K87ZZ4

I have had a knock/pinging problem ever since I dropped in a ZZ4 crate motor in my 87 (stock TPI). I replaced the knock sensor and crossed my fingers. It seems to be a bit better... not much knocking anymore, but still some pinging, especially at shift points under strong throttle while climbing a hill.

I tried backing off the timing, but when I got it back far enough to reduce most of the pinging (not all), it hesitates on hard acceleration :(

I would really like to solve this problem so that I can get everything out of the ZZ4 that it can give! Has anyone else had timing problems with a ZZ3 or ZZ4 application with stock TPI?

So, now I'm just trying to think of other parts of the ignition system that could be part of the problem... distributor (came new with the ZZ4), wires or plugs? I'm stretching here... but what about fuel delivery? Fuel pressure?

Any help would be appreciated since I'm uncomfortable pushing this engine too hard if it's creating detonation problems.

Corvette0096

You know the ZZ4 is 10-1 compression? That means you have to run 92 or better. What size of injectors are you running? Fuel pressure? timing? Here is what I have with no pinging. New chip,Svo 24's. Afpr Set at 45psi timing at 8 degrees. Did you change your harmonic balance? My old one was shot and the timing marks where way off.......

Corvette0096

The more i think about this i bet you are running stock injectors. I think they are 19's That will cause the pinging there.

K87ZZ4

I run 92 octane fuel. The first thing I tried, a long time ago, was some octane boost to see if that made any difference... it didn't. I'm running stock injectors from the 87 L98. I haven't measured fuel pressure, but have stock fuel pumps. Timing is set to what it was "as delivered", which, according to spec, is 10 degrees BTDC (there are no visible timing marks between 10 and 0). I did not change the harmonic balancer... so it has the one that was on the ZZ4, out of the crate.

So, did you run your ZZ4 ever with stock TPI? Or did you do all the mods when you put the engine in?

nsimmons

10 is too high back it down to 6 or in your case half way, can you hear audible knocking?

Run about a 70% 92 octane 30% xyelene (get it at home depot) mixture, this will raise the octane to 99.8 see if that eliminates the knocking. Octane boost is useless unless you use 20 bottles. I did this to track down my knocking problem and decide on an octane and timing to use.


[Modified by nsimmons, 10:22 PM 5/15/2002]

Aggravated4life

Im suprised that the ZZ4 balancer even fit the C4 chassis.I was told you have to install the stock C4 damper for chassis clearance.You had no problems or did you notch the frame a bit?
Maybe I heard wrong and it doesnt need to be changed.

Also,is your EGR hooked up and working?
10º seems too high for the stock programming,go down to 6-8º.

Also do you have a scanner?
We can take it from there.
:)

Corvette0096

I bet you have to go with bigger injectors.....And yah how did you get that balancer to fit????

K87ZZ4

It's true that the ZZ4 balancer did not fit the C4 chassis... but, instead of notching the frame, the shop mechanic installed shims at the motor mounts to raise the engine higher--we decided that was a better option than possibly throwing the balance off.

I can hear an audible pinging... I could hear the knocking before I changed the knock (EST) sensor. And I hadn't even heard of using a xylene mix... sounds interesting; any drawbacks?

The EGR is hooked up, and working. I tried plugging it, but that also didn't seem to affect the pinging, and it would set a code on long highway drives. So, I hooked it back up.

So, you're suggesting that 10º is too much timing for the stock ECM to handle, regardless of that being the timing called for on the ZZ4? The problem I experienced with running at 6º (or thereabouts) was a hesitation on hard acceleration, espeically after hitting a hard corner.

I don't yet have a scanner... but I'm thinking I'm going to need one to figure this out... so I just might be shopping for one very soon.

John Row

Xylene will raise your octane rating, but it will also reduce your peak power. Xylene doesn't have the same energy as gasoline, so you are basically diluting your fuel.

gtsyellow

sounds like your in need of some prom work and either more fuel psi or bigger injectors. if you have 19's i'd definatly pick up some ford 24's at stock psi they might work pretty well. and or spend $60 on a pressure regulator and spend a little time finding out what psi works for you. also you might post in the ecu prom tuning section and see what the guys can do for you chip wise. ed wright also does a ton of these, 6-8deg timing should be about perfect, 10 is a bit much on 92. you'd be amaized what you could get performance wise with some prom work and injectors that work if yours are going short...also you did't use the stock tpi did you? please tell me you at least bought a bigger base or heavly ported yours.

K87ZZ4

Sorry to have to disappoint you, but I did use the stock TPI, without modification :bb (at the time, I was interested in getting the car back on the road, having just spun a rod bearing in the L98, and was under the impression that the stock setup would not be a problem).

