Title says it all. I would like to know if the pistons are too noisy to allow the sensors to pick up knock events in their factory configuration.

Knowing this will help me determine what ECU (factory LH 2.3 and ezk or aftermarket standalone) to use for my 5.0 hybrid.

 

Who said they're not?

 

I use the Bosch (standard S4) knock sensor on two of mine an 85 and 86.5 and installed on two other S3's for future use with tuning.
No issues, just need to adjust sensitivity for standard engine noise per instructions of the monitoring device.

Dave K

 

Hi all... I am way on the downside of a steep learning curve. I have an 86...

Are there NOT knock sensors equipt, as standard? And, if not, if sensors were installed, how and where would they be wired? Are there unused ports on the ECU that would and are ready to receive a signal??? Just asking

 

I was hoping to hear more about this as well.
I will need knock detection in a future tune.

 

Knock sensors came in '87, I think (went from EZF to EZK ignition computers). Sometimes aftermarket knock sensors are added and have their own electronics to either alert you or provide an input to an (also aftermarket) ECU to retard ignition or something, but I suspect in this case you could use the EZK? Or are there other compatibility issues that would prevent that?

 

Well, I ain't adding an ECU!

Thanks Bureau!!! A thing that I happily DO NOT need to know right now, lol... All my learning curves are STEEP,,, and I IS on the downside of many... Can you believe,,,, working on a 2003Jag XKR Portfolio Edition Convertible that decided it needed to go for a swim after a Texas rain storm...?

V12 With a turrible exhaust restriction...

One, maybe two days to really work on them, a week. OMG

Just for the sake of mental health,,, maybe I shouldn't even be looking around on here just now, lol...

Thanks for the info!

 

Same block, similar piston design, adding S4 knock sensors to your S3 block will work fine. Greg has converted some 85/86 engines to S4 (EZK/LH2.3) electronics, Van's stroker is one. There is some harness work and the hall sensor needs to be added for knock-retard. The advantage is that it works, is reasonably straightforward, and there is a good knowledge base here.

There are other ECU choices of course, with their own harness and sensor requirements, and some are also documented here. There are advantages-- sequential injection with individual trim (if you have some way to measure individual-cylinder AFR or EGT), and COP ignition. But at the end of the day I think you would be hard-pressed to find any performance advantage, just more effort and/or money. Remember that Tuomo is running stock EZK/LH2.3 boxes on his turbo-monster, and it is not from lack of funding.

 

no they are noisy pistons. Halfway through the trip you have to slap them around and tell them you will turn around and go home.

 

For what it is worth:

The '85/'86 engines were the last of the 928 engines to ignore the fact that their pistons have offset piston pins, without having equal valve reliefs. This means that one side of the engine's will have 4 pistons "upside down" creating piston slap. This slap is difficult to differentiate from a knock....I certainly can not do it, when attempting to define a knock threshold with an aftermarket injection system.

I don't think it's a coincidence that all "S4" style engines ('87-'95) had this really "dumb" design error corrected by using symmetrical pistons (so the offsets could all be in the "quiet direction"), but was required to allow the use of knock sensors.

As Jim points out, I did convert Van's engine to '87 to '95 injection, to be able to use the much easier tuning and to be able to use knock sensors. However, although Van's engine retains the '85/'86 induction system (to look period correct) it no longer contains "stupid" pistons", but has pistons with corrected offsets. (Rights and lefts.)

Worth noting, I also converted Josh's 2 valve "Euro" engine to "87-'95 style injection, for the same reasons as I converted Van's engine, but it also has "corrected" pistons offsets, with a hall sensor added, so the injection system can differentiate which piston is knocking. (Getting the hall sensor "position" correct, so the preprogrammed Bosch knock sensing system would read correctly required considerable thought, for my dumb mechanic brain.)

 

If anyone needs them for any reason, I do have distributor cap replacements with a sensor boss to give the 85+ cars an alternative cam sync that can be serviced from the front of the engine. I am using a $30 Mercedes sensor with molded connector for a bit more reliable and weather resistant connection.

That will give the 85-86 a cam sync for per/cyl knock detection, but as stated above, its hard to say how functional it will be. I dont have any S3 cars here to do any logging with.

The new Plex Knock Monitor V2 has about the best filtering and analysis software out there in the "consumer" realm. If you can borrow one of those and do some logging, you should be able to see fairly quickly if you can discern the difference between mechanical noise and precombustion with the factory block locations.

https://www.plex-tuning.com/products...knock-monitor/

 

I know of a 928 S4 that someone modified by swapping in S3 pistons. This lead to about 12:1 compression, which I’m sure helped the naturally aspirated car pick up some hp on premium gas. The car was sold once or twice or whatever number of times and then turbocharged without the current owner knowing that the pistons were swapped. Long story short, the EZK detected the resulting knocks as one would expect given the compression ratio and weather. This is just one data point, but it points towards the EZK detecting the knocks equally well with S4 and S3 pistons.

 

I thought as much. Seems like adding a hall sensor to the 2 valve heads is going to be a massive pain as well.

Might be time to think of something else to run my hybrid instead of the good old LH2.3. The L jet is too "dumb" to do accurate fueling for it.

 

Blake, the reality is that any ECU needs some type of cam sensor to know where the engine is in the rotational cycle in order to implement per-cylinder knock sensing. For a 16v engine the distributor runs at cam speed and this would work. But your block is from a 32v, correct?

Jim

 

In addition to the 12:1 turbo motor evidence, I’ve got an opinion on this. The proper piston to wall clearances in 928s are so tight that it’s a naturally very quiet engine no matter whether the pistons are offset or not. This is because it’s an aluminum piston running in an aluminum bore.