NXSLT1

This is what I've got....... A lil Weiand 142 roots blower on 96 Trans Am bone stock LT1 with the exception of headers and true duals. I can not get this thing tuned to save my life! I'm only running 5 lbs of boost, i have a 2 bar MAP so I halved the timing tables, meaning 50 kpa is where it goes into boost so I adjusted the timing accordingly. I'm running about 6* below about 3000 rpm and a gradual max of 10* above 3000*. My first question is should this thing run on the stock motor with just 5 lbs and no more timing than that?

Here's the problem.......been working on the setup for 2 years and no matter what I do I get knock as soon as it goes into boost and it will pull every bit of my timing out and it just falls on it's face. It's just like clock work, see boost see knock. Every once in awhile it won't knock but that's very rare. It's has true duals so I can't hear if I'm getting knock or not. I've got WOT AFR set to a rich 10.5 and I've tried going up and down with that.

I'm getting some lean tip in so today I lowered the injector constant from 42lbs to 24 and it seemed to help with that but i still get knock.

I built an intercooler for it and got that installed last weekend. I'm not sure how well it's working because I believe my IAT is getting heat soaked because of the way I have it mounted in the intake manifold so I'm not sure how true the reading is. I'm either going to redo the IAT or get a thermocouple and stick it in the manifold in the airstream to get a good reading. I'm seeing 135* air temps just sitting there idling, that's why I think my IAT is heat soaking, I wouldn't think it should be that high just at idle, could be wrong tho.

I do not claim to be a tuner by any means so I need some major help. I've ran 102 octane in it, still got knock, I've ran 105 octane E85 in it, still got knock, even tried meth injection, still got knock. I don't know if it's real knock or not. I checked my exhaust out today and checked to see if it was banging around and found a couple spots where it was hitting so I fixed that and still get knock. I know roots blowers heat the air up alot more than centrifugals but damn it's only 5lbs. The blower itself gets a lil noisy when it gets warmed up so I've thought about trying to isolate it from the rest of the motor with a rubber gasket just to see if it's causing it but it seems like to me if it was a noisy blower causing it then I'd get knock all the time.

If anybody has any suggestions or wants to walk me thru tuning it then PLEASE feel free to post up. i'm about fed up with messing with this thing!!!!

Guest47904

10* at WOT??????? Way too low. I would expect to see somewhere around 32 to 36*. As far as knock is concerned, why don't you disconnect the KS and put a resistor of 100K ohms on the harness to ground. This will satisfy the PCM and will remove the KS as a possible source of retard.

While you have the KS unhooked, measure the resistance to ground to be sure it's between 93K and 107K. If it's higher, chances are it's not grounded to the block at the threads properly. If it's lower, the KS is shot.

With regard to the tune, why don't you either send your PCM to PCMFORLESS or at least contact them for suggestions. I would not have waited 2 years to take a different approach.

One last thing, I wouldn't run richer than about 12 to 1. Obviously 10 to 1 is a little too fat.

mdacton

He will do a base tune and email it to you if you can upload it yourself.......Probly worth looking into after 2 years

NXSLT1

I didn't mean I've been tuning it for 2 years, I've been working on the whole setup for 2 years. I built the intake manifold myself, actually this is the second design I have on there now, plus I built the CAI, intercooler, fuel rails and everything else that goes with it.

Explain the purpose of the resistor, are you just wanting me to bypass the knock sensor?? Reason why I haven't turned the knock sensor off is because I'm afraid if I'm getting true knock then there goes the pistons. I did zero the knock tables out once just to see how it would run and it ran like a scalded dog but I wanna know for sure I'm not getting false knock. Seems like if it was false then I'd be getting knock all the time or just randomly, this is pretty much like clock work, soon as I see boost I see knock.

I talked to Alvin at pcmforless awhile back and he said he wouldn't touch it thru an email tune, he wanted it there at the shop, Ed Wright said the same thing. I can't do that.

Injuneer

Are you sure it isn't the mechanical noise of the Rootes blower that is causing the knock retard?

Isn't Alvin the one at pcmforless that does the "chipped" cars through 93?

NXSLT1

I've thought about the blower being noisy and causing false knock so I'm gonna try to isolate it from the rest of the motor with a thick rubber gasket. But it seems like if it was a noisy blower then I would get knock all the time instead of just in boost.

I don't know what Alvin tunes but I do know he put a roots on his a few years ago and it ran fine from what I understand. That's why I wanted him to tune it. Wether or not he was stock or lowered the compression or what I don't know. You gotta remember this is a stock 10.5:1 motor plus a roots blower not a centrifugal. Roots blowers heat the air up quite a bit more plus they are full boost soon as you hit the throttle. That's why I'm having such a bad lean tip in issue, roots blowers need a huge pumpshot.

