rattling can sound in engine over 4k rpm

Ferraripilot · Post by **Ferraripilot** » Tue Jul 24, 2012 5:25 pm

I'm baffled by this. The engine runs fine and still makes very good power, and the MJ software is showing the engine is running perfectly normal, but above 4k rpm there is a rattling can sound inside the engine that almost sounds like detonation. Again, the software says it's running fine at all rpm. I know it's not detonation as I have dialed the timing way back to check that hypothesis only to find the rattling was still ever present. The engine never did this until very recently, and I've put about 800 miles on the system and engine so far (new engine)

here's what I've troubleshot so far:

-all wiring double checked
-sensor positioning measured, remeasured, tightened, gap to trigger wheel checked and is .019-.024 (no stone unturned with this one) with a .005 runout
-new magnecor wires
-checked coils
-plugs
-checked timing with a timing light (it's fine)
-leakdown test on each cylinder (less than 3%, new engine with gapless rings)

what the hell is this?? It *only* happens above 4k.

Ferraripilot · Post by **Ferraripilot** » Tue Jul 24, 2012 11:54 pm

I checked oil pressure tonight with a mechanical oil pressure gauge to absolutely rule out this being a mechanical rattle, which I did. Pressure is fantastic.

The heads are fresh with guides, new tappets, shims, valves, billet cams, this is NOT a mechanical issue. I'm getting a little frustrated with this megajolt....... First, I find out EDIS8 does not rev beyond 7400rpm which no one ever seemed to know about (engine needs to go to 8500rpm) and now it's rattling like an empty can filled with beans over 4k....... yet it runs fine

......

Post by **brentp** » Wed Jul 25, 2012 1:25 am

That is very strange. We've never had a report of rattling before! Can you swap back to the old distributor setup, just as a test, to see if the rattling occurs there as well?

Can you hear the rattling if the system is running on EDIS-8 alone (megajolt disconnected) ?

Ferraripilot · Post by **Ferraripilot** » Wed Jul 25, 2012 1:29 pm

brentp wrote:That is very strange. We've never had a report of rattling before! Can you swap back to the old distributor setup, just as a test, to see if the rattling occurs there as well?

Can you hear the rattling if the system is running on EDIS-8 alone (megajolt disconnected) ?

I will give that a shot. Thanks Brent

Ferraripilot · Post by **Ferraripilot** » Wed Jul 25, 2012 11:07 pm

Ran engine in limp mode with EDIS8 only. It ran well until about 4k rpm when it started to misfire, lots of popping etc. It also made the rattling sound, but the sound was not as present.

I pulled the thick aluminum cam belt cover which I have the VR sensor attached to and made sure it was locked down tight as can be, which it is. I also put a buffer of very hard gasket-like material between the sensor and the aluminum cover it is bolted to which should assist in vibration dampening to the sensor.

I have ruled out the aluminum belt cover I have the sensor bolted to providing a frequency which is only making itself known at a certain rpm as this issue has only arisen in the past couple weeks now. I put several hundred miles on the engine with no problems.

Is it possible that the shielded wire I'm running has deteriorated or gone bad in some way causing the erratic signal above a certain rpm? Or has the VR sensor gone bad? I would think it would be one of the two.

Ferraripilot · Post by **Ferraripilot** » Wed Jul 25, 2012 11:28 pm

Here's the vid I made shortly after I completed the rebuild showing the engine and the MJ working just fine (engine was a bit rich at the time but that's okay!)

http://www.youtube.com/watch?v=oEm6BGwTyuc

See, I'm not crazy. Not much anyway.

Post by **brentp** » Thu Jul 26, 2012 5:31 pm

Normally misfires occur due to vibrating sensor brackets, but I see that yours is bolted right to the case. Hm.

Can you put a timing light on the engine with the Megajolt disconnected, and observe what the timing looks like above 4000 RPM?

Ferraripilot · Post by **Ferraripilot** » Thu Jul 26, 2012 5:57 pm

brentp wrote:Normally misfires occur due to vibrating sensor brackets, but I see that yours is bolted right to the case. Hm.

Can you put a timing light on the engine with the Megajolt disconnected, and observe what the timing looks like above 4000 RPM?

This is definitely a strange occurance as this is where everyone bolts these sensors to when Ferrari guys go distributorless with these engines. As I said before, since then in an attempt to fix this I removed the sensor and placed a gasket-like material under the sensor to attempt further vibrational dampening but this was to no avail.

