spark knock problem
 

I'm lost on this one guys and would be thankful for any advice.

When my 90 is all up to temp I get this spark knock during part throttle. It happens at part throttle with a moderate load like going up hills at less than 40 mph in 4th or 3rd. Sometimes I can even hear it on level ground at the same mph if I'm in 4th and give it small throttle input. I would like to add that this happens regardless the chip I use in the ECM. I have 3: AUAH, AYBK, and Marc's generic mail order piggyback.

I am not getting any DTC's, let alone the ones that signal a knock sensor problem. It has done this as long as I have owned the car. It seems to me the hotter the air temp gets, the worse this knock gets. Above 80* air temp is when, cooler air and it doesn't seem to do it...but I don't know if that is related to anything?

I used to put it down to the odd bad dose of fuel, but I try to stick to the name brands from stations that I know to move volume.

I have a new knock sensor that I was going to put in, but I was thinking what do I do if that doesn't address this issue? I was thinking that I could hook up the scanner and drive around and when the knock happens give a glance to see if it gives me anything to go on? I'm not real sure what to look for, knock events or what? My scanner has a line items "Knock Counts" and "Knock Retard".....is that what I should be looking at? TIA:o

:cheers:
Tom

I just want to state something so that there is no doubt about Marc's piggy-back thing. My car has done this since I bought it, AUAH or AYBK not withstanding. I just got a really bad load of gas last week and it kind of brought this to a head for me. The bad gas is gone and the knock is back to it's normal symptoms which the car had before I bought Marc's "chip" thing. I don't want anyone seeing this and connecting the knock issue to Marc's chip.

Re: spark knock problem
 

Hey Tom, those are exactly what you should look for. When there are knock events, the "Knock Counts" should increment. This should also trigger knock retard, and the timing advance will be decreased.

In addition to the knock sensor on a '90, there is a piece of circuitry that filters the sensor events and turns them into feedback to the ECM. It's on the passenger side of the engine bay, a sort of flat square piece. I can't think of the name of it at the moment.

I believe the car tests the knock sensor by intentionally advancing the timing until knock should happen, then checking to see if it gets feedback.

Re: spark knock problem
 

Tom,

The calibration has modifiers for IAT etc. Those richen or enlean the base fueling depending on environmental conditions. You are hearing it but I"ll bet there's knock prior to the point of it being audible. If its there at tip-in, the Acceleration Enrichment can be both for TPS and MAP deltas. The AE is the pump shot adding fuel and allowing the INT and BLMs to catch-up. It gets decayed out when everything stabilizes. If you have a scantool, can you datalog? I'd want to see what's happening to the BLMs and INT when you go to accelerate or when you go up a modest incline.
Also, pull the plugs and see if there is any indication of detonation. Depending on what plugs look like, you may want to try a colder one.
I'm assuming FP is fine and filter is clear. Is motor stock?

Re: spark knock problem
 

http://i215.photobucket.com/albums/c...wtownCT016.jpg

Thanks Bob for chiming in! In this photo, over by the washer reservoir cap, is that the box you're referencing? I think that is the ESC electronic spark control module...I fairly sure.

Re: spark knock problem
 

I took a little timing out of my Haibeck calibration right around 3800-4500 rpm in the middle Kpa map ranges. I used the tuner pro smoothing function to ramp the values. I left the 2000 and under range completely stock VE and spark etc for emissions testing and catalyst lifespan. I also cut back on AE in that range as well.

It still makes power at full throttle past 5000 rpm, just the 91 octane and 90 deg weather at dead sea level didn't work with the generic tune (not knocking Haibeck at all- pun intended), but nobody can possibly tune for all elevations and fuel blends across the country. The off-the-shelf tune did work well in Phoenix (1100 ft elevation) in 90 deg spring time temps- go figure- I think the LT5 is Kpa/ map sensitive, especially since 92 octane was the norm 20 years ago.

Re: spark knock problem
 

I knew I should have gotten around to learning this stuff sooner! :neutral:

Dom, I will have to go look at the manual for my scan tool and I'll report back. I have no idea because I have never been this deep into it's usage beyond doing a closed loop scan at idle :o.....I know, I know, then why have a scan tool...I'm a bit slow on the uptake because I don't play well with software.:o

The motor is bone stock. I didn't change the plugs this year, but in the past yrs I generally do so every spring in prep for my emissions inspection. I have never seen anything on the plugs. I have a picture chart for reference use, and my plugs are almost like new at every change. I can take pictures of past plugs & post'em....but I swear there is no fouling, no heat discoloration, no metal pitting or/and transfer & no insulator erosion or pitting....although this set in there now will have been in service for about 8 or 9 thousand miles by now and I shall pull them & look. The fuel filter is in service for two yrs now. The pumps tested okay last year, but I'll run a test now to lock that down.

Thank you Gentlemen, Bob and Dom, for help!:thumbsup:

:cheers:
Tom
Forgot this, I use delco 41-602's gapped at .035

Re: spark knock problem
 

could be tip in knock, but i'm not sure

Re: spark knock problem
 

Mike, thank you also for sharing your knowledge!
:o I should say that to be honest, when you and Dom start speaking in "tongues" ( read that as ECM speak! ) I struggle to understand most of what you are saying. I left cars & went to boats in the late 70's just about the time electronic carbs came in so to say that I'm behind the curve is not accurate....it's more like I can't even see the curve from where I'm standing. :redface:

Re: spark knock problem
 

Mike,

R U saying you cut back AE on the <2K range or in the 3800-4500rpm range?
The LT-5 uses a Speed Density system, so I guess it is MAP sensitive. The calibration you had may have been fatter in the higher kPa range since the motor would be operating there more often in Phoenix. Drier air too. Moving to SoCal, the VE could have been a bit lean in the lower VE range.

Re: spark knock problem
 

yeah, I cut back or totally zero'd AE in the range which I believe the CA state inspection system runs their IM-240 equivalent (4 minute dyno test- really it's about a minute nowadays). That's all below 2000 rpm mostly at light loads. This also tends to keep the mixture leaner during light cruise which should help with economy and Cat lifespan.

Then I reduced/smoothed out the timing in the range it pinged and where I believe the load points to be KPa wise. I didn't take a lot out

the only mods I have done since was to go to a 2.5" Corsa from a 3" B&B I traded and it 0-60's ever so slightly quicker, but I haven't re-dyno'ed it or anything. I doubt it would be leaner- but that's really a guess.

I will probably be buying an emulator gizmo soon because I want to datalog or at least hit trace a few maps just to be sure where it really operates in certain modes.