Shaky Idle

[OB1214]

Received my New to me, Basically brand new Compression tester in the mail the other day and still have had enough time to take the plugs out and test however I was doing some reading about the PCV system and came across this website https://www.aa1car(DOT)com/library/pcv.htm
and scrolling about halfway down the page under the PCV Problems it states the following:

"On late model vehicles with computer engine controls, the engine management system will detect any changes in the air/fuel mixture and compensate by increasing or decreasing short term and long term fuel trim (STFT and LTFT). Small corrections cause no problems, but large corrections (more than 10 to 15 points negative or positive) will typically set a lean or rich DTC and turn on the MIL.
Problems can also occur if someone installs the wrong PCV valve for the application. As we said earlier, the flow rate of the PCV valve is calibrated for a specific engine application. Two valves that appear to be identical on the outside (same diameter and hose fittings) may have different pintle valves and springs inside, giving them very different flow rates. A PCV valve that flows too much air will lean the air/fuel mixture, while one that flows too little will richen the mixture and increase the risk of sludge buildup in the crankcase."

I was curious to know if this is true? I find it hard to believe that this little PCV Valve is the cause for my issue however I figured I would share my finding and let you guys who have more experience confirm or deny what I think.

The PCV Valve in my truck currently is good, and you can hear the ball rattle around if you shake it, but it might not be the correct one.
The markings on the valve read:
AC ROCHESTER
TYPE CV 769 C

If anyone can confirm or deny the statement I read from the website or if this is the proper PCV Valve for a 96 k3500 With a gen 6 454 Vortec that would be great.
Thanks,
OB1214

 

[Schurkey]

PCV valves suck. There has been a million part numbers, and nearly zero information on what makes them different from each other--flow rates, vacuum sensitivity, etc.

SURE, the wrong PCV can cause mixture issues, but I won't say that it's likely.

Look up your vehicle on a parts-store web site--O'Reillys is pretty good, and they may sell AC PCV valves. See which one they recommend.

 

[OB1214]

PCV valves suck. There has been a million part numbers, and nearly zero information on what makes them different from each other--flow rates, vacuum sensitivity, etc.

SURE, the wrong PCV can cause mixture issues, but I won't say that it's likely.

Look up your vehicle on a parts-store web site--O'Reillys is pretty good, and they may sell AC PCV valves. See which one they recommend.

Ok thank you I will report back in a couple of days when I have my compression results.

 

[PlayingWithTBI]

PCV valves suck

That was 2/3rds of a pun - P U

 

[OB1214]

So I finally ran a Compression Test on my motor and I am extremely pleased to say I have 150 psi in ALL 8 cylinders, this motor has 242,000 miles on it (fun fact, that's the same distance to the moon... I just arrived at the moon about 3,100 miles ago hahah) Anyways, I tested the compression with my Mac Tool compression gauge, and 150 psi is within spec with a high of 150 psi and a low of 105 psi.

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I retested my vacuum and had 19inHg.

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My cold oil pressure is 75 psi, warm at an idle 20 psi and cruising is 40 psi. This is checked through the gauge on the dash; when I get back home from school in about 3 weeks, I will confirm this with my mechanical oil pressure gauge.
My father did some reading and forwarded me a post on:
https://www.chevytalk(DOT)org/fusionbb/showtopic.php?tid/338629

Post #2648178 (4th post down from the top) "For ALL HEI and MSD< gaps NO LARGER than .045 are the maximum. GM had used .060 and .080 to try to capture a fuel/air molecule to light off as they went into more and tighter emissions regulations and tuning.
Those .060 and .080 gaps did one key thing, they killed both in cap HEI coils AND HEI modules, quite regularly. Only when the gaps were reduced back down to .045, did the overload induced failures cease." -IgnitionMan

This may be why I fried BOTH my HEI coil and ignition module more than once.
Since I already had the plugs out, I replaced them with some AC Delco and gapped at 0.047" my old plugs only have about 7,000 miles on them but I didn't have AC Delco's. The old plugs that I originally bought I gapped them to 0.060" as the book requests.
The plug in the picture is what all 8 plugs looked like, none of them were covered in oil, or gasoline when pulled out, these were the plugs with about 7,000 miles on them.

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When I buttoned everything up, I fired it up and was STILL running with a little shake. I took the truck for a spin and plugged my scanner into it and my fuel trims have gone down a little more which is good.
Driving at 1565 RPM
Bank 1: +7.0%
Bank 2: +4.7%

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I also replaced my PCV valve for all of 2 dollars to 'check' that off the list, and no change.
I was wondering what you guys think, and what else I should test. Please let me know.
Thank You,
OB1214

 

[Schurkey]

1. For 7,000 miles, those plugs look terrible. You've got something in the combustion chamber that shouldn't be there--oil, most likely.

2. When you're buying those fine-wire spark plugs, you're not supposed to open or close the gap from the manufactured setting. Doing so can damage the fine-wire center electrode, or break-off the platinum or iridium nugget on the side electrode. If the plugs aren't gapped right to begin with...there's a fair chance that they're counterfeit plugs.

 

[OB1214]

1. For 7,000 miles, those plugs look terrible. You've got something in the combustion chamber that shouldn't be there--oil, most likely.

2. When you're buying those fine-wire spark plugs, you're not supposed to open or close the gap from the manufactured setting. Doing so can damage the fine-wire center electrode, or break-off the platinum or iridium nugget on the side electrode. If the plugs aren't gapped right to begin with...there's a fair chance that they're counterfeit plugs.

I never have to top off oil, between changes. Every 3,000 miles give or take 100-300 miles over. Doesn't seem that I am burning oil either or leaking it. If i was burning oil wouldn't I not have compression?
Bought my those old plugs from my dealer at parts authority and they are ngk.
Let me know what you think.
OB1214

 

[Schurkey]

My Trailblazer goes 26,000 miles between oil changes. 3000 miles is CRAZY with modern oil, feedback fuel injection, and overdrive transmissions, unless you're working the truck to it's rated capacity (or beyond.) Mind you, I change the filter and top-off oil at 13,000 miles, and I typically need to top-off the oil a few times--it burns a quart to 4,000 or so.

Consider going 6,000 miles, then send off an oil sample for lab analysis. I bet they tell you the oil is still fit for service. Then go 9,000 miles, and send another sample.

I'm going to change oil on my plow truck at about 3000 miles, sometime this spring. It'll be four and a half years since I bought it, and this'll be the first oil change. I'll send a sample to the lab and see what they say.

Compression is handled by the top ring. OIl control is handled by the "oil ring" and the second ring. You absolutely can have compression and still use oil. It could be coming down the valve guides. It could be sucked past the PCV baffles..

The deposits on your plugs at 7,000 miles are excessive. I can't tell you whether that's from oil, or antifreeze, fuel deposits, or something else.

Recommended plug gap is .060 for all gasoline engines in '97. Same plugs, too--AC 41-932 (or equivalent.)

 

[WhiteUCF]

Deposits like that at 7k aren't exactly normal BUT could be in your case. Not knowing how the engine was treated and maintained in the past could be indicative of carbon deposits being burnt up since you've put the effort into making the truck happy with new parts. Taking into consideration the evap issue you're having, and not having a quality part, in theory could be your exact issue. Since the new parts fixed it for a minute, get a good one and see what happens after that.

Here's what I'd do before changing parts. Give it the ol' Italian tune-up. Put it to the floor. Do it for Dale. Get that old gunk burnt out. Sometimes it's that simple. A lot of us tend to think more than we should. Being a former European car tech and dealing with those difficulties, sometimes the simple things go overlooked because you know too much. The simple things become complicated because what's actually just a bad coil pack makes your brain think capacitors in the ecm.

Schurkey, what oil and filters do you use? How did your tests come back? We all know modern oil can do it and the filter is the failure point, which you're obviously smart enough to abide by. I'm sure we've all speculated trying it but I surely don't have the stuff between my legs to actually try it!

 

[OB1214]

My Trailblazer goes 26,000 miles between oil changes. 3000 miles is CRAZY with modern oil, feedback fuel injection, and overdrive transmissions, unless you're working the truck to it's rated capacity (or beyond.) Mind you, I change the filter and top-off oil at 13,000 miles, and I typically need to top-off the oil a few times--it burns a quart to 4,000 or so.

Consider going 6,000 miles, then send off an oil sample for lab analysis. I bet they tell you the oil is still fit for service. Then go 9,000 miles, and send another sample.

I'm going to change oil on my plow truck at about 3000 miles, sometime this spring. It'll be four and a half years since I bought it, and this'll be the first oil change. I'll send a sample to the lab and see what they say.

Compression is handled by the top ring. OIl control is handled by the "oil ring" and the second ring. You absolutely can have compression and still use oil. It could be coming down the valve guides. It could be sucked past the PCV baffles..

The deposits on your plugs at 7,000 miles are excessive. I can't tell you whether that's from oil, or antifreeze, fuel deposits, or something else.

Recommended plug gap is .060 for all gasoline engines in '97. Same plugs, too--AC 41-932 (or equivalent.)

26,000 miles on an oil change. Now thats how you kill your motor. I run 10W30 conventional. Besides my shake in the idle the motor looks, and is within all top end specs, just like a new motor that rolled off the showroom floor. I'm making compression, EVERYTHING in the cylinder is sealed; if a valve seal or stem seal or rings were bad I wouldn't be making compression, and I will also have excessive amounts of blow by. Also note I don't have any blow by in the crank case. It's not a cylinder related issue I can be certain. Spoke to my buddy who use to rebuild small and big blocks and raced stock cars about the issue. He said almost exactly what IgnitionMan said as I quoted in my last post GM was trying to make their emissions tighter and gapped the plugs much bigger, which actually made the motor run like poop he said to gap them at 45 thousands. He also said that the plugs were mostly due to lean condition and that my timing was fine. He did tell me that since it have a little shake in the idle and not at 1000, 2000, 3000 etc it's mostly because there's "slop" in the timing chain at an idle, and the chain becomes tighter as the motor revs up. I will be looking at this with a timing light and lock out the advance timing in the distributor. Keep in mind that my motor has more miles than GM thought it would get. They say the timing chain lasts the life of the motor. BUT what IS the life of the motor 100k 200k 250k. This leads him to believe and has convinced me that the chain is tired and should probably be replaced. I will be looking there for the time the being because I'm making perfect compression, adequate fuel pressure, no vacuum leaks, and spark. The timing in the motor with the chain may be slightly off due to slack. My fuel trims have gone down significantly today as I took it on a road trip and drove about 250 miles.
I will post pictures tomorrow of my scanner with fuel trims at different engine speeds. The fuel trim definitely went down because I regapped the plugs to 47 thousands. That and the PCV were the only thing that I have changed since the start of this thread.
OB1214