Scottie-GNZ Posted April 20, 2001 Share Posted April 20, 2001 While crawling around under the car tonight, I noticed that where the DP bolts up to the exhaust is touching the bellhousing. Started looking closer and also noticed marks in the framerail next to where the crossover pipe bolts up to the pass side header. Looks like there is enough clearance but if there are marks, it must be rubbing under extreme torque. So, what does all of this mean? False knock! All that metal to metal vibration is probably being picked up by the knock sensor and the chip is retarding the timing to protect the engine. Coincidentally the knock sensor is in the back of the block, about 1.5" from the bellhousing! Seems like the most reasonable explanation for the chip retarding timing when the mixture is rich......Hmmmmm. I could leave it alone and disconnect the sensor to validate my theory......NAH, I am not that brave. Where's my grinder? ------------------ Scottie 71 240GN-Z Scottie's GNZ Quote Link to comment Share on other sites More sharing options...
pparaska Posted April 20, 2001 Share Posted April 20, 2001 Stuff like that makes me hate knock sensors. The "hydraulic adjusters" in my Eclipse get a bit noisy and the knock sensor starts hearing them and pulls a ton of timing out. Sounds like you've found your ticket to teh 10s! As soon as you can get some good CVs in the back . Quote Link to comment Share on other sites More sharing options...
Drax240z Posted April 20, 2001 Share Posted April 20, 2001 Yeah knock sensors are on the borderline for me. A nice safety device to be sure, but not worth the hassle! I had lots of problems with my knock sensor on my celica... PITA. 10's here you go! ------------------ "Nothing is fool proof to a sufficiently talented fool." Richard Lewis - 1972 240z, Powered by a Nissan 2.8L Turbo Inline 6. Drax240's Turbo Site Beginners Turbo FAQ & Answers Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted April 20, 2001 Share Posted April 20, 2001 Scottie; cant wait for the "Going In Party"; going in to the 10's that is. We're all anxiously awaiting to hear your story of confirmation after your next outing at the track; dont keep us in suspense too long. Kevin, Yea,Still an Inliner) Quote Link to comment Share on other sites More sharing options...
240Z Turbo Posted April 21, 2001 Share Posted April 21, 2001 I thought I was hearing something when you were going down the track! It went something like: dink-dink-dink.....ding.ding.ding......dink-dink-dink-ding-dink.....ping-ding-ding! I pulled out my old code breakers book and had it translated. You would be shocked at what it said! It translates into, "get rid of that POS stock GN computer and get a real programmable unit that doesn't screw up every time you hit the track!" Quote Link to comment Share on other sites More sharing options...
blueovalz Posted April 21, 2001 Share Posted April 21, 2001 And all this time I thought you six-ers didn't have a sense of humor. Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted April 21, 2001 Author Share Posted April 21, 2001 Sense of Humor? Terry, that is nervous laughter you are hearing. James, how dare you put POS and GM in the same sentence. You are getting me so ticked off I am thinking about coming up there to the Panhandle and ripping that damn I/C out of your car I guess all those 3700lb hi-10 sec GNs running the POS ECM must have a good tail wind. No need to worry, technology-boy, old Gramps here is going to have his breakthrough soon and what I told you a while back still holds true. "Come with a 10.90 or come prepare for an ass-whuppin" and if you can run quicker than that and beat me, my hat is off to you, after I slit your tires . Beating up on 13-sec Moosestangs dont mean diddly-squat. Only thing that counts is that little sliver of paper that says "10.90" or in your case "11.90". What is taking you so long to put that puppy on the track? I have been through a driveshaft, a CV and a pair of DRs (wait, there is still life in those stickies) waiting for you. Lemme guess, you are waiting for Desktop Dyno to register 500RWHP. I am CALLING YOU OUT to come shut me up. Oh wait, you're the one doing all the woofing The GNZ was, is and will always be a low-budget project (I hear you snickering), but if you continue to tick me I just might have to put a BFH to one of ceramic piggies and spring for a set of heads and a real turbo. Let the WOOFING begin. Yes dear, coming dear. Gotta go folks, time to cut the grass. ------------------ Scottie 71 240GN-Z Scottie's GNZ [This message has been edited by Scottie-GNZ (edited April 21, 2001).] Quote Link to comment Share on other sites More sharing options...
