Various engine problems - advice?

It seems my car is getting slowly worse and various things have occurred with the engine, which aren't so good. In fact its all quite annoying. I have various ideas and things to fit to try and improve matters, but I thought I would post some stuff here about the problems. Not so much because I am expecting "the answers" from anyone, but just in case someone else has experienced anything similar or has any suggestions. You never know, many heads are better than one

(Car is 2000 MY S40 T4 + mods as described in my sig).

So, the symptoms. Well it all began with:
- generally seemed a bit less responsive under hard acceleration / boost
- occasional "stutter" under high boost (so > 3000 revs)

Also I noticed:
- this seemed to occur more after a hard run
and
- if you declutch after hard acceleration, and let it drop to idle, the revs drop right down to about 500rpm before settling back to normal 750 to 850 rpm

Hmmmm.....

Now my thinking for the first couple of things was that it needs a new fuel pump. Also the fuel pump is very, very loud at the moment it whines like a good 'un. This also makes me think it needs a new fuel pump asap. And sure enough a new one is on the way (I've had some problems with getting hold of this due to some g!ts I ordered it from messing me about - described in another thread), anyway it is an uprated 255 litres/hour walbro one and should arrive tomorrow.

My feeling was that the car was getting starved of fuel under sudden, high demand conditions. But to further try and check things I rigged up the diagnostics on the computer and checked out various things whilst driving along.

I discovered that at idle, all the measurements for everything where in spec. Driving along, everything seemed fine the usual stuff like coolant and air temperatures etc. (Edit) also should point out the boost gauge says boost is fine, holds boost fine, boost pressure all as expected.

What was interesting though was that the front o2 sensor readings seemed to go and stay particularly low voltage = weak a/f mixture under hard acceleration and high boost. Now the diagnostics only updates every 1/2 second but you can kind of get readings at different instants if you monitor the same parameter on more than one channel (won't explain this further). Even so, under low acceleration / no boost the front o2 sensor showed switching between rich/weak/rich/weak etc. as expected but under high boost it remained quite weak for a bit. I forgot to monitor injector opening during this time though.

Anyway that made me feel like my diagnosis was sound.
Although I'm not so sure it can explain the idle speed dropping like it does. Note that I have very recently given the idle valve and throttle body a good clean out, note also that the throttle potentiometer readings are in spec and the idle control valve opening at idle is also in spec.

But then I changed the spark plugs earlier. Although the current NGKs had only been in about 2000 miles I had got some of those denso iridium ones.

I was very suprised to see that the plugs were very carbonised. It indicated to me that the engine was running rich, which wasn't particularly what I expected to see!

I wondered if this could solely be explained by the presence of the dump valve and the fact each time I throttle-off there is a realease of metered air into the atmosphere hence the engine gets less air than it thinks it does. But this only happens briefly when you close the throttle, can it really explain everything? (Edit) Thought I'd add that I have been using a lot of "add to tank" fuel additives lately, some redex to clean up the fuel system and some octane booster. Dunno if these could make a difference?

Perhaps it is still a fuelling problem? If the engine runs weak under high boost due to low pressure then maybe it overcompensates when going back to idle? could this explain the idle dropping thing as well? Perhaps the fuel pressure regulator is also knackered? I have tonight cleaned the vacuum hose to it, was a little oily but not blocked. Will see if that makes any difference.

The other bad thing that happened... after the new plugs, took it out and was stuck behind something but when the road cleared I accelerated but all I got was what felt like a serious rapid sequence of misfires at about 3000 revs til I backed off somewhat. This happened repeatedly but then it was all alright again?! One possible explanation was that there was a bad contact between the HT end of the coil pack and the plug on no. 4 cylinder. I checked it out and on this one the spring had lost its "springyness" if you see what I mean, I have ordered a "new spring and rubber" kit. I mean the spring in the end of the coilpack lead. The 2 HT leads are new BTW and no. 3 seemed alright, although I thought I'd get that one a new spring as well. Even from volvo they can't be much!

Now the funny thing was there was NO FAULT CODE saying "misfire" nothing at all, once again as per usual the car is convinced everything was a ok which is just plain frustrating. What makes the car detect a misfire? Does anyone know? Can it only detect it from the sudden spurt of unburnt fuel emission? If so, how is it sensitive enough to know which cylinder it came from - can it be that quick to respond? Perhaps there was just a low spark and the car cut the fuelling drasticly to one of the cylinders, I don't know. Either way you'd think it could've been ar*ed to raise a fault code, but no it couldn't be. Anyway since then I've pulled the spring out a bit. And is hasn't come back. But the other faults remain.

