Ok for those of you who read my last post about engine knock... ignore that; this is totally unreleated!

Basically I'm hearing a tapping sound from the engine bay which only occurs under heavy acceleration. I'm guessing it's probably ping because I never rev the engine that high (I couldn't if I wanted to, I don't think--doesn't this thing have a rev-limiter?). But, I also never listen long enough to try to figure it out because I always back off the accel immediately as I hear it. The sound goes away after I ease up on the throttle.

If it is ping/detonation, where do I need to start checking first? The only thing I can think possibly is the fact that I swapped out my stock L98 injectors for Ford Mustang injectors (Bosh Pink injectors), which as I understand have a slightly lower flow rate than the stockers. I was told that they shouldn't cause me any problems, tho, and I know certainly enough people here have made that same swap and been happy with it.

Thanks.

 

My guess is ping.

However, I get a brief "crack" or ping in upper RPM when I stand on it. For my car it definitely sounds like a ping. I don't know why it doesn't last. Maybe the engine hits a point where load is relatively high for a given power output, hence the short-term ping. Don't know. I'm no expert. It's an 87 with tpi, manual and 3.45:1.

Again, regarding your car I'd guess it's ping. I know this doesn't help solve it, but does let you know it may not be uncommon.

Rich

 

Yeah I'm really thinking ping also. It's hard to describe the quality of the sound, but the frequency is rapid and generally in time with engine speed.

It concerned me today because I got down on it with my windows open and another car on the passenger side. You know how you can hear all sorts of sounds your car makes when you're driving close to something with your windows open because the sound reflects, and I noticed that the sound is considerably louder than I would have thought from just sitting in the cabin with the windows closed. I guess it was the volume of the sound that made me consider the possibility of valve float.

 

Whats your timing set at? Whats the plug gap at? Recent tune up?

 

More than likely it is not valve float. When valve float occurs, the engine will not want to rev up any higher due to the valves being open which causes compression to bleed off, erratic or incomplete combustion, and the possibility of stalling out the incoming air charge(if the intake valves are open) Ping or detonation can sound different depending on the severity of the detonation. Some engines it can sound like a tapping metallic sound, others sound like marbles rolling around inside of a coffee can! What kind of gas/octane are you using? Have you tried 93 octane? There are a few things that can cause detonation/preignition...

1. Octane that is too low(on either a high compression engine or an engine that has overly advanced ignition timing)

2. An engine that runs very hot/overheating

3. Ignition timing overadvanced(as mentioned above)

4. Carbon deposits/buildup on valves, piston tops, combustion chambers, or spark plugs. The carbon buildup holds heat, and can prematurely start combustion of the new air/fuel charge before the spark plug even fires.

5. Engines that run excessively lean have a higher tendency to detonate because a lean mixture burns hotter than a stoiciometric one.

If you don't want to get into adjusting anything engine wise right off the bat, then I would switch over to 93 octane, and run some type of engine decarbonizer/fuel system cleaner first. See what that does. If it persists, then it's time to check and possibly adjust the timing.

 

check the timeing , back it off to 6 deg BTDC . It's a start anyhow.

 

I'll check the base timing tomorrow (I'm finally home and actually can now).

I am using 93 octane and always do for this reason, but it still pings. I've rebuilt this engine but rebuilt it to mostly stock spec (L98)--so it's not a high-compression engine by any means.

As for the timing, however, wouldn't the fact that I've rebuilt make the timing I should set it at arbitrary and really specific to my engine? I know I was told that stock timing would be irrelevant after I had it rebuilt. I did mark the balancer for new TDC, for whatever that's worth.

In general, when I set the base timing (with the brown wire disconnected, of course), I set it for whatever I get the best quality idle with.

 

Just for shizits and giggles, is it possible that you have an exhaust leak? At idle, the exhaust flow is minimal and at reduced pressure, but once you get on it the exhaust flow speeds up, pressure goes up, and if you have a bad gasket or loose O2 sensor somewhere, it could make a noise. Just a thought. A few questions for you...

1. You said that you rebuilt the engine. Did this occur after the rebuild, or is this an ongoing issue?

2. Do you have the factory distributor with the built in timing control(EST)? I am not familiar with it, but it may be a part of the problem.

3. Are you using the factory timing chain cover and timing tab? If so, are you sure that you have the timing tab in the correct location?

4. Why did you have to make a new line on the balancer for a *new* TDC? For some reason, this worries me. What kind of rebuild did you do? A new crank, internals, etc. or did you just reuse you old parts but have them machined? The only way that there should have been a need for a new TDC mark is if you were using the factory balancer with the elastomer surround and it slipped. If that is the case, then a new balancer would be a good idea.

Also, you had said that you changed out the injectors with those that have a smaller flow rating than the stock units. There MIGHT be a possibility that the injectors aren't capable of flowing the amount of fuel that your particular engine needs. This would be more prevalent especially if you changed the camshaft, ported the heads, changed over to a more efficient intake manifold, or use long tube headers(the long tube headers coupled with a camshaft that has a good amount of valve overlap could cause the scavenging effect of the exhaust to essentially *suck out* some of the initial air/fuel charge casuing a lean condition). The only real way to tell would be to hook up an Air Fuel ratio sensor/guage and measure the voltages that the sensor puts out and see if it correlates with what the specs are.

