940 problems, please help!

[byrolinda]

J reg Volvo 940 2L . Following a disasterous overheating situation on the motorway (knackered water pump), I have spent untold hours and quite a lot of money on having cylinder head skimmed, regrinding valves and generally refurbing. Today was the day for finally firing the engine again. NOT a huge success!

It runs, but poorly. Initially I have to give it a bit of throttle to keep it from stalling, the oil light comes on although the level is fine on the dipstick. The engine is constantly misfiring with occasional bigger 'hiccups' which sound a bit worrying. Power is poor. The plugs, which were new, look now as follows : No1 - clean; Nos 2 and 3- light brown deposit; No 4- black sooty deposit. This after about 10 mins running.

Timing belt set up as per Haynes manual, HT leads in correct order.
I did tug quite hard on a thin rubber cable which leads to the under side of the fuel injector bar thinking it was a hose, but it seemed to have wires inside it .. could this be the cause of my problems?

I have never done this sort of work before, but worked very carefully and methodically checking everything as I went along. Very disappointed today. Any thoughts MUCH appreciated.

[Steve940estate]

If the engine is running slowly the oil light might come on because of this, if it stays out when the idle speed is increased then it might be ok. My brothers car had a oil light on so we fitted an oil pressure gauge instead of the pressure sensor just to see what was happening. Turned out to be the sensor in this case.

The plugs would indicate something is up. Is the clean plug wet after running or dry ? If it's dry then perhaps the wire you tugged was to one of the injectors. If it's wet then you aren't getting a spark.
If you are getting a spark and fuel to all cylinders then re-check the leads are on the cap ok. Might be a good idea to check the camshaft is ok as it could be 180 degrees out or just a tooth or 2.

It's more than likely something silly so carefully checking what you have done will probably give you the answer.

[byrolinda]

thanks for reply. No 1 seems dry, but will look again tomorrow .. i also managed to flatten the battery ... someone else said the cam could be 180 out .. it seems ok as lobes are in the correct position for firing position 1 as described in manual. Also it seems to me that the sprocket can only fit in one position and the mark is in line with the corresponding mark on the cam belt cover. I'm still not sure what the rubber tube thing does .. I'll try to identify it. Cylinder 4 definitely too rich

[emmerson]

Sounds to me like you cooked its pistons awell as the head.

[Steve940estate]

Your probably right about the camshaft, there should be only one mark on the sprocket.
Hope it isn't something more serious.
Did you have to re-shim the valves after grinding them, not something I have done on a Volvo yet as any grinding of the seat would close the gaps up a bit.
It might be a couple of things causing the problem so keep looking. If you get to the stage where everything else is ok there are a couple of temp sensors on the head under the inlet manifold. If the engine has got hot they might have been cooked. One is for the gauge the other to let the ecu know how hot the engine is. Go round and check all the electrical connectors that have been disturbed as well.

[byrolinda]

actually I removed, cleaned and replaced (put back) those two sensors .. one of them did have a slightly melted casing ... pistons seemed ok, I cleaned the heads and cylinder bore carefully, and all seemed in good condition for the mileage (106k). There were no shims on the tappets I will check clearances

[Steve940estate]

I can't remember which is which (out of the sensors that is). If it was faulty it would cause a general running problem but not cause one cylinder not to work completely. Same goes for the tappets. They would need to be wrong by quite a bit .
If things got that hot then you might have a problem with other parts close to the engine or near to it.
I've run out of suggestions really. Do some checking, a few more clues might give someone an idea.

[grass hopper]

a compression test is recomended next.:lightbulb:

[byrolinda]

Thanks guys!
Did compression test this morning ...
Cylinder 1 ...1000 Kpa (172 PSI)
Cylinder 2..... 900 Kpa (152 PSI)
Cylinder 3 ... 1000 Kpa (172 PSI)
Cylinder 4 ... 1300 Kpa (212 PSI)

There's obviously a huge discrepancy between nos 2 and 4!

No 4 is the one blackening the spark plug. All injectors are working though I haven't managed to test them very accurately for relative amounts of fuel they're firing .. haven't found enough suitable tubes.

[Steve940estate]

I can't remember what the figures mean exactly. The low one could be a piston rings or bore problem or it could be that the valves on that cylinder are getting stuck or can't close properly. I think you can see the valves working on the gauge by doing it a certain way.
A drop of oil down the low one might help and that would indicate bore or piston problems.

Time for an expert to comment as I am guessing a bit now.

[byrolinda]

Actually my PSI conversion seems to be incorrect .. I read it off the gauge, but does not correspond with online converters which give me
Cylinder 1 ... 145 psi
" 2 ... 130 psi
" 3 ... 145 psi
" 4 .... 188 psi

which does not look good for an engine on 106k! Does anyone know what it should be, ideally?

[grass hopper]

of the top of me head around 180 psi is fine.the lower readings will cause running problems.

are the tappet clearances ok ?

inlet should be 0.20mm
exhaust should be 0.40mm