800, 1600rpm misfire/vibration

[ByronRACE]

My 12K mile old 03 bone-stock Marauder has developed a misfire/vibration that is not flagging the MIL nor setting a code. It can be felt faintly at 800rpm and 1600rpm either in park/neutral or in drive.

I've read everything I could find (used search), and didn't find anything I either havn't thought of or havn't planned to do next...but I thought I'd post a plea for help anyway.

Done so far:

- Scan tool, pulled codes - none
- Scan tool, checked all sensor outputs with datastream - all are correct
- Long term fuel trims are under 3%
- Pulled all 8 plugs. They show even burn. No cracked anything.
- Compression check 230,230,230,230,220,220,217,22 2 in numeric order.
- I thought the bank to bank variance was interesting but inconclusive.
- Checked all 8 plug bores. They show no water, oil, etc.
- Changed all 8 plugs to new; gapped to .045" intentionally; no change
- Inspected all 8 plug boots; appear as new
- Inspected all COP connections; appear as new
- Ran engine without accessory belt; no change
- Ran tank dry, replaced fuel; no change
- Scoped all 8 injector inputs. PW is the same on all 8.
- Fuel rail pressure is constant.
- Ran injector cleaner in the tank anyway; no change (yet).

Nothing helped; still has a steady slight miss at 800ish and 1600ish rpm that shakes the engine and chassis and can be felt during steady cruise at 1600rpm. It doesn't seem to get worse or better with load. You can't feel it at all at heavy throttle.

So what would you recommend I try next?

On the list...

I have not yet purchased a cop module and swapped it in.
I have not yet changed/checked the springy thingies.
I have not yet changed the boots.
I have not yet scoped the spark waveforms on the primary or secondary side of the coils.

Is there something common I should be doing, or just run down the items above?

The car drives fine, but feeling this miss is driving me nuts! :help:

Thanks in advance for any advice,

Byron

[Blackened300a]

Consider this normal. There is a sweet spot in the engine at around those RPMs that you'll feel a vibration. If you do a search, you'll get more detail on this.

[Marauderjack]

Mine does this as well.....I thought it had to do with the blower but a call to Dave revealed that it is VERY common in FI cars with no load!!:confused:

I would guess it is the EEC trying to make it as lean as possible for emissions reasons!!:mad:

How is it when you drive it (load engine) at those engine RPM's??:cool:

Marauderjack:burnout:

[Stranger in the Black Sedan]

My stock 23k mile MM has the same vibration. I was concerned at first but figure it is just a finicky characteristic of this engine.

[ckadiddle]

I had noticed an intermittent rough idle in my 03, which was built in Jan03. Mentioned it to dealer while in for other service, they changed out the plugs with a newer spec "updated" plug. Definitely helped the idling, and the car definitely ran a little stronger after they were installed. Don't know if this would be related or not, but it sounds kinda sorta similar if I squint really hard. Maybe someone can come up with part numbers.

[ByronRACE]

Thanks guys, I knew I came to the right place.

I have a wideband and the ability to run the engine full open loop and richen it some to see if it goes away and am willing to do so if you guys would like to know if it is because of fuel enleanment. However, I think the answer is "no" because it does this at cold start when the mixture is quite rich.

If you drive it under load, yes you can still feel it...if you're being anal retentive. Under normal use, you'd never notice it. Now that I'm trained to detect it, I feel it all the time of course.

"Consider it normal" is ok with me now that I know others do this. I did search for a few hours before posting and was unable to find information like what was just offered, so thanks for that. I don't mind intrinsic vibration if that's what it is.

I'm currently running autolite 764's (non-platinum autolites, same heat range as stock) as a test. I gapped them slightly tighter than stock as well. No effect what so ever; runs/drives the same.

I'll probably go through the "swap the cops" exercise anyway. The packs are about $25ea and a whole set of 8 new boots/springs is $28. I'll play around with it a bit more and if I get anywhere, I'll post. I'll also go dyno it again and make sure the curve overlays from when it was new as a sanity check.

After reading all the posts about the blown marauders, it's going to be really hard not to modify this one. This is supposed to be my "nice daily", but I'm getting the itch to mess with it. I hope my nutty Cobra Kit gets out of the body shop soon...or the marauder is going to get messed with for sure! LOL

Thanks again,

Byron

[Blackened300a]

I did search for a few hours before posting and was unable to find information like what was just offered, so thanks for that. I don't mind intrinsic vibration if that's what it is.

