Ok, I have an 88 IROC with a 350 and auto. I also have an Auto Xray and know that I am getting about 20-30* of knock retard at WOT. I dont get knock at idle or when I accelerate really slow. I have already replaced the knock sensor and the ECM. I swapped out the ESC with another one and still have the same condition. Can anyone help me? I need to get this fixed to race again! Please dont just say "Search", because I did and found nothing that would apply to this. Thanks for looking. Thomas

 

I would start by checking your base timing. If you have done any work on the car recently, the distributor may have gotten moved a little. It is easy enough to check...

 

If the timing checks ok, the balancer may have slipped and then later had the timing adjusted to the new, and wrong, setting.

 

I checked the timing after I started to notice the problem and it was at 6* like it should be. I will double check it tomorrow, just to make sure.

How would I go about checking on the balancer?

 

Thats a little more difficult. The hard (and accurate) way is to get the #1 piston at TDC and see where the pointer lines up. That means pulling the #1 plug, and moving the piston to the top. I've found that a zip tie works wonders, at least you'll get pretty close.
Easy way is to look at the balancer itself. Most of the ones that have slipped (but not all) show signs of having moved, like a shiny spot where the 2 pieces meet, or one piece isnt lined up well with the other. I have seen them not lined up to about 1/16" off, but much more than that and I'd say it has moved from where its supposed to be.
I'd also have to guess that if the problem started without changing the base timing, the balancer is probably ok.

Carbon buildup can cause excessive knock too. Some GM top engine cleaner or similar, or misting some water into the intake while its running will clean most if not all of that out of the engine.

 

I double checked the timing today, it is at 6* BTC at idle. I also checked the timing while using the Xray, and it is dead on with the balancer. Any other ideas? I really need to get this fixed. I really dont want to buy another knock sensor. Thanks for the replies.

 

How do your plugs look? Do they have pitting on them?
Do you have EGR and if so are you sure it is operating properly?

 

you are unplugging the ESC wire when you do the timing, right?

 

92 zzz
I just put in new Bosch Platinum 2's about a month ago. The old plugs looked normal.

91L
Yeah, I did. The only time I didnt do that is when I was looking at the timing with the Xray.

Does anyone think that I should use some teflon tape on my sensor? I really dont want to drain my cooling system because I just did a flush and added WaterWetter and some other stuff.

 

I would say that teflon tape is worth a try. I wouldn't lose any sleep over draining the cooling system. If you just flushed it then all you need to do is refill it, right. It sucks though!!

 

did your problems start when you put those bosch plugs in? The more i try fancy plugs, i think the more trouble they are worth. maybe their heat range is off or they are for some reason causing knock. try a set of regular 0.99 autolites and see if it changes. at least, that's what i'd do. have you always had the retard problem?

are you truely getting 20 to 30 (twenty to thirty) degrees, or 2.0 to 3.0 degrees? my 91 L98 runs down the quarter with an average of 2 degrees across the whole run, party due to false knock on the shifts.

 

Yeah, I agree. At least try a cooler heat range to see if the knock gets less extreme. I didn't see, what level of performance does is your engine in roughly, stock, mild mods., heavy mods., race? Basically i am asking what your compression ratio is and what type of cam, heads, induction, if any deviation from the factory is present.

 

The tape doesn't work. I have tried. The knock gets the reading from the finger on it. All the threads do is ground it to the fire wall. Good luck with your findings.

 

91L
I dont know if I had the problem before that. I had changed the plugs before taking it to the track with the Xray. Yes, I am REALLY getting 20* to 30* of knock retard. I will try to get some cheap plugs today, any one that I should get?

92 zzz
My engine is almost stock, as far as I know. I dont know if anything was done internally to it before I bought it. It runs really strong.

88B
Thanks for the advise. I wont try it, then.

 

what were you track times with the xray hooked up? If you are anywhere in the 14's then I'd say it's false knock. 20 degrees of retard should make the motor rather lame.

as for cheap plugs, i'd just get whatever the auto parts store lists as the correct application from autolite or NGK. i woudln't get any specialty plugs. for example, the ac delco rapidfires, only have about 10 different model that is used on a lot of applications.. i don't like fits-alls!

i think before you spend the $ on plugs though i'd try to determine if it's real knock or not. your 1/4 mile ET and MPH will help indicate if you are down on power or not.

did you get the chance to see if the balancer had slipped?

 

91L
The last time I ran at the track, I ran a 14.52 (corrected) @ 93.5 mph. I know my car can do better. I had my trans rebuilt about 8 months ago, and my rear rebuilt with US GEAR 3.73's last April. I am not even close to redline at the end of the 1/4.

