oscillating idle and lack of power

[Pex]

After the full rebuild of my front suspension, carburettors etc I also removed the distributor and replaced it with a MegaSquirt EFI system to handle the ignition and thought that should make it easier to dial in a good idle and even some more power, but no

I have had oscillating idle and lack of power above 2000 rpm, lots of noise but not much happens above 2000 rpm. But still on lower rpm when cruising it actually runs better then before the rebuild so somthing must be right.
I did all the recommended setups on the carbs and tuned them as good as I could but without any luck.
I tried some of the ignition maps found here without any noticeable improvements and created a basic map based on the factory settings or very close.

Today I took a new look on the carbs.
Adjusted the needles with a tool ( do not know the name but it has metal strips in different thickness ) to be exactly 0.05 mm above the piston.
Jet at about 65 thou (1.6mm) down from the bridge.

I checked the float bowl level and here comes the strange thing, all float needles closed at 11mm but still one carburettor had a higher fuel level and actually floated the jet on the rear carb having the level at the same height as the bridge.

I suppose the fuel level should be at the same in the jet for every carb so I had to change the float bowl height by using 12-13 mm instead of recommended 11mm. Now all jets and fuel level looks like the one in the picture instead of having the fuel level at the same height as the bridge.

After the fine adjustment it runs much better on idle, the oscillating is almost gone, definitely an improvement. I took a small test drive and still some lack of power when accelerating maybe a little stronger but less noise at least. The eventual difference in needle heigh, fuel level in the jet and the jet height seems to cause the oscillating.
Hopefully I can re-tune the carburettors now since the start point is better than before.

[christopher storey]

Pex : I'm not sure what you mean by "Adjusted the needles with a tool ( do not know the name but it has metal strips in different thickness ) to be exactly 0.05 mm above the piston."

The shoulder of each needle should be exactly flush with the base of the piston . If you have set the needles higher than this then you will find it very difficult to get proper mixture strength because the mixture will always be richer than it should be in relation to the level to which the piston is being lifted

This may well be the cause of the oscillation ( which I suspect is what we call "hunting" - which is when the engine makes a rhythmic thrum- thrum noise )

I am sorry if this is not as clear as it should be ( unfortunately my Swedish daughter-in-law is not here to translate for me ) but I hope it may help

[Pex]

Oh, I wish my English where better :-)

The needle has like a waist, by using a thin metal strip (0.05 mm) in the needle's waist while pressing the needle to the bottom of the piston, I can secure that all needles are exactly the same.
0.05 mm isn't much so the needle are near flush to the pistons, a picture maybe clear things out...

The different fuel level despite the correct float bowl height puzzles me though

[Tom W]

Hi Peter, the tool you’re referring to is a set of feeler gauges.

Your ignition map looks like you don’t have any vacuum advance programmed in yet. That shouldn’t be the cause of your problem though.

Somethings not quite right if you need to set the floats differently to get the same fuel level. It suggests the one float isn’t floating as high as it should. I’d check they all weigh the same. One could have a leak, and be full of fuel, or been repaired in the past and ended up a bit heavier. The objective is equal and correct fuel level though, rather than identical settings.

Are the carburettors balanced, and is the linkage set so the throttle butterflies all open the same amount?

[abowie]

Pex : I'm not sure what you mean by "Adjusted the needles with a tool ( do not know the name but it has metal strips in different thickness ) to be exactly 0.05 mm above the piston."

He's done exactly what I do.

0.05mm is 2 thou. I put the 2 thou feeler gauge in the groove on the needle and use this to positively locate the needle. This way you are sure exactly where the needle is and all 3 are the same.

As to the tuning problem, Peter I'm not sure what's going on but it must be fairly fundamental.

If you have the carbs tuned correctly and the timing set properly it should run well.

Have you checked TDC on #1 piston to ensure that your harmonic balancer mark and distributor drive are all correct? Are you sure your cams are installed properly and timed at TDC?

Are the carb needles and jets the correct ones? Have you got a big air leak somewhere that you haven't noticed?

