Buick Riviera Tune Up

[Adam]

The previous owner told me the car "just had a tune up". Turns out that wasn't really true.

I've been dealing with random misfires and engine stalling for a little while. I finally decided to look at the state of the ignition system. After some investigation, it appears that the "tune up" consisted of replacing one ignition wire and spark plug. Sigh. How could I tell, you ask? The replaced wire didn't have the OEM cylinder number labelling on the wire. Also all the other cylinders still had that, so they were still original at 130k. Conveniently, when they replaced the one ignition wire (cylinder #4, middle rear) they threw away the factory plug heat shield. Because of course they did. In related news, the plug boot had heat damage. I found one on Amazon.

https://www.amazon.com/ACDelco-8006-Ori ... 000K04C36/

The other wires were in reasonable shape except for #6 (drivers side rear). The wire jacket was broken all the way through, Iwas only partially was sure I had found the source of the misfire.

I also found the "tuned up" cylinder now had high performance Autolite Platinum. Which might have been an improvement over the Champion Platinum plugs in the other 5 cylinders. Regardless, there are now all AC Delco plugs.

Figuring I had fixed it forever, I went to leave for a test drive. Not fixed. During the parts replacement, I had noticed that two of the ignition coils had been swapped around. The OEM coils have the cylinder numbers printed on them and the front two had been swapped. Figuring these were due (and cheap) I replaced all 3 of them. Now it is fixed forever.

One thing to note is with all of the misfiring and stalling, I never saw a Check Engine Light for misfire. This is due to the Wasted Spark system the 3800 (and other engines of that era) used. Each coil has two leads for plug wires and fires both of them at the same time. That means that while the cylinder on the compression stroke fires just before TDC, the cylinder that is just before TDC on it's exhaust stroke fires as well, which doesn't really do anything other than making the timing calculation simpler and system cost less. As long as one of the two leads on the coil fires, the PCM doesn't detect a misfire. Besides the 3800 V6, they also used this system on most of the 4 cylinder engines of the era. Like Ed's Saturn SC2.

No, I didn't take any pictures.

[Adam]

I took a picture today. I can't share it because the maximum allowed upload file size is 5MB. So I need to re-size my photo for upload? What is this, 2001?

[kevm14]

Try now. I submitted a ticket to modify PHP.ini. I couldn't do it myself because I don't really control my own Apache (at least I don't think so). I suggested 100MB and that is what they set the flag to:

Code: Select all

upload_max_filesize = 100M

[Adam]

Nope, I still get:

The file is too big, maximum allowed size is 5 MiB.

[Adam]

Do you/they need to restart apache?

[admin_repair]

Board setting was 5MB. I changed it to 0 (unlimited). Also raised max attachments (per post) to 25.

EDIT: Didn't take because ImageMagick path was /usr/bin/ and apparently that was wrong. I removed that link and it finally took the changes. I don't know if it needs that utility to make the thumbnails. Since the path was not found it will probably continue to work fine. Let's find out.

[Adam]

Fixed forever?

[Adam]

Hooray!

Now on the the rest of the story. I thought it was fixed after an extended test drive on Saturday with no issues. Then Monday I initiated a cold start, turned on the A/C and put it in reverse, rough running ensued. I drove it anyway, of course, and the "stall during a turn" problem didn't come back. Yay?

Anyway, I had ordered a throttle body gasket with the coils, so I figured I'd give it a good cleaning for good measure.

So dirty. The moist parts might be related to me not draining the coolant some before unbolting the throttle body.

Figured it might be IAC passage related, but that didn't look too bad.

I cleaned it thoroughly.

Fixed? Nope.

So what's next? I was checking the vacuum harness for cracks and breaks in the rubber connectors and I broke the rubber T on the front of the engine that provides manifold vacuum/boost to the MAP sensor and the fuel pressure regulator. Sigh. Conveniently, you can still order the harness, so stay tuned!

[Adam]

Fun fact, the throttle body is branded at 'Hitachi'.

[kevm14]

I think the VQ30DE used a Hitachi MAF. I could check. It's in my basement.

You could use the Tech 2 to see if that roughness is registering as misfires. I guess it doesn't have to be ignition. It does sound vaguely like IAC type issues though. The actuator could be a little tired and less responsive than ideal. Could look at commanded vs actual IAC values during that type of transient event and see how well it keeps up.