Help needed
 

Hello my 940 has a problem its a 1997 2.3 lpt. If i start it it dies give it some gas it will stay alive take my foot off the gas and the rpm drops to the point of stalling & engine light comes on. If it doesnt stall it will hover around 450-500 rpm. I have tried fitting a new coil, crank sensor, and ignition module still has the same problem. I have tried a different fpr rpm increases if i pull the hose. Has a new distributor & arm new fuel pump etc. I have cleaned the eart leads on the manifold resoldered points in radio suppression relay & fuel pump relay ( clicks when priming ) rsr clicks after a few mins of ignition being cut. Now one thing i do notice is the longer of the two injection resistors gets red hot cant even touch it hot. Any ideas as to what the problem could be would be a great help.

From your description, it sounds suspiciously like the MAF or dodgy fuel. Could also be a vacuum hose off somewhere, a split in the hose between the MAF and the main air intake to the throttle body - in fact one of several possible causes.

However, you've given yourself a huge headache already by throwing parts at it. Sometimes even new parts can be faulty and cause similar symptoms.

As we have to start somewhere, what are the plugs like, what is their gap and when were they last changed? What about the HT leads?

Was it running ok before this happened and did it do anything strange befre it happened? Did it just die or was it that you came out one day and it wouldn't start?

just keep throwing parts at it. Eventually you will have changed everything and the problem will be solved.

Have you thought of changing the transmission fluid? I had one once.

On a more serious note, the engine is running. You've replaced everything that, if they fail, cause the engine to stop running.

Here are your clues - the fuel pressure regulator disconnect INCREASED engine speed, and the injector ballast resistors are unusually hot.

Try disconnecting the injectors one by one while the engine is running. Tell me what happens.

Its always taken a few to many cranks before it fires up for my liking. But just started to die once fired up just the othe day. So i checked the coil & the spark looked very weak ordered a new one not the issue. Plugs were changed less than 1k miles ago gaps are good. Dizzy cap & arm done not long ago as was pump & filter. Looking on forums for simular symptoms pointing to pump relay, radio suppression relay, ignition module. However none of these sorted the issue. I dont see it as throwing parts at it as once changed if its not the problem il swap them back over & put the new part in a box no doubt them parts will go at some point & il have a spare already.

The resistor thats getting hot is for the lights dip ive been told.

But what are the gaps? How big?

I thought it was probably the dim-dip resistor getting hot, usually only one injector resistor or the same number of cylinders, in your case, four.

Couldnt tell you off hand but it wouldnt hurt to check them anyway. i did at time of install though & car was running fine up until this issue popped up.

What did you set them to?

They were gapped at factory i only double checked them before installing them just cant remember what it was.

What make are they?

what is this dip beam/flash resistor people are referring to? I've never come across one before...

REference to a wiring diagram would be cool!

Volvo plugs.

The longer one is the light resistor the other injector resistor.

huh - waddayaknow.

The diagrams I have (940 1995) show this as an electronic unit.

So i think i may have found the problem. This morning I built a led code flasher and got on the fuel pin code 223 icv signal missing or faulty. Has a near new one on there but it was a cheapy one. Il try a bosch one from someone & see if it works.

I was just about to mention the idle control valve, mine gets oil in and gums up. I think the breather pod is blocked on mine so it builds too much pressure in the crankcase and forces some oil out of the breather which in turn blocks the idle control valve and coats the throttle butterfly.

I get similar idle problems to you but not as bad, I find if I rev it into the higher RPMs on start up it usually idles better after that as it clears things out a bit (gives an oily smoke puff from the exhaust and then it's fine until it blocks up again).

There you go Ash - Pg 26, item 7/75 :

http://www.myvolvolibrary.info/Tech_...ction-3-39.pdf

A law was passed here that from 1/7/86, all new cars must have dim-dip lighting. In simple terms, if the sidelights are on and so is the ignition (ie engine running) then the dipped beam headlamps should operate at reduced intensity. This was meant as an accident-prevention measure so people couldn't drive on sidelights alone after dark. Wikipedia explains the rest, although it disagrees with me on the date :

https://en.wikipedia.org/wiki/Automo...#Dim-dip_lamps

That would be why you've never come across it! :tongwink:

Some systems, notably Ford that was implemented by Bosch used a bespoke relay that was incredibly prone to failure and complicated to even try and fix. They were also f-expensive from Ford dealers. In the light of the EU throwing their toys out of the pram and the subsequent lack of need to fix dim-dip if it stopped working, mostly if it packed up it was ignored. ;) :D

You're lucky then - they come pre-gapped to 0.65-0.7mm. Default gap on NGKs is 0.9mm which is way too large. No reason to suspect the gap would increase substantially over 1k miles so (for now at least) you can probably ignore them. ;) :D

By the way, FYI the ICV won't effect running on the throttle - clue is in the name - Idle Control Valve.

Also, your Volvo can't be scanned with a generic OBD-II scanner, it still used Volvos own OBD system that isn't recognised as one of the default protocols.