 

what was your 60ft? I'm willing to bet money that if you can run a 93.5 in the 1/4, that you aren't getting 20-30 of retard. that much retard would probably put you below 90mph. the auto xray is giving you wrong data or displaying the data incorrectly or something. I run a nearly identical MPH with only 2-3 degrees of retard. I see the guys on here who claim 95-96 on stock L98's, but I don't know what they are doing, they must have ringers, because my 90k-old L98 is tuned up and running fine and is a 93mph uncorrected car.

with 3.73's at ~94mph you theoretically should be going through the traps around 5100rpm in 3rd. What actual RPM's are you turning through the traps? an L98 TPI is weasing for air by 5100rpm and that would hurt your MPH a bit too.

edit: the reason I ask your 60ft time, is I think from the MPH you have the power to get yourself into the 14.3's corrected. I'm guessing your 60ft was around 2.1x. My car (91 L98) will only do 14.8 - 14.9 uncorrected on a 2.1x 60ft. but on the 1.98 60ft is how i got my 14.46 uncorrected.

 

check the carbs

 

Hot
Ummm.....I have TPI, not carbs. Thanks anyway.

91L
Sorry, but the last set of numbers I gave you were a little off. My 1/4 time was 14.66 @ 91.73 (15.23 @ 88.25 uncorrected). My 60' time was 2.123. You made a good guess at that! I have my slip right here with me and the numbers just dont look right. Do you think it has anything to do with my prom?

By the way, thank for your help. Thomas

 

well, your times are certainly a bit off for an L98 I'd think, but i would think (have never tested it!) that 20-30 degrees of retard would hurt you far more.

how was your engine temp on that run? TPI motors seem to be quite heat sensitive, so if you made the run at 220+ then you could expect lower mph than if you made the run at 180.

I don't think any of this has anything to do with your PROM presuming it's an unmodified prom and the check engine light isn't coming on.

does the auto xray report knock counts? if so, how many counts did you get in the 1/4?

other than that, i would go through all the other suggestions on this thread and see if you can find anything. something is definately a bit off. The idea of a slipped balancer has some credability to it: let's say the balancer slipped 15 degrees retarded. so you reset the timing 15 degrees more advanced than it's supposed to be. then going down the 1/4, the computer is constantly sensing knock, pulling 20-25 degrees out to get it to quit knocking (you have to pull more timing out to make knock go away once it's started) and then adding it back in and the loop repeats. however the 25 degrees the computer is reporting, is only about 10 degrees in real life, because the distributor is set 15 advanced because of the slipped balancer. there's no way to (accurately) check this with the xray, you actually have to bring #1 to TDC and look at where the balancer is in orientation to the timing marks.

 

How many miles on the motor? I had a knock issue where I couldnt get rid off the knock (couldnt hear it but the sensor picked it up)even with me lowering the timing to 26*max it still knocked.Then a couple of weeks ago I go to get it dynoed and on the second pull POP six bearings spun and two pistions locked on to the connecting rods.I hope this doesnt happen to you but just a heads up.I had what I thought was false knock for about a year before the engine let go!

 

The first thing I'd do is take the KS out of commission and see if you're gtting any REAL knock. You know, the kind you can hear with your ears. If you're really knocking so bad the ECM's pulling out 20+ then deactivating the KS you should hear "3 rocks in a coffee can" if it's real knock.

How to: Instead of plugging the KS wire into the KS jsut run it to a cheap 3900 Ohm resistor (Radio Shack: $.25) and then from the other side of the resistor to a decent ground wherever is convenient.

You'll have to reset the computer by disconnected the battery cable afterwords. If you don't it'll take about 1/2 hour of driving around under various RPM/load conditions for the ECM to "unlearn" all that knock retard (yes, it keeps track of it jsut like the block learns in the fuel curve.

Once you know if it's real knock or not you will have much better luck diagnosing it.

 

91L
If I remember correctly, my temp was right around 180* or so. I have two manual fan switches and a 185* stat. The Xray does count knock, but for the last few runs I made, I didnt write all that down. If my balancer had slipped, wouldnt I get knock all the time? I am only getting it at WOT when I punch it. If I accelerate slowly, the Xray doesnt read any knock.

E-man
I dont know exactly how many miles are one it. The car itself has 161,000. I bought it in December or '01. I hope I dont blow it, because it is my daily driver. Thats why I am trying to get if figured out.

Damon
Can I just try wiring a switch into the KS line to keep it from reading anything? Willie and myself can not hear any knock, even when the Xray picks it up.

 

Well, I think it is all false knock. I went out and got some race gas (106 octane) and ran my tank dry. Put it in and ran it a bit, then used my Xray to see what was happening. I still got knock, but only about 8 to 10*. I disconnected my knock sensor and didnt get any knock. I am thinking that my sensor is just too sensitive. Any other possibilities? Thanks for all the replies, guys! This is the best board for third gens. Thomas

 

if you REALLY think its false knock you can go to a plumbing or hardware store and get a 1 inch fitting to move it out from the block. I had to do it I also put 6-8 wraps of teflon tape tape(for what it's worth). It helped me a great deal.

 

replace the knock sensor. the SES lamp doesn't always come on when a sensor is bad. it may be functioning but within "good" parameters. those parameters can be rather broad.