Will report more when new fuel pump fitted but that might not be for a bit.

Any advice / info is appreciated, thanks for reading

In the constant conflict of me vs the car, it looks like the car has started winning a few battles. But I'm determined to win the war, but I might need a little help from you guys

Cheers,
Pete

[johnswlondon]

very puzzling problem,the temptation is to start replacing everything in sight only to find the problem remains!

i think the condition of the spark plugs will always give the best indication of whats going on and its cause.

one way or another the fuel isnt being burnt cleanly,with the mixture being too rich.if its your fuel pump,which you suspect due to the hesitation,i would have expected fuel starvation and the plugs to be pitted.

i would be very interested to hear the co2 reading from the exhaust to know if your lambda probe isnt playing up,because this increases the fuel to ensure the cleanest burn and minimum co2.

the wrong spark plug gap can also cause hesitation at certain rpm,it can usually be spotted by a slight misfire at idle,with your ear near the exhaust

ive never bothered to look but i assume the car has points in the distributor cap even though its contactless,this can also cause hesitation if worn or dirty

[scottishvolvo]

Pete have you tried a compression test on the cylinders to check if any might be passing.
Chris

before condeming the pump have you tested its output pressure at the fuel rail test port?

Thanks for the 3 replies so far chaps... keep them coming, people

To answer some of the points you all raised:

1) chow: No I haven't checked the fuel pressure due to lack of a fuel pressure gauge but the new pump is winging its way here hopefully now (didn't arrive today )... anyway it is making lots of noise and getting worse so one way or the other, it ain't right!

2) chris: No I haven't done a compression test. I do not have a fitting which is small enough for the small spark plug hole on this car.

But I think this would tell me all is ok. The plugs are the same for all cylinders. The engine starts, idles and generally runs ok just a bit hesitant at hard acceleration I feel and the other minor things mentioned above.

3) john: On these cars there is no distribution of the HT there are two coil packs each feeding 2 cylinders so at any one time there are 2 sparks one of which is a "wasted spark".

Yes it is possible that the front o2 sensor is faulty, I do not have an exhaust gas analyser so I cannot easily check the emissions from the pipe.
But the car reports no emissions faults, and so I presume that this would mean either both o2 sensors were faulty or the cat was strangely knackered which all seems a bit unlikely otherwise the car would detect a problem by comparing readings before and after the cat. If I can find one cheaply e.g 2nd hand I might invest in an EGA - could be worth having. Would be more useful to use if I could read the CO before the cat though.

I was thinking of posting up a picture of the plugs, and also a picture of the previous set which were in the car up to about 2.5kmiles ago. Of course this means finding both sets - they will both be in the garage somewhere, but no doubt somewhere amongst all my junk!

IIRC the previous plugs (which had no doubt been in there for eons) looked all ok. It would seem strange for the car to have a sudden major mechanical failure recently, and all of a sudden, so it would seem like perhaps a sensor failure or something I have done. Since I last changed the plugs - over the last 2k miles - I have done the modifications shown in my sig. The only other significant thing to do with the engine has been new cambelt done at same time as the plugs. And well, if I'd got that wrong the car would either have introduced the pistons to the valves or would just plain have run like sh!te. Plug gaps on the previous set of plugs I am sure would have been set by me to be within tolerance; on these ones they are 0.75 to 0.8mm (spec is 0.7 to 0.8mm).

So, I am now wondering if the rich running is solely down to using an atmospheric BOV? It would be good if someone else with one could tell me how their plugs look. I am getting a bit fed up with this thing (despite having a photo of it in my avatar) not only is it not too loud, but it was potentially giving me gyp to do with the fluttering air noise (see another thread somewhere) and it wasn't exactly free to buy either!

Wasn't able to investigate anything further tonight; now it is too cold and dark I'm fed up of going out there in the cold and freezing my bowl-lax off, car been running as ok as normal today (i.e no more dodgy misfire type things).

Thanks again, any more suggestions welcome esp. re. spark plug condition in those with an atmospheric BOV.

Cheers, Pete

[johnswlondon]

when you say you changed the spark plugs earlier,did the fault arise at the same time?i only ask because on my last volvo i changed the original volvo spark plugs and it never ran the same again so i put the originals back in.

in total they covered 160,000 miles!