Ok, so I have an 86 with the LG4 carb'd 305 engine. I replaced the ECM recently and it has been running like a champ! Very smoothly, slightly faster than a turtle with rheumatism.

It's just that every once in a while the car will wind down. I could be on the highway cruising along, and all of a sudden I am losing power. No amount of foot-stomping has any effect. When I pull over, the car dies. If I start it again right away I might get 3 feet before it dies again. If I wait five minutes or so, it starts right up and away I go.

So, I got to thinking, something must be heating up on long drives and causing an issue, but it cools off again in about 5 minutes. Electrical? Maybe the coil? So, I get new cap and rotor, and a new coil. It's about time for a tune-up anyway. I look at the cap. There is a hold-down screw between 2 and 7, and the plug-in parts are between 7 and 5. Ok, sounds easy. I assemble the new coil/cap combo, like I have done about a dozen times before on other cars. Reattach all of the plus and nothing. Just cranks away. Maybe I made a mistake, and shift all of the wires counter clockwise one spot so that the #1 plug is in the 5:00 position. Still no start, but it huffs a little. Just for fun, I rotate everything back to start and clockwise a step. Nothing. I have not moved the distributor itself at all. Hmm. Maybe the new coil is bad? It could happen. Put the old coil and cap back together (I have to keep switching the ground prong back and forth) and tried it with no luck.

This thing was running just fine before!

I used a tester and I am getting spark from the distributor to the plug.

Wracking my brain on what I have done wrong.

Any ideas? I have been rebuilding caps, rotors, distributors since the 80's and have never run across such a problem. Unless the ICM is fried.... I haven't changed that, but figure it would have shown up as an issue long before now.

Tony

 

Carry a can of starting fluid with you. Next time it does it, see if it'll start on a shot of that.

 

Starting fluid does not help. Nothing happens, just cranking. If I move the plugs 2 places over counter-clockwise I get some noise, but nothing like starting. That puts the #1 plug wire in the 4:00 position.

I popped the cap off and bumped the starter to bring the timing mark on the engine to where I could see if from the driver's side, where I would expect it to have timing marks if it was a standard engine. Crazy thing is that the rotor points to the 11:00 position, more or less. It looks like it is 180 degrees out. I did not pull the distributor, and the rotor only goes on one way, so I have no idea. My old, addled brain is really confused!

Now, the crank turns twice for very cam turn, so maybe I am looking at the exhaust stoke. But dag on, this is frustrating. Putting the #1 plug at the 5:00 position does nothing! If I bump the starter so the rotor is in the 5:00 position, there is no timing mark showing.

 

OMG! I finally figured it out, and it's stupid!

I looked at the wires on the cap, and they were numbered, so I pulled them without really examining. Well, someone must have done a crappy wire replacement on the car before I bought it, because the wires lead to the wrong plugs! For example, the #5 wire was attached to the #1 cylinder plug. So, I am going to pull the wires from the plugs and put them on the correct ones. I am guessing I'll get good results.

 

Disconnect the ignition coil wire. Pull the #1 plug, Have someone bump the key while you determine the compression stroke (and TDC,) of the #1 piston, then see where your rotor is, and adjust accordingly so that the rotor contactor is at the #1 plug on the cap.
You don't need to look at timing marks until you get the wires and the cap where they should be. Make sure the firing order is correct. And its 1 8 4 3 6 5 7 2.

You don't need to concern yourself with advance/retard until its running.

 

Turns out that none of the plug wires on the diver side were going to the correct cylinder as far as the number on the wire indicated. Passenger side looked fine. I rerouted the wire and set them so that #1 was in the 5:00-ish position. After letting it crank for a minute or so, since I probably soaked all my plugs, it finally fired. The engine stumbled for a bit and I let it run long enough to warm up, then took it for a drive.

Everything is fine!

I guess the moral of the story is not to assume the person who worked on the car before you got it did everything correctly.

 

That person is usually me! Glad to hear you got it sorted out.

 

Just a follow up question, because that's how my luck goes.

I noticed that the #2 wire had a burn mark in it, so I decided to go ahead and replace plugs and wires (just over 30k miles, but it is 37 years old). After assuming many different yoga poses, I got the passenger side changed. Started the car and pulled it back into the garage. Two days later I go to pull it back out into the driveway to get the driver side, and the car is running super rough! I made sure all of the passenger side plugs had clicked onto the cap and the plugs. No problems. So, I went ahead and changed the driver side. Restarted the car and it was still rough, like I had some wires mixed up. Getting late in the day, so I pulled it back into the garage.

Next day, I pull the car out again to check things out, and the car starts on the first turn of the key and runs so smoothly you could build a house of cards on the hood. I took it for a drive and it was awesome. Smooth and relatively powerful for that engine. Nice. Garaged the car again.

