Engine: 850 T5/R Engine shunting at low rpm

[Clark]

Dear All,

I had a historic MOT minor advisory (engine oil leak) looked into last week and it turns out there was a minor leak from the turbo feed pipe. The turbo oil feed gasket has now been changed and oil leak rectified (along with a new clean MOT before I stick her up for sale)...however she now:

- idles rough i.e. intermittent vibrations during idle. Almost like a chugging. the rev meter does not move though.
- accelerates and cruises rough aka chugging/shuddering below 2000 rpm
- general lack of power at low rpm
- you can tell from the exhaust gases that something is wrong as the gases stop and start intermittently. The flow isn't linear and smooth

I can't see how a lower engine bay steam clean and turbo oil feed gasket replacement could cause this so I was thinking:

- loose vacuum hose somewhere
- engine misfire
- MAF fault

Any thoughts would be welcome.

[richmac]

Hi Clark,

Strangely, I've spent the last 2 days trying to diagnose what sounds like exactly the same issue. I was about to post the following but hope you don't mind my putting it here to avoid thread split.

'Does anyone have any experience of diagnosing/ treating the following, please?

1998 V70 2.5T auto, 200K, stage zeroed 2 years ago, all Volvo parts except for Magnecore reds.

Symptoms:

Immediately after a mile long, steep, dual carriageway climb, the car felt as though it was missfiring if I needed to accelerate and the whole car started shaking at idle. It is driveable but better at higher revs (2500+).

There are no warnings or codes and the temperature is solid. No oil or water mixing. PCV is good as is head pressure.

The exhaust sounds like a big V8 and has a rich smell.

The usual investigations found:

#4 plug dark and slightly wet but no obvious smell. Plug changed without effect.

Compression test:

#1,2,3 + 5 @ 152
#4 has no compression at all!! No change with oil added.

I believe I may also have an exhaust gasket leak ivo #4.
I think this is an exhaust valve issue but is there anything else I can do or check without taking the head off?'

I hope any replies help us both. My only advice apart from all the usual checks would be to do a compression test.

Best regards,

Rich.

[Baffler]

@ Clark

Checking for moisture build-up in the distributor cap after the steam clean would be my first port of call. Clean with contact cleaner and thoroughly dry afterwards with hairdryer/heat gun/compressed air.

If all looks clean and bone dry I'd then be checking if the Engine Coolant Temperature (ECT) sensor isn't going bad. Resistance values are posted somewhere on the forum.



@ Rich

You've a lot going on there and initially sounds as though it's over fuelling. Could be ECT, as above, or front Lambda sensor but you'd usually get a code for the Lambda.

Due to no compression on 4 it may also be that it's not igniting the fuel correctly on that cylinder...hence the rich smell from the exhaust. Have you tried to get a mix of ATF and acetone down into cylinder 4 and leave it soak overnight or as long as is possible?

An oil change would be advised if you manage to restore compression.

[Shinsplintz 101]

Sounds like moisture trapped in one or more connectors causing poor running/ misfire.

Grab some electrical cleaner spray from motor factors and start unclipping, cleaning (ie driving out water residue) from male and female connectors.

1st port call would be Idle control valve, due to symptoms described, but worthwhile just doing everything you can see.

Word to the wise. Don't steam or wet clean these engines unless everything electrical is taped up - most of us have learned that hard way, and those that haven't will - 25yr old electrical connections in an engine will be porous, especially when hit with pressurised water / steam. Best bet when faced with an oily mess underneath is a gallon of brake cleaner, hand pump spayer and a nylon type paintbrush to agitate worst bits. The brake cleaner will rinse off the oil then just evaporate.

Hope you get it sorted, nothing more irritating than a car that start playup right as you try to sell!

Cheers, Morgan

[Shinsplintz 101]

Unlikely it got inside the dizzy cap, although possible,
but do check King lead and HT lead boots at cap.

[Shinsplintz 101]

Originally Posted by richmac

Symptoms:

Immediately after a mile long, steep, dual carriageway climb, the car felt as though it was missfiring if I needed to accelerate and the whole car started shaking at idle. It is driveable but better at higher revs (2500+).

There are no warnings or codes and the temperature is solid. No oil or water mixing. PCV is good as is head pressure.

The exhaust sounds like a big V8 and has a rich smell.

The usual investigations found:

#4 plug dark and slightly wet but no obvious smell. Plug changed without effect.

Compression test:

#1,2,3 + 5 @ 152
#4 has no compression at all!! No change with oil added.

I believe I may also have an exhaust gasket leak ivo #4.
I think this is an exhaust valve issue but is there anything else I can do or check without taking the head off?'

I hope any replies help us both. My only advice apart from all the usual checks would be to do a compression test.

Best regards,

Rich.

With no compression on cylinder 4 you either have worn piston rings or the valve stem seals have failed, the lack of pressure is causing a miss fire in that chamber (rough running) and unburnt fuel is being flushed out on the exhaust cycle - hence the running rich symptom / V8 smell.

Sorry to.be the bearer of bad news, but you've got to pull the head off and take a look. Best case, head work, worst case bottom end rebuild. If you need the car back up quickly then dropping in a used donor engine might be the way forward.

Good luck.

[richmac]

Thanks all. I've tried engine oil in the cylinder to confirm the seals are good but not ATF. I flushed the cylinder and air intake system with carb/intake cleaner and this actually helped a bit but I'm still overfuelling badly at idle and on demand. I've just put lifter lube in as a long shot.

I found and did the 'paper over the exhaust check' this morning and the engine is strongly in a blow + suck mode so it's definitely a valve issue.

Unfortunately, Shins, I have to agree with you.

[Shinsplintz 101]

No idea how good with the spanners you are, but stripping down the top end to send away for new seals, valve lapping and a skim isn't too tricky - or that expensive - just keep track of everything and take lots of photos so you can put it all back together again! Plus you can take a look at the bores at the same time.

If you go down the engine swap route I've got an 80k mile 2.5 lpt engine up for sale which would you could drop in. Just check the sales section and follow the link to my eBay sales threads. 25% off list for voc forum users.

Good luck getting it sorted, whichever way you decide to go.

Cheers, Morgan

[Shinsplintz 101]

Clark. Apologies for the thread jack.

[Luxobarge]

I think I'd be taking the cam cover off first, before taking the whole head off, to see if I could find a sticky valve on cylinder 4 and maybe free it off??

Might get away with it, and it's a LOT less work.

Again - sorry for the thread jack - @OP - could well be a vacuum hose split or been left off, check them all including whether they're in the right place too. Replace any that are even slightly dodgy, it'll pay in the long run.