Rugh Idle and miss

darkred87T

Active Member
I was under the car today trying to find a rattle. It turns out it was the intercooler rattling against the front sway bar. Anyhow, While I was under the car I noticed this, (see pics below) between 3 and 5 cyl. I did a compression test and found cylinder 5 to be between 15 and 20 PSI lower than the rest. Numbers 2, 4 and 6 show about 165 PSI compression. Number 1and 3 show about 155- 160 while 5 shows about 145 PSI.

Then I did a leak down test with 80PSI and found number 5 cylinder only holding about 15 PSI while the rest of the cylinders were holding about 60PSI. I might have found my idle problem. Who knows, I'll replace the left side head gasket and keep you posted.
 

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turbojimmy

Supporting Member
You forgot to mention that you can't feel the compression coming out right there but it will suck in Gumout sprayed in the area. How is this possible? I would agree that that appears to be a blown head gasket but I'm wondering why it would suck and not blow ;)?

Jim
 

turbojimmy

Supporting Member
Mike (DarkRed87T) and I got the offending head off the car yesterday. That gasket is definitely blown. It's weird though. The ring part of the gasket is still in tact, but it looks like the pressure got past it and blew out the gasket anyway. I think it's been like that for a long time - he's been running low-12s with it that way.

Each of the valves is chalky white, which I guess means it was lean. It was sucking air in through that hole.

If Mike ever gets his lazy butt out of bed today (so what if he worked all night?) I'll get some pics of the gasket and head. I think this mystery has been solved!

Jim
 

darkred87T

Active Member
I finally got my lazy a$$ out of bed after getting out of work at 5:00am. I snapped some pics of the head/ head gasket. It think I might have found the my idle problem. :biggrin:

Look how #1 cylinder intake valve is a nice toasty brown while 3 and 5 are powder white:
 

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VadersV6

Active Member
I had a million things go wrong with mine all at once, and they all seemed to be oil supply related. I used to have 150psi in all cylinders, and now I had 120, and I found I had 60psi in #5. Tore it all down and the HG seemed ok. I saw a little ding in the fire ring...dont know what from, but i didnt see any signs of leakage there or anywhere else. The #5 cylinder with 60psi, even had a perfect colored spark plug, which looked identical to all the others. So that told me its not the rings, cause if the rings were that bad, I'd have oil everywhere. But if the top ring is cracked, and the oil scraper is still good, then you'll end up with a case like mine. I rebuilt the heads myself at work, did some porting, changed all the gaskets out, deck stoned all the surfaces...got it back together and i still had 60psi. I was so pissed. I had gotten sick from tearing the motor down in the dark, in the rain...all for nothing. I saw a light gouge mark in that cylinder wall, and I'm thinking the top ring cracked. I lost the turbo right before that. I think the oil feed line to the turbo got clogged, and the turbo disintegrated. Then all the metal went through the motor and killed it. I bypassed my oil cooler a long time back and I think this had alot to do with the gradual clogging of the turbo's feed line. So to people out there with F-Body radiators, who bypass the oil cooler- Dont do it!
So what Im saying, is that I had the same thing as you, but swapping out the HG's didnt fix it.
 

turbojimmy

Supporting Member
So what Im saying, is that I had the same thing as you, but swapping out the HG's didnt fix it.

It sounds like you had a frustrating time with your car. I'm thinking the head gasket will fix this one, however. It's a fairly fresh rebuild with a new GT turbo and the stock oil cooler in place. You can see the smear mark on the head where the compression was exiting. If this is not the problem then it has to be a big part of it. The car has always acted lean but we couldn't find the source of the unmetered air until now.

Jim
 

darkred87T

Active Member
It may or may not be my idle problem but there's no point in continuing to bang my head against the wall until I get this straightened out.

The right bank looked great. It had the same compression on 2, 4 and 6 and the same amount of leak down. The left bank was all over the place. I didn't even have to look close at the needle on the compression guage to see that it was lower on 3 and 5. None of the cylinders were as low as 60PSI however the head gasket wasn't completely blown out either. You can see in the picture where it was drafting air.

I'm going to do another compression and leak down test when I get the head back on it.

Thanks for the replies. Keep them comming.
 

Saladin45

There is a darkside
Please keep the information flowing guys.

I am having a similar problem on my 84.

The engine starts up fine and everything, but idles terribly and misses. I've got a high rpm when idling, and a few of the local Buick guys took a look and said that they thought it was the throttle body. I bought an o2 sensor and am about to slap it in within the next few days to see what happens.

This miss and the high idle are all that are stopping me from getting this thing back on the road.
 

darkred87T

Active Member
Did the head gasket. I brought the head down to a machinist who said it was warped and replained it. You would think that would have had SOMETHING, at least SOMETHING to do with why it won't idle. Nope, same thing no change.

I
 

turbojimmy

Supporting Member
Did the head gasket. I brought the head down to a machinist who said it was warped and replained it. You would think that would have had SOMETHING, at least SOMETHING to do with why it won't idle. Nope, same thing no change.

I

I drove it and it's vastly improved over the way it was before.

Do yourself a favor and just sell it. You will never be happy with it.

Jim
 

darkred87T

Active Member
I can't sell it. It's not worth anything the way it is.

It's still getting air from somewhere. Idle BLM's are pegged at 160 as usual.

I'm going to do a compression test on that left bank again. Before, I was getting lower compression on that side than the right side. It might be the same.
 

darkred87T

Active Member
Actually, as a serious update it does run alot better. It's not just my imagination this time. It starts right away as opposed to turning over and over before. The RPM's don't wander up to 1200 everytime I start it anymore. The idle is smoother however it's still not quite right. It's a little rough and has a slight hesitation and flat spot.

