1994 940 B230FB misfires like morse code

[Speedmonkey]

Hello Wise men from the Volvo world

My name is Bas and I'm from the Netherlands. And I have a small problem with my white Swiss import 940 Polar B230FB: It misfires like it's sending out morse code. Any time, every time. At idle, half trottle, full trottle, warm engine, cold engine...

I'm chasing this inconveniece for 6 months now and I'm getting desperate. I tried every trik of the book, the book that I know, and still cannot find it. No error codes, no CEL nothing

What I did:

Checked every relay
Cleaned every connector
New Knock sensor
New AMM
New TDC sensor
Measured ECT sensor
Measured Lamdba sensor
Tested all the wiring
Rebuilt distribution, twice
New distributer, wires, plug, rotor
Checkes valve clearance
Checked fuel pressure
Replaced fuel pressure regulator
Extended vacuum tests
Tested every resitance en control voltage for the LH computer
Exchanged LH and EZK
Exchanded the spark amplifier thingie
New intake gasket
Checked all grounds, made new one from head to chassis
Checked play on distributer axle
Short wired Radio relay
Exchanged injectors nozzles
Cleaned and exchanged Throttle body
Cleaned and exchanged CIS

So....is there someone who could't point me in the right direction.THE PERSON WITH THE GOLDEN TIP WINS ETERNAL FAME!!!

Thanks guys!

[volvo always]

Are the spark plugs getting wet due to possible faulty head gasket?

Is the air filter clean and not restricted? Is the exhaust sooty. Running rich/lean? Has the mixture been adjusted?

As you can see I'm no mechanic!

James

[bluebrickrick]

I was dogged by random inexplicable stops and hesitations which recovered (see 945 niggles thread), found it was down to an intermittent electrical connection to the fuel pressure pump (underneath pump not the one inside tank) - could conceivably be something similar as you seem to have covered most else?

Happy hunting & good luck

Rick

[Alasdair1]

Is it misfiring as well as back firing. Sometime tricky to tell but it might be worth a compression test. If one of the valves is sticking or worn it could cause the symptoms by dumping unburnt fuel into the exhaust? You seem to have tried everything else judging by your list. The only other would be a broken wire that's causing an intermittent fault that's been missed.

Alasdair

[Speedmonkey]

Hi Guys,

The sparkplugs are coffee brown leaning to whitish...We also measure almost no CO. Also after blipping the throtlle multiple times...

Wireloom is OK. I checked the injector signal and the sparke signal with the scope last weekend en couldn't find any interuptions in those. So yes it might be a sticky valve (vacuum meter should answer that) or possible a leak in PCV (crank case vent).

There is a small backfire when you release the throttle...Fuel pressure is at a steady 3 bar...

this weekend I'll try to continue searching...

Keep you guys posted...

[Laird Scooby]

Is it automatic? If so when was the ATF last changed?

Sounds like i've gone off at a tangent but i've known dirty ATF cause misfire symptoms, even when idling but particularly under load.

Also have you checked the engine mounts for security and the earth strap from battery to starter motor?

[aardvarkash10]

"Almost no" CO is on the same usefulness scale as the "****-all".

Given everything you've replaced so far and still the same problem, this reeks of needing a "first principles" approach. Compression, cylinder leakage, timing (cam and ignition), then full fuel and ignition diagnosis sequence.

However if I was asked to guess, and with that limitation in information noted, you are describing classic lean fuel symptoms.

[Laney760]

Water in the fuel tank? Happened to me, the mis-firing was horrendous. I chucked in a small bottle of meths and it almost all stopped, second treatment it stopped altogether. Until you burn off the water with the meths no amount of re-fuels and top ups will get rid of it

[Laird Scooby]

Good point about the meths - used it (and recommended it) many times myself but maybe the problems i've had when i've used it haven't been as severe as yours because it's usually cleared when moving and/or the revs are higher but back at idle.

Whichever way you look at it, the meths gets rid of conensation in the fuel tank which can and will cause misfiring.

[Speedmonkey]

Hi Guys,

First, it's a manual...

Water in tank is a good option! Never heard that one before!....What is "meths" and how is it used, I like to try that one! Is it methyl alcohol? How much do you use?

Almost no CO means not even 1% also with blipping the throttle...Yes that means the car runs lean...But why...