85 GW AMC 360 rough idle w heavy exhaust

[Bentley]

Hey gurus, I’m at a total loss and hoping you might have some insight.

85 GW, AMC 360, Motorcraft 2100 carb, Motorcraft distributor w TFI upgrade and MSD 6a ignition module

The GW has been a high school daily driver for my kids for years with no major issues until a few months ago. After driving in town for 10-15min, it would simply stall out and not re-start for anywhere for 30min to 1 day. As time wore on, it would die (without any hesitation or stuttering) sooner and sooner, and it took longer and longer for successful re-start until it’s finally would no longer restart.

I initially started by replacing the mechanical fuel pump, but then turned my attention to the ignition, and since I had planned for the TFI upgrade anyway, I figured now is the time to do it.

Replaced:
Coil
Larger cap & rotor
Plugs & wires
Ignition switch
Starter relay solenoid
Ignition mod swapped for MSD 6a

At this point, the intermittent spark continued and the old battery was giving up, so replaced the battery and had the starter checked to confirm all was in order. During the instances when it would actually start, it ran much more smoothly than it ever has before, but inevitably it would suddenly die as before. After checking/re-checking my wiring and grounds and scouring the forum discussions, I found a forum comment that was confirmed by the tech support at MSD that suggested the magnetic pickup might be the issue for the intermittent spark signal.

Since I was reusing the distributor, I marked the rotation of the distributor base relative to the block, and the rotor relative to the cap before pulling the dist to swap the mag pickup. When I reinstalled the distributor after swapping the pick up, it wouldn’t seat so that my prior rotational marks lined up exactly. I didn’t have a helper to assist in confirming Top Dead Center, but I was anxious to see if the new pick up made a difference, so I turned the key, and the starter would barely turn over. I decided to stop until I had a helper before moving forward.

The next day, I pulled the distributor and #1 plug, and while rotating the crank by hand and using a wooden dowel in the #1 plug hole, found TSD. That rotation also matched up the timing mark on the harmonic balancer for TSD. Reinstalled the distributor, and wouldn’t you know, the rotor matched up with the number one plug wire, and the base was back to its (+/-) original rotation.

Turned the key, and it fired right up, but stuttering a bit and blowing heavy smoke from the exhaust….something it’s never down before. Rotating the dist a bit smoothed the rough idle somewhat, but it still has massive hesitation upon pressing the accelerator.

So pulled the 2100 Motorcraft carb and confirmed the power valve and accelerator pump were still good. Also swapped the PCV valve that I found was clogged full of oil/gunk.

Still starts on the first crank, but with a bit of rough idle, bogs down/hesitates significantly upon acceleration (almost like it wants to backfire)…and blowing smoke

It started running rough only after the dist/mag pickup removal/re-install sequence. There also is now a loud hissing sound coming from the passenger rear of the engine.

The antifreeze in the radiator looks pristine, but the oil on the dipstick smells of fuel.

Thank you in advance for any ideas or directions you might have!

Sam

[letank]

Welcome to the asylum, this is a quite a work list, cheers to your hard work.

First, any smog equipment still installed, how many miles and how many years and miles driven since taking ownership.

I would start by trying to do some measurements, engine vaccum, at sea level an healthy engine can be around 18 to 20mmHg, if issues it can over in the 12-14 and be unsteady.

next is your timing, you will need a timing light, the one with the advance dial is a good choice to do measurement above idle speed when the mark is going to disappear from your viewing, at idle with distributor vacuum plugged with a golf T or any good piece of hardware , a good number is 12 BTDC, at altitude increase 1° per 1000 feet.

As you mentioned a calked up PCV, do you have a right pathway for the PCV to the charcoal canister... the PCV is a fancy name for a controlled vacuum leak, too much and the engine will not run properly, missing vacuum hoses will create an headache as well.

So check your vacuum diagram stuck on the valence to what you have, here is the one on my 85 -California smog

85smogTag.jpg

Also, check that your MSD has a very good ground...

I have not mention voltage at the coil... but since it is a new list of items, I avoided to add confusion.

[Bentley]

Thanks for the feedback letank!

Odometer currently at 160,000. Found this rig in the weeds along a dirt road 5yrs ago and have driven about 25k since then.

Vacuum has generally been about 16mmHg during prior carb adjustments, but I haven’t checked currently…I need to pull it out of the garage to take some readings due to the massive amounts of exhaust.

MSD is grounded direct to batt neg.

I’m perplexed on how to check timing given the location of the tag (about 10 o’clock position). The only way I’ve been able to see the tag (and timing mark) is to stick my phone up between the belts and fan.

The PO had stripped the vacuum lines and smog/air pump systems, so PCV just goes directly to the rear of carb and no connection to the canister (which was removed with the vacuum/smog)

[Stuka]

The hissing sound makes me think vacuum leak.

Take something like brake clean, and spray it around any vacuum lines, base of the carb, etc. If the idle jumps way up, or smooths out, you found your vacuum leak.

There are vacuum ports on the back of the carb, and on the back area of the intake. Possible a line cracked, a vacuum cap broke, or the carb gasket didn't seal well after reinstalling it.

[tgreese]

The hissing sound makes me think vacuum leak.

+1

With all the emissions hoses gone, it seems likely that a vacuum cap has come off or has rotted away. This will make the engine run super-lean and possibly cause hesitation and so forth. With the EGR valve gone or disabled, the engine is already running leaner than normal. At a minimum, you need vacuum connection to the power valve on the carburetor, vacuum to the vacuum advance on the distributor, and PCV connected to vacuum at the base of the carburetor. The vacuum diagram will show you the location of the vacuum taps that normally go to the emissions devices.

TSM.png

[Bentley]

Thank you all for the guidance. I've started working through the suggestions above, but daily work and the arctic temps of the past week+ have kept me out of the poorly insulated garage. Stay tuned and I'll update as I am able to tear into things again this week.

[letank]

After driving in town for 10-15min, it would simply stall out and not re-start for anywhere for 30min to 1 day.

So pulled the 2100 Motorcraft carb and confirmed the power valve and accelerator pump were still good.

Still starts on the first crank, but with a bit of rough idle, bogs down/hesitates significantly upon acceleration (almost like it wants to backfire)…and blowing smoke

BTT, thinking about it, open the air filter cover and observe the choke valve, it is electric and should open slowly, it is fed by a switch called an oil pressure switch NOT a oil pressure gauge. If the oil pressure is not correct aka low the choke will not open, the engine will stall. The switch is burried by the oil pressure sender.

It happened to me as well in the first years of ownership... the switch is a pain to reach... what I did , was to make a cage out of 12 or 10 gauge solid electrical wire to keep the choke fully opened... in my case with our moderate climate it would start no matter the temperature... except in the mid 30's...


Viewed upside down the middle loop goes over the air filter cover bolt

ChokeHolder.jpg

[Srdayflyer]

have you verified fuel pump output and pressure , i have seen the finger screen in the fuel tank rotted away and get sucked into the fuel pickup line, blocking fuel flow, tis a screen filter that rarely if NEVER gets changed there is a round access cover under the rear seat to get access to the sender and screen, i would check this as a possibility, as it is highly overlooked and being over 40 years old i doubt it is still intact,