Rapidly moving vacuum gauge at idle - smooth above 1k

[BigBlockMopar]

Geoff,
I think the (some) lifters are actually still pumping up a little during idling, and thereby taking up any slack in the spacers I made, and remove any lash as a result.
Mild steel (tubing) was used for the spacers, knowing I would have to reset lash a bit more often than normal.

Iginition system has been on the car for well over a year without issues. It's MegaSquirt3Extra driving a HEI-7 module and MSD Blaster SS coil. Using a dwell table from 2.5ms at idle to 3.1 at around 3000rpm and decreasing to 2.0ms at 6000rpm.
The still new Iridium plugs were taken from the previous (318ci) engine which could idke all day in Drive at 500rpm if needed.
Don't recall the type of the plug at the moment.

Trying a big lash would be an easy test to do.
Then I could decide about the next step.

The overly advanced timing is liked by the engine because it is missing some compression at idle.
I tried upping the idle advance today a bit more and the engine seemed to like that even better.

I've opened up the engine today and checked all the spacers in the lifters. A few where slightly shorter in size I recall because if the manual cutting of the tubing I did at the time of the build.
Remade some of the spacers so all lifters where now at equal heights with their plungers very close to the spring-wire.
Relashed everything to .003" but didn't fix the issue as of yet.

[groberts101]

Gday mate

Thirty degrees of timing at idle on a small cam seems a lot. Notwithstanding that LPG* respond well to a lot of initial, it seems an excessive requirement for best idle on a cam with 212 degrees at 50thou. (I use 24 degrees initial at 1200rpm on a Gas Research LPG setup, but that's with a 240@50 solid flat tappet)

I'd be looking closely for something ignition related, assuming that the conversion to solid lifter hasn't done something unusual to the effective cam specs.
Regards
Paul

* I'm assuming again that the engine is currently on carbed LPG- I note the reference for injected LPG later.

Might seem like a lot but it's not once you begin to understand the physics of slower moving and far less dense fuel mass. Give the engine what it wants to make max manifold vacuum and get the fueling right and it's not uncommon to hit 50 degrees or better even with higher compression ratios used in conjunction with smaller to moderate sized cams. And bigger cams like the one you mention will easily absorb more ignition advance if the fueling is set up right to avoid leanout.

Again.. the engine will let you know via increased manifold vacuum what it prefers over some preconceived notion of what it should be. My last 11.6 scr 383 took 54 degrees up to about 1,700 rpm at which point the msd programmable 6al box started ramping out the timing until it hit 37 degrees @7,100 rpm using the high speed retard function.

[Baprace]

Just as a quick check and problem direction indicator. Back off (open) all the valve lash settings about .020" on all the valves and run the engine at idle. I
It will be obviously have a clatter but if that smooths the vacuum readout then you just have a tight valve in a cylinder and you can reset the lashes and stop the problem.

I think Newold1 has the problem identified, I agree with him, it's the only thing that makes any sense if you have decent guides, keep us posted.

[BigBlockMopar]

Was able to re-lash the valves today at .020".
Engine liked it and ran much more stable at idle and in Drive. Was able to adjust the idle down in Drive, even to 450rpm without stalling.
Valves made some more noise, but not that much more as I expected.
But, even as the engine did run better, the vacuum needle was still rapidly bouncing like before, pretty much no change so there's still more to be fixed.

Which started making me more suspect of the current rockers being part of the problem too. I bought these cheap ProComp 1.6 rocker rollers once off Ebay thinking it would be a 'nice' set for a stock-like engine.
I still had a set of 1.5 Crane rockers on the shelf so installed those and after I got the valves lashed at .003" I cranked up the engine.
Low and behold the engine idled fairly smooth (but still vacuum needle vibrations), but most of all a lot quieter than before.
Took the car for a drive home but noticed valve lash appearantly shrunk a bit as the engine didn't ran smooth anymore once some heat got into the engine. So I need to double check what the hot-lash is and adjust the cold lash for that.

[cjperformance]

Just one really oddball thought to try- do you run a pcv valve?
If so where does it enter your intake manifold & can you disconnect it and give the idle vac a test. On some intakes the placement of the pcv can affect idle quality, it is more likely on a single plane or some efi intakes but possible on a dual plane.
Just a shot in the dark but worth a thought.

[groberts101]

^^^good point to check. Another thought to add into the "what if" category.

IF.. you have a distributor with vacuum advance hooked to this engine?.. it could be adding some erratic timing fluctuations into the mix as well. And if it's hooked to a ported vac source that could explain why it stabilizes the needle once the rpm's come up a bit. What distributor is being used?

[BigBlockMopar]

I've tried pinching the pcv line closed a couple of times.
Idle rpm drops a bit and becomes a tad more stable, but is not the cure unfortunatly.
Pcv is fed into the carb's base at the rear and is divided over all cylinders. An oil seperator is added in the pcv line to prevent too much oil vapour inhalation.