Guest Frank280z Posted April 21, 2001 Share Posted April 21, 2001 Ah Scottie!!! You're too much! lol....The 10s. NICE!!! ------------------ Build it. Drive it. Improve it. http://www.angelfire.com/extreme2/frankzpage/ Quote Link to comment Share on other sites More sharing options...
Drax240z Posted April 21, 2001 Share Posted April 21, 2001 LMAO!!! I predict than when this race finally comes, you both run high 12's. It would just fit. ------------------ "Nothing is fool proof to a sufficiently talented fool." Richard Lewis - 1972 240z, Powered by a Nissan 2.8L Turbo Inline 6. Drax240's Turbo Site Beginners Turbo FAQ & Answers Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 23, 2001 Share Posted April 23, 2001 Or Double red lights... haha... Lone Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 25, 2001 Share Posted April 25, 2001 Scottie- Possible. I'm interested to hear what you find out in your test. I am by no means an expert on the knock sensor feedback interpretation by the ECM, but was under the impression that it was tuned to pick up the higher frequency noise generated by actual detonation in the combustion chamber. i.e. so that not every shake bump and rattle would cause what you are describing. Steve Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted April 26, 2001 Share Posted April 26, 2001 Nah, the knock sensors will pick up all sorts of things - I'm told that gravel hitting the exhaust can even set it off - no kidding! I had a GM knock sensor on the Mustang when I was running a DFI - free revving the motor I could occasionally get it to register valvetrain noise as knock! Needless to say I didn't use the knock sensor much. Banging the pipes on the chassis would certainly set it off - I've little doubt. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 26, 2001 Share Posted April 26, 2001 Scottie, I had the same sort of thing happen with my lt-1. The knock sensor was picking up a metal to metal vibration and retarding the timming when the mixture was rich. It was a pia to find but the grinder did solve the problem. Mark Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted April 26, 2001 Author Share Posted April 26, 2001 Despite being confident that I have eliminated all possible causes of false knock, the problem persists. Took the car for a quick test last night and got the following results: 60' - 1.78 (.23 off my best) 1/8 ET - 7.26 1/8 MPH - 98.85 (new best) 1/4 ET - 11.25 1/4 MPH - 121.62 The ET between the 1/8 and 1/4 was 3.98, also a new best but still the computer is sensing knock and pulling out timing despite being rich. That was not a bad run considering and where the hell is my quick 60' times when I needed it? Coulda, shoulda, but a 1.60 60' would have consoled me some. Back to the drawing boards. Possible defective sensor, FP not putting enough at high RPMs or experimantal chip just not compatible with my setup. I made a couple more passes and gave up. On one pass I had 14.4* of retard on the 1-2 shift (car ran 11.22 @ 119.55) and on another I had tire spin and the 1-2 shift happened at 5600 and I had 19.2* retard (car ran 11.38 @ 119.23). I am only running a total of 24*! Did not think a car could run on only 4.8* much less flat out . I wonder how long it really takes for the engine to recover from that. Only positives were the cars I ran against. A nice S-charged early Mustang Cobra with slicks, the Impala SS I mentioned in another post and a big block Dodge Dart with Hilborn injection and huge slicks. His 11.57 @ 115.66 to my 11.45 @ 119.30 bucking all the way down the track I am having so much fun I could just SH*T, so with that, here is a little humor: http://www.turbobuick.com/bb/Forum13/HTML/011541.html Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 26, 2001 Share Posted April 26, 2001 Yes BLKMGK, don't be so quick to place the blame before the investigation is complete! Effective detonation detection is not only a function of sensor capability, but also of software interpretation. I might be giving the '87 GM software a bit too much credit, or I might not be. I know this is an area of automotive electronics which has progressed substantially within the past several years as engines are tweaked tighter and tighter to get the lowest emissions levels, best fuel economy, and most power. Sensor technology has also improved. I dare to say that most aftermarket FI systems / knock detection systems pale in comparison to the capability of the better OEM systems. No where near as much research has gone into the aftermarket software to make such a system accurate and effective, which often has to be done on an engine-specific basis. Also, be careful not to make a faulty diagnosis. Problems can be intermittent, and sometimes seemingly insignificant changes can affect things like this. Just my 2c. Steve Quote Link to comment Share on other sites More sharing options...
