Help interpreting scan tool data - Page 2 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 09-14-2005, 09:10 PM   #11
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Anyone think its possible that he has some hella bad gas? I noticed just a mentioned earlier that the EGR was dropping off the face of the earth... And the timming for Bill is all over the place.... What the heck is going on there?

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Old 09-14-2005, 09:12 PM   #12
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Yeah - the hard way- copy by hand in car, come in house, type up on spreadsheet, print and scan for me. Oh yeah, I shouldn't leave out- try to save and lose the file!. Thanks, Don for going to the trouble, EGR is different. But mostly, so is KR! Notice how your O2 cross counts are way lower than mine too. Probably because your engine is in tune and mine isn't even close. BTW, you came very close to matching the performance parameters- That is skill!

Would have been here sooner, but I just came in for dinner after installing 12 new lifters. I haven't fired it yet, but I'll tell you what- I have kind of a bad feeling about that being the problem.

Will- I removed the crossover pipe to remove the LIM and all the exhaust parts looked really clean and tight. But I did not inspect them specifically looking for problems. I will check that stuff out when I fire it up later tonight.

Back out to top up coolant and fire the booger up!

Thanks very much for the help so far, guys. This is really sucky performance.

I just wish I knew a little more about what I was looking at when I see the scan data.
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Old 09-14-2005, 09:42 PM   #13
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If you ask me, I don't think that the EGR is functioning right, and your O2 Sensor millvolts are fine. They're supposed to jump high/low for the rich/lean conditions.
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Old 09-14-2005, 09:48 PM   #14
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New lifters and guess what? The tick tick tick tick tick tick tick tick tick tick is still there. Sounds just like a bad lifter but not likely now huh? So I plug in the scan tool in the driveway and slowly raise the rpm watching KS count. As the speed increases suddenly the counter starts going crazy picking up one of the several knocking sounds coming from the engine. With the hood up, and the driver'* door open sitting in the driveway next to the garage and house you can hear all kinds of light knocks. I know the balance shaft bearing is a little worn so that could be one. Now I am wondering if I have a bad piston pin. Oil pressure is OK and the sound is higher frequency than a rod knock. I have heard a lot of those in 3800s.

Don - I don't think it'* bad gas cuz the problem has been around for several tankfuls. Bill - Can a cracked exhaust produce a metallic knocking sound or am I resigned to pulling this engine? (I think I know the answer)
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Old 09-14-2005, 09:55 PM   #15
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Quote:
Originally Posted by bill buttermore
New lifters and guess what? The tick tick tick tick tick tick tick tick tick tick is still there. Sounds just like a bad lifter but not likely now huh? So I plug in the scan tool in the driveway and slowly raise the rpm watching KS count. As the speed increases suddenly the counter starts going crazy picking up one of the several knocking sounds coming from the engine. With the hood up, and the driver'* door open sitting in the driveway next to the garage and house you can hear all kinds of light knocks. I know the balance shaft bearing is a little worn so that could be one. Now I am wondering if I have a bad piston pin. Oil pressure is OK and the sound is higher frequency than a rod knock. I have heard a lot of those in 3800s.

Don - I don't think it'* bad gas cuz the problem has been around for several tankfuls. Bill - Can a cracked exhaust produce a metallic knocking sound or am I resigned to pulling this engine? (I think I know the answer)
I don't know what to say there... I hope its not the engine... I don't think I have ever seen my car pull timming... I have seen the knock counts rise, but the KR was always 0*... I have a lifter tick, But even at idle you'd have to really listen for it...

I'm just not sure..

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Old 09-14-2005, 09:56 PM   #16
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You are running a little lean but so is jr'*...
How were your lower intake manifold gaskets when you replaced the lifters?
Maybe they were leaking oil?
What do your plugs look like?
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Old 09-14-2005, 11:05 PM   #17
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As Bill mentioned, check the exhaust manifolds for cracks, or a bad gasket at the downpipe or cat.

Also, have you had the knock sensor out at any point? Sometimes they can become packed with sludge or worse, it could be over torqued. Series II spec is 14 ft. lbs. torque, any more and you risk the sensor hearing false knock.

Cheers,
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Old 09-15-2005, 12:12 AM   #18
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The cracked manifolds or exhaust leak will be REAL KR. But with the frequency you're getting a lifter could be the cause for false. Your thoughts on a piston pin (the pin holding the rod to the piston itself) could have merit, as on the L27 and L36, they're floating pins, where on the L67 they have bearings. There'* so many things, you're not likely to narrow it down unless you get the stethescope out. And I'd use a real mech'* scope, not a screwdriver for this one.

Do me a favor to rest my mind. On a COLD engine, before you fire up, spray some soapy water on your manifolds and heads. ALOT. While it'* wet, fire it up and look for bubbles. use a 50/50 mix of dish soap and water. You have to be quick before it starts to heat up and evaporate. Try to rule out an exhaust leak first.

But in the long run, if you HEAR something, odds are the knock sensor can too. I have to trust your ear on this one. If you hear something, odds are it'* false. If you don't, it'* got to be real. This will determine where you look for the problem.

If you think it'* a lifter, try a bit of diesel or marvel mystery oil in your engine oil to thin it out some. Any lifter clatter should go away temporarily.
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Old 09-15-2005, 12:27 AM   #19
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Quote:
Originally Posted by Foghorn
As Bill mentioned, check the exhaust manifolds for cracks, or a bad gasket at the downpipe or cat.

Also, have you had the knock sensor out at any point? Sometimes they can become packed with sludge or worse, it could be over torqued. Series II spec is 14 ft. lbs. torque, any more and you risk the sensor hearing false knock.

Cheers,
I'm trying to think of a way to check it for cracks with smoke or something easy, but I can certainly use my mechanic'* mirror and inspect for any visible cracks. Could be a bad gasket at the cat - though it has never been apart since I have owned it. The donut on the downpipe is new, and the joints on the crossover are clean and nice.

Now, that overtorqued business is a distinct possibility. I had this motor out last winter to install new seals all around and do work on the LIM and UIM and stovepipe. I did remove the knock sensors, and they were covered with sludge (probably helped to lower their sensitivity). I cleaned 'em out real nice. I recall that one of the sensors came apart when I removed it, so I had to buy a new one. I bought an AC delco. But I am not sure at all if I was aware of the proper torque spec. I remember that I used thread sealant on the old sensor after wire brushing the threads to insure no coolant loss. The new one went in with just the red stuff that comes on the threads. This is a distinct possibility - and I am grasping at it since it is so much easier and cheaper than a complete tear-down. BTW, I have read here to use RTV silicone on the threads, while other sources say use nothing. I don't want to be leaking coolant here. With my current situation, I would not be upset if a little RTV made my sensors a little less sensitive.

I will investigate these things tomorrow when it is light outside, and let you all know.
Thanks for the help,
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Old 09-15-2005, 12:32 AM   #20
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Bill,

The RTV will not reduce the sensors sensitivity unless you entirely coat it with the stuff. On the threads is fine, and preferred. You need SOMETHING there to make sure any movement of the sensor to the block will not be interpreted as knock. The knock sensors listen for knock through the coolant. As long as the END or face of the sensor is clean, use whatever you prefer on the threads.

It might be interesting to disconnect them one at a time for back to back scans.

Might help isolate the problem to the front or rear sensor or to the front or rear bank for false KR.
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