Tach flutter and knock simultaneously?

[bjzq8]

New to the forum...new to SyTy's too.

Just got my 1992 Ty last week...75K miles.

Previous owner says that every "consumable" ignition component (plugs, wires, cap, rotor, etc) has been replaced very recently. It has ATR plug wires, and AC plugs. It also has an ATR Pitbull chip. Stock everything else...stock boost, and somewhere in the neighborhood of 15psi of boost on the stock guage (inaccurate, I know...)

Acceleration from a dead-stop is beautiful. But in a 50-mph roll on from relatively low rpm, I get several seconds of audible knock, accompanied by the tach jumping. The tach doesn't always do this, just on occasion. Now, I have a bit of background as a GM tech, and this is what I make of it...the TACH signal is basically just a signal put out whenever the pickup coil gets a spike. So these tach jumpings would make me think that either the ignition module or pickup coil is bad. I suppose you might throw in bad grounds or a loose connection. But it only seems to do this under heavy acceleration, and is always accompanied by knock.

The vehicle runs great every other time. It has an admirable idle for what it is, and goes like stink, like it should. I seem to have a rather long spool-up time from a non-boosted launch, like maybe .5-.75 seconds. Anything I should worry about?

Sorry for the long first post, but I thought I'd throw a bit of everything in here. I've searched the archives and have come up with ignition wires, ignition wires, ignition wires. But I'm reluctant to replace some brand new ones...unless that's really the problem. Everybody else seems to have idle tach bounces...mine is fine at idle. By the way, my background is Fieros, specifically V-8 Fieros (www.v8archie.com). Which are bears to work on, as you can imagine. So I'm in vehicular valhalla with my Typhoon! Might be difficult, but certainly not a hothead Fiero! Thanks for all of the advice!

Bill Jenkins
1992 Typhoon #1752

 

[Hu Ryde]

Bill, welcome aboard. What all do you know about your truck? Previous owner said recent tune up but is it really? Is it the right stuff? Some caps act funny on certain truck and such. Red Conrads work best in my truck and many others. What kind of plugs? These things are picky with plugs NGK UR5 or UR6 is the best in my books. What about your chip? Stock or another? Do you have any sort of scan tools? Datamaster. Diacom, etc... THese programs give details of what's going on in the motor. You said an audible Knock, that's bad in any situation. Is it motor knock or maybe a motor mount, they are know for going out, what about a backfire, could it be that? What's base timing? Fp? Give us details and we will try our best to tell you what's wrong with your truck without even looking at it. Where are you located? If you dont have a scantool someone near might be willing to help. Good luck and have fun with it.

 

[Daron]

Regardless of what the previous owner told you, I would go thru the ignition and do it so you know it is "right" by using the suggested components. I would also change the fuel filter, oil and any other fluid you can find, as well as conducting a vacuum line witch hunt.
Tach flutter is almost certainly ignition related. I only know of one person that had a jumpy tach and couldnt resolve it with ignition parts ( barring the folks with the SMC alky kit).

 

[Loeryder]

Congrats on your Ty!

Tach dancing is ignition related.
Wires, Cap n Rotor, plugs are all in order here.

Next thing, if you HEAR AUDIBLE knock, get out of it quick.
Don't keep pressing the pedal to see if it goes away, or your motor will be fubar in no time.

Best thing you can do is start learning everythig it takes to keep these trucks running their best.
The SyTy FAQ goes into good detail on the common things.

 

[Rick Krupa]

I would suggest getting a piston stop and checking TDC and then timing for your knock problem. You'll never know what the previous owner did so you should start from scratch instead of guessing.

 

[bjzq8]

Thanks for all of the reply's.

First off...

It does have an ATR Pitbull chip in it. It does not look like the IC pump is doing anything, although the fuse isn't blown. Should I be able to tell that the pump is doing something? Obviously if the IC pump is dead, those higher manifold temps aren't going to help.

I have been over every vacuum line on the thing, and none look broken, cracked, or frayed. I haven't done the carb-cleaner test yet. No inordinant whistling. That doesn't mean that there isn't one, but I'll look.

It is definately chattery detonation, and not a motor mount or anything. It's really the loudest I've ever heard in any vehicle (my Fiero exhaust is loud, and it's behind me anyway.) In any case, I hear just a couple of pings and immediately get out of it. It only happens when I snap the throttle open from 1500 rpm or so, and it makes the 4-2 downshift.

I will go back over the ignition system with a fine-tooth comb. I will try swapping out the plug wires, too. If that doesn't work, I'll swap the ignition module. Thanks for all of the help!

Bill Jenkins
92 Typhoon #1752

 

[bjzq8]

Just thought I'd add a few more details...

Pulled the cover off of the IC pump fuse...sure enough, blown. I'm not going to bother seeing if the pump is "really" bad enough, because otherwise it wouldn't have blown a fuse. I'm ordering a Jabsco pump. So I can only surmise that the lack of intercooling, coupled with the stock metal lines to the intercooler, would make it a bit more prone to detonation? Scan tool (laptop based) is on its way too! Thanks for all of the help!

Bill Jenkins
1992 Ty #1752

 

[V6 Kompressor]

Welcome, and are you related to this guy from Malvern, PA?? You know the one that more or less builds Small blocks for max power?

 

[bjzq8]

Bill Jenkins...

Bill Jenkins...

Nope...no relation to Bill "Grumpy" Jenkins. I like to think that everybody asks him the same thing about me..."are you any relation to that guy in Illinois?"


Truck is running great now. I still get a decent amount of audible knock if I hammer it from low rpms on the street, but I've learned to feather the throttle a bit...I have yet to get my cable for my Datamaster to find out exactly how much knock retard I'm getting.

With the onset of cold weather, I've noticed that my truck is a LOT stronger and more knock resistant! Some kids in an IROC passed me the other day, and I hammered it after he passed me. Flew up to his bumper and stayed there (I had to let off) up to about 100 mph, after which I let off. Point made, I think!

 

[Mad Mike]

I just had the same problem which was well documented on another thread. I changed everything iginition wise, checked timing, vaccum leaks, and fuel suystem etc. I had horrible audible knock back by documented diacom data. Found out my problem was the harness which runs from the coil to the back of the distributor. The wires are pink and white and have a connector on either end. They are cheap and definately a problem area and IGINITION RELATED. Try it and keep us posted.