940 acceleration
 

I have an odd issue with my 97 940 turbo, completely standard apart from an mbc set to 8psi.

Sometimes I put my foot down and it goes like poop of a shovel, other times my mate in his 95hp 360 can easily keep up and even goes faster occasionally. No warning lights on the dash and I have had it on the smoke machine at work to look for vacuum leaks but there aren't any.

Usually if I build up the speed slowly and don't use full throttle it seems to accelerate quicker too!

Any suggestions?

First thought on that is the fuel filter Luke. Second is a dirty MAF, third is a sticky/lazy FPR, fourth, broken/loose baffle in one of the exhaust boxes causing a temporary blockage (could even be the cat) and fifth is a sticky wastegate so it's not giving you the boost you should be getting.

Could also be the fuel pick up in the tank but the only way is to check through everything methodically. Might be a lazy/worn fuel pimp as well, got a feeling you said you changed the pump though or was that your mate who has bought the red one?

Brilliant advice as usual Dave, that should give me some.stuff to play with!

Yeah it was my mate who fitted one to his red 940.

If a lighter throttle is working think about weak spark.

sucked inlet hose between turbo and air mass measure (Filter)
feel if this is soft.
good luck, Kay

The one going from the AMM to the turbo? If so then I can squeeze it quite easily.

I will pull the plugs, clean and gap them too.

You could try putting a few hose clamps around that intake hose to make it keep it's shape. Never tried it myself, but it sounds like it would work.

yes, the hose between AMM and turbo

the hose clamps will help if you stitch the hose to the clamp and seal it afterwards.

No joke, stitch it with stainless steel wire or buy a new hose.

good night, Kay

Pulled the plugs out earlier, all need gapping again to 0.7mm, number 4 and another cylinder were way too big, amazing how much difference there was in the electrode gaps seeing as they are all less than 10k miles old and were all set to 0.7mm.

So far it seems to be running nicer and I haven't lost power when booting it!

That's kind of worrying Luke. If everything is ok, those plugs should only be 0.8mm at the most after 10k miles.

What plugs are you running in it? (Make and type)

Which two were the largest? You've said #4 and i'm guessing #1 was the other with #3 a second choice. It sounds as if the two largest gaps were running lean - did those plugs have a whitish, glazed appearance?

Couple of things worth doing, compression test on all 4 pots, injector flow test on all 4, check injector "O" rings particularly where the injectors go into the manifold and check the manifold for corrosion at those points, check the inlet manifold gasket for leaks, also check all your valve clearances if anything is untoward in the previous tests.

Glad you've found the main symptom/cause of the rough running but what has caused it in such a short mileage? :thumbs_up:

I thought that too Dave but didn't have time to look in to it properly as it was on my 30 min lunch break.

NGK BPR6ES

I can't remember exactly but I do think it was number 1, I pulled number 2 first and that wasn't so bad so it has to be 1 or 3.

Yep they were all peach coloured but I definitely noticed a bit of a white glaze on number 4.

I was actually hoping to do a bit compression test this morning at work but I ended up running behind schedule so I couldn't get in early. I am going to do one tomorrow though as I'm driving down to Bristol as my Dad has just won an auction or an 850 saloon.

I have suspected the injector seals are leaking for quite some time now as the engine bay has a whiff of petrol about it.

I have done a smoke test and it didn't leak anywhere so I assume the inlet gasket is fine but I will spray some wd40 around it while running and see if anything changes.

I also went to order a fuel filter earlier (I do listen to your advice Dave) and got a call from my wife saying her car has failed the MOT so that will have to wait until pay day now.

I will be getting some camber adjustable top mounts in a couple of weeks too as the outer edges of the tyres are wearing rapidly thanks to the camber. I don't like the official Volvo mod and when I lower it I will have to adjust it again anyway so I might as well set it up properly!

You can still get the volvo spark plugs from a dealer .

On the basis of what you've said there Luke, i'd plump for dirty injectors. As you've got a half-decent run tomorrow, chuck some injector cleaner in the tank before you leave.
If you haven't but just happen to have some ATF-U around, if you have a full tank, add 50ml (that's a pub double measure of spirits so not a lot at all!) to the tank, if it's half a tank, just add 25ml.
If you're going to brim the tank, add the 50ml just before filling up. :thumbs_up:

Then check the colours on your plugs when you get back.

Certainly the right plugs/gap etc, i don't know who makes the plugs for Volvo but i suspect it's Bosch and it could come from one of their South American plants where stuff has a less than satisfactory reputation. I can't remember which plant it is (Mexico i think but not sure) and Bosch have more than one S American plant but when you're paying a lot extra for a Volvo branded plug over what an NGK is, i'd stick with the NGK personally.

