pinging sound in engine of 1991 740

tuvmeister · Post by **tuvmeister** » 25 Jul 2004, 01:40

hey everyone,
lately ive been hearing pinging sounds from my engine. ive looked on the web and it seems that this problem is usually associated with low oil. But I had my oil changed at one of those EZ Lube places less than a month ago! why is my engine making this scary noise? please help!

ozzimark · Post by **ozzimark** » 25 Jul 2004, 08:45

like when you turn off the engine after running for a while, and it sounds like oil dripping into a metal pan?

tuvmeister · Post by **tuvmeister** » 25 Jul 2004, 11:54

no, actually i hear the sound when the car is running, usually when i'm sitting at a red light in Drive and the rpm intermittently increases ever so slightly. it sounds kind of like rocks or some other small object being thrown around in the engine, like a rattling sound.

potroast · Post by **potroast** » 25 Jul 2004, 12:11

that's premature detonation. It occurs when there is combustion in a cylindar before there is a spark from the plug. this is *very* bad.

Are you turbo? what plugs are you running? What brand and octane gas are you running?

If you're running a low-octane fuel, try running something higher. for example, 93 octane may solve the problem because it resists detonation better than 87.

If you are turbo, you *must* use at least 91.

Again, premature detonation is very bad.

tuvmeister · Post by **tuvmeister** » 25 Jul 2004, 14:25

hi, thanks for the reply. i don't have a turbo, just regular 740, and i do use lowest-grade fuel (u know in southern california gas prices are crazy), but if you think using a higher octane gasoline will solve the problem, then i guess i'll try that. btw this has been going on for a while; are there any long term effects that may occur? and is there anything else i should do to make sure my car won't die on me?

potroast · Post by **potroast** » 25 Jul 2004, 14:33

if the premature detonation continues, then you're looking at a bent rod and some other expensive engine work.

I live in socal, and it's been getting very hot lately. On my supercharged truck, I've had to run a new fuel map to prevent ping. When it's hot out, you can't make as much power safely.

I know prices are expensive, but try running 91 (since that's all we get easily in socal) for a full tank to see if it helps.

Does it only ping at WOT? Does it always? Are you throwing a code? (Read codes in bank A2)

Temperature is the #1 cause, but it can be other things, too. Also, how's the engine temp look? Are you raising above 1/2 way at all? (even a smidge above isn't great)

Volvord · Post by **Volvord** » 25 Jul 2004, 19:21

First of all don't panic. It is almost impossible for an engine to detonate when idling at a stop light, detonation occurures under power conditions when accellerating.

I would suspect either a valve adjustment, where there is too much clearence between the camshaft and the valve buckets, this is a regular maintenance item and should be checked every year or two.

The second thing it could be is the700 series uses hydaulic motor mounts, when these fail it allows the engine to sit lower, often with the oil pan sitting on the crossmember, you will hear lots of loud noises if this happens. This situation can also cause the engine cooling fan to contact the radiator shroud which will make a buzzing or rattling noise.

The third possible problem could be an exhaust leak, either at the manifold or the exhust flang, this will cause an noise that clould be mistaken as detonation.

Guest · Post by **Guest** » 26 Aug 2004, 15:03

interesting. ver few on this board seem to have any mechanical knowlege. in fact Volvord 784VC seems to be the only one.

oh, another possiblity could be low oil or spun bearing.
just because jiffy or ez lube changed the oil, doesnt mean you have to put your engines life in their hands. always check the oil after you leave their shop so make sure nothing is leaking and that they didnt forget to actually add the oil. it happens.

ryann · Post by **ryann** » 29 Nov 2004, 15:15

another possibility: the engine in your car is a B230f, which is notorious for piston slap. as the piston reaches the top of it's stroke in the cylinder, there is enough freeplay between the two that the piston rocks sideways a bit, making a "clocking" sound. this sound is particularly audible at lower RPM's such as idle. i have seen a piston in an older B230f with the head removed be wiggled back and forth by a mechanic's hand, and I also have a B230f equipped '86 240 wagon that has been making this noise for the last 50,000 miles with no ill side effects other than sounding like impending doom. the dealership might tell you that your engine needs a rebuild, or that your pistons need new wrist pins, but I'd drive it until it dies (which could be at 250k miles!)