Mike kZ Posted April 27, 2001 Share Posted April 27, 2001 Scottie, I love the one with the bomb squad! Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted April 27, 2001 Share Posted April 27, 2001 lil - most of the aftermarket ECUs that have knock detection USE the OEM GM sensors like the one on Scotties car - I HAD one. Same part numbers and all I'd bet. My MAP sensor was the same too It's a little piezo microphone type deal in a silver can that's screwed into the block. It then had a single wire that ran to a GM black box that interfaced with the ECU. The little black box looking thing was the only part that I BELIEVE changed between 6 and 8cyl cars. Back in '87 the GN and the TPI cars were some of the of th efirst American cars running around with knock sensors. Ford still doesn't really seem to use them and the SVO is the only Mustang I know of to have a knock sensor (I think). Scottie - fire up the datalogging and go tap on the exhaust pipe - does it show anything? Obviously it could be somehting else including knock but if I saw ANY sort of contact on the exhaust system and was having knock sensor issues I'd clearance things ASAP! Scottie, try this - reduce the boost way down and unplug the knock sensor. How does the car perform? Maybe just reduce boost way down and leave the sensor plugged in to see if it still picks up stuff? You're running race gas and not a ton of timing so if the boost is down then anything it picks up has got to be coming from elsewhere, yes? Quote Link to comment Share on other sites More sharing options...
clint78z Posted April 27, 2001 Share Posted April 27, 2001 Yes the knock sensor is just a peizoelectric microphone. Whenever a noise is detected it creates a voltage based on how loud the noise is. On GM vehicles there is an ESC (electronic spark control) module. This is basically a filter for the ECU. It determines whether the voltage from the knock sensor looks like a detonating engine, or it is background noise. The ESC module then gives power to the ECU if it senses knocking. The ESC modules are designed specifically for that engine. I read an article that said detonation actually occurs before it is sensed. The detonation sensor usually cannot detect very minor detontation, but it's better than a poke in the eye. As for aftermarket ECU's with detonation sensors, I do not see how they determine what is normal noise for that engine and what is detonation. Mabey you set the filtering yourself?? Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted April 27, 2001 Share Posted April 27, 2001 Firsty I was wrong about Ford's use of th eknock sensors, they're using them today on at least a few hi-po cars and maybe more. I'm betting OBD-II had something to do with it! The Cobra and Lightning both use them and I'd bet it's a pretty sophisticated system too. As for the ESC module, yup that's what the DFI uses. And no with the older DFI you had NO control over how sensitive it was but I think you might have been able to adjust how much timing it pulled - it's been awhile since I've used the really lousy DFI software (ahem). The newer systems might be more flexible and I'd hope that they're using updated electronics and sensors. Anyway, Scottie is stuck with stock electronics and considering that he's been able to modify the stock programming and do data logging I cannot imagine him wanting to change that. So, what can he do to diagnose this? I think I'd start by clearancing things, sounds like he's done that. Next if it's still occuring I think I'd step backwards on the tune to where it's tame and he can expect no knock, if it's still retarding then I'd suspect the ESC module or more likely the sensor. Since there's a whole ton of programming going on I'd step back to an older more docile PROM too - just in case. Maybe even some electrical interference? Scottie is it possible something in the motor has changed? Oil getting into the intake charge? How do the plugs look, any metallic deposits to indicate knock? Can you datalog fuel pressure? Heh, I'd be tempted to pull the knock sensor's lead and listen to it one time to see if you think it's knocking but after the "fun" you had getting the heads to seal the last time perhaps it's not worth a potential head gasket failure. Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted April 28, 2001 Author Share Posted April 28, 2001 Jim, is'nt time for another trip to FL? We could have a lot of fun chasing this down. I believe I have clearanced everything. I plan to replace the sensor, regardless. If I still get knock, I will detune it by running the chip in street mode but the richest fuel setting. That puts the timing at 18* and puts me in the less timing/more boost mode. I am also going to tee into the vacuum hose at the compressor to add another boost gauge to see the boost differential. My buddy just bought a new gadget and we will test it on my car. It is a digital device that accepts 2 temp probes and an EGT probe. The 2 temp probes will be placed at the turbo outlet and the TB to measure temp differential. The device also has an optional s/w package that can datalog the temps and EGT through the run and replay it on a laptop. Neat. "Great" minds think alike. I am running enough octane, only 21# boost , O2s indicate rich, everything clearanced, therefore it should not be knocking. Only thing we do not know is the inlet temp and whether or not I am losing boost and the compressor is really spinning at 30# Frustrating, but a heck of a learning experience and a lot of seat time. [ April 27, 2001: Message edited by: Scottie-GNZ ] Quote Link to comment Share on other sites More sharing options...
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