ImportsRsloths

Been having a heck of a problem fixing this.... hasnt been right since we replaced the 305 with a 355. The KS is not setting off any knock and the car sets no codes..... As you rev the engine, the timing retards instead of advancing...... IF you disconnect the black and tan wire for setting the timing, the cars idles fine and revs fine (havent tried driving it this way) but it sets off the code for that (i think its 43)

Here is another post with i think the exact same problem!
https://www.thirdgen.org/techbb2/sho...g+is+retarding


I think the computer scanner was showing like .45 of knock????? (im not 100% sure, but it wsa the guy helping me's scanner)

ede

using a 350 knock senser, i think there's a diffeance. you can put a resister in line from the knock senser to reduce knock counts, i forget what size. do a search it's been posted here before. you can put a couple of wraps of tape on it, should of any way to stop leaks, and reduce the sensitivity.

Grim Reaper

The 305 vs 350 knock sensor is important for SD cars. If your car is SD, then do change it. But it's not important on MAF cars.

But, iff you are NOT getting ANY knock counts and NO knock retard indicated, yet your timing is retarding...then it's inside your eprom's spark advance tables. Or, the "knock retard's attack" rate is too sensitive (you can control the knock sensor within the eprom btw).

I just recently met a guy who couldn't understand why his timing was "so erratic". When we pulled his "custom eprom", I showed him how badly written the spark tables. Basically the worst I had ever seen...a monkey tapping on a keyboard could have done a better job.

If you have a MAF car, then I highly doubt your Knock Sensor is the problem and willing to be it is inside the eprom and how the spark advance tables were done.

Find someone with an eprom burner and get them to read your eprom to check out your spark tables. Also, as a "brief test" consider re-using your older eprom. Be extremely careful (as you probably have changed injector size and may be running lean), but see if the "retarding" magically goes away. This isn't necessarily a "conclusive test", but if your older eprom doesn't retard the timing, then you know that is something in the new eprom.

ImportsRsloths

Hey glenn well i gotta give you credit your ALWAYS trying to help me Thanks!! The computer was going crazy and that actually was the problem before..... that is with the STOCK prom in it though...... does the same thing with the ed wright chip to though...... the knock sensor in it right now is actually off of an 85 vette which i just called auto zone and is actually a different part # so that might be the problem right there......

ImportsRsloths

And it runs really rich with the stock LB9 prom as the 305 had 19lb injectors and the 355 has 24 lbers

Grim Reaper

No problem. I would like to see you resolve this problem.

1985 TPI is weird and different from all other versions of MAF (86-89). Are you using an 85 Vette ECM? If not, then you shouldn't be using an 85 Vette's knock sensor. I would expect those to be different.

With MAF cars, the major difference between a 350 vs 305 eprom are the injectors. Unlike SD, MAF eproms don't know the displacement of the engien. Only how much air is flowing and the injector size.

For MAF cars you MUST have the eprom's injector size match the actual injectors you are running. A guy with a 305 MAF can reuse his old eprom as long as he installs the same injectors if he switches to a 350.

If the MAF car, changes the injectors (as most guys do), then you MUST get the injector size changed. With a 305 eprom, the ECM is expecting 19 lbers, so it gives a longer "pulse width" than it would if it knew 24 lbers were installed. Thus, you are running pig rich.

Also, it's been my experience that you "need to play" with the injector constant (especially if you are running higher fuel pressure) and using "new" injectors of a different rating and possibly manufacturer. When I swapped to SVO 24#ers, I found that I had to try "various injector constants" until I found one that ran "reasonably close" to 128 overall (and then I "Fine tuned" my VE Tables from there.

FYI, the injector constant of "24" was too lean and I had to richen mine. You may find that with your setup (once you get all the other problems sorted out), that your Injector Constant could use some "tweaking". It's not uncommon.

Damon

If you are concerned that you are getting false knock signals from the KS you can bypass it easily (if only for diagnostic purposes) by running the KS wire through a 3900 Ohm resistor and then onto ground. The ECM will think the KS is functional but it will never read ank knock- guaranteed. If you do this you must either reset the computer by disconnecting the battery cable OR drive the car around for an hour or so- the ECM remembers under what conditions it hears knock and takes a while to "unlearn" it by driving around, unless you manually reset the computer, which accomplishes the same thing instantly.

ImportsRsloths

Yeah Glenn thats the real reason i bought the Ed wright chip to match the 24lb injecter constant, not really at all for the power even though it should add some............ And im going to put on the new knock sensor tommorow so ill keep you updated on what happens.

breathment

just curious if this is true? i recently replaced my knock sensor after suspecting it giving me false knock readings. and right after i replaced it. im getting WAY less knock retard. but still too much for my likings. running stock base timing and 93 octane..