Misfiring M52

[HarriG93]

Evening all,

Need a bit of a hand here.

I decided to try and get my 2000 Z3 2.0 back on the road after 2 years laid up, since y’know, lockdown. She’s an M52TUB20 with 128k miles on the clock. An absolute shed, but she ain’t half pretty.

Just before I took her off the road, I’d spun off a greasy roundabout (doh) into a grass verge. Car seemingly unfazed, I continued on but the next day when driving home a few seconds after pulling away, I noticed a severe loss of power and change in noise - throbbing like a diesel ship engine, dugadugaduga.

Managed to limp home, struggling to get over 50mph and 4k, then suddenly on the home stretch she roars back into life.

I assumed coil pack, and took her to the local garage who changed three of them and then I put her in the garage.

So, this week I put her on trickle charge and she started first time. However, the misfire is still there. First 30 seconds she’s her normal totally smooth Straight 6 self, then suddenly the idle drops revs and the dugaduga returns.

It’s a throbbing, lazy and slow revving with severe loss of power. No smoking, no smells, seems to warm up to the right temp. Of course, she could do with oil change but the oil and coolant are all topped up.

I changed the remaining three coil packs and all 6 (admittedly worn) spark plugs myself (first time I’ve ever done anything mechanical - was well chuffed) and again, she started wonderfully and then 30 seconds in.... dugaduga!

I’ve got it booked back in with the local garage, but given they didn’t solve it last time, I want to make sure I know which direction to point them in.

My thoughts would be fuel injectors as next line of attack but as Covid-19 done me dirty, I need to be avoiding any unnecessary big spends so want to make sure I get it right.

Thanks in advance!

Harrison

 

[t-tony]

Hey Harrison, firstly welcome from me near Lincoln. Secondly what you really need is to get a code reader hooked up to your car to see if there are fault codes stored. Where are you located? If you don't have or don't know anyone who has a code reader I would check the big induction rubber between the air filter box and the induction manifold. The "spin" off the roundabout could well have caused the engine to move enough on is mountings to dislodge or even tear the boots. I can read the codes if you're anywhere near me.

Tony.

 

[HarriG93]

Hey Harrison, firstly welcome from me near Lincoln. Secondly what you really need is to get a code reader hooked up to your car to see if there are fault codes stored. Where are you located? If you don't have or don't know anyone who has a code reader I would check the big induction rubber between the air filter box and the induction manifold. The "spin" off the roundabout could well have caused the engine to move enough on is mountings to dislodge or even tear the boots. I can read the codes if you're anywhere near me.

Tony.

Thanks Tony.

Funnily enough, I bought the car from a chap in Lincoln 3 years ago, though the car is currently in my grandparents garage in Scotland.

However, took your advice and bought and OBDII and took screenshots of the data when initially idling nicely and again when it starts misfiring.

 

[t-tony]

Engine coolant temperature way too low. Probably needs a thermostat. Did you check the intake boots thoroughly? Try spraying some carburettor cleaner around the intake manifold and intake boots while it’s running and note any change in engine tone.

Tony.

 

[HarriG93]

Engine coolant temperature way too low. Probably needs a thermostat. Did you check the intake boots thoroughly? Try spraying some carburettor cleaner around the intake manifold and intake boots while it’s running and note any change in engine tone.

Tony.

Everything (to my untrained eye) looks all good, but I tried disconnecting the MAF which looked remarkably clean.

Tried running the engine without reconnecting and it seemed to run absolutely fine. Occasionally drops revs slightly for a split second, which it’s always done, but otherwise I couldn’t hear a misfire though the OBD still picked it up.

I did hear a very faint and distant near constant popping sound from the exhaust and a slight tapping from the engine bay when sat in the cabin but couldn’t really hear it from outside.

Read the below data with the MAF disconnected.

 

[HarriG93]

However, I got misfire codes on cylinders 1, 2 and 3 even though it sounded fine and revved cleanly. First time I’ve had cylinder misfire on cylinder 1.

 

[colb]

The high fuel trim on the first set of data you posted would lead me to suspect an air leak in the induction or vaccum system, check for holes or splits in all rubber parts of the system from Maf onwards. With the Maf disconnected in your second set of data its no surprise to see no reading for that, disconnected the car will be running on default settings. Now you have a code reader, clear the codes you have and the MIL will turn off, run the car again and read it again to see what returns. If the fuel trim is still high then look for the air leak in the rubber parts, replace any found split or holed. Clear codes and run the car again followed by reading for codes again. To be absolutely sure you have an airtight vaccum system a smoke test is best for finding any leaks you can't find visually.

 

[HarriG93]

The high fuel trim on the first set of data you posted would lead me to suspect an air leak in the induction or vaccum system, check for holes or splits in all rubber parts of the system from Maf onwards. With the Maf disconnected in your second set of data its no surprise to see no reading for that, disconnected the car will be running on default settings. Now you have a code reader, clear the codes you have and the MIL will turn off, run the car again and read it again to see what returns. If the fuel trim is still high then look for the air leak in the rubber parts, replace any found split or holed. Clear codes and run the car again followed by reading for codes again. To be absolutely sure you have an airtight vaccum system a smoke test is best for finding any leaks you can't find visually.

Super helpful and many thanks. Actually, digging around I noticed what I think is the alternator cooling duct has come loose - gapingly loose!

Not sure this would be contributing to it P0170 though, but car is booked into local garage tomorrow morning. Not holding out much hope with them though, given they’ve misdiagnosed before.

 

[t-tony]

That is a fuel trim fault code, almost certainly due to a split induction boot allowing unmetered air into the engine which the O2 sensors do not have enough "range" to correct.

Tony.

 

[Mario]

I am with the air leak guys here - but reading your story if you spun the car maybe the exhaust hit something and you might have a split on the exhaust manifold or somewhere before the LAMBDA sensors and you have air coming in - if you can't find the air leak on the intake check the exhaust.

 

[Lee]

It's quite clear to me, look at the fuel trim on bank 2, way to high you must have an air leak.