M20 b25 slight misfire

[Gaffasgaff]

Hello guys . So I have noticed when holding the revs around 2500 rpm I'm feeling a slight misfire while my hand is on the inlet manifold .
Whilst I was on furlough I have done a fair bit of work to the engine .
I replaced the head gasket. Had the head tested skimmed and rebuilt . Full service oil , oil filter , air filter , fuel filter , new spark plugs ( gap checked ) Genuine HT leads and cambelt .
Fuel pressure tested all came back ok .
Compression tested all 6 cylinders came back above 150psi .
Afm bench tested by first testing the temp sensor pins 4 and 1 all came back good operating correctly. I put a 9v battery to pin 4 and 3 and tested the voltage at pin4 and 2 and voltage increased smoothly when opening the door to the afm . No problems there . I'm very certain there is no vacuum leaks at all .
Really confused . I have replaced the coolant temp sensor a while ago now so that's been done . . This was doing this before I done all the work to the engine .

Need some expert advice please

[ah]

You would be better
Putting this in E30 technical help

[Gaffasgaff]

You would be better
Putting this in E30 technical help

Ok thank you . Trying to figure out how to delete this post and upload it on the technical page

[BenHar]

How long since the injectors were serviced?

Ben

[Gaffasgaff]

How long since the injectors were serviced?

Ben

Hi Ben. I have never had them serviced . But I remember around 5 years ago I had them out changed the rubber o seals and made this tube to go over the injectors so that I could spray carb cleaner through the injectors to clean out any gunk . . I have recently had my stethoscope on each injector while the car has been running and they all pulse the same when car is running .

[BenHar]

It may not be the cause, but they are would definitely benefit from a full refurb.

Ben

[Brianmoooore]

Topic moved.
Are you sure there's a problem? The straight six is an inherently balanced and smooth engine, but it's still an ICE with three bangs per rev., so won't be as smooth as an electric motor.

[Gaffasgaff]

Topic moved.
Are you sure there's a problem? The straight six is an inherently balanced and smooth engine, but it's still an ICE with three bangs per rev., so won't be as smooth as an electric motor.

Topic moved.
Are you sure there's a problem? The straight six is an inherently balanced and smooth engine, but it's still an ICE with three bangs per rev., so won't be as smooth as an electric motor.

Hi Brian. Well it just seems strange . Its not smooth at all while holding the revs . Definatly feels like something ain't right . I will try and take a video of it when I get chance and upload it . Idles totally fine . Only happens when revs are held around the 2500 rpm. Really could do with a comparison with another m20

[paultv]

Do you feel any missing or lumpy response under load..ie whilst accelerating away in 2nd...can you feel hesitation or anything as you pass through the power band?

Paul

[Gaffasgaff]

Do you feel any missing or lumpy response under load..ie whilst accelerating away in 2nd...can you feel hesitation or anything as you pass through the power band?


Hi Paul .Last Time I drove it was in June last year . I didn't feel any hesitation or lumpy response.
Paul

[fixedwheelnut]

Do you feel any missing or lumpy response under load..ie whilst accelerating away in 2nd...can you feel hesitation or anything as you pass through the power band?


Hi Paul .Last Time I drove it was in June last year . I didn't feel any hesitation or lumpy response.
Paul

If it hasn't been run since June there is a good chance carbon has built up from consecutive start ups and idling, you might be feeling the carbon burning off, I wouldn't worry too much until you have driven it on the road and see how it performs, the other cause of lumpy running could be an air leak so if you have access to a smoke tester that will save you hours of guess work.

[Tineca]

Pop the old plugs and leads back in just to eliminate. If it wasn't there before then something isn't right. Is it timed up perfectly?

[Gaffasgaff]

Pop the old plugs and leads back in just to eliminate. If it wasn't there before then something isn't right. Is it timed up perfectly?

Hi . It was doing the same with the old leads .
100 percent timed correctly .

[Gaffasgaff]

Do you feel any missing or lumpy response under load..ie whilst accelerating away in 2nd...can you feel hesitation or anything as you pass through the power band?


Hi Paul .Last Time I drove it was in June last year . I didn't feel any hesitation or lumpy response.
Paul

If it hasn't been run since June there is a good chance carbon has built up from consecutive start ups and idling, you might be feeling the carbon burning off, I wouldn't worry too much until you have driven it on the road and see how it performs, the other cause of lumpy running could be an air leak so if you have access to a smoke tester that will save you hours of guess work.

Hi mate hows it going . I will do a smoke test on the intake system . I have sprayed carb cleaners around the intake hoses ect and there is no change in engine note . I might get the injectors tested professionally and see how I get on . But first I will smoke test