I put a timing light on it with EDIS8 only and it showed a steady 10 degrees until around 3900-4k when it started misfiring. I did the same with the MJ and it showed normal advance and operation above 4k but the rattling sound was ever present as was some misfiring. It almost seems as if over 4k rpm the system is constantly cutting in and out recatching itself into somewhat normal operation, but the datalogs look fine.

Post by **brentp** » Thu Jul 26, 2012 7:52 pm

So what did the ignition advance look like after 4000 RPMs? did the timing jump / look erratic?

If I were personally diagnosing this, my next step would be to put an oscilloscope on the sensor to see what the waveform looks like at varying RPMs. It sounds like to me the EDIS module is losing / re-acquiring sync with the trigger wheel, as you're suggesting. Do you have anyone that can help you with a next step like this?

Also, might be a shot in the dark, but - do you have another EDIS-8 you can swap in, as a test? Also, check all of your power and ground connections. Are you using a star-grounding pattern for everything? including the shield wire for the VR sensor? Are you using resistor or non-resistor plug wires?

Ferraripilot · Post by **Ferraripilot** » Fri Jul 27, 2012 12:04 am

I had a thermodynamics epiphany this evening regarding this, but first I will answer your question Brent. Ignition advance north of 4k is very smooth, I even checked it in the dark with a timing light just to make sure I wasn't missing out on some subtlety that my eye would not catch in the light. The engine runs flawless, wonderful power.

The only item on the engine I changed since completing the rebuild is the exhaust. Within the past say hundred miles I installed a stainless steel exhaust (it's way awesome btw, but my gosh the 'Ferrari tax' is killer) to replace the aging Ansa Sport. I suppose I never really noticed it fully, but I'm wondering if it's possible that this new exhaust has amplified a harmonic that the previous exhaust either covered up or simply could never produce. This engine has no cats, so it's just manifolds to muffler, and out.

The idea of a finely tuned exhaust is to produce a reverse sound wave to the exhaust valve to aid in scavenging exhaust gases from the cylinder(s). This ever present 'rattling' sound could be a result of the engine coming 'on cam' around 4k (I am running very hot rally spec cams and lots of compression) meaning volumetric efficiency is beginning to peak and the exhaust is responding directly to the frequency provided by the engine thus providing this rattling feedback with this particular exhaust, when all the exhaust is doing is its job (the harmonic wave made by scavenging is the muffler creating a reverse wave at the valve, but it could also be amplified by the waste spark on the exhaust stroke). This makes perfect sense to me as the volumetric efficiency of this cam profile when mapped with the piston speed at 4k rpm and referenced to head flow bench tests shows torque takes a big jump at 4k rpm and peaks at maximum cylinder filling which for this engine is theoretically 5800rpm, then the rattling sound somewhat dampens on up to redline (which I unfortunately cannot reach yet due to the limitations of EDIS8 lol). But above 6k the sound is less present on up to 7400rpm when the rug is pulled out from under me with EDIS8. Lastly, the manifold piping and muffler itself are obviously very short being a mid-engine car so any exhaust harmonic relating to scavenging is going to be further amplified by a muffler made of harder materials and of different baffling.

Sorry for the lengthy diatribe, but the above actually makes some sense and there was of course no way I could have attributed such a noise to something as trivial as an exhaust.

Or, am I flat wrong? I'm open to comments. thanks all

Post by **brentp** » Sat Jul 28, 2012 3:04 am

Can you swap back in your old exhaust, as a test?

Ferraripilot · Post by **Ferraripilot** » Sun Jul 29, 2012 1:25 am

brentp wrote:Can you swap back in your old exhaust, as a test?

I certainly will, hoping to have time to do it this week. This of course has me very curious and concerned. Will report back once done

Post by **brentp** » Sat Aug 04, 2012 3:45 am

Any news on the exhaust swap?

Ferraripilot · Post by **Ferraripilot** » Tue Aug 07, 2012 3:44 pm

No exhaust swap yet because I wanted to make for darn sure the engine was running properly as I knew it indeed has been. So, I ran it over to the dyno which confirmed this. It's making wonderful power and there are no strange oddities on the graph showing ignition issues, which with Ferrari's -especially older Ferrari's- the dyno is where ignition problems really make themselves known.

Swapping the exhaust is a major pain of a process and I will try and get to it this weekend.

Post by **brentp** » Thu Aug 09, 2012 3:58 pm

Well, that's good to hear!

Has anyone else in the Ferrari community complained about the same sound anomalies using that exhaust?