Cheers,

[Pex]

All linkages are without any play and the and butterfly valves closes correctly( everything is new), no airleaks.
The needles are new from SNG, UM I think it was, I have a mangoletsi sport air cleaner from SNG instead of the original which should make it run a little lean but I thought switching needles to recommended for this air cleaner if I noticed any problems.
I hope not that this is the reason for the lack of power above 2000rpm

FYI, the car runs perfect while cruising (55 miles/h) after the rebuild, it's the acceleration that's been missing ( even if the idle has been not as smooth as I thought with the new ignition system).

After yesterdays recalibration of float bowl level, needles and jet height, the oscillation is almost gone and it runs even smoother around 500 rpm than before on 700rpm. Before it dipped from 700rpm to 500rpm every 8 second and then immediately back on 700rpm, now it stays on 500 rpm with small variations up to 550 rpm which confirms that the Fuel level is crucial for a stable idle which many has discovered after what I have read on this forum. I did check the float bowls during the rebuld of the carbs but couldn't see any repair or similar but I didn't weigh them which will be the next step. I really want to understand why the fuel level differs on this one.

One thing I have forgot to mentioned is that the engine temperature is only around 65 deg celsius when driving a very hot day (this Saturday when I took her for a test drive before the yesterdays recalibration).
See the third diagram's white line in the picture, the only time it gets up to 80 its when I was parking. I ordered the recommended thermostat from SNG but now I'm not that sure.

I did also checked that TDC (no1 piston at top),harmonic balancer mark was correct since I had to align the sensor for my waisted spark ignition, but the position of the cam I didn't check.

I will leave the float bowl level on rear carb for now and see how she runs during this week while checking the spark plugs and tune the carbs more accurate after yesterdays recalibration.
I now realize that maybe the needles are wrong and the temperature is to low for the engine to perform as it should.

[Pex]

Took her for a drive today after learning the mixture a little (spark plugs where a little black after yesterday’s drive), definitely better idle and response when accelerating but still not acceptable.
Seems like it going in the right direction at least.

Found out that it isn’t that uncommon to have a higher fuel level on the rear carburetor.
This is one discussion on the topic,
https://forums.jag-lovers.com/t/e-type- ... jet/119111

[MarkRado]

Peter,
try UE needles, thats what the Mangoletsi filter requires.Worked on my car.

[Pex]

Yes, it is my plan to change needles but I just haven't done it yet.

Maybe I'm just to sensible about the idle, it does idle quite well and I can easily have it idle on 500 rpm but it should be more stable IMO. At 700 rpm it still falls down to 650 rpm every 8-10 second and the interesting thing is that the manifold vacuum also drops dramatically which I monitoring in my tuning software, maybe the fuel/air mixture is way to lean because of the new air filter.

I don't know if the needles is a problem or not yet but I have started to eliminate other possible causes why I can't get the engine to run as good as I think it should.

Still, I can live with the idle but full throttle worries me more.

So far I found the fuel level problem in the jets which I still don't understand but is corrected with less oscillating idle now.

I noticed that the tachometer showed 100-200 rpm less then the tuning software and since the tacho feed +12V to the ignition coils it should be the same! I did found a connector to the ignition coil which was way to loose so I removed it and welded the cords, now the tacho is more accurate.

Took her for a short drive and this also (in my mind at least) made a change when accelerating which it should... if it missed some sparks before.

The ignition map can be better at load i suppose, still working on it.

Unfortunately the weather in Sweden right now isn't what I would like it to be so I haven't been able to fully test my fixes yet.

[Gfhug]

Peter, just a reminder that you should aim for 700 rpm idle on your 4.2 engine not 500. To help eliminate chatter from the constant mesh gears in the all synchro gearbox.

Good luck getting it all smooth

Geoff

[Pex]

Finally found some UE needles at a Swedish "carburettor firm", they also told me to try use their oil (SAE 20) instead of the red ATF oil I always used before in carbs. The guy I talked to said it could be to thin and cause some of the oscillating at idle since the pistons needs more damping which make sense somehow.