With the camber mod, check your strut tops on the inner wing, you may have an alternative set of holes you can fit the tops to. For now, until you finish the suspension it would save scrubbing out tyres so quickly. I know it's not your preferred solution but would surely be better than new tyres every few months?

What sort of car has your missus got Luke? Also what did it fail on? :thinking:

For the sake of £12 for genuine volvo plugs on ebay which are 100% known and proved to work properly that's penny pinching for the sake of it !

Back in the day any volvo which had plug problems had NGK or champion plugs in it and the problems were cured by fitting the proper volvo plugs ..

I hear what you're saying and would agree whole-heartedly about Champion plugs, surprised to hear any NGK was causing problems though.

I'm not saying it can't or could never happen just that it's extremely rare. I have however heard of Volvo plugs failing and experienced (on more than one occasion) Bosch plugs failing. Most memorable time was New Years Eve about 30 years ago when a group of friends and i decided to go down to London just for the road trip and to see the celebrations.

Turned out to be a bit of a damp squib as the celebration areas were cordoned off to vehicles so we turned round and went home.

Thanks to not knowing London very well at the time, i ended up coming back via Luton by which time my car would barely run thanks to the Bosch plugs that had only been in less than 2k miles.

Only plugs available were from a 24/7 Shell garage and those turned out to be Champion plugs in a set of 4 in a blister pack.
They got me home - just - and struggled to work the day after. A set of hotter plugs later (still Bosch) and it was running again for about 5k miles, at which point i had to change them again, this time for NGK and they lasted a lot longer.

It might seem like pointless penny pinching going for NGK plugs but IMHO it's the better choice. We've all heard about genuine Volvo water pumps that are failing in short order these days and the general standard of replacement parts (both genuine and aftermarket) seems to be dropping dramatically in recent years.

When i first got my current 760, it was running quite nicely so the plugs weren't the top of my priority list to check/change. A few months into ownership they did start misfiring slightly. The gap was up to about 1.3-1.4mm on most of them when i checked them, indicating they had been in about 60-70k miles. I did find a receipt for when they were changed about 10 years previously and the mileage on the MoT history tallied with that at about 160k miles (by this point it was on about 216k) and re-gapping them to 0.7mm got rid of the misfire until a new set was fitted.
Those plugs were all NGK - the ones that had been in since Fred Flintstone was in nappies and the replacement set. No problems yet although i did renew them replacement set after 6k miles when i also renewed the plug leads.

Given my experience with Bosch plugs over the years, i doubt they'd still be performing after that length of time.

With all due respect you are supposed to change the plugs every 12000 miles :angel_smile:

except in recent years with petrol making a comeback it can be 36000 or 72000 miles .

I know which is why i was astounded to discover/work out that the set in my 760 when i bought it had been in there at least 10 years and some 60-70k miles! :err:

The fact they were still working as they should (despite the gap big enough to drive not just one bus through but a whole fleet) was even more amazing.

The reason i changed them again some 6k later when i renewed the plug leads is i had them sitting there and as i was already halfway there with changing the HT leads, decided it would save me a job later.

In terms of extended plug change intervals, i have heard of some models that are only specified (by the manufacturer) at 100k miles - at the same time the coil packs must all be changed - all 8 of each, plugs and coil packs! :eek: As you might guess, that's on a Lexus V8 and the plugs are some special iridium jobbies, an eye-watering price each as are the coil packs from Toyota/Lexus.

However, those engines are designed to operate with iridium plugs and the plugs are designed to operate for the extended period.

The cost is still prohibitive though, a "normal" plug is also specified with a more normal interval of 12k miles which IMHO is a good thing for at least 2 reasons.

First, it means the plug can't seize in the head through electrolytic reaction and secondly, 8 (or even 9) normal plugs are a hell of a lot cheaper than 1 iridium thing from Lexus.

I no longer have the figures to hand but was told them by a friend a couple of years back when he bought an LS430, plugs (IIRC) were about £50 and coil packs about £80 each.

On a V8, that's a lot of money!

He bought 10 ebay special coil packs for £80 (on the basis one coil pack would fail quickly and one would be DOA so still had 8 good ones) and a set of normal plugs, being of the same mind-set as me that it reduced the risk of the plug seizing in the head.

All that aside, it doesn't solve the underlying problem on Lukes engine where it would seem 2 pots are running lean, causing the excessive gap to be created on two of his plugs. :thumbs_up: