96 "88" Has Intermittent Misfire - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 04-27-2014, 09:29 PM   #1
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Default 96 "88" Has Intermittent Misfire

Aloha All,
The old "88" is starting to give trouble. Bought the car back in 2007, and it had 64k miles on it at that time.
Had a few problems through the years, but nothing out of the norm. The plugs and wires were replaced about 6 months ago @ 107k miles because the engine developed a miss now and then. The miss went away once the new plugs and wires were installed. I would like to add that OEM plugs and wires were installed.
Last week the engine developed a miss again. I thought that it was kind of strange that a new set of plugs and wires started failing after such a short period of time. The car now has just over a 110k on it, so I doubt that the miles could be an issue.
The plugs were pulled, and all looked fine, with the exceptions being #3 and #4. The 3 and 4 plugs looked fine as well, but they did differ in color enough that it was noticable. Almost as if they had a little richer fuel mixture. All plugs tips were white with just a tad of tan on one side of the tip. The number 3 and 4 plugs had a slightly larger and darker deposit on their tips.
My first thought was a failing coil, but 3 and 4 are on different coils.

Another issue. Once in awhile a code for the purge solenoid will set. I believe this is due to a poor seal at transmission vaccum modulator line connection. That connection is on my list of needs fixed asap.
I might be wrong, but I do not feel that the miss and the purge solenoid code are related. Any thoughts on this are welcome.

The miss was minor, and started showing up after the engine was hot, and when the engine was under a load, such as taking off from a light, or climbing a hill.
The miss is somewhat worse now, but I guess that isn't bad enough that the scan tool can detect it.
Any tips on how a guy can find out if one or more of the coils on this 3.8 are going south?
Thanks for any tips, or advice.
Aloha.
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Old 04-28-2014, 12:28 AM   #2
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Purge solenoid code has nothing to do with the vac line to the modulator...they are separate lines.....however, a vac leak can cause a possible lean misfire or hesitation....

You replaced the wires and plugs.....if they are ok, could be a coil.....A spark tester would tell if the coil output was ok.....
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Old 04-28-2014, 02:14 AM   #3
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There seems to be some confusion about the vacuum modulator and the purge solenoid relationship. For some reason, the modulator keeps coming up as part of the problem, and maybe what I thinking is the purge solenoid isn't, but if what I'm thing is the purge solenoid actually is the purge solenoid...it shares the same vaccum line as the modulator. IDK, there'* 3 different parts that fit the bill of being the purge solenoid, and I'll be darned if I can tell which one it actually is. According to a couple of pictures, and locations of the solenoid, the one that I'm looking at is the part.
I understand about relationship between a vaccum leak and a lean burn situation. This doesn't feel like a lean condition. There'* no sign pinging, and it flat falls apart when pushed. It'* back to where it was before the new parts were installed.

I did find one coil that read about 10 ohms under the other 2, and although I doubt this is the cause, I replaced the coil with a know to be good used one. I have yet to test drive the car since the coil replacement because it'* late, and it takes the car awhile to act up, but tommorow is another day.
Thanks for help.
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Old 04-28-2014, 08:26 AM   #4
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on 3800'* the crap plastic lower intake manifold gaskets and crap plastic upper intake would be number two cause on my mind, second to plugs/wires. coils wouldnt even cross my mind unless you had 150 to 200k. are you loosing any coolant? has either been done already?

there are felpro aluminum update lim gaskets and dorman upper kit as well as aluminum elbows, the dorman kit comes with new egr design and all the other gaskets.
https://www.gmforum.com/mechanical-1...2005-a-304071/
https://www.gmforum.com/mechanical-1...ts-l36-297702/
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Old 04-28-2014, 11:42 AM   #5
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The miss was minor, and started showing up after the engine was hot, and when the engine was under a load, such as taking off from a light, or climbing a hill.

That is a "classic" secondary ignition problem....new plugs and wires?.....if ok, definitely check out those "18 year old coils".....
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Old 04-28-2014, 01:12 PM   #6
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i take care of a few 3800'* and have cars with the same pack, and dont remember replacing a coil, and most of them had 2 to 300k. last thing i remember putting a coil on was my 2.8 cutlass, had like 200k. sometimes you have those symptoms and all you have to do is clean the terminals with scotchbrite or fine sandpaper and or the tabs on the icm and put some dielectric grease on it.

if you are loosing coolant though it will act similar(misses that are otherwise unexplained). i have had to do the upper at least on all, twice on the bonnie i have now and the last time i did the lower too and it was awful
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Old 04-28-2014, 11:04 PM   #7
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Wow, I have replaced many coils.......some with way less than 100K on them.....

Spark tester detects them easily......replaced more on 3.1/3.4'*, than on 3800'*, but I have replaced a lot of them.....before the 3.8'* went to 3 individual coils, we were replacing those Single Magnavox coils all the time....while 3 coils was a huge improvement, they still had failures....

In some situations, the coil was replaced because of arcing between the ignition wire and the coil terminal....so bad that sanding/cleaning the terminal, made a poor connection with the new wire....and usually led to a comeback later on....
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Old 04-29-2014, 02:10 AM   #8
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Quote:
Originally Posted by jwfirebird View Post
on 3800'* the crap plastic lower intake manifold gaskets and crap plastic upper intake would be number two cause on my mind, second to plugs/wires. coils wouldnt even cross my mind unless you had 150 to 200k. are you loosing any coolant? has either been done already?

there are felpro aluminum update lim gaskets and dorman upper kit as well as aluminum elbows, the dorman kit comes with new egr design and all the other gaskets.
https://www.gmforum.com/mechanical-1...2005-a-304071/
https://www.gmforum.com/mechanical-1...ts-l36-297702/
I do have my concerns about the intake, and even bigger concerns about the head gaskets.
The problem at hand seems to have been cured...for now. As I said earlier, I doubt that the one coil with the 10 ohm lower reading was at fault, but hey, the engine is running fine since I replaced it.
Replaced some really bad vacuum line connections, but it'* still giving a p1655 code. Guess I'll replace the purge solenoid and see if it cures the problem.

Thanks for all of the help guys.
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Old 04-29-2014, 02:12 AM   #9
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Quote:
Originally Posted by Tech II View Post
The miss was minor, and started showing up after the engine was hot, and when the engine was under a load, such as taking off from a light, or climbing a hill.

That is a "classic" secondary ignition problem....new plugs and wires?.....if ok, definitely check out those "18 year old coils".....
My thought as well.
Thanks.
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Old 04-29-2014, 02:18 AM   #10
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Quote:
Originally Posted by jwfirebird View Post
i take care of a few 3800'* and have cars with the same pack, and dont remember replacing a coil, and most of them had 2 to 300k. last thing i remember putting a coil on was my 2.8 cutlass, had like 200k. sometimes you have those symptoms and all you have to do is clean the terminals with scotchbrite or fine sandpaper and or the tabs on the icm and put some dielectric grease on it.

if you are loosing coolant though it will act similar(misses that are otherwise unexplained). i have had to do the upper at least on all, twice on the bonnie i have now and the last time i did the lower too and it was awful
I had one coil that read a little lower than the others. I replaced it and the engine now runs fine again, but...I'm not so sure that removing and installing the coils didn't make a better connection somewhere.

Thanks for the help.
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