I will change needles asap and hopefully it will be a difference now when accelerating.

[Gfhug]

Peter, a general rule is to use engine oil in the carbs.
Let's hope this change will do what you need and get a nice, smooth engine

Geoff

[ralphr1780]

Peter, when looking at your timing map the advance at 500rpm is 13, while at 700rpm it is 10 and at 1000rpm it is 11.5. Strange. Plus there is no correction for the load.
Any reason why you did not load the standard map for a 4.2 engine?
Your engine idle is stable at +/-500rpm, but hunting at 700...
I had also a hunting idle despite the carbs were all perfectly set, a 2 degrees advance correction of the offset solved it very simply.
I suggest you reconfigure the map as per stock:



As often said, majority of carbs issues are electrical!

[Pex]

First of all I can say that new UE needles made a huge difference, now the engine responds at WOT (wide open throttle) as expected, much more response and acceleration. Probably needs some fine tuning on the mixture but it quite good as it is

Regarding the ignition map I am a little confused when I look at the "base map". Just to be clear here, at idle it stay at upper left corner and at WOT we aim for lower right corner which give max advance 29deg at "max acceleration", or have I got the idea wrong here? (Mine is idling at lower left corner, 0% load).
My idea of 100% load is WOT, pedal to the floor if you see what I mean and our scale is opposite of each other.

I had the impression that max advance was 34 deg or even a little higher at WOT. What I see in the basemap is max advance 34 deg at what I assume is at "cruizing" on the highway (high rpm and little load).

Please correct me if I'm wrong but IMO there should be a somehow linear increase of advance at WOT, from about 10 deg from slow drive and when accelerating the advance should aim for >34 deg at about 3000rpm and then flatten out.

In my map, I have so many more cells to play with so I can spare one column just for "stalling". I have my idle never below 700 and never higher then 800 so the advance is steady at 10 deg. If the engine stalls for some reason and get below 700, the higher advance raises the idle back to 700rpm/10deg advance. This is a common way to build a ignition map.
And my map is build on the base map except for the "cruising part", about 12deg at 1000rpm and 29deg at WOT ( if I interpreted your map correctly), the rest of the cells are just interpolated.

FYI, I will start with the base map again now when the carbs are working better but I will definitely aim for 34deg or more at WOT.

[Tom W]

I think it depends on how the map quotes load. In the map Ralph posted above, load looks to be a percentage. So accelerating at wide open throttle the advance curve would follow the bottom row of the map. Deceleration from max revs to idle, with the throttle closed, would follow the top line, right to left.

If you’re using vacuum to measure load, 100 on the load scale would be no or minimal vacuum (atmospheric pressure), 10 on the load scale would be maximum vacuum (below atmospheric pressure). You’ll need to know what absolute values equate to minimum and maximum. If you’re using the original vacuum pickup point on the carbs, then the distributor data from the factory workshop manual will give a good starting point.

If you’re measuring load with a throttle position sensor, then closed throttle would equate to no load, and somewhere towards wide open throttle would be 100% load. The exact values will require some experimentation.

[MarekH]

Your MAP sensor seems to read quite low values quite often. I wonder about its positioning and whether a lower lag factor may help. Often constricting the tube to the sensor helps reduce fluctuation.

This isn't the cause of your problem as you have your ignition set independently of MAP, i.e. only varying with rpm, rather than with both load (MAP) and rpm.

Expect to idle at about 40kPa ish for standard cams and higher than that with hotter cams. You get down to below 20kPa quite a lot. 20kPa for a load is low, e.g during overrun when going downhill with the throttle shut.

You can balance your idle using the ignition advance if you want to. Higher advance will make the idle faster and lower advance will tend to stop the engine racing. The typical trick is to make a little pocket or dip where you want idle to be and the car always has drops back into the pocket in the advance map at idle because the advance setting chosen stops it from racing away at high rpm, but boosts it at low rpm:- one reason the idle picks up from 500rpm is that you bump up the advance by 3' as revs drop to 500rpm.