I've even had the timing as low as 5* in WOT and still got knock. I've had the AFR from 10 all the way to 12, no change. Yesterday I did drop the injector constant way down to try to help the lean tip in issue. It would go up to about 17:1 for a second when I gave it any throttle at all. It did help that issue, now it will only go up to about 15.5:1 and the car was more responsive in cruising throttle but now my WOT AFR is at 9 or below and I've taken out all fuel that I can in the PE tables. Only thing I can do is bring the injector constant back up and that will make my lean tip in issue worse again. I need a "pumpshot" setting like the 93's have. I emailed tunercat last night and asked them if it was possible to make a pumpshot table for the 94-95 obd1 cars (I did the obd1 conversion).

I'm wondering if this setup can even run with this much compression but then I read about a guy over on LS1tech that is running 18lbs on a 10:1 motor on pump gas, go figure.

roguedriver

Sounds like you have tunercat. Email me your current .bin file and let me take a look at it. Curious to see how you have it set up. Like stated above, sounds like you have your timing way too low for one. I know your seeing knock, but it doesn't sound like its timing related at this point. Also it's too rich. You should be shooting for around 11.5:1 to 12.0:1 with no meth injection (assuming your not using it at this point). With the .bin, shoot some specifics about your setup like throttle body, if TPS sensor, where is voltage set up at, size injectors, fuel pump, cam etc. Maybe i can throw some suggestions your way.

Ken R.

NXSLT1

What's the address??

WS6T3RROR

What mode is the car running in? sd or maf moder or what, i may have some ideas, but i'd want more specifics on the car before i say anything, its too easy to wax a stock piston if you do the wrong thing.

NXSLT1

It's running in MAF mode with a 2 bar map. Basically all I've done is half the timing tables and take out a bunch of timing from 50 kpa up and then adjust the PE tables. I'm running OBD1 but didn't change out the knock sensor. I was told all you have to do is turn off code 43 and you don't have to change out anything. Also have the LT4 knock module.

As far as mods here they are........roots blower running 5 lbs, 42 lbs injectors, 52 mm TB, pacesetter LTs, true duals dumped, 2 bar MAP, MSD coil, autolite 104 plugs gapped at .045, fuel pressure is around 45 going up to about 52 in WOT.

The car runs very smooth at part throttle, no hiccups or backfires or anything but as soon as it sees boost I get knock no matter what. The only time the knock isn't quite as bad is up in the rpm range, like past 4000.

NXSLT1

Just sent you an email rougedriver.

dookie454

[QUOTE=NXSLT1;5022625]
That's why I'm having such a bad lean tip in issue, roots blowers need a huge pumpshot."

Not sure what to say about your knocking problem but to cure the lean tip in try lowering your injector size even more (quite a bit) - this will increase the actual size of your pump shot since there's no other way to adjust it (increasing it by telling PCM you have smaller injectors). YOu will run richer which can be resolved by running Speed Density and lowering your VE tables.

I had lean tip in bad with my 83lb injectors, during my 2 bar conversion I initially went to 40lb/hr which made it run the same as the 1 bar with 83lb/hr (Still had lean tip in) so I lowered it to 30lb/hr and all lean tip in went away.

It's worth a shot... good luck. I had to lean out the cranking fuel and all other fuel tables (no MAF) it wasnt much work but definately worth the hassle.

NXSLT1

Yeah I tried that already and it did help with the lean tip in but then my WOT AFR was at 9 with all fuel pulled out of the PE table. I wasn't running SD tho. I'm thinking about trying SD tuning this week sometime.

WS6T3RROR

Far as I know knock sensors are not compatible between obd1 and obd2, I soldered a resistor into my pcm when I did the conversion because I had a brand new obd2 style knock sensor in my block. That may be your problem with the knock retard. Or it could just be the sound of the blower messing with the knock sensor. When you say you cut the tables in half what sort of readings would you be seeing if you werent getting knock? ie whats your table look like.

do you have any logs of this thing cruising that you could post?

NXSLT1

If you turn off code 43 then it doesn't matter what knock sensor you have. Yes the two different knock sensors read a different resistance but turning off the code will eliminate that problem. I ran it like that for quite awhile before I put the blower on it and wasn't getting knock. I did have to install the LT4 KM right after the header install because they were causing false knock.

What I mean by halving the timing tables is since I have a 2 bar map that means 50 kpa would be 1 atmosphere or 0 vacuum. Anything above 50 kpa would be boost so starting at 50 on the tables that's where I would start my timing for boost. It's starts out around 4* and goes up to maybe 6 or 8 on the first table then the upper rpm table it goes up to about 12.

Yesterday I had my dad rev the car up while I was under it so I could see if the exhaust was hitting anything and I noticed my driver side motor mount had ALOT of play in it. I don't know if it's banging metal to metal or not but if it is that could be another cause. The car sat for 8 or 10 months while I was building the intake and everything for it, I don't know if the motor mount deteriorated in that time or if it's been like that awhile. I'm still gonna isolate the blower like I said and I'd really like to run the duals on out the back of the car and quieten it down so maybe I can hear knock if it's actually happening but nobody around here will attempt to run it over the axle. Wish I had a bender!

I can send you the tune file if you have tunercat and also a log file if you want.