Cold running issues

[Laird Scooby]

Originally Posted by Forrest

The main pump had been noisy since at least 2009. I have almost certainly been running the car with a failed in-tank lift pump for over ten years and 100k miles.

I replaced the main pump in late 2018 with a new Bosch unit. Of course, the new pump became noisy almost immediately. I finally decided to tackle the in-tank pump because of the early stages of this problem; so yes the fault does predate the new lift pump.

It has crossed my mind that the 2018 replacement main pump has worn prematurely because of being used for two years without a lift pump. Especially since I hadn't been aware of it being noisy recently, even before replacing the lift pump. However, I thought the main pumps tend to either work or not rather than exhibit intermediate failure modes. It also seems odd that this problem is only noticeable when the engine is started from cold.

That suggests that (for now at least) it would be reasonable to assume the in-tank and main pumps are doing their job.

I'd be inclined to look at the CTS and the ignition components as suggested. The CTS has two thermistors inside, thermistors don't live forever and after 10 years begin to degrade, it could well be yours has degraded to the point where it's giving problems.

[Forrest]

Made a bit more progress with this today.

I decided to do a bit of testing and the Laird’s theory that the fuel supply is OK looks sound. I hooked up a fuel pressure gauge to the Schrader valve on the fuel rail and first turned the ignition to position 2. The pumps could be heard operating and the pressure went up to 20psi. The pumps then stopped and the pressure stayed steady at 20psi. When I started the engine the pressure went up to 40 psi and stayed there. Revving in neutral caused fluctuations in the pressure. The problem persists. Engaging gear and flooring the throttle caused the pressure to rise to about 48psi but no increase in revs.

Upon turning off the ignition the pressure stayed at 40psi for the length of time it took me to change the distributor cap. That was substantially longer than the normal twenty minute test!

The distributor cap and rotor arm were in a bad way, as predicted. I think they may be the originals at 26 years and 275k miles. Picture of the old cap attached. I didn’t bother to photograph the pieces of the rotor arm which was well and truly stuck and disintegrated while being prised off. New Beru cap and arm fitted. Car starts and revs a bit cleaner but the problem persists.

A couple of potentially relevant things occurred during this. When I first started the car after attaching the gauge I accidentally left the lead off No 1 fuel injector. The car started and didn’t run noticeably worse than it did with that connected. Does this indicate a problem with that cylinder/injector/spark?

Also, at the end, I decided to relieve the pressure on the fuel rail by attaching a vacuum pump to the fuel pressure regulator. Despite pulling -28 inHg on the vacuum port the rail pressure stayed at 40psi. This presumably indicates the FPR is not working. Could that be causing problems?

Next step is likely to be removing and cleaning the idle air control valve and throttle body and while they are out of the way swapping the ECU temperature sensor. I’ve got a new spare somewhere if I can find it.

[Forrest]

A couple of videos to attempt to show what the fuel pressure is doing

Revving in Neutral

+ YouTube Video

Booting it in Reverse

+ YouTube Video

And, yes, it does currently have the worst case of lacquer peel on the bonnet you’re ever likely to see. If I can fix the engine and decide to keep it I shall get that resprayed. I did actually buy the replacement for this car, another 940, back in 2011.

[Laird Scooby]

Is that how the cap came off? With the carbon brush in the middle missing?

If so it's a wonder it was running at all and you probably did it a favour accidentally leaving #1 injector connector off, gave the plug a chance to dry out a little before you replaced it!

With the engine running (you can have the pressure gauge on as well as that may give an extra clue) remove the vacuum hose from the inlet manifold to the FPR on the FPR end and plug it - you can use your thumb over the end if you like.

Observe the stub on the FPR - does fuel come out? If so you definitely need a new FPR but it's also worth checking that the stub on the inlet manifold is clear and the hose between it and the FPR is in good condition - not split/perished and sits tightly on the stubs.

Fuel pressure should be 43.5psi above manifold pressure so at idle when it's pulling about 20"Hg vacuum (about -10psi) the pressure should be about 33psi.

