Misfire under low revs- come on what am I missing?

[bigwinn]

Right

Two cars now- fine before but after doing works there is a low end, low revs misfire. Only really manifests in high gears (4/5/6) when at low speeds. Gets worse when hot- in fact non existent when cold.

Both times this has happened after I’ve done the usual engine works- vanos, water pump, thermostat, sparks etc.

I’ve connected inpa and can’t see anything obvious.

Checked fuel pumps and no issues

Looked at rough running and if there is any- I’ve changed coil packs, sparks, checked earthing points.

Checked for obvious air leaks and collapsed vac pipes. Checked for air leaks on the CCV etc. looked at the elbow usual suspect and all round that area including the sound generator. Checked oil cap seals etc.

In short- I can’t figure out what could be causing this when it wasn’t there before. It’s hard to diagnose as it only manifests when it’s moving so you can’t check much when stationary.

Come on- what am I forgetting or missing- nothing off bounds I’d rather own up to something stupid rather than this annoying rough running.

Thanks in advance

 

[enuff_zed]

Assume you're using a good brand of plugs?
In fact are all the components the same brand each time?
Can you see if the cam timing is moving properly? My autophix show live data. Wondering if its not at the right angle at low revs?
Do you do any adaptation resets?
Worse when hotter may imply mixture problems. Hot air, not so dense, so mixture is too rich?

 

[enuff_zed]

And more thoughts..................
Have you fitted new coil packs or ones from one of your fleet?
Also, do you check the plug gaps before you fit them? They don't always come correctly set.
Are you filling up at a cheapy garage with dodgy fuel?

Need to find the constant between both cars methinks.

 

[Zedebee]

Is it actually misfiring or just “bogging down” (which I associate with no firing at all)?

My 3.0Si, which to the best of my knowledge has never been tampered with in any way, pulls cleanly from 500rpm in any gear; whereas the 2.5i which has been through 12 owners and god knows what, bogs down in 3rd gear on an open throttle at anything less than 1000rpm. Above that, it’s fine. I thought it was a tired VANOS but maybe it’s the result of some other intervention.

 

[bigwinn]

Assume you're using a good brand of plugs?
In fact are all the components the same brand each time?
Can you see if the cam timing is moving properly? My autophix show live data. Wondering if its not at the right angle at low revs?
Do you do any adaptation resets?
Worse when hotter may imply mixture problems. Hot air, not so dense, so mixture is too rich?

I’ve put the plugs back to a known hood set of ngk
I’ve not gone near CPS sensors yet but for them both to fail…?
What’s an adaptation reset?

Agree on the richness issue when hot- I’m thinking smoke test next

 

[bigwinn]

And more thoughts..................
Have you fitted new coil packs or ones from one of your fleet?
Also, do you check the plug gaps before you fit them? They don't always come correctly set.
Are you filling up at a cheapy garage with dodgy fuel?

Need to find the constant between both cars methinks.

Swapped coil packs no difference
Plug gaps checked
Different garages

 

[bigwinn]

Is it actually misfiring or just “bogging down” (which I associate with no firing at all)?

My 3.0Si, which to the best of my knowledge has never been tampered with in any way, pulls cleanly from 500rpm in any gear; whereas the 2.5i which has been through 12 owners and god knows what, bogs down in 3rd gear on an open throttle at anything less than 1000rpm. Above that, it’s fine. I thought it was a tired VANOS but maybe it’s the result of some other intervention.

Did the blue 2.5 do it with you- I thought it was pre/post cat issues but that wasn’t the issue

 

[Zedebee]

Is it actually misfiring or just “bogging down” (which I associate with no firing at all)?

My 3.0Si, which to the best of my knowledge has never been tampered with in any way, pulls cleanly from 500rpm in any gear; whereas the 2.5i which has been through 12 owners and god knows what, bogs down in 3rd gear on an open throttle at anything less than 1000rpm. Above that, it’s fine. I thought it was a tired VANOS but maybe it’s the result of some other intervention.

Did the blue 2.5 do it with you- I thought it was pre/post cat issues but that wasn’t the issue

I’m not aware that OBY did it, but then that car did seem to run better than a 2.5i should, certainly louder and faster than it’s twin.

 

[enuff_zed]

Do you do any adaptation resets?

When I do the vanos I use the Autophix to reset the adaptations to the basic factory settings. It mainly just makes it quicker for the ecu to relearn it all rather than have to overcome all the changes it has made to compensate for worn vanos seals.
Just wondering if its just taking time to settle down.

 

[bigwinn]

Is it actually misfiring or just “bogging down” (which I associate with no firing at all)?

My 3.0Si, which to the best of my knowledge has never been tampered with in any way, pulls cleanly from 500rpm in any gear; whereas the 2.5i which has been through 12 owners and god knows what, bogs down in 3rd gear on an open throttle at anything less than 1000rpm. Above that, it’s fine. I thought it was a tired VANOS but maybe it’s the result of some other intervention.

Did the blue 2.5 do it with you- I thought it was pre/post cat issues but that wasn’t the issue

I’m not aware that OBY did it, but then that car did seem to run better than a 2.5i should, certainly louder and faster than it’s twin.

Agreed- was the best 2.5 I had

 

[bigwinn]

Do you do any adaptation resets?

When I do the vanos I use the Autophix to reset the adaptations to the basic factory settings. It mainly just makes it quicker for the ecu to relearn it all rather than have to overcome all the changes it has made to compensate for worn vanos seals.
Just wondering if its just taking time to settle down.

I’ll see if I can do similar with inpa

 

[patriot66]

Hi Stu. Is the DISA ok ? Also, I had similar on a E39 530i M54 many years ago which turned out to be a hairline crack in the MAF body which didn't manifest itself until things had warmed up

 

[enuff_zed]

Pretty sure you always check the disa and modify Stu, but maybe the seal is leaking?

 

[enuff_zed]

Or the breather pipe from the front of the top cover not sealing properly after you've done the vanos?

 

[bigwinn]

Hi Stu. Is the DISA ok ? Also, I had similar on a E39 530i M54 many years ago which turned out to be a hairline crack in the MAF body which didn't manifest itself until things had warmed up

I have a spare so well worth a swap over- good shout!

 

[bigwinn]

Or the breather pipe from the front of the top cover not sealing properly after you've done the vanos?

worth a look as it may have unseated underneath

 

[colb]

Airleak still a possibility when its warmed up and opens up a crack in something, certain way of finding a problem like this is a smoke test. Its not just the rubber and plastic vaccum hoses that develop splits and holes, some of the plastic componants and O ring seals can end up being the cause of vaccum leaks. A quick look at the fuel trims in live data on diagnostics is worth a look, if they are high the exhaust sensors may well be picking more air in the exhaust than what the Maf had passing through it. Fools the DME into thinking its running lean and commands more fuel at the injectors to richen the mixture. It will keep doing this till its adding up to 20% more fuel then give up and set the EML to draw attention to whats going on. When smoke testing pay particular attention to the dipstick tube, the O ring in it can fail and cause a vaccum leak. Also take your time to inspect the plastic cam cover, cracks in that can also cause air leaks. Dealt with a 2.2 where the cause of an air leak was the cam cover cracked and crumbling around No4 plug well. Down to plastic being age related and weakened through repeated heat cycles. Vaccum leaks are quite a common cause of crap running, these engines are reliant on a good vaccum system.

 

[bigwinn]

Thanks Col- its going in for a new clutch next week so will ask them to smoke test see if there are any obvious holes!