Heavy shaking at high rpms.. any ideas?

[demonte1997]

I was entering the interstate and accelerating quickly to pass an 18 wheeler. I think the tach read around 5-6K rpms when the car all of a sudden began to shake pretty violently. I let off the gas the everything returned to normal.

Just for background, I was 2 hours into my 3 hour trip. Most of the trip was highway. I finished the drive without the problem reoccuring but I made sure to never rev past 3Krpms.

The car has a history of not starting occasionally ever since day 1.

The fuel injectors, plugs and PCM were replaced at 5Kmiles.

Car has about 42K miles on it now. Before this happened, I've heard some jingling any time the engine is revving high (almost sounds like a timing chain). I thought it was just pinging from the 87 octane. Not sure now..

Any ideas for what is going on? I thought it was the tranny, but a few people have said it probably isn't. If it's the engine, I don't understand why it didn't trigger a SES code.

Thanks in advance fellas. I'm hoping to troubleshoot this myself, so I don't have to rely on the dealership.

[SappySE107]

It sounds like either the coil pack or the knock sensor going crazy and cutting spark timing to its max (15 degrees on the OBD1, not sure on your computer). The coils really only have a problem with high heat, which yours are in no place to really have this condition. That doesn't mean its not a coil but at that milage and if it doesn't happen all the time, especially low rpm, then I would go with the knock sensor. However that would throw a code when it happens. Very odd indeed.

Jingling at high RPM doesn't make much sense. That is not a good sign. I would use midgrade and see if that helps. Premium isn't worth it but with 9.7:1 compression and high RPM, mid grade is a good choice.

It could also be your plug wires, but at that it could be a fuel filter as well.

[demonte1997]

Thanks Ben. I was thinking coils..

This engine has been pretty finicky from the start. I'm not sure what everyone else's LQ1 does when they start it but mine buzzes for at least 10-15 minutes while the cams wait to get oil. (I think that's what causes that metallic sound). Sometimes I try to start it and it wants to start, but won't fire. It will even backfire when it's first started.. only happens occasionally and I guess that is due to the rich condition when first firing up the engine.

I love the engine, don't get me wrong. Just don't want it to leave me stranded.

[SappySE107]

Yours should have the revised oiling setup so there isn't any issue with oil on startup. I dont have any buzzing or clicking or anything, its smooth as can be for the cam mod and porting. Backfiring...wow. I dunno but it doesn't sound like its running 100%.

[Lyle's GTP]

Yah, you got some problems there. Even with the old oiling system, It wouldn't take 10-15 minutes to stop making noise. Maybe a couple max. Sounds like bad timing, either electrical, or mechanical. That's my guess. My ignition would only act up in high gears and low speeds. What year?

Lyle

[demonte1997]

It's a 1997.

Could it also be a weak injector? That was my only other idea.

This car has received 87 octane it's whole life and it was never driven hard. It failed the NO2 test for emissions when I first bought it. Chevy told me to drive it kind of hard to blow the NO2 out of there.

My uncle had it before me and he really never drove it at all. It had 21K miles on it when I bought it approximately 3 years ago. Perhaps this engine wasn't broken in properly.

I don't think the fuel filter has been changed ever... unless Chevy does it at their 30K mile service.

The timing on this car cannot be that great because I tried to pass a Lincoln Towncar on the highway the same trip I described above and the Towncar was having no trouble keeping up with me even when I had it at WOT. It only has 40K miles but it's 7 years old and still is running on the original timing belt. I'm guessing the belt has stretched a little since the engine was originally timed.

What can I say? This car is an enigma.

[ryan.hess]

It's a 1997.
Could it also be a weak injector? That was my only other idea.

Doubtful. It wouldn't idle properly (or at all), since at idle, the time open is the minimum, if it were weak, it wouldn't open at all.

The timing on this car cannot be that great because I tried to pass a Lincoln Towncar on the highway the same trip I described above and the Towncar was having no trouble keeping up with me even when I had it at WOT. It only has 40K miles but it's 7 years old and still is running on the original timing belt. I'm guessing the belt has stretched a little since the engine was originally timed.

It is entirely possible that your timing on one bank slipped a tooth. That would cause horrible shuddering at high RPMs, and potentially no power. Of course, that's kind of a pain to check... I'd suggest inspecting the plug wires carefully... If one isn't seated right, or has a nick, it could "cut out" one cylinder at inopportune times (and possibly only at high RPM ranges where vibration is the most). But then, those towncars have a mighty V8, so you're comparing sticks and banannas.

[Cliff8928]

Man, a towncar is just a overweight crown-vic... a DOHC should be able to have no trouble overtaking one..

Cliff Scott
89 BerettaGT
89 Volvo740

[dohcfiend]

buzzing at startup

my 94 done that be4, it was a buzzing/grinding sound? for me the modulator on the tranny was the culprit it had a kink in the hose.

[demonte1997]

Four things:

1) I agree that the DOHC shouldn't have trouble edging out a Town Car.

2) Would the transmission make that sound when it's just in park? After 15 minutes of buzzing, the sound goes away. It's only on cold starts.

I've only driven it once when it was buzzing (usually I let the car warm up until the sound goes away). The car sounds pretty funny.. the buzzing coincides with the revs b/c it buzzes a little louder as the engine winds up.

3) I tried to get the car to buck again by running it down one of the back roads here. I had it up to 6Krpms and it was perfectly fine. How is that for troubleshooting? The only differences between this and the time before are that this time the car was on flat ground and it had only been running for 15 minutes, rather than almost 3 hours.

4) Could the shaking have been caused by impurities in the gas?

Thanks for all the suggestions thus far, I really appreciate it.

[dohcfiend]

for mine the buzzing would persist only in park, but i didn't try neutral and i didn't wait 15 min to see if it went away. by opening the hood i could easily tell that it was coming from the tranny(of course i don't have an airbox in my way either). if i reved it a little it would go away but would return as soon as the car returned to idle speed. it was luck really first i checked the fluid level it was ok but i added a 1/4 of a quart. then i saw the vacuum modulator i grabbed it and turned it slightly and by doing that it straighted out the vacuum hose and the buzzing stopped.

i am not a tech or anything but i will throw this out there. the jingling or whatever could it be a tooth or metal contamination in the diff?

[gpse3400]

Change the spark plug wires and be done with it.