Rough Idle, Engine Vibration

[roverdevin]

I have had a persistent and annoying problem with my 2.25 at idle, and I just cannot seem to solve it.

I have a 2.25, 0.060" overbored with 8:1 head and Weber 34ICH. Compression on all cylinders is great, and overall the engine seems healthy.

First, the engine seems to pulse, wander and even miss at idle. Furthermore, I cannot bring the idle much below 950-1000, but I would love to see mine tick over at 700-800, as I have seen others do. Adjusting my idle jet sometimes helps, but after a few miles he problem is back. Could this be an air leak? Idle jet fault? timing problem?

Second, the engine vibrates at idle and certain RPMs throughout the spectrum. It is definately RPM related. The engine has been rebuilt, about 5 years ago. At my idle, 950RPM, it rattles the whole car. Could this be engine mounts? Unbalanced crank? Timing?

Third, I have noticed I seem to have an unnatually high exhaust pressure...it comes out with quite a force, and a smart "putt putt"...it seems even more so than most land rovers. Is this a result of the 8:1 head or the 0.060 overbore? The exhaust is stock.

Fourth, Im getting a "snap crackle pop" from the exhaust on overrun, but give it the SLIGHTEST bit of gas and it stops. Is this timing, fuel lean or fuel rich?

Any advice would be helpful. I am tired of jealously listening to other land rovers silently tick over at low idle while my poor beast shakes itself to death.

Thanks,

Devin Biln

[Roverworks]

Devin, there is much more information needed than you have provided to even start diagnosing your engine's fault...Is the stock cam installed? Which distributor are you using? (They are not all the same) has the engine ever run properly? I would suggest you attempt further diagnosis by use of a vacuum gauge attached to the intake manifold (not the carb)...Get a good mechanics test chart for interpretation of Vacuum readings. With a vac gauge you can accurately test and/or confirm, correct mixture, valve timing, ignition timing, ring condition, valve condition, vacuum leaks, weak valve springs and much more. I find the vac gauge as useful (if not more so) as the compression gauge. Actually, all you guys and girls should have one and know how to use it...You do not hear much about them anymore as they are of very limited use on fuel injected cars but when the Series LR's were new the Vac gauge was in the top drawer of every good mechanic's tool box.
Alan Simpson
http://roverworks.com/

[roverdevin]

Alan,

Thanks for the advice...I do have a vacuum guage somewhere, so i'll dig that out and work with it. I was not involved with the rebuild of the engine, but to the best of my knowledge, the stock cam was used. The distributor is a late Lucas type (without thumbwheel adjustor). I forgot to mention I have a pertronix pointless ignition installed.

I can get the engine to run quite well with a comprehensive tune up, and it will do so with a good low idle for a few days...then it'll start to stall at idle...i turn the idle up as a patch-fix, and either live with it at a high idle, or start all over again. The single biggest factor in smoothing it out seems to be adjusting the idle jet on the 34ICH...a teenie trn this way or that sets everything smooth...but it seems to shake out of adjustment, even with the set screw tightened.

But thank you again, I will pursue the vacuum approach next chance I have some time to devote to car matters.

Devin

[DaveB]

Hi Devin,

Had similar problems on mine with both the single barrel and 2 barrel weber. Thought it mostly to do with the fact that I was fiddling with various carb setups -- which is probably a factor. I too had regular bouts of dieseling and run-on. Thought those were the result of too high of idle not letting the engine stop properly.

I actually got used to shutting it down by letting out the clutch in first while turning off the key.

I'm not discounting what Alan is saying about vacuum, in fact, Alan, when are you going to put on a vacuum guage tech session for us?

But I found my problem had to do compression of the head. (definitely still related to vacuum issues) It was freshly redone, with about 8:1 compression (although one never really knows unless you take the time to measure deck height plus head cavitiy volume with a burrette and apply appropriate math).

Someone suggested I was getting carbon hotspot buildup causing the run-on and that I should spray a litre of water (carefully, not causing it to hydraulic -- check with your local mechanic to be sure you're doing it right) through the carb while it is running to break up the carbon. This is something we used to have to do when I was working in mechanics so it made some sense. Did this and it temporarily suspended the run-on and rough running, but came back in a few days.

So, thinking too high of compression, I fueled up 2 tanks of supreme unleaded (91 octane. Not the super expensive Chevron 94, just 91 that everyone has). Within a tankful, things had smoothed out, and the run-on was gone. Also the idle could be set much lower.

I think it's the additional cleaning additives that are added to the supreme fuel that are keeping it running better. My theory: if 8:1 compression is hitting close to the max that regular fuel can handle without severe ping and runon, then a little bit of carbon actually uses up space in the combustion chamber, thus effectively increasing the compression. The more carbon, the higher the compression and the more rough running and predetonation due to carbon hotspots.

I now always pay the extra for supreme, and while it hasn't really increased my power, it has definitely kept the truck running smoother.

Just my two bits worth...

Dave

[roverdevin]

I hooked up my vacuum gauge to the intake manifold and got the follwing readings...

1) At idle 1000 RPM.........fluctuating quickly and evenly between 15" and 18"
2) Quick throttle tap......down to 0, then to 23", then back to fluctualtion for idle.
3) Steady increase in throttle 1000-6000+ RPM.......needle steady at 20-22".

