1998 940, new to me and a few issues to sort!

[griston64]

Parts for Volvo's online have Bougicord leads.

[dave88sw]

Thanks for the suggestions so far.
The leads I ordered from partsforvolvos, although I've just noticed that it says bougicord or Bosch.

I've checked the crank sensor, the wire is in good condition, I'd guess at a recent replacement as it's very clean.

How would I test the coolant sensor or is it a case of replace it and see?

I've checked the fuses mentioned, they couldn't be cleaner and no discolouration of the white plastic of the fuse box from heat.

I have no lights on the dashboard so is it likely to have stored codes? Either way, I'd like a code reader for it, I'll get in touch with Loki.

Mine being a late model only has the one in tank pump, which must be pumping because the car runs.

Unfortunately the parts I ordered haven't arrived yet so I've got no further with it.

Thanks
Dave

[Laird Scooby]

Originally Posted by dave88sw

Thanks for the suggestions so far.
The leads I ordered from partsforvolvos, although I've just noticed that it says bougicord or Bosch.

I've checked the crank sensor, the wire is in good condition, I'd guess at a recent replacement as it's very clean.

How would I test the coolant sensor or is it a case of replace it and see?

I've checked the fuses mentioned, they couldn't be cleaner and no discolouration of the white plastic of the fuse box from heat.

I have no lights on the dashboard so is it likely to have stored codes? Either way, I'd like a code reader for it, I'll get in touch with Loki.

Mine being a late model only has the one in tank pump, which must be pumping because the car runs.

Unfortunately the parts I ordered haven't arrived yet so I've got no further with it.

Thanks
Dave

To test the CTS you need your multimeter, set it to resistance and then unplug the CTS. Probe the pins on the CTS with one probe of your meter, the other should be on a known good earth point, preferably on the head.

At 20C you should read ~2500 Ohms on both pins WRT earth, it will be a bit more than that with the engine cold at the moment, at 80C you should get about 330 Ohms and at -10C about 9400 Ohms, all these figures +/- ~12% - do a final check pin-to-pin which should be the sum of each pins resistance to earth so for example if each pin reads 3000 to earth then it should be 6000 between the pins. Also worth checking that some numpty hasn't wrapped PTFE tape round the threads of the sensor as you may get ok readings at one point but not others. It will insulate the sensor body from the head electrically and isn't needed for sealing anyway.

As for fault codes, yes the ECU can store them without lighting the EML and this can effect running. The EML should light with position 2 of the ignition key with the other warning lights and go out once the engine has started. That's why i suggested pulling fise #1 to reset the codes in case you had historic codes causing a problem.

[Rversteeg]

i was thinking in order of likelihood; ignition amp, fuel pressure regulator, failing fuel pump, coil?

Fuel pumps are known to fail, but you have one of the last series 940s with the improved turbine type fuel pump. Apparently Volvo kept on improving their products until the very last series. Still my turbine type fuel pump failed last week after 400K miles, so even the improved ones can fail. I am running on LPG, but the system always starts on petrol. The last few weeks I did notice an occasional hesitation on cold starting. Usually it fires and picks up speed right away, but now it sometimes hesitated, spluttered and stopped again. Restarting is slightly more difficult and needs a foot on the throttle. This hasn't happen again after I exchanged the fuel pump, a bit soon to tell now, but it could have been related to the fuel pump as well. I seldom run it on petrol, so I can't tell you if it also misfired.

You could try if letting the fuel pump prime improves starting. Just wait a few seconds before turning the ignition key from the first position to cranking.

I have never heard of a failing coil, it is certainly not a common fault.

[dave88sw]

Brilliant description to test the cts, thanks very much.
Mine appears to be fine, very similar numbers to what you suggest and it changes as the engine warms up so that suggests it's working.

Interesting about the fuel pump, I guess you cant complain if its lasted 400,000 miles! Mine is on 132000. I'm still waiting for my order with the fuel filter and fuel pump relay so I've not replaced them yet.

I wont look too hard at the coil if they're not known to fail. Is there anything else I can test while I'm waiting for bits? I'd like to rule out as much as possible. Can you test the ignition module/power stage?

Thanks again
Dave

[Laird Scooby]

Originally Posted by dave88sw

Brilliant description to test the cts, thanks very much.
Mine appears to be fine, very similar numbers to what you suggest and it changes as the engine warms up so that suggests it's working.

Interesting about the fuel pump, I guess you cant complain if its lasted 400,000 miles! Mine is on 132000. I'm still waiting for my order with the fuel filter and fuel pump relay so I've not replaced them yet.

I wont look too hard at the coil if they're not known to fail. Is there anything else I can test while I'm waiting for bits? I'd like to rule out as much as possible. Can you test the ignition module/power stage?

Thanks again
Dave

The easiest check for the ignition amp is by substitution but normally if they give trouble, they do it hot. I'd suggest purely as preventive maintenance, undo the two screws holding it onto the heatsink and unplug it.
Remove it and clean the aluminium back of it and the heatsink where it mates with a non-abrasive cleaner and polish them up as shiny as you can get them - this is surprisingly important!
Smear some new heatsink compound on the back of the amp, offer it up to the heatsink and move it around to spread the compound evenly on both then refit the screws and plug.

