ld63

About a week after installing new MHP Gen 2 headers and new V5 EC header tune and I’m getting a metallic/hollow feeling coming through the pedal at high RPM - only when the car is fully warmed up. It goes from the smooth throttle increase to suddenly feeling like I can “feel the engine vibrating through the gas pedal” in my right foot along with loss of power. Very strange. In addition to this, the car has a slight rough idle as well - a gentle vibration when stopped. No CELs.

A bit of back story - It turns out my original installers left the passenger heat shield on (which, per MHP instructions, needs to be removed). I had another shop clean everything up today, removing the passenger side heat shield, reworking clamps and adjusting the pipes to clear the cross bars. Unfortunately , the same issue happened after I drove off and the car warmed up fully.

In contact with the various vendors, but no solid leads on this. I’m getting a bit frustrated as I really just want to get some good driving in with the new headers.

Some speculative questions/comments:

1. Several folks running headers have reported similar issues with the aluminum cross-bar in place, and removing this completely results in a drastic improvement. MHP Gen 2 are designed to clear the this bar, but I just checked and it barely clears them (can maybe fit a pencil in the space). Worth removing this?
2. Symptoms sound a lot like knocking/pinging symptoms I’ve read about, but mentioning this to EC and they do not seem to be thinking along those lines. I asked if there’s a chance the header tune is running lean up top, and they said of course not.
3. Could it be traction control kicking in? I generally use sport mode, but maybe with the new set up it feels different.
4. I recently installed ROW airboxes and AFE pro dry S filters, however the main issue was present before that (though the slight rough idle may have started after that). And, no CELs since upgrading airboxes.
5. Perhaps I filled up as a bad gas station? My last fill up was not at normal station, but at another Chevron across town.

Thanks in advance to anyone with suggestions.

CarHopper

Here's what I would do if this was happening to me.

I'd put the stock air boxes back in and drive casually through that tank of gas. Then fill up at a normal station, premium of course.

If the problem persists I'd seek out getting a custom tune via dyno.

Off the shelf maps, even for headers, can only be so specific. That's why I'm willing to be EC is telling you that you aren't leaning out. They've probably designed that OTS header tune to be on the conservative end anyway.

While it is convenient that they have the options available to send you tunes for the mods that are on your car, each car is going to be a little different. That file may be just off enough to make your car feel the way it does.

Best thing to do is dyno tune it though.

As for your first bullet point, I can't help you there because I don't have LTH's.

Good luck, hope others chime in with help as well.

Merc63

Remove that cross bar. It's a pain in the *** and probably hitting once the exhaust heats and expands.

Put the car on the dyno with an exhaust sniffer and plot the AFR to be sure and check the graph to make sure not drops in power etc.

ld63

Thanks very much for the suggestions! I removed the cross bar last night, but didnt get a chance to romp around. Also, got a new tune file this morning and am currently testing it out. Will report back once I get a few drives in!


In the meantime - anyone else with headers+tune feel anything at all 'through the pedal'? Manual mode, sport mode traction, car fully warmed up (220+ degrees) pretty much flooring it from a dig. Do you feel anything in the pedal when the dash starts flashing red to upshift?

I am Jeff

Did you ever find out what was the cause of the rough idle and knocking/fluttering sound?

ld63

Hey sorry for not providing an update. I’ve not fully resolved this issue yet, but have received a number of new tune files have progressively improved the symptoms (but not completely resolved yet). The tunes have done nothing for the rough idle - still present.

I’m scheduled to go back to my local shop tomorrow morning to triple check the header install, and to check my motor mounts etc..

I also disconnected the battery this morning and noticed a slight improvement in shift points, but still idling rough. (And I’ve been avoiding pushing it too hard so haven’t tested for pinging again).

Couple of other data points: I had another C63 owner drive my car and he felt the symptoms as well. I also checked with a second owner who has nearly the same set up (same headers and tune) but he did not experience these issues - though he’s running higher octane. He’s had his fair share of issues but not these.

Some concerns: Tuner keeps removing timing, so perhaps we’re ‘tuning around’ a mechanical issue, as this is a pretty common set up (though, a few newer variables are in play for the tuner: 507 edition and Gen 2 MHP headers vs. Gen 1). Original installer pulled the engine to install headers! Not sure if remounting could have caused a rough idle.

FYI MHP and Eurocharged have been very supportive throughout the ordeal.

desired_speeds

load back to stock tune and go from there. My friend's CLS63 had this shudder after he got a tune for LTHs and they replaced everything down to the torque convertor at the dealer and at the end they reflashed the ecu/ trans to the latest software and it went away.

