Odd occasional hesitation under acceleration/boost

[AllHailKingVolvo]

Thanks both!

I fitted a new set of the grooved electrode NGKs this morning (I forget the number, BKR6E I think but not sure), they have definitely improved the running, the idle is now silky smooth but the hesitation in higher gears under load is still there, if a tiny bit less than before.

I now have new cap and rotor arm, should have leads and dizzy o-rings tomorrow so will fit the lot and see how we go. I noticed when checking for arcing at night a couple of nights ago, that a spark was visible inside the distributor cap at idle...but then yesterday evening it was no longer visible. Very odd.

It may be a coincidence but the noticeable increase in hesitation coincided with me asking my very mechanically savvy stepson (with whom I rebuilt my 744 and trust with most jobs) to check the oil level. He checked it and topped it up to "full" whilst the car was running (I KNOW...) and I drove it about for a day before I found out. It was overfilled by about 3/4" on the stick and I drained out somewhere near half a litre of oil or just over to bring it back to where it should be.

One possible theory is that the increased oil level forced some oil past the rear crank seal and/or distributor seals (or indeed out of the cap and along the rocker cover) and into the distributor, causing the slightly shonky running.

Either way, all of that will be off and replaced tomorrow, so will report back on what I find when I crack the cap off!

[Laird Scooby]

Originally Posted by AllHailKingVolvo

It may be a coincidence but the noticeable increase in hesitation coincided with me asking my very mechanically savvy stepson (with whom I rebuilt my 744 and trust with most jobs) to check the oil level. He checked it and topped it up to "full" whilst the car was running (I KNOW...) and I drove it about for a day before I found out. It was overfilled by about 3/4" on the stick and I drained out somewhere near half a litre of oil or just over to bring it back to where it should be.

Check your flame trap Phil - it may have disturbed enough crud to cause a partial blockage in it.

When you checked the arcing a couple of nights ago and you saw some arcing in the dizzy cap, was it more humid/damper than the next night where the arcing was no longer visible?

My line of thought is there is a hairline crack in the dizzy cap and under damp conditions, it's providing an arc path.

[AllHailKingVolvo]

Originally Posted by Laird Scooby

Check your flame trap Phil - it may have disturbed enough crud to cause a partial blockage in it.

When you checked the arcing a couple of nights ago and you saw some arcing in the dizzy cap, was it more humid/damper than the next night where the arcing was no longer visible?

My line of thought is there is a hairline crack in the dizzy cap and under damp conditions, it's providing an arc path.

That's a very good point re the crack in the cap, it was a bit more damp when I spied the arcing. I'm looking forward to getting it all apart tomorrow and finding out more, weather permitting! I cleaned the FT and fitted the new PCV yesterday after draining out the excess oil but will check again tomorrow in case anything has been dislodged since then.

It's a rum one...if my sleuthing doesn't clear it up, I'll find someone locally who can pull the codes from it and see if there is anything afoot.

Stumbling aside, it's a lovely drive. Have spent most of today running errands in it and motoring to and fro, and it's supremely comfortable and capable. Once the miss is ironed out it will be a great daily driver!

[AllHailKingVolvo]

So, new cap and rotor arm went on today...old units weren't in bad shape (a little marking to the poles and the rotor arm contact but nothing out of the ordinary), but the new units went on regardless, as did a fresh set of both O-rings, despite no oil ingress. Better safe than sorry!

The car seems a little more sprightly at the bottom end, but the hesitation is still there in third/fourth/fifth.

I've still got the new leads to fit, but they didn't arrive today...tomorrow will probably be the day they land, so will fit them and see what transpires.

The coil contacts look to be in good shape, I haven't checked the RSR yet but that is next on my list. Once I'm satisfied everything on the spark side is good, I will start investigating the fuel side. I've got a fuel filter to fit, so will do that, test the car and, if no improvement, check pressure at the rail. I have a bottle of the excellent Forte injector cleaner due to arrive tomorrow, so that will go in as soon as the filter is done and we'll see where we are.

If the pressure is good at the rail but the hesitation persists, it may well be necessary to drop the car down to Volvo in Yeovil for a diagnostic sesh, they are very reasonable with this stuff and sorted out various niggles with my old 240 that I couldn't quite get dialled in myself.

[AllHailKingVolvo]

Removed the RSR and re-flowed the solder joints just now, and whilst there were no obvious dry joints, this seems to have improved things a little. It all seems to be incremental, the car is definitely a bit more lively and less flat... although hard to get a read in these horrendous conditions!!

Leads next, and we'll see where we are. I think the misfire is as a result of the car not having had much use (75k miles in 23yrs!) and an assortment of tired leads, relays and sensors. I have a new knock sensor and CPS on the way too, neither were particularly expensive and can only benefit the car in the long term. The knock sensor has been bathed in oil in the greasy spot beneath the intake manifold for God knows how long, so a fresh one can only help!

[Laird Scooby]

Silly thought just crossed my mind Phil, triggered by the mention of the knock sensor.

You are running it on Super unleaded, aren't you?

[AllHailKingVolvo]

Originally Posted by Laird Scooby

Silly thought just crossed my mind Phil, triggered by the mention of the knock sensor.

You are running it on Super unleaded, aren't you?

I am, yes...well, Tesco Momentum 99 for this tankful, normally V-Power.

[Laird Scooby]

I've never had much faith in Tesco fuels but that aside, when you next fill up, try BP Ultimate - all the red-blocks i've ever had ran better on that than anything else. Likewise my 760 and Rover too.

[AllHailKingVolvo]

Originally Posted by Laird Scooby

I've never had much faith in Tesco fuels but that aside, when you next fill up, try BP Ultimate - all the red-blocks i've ever had ran better on that than anything else. Likewise my 760 and Rover too.

That's handy-I live opposite a BP garage! I've had good results with it in the past in my old 744 so will try it in the 945. I don't usually use Tesco fuel (especially after hearing it referred to here as "panther p*ss" which always makes me laugh whenever I drive past a Tesco station!) but it was one of those "uh oh, I'm on empty and Tesco is there" moments!

[Laird Scooby]

I don't know for sure who supplies Tesco but i do know when it was tested on another forum i'm on, Tesco came out worst for power, economy, general running etc. The top two (at the time, a few years back now) were Shell V-power and BP Ultimate with Sainsburys on a par with BP - back then BP had a barrelage agreement with Sainsburys so you got Nectar points on both fuels - now Nectar has switched to Esso and both my beasts are lack-lustre and thirsty on both Sainsburys and Esso.
Shell was top on one sort of engine, BP top on the other, both V6s but slightly different despite both being Honda. (J series and C series if you're interested, Shell better in the J series).

However i've switched back to BP properly and while it's early days (only part tankfuls in both so far) the economy seems to have improved and the performance definitely has.

As for "Panthers p!ss", i'd say that's an insult to the panther!

I say Shell came out on top when it was tested - there have been many posts about how it doesn't seem to do the job any more (it never did in either of mine, BP for them) and those who had previously used Shell are now on BP with the slight caveat that it can vary from garage to garage - if you find a BP garage that serves petrol that doesn't seem to do the job, switch to another and stick to the one you find that does what it should.