Distributor is an original Chrysler LeanBurn, so no mechanical or vacuum advance incoporated.
The MegaSquirt ecu takes its vacuum reading from the carb's full vacuum port. The cam is stock enough (no lope) to keep it there, and the previous engine has been run this way for well over a year.
I've been playing with ignition map fields where the idle rpm is hovering recently where I found the engine liked to have more advance at idle (30-31 deg).
Now today with the 1.5 ratioCrane rockers installed I've pulled back the timing to around 24 at idle.
(I can switch between 2 timing maps with the flick of a switch on the dash while driving).

The engine does have more low end torque now, especially when cold, until the lash becomes negative/preload I suppose and vacuum and idle quality start to suffer.

[groberts101]

Ok seems to make more sense now. Are you implying that the needle is becoming more stable with less idle timing?

If that's the case in comparison to the higher base map of 30-31 degrees?.. then I wouldn't discount the possibility that you are only masking a cylinder or 2's effect on the needle. Basically.. if you are reducing base timing and the manifold vac has dropped?.. then you are diminishing each cylinders pull on the manifold and bleeding off bmep. That then gives a false positive that you are correcting the fluctuation issue when in fact it has just been diminished. Sorry if that's redundant.. been a long day and just trying to convey my point, is all.

PS. If the engine makes more idle vac with 30-31.. but producrs better off idle torque with 24?.. then maybe redo your map to allow both to happen in consecutive fashion? One of the reasons programmable iginition maps are so awesome.

[groberts101]

On the rethink over that last PS.. I'd venture to say that IF this engine makes more idle manifold vacuum at 30-31.. but more torque off-idle at 24?.. then you need to add a bit more fuel into the off-idle map to coincide with that higher base timing.

Remember that higher ignition advance has the effect of leaning out the pipe.. so more fuel is typically needed to help compensate. IOW, forget specific AFR.. shoot for highest manifold vacuum that is possible at idle and ramp timing away from that point upwards into the rpm range while feeding enough fuel to keep power where it needs to be.

[BigBlockMopar]

The MegaSquirt setup is only controlling ignition, not fuel. Fuel is still 'metered' by the IMPCO carb.

I used to run 24° at idle (in Drive) on the previous (318ci) engine.
With the 360ci engine swap, and its vacuum issue at idle, I upped the advance to around 31°. The engine liked that better.

Now that I changed the cheap noisy 1.6 rockers for a set of 1.5 Crane rockers, I feel the engine is making a bit more power down low.
So the ProComp-rockers added another variable into the mix of issues (who would've thought? ), which only came apparent when really tight lashes needed to be kept.

I'll be resetting lash in a moment, which will hopefully cure the hot-running vacuum/idle issues.
After that I'll do another compression test with a screw-in type gauge. But maybe a leak-down test would be more appropiate.

[user-23911]

You haven't said if your 24 deg or whatever it is at idle is taken from a timing light or from the megasquirt?
Are they the same numbers?
I'd say, very unlikely.

[BigBlockMopar]

One of the first things one has to do with a MegaSquirt ECU is to sync the timing with the engine.
MegaSquirt has a 'fixed timing' option which you set at 15° so you can digitally sync the trigger-angle and base-timing accordingly so it matches the timinglight.
After that's done one can activate the timing table again.
But it never hurts to verify this once in awhile if they still match.

At the moment I'm not too worried about where the timing wants to be, as long as there seem to be some 'hardware' issues.

[cjperformance]

Another out there one to check. Rotor phase at your advance level, a fixed shaft dissy will shift rotor phase as an ignition box adjusts timing, higher spark energy required for , compression and lpg, you have both, the old engine had lower CR. If you were close to getting any cross firing before youll be closer now. With Lpg as a fuel crossfire related miss fires can be worst just off idle with high spark energy systems.
Have you checked rotor phase?
Just trying to cover all bases before you strip this thing! I still think you need to go back to hydro lifters to match the cam or a matching solid setup for this application.
And double check guides and seat concentricity.

[BigBlockMopar]

The Chrysler Lean Burn distributors have the correct rotor phasing from the factory as they where made for computer controlled ignition. I checked and confirmed the rotor phasing during installation on the previous engine.
This was one of the reasons I wanted to use one of these distributors in the first place. The lack of mechanical and vacuum advance mechanisms were very welcome too.

Thought about putting in a new set of hydraulic lifters in the engine, even thought about upping to a roller cam.
But if the problem does lie in the heads/valves, then I'm just wasting money and time with no improvements.

Going to spend some more quality time today with the engine and really try to identify the cylinder that needs attention.
I do think it's only 1 cylinder that's having issues.

One thing I've found happening during all this time is the idle-quality gets worse as the engine warms up.
With a cold engine it can idle (with trans in Drive) without much issues, but when the engine is warmed up it almost wants to stall and is obviously missing (the compression of) one cylinder. This is where the vacuum needle swings are the greatest.

Hope to locate the bad cylinder today and which valve has issues. This has taken long enough.

[cjperformance]

Good choice on using the ELB dizzy as a base, rotor phase always worth a mention for odd problems but if all good there it looks like you're getting closer to a head removal.
How does this engine run down at say 700rpm and only 10/12 deg of timing? With your cam and comp values on lpg it should be pretty smooth. Not optimal but it should be fine.