and then the same problem came back again?

I'd try one more coil before I started to look at the stuff inside the distributor (module, most notably).

Yes, the coil armature should be grounded but I've run them many times the same way you have done for your diagnostic tests and I don't recall ever killing one.

FYI- The rivets are pretty easy to get out. Just grind the heads off them and punch the pin out with a drift. Replace with some small nuts/bolts and locktite the threads so they can't come loose.

 

Yes, the new coil worked great. No misfire at all, for about a week. Then it creeped back in again.

I'll try another coil, and with the long weekend I should be able to make it to a place where I can dremel off the rest of the rivets (I got the top two off while taking out some rage on them with a pair of channel locks LOL).

If it goes bad again, I'll get the module and make sure I use the dielectric grease packet it comes with.

 

I replaced the coil again, New coil started to misfire after 24 hours. Gonna do the wires and the ICM this weekend, anything I can do to narrow it down?

 

A bad module can take out a coil.

Best to replace them both when one goes out.

 

.... and if you're going to do the module you should also replace the condenser (capacitor) right next to the module. Round shiny thing with 1 wire coming out of it. They're cheap and there's really no reliable way to test them on the bench.

 

My car has no condensor. I did the module this weekend, with mixed results. One thing very noticeable, was that the plastic connector that goes to the coil (green and yellow wires) which is marked "P" and "N" was completely melted and quite destroyed. It literally fell apart when pulling the connector off the old module. Luckily I believe I remembered which wire went where (Green towards the firewall, yellow towards the front of the car???) and the wire, while still intact, is just a tiny bit corroded, and slightly loose. Not loose it's falling off loose,
just loose enough so that I can take it off with no resistance.

From schematics these wires seem to be coming from the pickup coil. Any way to replace the wires, with one that has an intact connector? Would soldering them on be practical? Anyone ever had this happen? Could this be the cause of my misfire?

I wanted to see what the board thought, so I put it back together and while better than before, there is still a slight misfire LOL....

Before this, the car would (seemingly randomly) just about buck when I hit the accelerator, and I would hear it spitting and coughing as it worked it's way up in RPMs. I would guess about 1-3 misfires per second while under 1/3 throttle acceleration.

Now its just about 1 every 2-4 seconds, with the occasional fit...

 

BTW I got the rivets out, and the newest (third one) coil installed properly with bolts and the brackets.

 

Melted/corroded/loose wiring is never a good sign and yes, it could definitely be the cause of the misfire. The real questions is WHY it would have melted. A bad coil and/or module could do that over time. I think you're on the right track. Keep an eye on the wiring repairs you have done over a period of days/weeks and see if it is melting again or if it's doing fine. If it looks like it's melting again you're going to be back to where you started pretty quick. If it's doing OK I doubt you'll have a return of this problem.

 

Any idea's how I can replace the wiring for the pickup coil? I suppose I could cut the wires, and put in a new connector i get off of a junkyard car.

Is replacing the pickup coil difficult? I.e. Could someone who has never done such a thing before, complete it in say an afternoon?

I assume you need to remove the distributor completely, and that just kind of makes me very nervous that I'll never be able to drive the car again

 

The pickup coil itself isn't much money but installing it does require yanking the distributor, taking off the distributor gear, removing the distributor shaft from the housing (not easy on an old motor with oil crud caked up around the shaft), then you replace the pickup and put it back together in reverse order.

R & R distributor how-to:

Before you yank the distributor mark the direction the rotor is pointing ON THE FIREWALL OR OTHER SOLID POINT. That's the direction you want it pointing when you drop it back in (so it's not off by a tooth or two or three).

ALSO, before you yank the distributor you want to make ANOTHER mark (also on the firewall or other solid point) indicating the direction the BODY of the distributor is pointing. This is separate from the mark for the rotor. Might use the direction the electrical connections on the side of the distributor are pointing as your reference. When you drop the distributor back in you again want to line up the distributor body with the mark so that your TIMING is reasonably close. I say REASONABLY close becuase you're guaranteed to be off by at least a few degrees just "eyeballing" it back into place. Once you get the motor fired up you STILL need to set the timing properly with a timing light, using the proper factory procedure to set base timing.

When yanking the distributor the rotor will turn CCW about 30* as you pull the body of the distributor up out of the engine. That's becuase of the curved gear teeth on the distributor gear. When you go to reinstall it make sure you start the rotor pointing about 30*CCW from that rotor mark you made on the firewall and it should drop right back in, rotate 30* CW as the body of the distributor drops back into the block, and come to rest pointing in the original direction as when you took it out. If not, yank it and try try again.

Make sure the distributor body actually seats ALL the way down against the intake manifold when you reinstall it. If it doesn't want to go down the last 1/4" or so, the distributor gear isn't meshing with the oil pump driveshaft notch. The driveshaft is just a slotted shaft (inside the engine- you can see it if you look into the distributor shaft hole with a flashlight) that fits the slot on the bottom of the distributor gear. If the 2 slots aren't lined up they won't drop together and the distributor will not seat all the way. If you run into this problem it's handy to have a LONG regurlar screwdriver so you can give the oil pump shaft a little bit of a turn to get it to line up with the distributor gear again.

SO...... in summary, the 3 things you want to get to line up are:

1. Disributor shaft must mesh with oil pump shaft to allow distributor to drop in all the way.

2. Make sure the rotor is pointing in the same direction as when you pulled it out. If it's off by a tooth it will be obvious- the rotor will be pointing in the wrong direction by more than 20* from your firewall mark.

3. Make sure the distributor body is pointing in the same direction as when you pulled it out- as close as you can get it to the original position using your other firewall mark.

Then set your timing when you get the engine fired back up and you're good to go.

 

Gosh I hate cheap spark plug wires. I replaced them with another cheap set, problem resolved...

Great instructions on the distributor removal, I'll get into it in another few weeks, thanks again