Unfortunately, I must amend my comments about the knocking :( I just went out for lunch and got a little into it and ran into a VERY loud knock... the kind that makes me think I'm doing some damage. I was in first gear, probably at 1/2 to 3/4 throttle (definitely not at WOT), in the neighborhood of 2,500-3,000 RPM, going uphill over a freeway overpass (not terribly steep) and it knocked badly. The car was kind of cold (coolant temp about 140º), which normally keeps it from pinging as bad.

Can someone help me understand how the EST (spark timing/knock sensor) system is supposed to work? Is the EST system routinely detecting knock and retarding timing? Or, is it only really functioning when you are getting into it really hard and under a heavy load (such as pulling a hill)? I confess I expect the EST to kick in and retard timing only in unusual circumstances and that the ECM program handles normal operation and sets timing so that it doesn't ping or knock. So, if I'm wrong about that, then the EST system could still be part of the problem.

Then again, it sounds as if the stock TPI and ECM program is just a mismatch for the ZZ4 and I should look into bigger injectors, more fuel pressure, and buying a chip or doing some PROM work. The only part that's confusing is that it seems some people have put a ZZ3 or ZZ4 in, with a stock TPI, and not experienced the timing problems that I am. I just want to make sure I'm not solving the wrong problem, of course.

jmr302

What sort of cam does the ZZ4 come with? We'll need the duration@.050, the max lift specs, and lobe separation angle.

I think the stock fuel injectors are fine with this combination unless the cam has too much duration. Especially considering the stock plenum, runners, and base. You could really unlock some performance by replacing these parts with an aftermarket combination like the Super Ram but running them now is not going to cause massive pinging problems. Something else is going on here.

If you've got a laptop you can buy a cable from akmcables for $90 or rent a Diacom setup from TPIS for $50. There are other options if you don't have a laptop but I'm not familiar with them.

nsimmons

a stock tpi is fine for a zz4, my friend had a zz4 in his stock crossfire and it ran fine, just down on power

Corvette0096

You really need to pull a plug..

K87ZZ4

I may have a laptop I can use.

The specs I found for the ZZ4 are:
Intake: 208º @ .050; .475" lift
Exhaust: 221º @ .050; .510" lift

I will see what a plug or two looks like this weekend.

Hmmm... if a ZZ4 is running OK under a stock Throttle-body injection setup (which I assume is what Nick's friend is running), I would expect a stock Tuned Port Injection setup to be an even better fit, eh? At the very least, it tells me that this should be working OK and that it's not just a mismatch of the ignition/fuel delivery system and the long block.

mash557

What kind of exhaust is on the car? Are all the converters intact and original? If so they could be restricting exhaust flow enough that it is diluting the charge and causing the pinging. Of course if you have no converters then all this is out the window. Good Luck.

BBA

Basically, it allows the ECM to control engine timing until it senses a knock event, at which point it will override the ECM pulses to the distributor and retard timing by 15º. It does this in duty cycles, so the 15º will not go full time until quite a few knock cycles are sensed. If too many knock cycles are sensed and the 15º retard does not correct it, it puts the engine in limp home mode...without retarding at all, so the motor starts really pinging and billows black fuel smoke, which is the case with I bet 90% of L98 engines on the road today.

You have to look at it from a "what will cause a knock sensor event" type of logic to fix it. The first thing is engine noises...like worn AC compressors, worn out water pumps, bad alternator bearings, etc... because all of these could supply enough noise to trigger a false knock event.

The best way around it in general with a hi mileage L98 is to disconnect the knock sensor and connect the sensor wire to a 5K Ohm resistor tied to ground. Then changing engine timing will have exactly the effect you want it to have.

CORKVETTE1

to john row do you know for fact to backup about xyelene, just curious. :confused:

nsimmons

xylene is 116 octane, toulene is 115, do a search on octane and xylene..you'll find mixes for home made boosters

true it doesnt have as much energy as gasoline, but you can use it to help eliminate knock. I use it to track down problems and eliminate lack of octane as a cause for knocks, i dont run it for more power. There was a big discussion about toulene and xylene not long ago, doesnt anyone remember it?


[Modified by nsimmons, 9:16 PM 5/16/2002]

merrick

"It's true that the ZZ4 balancer did not fit the C4 chassis... but, instead of notching the frame, the shop mechanic installed shims at the motor mounts to raise the engine higher--we decided that was a better option than possibly throwing the balance off. "

How much shims did you add? In my opinion this is a bad idea. This would alter the geometry of the drivetrain. This may cause driveshaft vibration, U joint wear, and transmission seal/bushing wear.