Also, I'm interested in where your coolant sensor is plumbed in - I find it hard to believe that it is 65'c when running. It shows temperature in the 80's at the beginning and end of the log which looks right, but either the thermostat then sticks open, or the sensor is mislocated in the path of cold water during normal running.

Your lack of power at medium/low load is probably not helped by the lack of advance.

Ralph's ignition map is simply upside down compared to Peter's. They both look to be using MAP as the load.

kind regards
Marek

[Pex]

I use map and rpm to dial in each cells ignition advance, rpm via sensor and toothed wheel on the camshaft.
Haven't had time to play with the ignition yet but my plan is to use the base map provided here and just increase the advance at WOT a little. First I have to fine tune the mixture after changing needles but it felt very promising when I drove her last time.

The vacuum is fetched between the vacuum canister and the intake manifold which should be a proper place, think most people done the same when they upgraded the ignition from what I've seen. The map value (Load) usually is about 30 at idle and seems to work fine up to 100% Load (WOT). As you noticed, the pressure drops very low when I close the the throttle.

The temp-sensor is placed between the two lower hoses at the cooler which is the return of cooled water, maybe it should be better placed on the top cooler hose from the thermostat house for more accurate reading, but the temp gauge also shows low temp so I have to check it out.

The temperature has been bothering me, there is a new thermostat installed but maybe I have the wrong one since the small bypass hose is always fully open and I have seen other thermostat that is "deeper" and cover the bypass slot in the thermostat house. Maybe someone can guide me a little regarding the correct thermostat.

[Tom W]

It sounds like you have the vacuum take off in the same place the original vacuum canister was fed from. In that case, I would take the vacuum advance values from the genuine workshop manual, and base your map on that. There will be a bit of maths to do to populate every cell. The workshop manual data is quoted in additional distributor degrees for a given vacuum value. It also shows the level of vacuum required before there is any additional advance, the vacuum value at which maximum additional advance is reached, and the maximum additional advance value itself.

Regarding your temperature questions. If you’re using temperature as a variable to adjust advance, then you need the sender in the inlet manifold, ideally where the gauge sender goes. If it’s in the bottom hose, then it won’t see much increase in temperature until the thermostat opens, by which time the engine will have already been increasing in temperature for some time. If it’s a really cold day, the thermostat may never open on shorter journeys.

The thermostat should have a little disc on it that closes off the flow to the bypass when the thermostat opens. Without blocking the bypass, you run the risk of overheating, as hot water gets recirculated. Of course, if your temperature sender is in the bottom hose, the sender won’t see any of this.

[MarekH]

Peter,
Your camshaft rotates at half the speed of the crankshaft, so bear that in mind when you populate your advance map with numbers - you will never see 3000-6000rpm on the table because 3000 camshaft revolutions equal 6000 crank revolutions and "rpm" conventionally refers to crank revolutions unless otherwise stated.

Your MAP sensor wants to read the air pressure inside the manifold, not halfway to a dead end one way vacuum valve that's active when the vacuum tank is being exhausted by the use of brakes. As you have it, that's not a Manifold Air Pressure sensor and so your commanded ignition advance will vary or pulse with use of the brakes as the vacuum cannister recharges.

Now we know why your idle oscillates.

Connect the MAP sensor directly into the the large inlet plenum, preferably where it sees all six inlet runners evenly, not where it sees the vacuum canister take-off - this is not representative of the load that the engine is under and hence of how much ignition advance you want to command.

Your temperature sensor is less critical, as all it will ever be used for is maybe activating the radiator fan. Conventionally, you'd want this to be positioned at the water exit from the back of the engine, before the water is divided by the thermostat. Putting it anywhere else means it's water flow is influenced by other factors and this explains your meandering and sometimes low temperature readings.

There is plenty of guidance in the Megasquirt manual as to where and how to set up these sensors.

kind regards
Marek

[Tom W]

Peter, by vacuum canister, do you mean the vacuum advance canister on the original distributor? Or do you mean the reservac vacuum tank for the brake servo?

I think Marek and I have interpreted what you’ve written differently.