strange scanmaster readings... what the?

[stealth908]

(sorry for the long thread, but i need help)
since i got my new chip from eric marshall, the car has run flawlessly with perfect scanmaster readings. from 800-850mv, and no kr. until last week...

i just moved to texas from new mexico, and the car has been sitting for about a month. the elevation drop from nm to tx is about 3000 feet. when i went to pick the car up out of storage, it started up and ran fine. cool.

about a week ago, i was on the freeway, and i was playing around with a crotch rocket. it was hot out (about 100), and the a/c was on. we were doing 100 plus at WOT for about a mile. when my exit came up, i got off, and pulled into the bank. the temp gauge was at about 205 deg. so, i check the scanmaster. it said 736 mv 1.6kr. the line from the boost gauge had popped off, and created a vacuum leak that must have caused the low o2 reading. i figured "easy fix, problem solved".

got some new meats on the gn. i figured i'd test 'em out. the grip very well. i'm happy. until i check the scanmaster again. it was about 95 deg. out. 853mv and 2.8kr. what the f&*%! i figured, false knock at first. then i remembered something. i used to run about 94-95 octane xylene mix. the gas i just put in the car said 93 on the pump. so, i put a whole gallon of xylene in the tank. i should have about 95-96 octane now. once again i figured i was golden.

this morning it was about 70 degrees out. i wanted to see if i had my problem whipped. did a short blast to 55 from a roll. 836mv and 15.5kr!!!! huh? that's impossible right?

at lunch today i was getting on the freeway, and it was about 80 deg. out. blasted up to 75 mph with 850mv, and 0 kr. on the way back 356mv and 0kr. this run was very short. maybe 100 feet? but still, how can that be?

so, i'm wondering. why the erratic numbers? is 15.5 kr even possible? the car seems to run great the whole time. my knock gauge doesn't read any knock. i'm confused. please help. i don't want to tear my car up.

[Nasty Wendy]

I'd think that a retune would be needed for a 3000ft elevation difference. You are probably to lean now. And for the record severe knock can exceed 15.5 degrees. I'd start by adding some fuel pressure but another chip maybe in order. And you can't expect the O2 sensor to give you dead accurate numbers, its really only good to let you if you are lean or rich. Were all of these readings taken during WOT operation?

[ULYCYC]

I gal of Xylene added to a tank full of 93 to make 18 gals is only 94.3 octane. You need to have a fixed octane level of fuel of a given amount to figure out a problem. It can be 93 one day then 95 the next. If your boost level and timing is not going along with this you will have problems and also impossible to figure out what's going on. Start with a fresh tank of 93 or what ever is available. Then adjust you boost until you get zero knock at WOT. If you want to increase boost then add the Xylene and up the boost and adj until no knock. When that tank is empty then lower the boost to match the fuel used. The 02 readings are not accurate so don't rely on it.

[stealth908]

all WOT readings.

just to clarify i added the xylene, then topped off the tank. so like i said between 94-95 octane.

what i don't understand is how the readings for kr can be so erratic under so many differing conditions. like no kr on a hot day/ high octane. then 15.5 kr on a cool day/high octane. then 1.6 kr on a very hot day/ low octane. it just doesn't make sense to me.

one more thing... would being in open loop cause these problems.

i will see about getting my chip re-burned. i don't remember having to give that information when i ordered the chip though. wouldn't the engines sensors make the proper fuel corrections for the elevation changes?

thanks for the input guys.

[ULYCYC]

The timing and boost is set for what octane is given to the chipmaker. You would have to ask him if altitude is a factor in his settings. He will also give a suggested fuel pressure setting. Open loop will not effect WOT results.

[stealth908]

also, i realize that knock retard can go deeper than 15.5. the car runs great though! with a timing retard that high, the car would definately run like ****. so, i guess that's why i'm so confused. if the scanmaster is reading that much kr, i would feel it but i don't. know what i mean?

on the other hand, here's something that i figured out though. lower elevated areas have dense air mass right? more air means more fuel, and more power output potential. this could increase the output of the turbo. well, something i forgot to mention is the increase in boost. now instead of peek boost at 15 psi, i get 18psi!!! i noticed it yesterday, after i fixed the vacuum hose. i'm thinking the low psi was due to the broken vacuum hose. this could cause the 15 psi reading on the boost gauge right? then when i fixed it, the increase in engine output caused an increase in turbo psi. since i put only 93 octane in, it wasn't good enough for 18psi. 93 octane might have still been in the fuel line when i got the 15.5 kr reading. somebody tell me if this sounds right.

please keep the input coming. so far i've learned alot about fuel injection, and turbo chargers. i believe this is the best way to learn anything. hands on.

[ULYCYC]

15.5* is way too much knock. It will damage your engine. Try and lower the boost and see if you can get it to "0". If it don't drop it may be false knock.

[stealth908]

ok, i'll lower the boost until i get 0 kr all the time. thanks

[Steve V]

I bet it's false.Do you have poly motor monuts,is youe engine hitting the right control arm or fram,heater box?Stand on the gas and the brakes and have someone watch to see how far the motor twists to the right. My GN does something similar and my THDP was hitting in those areas,I have the HRparts mount on the left so I am confused

[77tech9]

Bad ground on scanmaster can result in weird stuff happening like that.

[stealth908]

i'm gonna tap into another ground.

i have the motor strap, and the motor doesn't flex very much with that on. the motor mounts are stock. i'll put the car on a lift and check for clearance problems. i can hear something rattling at a certain rpm in park. thanks

[stealth908]

ok, now this is really making me mad. the car started to detonate really bad. like, instant red lights on the knock gauge. i could hear the detonation over my friggin' stereo! so i check the scanmaster, and it doesn't show anything!!! the little decimal light just flashes. this is after a full throttle trip. why the hell is this happening. it comes on and reads the ecm fine. but it just won't record my WOT runs.

what caused the detonation was the hose popping off of the turbo inlet. i noticed this after i couldn't get the thing to quit detonating. what is this hose for??? what's it's function? can i zip-tie the hose onto the fitting to keep it from popping off again. why did it pop off?

[stealth908]

yep, scanmaster is defintely not recording. what's wrong?

[EricStage1]

For Scanmaster to record, TPS must exceed 3.00 volts for at least 1 second.

Eric

[BJM]

I had a tough time with knock one time I was starting to think my motor was hurt. It was a bad tank of gas.