A couple of new questions about SD /MAP sensors.

One as I will be using my vans stock OBDI TBI PCM modified to MPFI TPI: will the knock sensor work? I read somewhere a TPI knock sensor is different to a TBI version.

Rich

 

What year? The ESC function on later modes was integrated into the ECM. Further, the KS variations normally relate to the engine installed, and not necessarily the fuel management system. For example, the smaller bore 305s needed a more sensitive KS to detect detonation, whereas a 4" bore engine (350) needed a less sensitive sensor to achieve the proper signal level.

 

Knock sensors are by frequency range - which is dictated by bore size. Not fuel injection type.

GD

 

So a knock sensor for a 350 will be the same for a .030 over bore?

Thanks.

Rich

 

That OEM 350 sensor will be as close as you will find to ideal.

 

Thanks guys...

Rich

 

If you go to a stand-alone ECM, you can wire in a wideband knock sensor and then tune for the frequency best suited to the engine.

GD

 

So far my research has shown the factory PCMs are stronger and break less. And as I can buy them all day long at around $20.00 to $40.00 they seem a great deal.

Also with OBDI PCMs it is much easier to tune, and much less involved with the rest of the car/truck.

OMG A friend has a let model Dodge truck and he got check engine light for a burned out tail light. Any one can say NannyPCM??

Rich

 

The few tuners I talked to and the tuner that wrote my initial start tune advised me to eliminate the knock sensors on a holley Efi. I'm na so that may play into that.

 

Interesting but seems like a bad idea, the whole point is for the PCM to advance timing just before real knocking, thus giving the most power depending on how good the fuel is. The knock sensor can save your engine from self destruction.

So I plan on having one.

Rich

 

Knock sensor is a good idea but an excellent tuner can do without. The Holley ECM's are junk for reliability I agree there, but there are other's that don't have those problems. I tune and sell LINK, which has a lifetime warranty (which I have yet to need). Holley is like 90 days - after that you're just SOL. Factory ECM's aren't without their problems - I've encountered plenty of failures and they are OLD. Old circuit boards crack, solder joints fail, capacitors leak, etc. And they have a lot of smog related features and "open source" tuning that's not always well documented and usually of questionable utility for hot rodding.

The reality is that a well built 350 running NA in a van could suffer inaudible detonation all day long and never be hurt by it. The engine design was from a time before really excellent fuels, and before detonation could be easily avoided. Most of the carbed SBC's out there are tuned by ear by twisting the distributor till you can't *hear* the pinging, or till your ET's drop and then go back to the previous setting..... there is absolutely inaudible detonation likely occurring at some points in these engine's lives but it has no measurable effect.

More modern engines will have their pistons, cylinder liners, or rod bearings destroyed by even mild inaudible detonation. For the 1950's designed SBC it's really for emissions, economy, and best performance. The likelihood of detonation-caused mechanical damage is nill.

GD

 

OK I am interested..can you email me a phone number so we can talk??

I am at racprops@***.net

Rich

 

I questioned it for sure. Knock sensors can be tuned. But where do you start? Is the frequency different in different blocks? Dart vs standard sbc block? Factory bore walls vs bored walls? Different one wires have different frequencys. It can get really really in depth.On the Holley forums one of the moderators had the most in depth knock sensor tuning I have come across anywhere.

https://forums.holley.com/showthread...ors-Holley-EFI

But I have to listen to the experts who actually tune these. More often than not they eliminate them because alot of false knock. In my case I did.

 

Thanks, I will read that.

Rich

 

False knock does come up sometimes - many high performance engines are very noisy inherently due to forged pistons, solid lifter valve trains, rigid engine mounts, and fabricated exhaust headers...... sometimes it's just impossible to get anything useful from the knock sensor This is especially true of cars that come in for tuning that were not built by a professional shop - often these are home built and the customer has no real knowledge of tuning or what's important for it to go smoothly. They don't think anything of an exhaust that's touching the frame somewhere, or those clapped out motor mounts that aren't insulating the engine from the cradle, etc. And a lot of factory ECM's as well as *most* tune's that experienced tuners generate ignore the sensor above some threshold RPM just due to the signal being ridiculously noisy. (knock sensors are really just microphones tuned to listen at a specific frequency). It's also time consuming to setup knock control, and is an additional charge.... one of the "ala carte" options like launch control, nitrous, etc. On the dyno it's pretty easy with a SBC to advance the timing till you can see the power drop (detonation or fell off the back of the power curve) and then pull it back a few degrees for safety. Proving noise or false knock sometimes involves a tank of C16, etc - something with so much octane that you'll fall way off the back of the HP curve before you ever get into detonation.

Essentially the tuning strategy is to use the factory narrow frequency knock sensor that best matches your bore size, tell the aftermarket ECM what frequency to listen for, and then you essentially have to do dyno pulls at a "safe" timing level while doing datalogs of the knock sensor voltage. This gives you some basic information about the voltage thresholds vs. load vs. RPM and you can setup your knock sensor gains and your retard map usually about 15-25% above these "background noise" thresholds. Then you advance the timing till you start to see what rpm and load conditions generate detonation activity so you can test it..... there's other helpful tools like det cans, and just seeing the dyno numbers, and having someone watch the tailpipe for black puffs during your pull. Detonation smells just like gun powder and gives a black puff from the exhaust that's pretty obvious to the trained observer. It can easily take several hours to get a good baseline knock strategy going and the best way to go about this is really to have a professional do it on a dyno then get familiar with datalogs and do some adjustment as you drive and see what it wants under various conditions.

There are also ways to use newer LS "flat response" knock sensors that will hear across a huge range of frequencies. Here's the NPT adapter I'm using with my Vortec on LINK:

https://www.eficonnection.com/home/p...e-knock-sensor

GD