One owner 1994 Marquis 4.6L , currently has 74k miles. Perfect car until recently. While driving at speed, engine runs great then may chug once or twice in a row, then runs great again. May go days to weeks before acting up again. The sound and feel reminds me of an older carberated engine that would occasionally backfire through the carb. Also chug causes car to jerk like you have hit something. Wierd. After chug happens, "check engine" light comes on. Light stays on momentarily, then goes back out after chug incident has passed. Have yet to check for code errors as I believe light is caused by chug and would not reveal true cause. Just wondering if anyone has heard of this problem. Sully

 

That sounds like the same problem im having. Although with mine it feels like the transmission slips a tooth or torque converter jumps a gear. Its like a "bump". Jus got it back from the transmission shop from having it diagnosed, didnt find anything wrong on the extoerior, like u-joints or mounts, but i didnt have him drop the pan cause that would have been $150 i couldnt spend. But i rane the self test with my test light and i think it came up with a problem with the EGR, but its hard to count them damn lights. The only differnce i have is mine happens evertime i drive over about 10 miles. But im no sure what the problem is.

 

90 Cougar 3.8

 

on amazon, you can get a code reader that gives the code number, not the blinking light for for OBDI for $30, it does cylinder balance test also. great investment so far----i was given a code for my EGR, changed it, and my problem slightly got better, but didnt fully go away, it might be my transducer going bad, but gonna change my filter today and see what shows up

 

ok, just got back in from changing the tranny filter, and........... i found several shards of metal that look like fingernail clippings......looks like its time for a rebuild.

 

PROBLEM SOLVED. Finally found the "chugging" problem with the 94 Mercury Marquis. The left coil pack appears to have been breaking down due to age and/or heat which was causing a voltage drop to it's associated spark plugs. This drop in voltage was causing one gigantic "miss". Since this problem was so intermittent, it was very difficult to diagnose the cause as a coil pack. It would run fine and then all of a sudden, "chug" (miss) and then be fine again until the next time. It may be days or even weeks before it would do it again. When it would happen though, man you knew it..!!! You would think if it was going bad, it would be an easy find. Anyway, replacing the left coil pack so far has the ole Marq running like a new one without any signs of the old problem. I hope this helps someone....Sully

 

PROBLEM SOLVED. Finally found the "chugging" problem with the 94 Mercury Marquis. The left coil pack appears to have been breaking down due to age and/or heat which was causing a voltage drop to it's associated spark plugs. This drop in voltage was causing one gigantic "miss". Since this problem was so intermittent, it was very difficult to diagnose the cause as a coil pack. It would run fine and then all of a sudden, "chug" (miss) and then be fine again until the next time. It may be days or even weeks before it would do it again. When it would happen though, man you knew it..!!! You would think if it was going bad, it would be an easy find. Anyway, replacing the left coil pack so far has the ole Marq running like a new one without any signs of the old problem. I hope this helps someone....Sully

 

That could be your gauge, all cars will read around 30-40psi at idle then goto 60 when accelerating.... it depends, now if you have alot of miles on the car, over 200K then it could be a weak pump.

 

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