From what I can see on different web sites, thins would indicate an ignition timing problem or sticking valves, is this correct? If it is a valve problem, what are some of the possible remedies?

[roverdevin]

Apologies for the deluge of postings by me, but now that I have even the slightest of leads, I'm all excited to pursue it!

All my vacuum readings, in my new found understanding of the art, seem to point to a problem with the valve guides.

My engine was rebuilt about 4 years ago, and new valves and valve guides were installed. It threw a pushrod at about 800Mi after the rebuild, and I was advised to put it back in, remove the valve guide oil seal and allow it to break in a bit more, the dislodged pushrod likely being the result of the engine not being broken in (tight valve guide/seal). I have never had problems with the pushrods since. I have been quite diligent with oil changes every 2000-3000Mi.

Would a missing valve guide oil seal result in a 1-3 inch fluctualtion in vacuum at idle, or is it more likely to be the guides themselves?

Devin

[DaveB]

Do you get a puff of blue when you start up after more than 30 minutes? If so, oil may be getting down the guides. If not, your guides and seals are probably OK.

Dave

[Roverworks]

Devin. Were you sure the push rod that was thrown was straight when you reinstalled it? A bent push rod would provide a fault such as you describe.
Alan
http://roverworks.com/

[roverdevin]

There is no big oily cloud when I start up, and oil loss is negligible.

WRT the pushrod, It was not me but an experienced and licensced mechanic in the Vancouver area who re-installed it. He said the Pushrod looked straight and ok, but was just a bit tight in the valve guide, hence the removal of the guide oil seal. He suggested it was due to the quite recent rebuild.

I will definately dig around in there next time I have the valve cover off for my spring tune up. Is there any way of checking the condition of the valve guides without removing the springs?

When messing about with the timing and carb idle jet, I can get the vacuum at 900rpm idle to around 20", but stull rapidly fluctuating by about 1-2 inches.


Alan, Dave--the advice is much appreciated!

Devin

[Roverworks]

Devin. My final thoughts on this...Check your valve lash and while you are there check the suspect push rod. A cylinder leak down test would now be indicated to confirm the diagnosis of a valve problem. If your valve lash is too small or large it could be causing the problem. Also, It is possible your lifter assembly was damaged when the push rod went it's own way. Everything points to head removal....

Alan
http://roverworks.com/

[DaveB]

Sorry to post this so long after the fact, but I just came across a very cool site that explains what various vacuum readings mean using animated graphics.

Thanks to Rick Grant on the LRO list.

http://www.users.bigpond.com/ergoff/vac1.htm

Dave

[roverdevin]

On the extremely welcome and helpful advice of several members, I have been doing all sorts of diagnostic tests to try to sort out my idle woes.

Vacuum test indicated possible leaking valves. Compression test is 145, 147, 147 and 150, or, quite good. Cylinder leak down test is another story.

According to my crude measurments, I am getting around 15-20% leak down in all four cylinders, and listening for air leakage tells me the bulk of this is leaking past the inlet valves in all four cliders. Air escape past the exhaust and rings seems minimal.

To all those engine-knowits out there...

Is there any significance in the fact that all 4 cylinders are leaking about evenly and through the inlet valves? Does seemingly excellent compression with these leak-down results tell me anything special? Or have I messed up the test?

I am in the process of budgeting for a head tear-down, but I wonder if carbon build up could have anything to do with this?

Any advice is appreciated! I'm enjoying venturing into that final unknown-to-me frontier (engine) in Land Rover ownership.

Devin Biln

[DaveB]

Hi Devin,

At this point, bracing for a teardown, it's certainly not going to hurt to try some carbon removal. It worked for me and made a big difference. I would try both the water injection (being extremely careful not to hydraulic your engine) and a couple of tankfuls of good gas.

I used a sprayer bottle similar to a windex bottle for mine, misting the water over the top of the carb air intake and with the other hand keeping the throttle going cuz it wants to stall when the water hits the combustion chamber.

Or perhaps you could use that product, CarbOut, which produces some interesting smells and glorious amounts of white smoke. Wait till mosquito season cuz you'll fog the entire neighborhood and the neighbors will be really happy if you tell them you're helping get rid of bugs.

Dave

[roverdevin]

Dave,

Good gas? GOOD GAS!!? Have you seen the price of "BAD" gas??! :( :(
Water is a little more in my price range, I'll try that option! :lol:

All kidding aside, I will definately try this before messing around with the head. With all 4 inlet valves leaking equally, a relatively recent rebuild and tens of thousands of miles on the cheapest gas my money can buy, I wonder how much of my problem could be due to carbon. I don't plan on having time/money for the head work till July anyway, so that gives me a few months to tinker.

I like the sound of billowing smoke and neighborhood spectacles...A good show must mean it works, right?

Thanks for the advice,

Devin

p.s. How about mailing me a couple jerricans of the cheap valley gas?

[DaveB]

Abby and Mission gas is definitely cheaper. Last night I filled my car with regular at 82.0 at the Shell in Mission. It's been hovering around 85.9 the last few days, but I noticed it up to 95.5 this morning. As usual it will stay high over the weekend...

There is one place on 8th avenue, a Turbo station, which still has diesel at 70.9 as of yesterday around noon. They are always cheaper as they aren't in any municipal zone so don't pay as much tax, from what I understand.

Dave