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740 Spark Knock? b230ft with BPR7ES

HarryK

New member
Joined
Jun 14, 2016
Location
Asheville, NC
Hi all,

I'm having an issue with a knocking sound under acceleration/any throttle input. Pretty quiet at idle.

The motor is a stock 1994 B230TF from a 940 turbo. I had a saga with shorted melted plug wires (thanks for making them too long IPD) and then different connection types when I replaced plugs and wires ect. Now all is sorted with BPR7ES and a plain set of Duralast wires. Plugs were gapped at .030 in and are now gapped to .032 in, with no change. The motor has been healthy in the past, so I doubt its mechanical knocking especially considering that I've had all these issues with the plugs and wires lol. The plugs are torqued to 18 ft lbs. The wire from the coil to the distributor is the IPD blue wire still, just haven't changed it. The distributor rotor and cap are new too.

I took it to a specialty shop a while back and they told me the timing was off - not sure if they advanced or retarded it. I don't trust what they did because they didn't even notice the plug wire that was melted and causing a misfire... whatever.

What is y'alls take on the knocking sound? Should I change to a regular copper plug or a BPR6ES or just triple check all of the plugs? Does it seem like the timing could be an issue? I'm about to list the car for sale so I don't want it sounding like its about to blow lol.

Thanks
 
Since you are using a one step colder plug. My take is that you are having spark blowout under boost. Your engine doesn't need colder plugs. Get the stock BPR6ES in there and gap to .028".

Make sure to use premium gas as these engine are optimized for 91 octane.
 
Sounds like pre-detonation to me(pinging), spark blowout is more like a collapsed turbo intake tube. You lose all power when it happens.. Sumptin aint' right, but I would say it ain't the spark plugs.. I ran 8es NGKS and about .022 gap and 20 pounds of boost from a 15g otherwise I had spark blow out. Two numbers colder and tighter on the gap to eliminate the blow out with all dat boost and tiny turbo. So maybe the shop is right saying your timing is off. But not sure why it would be, you can't adjust it with lh2.4 unless you mess with the ignition map..
 
If the knocking only occurs under acceleration, that is almost certainly detonation. What is the octane rating of the fuel that you are using. The recommended R+M/2 value in the owners manual for my 1987 B230 FT was 87 (or about 91 RON). I ran for several years just fine on 87; but, after about 10 years it developed mild detonation on acceleration. Switching to a mid grade 89 (R+M/2) eliminated the problem or at least reduced the detonation to a level that was no longer audible. There could have been a deterioration in fuel quality or the engine may have been suffering from a gradual deposit build up that makes it more prone to detonation.

If the timing is off, that could be contributing to the problem because you have reduced the range that the ECU has available to pull timing when it detects detonation. Check the timing with a strobe and if required set base timing as described in the service manual.

Check your knock sensor. I think EZK / Regina have a 'completely dead' DTC; but, I don't think the Motronic / LH systems have a DTC for the knock sensor. You could have a failed knock sensor or a knock sensor that is going deaf.

Have you fiddled with boost pressures? That would be a big contributor to increased detonation problems. Check your boost pressures to make sure they are in spec.

Confirm that your ignition timing is correct. If the timing is correct then try running a higher octane fuel. If you are currently running 91 R+M/2 and the problem persists and the engine is in stock tune, then check your boost pressures. If all that stuff is OK you may have a carbon build up issue. The build up can raise the combustion pressures enough to generate detonation. If you do a compression test and the test numbers on a 28 year old engine are the same as or higher than spec, you probably have a combustion chamber build up problem.
 
Thanks for the replies.

I figured out the real issue - one of the Duralast wires has a messed up connector that won't open up enough to fit over the actual spark plug end. It sits a few mm farther out from the block as compared with the other three plug wire ends. Luckily I had a spare Bougicord wire that I was able to plug in.
I did change the plugs to the 6ES with a .028 gap and the power is definitely a lot better.
The turbo intake hose is new and really solid.

The engine is still kinda noisy but it sounds like it did before this spark plug wire mess.
 
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