This does prove that it was an air problem and I cleaned up most of it. It still has some of the old symtoms on a lighter scale which tells me it's still getting air from somewhere.

The only thing I can think of is that the other head is warped and or has a bad head gasket also or something is still screwy with the side I fixed.

I hope this helps other frustrated "rough idle" Buick owners up to this point.
 

1turbo6

Member
I have had the same problem since I bought my car, high blm's (140) at idle and had a serious knock problem until I added alky. but the car idles rough, misses if you hold it around 15-1800 rpm. I swapped in a rebuilt engine and it still idles the same and is still lean at cruise. the only parts I reused are throttle body upper plenum and crank sensor. I'm not sure if a bushing in the throttle body can be causing this or not, or possibly the stock intercooler. the car runs great off idle but I feel like the alky is just masking a problem.
 

turbojimmy

Supporting Member
I have had the same problem since I bought my car, high blm's (140) at idle and had a serious knock problem until I added alky. but the car idles rough, misses if you hold it around 15-1800 rpm. I swapped in a rebuilt engine and it still idles the same and is still lean at cruise. the only parts I reused are throttle body upper plenum and crank sensor. I'm not sure if a bushing in the throttle body can be causing this or not, or possibly the stock intercooler. the car runs great off idle but I feel like the alky is just masking a problem.

That's exactly what his car did/does. It seems to run decent to me (12.0 in the 1/4 isn't too shabby given his mods) but there is something 'funny' about the knock. Without alky it will knock at very low boost levels, at least according to the gauge. I don't know if it's real or something is banging on the block causing it to false knock. His DP is hitting the floor so that might be it. But if that were the case the alky wouldn't make it go away.

Jim
 

VadersV6

Active Member
9 times out of 10, a rough idle/high blm issue, is a vacuum leak/leaks.
Check the condition of all your hoses.
Do you have the stamped steel intake gasket? Get rid of it and install a 1 piece felpro gasket, with "the right stuff" sealant.
Use a big hose and listen at the base of each fuel injector for a sucking sound. Odds are, one or more injector o-rings are cracked and leaking.
Check IC hoses and clamps for full grip and seal.
A working PCV system, with open breather elements on both valve covers, are in themselves, a massive vacuum leak. But most chips have been designed around cars like this, so they're somewhat adapted. But I found after a few years, that running a single breather on the passenger side valve cover, and capping the oil tower on the drivers side, does alot of good for driveability and seriously reduces fumes in the cabin. Personally, I made my own ball/spring PCV valve with zero backflow leakage. I have an aluminum oil breather tower and machined an aluminum plug for it with O-rings to seal it off. Its also drilled and tapped on the top, with a brass elbow. A hose runs off the elbow, to my PCV valve, to my own high duty catchcan, to the vacuum block line. I have a breather on the passenger side cover. i tried many configurations through the years and found this to be my favorite setup. Too bad my engine is toast....STILL.
So anyway, I found BLM's to drop by sealing off the big breather and just running 1 small one.
Also, after replacing all the hoses you can and checking all that stuff, clamp as many hoses as possible....like a hose clamp on every single hose on the vacuum block, and at every other end, and every accessory or source you can find. Cruise control is another source of leaks, as is the EGR valve. Ive made posts in the past, you can search and see what Ive said about all that. A slightly leaking EGR system can SEVERELY roughen your idle and screw things up. But work on the fundamentals above, first.
 

1turbo6

Member
I am running a felpro 1 pc intake gasket, all hoses are near new and zip tied. even if it was a vac leak why does it have the miss. the coil pack and module are also new gm. I tried everything I could think to try. it seems to me the poor idle/miss and blm's are 1 and the same issue.
 

1turbo6

Member
went over the engine today with propane. all vacuum lines seem fine also throttle body was fine .could the intercooler be leaking?
 

VadersV6

Active Member
The rough idle and BLM's are one and the same. Im not sure you read my whole previous post. You either have a vacuum leak or an EGR valve that's cracked open and leaking some exhaust into the intake. The EGR will do it every time. Pop the protective cap off the EGR, and get your fingers underneath on the diaphragm and pull up, then plug the vacuum barb with your other hand and let go of the diaphragm and see if it drops quickly. Also, while its idling, take the vacuum line off and feel if theres any sucking...if so, the EGR solenoid is bad. Also check the solenoid filter.
Read one of my old posts...you can go to the how to forum on (in this spot I wrote the name of another TR board and it was blocked by this site...I'm a member on MANY different boards and this is a first...EVER...the owner here doesnt "like" the owner of that site, so this is political and has nothing to do with helping the TR community out..there are some good how to articles there...use your imagination...southern california grand nationals dot com...may take a minute to figure out the name) and read a thing I wrote on how to set the cam sensor properly with no special tools. My name there is hionpsi. Double check the cam sensor, check the gap on both sides of the crank sensor and make sure its not dirty or loose. Check the grounds behind the passenger side head. Other than those, I guarantee it's either a vacuum leak somewhere or the EGR valve, which it sounds like. Check your charcoal canister purge solenoid to make sure it's not stuck (mine was) and check all the check valves for the hell of it. Also ohm check all your plug wires and replace the plugs, cause sometimes the porcelain cracks and the spark shorts out on the head. Ive been down this road in 10 different ways, so keep searching these things Ive mentioned. And by the way, the propane test NEVER works. I dont know why people keep pushing that test. Any vacuum leak thats severe enough to cause your motor to run like that, is going to be substantial, and you WILL be able to hear it with a long 3/4" hose. I thought my intake gaskets were fine, but after I ported my intake, I saw on the gasket that I had been leaking in several different places.
 
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