Cold running issues
 

Car is a 1994 Wentworth Auto estate with 275k on the clock. There are quite a few small things wrong with it but it has always run quite well. The ones potentially relevant to this fault are:

Speedo doesn’t work until about 20 minutes into a journey, then works faultlessly
PCV system is well overdue for cleaning
Ditto throttle body
Slow coolant leak somewhere, possibly the radiator, possibly the heater valve
Exhaust is starting to blow immediately after the cat
Hole in the turbo air intake hose

The problem is that it has started running incredibly badly following a cold start but then runs absolutely fine when warmed up except it will sometimes stall when braking hard, especially uphill. In these circumstances the dash lights come on before the engine cuts out and I have recovered from the stall on occasions by coming off the brakes.

The first sign of trouble was that it wouldn’t go above 15 mph up a nearby hill from a cold start when someone else was driving it. It has since got worse.

It starts fine, but smells like it’s running very rich. It idles quite low compared to normal for a cold start but revs grudgingly in park or neutral. As soon as drive or reverse is engaged it won’t rev and won’t really move at all. You can put you foot flat to the floor and it won’t move or go above 1,000 rpm. The engine continues running though.

If I disconnect the MAF it runs (even) worse.

I changed the timing belt a few months ago but this problem didn’t start immediately after doing so and it runs very sweetly when warm, so I don’t think it can be a tooth out. I did struggle with the timing marks. The car has previously had the head skimmed.

I have been running it knowing that the in-tank lift pump was faulty for too long; in fact probably about 100k miles and ten years. During this time I have fitted a new main fuel pump.

Based on this 2006 article, when these symptoms started I replaced the in-tank pump just after Christmas.

https://www.volvoforums.org.uk/showthread.php?t=14447

Doing so appears to have made no difference to this fault but the new lift pump does appear to be working and has placated the noisy main pump.

I know as I write this it sounds as though I have seriously neglected and abused the poor thing. In my defence, I have owned it since 1999 and managed to keep it on the road all that time and I keep up with most of the basic service items. It is the grottiest of four cars I currently own and I mainly use it for winter driving.

I’m minded that the air leak is the most likely culprit. I have tried a temporary repair with duck tape (which I don’t think has made much if any difference) and I have a new part on order. I have also tried removing fuse 1 to reset the ECU based on a theory, possibly spurious, that it has got used to running on restricted fuel. I shall know if I try to start it tomorrow if this has helped.

Any other suggestions of what to check or test?

Is the hole in the Air intake hose after the MAF/AMM? If so, correct that first. Otherwise, your fuel trim levels will potentially be wrong in relation to the amount of air your cylinders are actually taking in.

The excessively rich running seems to suggest the CTS under #2/3 inlet tracts on the head. Bosch 0 280 130 032 or 039 or 069 are the OE part numbers. I used an Intermotor one on my V6 and haven't had any of the alleged problems others have had using non-genuine items.

If you have a multimeter, check the CTS cold. Unplug the connector and (making sure you manage to check both pins) test the rsistance to the head which should be ~2500 Ohms +/- 10% @ 20C.

Given that it's colder than that at the moment, expect the cold readings to be ~3k Ohms from each pin to the head and as a final check, test between both pins which should be the sum of the two figures from each pin to the head.

Also sort that air leak as well! :thumbs_up:

Air leak is on the way to being sorted. Why did I buy do88 intake pipe? I nearly always go for Volvo parts. It has taken me all evening to transfer that wretched PCV heater. It came out of the old one easy enough. Hours of judicious grinding the flange down with a dremel and in the end took two kettles full of boiling water and much pushing and twisting to get it in place. All being well I will try it out tomorrow.

In case it’s of any use to anyone, some details as follows.

The intake pipe from the MAF to the turbo is p/n 3514480

The PCV heater is p/n 1357352

The hose clamp the MAF end is #9-85 68mm - 85mm

The hose clamp the turbo end is #75 58mm - 75mm

Fitted the new turbo air intake pipe this afternoon. No change.

The car started and idled a bit roughly seemingly running rich and with low RPM compared to what you'd expect just after a cold start. In Park it would rev freely to at least 3,000 RPM, the most I thought advisable on a cold engine. As soon as I engaged Reverse to back out of the drive revs went even lower to about 500 RPM. With my foot flat on the floor in gear it would not go above 1,000 RPM and lacked enough power to even move on the slight incline. As soon as I elected Park it would rev freely again.

I think removing the throttle body and idle air control valve, giving them a good clean and while they are out of the way checking and possibly changing the ECU coolant sensor would be a good thing to do. However, I'm not convinced faults there would cause such an extreme problem.

Is the ECU aware of what the gear selected or is it not that sophisticated? I'm starting to think limiting the revs to 1,000 RPM might be a processor somewhere rather than the random effects of unmetered air or a signal out of range.

What is different when the car is running cold compared to when it has partially or fully warmed up?

If it is running rich, it could easily "bog down" once in gear. Did it sound as though it was running rich when you put it in reverse?

Also worth checking the small carbon brush inside the dizzy cap and the plugs/leads. Regap the plugs to 0.65mm, if the gap is too large it can cause a weak spark that fails to ignite the mixture under load.

The distributor cap is original so it's certainly worth a look. I've got a spare somewhere.

I've just been reading on another forum about the possibility of the new in-tank pump being wired the wrong way around. This is possible because the new pump I fitted a few weeks ago did not have its polarity clearly marked. I wired it to match the original. However, I have encountered other non-OEM parts (e.g. mirror motors) that feature subtle reverse polarity issues. Removing fuse 11 does not seem to improve the situation though.

Removing fuse #11 won't improve the situation but could make it worse. However if the pump is running the wrong way then removing it may improve things.

However, has this happened since you replaced the pump or more recently?

Looking at the 1994 wiring diagrams, I don't believe the ECU or EZK talks to the gearbox. I might be wrong...

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.