1996
 

According service manual TP0005071 the reduced low beam (dim-dip) system was introduced in the UK only, starting from 1996.
"Reduced low beams for the UK:
The dimdip or reduced low beam is a new system for all vehicles. A resistance of 0.9 Ohm is used to lower the supply voltage to the headlights to about 9V."
You won't find this system outside the UK

Throttle position switch TPS
 

If the ICV does not work properly, also check the TPS on the throttle housing. When idling (not touching the throttle pedal), the orange wire (pin 1) should be earthed via the black wire on pin 2.

Thanks to all for your help & information. Il try another icv & see what happens. Spose this should teach me a lesson with buying cheaper parts as its the only non genuine part that i have replaced thats failed.

Tps shows increasing voltage when back probed and put through movement. But i do have a spare tps in my box should the original fail.

It might not have failed, if you still have the original clean it out with something to break down any oil in it and then give it a go again. The originals rarely fail,they are also a generic Bosch part so are used on other makes and models of car.

Yeah im just about to try the original one just to see if it clears the code however i think this one is toast. Neither of them are seized though and go through full movement.

I disagree. Take a look at the diagram and the explanatory note top centre on Page 26.

7/75 is the bulb failure sense resistor. Its shown simplified. In other diagrams, it is shown as a part of other bulb circuits. Its shown in the electrical distribution box on page 126 (just next to the fuel pump relay position)

The dim/dip voltage is electronically reduced by the electronic regulator component 2/3.

Unless the system had some form of modification or downgrade in later years, I don't know what the long resistor does, but its not dim/dip voltage reduction.

You're right Ash, i was still half asleep when i added that, maybe why i TARFU'd it! ;)

*** EDIT *** i have seen a dim-dip resistor used on other cars including Volvos so maybe they did add it in there and change that regulator for a dim-dip relay. You know what they say "Volvo reserve the right to change specifications etc"

A resistor would not make sense in that use anyway - the voltage drop would change too significantly if a filament went open circuit on one side, or if different wattage bulbs were fitted.

I strongly suspect the long resistor is something else, not related to the lighting circuits

0.9 Ohm resistor
 

It is actually item 7/46, a plain resistor, nothing else to it and it IS the one in the picture.

About the ICV, just ground pin 1 of the TPS and start the engine. Just to be sure...

Thanks Rob. ;) :D


You're right Ash and that has been the primary cause of failure of many dim-dip systems. It's how it's usually done though.

https://s19.postimg.cc/brewx3feb/dimdip1.jpg

https://s19.postimg.cc/o61oxez6r/dimdip2.jpg

That's a much simpler system but still uses a simple wirewound resistor mounted on an aluminium heatsink bolted below the LH headlamp on the car that diagram pertains to. Many others were done in a similar way. ;) :D

Dim dip resistor
 

Oh yes it is! :regular_smile:

Just to slightly drag this back the problem OP started it with (I know, sorry - btw good to learn what all those resistors do in the bay so not complaining).

If you wanted to I will be in warminster this weekend so you could try my icv from a known working car to see if the symptoms change/disapear.

PM me if you want to try it.

PP

While i remember it, pulling the vacuum hose off the FPR at idle and the engine speed increasing is a sure sign it's running too lean - almost certainly an air leak.

Like i said originally, check the hose between the MAF and throttle body for splits and security - also check the hose between the EICV and the inlet manifold for the same.

All air hoses are good no leaks & vac lines were all replaced not long ago. Heres one. the idle control valve is drawing 11.5 volts at the plug when i twist the throttle should that voltage drop ie when coming off idle cos mine stays the same no reaction from the tps to icv.

Pp
 

hello have sent a pm but as im new on here im unsure if you got it. That would be great i do have one coming but unsure of condition just borrowing to test. If it works il let you know on here before the weekend. Post code is ba12 9eb & house number 87. Many thanks.

There should be a feed of battery voltage to the idle control valve on a blue-yellow wire, other wire goes to the ECU and is red-black.

However that's for a 1995 model, not sure if they changed to a different idle control valve on later models.

Was that reading taken with the engine running?

No just on po2 of ignition. I thought as you press the throttle the tps clicks telling the ecu to come off idle stopping voltage to the icv.

FYI - (although off topic ... again) I have dim-dip fitted as standard on my Feb 1990 745 Facelift.

It is firing and supplying fuel, but you have not enough air or fuel.

Fuel pressure reg is a likely cause but pull the vac pipe off and check for fuel leakage or change in engine note.

Check for air leaks, throttle body gummed up (clean with intake cleaner).

That's a permanent feed to the EICV, without checking the diagram again i can't remember if it's ignition switched or permanent from the battery, it doesn't change with varying engine conditions. The switching is done on the other side of it by the ECU.

The TPS tells the ECU when the throttle is either at idle position or at full throttle, it alters timing, fueling etc from these signals and possibly might switch the earth return to the ICV off when not idling.



I have had dim-dip on all my 7xxs as well Bob, a 1987 740, 2 x 1988 740s and a 1988 760, all estates, auto and GLE spec although the best equipped is the 760GLE as it came with standard air-con.

Ash doesn't know what he's missing having never had to diagnose and fix a nasty dim-dip system! ;) :D