Got up this morning, decided to drive the TA to work. I drove about 10 minutes, and the car started bucking and running rough again. Turned around to go home and it smoothed out again for about 2 minutes, then I limped it home the rest of the way hoping it wouldn't die and leave me stranded.

No check engine light. New fuel pump, "new" remanufactured carb I put on about a year ago. I didn't change anything else. New catalytic converter, so not worried about it being plugged. As far as I know, the computer only really controls the carb and distributor, so I didn't reset it.

Only thing I didn't replace distributor-wise is the module. I am ruing out anything transmission related because the rough running does not change in drive or park.

I appreciate any ideas.

Thanks!
Tony

 

I would guess that the root cause is ignition related. Do you have a timing light?

 

Yes, I do. I can check the timing when I get home from work and report what it looks like. It may or may not be running rough. but I can check it.

 

Sounds like a bad ignition (spark) control module.

 

Darn it, that's what I was thinking. So, I replaced it with a new one this morning. Started the car and it ran beautifully. Turned it off to put everything back together, grabbed a water and jumped in for a test drive.

Turned the key and it started loping and muttering. It's really intermittent. Took it for a short one mile drive and it shook the entire time.

I have a new Summit Racing HEI distributor sitting on a shelf. I would just need a new carb and I could get rid of the computer entirely. I would rather not, though, since I am 80% determined to sell it, since I picked up my 911.

I am going to pull the fuse to the ECM for a while. Maybe changing all of that stuff messed up its settings somehow. I can't imagine how it would bug out, being so simple, but it does control timing, and it's free.

 

If you had an opportunity to check the timing, where is the base timing? With the EST bypassed, is the timing stable? With the EST active, where is the timing at idle, and is it stable or wandering greatly?

 

I threw a timing light on it this morning. With electronics plugged into the distributor, and the clamp on the #1 plug, I don't see any timing mark. If I unplug the pigtail to the dist, I still see no timing mark.

This all began after I replaced the passenger side plugs. Well, the morning after, that is. The test drive right after went great.

So, before I did anything else today, I pulled each wire, made sure the plug was snug in the head, and made sure all of the wires clicked into place both on the plug and cap. I am trying to stay calm and methodical. This is not making much sense to me. I could maybe rotate the plugs on the cap one spot and see if I get a timing mark to show up. When I manually bumped the engine and got a timing mark, I made that my #1 plug, which matches what quite a few people say it should be; about 5:00 on the cap. I would swear that when I took the plugs off originally, #1 was more like just after 6, and #2/#7 split the lock-down on the cap.

I am using AC Delco Gold Rapidfires gapped at 0.045. I'm tempted to put the old plugs back in that side and see if things clear up.

 

I ran out of time last night. I did pull the #2 plug and it was all wet. I cleaned it up with some carb cleaner and re-installed.

Just for fun, I put the timing light inductor on each plug wire and several of them show very inconsistent flashing. Could be my cheap timing light, but some of them showed strong, regular flashing.

So, I am going to pull the plus, clean the wet ones, and try again.

I just have to figure out why they ran great before, and are wet now. The old spark plugs looked good.

 

Update.

I went out this morning and tried some stuff (typing as I try to catch my breath from all the yoga I had to do). The problem started on the passenger side, which I had changed first. I tried putting the old wires back on, in case I had an internal break in one of the new wires. There was no change there. So, I pulled all of the plugs on that side. Two plugs were very dark, uniform, but dark. Insulator was black, too. Two plugs were sort of dark, but they also had gray ash on the electrode. That got me thinking about heat ranges. Maybe my new plugs were too cool?

I put the old plugs back in that side. They looked great for stock plugs with 32K miles on them. Started up the car and it ran nice and smooth. Revved it a few times with no issues. I pulled the plugs on the driver side and they were in pretty much the same condition. Put the old plugs back in there and took the car for a short test drive. Runs like a champ.

I misspoke in my earlier post about what the stock plugs are. These are actually AC Delco R43ts, not 45s. So I am going to order a new set of those.

Here's to hoping all of this ends up solving my original problem!

Lessons learned in all of this: be sure your wires are on the correct plugs, and get plugs in the correct heat range.

Now to tackle the heater core. I don't suppose any of you young whipper-snappers live near Cincinnati

 

The yoga routines are going to be very advantageous when you have to dive into the passenger footwell to free up the box, and then contort your forearms behind the right head in order to access and exchange the heater core. I did mine in about 1998 and immediately changed over to DexCool in the hope that I would never have to do that again. It's only been about a couple decades, so we'll see how that plays out.