Vibration - MercuryMarauder.net Forums (http://www.mercurymarauder.net/forums/showthread.php?t=22666&highlight=engine+vibration)

Engine vibration at 2000 rpm - MercuryMarauder.net Forums (http://www.mercurymarauder.net/forums/showthread.php?t=25066&highlight=engine+vibration)

Vibration - MercuryMarauder.net Forums (http://www.mercurymarauder.net/forums/showthread.php?t=6699&highlight=engine+vibration)

Heres a few threads with some info on what you are feeling

[ByronRACE]

Anyone have compression check numbers other marauders with this vibration?

Noone has commented about mine. I think it's odd one bank reads 230 and the other bank reads around 220.

Considering the firing sequence and uneven compression bank to bank, this sounds like a recipe for harmonic vibration such as this. That's a 5% variance bank to bank. I would also expect it to have 2 beat frequencies. I havn't measured the beat frequency of the vibration, but I'm a nerd...and may play around with that.

Byron

[ByronRACE]

So, sitting in my driveway tonight I estimated the beat frequency of what I'm feeling.

At 800rpm, I estimated about 6-8 beats per minute (Hz)
At 1600rpm, I came up with 13-16Hz.

I went in the house and did some quick math and it would suggest that what I'm feeling is a single cylinder event...so not bank-to-bank as I was pondering.

http://racesystems.com/temp/clip1.jpghttp://www.racesystems.com/clip1.jpg

At 800, I guessed 6-8Hz, and ignition events happen at 6.67Hz.
At 1600, I guessed 13-16Hz, and ignition events happen at 13.33Hz.

Seems a little too coincidental to ignore; normal or not.

Hmmm...

Byron

[Power Surge]

Byron, you think too much :D.

[JMan]

Byron,
What brand of scan tool do you have and will it access Global OBDII Mode$6? You can look at historical misfires in Mode$6 if it's not written out of your tune. A stock tune will record misfires below the threshold of code setting (20%). These records are "readable" by cylinder. If you need help, PM me.

If it's any consolation, My Vic has always had an exhaust vibration at around 1500rpm when cold. It also idled roughly without the a/c on. Later factory flash calibrations eliminated the rough (uneven) idle but I still have the 1500rpm vibes when it's cold - Florida cold that is!

Best luck,

J

[ByronRACE]

I replied to this thread last night...and today I don't see my post. Odd.

I have access to an NGS Star tester; I'll try what you suggest, thanks.

Sal! Stop following me around man, you're creeping me out! LOL How's the trogdor-vic treating you? I see KarKraft has the new supercharged 5.4 mill; complete; for $14,500...think that would fit in a Marauder? Heh heh heh.

http://www.karkraft.com/search.htm

[Power Surge]

Sal! Stop following me around man, you're creeping me out! LOL How's the trogdor-vic treating you? I see KarKraft has the new supercharged 5.4 mill; complete; for $14,500...think that would fit in a Marauder? Heh heh heh.

http://www.karkraft.com/search.htm

Trogdor, the Burninator!!

I'm not following you around, you just keep buying the same vehicles as me :D.

[ByronRACE]

So I'm the stalker, I see how it is. LOL. :bs:

[magindat]

This might sound naive, but I had a slight vibration at just below 2K under load. It went away when I swithed to underdrive pullies. I didn't go UD for that reason. My daughter noticed to new found lack of vibration and the closest change I could recall was the UD crank pulley.

Go figure....

[Bradley G]

I have always noticed this little vibe@1800-2100.


When the new Ford Reman longblock motor was installed, the vibe was noticably different(much more pronounced)I chalked it up as inheirent to the new mill.
It wasn't until the Blower was going on, I realized the New motor had a harmonic dampener from a 2v 4.6.
The lower crank pulley holes were not the same as the correct balancer.
Once it was replaced with the correct balancer pulley.
Vibe was back to minimal 1800-2100 range.
Check your bottom pulley.

[ByronRACE]

My 03 Marauder has just passed 22K miles, and the vibration is still there...though more noticeable at 800ish rpm and not hardly noticeable above that.

I've done some testing lately that appears to be leading to an answer; so I wanted to report my findings.

I found a slight surface temperature difference in one exhaust port if the engine is held at the RPM where the vibration is the strongest...which is about 850rpm. This was measured using an IR thermometer.