Given the symptoms you've got, inspect the inside of the dizzy cap, particularly the carbon brush to make sure that it's there and not broken. Mark the leads (Tipp-Ex stripes on the leads work well to number them) and take photos of there positions for reference whn refitting before you remove them, it can be a confusing cap!

[dave88sw]

Thanks, that's good advice about the heatsink on the ignition amp, i'll definitely do that once i've got it running right, as it misfires right from the first start up, i can't imagine it's causing my problem as it hasn't had a chance to get hot by then.

The distributor cap was replaced right before i bought it, i took it off the other day to check it hadn't been damaged in fitting but it's perfect.

I'm still waiting for my parts order to arrive, in it is a new fuel pump relay, filter and decent leads, i'm not holding out much hope for any of those things but i don't want to spend more money until i've tried them. Hence, hoping to test as much as possible before buying parts.

Thanks for the help so far, hopefully the parts will arrive Monday.

[Forrest]

Based on my recent experiences of chasing poor cold running performance on a slightly older 940 I’d recommend checking fuel pressure at the rail, if only to eliminate fuel supply from your enquiries. There will be a Schrader valve under the rail between 1 and 2 injectors. If you buy a gauge for this purpose make sure its connector is suitable to access this. A flexible hose or 90-degree connector is best.

Also, check for misfiring. One of the multiple faults I had was a faulty HT lead causing arcing between the distributor cap and the bulkhead.

It’s also cheap to check/clean the idle air control valve and throttle position switch. If you’re having to open the throttle to keep it running it’s possible there’s an issue there.

Air leaks have already been mentioned. I found I had a hole underneath the turbo air hose letting in unmetered air.

I also cleaned my air mass sensor. This needs to be done carefully using a suitable spray. I used plastic-friendly carb cleaner.

Good luck tracking down the problem. It can be extremely frustrating.

[dave88sw]

Thanks, i'm hoping a friend has a suitable fuel pressure gauge for me to borrow. I've put cleaning the IAC valve and throttle body on the "to do" list.


My parts finally arrived today, i didn't have a lot of time this evening to play with the car but i've fitted the new bougicord leads and it definitely runs better. I'm not sure if it's quite 100% but a marked improvement. I'm starting to think that my issues are a combination of things rather than 1 fault. The garage who looked at the misfiring for the previous owner replaced the Dizzy cap, rotor arm, leads and plugs but it was all cheap crap by the look of it (except the plugs, which were NGK, are BPR6ES the right plugs? I've seen other numbers suggested elsewhere).

With that in mind, i'll be cleaning anything i can, replacing the cap and rotor with genuine and hoping that's all the misfire is.


The only thing that still worries me (although i've not experienced it yet) is that the previous owner had issues with it cutting out and only restarting after 10 minutes. Looking on google suggest the fuel pump relay as a likely culprit, or the ignition amp, I have a new fuel pump relay coming and i'll renew the heatsink paste on the ignition amp, is there anything else i should be checking? I really need to make sure this car will be reliable, not least because its got big shoes to fill, i'll be selling my 98 V70R to run this.

Thanks again
Dave

[Laird Scooby]

Originally Posted by dave88sw

Thanks, i'm hoping a friend has a suitable fuel pressure gauge for me to borrow. I've put cleaning the IAC valve and throttle body on the "to do" list.


My parts finally arrived today, i didn't have a lot of time this evening to play with the car but i've fitted the new bougicord leads and it definitely runs better. I'm not sure if it's quite 100% but a marked improvement. I'm starting to think that my issues are a combination of things rather than 1 fault. The garage who looked at the misfiring for the previous owner replaced the Dizzy cap, rotor arm, leads and plugs but it was all cheap crap by the look of it (except the plugs, which were NGK, are BPR6ES the right plugs? I've seen other numbers suggested elsewhere).

With that in mind, i'll be cleaning anything i can, replacing the cap and rotor with genuine and hoping that's all the misfire is.


The only thing that still worries me (although i've not experienced it yet) is that the previous owner had issues with it cutting out and only restarting after 10 minutes. Looking on google suggest the fuel pump relay as a likely culprit, or the ignition amp, I have a new fuel pump relay coming and i'll renew the heatsink paste on the ignition amp, is there anything else i should be checking? I really need to make sure this car will be reliable, not least because its got big shoes to fill, i'll be selling my 98 V70R to run this.

Thanks again
Dave

Those are the correct plugs but are they correctly gapped? Should be 0.65-0.7mm. Most NGK plugs come with a factory set 0.9mm gap so if they just removed the old and fitted new without checking, they could be causing part of the problem.

Check fuses 1, 11 & 13 for cleanliness on the blade and also that they are a snug fit in the fusebox with no signs of heat in the fuse box where they live. If all is well, renew the heatsink compound on the ignition amp, polishing the back of the amp and the heatsink as bright as you can - don't use anything abrasive!