1994 940 first rough idle and hesitation, now no start

volvii · Post by **volvii** » 10 Jun 2014, 12:26

HI folks,
I hope to get some advice on my problem from you.
My 1994 940 non-turbo all of a sudden started to idle rough (constantly dropping and recovering rpm) and hesitate at rpm 1000-2000 when accelerating. Higher rpm worked quite fine, load transition seemed to be a problem. I believe I felt misfires.
After 2 days of above behavior, I changed all 4 spark plugs and cleaned the Air Mass Meter. I let it run for a while to see the result of the change and after 10min or so it died emitting some knocking noises.
It won't start anymore.

It turns fine, I hear the fuel pump relay when switching the Ignition to 'II', I hear the pump humming, I hear both while the engine trys to start up. There's fuel at the rail.
I just jumpered the Noise Suppresion Relay. I can hear the injectors (?) making a sound for a 1 sec when I wire the jumper.

I've been trying to connect the pieces by reading almost every post out there, but I feel I am stuck. Any ideas are highly appreciated!

Best
Volvi

I forgot to mention: Before these problems occured, ever since I bought the car 3 months ago, it would slightly drop RPM about every 15 seconds during idle. Like a clock. I never worried about it, but I though it could be related.
Oh, and there are no error codes.

93Regina · Post by **93Regina** » 10 Jun 2014, 21:06

volvii wrote:1994 940 non-turbo

VOLVO CRANK POSITION SENSOR 740 760 780 240 940 89-95: US $15.99

See: Intermittent Ignition Failure.

Is tach working?

volvii · Post by **volvii** » 15 Jun 2014, 02:42

The tach works. Today I unplugged the Radio Supression Relay to let it turn over for a little and get dry, as I thought it might have been flooded.
With the Relay back in place I then actually got it to start and idle on 2 or 3 cylinders, the entire car jiggled. I could rev it higher by slightly touching the gas pedal, same rough running, and with a small push on the gas pedal it died right away.
Later today in the darkness I wanted to see how good the sparks were, and then there were no sparks at all! Accordingly, there was again no way to start the engine.

So I am quite sure the problem is on the spark side, and not on the fuel side.

Does anyone know which pre-requesites have to be fulfilled for the ECU to iniate a spark?

volvii · Post by **volvii** » 15 Jun 2014, 13:41

Today, after unplugging the Ignition amplifier and re-plugging it, the engine wouldnt even turn over any more. Key in II, the fuel pumps could be heared, when I turn the Key everything dies, no engine turning..
I don't understand anything now. Please help!

93Regina · Post by **93Regina** » 15 Jun 2014, 18:17

volvii wrote:when I turn the Key everything dies

Have you charged the battery?

volvii · Post by **volvii** » 15 Jun 2014, 22:15

Yes, the battery is charged.

And I am back at where it turns over, but no spark (no idea what caused it to completely die before, it seems that was just a phase)

I replaced the ignition amplifier today, no luck.

Tomorrow I'll try a new CPS. Unplugging the old one did not change the behaviour, would this be a hint?

93Regina · Post by **93Regina** » 16 Jun 2014, 06:40

volvii wrote:it turns over, but no spark

I don't know your electrical system, without looking at a schematic, but check to make sure voltage is at coil's positive side. When tach works, this suggests there is voltage at coil, and other components are working.

Yesterday, it was stated starter would not roll over, but you didn't use a jumper wire to energize starter's solenoid.

Hence, I have no idea if you have an key switch issue, or something else. But, your symptoms sound more like a faulty CPS sensor, but then you threw a curve ball with that starter issue.

volvii · Post by **volvii** » 16 Jun 2014, 22:57

I really have no idea what this no turning issue is. It comes back sometimes after working on the car (changing a sensor, changing spark cables..), but then disappears usually after dis- and reconnecting the battery another time. I disconnect the battery of course while I work on the car. I am not sure if it is related to my no starting while turning over issue.

I just changed my CPS: The old one had no continuity between the two outer pins and between one of the outer pins and the center one.
The replacement CPS has ca. 170 Ohms between center and outer pins and about 1 Ohm between the outer pins.

Now I can see the rpm needle jumping again sometimes while turning over. So this seems to be a hit.

But it still won't start and I can still see no spark at Plug 1 and Plug 2 at least, while I checked the battery became really tired so now it is charging again.

I also ohm-metered the coil: main resistance is 0.8 ohms, secondary was around 4 kiloOhms. With the key in position II, I have 12V at the blue wire. The red/white wire has 2.9 KiloOhms resistance to ground. I don't really know what I am doing, but doesnt this seem very high?

Thanks a lot for the help so far!

93Regina · Post by **93Regina** » 17 Jun 2014, 06:08

volvii wrote:I can see the rpm needle jumping again sometimes while turning over.

That means coil is getting power, and ECU/CPS is working.

Fuel pressure regulator - Pull vacuum line off of it, and have someone watch its port when someone else cycles key.

Check spark plugs after cranking it; are they wet/dry?

volvii · Post by **volvii** » 19 Jun 2014, 00:05

I do not get a spark from the coil anymore, also the rpm needle stopped jumping-

I find it hard to tell whether the plugs are wet or not, but I definetly smell unburnt gas when I am turning over the engine.

What should the fuel pressure regulator's port be doing/what do I have to watch for?

Thanks for the help