Does this engine have a Mass air flow sensor? If so, it could be dirty, or not working properly causing the ECM to think that less air is coming in than there really is. So then the ECM will compensate by spraying less fuel.


Just throwing things out there.....

 

paulmoore,

All very good suggestions! Here are my responses...

RE: Exhaust Leak... I know what you mean about leaky exhaust making a noise--my V6 Camaro has a bad exhaust gasket/loose exhaust manifold bolt and it makes a very distinct sound all the time. This is not the sound my V8 is making only under heavy acceleration.

1. In fact, I never was able to drive the car before the rebuild. However, I have put maybe 30K miles on this rebuild so far and it has not always detonated like it does now.

2. The distributor is stock with a good EST installed. The distributor was rebuilt when the engine was out.

3. The timing chain was one of the areas where I actually did upgrade from stock. It's got a double-roller chain. The timing cover is stock, but the tab is not adjustable.

4. This sounded odd to me also, but this was what my engine rebuild book said to do. I have an orange mark on the balancer for the "new" TDC (as determined by the procedures in the manual) which is indeed different from the original mark on the balancer. It's off by maybe two circumferential (linear) millimeters. This is what I set my timing against, and I imagine the difference is due to the slippage around the elastomer as you said.

All of the non-moving components on this engine are original--intake, intake manifold, exhaust manifolds, heads. The crank and rods are also original, and the camshaft is new but is of stock specification. I made sure things were mostly stock because, at the time, I was afriad of mismatching parts (and running into problems like this, ironically).

Lastly, the engine does have a MAF sensor ('89 IROC) and it is a continual nuisance--just like my V6 '88 Camaro's MAF sensor. The thing will throw a code 34 at random, and this is probably the third one I've had on the car. I've gone through maybe 3 or 4 on the '88 car, so I've just learned to deal with bad MAF sensors. I expect I will have to continue to put up with this until I have the money to drop on a brand new MAF sensor (I've been putting in reman units).

I think a general tune-up is probably in order for my car anyway. I'm going to start with checking the timing, and if I can ever get my hands on some ECM diagnostics equipment, I would like to check the A:F ratio as you suggest.

 

Hmm, well I only have a few more possibilities then. If you did change the timing chain, did you install a factory one on it or did you go aftermarket? Reason being is that some aftermarket timingchains come with a 3 way keyway on the crank gear. With that particular chain, you can set the crank straight up, 4 degrees advance or 4 degrees retarded. This is base timing mind you so it can and probably will have an effect on idle, as well as either changing the RPM range of the engine either higher(retarded) or lower(advanced)

If for some reason the MAF did take a dump again, you mght be limp home mode, but I would think that you would really be able to notice that if it were the case.

 

paulmoore,

The timing chain is indeed an aftermarket one--I wish I could remember the manufacturer name... I know it's a "good name brand" and I'm sure that you'd recognize the name if I could remember. But it is a double chain and it does have the three-way keyway that you're talking about. It was not set to be either retarted or advanced.

The MAF sensor could be causing more problems than I give it credit for. I suppose I underestimate how much it actually does for the engine control. This particular MAF sensor has given me trouble before. What will happen is my car will be acting fine for months, then one day I'll try to start it and it will run for about 2 seconds and then die. I'll try that process about 5-8 times, and eventually I get it to maintain an idle, at which point the check engine light comes on. Then I check the codes when I stop the engine, and get the ole' familiar code 34. The check engine light usually turns off on its own after a while, and the odd starting condition also goes away, so I've taught myself to ignore MAF issues.

<pauses to go read engine codes...>

Yep, the ECM isn't throwing any codes right now ('cept code 12). And I haven't done anything to this car mechanically or electrically since I had MAF trouble.

Is it possible for the MAF to give "bad data" enough that it adversely affects engine performance but not quite bad enough to make the ECM throw codes?

 

Ok just went out and checked the base timing... this was done with the tan/black wire disconnected and with the engine at full operating temperature.

My timing dial on my timing chain cover is pretty hard to read and I'm also checking against the "new TDC" mark. That being said, I'm reading +9 degrees of timing at about a steady 650-700 RPM idle. By "+9 degrees", I mean to say that the dial is reading 9 degrees on the larger part of the timing dial--the one that gets higher as you go toward the passenger side of the car.

After I turned the engine off, reconnected the tan/black wire, then checked the timing again with the engine restarted, I was getting about +14 degrees at idle. This might be irrelevant, I'm not sure.

Only other things I can say are that...

1. When I revved the engine to about 3K RPM and then let off the gas with the tan/black wire disconnected, I heard a popping sound (backfire) out of either the exhaust or intake (couldn't tell from the inside of the car) on decelleration. This doesn't happen when the wire is connected.

2. The rate of flashing on the timing light was not constant at idle (even though the idle was steady)--that is, it looks like there was an occasional miss on the 1st cylinder. I did have the inductor as close to the plug as possible, but the timing light is also really old. Maybe it's just the timing light?

 

sancho wrote Usually when you get popping back through the intake its due to the engine running lean with too much ignition advance