Worth checking the return hose isn't blocked/kinked anywhere if the pressure is above this before condemning the FPR although you wouldn't get any alteration in fuel pressure then.

Listening to the engine on those videos, your vacuum is more likely to be about 10-12"Hg so only dropping 5-6psi from static to about 38psi on idle. Seems to be roughly what it's showing as you have a regualr misfire there.

There are two wires to each injector, a green (+ve) and a grey (switched -ve from the ECU) so you can do some basic fault finding with a short link wire. First link the greens on #1 and #2 injectors, see if #1 comes back to life. If not move the link to the grey wires on #1 & #2 and see what happens.

If there's no change, investigate the plug and HT lead on #1, it could simply be #1 is fouled badly and just not firing or perhaps #1 HT lead is dodgy/broken/loose.

Silly question but you hadn't had the plug leads off before this problem started?

[Forrest]

Originally Posted by Laird Scooby

Is that how the cap came off? With the carbon brush in the middle missing?

Afraid so. I’m guessing the black specs are the remains of the carbon brush. There also looked to be quite a hole bored in the centre of the rotor arm. Some of it may have been in there or else the hole and general blackness may have been a result of arcing.

Upon closer examination the old distributor cap appeared to be Bosch branded so perhaps it wasn’t original. It might have been changed when the leads were as a result of a fault about 15 years ago which turned out to be a relay or sensor.

The leads are Bougicord class E.

Spark plugs were last changed by me in July 2018 at 257k miles.

[Laird Scooby]

Originally Posted by Forrest

Afraid so. I’m guessing the black specs are the remains of the carbon brush. There also looked to be quite a hole bored in the centre of the rotor arm. Some of it may have been in there or else the hole and general blackness may have been a result of arcing.

Upon closer examination the old distributor cap appeared to be Bosch branded so perhaps it wasn’t original. It might have been changed when the leads were as a result of a fault about 15 years ago which turned out to be a relay or sensor.

The leads are Bougicord class E.

Spark plugs were last changed by me in July 2018 at 257k miles.

There's a wonderful technique used for shaping metal, often to make moulds for injection moulding of plastics and this technique is called spark erosion. I suspect your rotor arm has given you a private demonstration.

What gap did you set the plugs to when you fitted them? Worth resetting the gaps to 0.65mm and cleaning them anyway.

Think you said it had 280k now so the gaps will be about 0.2-0.25mm more than you set them or that much more than what they came from the factory which would have been 0.9mm so could potentially be 1.1-1.15mm - far too large for reliable running on a red block.

Even if you gapped them correctly when you fitted them, they'll still be approaching 0.9-0.95mm by now.

[Forrest]

I haven’t had much time today for the saga. My “support bubble” came to lunch. However, I did decide to pop out and clean the air mass meter just before it got dark. Valvoline carb cleaner seemed fine for this. It is supposed to be compatible with plastic and leave no residue.

Whilst I think this has made a slight improvement I have tracked down another possible cause or symptom of the misfire. I could hear arcing and in the twilight was able to see a spark between the new distributor cap and the earth wire that runs behind the distributor and attaches to the right hand side of the valve cover.

Is this likely to mean the leads have had it? Or could it just be the condition of the plugs which has already been mentioned and which I haven’t had time to look at yet?

[Laird Scooby]

Was the arcing failry close to where #1 segment is in the distributor? I'm wondering if just that lead has gone belly-up and the then "unclaimed" (by the plugs) spark is just finding the path of least resistance to earth.

[Forrest]

Unfortunately, no. It appeared to be nearer to 4 and 3 but I think that may have just been because that was where the earth lead passed closest to the distributor. I moved the lead down away from the HT lead connections and the arcing continued out of sight behind the distributor. I guess a 40,000V just finds the nearest route to earth.

[Laird Scooby]

Originally Posted by Forrest

Unfortunately, no. It appeared to be nearer to 4 and 3 but I think that may have just been because that was where the earth lead passed closest to the distributor. I moved the lead down away from the HT lead connections and the arcing continued out of sight behind the distributor. I guess a 40,000V just finds the nearest route to earth.

I don't suppose you have a spare #1 plug lead do you?