940 Rich start up.

[arctan]

Any pointers on the above please? Starting up around midday, so not that cold, say 10 to 15 celsius. Fires up quite quickly, after 15 or 30 seconds it goes lumpy, fair old rich niff from exhaust. Stabilised by taking revs up to 1500 for a minute or two. Then progresses like normal. Only recent activity was plug change from Volvo to NGK bpr7es (it's an lpg car). Three months ago I had oil and filter changed, preceded by flush with BG109 or 44, which released a few more horses. Idle was slightly irregular so throttle body cleaned, but IAC not done for a couple of years. By way of on going preventative maintenance, I was going to change the engine temp sensor. What with Covid, I can live with things as they are, but it would be nice to put my finger on what's happening. I have a homemade 'almost OBD' box which I can plug in, although engine light is not on.

John.

[Kev0607]

Hi there,

There's a few culprits:

-The Idle Control Valve, as you suggested
- The engine coolant temperature sensor, as you suggested
- Mass Air Flow Sensor
-Lambda Sensor

Was the car doing this before you changed the plugs?

[nutco]

[QUOTE=arctan;2616332 I was going to change the engine temp sensor. What with Covid, I can live with things as they are, but it would be nice to put my finger on what's happening. I have a homemade 'almost OBD' box which I can plug in, although engine light is not on.

John.[/QUOTE]

As you were thinking of changing the engine temp sensor what you can do is pull the lead off the sensor, now try and start the car and see if the symptoms have gone or changed, according to a family friend with 40 yrs a volvo tech taking the lead off gives the ECU a reading close to what a warm engine would

[arctan]

Originally Posted by Kev0607

Hi there,

There's a few culprits:

-The Idle Control Valve, as you suggested
- The engine coolant temperature sensor, as you suggested
- Mass Air Flow Sensor
-Lambda Sensor

Was the car doing this before you changed the plugs?

Thanks Kev.
I had the Lamda sensor on a list called 'might be nice but expensive at the moment'. Maybe after the temp sensor and the IAC. And MAF I hope not, but I'll read up.

Plugs in for 2 or 3 k then misbehaviour.

[arctan]

Originally Posted by nutco

As you were thinking of changing the engine temp sensor what you can do is pull the lead off the sensor, now try and start the car and see if the symptoms have gone or changed, according to a family friend with 40 yrs a volvo tech taking the lead off gives the ECU a reading close to what a warm engine would

Thanks. I'll try that.

[Laird Scooby]

I don't think it's any of the above John..

Firstly, what were your old plugs gapped to and secondly, what are the new plugs gapped to?

Now for what i believe is the main culprit. Normally you start on petrol and it changes within a few minutes to LPG, correct?
When did you last give it a good run on petrol only? Also where does your temperature gauge sit after 5-10 minutes from cold? Does it drop at motorway speeds?

I suspect where it's manily been run on LPG, the LPG is probably running a little lean (perhaps needs replacement filters) and the main fuel ECU has altered the fueling to compensate. This would give a richer cold mixture as well as normal running.

Usually the LPG mixture is "slaved" from the petrol ECU and adjustments are made to the injection duration to correct the mixture on gas.

Before delving into the CTS (which shouldn't be run disconnected as it puts the ECU into LImp Mode and won't start easily from cold), pull fuse #1 for a few minutes and refit to clear the fuel trims then start as normal, hit the LPG switch to force it onto petrol only and give it a 15-20 mile run round the M25 if you can manage to get away with that at the moment. then hit the LPG switch again to let it do its thing on LPG as it normally would.

If my suspicions are correct that it's running lean on gas, that would explain the short-lived plugs as it would "cook" them by overheating them due to a lean mix on gas.

[Rversteeg]

A lean LPG mix actually gives a lower combustion temperature, so I don't think the spark plugs will be cooked because of this.

[arctan]

Originally Posted by Laird Scooby

I don't think it's any of the above John..

Firstly, what were your old plugs gapped to and secondly, what are the new plugs gapped to?

Now for what i believe is the main culprit. Normally you start on petrol and it changes within a few minutes to LPG, correct?
When did you last give it a good run on petrol only? Also where does your temperature gauge sit after 5-10 minutes from cold? Does it drop at motorway speeds?

I suspect where it's manily been run on LPG, the LPG is probably running a little lean (perhaps needs replacement filters) and the main fuel ECU has altered the fueling to compensate. This would give a richer cold mixture as well as normal running.

Usually the LPG mixture is "slaved" from the petrol ECU and adjustments are made to the injection duration to correct the mixture on gas.

