I was having a problem with excessive knock retard even at idle (as much as 9 degrees at idle) and after trouble shooting and not finding any problems, decided I would try to bypass the ks alltogether by using an 3900 ohm resister run to a ground. The scanmaster is showing 0.0 knock retard now but I've noticed the blms registering 99 on the right and 108 on the left. The numbers go up with throttle but return to the low numbers when gas isn't being applied. I did have a lean condition that caused the scanmaster to register 160 so can I assume this is a rich condition? If so, what can cause this? Is it safe to drive the car? Thanks for any help you guys can provide.

 

What year car do you have?!? OBDI cars can't go any lower than 108 on the BLM.

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95 Z28 - 524hp Supercharged 383

 

I'm sure you know this but, just incase; blm's blow 128 indicate on the rich side and above 128 are on the lean side. And the previous post is correct! blm's can not get bleow 108 or above 160 on obd1 cars.

 

It is an obd1 car (94) and the problem has only occurred since bypassing the knock sensor. What happens when the blms go below 108?

 

Your car abruptly stops then explodes No seriously id like to see what another scanning software says like datamaster, because like everyone elses said 108/160 should be the limit.

Even LJ says the same thing:
http://para.noid.org/~lj/PCM%20Tutorial/PCMtutorial.htm

I wounder if its just something screwy with scanmaster...


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Ken Mook - 97' SS #2544
Advanced Tech Posting Guidelines

New Project Underway :0

 

108/160 is the default limit, but it can be changed with TunerCat. Maybe someone has reprogrammed your car before and changed the limits?

I did that with mine (80/200) when I was trying to figure out some injector problems...

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Solomon
What's life all about?
Silver '95 Camaro Z28 M6: 14.3 @ 98.7 - With problems, but will improve!
White '90 Cadillac deVille: 16.3 @ 81.4 - Not likely to change soon.
Learn the basics of tuning your OBDI LT1 PCM!

 

If you exceed the 108 or 160 value the ECM can't compensate for an overly rich/lean condition and the engine will, in fact, be running too rich or too lean.

Worked on a modified 87 T/A that was supposed to have 32# injectors installed but, in actual fact, only had 24# (we found out later). ALL block learns were PEGGED at 160! Yikes!

Something odd about this. I've seen the BLMs change SOMEWHAT from getting rid of high levels of false knock but this is a very large change. Did you make ANY other changes besides the KS bypass?

 

yes! below 108 would be very rich, and above 160 would be very lean. get the blm's at 128 and work from there.

 

The programming was done by Ed Wright. Even though I haven't seen it go back down below 100 since last week, mainly because I haven't driven the car much, I did notice it drop down to 107 tonight. Could bad spark plugs or plug wires cause an overly rich condition?

 

If Ed played with your BLM boundaries (as it appears he did) then a reading below 108 is possible. Obviously this means you are extremely rich, and either:
1. His tune is way off
2. Mechanical problem

There are tons of possible mechanical problems that could lead to a rich condition. Need more info.

Some include:
Leaky fuel injector(s)
Too cold of a spark plug
Too wide of a plug gap (misfire)
Bad opti
Bad coil
Bad ignition control module
Bad plug/coil wire(s)
Insufficient spark voltage (bad battery/alternator/aftermarket ignition box)
Incorrect fuel pressure
Loose vaccum hose to fuel pressure regulator
Incorrectly sized fuel injectors

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95 Z28 - 524hp Supercharged 383

 

Thanks alot for the replies. I'll investigate some of these possibilities starting with the spark plug wires.