Wobble64

Re the crossbar: I also messed with that because I had some noises (mechanical, not from the engine, turned out to be the transmission mount, not the exhaust). I now have the crossbar in with 1/2 inch spacers to make it sit lower. Now there is definitely enough clearance to the exhaust. Even with spacers the crossbar is not even close to becoming the lowest point on the car.
When doing that I needed 4 new 35 mm long M10*1.5 screws to allow for the spacers. The standard undertrays fit right over it without issue. They are flexible enough. It is very clean that way and probably a good idea for robustness.
Note: I am not sure this is really needed, but since I have it, I'll leave it in.


ld63 - I would really dig in and look for the underlying issue. If you change too many things it may actually get harder to find it. The car should not run rough with the standard tune - I bet there is something else, like an air leak on the inlet side, bad spark plugs, etc.

ld63

you guys think it's safe to run the stock 507 tune? (or even the non-headers v5 tune)?

Of course, I would not think to push the car hard, but perhaps the rough idle would clear up.

Wobble64

That just triggered a thought: What if your issue was also a engine mount or transmission mount like it was with me? That could also explain rough idle and some shaking, although more likely when cold rather than warm. Hmmm....

ld63

yeah I was thinking along those lines too.. and the fact my installer decided to pull the engine. The rough idle is definitely more prevalent when fully warm. Still going to have the shop check it out tomorrow morning.

Also I may try desired_speeds suggestion tonight and just put the stock tune on there, start it up, and let it idle. Maybe drive around the block at ~20 mph and see if it shakes at all..

Wobble64

I cannot imagine how a tune should lead to shaking at idle. Knocking is something else, it happens under load. Your issue must either be something mechanical like engine mounts or something else is way off after the engine pull, like an air hose not connected.

ld63

Took the car to ACG this morning. No issues found with the mounts, air hoses, etc. We could only speculate on a couple longshot possibilities, but overall the mechanical side of things is checking out..

I also had issues reverting my tune to stock last night (MyGenius related). Working with the tuner on that.

I did revert to the non-headers v5 tune today (which I ran for 6 months before headers) and the car definitely ran quite a bit smoother at low RPM, and the rough idle seemed to be down a bit too.

Also reverted airboxes from ROW to US but didnt notice much in the one drive since then.

I have yet another tune file with more tweaked timing that I've yet to install. Will throw that on tomorrow and continue the experiment..

As a next step, I may pursue a custom dyno tune and/or start reverting to stock if I cant sort this.

Thanks all for the help. Great to have a community to bounce ideas around.

Wobble64

Very, very strange.
Did you read out any error messages from the OBDII port? Any codes related to O2 sensors, misfire, running too lean?
Did you talk about spark plugs as a possible culprit with ACG?

ld63

I've done several OBDII scanner checks over the past days with my cheap scanner - no active or pending codes. All monitors ready. The other C63 owner I met up with also used his scanner and found the same (though he tried to 'delete codes' and it failed wit an error - which he found unusual). ACG mentioned they would connect to a star diagnostic check, which I forgot to ask about, but they also didnt say anything when I checked out.

Spark plugs were brought up by the other C63 owner, but I didnt look into this with ACG. Worth replacing these? I was thinking of doing colder plugs anyway w/ the long tubes.

Also installed the latest tune and romped around a bit. No knock symptoms as of yet, but the subtle omnipresent rough idle is still present. Also, switched to Shell V-Power (from Chevron Supreme) last fill up. Both 91 Octane.

btw - where did you get the spacers for the crossbar? Home depot has the M10*1.5 35mm bolts, but the biggest 1/2" spacers are just a tad tight for the bolts.

Thanks!

Wobble64

Regarding the spacers and screws to lower the crossbar under the new exhaust:


I wanted to have stainless steel in order to avoid rust over time, so I got my screws from Grainger (could not find what I wanted at the local DIY stores). Here is one that would work:
http://www.grainger.com/product/Skt-...Code=P2IDP2PCP


As spacers I got them from my exhaust installer. They are 1/4 inch aluminum discs, and I used 2 per screw, making the overall lowering 1/2 inch. I guess you could also use a bunch of large washers to add up to the 1/2 inch thickness you are looking for. Alternatively something like this:
http://www.grainger.com/product/Roun...AS01?$smthumb$
Unfortunately those sell in packs of 10 and are pricey.


Tractor Supply may have some more stuff in stainless too.


Good luck!

ld63

Great thanks Wobble64 for the tip on the crossbar!

And, perhaps my final update on this thread, I did an oil change a couple days ago and oddly enough the rough idle has all but disappeared! (bewildering but I'll take it). Sometimes I still think I feel something slight, but I know my sensitivity is sky high.

The latest tune file has also not produced any knock symptoms in 2 days.

I'll be keeping an eye on things, and probably doing some dyno runs to confirm the curves look good.

THANK YOU again for all the support!