My P5 "belted" me

Saudade — Mon, 18 May 2026 19:49:54 GMT

Well another issue and sorry for the long post.

I posted about the battery issue in my "Plugs Away" post. After replacing the battery, and changing the plugs/wires a few days ago, he goes out to run some errands and his battery light comes on again. It lights for a minute or so and goes back out. Double check the battery connections and triple check the Battery voltage under load and get the same results as before. High 13's at idle, no load. Mid 12s at idle with everything one. Rev to 2K and it's back up to high 13's even just over 14v.

So check the belts and notice the alt belt is a bit frayed and does feel a bit loose. So I replaced the the belts (pwr steering/ac as well, it was pretty bad). I also pulled the connector off the alt to spray some cleaner in it. Get the belts tensioned. Start it up and check for charging voltages, all looks good.

He goes off to run some errands and about 40 min later, tells me the battery light is on and this time won't go out. He makes it home and I put the voltmeter on and with the engine running it reads just over 12v Rev the engine and no change. The new belt also feels pretty loose and even squealed a bit when I rev'ed it (I had intended to retighten the belts after he drove it a bit anyway). Scanned for codes and got a P1631. While tightening the belt, I pulled the alt connector back off, sprayed some more cleaner in them, use my airgun to blow them out. Reconnect everything and it's charging again. I was pretty sure I fully seated the connector but perhaps i didn't and it came loose. I didn't see any signs of oxidation or other corrosion on either side of the connectors.

So it's definitely charging. I used some long alligator jumpers to extend my voltmeter leads into the cabin so I could monitor the battery voltage while driving. I also turned on combinations of head lights (with and without fogs) and AC (with different fan speeds) to see what happens.

In summary, driving with no lights or AC, voltage remains mid-high 13's even crossing 14v and coming back down but mostly high 13s. Come to a full stop, trans in drive, voltage drops a bit a first but back up to mid-high 13s. While driving (we're talking under 40 mph), voltage remains high 13s. Turning something on drops the voltage a bit but climbs back up. However with lights and AC on max, when coming to a stop, the voltage slowly drops to mid 12s. Accelerate (or just put in neutral and give it some gas), voltage climbs back up again into the 13s. My scanner is still unable to reliably test the battery (it's new), but the alt test still passes.

So while dropping to 12s concerns me, it seems to be fine once I get going. The FSM details how to check the charging system but not by measuring battery voltages (at least I couldn't find it). So before I start pulling up carpet and going through the detailed steps, checking voltage drops, etc., does this sound normal? I don't want to fire the parts cannon (again) and just swap in a new alt unless I have to do so. I certainly don't want to start tracing wires and probing connectors but will if I have to.

Thanks for any help.

Plugs away!!

Saudade — Fri, 15 May 2026 20:29:25 GMT

TL/DR version

Got a P0302 misfire code after finishing some other work (battery replacement). Pulled the #2 plug and saw it was pretty bad. Pulled the #3 and saw it was even worse. To add insult to injury, when I pulled the plug cap off #3, the small "rubber" boot came off and stayed down in the hole. Took a bit to fish it out and tore in up in the process. . so I decided to pull the others out and the rubber boot came off #1 and had to fish that out as well and tore in the process. So I ended up buying the kit to include all 4 of the plug "wires" and a set of plugs. Put everything back together and it runs great again. See pics below.

Here's the rest of the story.

My son drove to see a friend for the weekend. She lives about 70 miles away. He gets to the area and stops at a 7-11, car ran fine. He comes back out and the car wouldn't start due to a depleted battery. Gets a jump and it fires up. Goes to his girl friend's. Needs to move the car later and it barely starts. Next morning it won't start. I suggest he get a jump from his girlfriends car but leave the jumpers connected for a few more minutes to charge his battery up a bit before heading back. He drives home with no issue. Throw my scanner on, no codes, live data looks good. My scanner has a battery and alternator test feature. Alt tests fine, battery is "marginal". I put a volt meter on it and test under various loads (head lights, AC, radio, etc.). At full load at idle, it would read just over 12v. Rev to 2000+ and get high 13's, almost 14. Drop back to idle and drops back into the 12s. The battery was replaced about 3 1/2 years ago but there's no sticker or other date indicator about when it was made (it's an AC Delco). Alright, maybe it's time for a new battery. Put one in and now everything reads fine under load. He goes to run a local errand and calls to report that the engine "stutters" a bit when first accelerating from a stop in Drive. It's only for a second and then runs fine. he gets back and I drive around the tract and get the same thing. Just a quick "hiccup" and it's fine but it's repeatable. No CEL. I check for codes and there are none. Double check battery stuff and it's still good. Pull the intake tube off to peek in the TB and it's pretty clean. Clean the MAF, double check a few other connectors. All looks good. Since it only happens once warmed up and only when first taking off, I suggested we push through it and see if it eventually throws a code.

Well the next day it threw the P0302 code. I pull the coil and the plug and it looked really roasted. So I pull them all. When I pulled the coil wire off #3, the little boot on the end of the cap came off and stayed in the hole. I used a long pick to try and lift it out. It did not want to come out. I worked my way around it and it started tearing apart but I managed to get it out. So now I can remove the #3 plug. It was even worse. So I pulled the 2nd coil (on #4), pull the plug and it's just as bad as #2. The little boot on #1 also came off and stayed in the hole. After a bit more effort and swearing, I managed to get all of the pieces out. Pull the plug and it's equally bad.

Now, we've put about 40K on the car since buying it in 2017 from a local dealer (had 114K at the time).. He told me that the previous owner had the car recently serviced. I think not. Anyway, I put the new plugs (did check the gaps!) and new wires with the existing coils. Starts right up, runs smooth, no more "stutter". My son took it for a longer drive and reported it's running OK now.

So here are the plugs:

#1, #2, #3. Note 1 & 3 have almost no electrode left. (these are platinum plugs). I measure the gaps and #3 measured almost .070"!! #2&4 were around .050".

1, 2, 3, and 4. (in order). The ceramic bases look terrible as well.

The boots from #1 and 3#

So how many miles do you think those plugs have on them. I find it odd that #1&3 look the same but different from #2&4. I'm guessing the PO had the issue with the boots sticking and only replaced #2&4. What do you think?

Fortunately, he took it for smog testing before he left last week and it passed. Now that I cleared the codes, it will take a while for the readiness monitors to complete. I could not get it smogged until they do.

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My P5 "belted" me

Plugs away!!