89 740GL Sedan Non Turbo 286K error code 1.4.3. knock sensor

cgreygoose · Post by **cgreygoose** » 22 Mar 2012, 10:47

OK. I'm driving my 89 740 NON turbo an it runs loud an at times rough. Poor pick up but once on hgwy cruise at 75-80 nicely, albeit loudly. Shop told me motor mounts were bad, thus the loudness. However, my question is that when I insert the lead into position #6 I get the code 1.4.3. which I believe is the knock sensor. No error codes when inserted into #2 hole. I purchased a new knock sensor this morning but before I tear it apart is there a way to confirm that mine is bad? I've read in the forums that it must be the correct Foot Pounds in torque. Can I test the old one to know for sure? before I replace it? lastly, could this error code be incorrect? Thanks for your help on this one.

jason

Post by **billofdurham** » 22 Mar 2012, 12:54

Without a breakout box to connect to the ECU there is no real way to test the knock sensor. However, as you have indicated, the tightening torque is critical.

Two types of knock sensor have been used and the torque depends on the type. The attached is from one of my books which does give an indication as to how to check the problem.

740 Knock sensor.pdf: (126.64 KiB) Downloaded 188 times

I would be inclined to clear the code first and run the car to see if it returns.

Bill.

cgreygoose · Post by **cgreygoose** » 24 Mar 2012, 20:41

So I assume a break out box is a special diagnostic tool?? I remember back in the day with my VW I would use a timing light to find & correct timing. I wonder, does the 1.4.3 code specific to the knock sensor or is it just pointing me in the direction of a timing issue. apart from some of the sluggishness in accelerating from 10-40 +/- once at highway speeds it runs pretty smoothe for 286K. What other symptoms do you think I would be experiencing if my knock sensor was bad or not torqued properly? Plugs look fine, good gas mileage, no smoke etc. I'll check torque & go from there. thanks,

jason

cgreygoose · Post by **cgreygoose** » 24 Mar 2012, 20:42

forgot. I did clear the codes and it came back on later that day.

Post by **jimmy57** » 24 Mar 2012, 23:30

Knock sensors can only be evaluated by monitoring using a scan tool on the control systems that allow it. Your 89 is not one of those capable. In that case inspection of the wiring and connections at both ends is made and then sensor replaced.
The sensitive knocks sensors were used 84-87. You should be fine with a 15 ft-lb torque on the domed domed shaped later sensor your replacement should be. The terminals at ignition control unit above brake pedal under dash can be the issue on 89's. The weak tension terminals were used and they can get contact issues. Usually pushing the fingers of terminals inward with a pin and then spraying the whole plug with at least WD-40 if not something with more staying power like dielectric grease.
The testing per volvo manual for that year is to check wiring and then replace knock sensor. If the engine load is high (heavy throttle) and the RPM exceeds 2700 then the ignition ECU will have evaluated KS and set code if the KS signal is low. The KS is a piezo crystal and ohm meter readings do not test it. It makes a voltage pulse when knock shockwaves occur but has a very high almost open circuit resistance value otherwise. IF I were a mean person I'd tell you to clamp the knock sensor between jaws of a vise with low vise pressure and then put your finger on the two pins and strike the vise with a hammer sharply. It won't hurt you but it can be a jolt. The spark source for those no-battery BBQ grill lighters is a spring hammer blow to a piezo crystal.

cgreygoose · Post by **cgreygoose** » 03 Apr 2012, 22:31

Sorry for not posting sooner. I ran out of funds, then was able to buy the new KS but the store did not have a torque bar that went low enough. So I have the KS but still haven't found a torque with low enough ft/lbs. I did unplug the KS on my Volvo 740 and went ahead and started the car and took it around the block a few times with no real difference. My first thought was, Yes!! of course this i the problem, but now I'm not so sure. What should I have experienced once I unplugged the KS? Should it drive just the same whether or not it's plugged in? Anyhow,until I can get that torque bar I'm stuck with it as it is, which is that it's getting lesser pick up and seems to "bog" down upon heavy acceleration but once it's up to 65+mph it's driving like a champ, though it's loud. I will dig around under the driver's dash by the brake pedal. Why is this year & model so difficult to locate a manual? Haynes don't carry one for this one. Bizarre.
I need used injectors too. Any good sites for used ones that are affordable and in working order?
Thanks.