[LuukvdHeiden]

Hello all,

My 92 lpt has a not too loud yet distinct, rev-related knocking sound at around 1750-2200 rpm. I feel it through the clutch pedal as well; seems to get a little louder with the clutch depressed, but it's there when i dont use the clutch, too. It does not get louder under load, but i do feel the engine doesnt run as smoothly as it should from about 3000 rpm on.

A bit worried about this, so advice appreciated!

Cheers,

Luuk

 

[16saabs]

check engine mountings

 

[woywitka]

as well as the inner c/v joints. if your getting vibrations like that it is prob something to do with the driveline or as stated above engine moutings. does the shifter vibrate?

 

[LuukvdHeiden]

top end/big end?

i checked again today, under the hood, and then in fact it is pretty loud and metallic; seems to come from the engine, is rev-related and occurs especially when depressing the accelerator pedal quickly (run the engine at 1500 rpm, then quickly depress the pedal, the sound is most obvious and pretty distinct at around 2000 rpm, when revving harder it disappears ( or is drowned out biy other sounds, i dont know) but, as stated before, the engine sounds far from sweet.

Definitely not a driveline issue (i had that before) and i dont think it's engine mounts either. I do hope it's not a top end or big end bearing.

 

[ProfZ]

Check your knock sensor!

The pins in the sensor's connector sometimes come out--this happened in our 1990 900S. Pull off the connector, and make sure the pins will not push out when the connector is plugged back onto the sensor. Then, if this doesn't help, test the sensor itself (see Bentley manual).

 

[LuukvdHeiden]

knock knock

Thanks, i will check. Didnt know the 900 lpt had a knock sensor? does it have one?

 

[Kaas]

I had the same problem with my lucas fpt! I think your timing is off! Does the sound sounds like piston tilt? I adjusted my ignition down and the sound is allmost as good as gone

 

[LuukvdHeiden]

tilt

dont know what piston tilt is, but it sounds awful

i'll check both the knock sensor (if i can find it) and the ignition timing.

 

[cdaly]

The LPTs have no knock sensor. That's only used by the APC system on turbos and by the EZK ignition on N/A cars.

I did have a noise something like you describe some years ago on my LPT. Turned out to be big end bearings due to being driven with a blown head gasket for a few hundred miles before it was discovered. Water had blown into oil so there wasn't proper lubrication which caused premature bearing wear...

 

[LuukvdHeiden]

thanks. that doesnt bring a smile to my face, though.

 

[LuukvdHeiden]

I checked the ignition timing and it appeared to be at over 20 degrees. After correcting this to 15 degrees, the engine ran much smoother. I still hear the knocking sound though. I still havent found out what it is. If it would be big end bearings, i fear i will have to get rid of the car; it's a 5-door, cosmetically not in very good shape and i need to replace the springs on all corners; gearbox is a bit of a pain when cold (esp. shifting to 2nd gear); on the other hand it already cost me quite a bit of money.

At higher speeds i hear nothing, it is especially noticeable when you rev the engine quickly without load in the 1750-2500 rpm-range. i am pretty sure it is the engine and not ancilliaries, but how do i find out whether it's going to be an engine-out affair or not?

 

[LuukvdHeiden]

Went to see a reputable Saab specialist, and he needed only 30 seconds to tell me what the knocking came from: worn big end bearings. His collegue confirmed the diagnosis.

darn!

 

[Jezzadee]

cdaly gets the prize. Again .

Good luck with it.

 

[LuukvdHeiden]

i think i need a talk with the 'specialist' who installed this engine 5 months ago as a 'good used engine'- apparently without even checking the bearings.

By the way, Jezzadee: i saw eurocarparts now also have 'sports' front springs bij ventura too. Actually i was thinking about replacing the springs on all corners - until this little problem popped up.

 

[Jezzadee]

I'm considering them because my front suspension needs doing, but according to this thread they are even stiffer than the Ventura heavy duty springs. That might not be the best setup for me given how rough the roads are here.

 

[LuukvdHeiden]

Went back to the guy who put in this engine; agreed with him that he would have a used shortblock checked by a reconditioning firm and then replace mine at no cost. Also agreed that i would be around in the shop when he changes the engines, so i can see exactly what happens.... sounds like an okay deal to me.

 

[Saab-Daniel]

It does indeed... Hope you get everything settled, so you can get your car back on the road! Keep us updated!
Daniel.

 

[woywitka]

all Saab's have knock sensing don't they, integrated into the fuel system? the turbo's just have the apc which uses knock sensing to open the wastegate.

 

[LuukvdHeiden]

On the road again! engine shortblock was exchanged for a good used shortblock (bearings and bores checked and new piston rings) and it runs fine ).

 

[cdaly]

all Saab's have knock sensing don't they, integrated into the fuel system? the turbo's just have the apc which uses knock sensing to open the wastegate.

No. The APC turbos have it for boost control, the 900i with EZK ignition has it for ignition timing control. None of the others have it.