My injector pulsewidth is even across all 8 cylinders when held at this rpm; within 0.1ms so the fuel metering should be the same. I've also moved the injectors around and the colder cylinder remains.

I read the plugs, they look very similar.

By pulling the injector plugs while the engine is running, I can tell you I *think* it's #5...but I'm not 100% certain. It runs amazingly well on 7 cylinders and it's hard to judge if the misfire creates the exact same vibe or not. When I unplug #5, it *seems* to be exactly the same vibration; only stronger.

If I lock the EEC into open loop and lean the AFR out to 15.5:1, the harmonic vibration picks up new beat frequencies and it feels very similar, only more frequent. If I richen the AFR to 13.5:1, the vibration goes away completely.

Personally I think it's a lean condition in one cylinder, probably due to airflow distribution in the intake manifold. I do not believe I have a leak, but I guess the next step is to pull the lower intake off and make sure. If no leak, I'm not sure what to do next. I'll report my findings.

Does anyone know if there's a way to bias one cylinder slightly richer while still retaining closed loop fuel control? It was my understanding that Fords calibration did per-cylinder fuel trim and would trim out a one-cylinder lean condition. After scoping all 8 injectors, I tend to believe this is probably not the case on the Marauder...as they are all within 0.1mS of each other. My pickup injector pw is not grouped nearly that tightly.

If I can't find a way to do this to one cylinder, I'll lock the ECU into open-loop and find a way to make one cylinder richer either by ordering a custom injector for that hole, or building a signal molestation box that grows the pulsewidth slightly.

Anyway, I'll report my findings as I find time to mess with it. I can't leave stuff like this alone; it's like a scab that never heals.

Byron

[Bradley G]

You are Da Man! Byron!
very interesting read!

[JMan]

You are a man after my, uh, well, . . . Nice bit of technoid testing there, bro!

A couple of observations (a.k.a. opinions - you know how those are).

The miss is on the same frequency and timing as the #5 cylinder. It could be the cylinder opposite in the firing order (during the intake "event"). 1-3-7-2-6-5-4-8 Odd but possible!

Fuel metering on EEC-V is done by bank and not by cylinder. A faulty cylinder will skew a bank, but just slightly. A gross failure will shut down an injector on a single cylinder however. This is not a factor here! Your Long Term Fuel Trims will show the culprit bank by adding up to about 6% for a full misfire. That is not a typo.

[quote] Personally I think it's a lean condition in one cylinder, probably due to airflow distribution in the intake manifold. I do not believe I have a leak, but I guess the next step is to pull the lower intake off and make sure. If no leak, I'm not sure what to do next. I'll report my findings.
[quote]

This could very well be the proper correction. Before you pull the scab, let's think about what could cause this.
Intake leak - either external, internal, or EGR/EVAP (Either could intro unmetered gases and be unproportional). EGR/EVAP can be easily bypassed for test purposes.
Valve issues - either intake or exhaust, cam lobe wear, follower/lifter issues. Not as likely but still possible on a four valve. An issue like this typically would be noticeable at different engine speeds.
Injector or driver circuit - All the injectors are individually controlled and therefore susceptible to faults in circuitry (Corrosion, chafing, connection, PCM, etc.) Those faults won't show up in a voltage waveform. Do you have a low-current probe for your lab scope?

Keep in mind that just off idle (TPS - Partial on the NGS), the PCM opens EGR and advances timing along with a higher manifold pressure yielding greater cylinder pressure. This is an idyllic setup for a lean misfire to occur. It also is a good spot to expose a one-electron-wide path through the coil boot to ground other than through the plug. The quote below parallels this thinking-
[quote] If I lock the EEC into open loop and lean the AFR out to 15.5:1, the harmonic vibration picks up new beat frequencies and it feels very similar, only more frequent. If I richen the AFR to 13.5:1, the vibration goes away completely [quote]
It is not likely you have an out of calibration EGR or DPFE. That would cause broad issues not single cylinder issues.

You didn't mention which exhaust runner was coolest and by how much. That would be a prime suspect!!! Coil boots are cheap. They can be swapped around pretty easily on bank one. Bank two is a little pain, though. Alternately, if the NGS Mode$6 data doesn't work, a Ford PDS or IDS can give you live cylinder balance graphs to hint towards which is the bad guy.

Lastly, your question was is there a way to enrichen one cylinder during normal operation. Yes, don't go there yet! You are being analytical to the max. I fortunately don't see 850rpm for very long:burnout:.

Best luck,

J