Right, this is the result of a 3 month investigation. The culprit in question is a 1996 940 B230FK. When the car was first purchased it started and ran just fine, was a bit lumpy and hesitant flat out on the top end but never the less, perfectly drivable and really sensible on fuel, 400 miles on 65L of fuel. A couple weeks later it would need an extra few cranks before it started in the morning, 3 turns became 4 and 5 and 6 and so on until today where it takes a good 3 maybe even 4 goes to get it started. Once it gets running it idles around 500 rpm and then slowly increases to 1000/1200. Sometimes it’ll even peak at 1800 and then suddenly drop to 400 and back up again. That’s just the idling, next there’s the driving. It seems to hate pulling off from a standstill, it struggles between 1000 and 2000rpm, once it gets enough boost it’ll go alright, until the 3000rpm Mark that is where it’ll experience what I can only describe as a brief fuel cut, it feels as if you got rear ended basically. That’s the driving side of things. Next there’s the potent and overpowering scent of petrol. It bloody reeks, as soon as it starts it smells as if it was pouring fuel out of the exhaust, that’s outdoors, let alone indoors.

It got diagnosed with a faulty MAF so that got changed along with the following.

idle control valve
coolant temp sensor
O2 sensor
crankshaft position sensor
fuel filter
air filter
oil and filter
fuel pressure regulator
4mm vacuum lines ( manifold to actuator to turbo, manifold to fuel pressure regulator, manifold to pcv y joint, throttle body to charcoal canister 4mm and 6mm lines)
spark plugs (gapped at 0.7/0.8mm)
ignition leads
ignition coil
rotor arm
distributor cap

removed the egr and left the control valve still connected (made no difference)

the pcv box has been cleaned and leak tested the put back with a new oil seal. All the 16mm pcv piping to the intake has been replaced. Passed glove test with flying colours.

At this point I’m starting to run out of options, the throttle body has been cleaned, the throttle position sensor clicks as it should, all the inlet gaskets and injector seals seem mine( sprayed brake cleaner on them and it made no difference whatsoever)

I’ve installed a boost pressure gauge and idling at 1000rpm it shows negative 20psi, if that’s enough vacuum I don’t know what is.

The best part about it is we’re talking about a 97000mile example, it’s mint inside and out. The cam looks golden and brand spanking new, it’s looks like a really healthy engine yet it does all this.

the green pipes are the pcv to intake via a catch can.
the red line is the boost gauge signal.





any advice would be more than welcome
thanks in advance
stronzo

 

I don't see an obd1 box under the hood - what codes have you gotten from the obd2 port?
If the fuel pressure is normal - something is making the injectors spray too often/too long (electronically) or one or more is spraying when it's not supposed to. Have have pulled the injector rail with fuel lines still connected and visually watched the injectors spray with engine spinning over and checked for leakage with the fuel pumps on? Have you verified the signal from the engine speed/'crank position sensor is only once per revolution?

Idle speed - with the throttle switch in the closed/supposed to be idling position if the idle speed gets up to 1800 or so rpms - the injectors are shut off to lower the idle speed. So that's a normal thing. Yes a climbing idle is not normal but the sudden drop to 400 is.

When checking for vacuum leaks it's best to use carb cleaner instead of brake cleaner - something about some brake cleaners generate poisonous fumes when burned.

Have you checked the short straight intercooler hose from the intercooler to the intake pipe for a hole or damage on the bottom? (they fail and open up under boost) And all the other intake hoses?

Nice looking engine compartment - someone has spent some time in there!

 

Hello mr hoonk and thanks for your words, I’m glad to say that I’ve actually not done any of the above which means there’s more options now.
I’ll start with the crank sensor as it seems the easiest thing to do and get out the way, do you just check it with a multimeter? If so, under what parameters?
I actually didn’t even know it had an obd2 port, never really looked for it, one thing I did look for is the diagnostic gizmo in the engine bay which I’ve not found. I had it diagnosed at a local specialist instead.
All the intake hoses need changing really as they’re a bit old but still in ok condition, there’s no blatant signs of failure, the hard plastic ones seem in near perfect shape. I’ll try all the above and see what we find. I’ve cleaned that engine bay as best as I could without getting things too wet, it has come up quite well actually, indeed, thank you😊.

 

Right, this is my first thread, so I’m unsure how this forum works when it comes to replying, I’ve tried replying already but it doesn’t seem to have worked, not sure if I’m doing something wrong or there’s a glitch or some sort.

Anyhow, I’ve just checked all the above apart from the crank position sensor signal which I doubt has anything to do with it as it made no difference changing the sensor and the new unit is Bosch which has very low chances of failing out of the box.

Just had the entire manifold of and torn apart, cleaned it inside out along with the throttle body and all the vacuum fittings and holes.

Removed cleaned and re installed the injectors and the seals.

all hoses and pipes seem to be in acceptable condition. Injectors don’t seem to leak however they didn’t fire whist off the manifold, the car however did start once re installed. The idle is still high, 1000/1100rpm I’ve still not driven the car as I’m waiting for the gaskets to cure a little more.

The obd tool I have doesn’t work on this. I’ve read that despite the port looking like an obd2 and practically being one, it’s not compatible with conventional obd2 readers and apparently you can make one of your own for £30 or so. I’ll try re setting the lambda light to see if it comes back on, not like it’ll make any difference but at least it’ll be out of sight. I think I’ll have to take it to a specialist if it carries on this way. Driving it earlier was horrid, had no power at all, it would fuel cut all over the place and it just wasn’t keen for it.

Must be a Friday car🤦‍♂️