Buick running issue problem opinions

Re: Buick running issue problem opionions

Check manifold vacuum to see how much vacuum you have at idle and record it. Watch the needle to see if it bounces at all, it should stay steading. A bouncing needle will indicate possible valve problem.

Also you should take a pair of needle nose pliers and crimp of all vacuum hoses one at a time to see if that changes anything. Check things like the brake booster, pcv valve, vacuum advance etc.

When you did the leak down test did you use a proper leak down tester? or just a hose from your compressor? Was the piston @ TDC? You need to listen for the leak and where its coming from, if its getting pass the rings you will here the air leaking from the hole with the oil filler cap removed, if its leaking past the intake valve you will here the leak coming from the carb, if its leaking past the exhaust valve you will here it coming from the tail pipe. It is NOT acceptable at all to leak past the valves.

When I do a compression test I pull all the plugs one at a time and inspect the plugs carefully for carbon tracking from a crack, look at the color of the plugs to make sure there isn't a oil problem from a bad oil ring or valve guide.

Same with cap and rotor, check for any kind of tracking etc.

Check the spark plug wires with a ohm meter to make sure they are good. Chris

 

Re: Buick running issue problem opionions

If #3 and #5 are weak when doing a cylinder balance test, I'd re-test #2 and #8. Misfire could be idle-mixture fault and/or a cracked intake manifold exhaust crossover passage affecting one side of a two-plane intake manifold (unintended EGR).

 

Re: Buick running issue problem opionions

Check out this page for tips on interpreting readings from the vacuum gauge:
http://www.secondchancegarage.com/public/186.cfm

 

Re: Buick running issue problem opionions

Nice site :TU:

 

Re: Buick running issue problem opionions

I did check for vacuum leaks several times. I checked and removed hoses and sprayed all around everything several different places. No leak or change ito engine RPM Pulled all the plugs and checked for fouling and carbon tracking. Odd enough they look like they are all firing and the same. The first time I did a Leak down test I used a tester. This time I removed the rocker shafts and screwed a fitting in the spark plug hole and pumped 120 PSI of air in each cylinder. (which held very nice) I then tapped each valve to see if the air would escape and then recover (which it did). I did another compression test of all eight cylinders and none where under 138 psi. I added oil to a couple and not much change a couple pounds.
I did use a vacuum gauge on the car a while back I do remember it was steady and something around 18 or 19 inch pounds. I will have to do that again to make sure.

Odd enough pulling the wire off while running does make a difference to all cylinders. Number 7 seems the weakest now. I have had two other mechanic friends over to look at the car. I myself am a master certified ASE mechanic.( which means nothing..LOL) This is a very strange issue that none of us can pin point. I am sure it is something stupid or simple.

I once had a big block 454 that was rebuilt. The car would run find and strong for weeks . All of a sudden you would come to a light and it would start running rough and idle all erratic. You could hear a slaping/ticking noise as well. Shut the car off or keep driving it would eventually go back to normal only to happen again at a later time. I rebuilt another 402 ( the number matching engine and put back in the car) After the 454 was removed I started a tear down. To my surprise the new timing chain had a crap load of slack in it. The chain would start bouncing around hitting the side of the timing cover. IT caused the timing to get all out of wack. I installed a new timing chain in it dropped it in my friends Chevy C30 and have never had other issue. I would have never guessed that was the issue. Just goes to show you don't rule anything out.:idea2:

---------- Post added at 08:26 AM ---------- Previous post was at 08:22 AM ----------

Yes very nice site I agree

 

Re: Buick running issue problem opionions

When the engine is idling, does the timing light show a steady spark timing or is it bouncing around?

How much play is there when you roll the crank back and forth before the the distributor shaft or the valve train moves?
That should give you some indication of timing chain slack.

Paul

 

Re: Buick running issue problem opionions

Timing light shows pretty steady.
Great idea on the crank/distributor shaft test. Will do that later tonight along with the coil swap.

 

Re: Buick running issue problem opionions

Ok update .....spent 2 hours on this thing. The cylinder in question is # 6. Pulling that plug wire off doesn't make a much of a difference . 3 and 5 are now hitting fine. 7 is weaker then the rest but does make a difference. Compression test on that cylinder (6) is 120lb first hit and then to 150 lb. Inspected all plugs and gapped 0.35. New wires and checked timing. Installed new coil. (still same issue) checked cap by removing it and inspecting under good lighting . ( ordered a new cap to install later) just for kicks. Removed rockers and checked for proper movement. Everything seems in check.

Check timing chain slack be moving crank and watching distributor . Seems fine moces right away both directions.

Hooked up a Vacuum gauge and Tested. Reading was nice and steady at 18"- 19" . Engine was still running rough at higher RPM almost like a ignition issue but vacuum was steady as it gets. Using the above link posted on Vacuum as a reference . I just don't see any issues with valves are compression.I have checked every aspect of this engine possible without tear down I thought maybe the exhaust may be stopped up as it doesn't throw that much Exhaust out the pipes, however the vacuum gauge doesn't lie.

I am totally stumped with this situation. It just doesn't make since with the readings I am getting. I have been working on cars for a long time. I have a tough one here. Going to put on a new cap and then if that doesn't work take the intake off and inspect the cam for wear. .

My 38 chevy that I have been working 10 years is not to happy with me taking on another major project ;-)

 

Re: Buick running issue problem opionions

Something to consider checking since you don't know the history of the engine is, the lifter preload. If the heads were milled to much by a previous owner,the pushrods could have to much preload causing the valves not to close all the way when the lifters are pumped up with oil pressure when the engine is running.

Just cranking it may not be enough to pump the lifters up when doing a compression test,so that may be why everything is checking out OK? And wouldn't be detectable with a leak-down test either because the oil bleeds out from not pumping up the lifters with oil pressure.

The fix would be a set of adjustable push rods.

Goodluck,I hope you find this gremlin,whatever it is.

 

Re: Buick running issue problem opionions

^^^ that would be a good one to check ^^^

You should be able to use a drill as you would when you prime the oil system to keep constant pressure. You will need an extra set of hands to do this but it should work.

<o></o>
Nelson<o></o>

 

Re: Buick running issue problem opionions

Its been awhile since I ran into a problem with preload but a Delphi lifter like TA sells will work fine with a max pre-load up too .200-.250 so I don't that will be his problem. Chris

 

Re: Buick running issue problem opionions

did you ever check your damper to see if it moved , Larry or one of the guys could explain how to check it better than i could.

 

Re: Buick running issue problem opionions

Lifter preload is not a issue. As is was checked as described and while engine was running with valve covers off.
Damper was checked using the Piston centerline method. iT is prett much correct

I was out in the Garage for 10 hours yesterday working on several things including the car. Pretty much worn out today. However the next step is to rip the intake off the car.I hope to see somthing. After that timing Cover, then the heads. Just doesn't make since with the compression I am getting. First Pump 120 psi and then right to 150 . Cylinder 6 is just not hitting right. I am hoping for a cam issue ( such as bad profile due to wear) or something simple. Whatever it is I have never seen anything like this problem with all these test passing and in spec.

A car with a good ignition and fuel with 120lbs plus compression and a steady 19 inches of vacuum should not be missing! :af:

---------- Post added at 03:31 PM ---------- Previous post was at 03:30 PM ----------

Thanks me too my friend. I got taken on the car as it is . I need no more surprises. Would not be so bad except I have another hugh project going on. Will keep posted on finding and then keep everyone posted.

 

If this car has headers a quick check of the tube temperature will tell you which cylinders are firing week. You can check by hand when it is cool and you first start it but you need to be quick not to burn your fingers. If you have an infrared temp gun would be nice. Just another thought. <o></o>
<o></o>
Nelson<o></o>

 

Update on the engine. I pulled the intake tonight (even though I said I wasn't going to go out in the garage) I had to plasma cut 2 center bolts out by the heat choke riser which took some time. The intake has not been off in years. However years ago it has been off( blue permatex around water jackets). Anyway after looking at the cam and lifters they look great. minimal wear. I took and poured gas in each intake valve and they are still holding the gas. After looking at the engine (as much as I could see through the lifter valley) It appears the piston skirts still have knurls on them and nice and clean. I measured the valve steams and spring height all is good spec. no intake gasket issues or head susrface issues. head # 1231786 K 30 date code

I started to take the timing cover off but bolt are frozen and I know what's going to happen. Part of me says no being everything is in good shape. I just dont get it ..this is the craziest deal every in my years of cars.
I did check the header tubes and they where all pretty much the same. 4 and 6 are close together so maybe the heat transfered. I just dont get it....to be continued o No:

 

sorry didnt read that you were a master tech i guess you know how to check the damper. how about something simple you might of over looked, like the resistor wire[are you running points] or dist cap or rotor that was not made right to start with. the postive and negative wires are crossed on the coil. am just throwing stuff out there.

 

Re: Buick running issue problem opionions

What vacuum fittings are on the #6 and #7 runners? Again, 6 and 7 are on the same plane of the intake manifold.

 

Well here is a update.....

I ripped down the timing cover . Broke one bolt off still in timing cover and cant get out. Did manage to get it out of block. Think I might have found the issue. The timing chain is very loose. You can see where it was hitting some on the cover. Lining the dots up you can take and pinch it together and pretty much bottom out on the gear ( at least a 1" both sides). It has steel gears and like I said before the engine has been apart at one time but many years ago. I was heading this direction since it was similar symptoms to the 454 I had mentioned earlier

Now the second part the heads may have to come off just to get the dang header bolts out. I am going to soak them with JB-80 for several days and try to work them out. Got 4 out but the others not goin to be easy. Going to cut the headers off the car with sawzall to make easier access. They are junk anyway . May try some heat if possible.

Seems this thing just wants to make me work extra hard.

 

Try these, much better penetrating oil. <o></o>
Kano Aerokroil Penetrating Oil<o></o>
Liquid Wrench<o></o>
Wintergreen oil<o></o>