Before delving into the CTS (which shouldn't be run disconnected as it puts the ECU into LImp Mode and won't start easily from cold), pull fuse #1 for a few minutes and refit to clear the fuel trims then start as normal, hit the LPG switch to force it onto petrol only and give it a 15-20 mile run round the M25 if you can manage to get away with that at the moment. then hit the LPG switch again to let it do its thing on LPG as it normally would.

If my suspicions are correct that it's running lean on gas, that would explain the short-lived plugs as it would "cook" them by overheating them due to a lean mix on gas.

Hello again Dave. Hope you are keeping well. I did the plugs because I had them lying around, and the old ones were a least a year old. I was curious if the car would run better on NKGs. One of them (Volvo standard plugs) that came out had a slightly bent earth electrode, so a bit more of a gap...
Hands up, I didn't check the new plugs gap! I've just read someone saying 'there is no such thing as a pre gapped plug'. Slapped wrist and all that. If it was a pre electronic ignition car (my comfort zone), a gauge would be automatic. Getting lazy (and stupid) in my old age.
I have an idea that lpg cars might or might not benefit from a smaller gap?
Having had bad ignition experiences with lpg ignition in earlier times, the rest of the system is quite young. Perhaps I really should find my feeler gauge...
0.7mm or even 0.6mm ?
I'll do the fuse out, and twenty miles on petrol on the M1, then toggle to LPG later this week.
One other thing, maybe not related. When I open the petrol filler cap, about once a month, there is a whoosh of air. Don't know if it's out or in. Breather tubes around the pump/ system, that aren't breathing? I will check if it does that before a cold start.
And I haven't done the lpg filters for ages. I'll order them now, as it's a pain when they eventually start to block.
PS. I do some of the work myself, and a good mechanic under my partial supervision does the rest. I'd like to do it all, and did try to in earlier times, but back says no, expensive, quite often! Eg. I replaced the lpg injector cables and sockets six months ago, old ones petrified and fracturing. And chock blocked on to old leads near distributor. New silicone leads and glass fibre heat shield tubing etc. Soon, when its warmer, I'll get the iron out, and do some cautious leaning in, with 'back breaks' as needed.

[Laird Scooby]

On the standard car, 0.65-0.7mm is the standard gap. With the LPG, i'd be inclined to drop to 0.6mm as you suggest John.

There shouldn't be any connections on the LPG system that are choc blocked - ever!

Correct method is either soldering or manufacturer type crimps, as i (and many others) call them "W" crimps as the die to shape them is a rounded W shape. The crimps with the plastic red, blue or yellow sleeve have a tendency to pull out, some people insist on soldering them in as a means to prevent this but it can cause other problems.

Some may argue the point about the W crimps, however the manufcturers of the LPG systems use them (and often supply them in the installation pack) in various things including the main LPG ECU multiplug so IMHO, they are every bit as good as is needed.

I feel your pain with your back, "back breaks" are definitely needed! When you have the LPG filters and change them, try and coincide that with the #1 fuse out and blast up the motorway, hopefully you'll find that is all it is. If not, we'll have to look for the more obvious. Also worth cleaning out your AICV and also PCV system, probably on separate days and when you have nothing important planned for at least the next day.

[arctan]

Originally Posted by Laird Scooby

On the standard car, 0.65-0.7mm is the standard gap. With the LPG, i'd be inclined to drop to 0.6mm as you suggest John.

There shouldn't be any connections on the LPG system that are choc blocked - ever!

Correct method is either soldering or manufacturer type crimps, as i (and many others) call them "W" crimps as the die to shape them is a rounded W shape. The crimps with the plastic red, blue or yellow sleeve have a tendency to pull out, some people insist on soldering them in as a means to prevent this but it can cause other problems.

Some may argue the point about the W crimps, however the manufcturers of the LPG systems use them (and often supply them in the installation pack) in various things including the main LPG ECU multiplug so IMHO, they are every bit as good as is needed.

I feel your pain with your back, "back breaks" are definitely needed! When you have the LPG filters and change them, try and coincide that with the #1 fuse out and blast up the motorway, hopefully you'll find that is all it is. If not, we'll have to look for the more obvious. Also worth cleaning out your AICV and also PCV system, probably on separate days and when you have nothing important planned for at least the next day.

I know. The choc block is disgraceful. I don't have these 'in stock' in the shed, I just needed a very quick solution in the cold. I used to solder up miles of microphone and 90 wire multicore cable in earlier times. RS days. I have heatshrink and gun. Crimps are nice, esp on larger wires- these are thinish fellows (where the new long injector 'tails' join the old un perished bulkhead loom).
Temp gauge is behaving- I did have a fractured thermostat- stuck open- the gauge tracked my wind over radiator speed, and other events. Novel, but not good.
Filter ordered just now. (Last done 2015, £20).
AICV on the list, PVC cleaned with new separator box in the last year. Must find a feeler gauge...