Detonation?

[francis_sawyer]

Hi,

I'm not new to the forum. Have been Trolling for a couple years now. '92 MTX, 139,000k, Silver

I've had my SHO now for a couple years, lots of work (read money) invested in it. Anyway after having a new AC clutch, transmission, water pump, 60k, nearly all suspension done on this car. I think I am ready to look at performance upgrades now. Unfortunately before I go there I want to take care of one more thing.

For about year now I hear a weird clacking sound. I would swear it's pinging, as it sounds just like detonation I used to get on my old '81 Trans Am when I'd advance the timing too much. The problem is it comes and goes. And I can't easily reproduce the problem.

I've had it checked twice, the one time I got a mechanic to hear the sound he just said "Huh, that's weird." These are the facts:

1. Under normal driving conditions my car's temp is usually hangs between the "L" in normal, or just under it.
2. If I kick the air on 2/3 or above and there are several people in the car, or if I am in a lot of stop and go traffic on a hot day, the clacking can get pretty bad.
3. It will not make the sound floored, or in the upper RPM ranges. Only in the 2k to 3.5k range. Mostly when going up hills, although I have had it do it going down hills.

Anyway that is the gist of it. And it is a nuisance as it does hurt performance when the engine warms up above say about "A" in normal. And I don't want to **** my engine putting NOS or a blower on, especially now that I've invested as much money as I have.

Also if it's your opinion that it's the knock sensor is it worth doing the CPS too while I'm at it? (Found out the CPS is only $36).

Any takes would be appreciated.

Thanks,

Bryan Nelson

 

[jelloslug]

First, it sounds like you thermostat is shot. Thats why it's not getting very warm. The other possablty is that the sender is messed up. There are 2 temp senders, one for the gauge and one for the computer. The one for the gauge is near the T-stat housing toward the front head. Now for the ticking, does it do it at idle? Does it sound like its comming from the top or the bottem? It could be a timing chain tensioner, mine were bad and it sounded really bad sometimes and sometimes they were fine.

 

[sdpatt]

Your thermostat sounds fine. The temperature under most conditions with a 180F thermostat will be around or below the "L" in NORMAL on the gauge.

What grade of gasoline are you using? Premuim, with an octane greater than 91, is recommended. Ever higher octane numbers may be needed to prevent preignition (pinging) after carbon deposits have been created in the combustion chambers. You may find a benefit from a fuel system cleaner that addresses these types of deposits.

Without hearing it with my own ears, I would ask you to make sure that the sound is indeed preignition rather than a connecting rod bearing knock. The conditions you describe under which you hear the sound would be conducive to a preignition condition. If this is frequent, you may need to replace the knock sensor.

However, since you described a performance effect, the knock sensor may be retarding the ignition timing to some degree to prevent the pinging. You could perform the KOER test to check for an output from the sensor. If you hear a ping during the "goose test" and do not receive a 225 code, the sensor is suspect. If you don't hear any pingnig and get the code, that does not mean the sensor is non-functional.

The knock sensor is located in the center of the valley, below the fuel rails. See the image below to help locate the knock sensor. It is in the center of the image and is located between cylinders #2 and #5. It requires a deep socket or O2 sensor socket(?) to replace. To access the sensor requires the removal of the intake manifold and fuel rails. You should have the injector to head seals in hand to replace the originals since they will likely be as hard as rocks. The knock sensor is more easily replaced during the valve gap adjustment rather than the timing belt service.

If the crankshaft position sensor is operating properly and not creating an engine cut-out condition or EEC error code, leave it alone until the next timing belt change or until it fails. There is not much to be gained in replacing it by itself. I would purchase the part and keep it until it is needed.

 

[francis_sawyer]

Hi Guys,

Thanks for the help so far. I run strictly 92 or higher octane. And I put fuel injection cleaner through about once every three or four tankfuls.

Sorry Jelloslug, I didn't explain that very well. I don't think it's the temp sensors as the temp will increase, (I had it at "N" in July crossing Kansas on a 109 degree day). But average temp is low. It's only when I'm in a LOT of stop and go traffic, and cranking the air on (like yesterday it was 89) will usually cause the temp to shoot up pretty quick in stop and go. Then I really notice the noise.

For instance I've already driven nearly 80 miles today, (onsite computer guy), and haven't heard any noise yet. But it's not hotter than 70, and the air isn't on. Also it's only under a load, I can never get the car to make the noise if it's in neutral.

Also thanks for the pointer Sdpatt. I'll have to pick up a tester on my way home tonight. I sure hope it's just the knock sensor. That's why I was curious if there was an easy way to find out. Also any recommendations on where to get a manual. Every time I walk into a local shop the clerks just roll their eyes when I say SHO.

P.S. What happened to the FAQ's, couldn't find 'em?

 

[Slo-Sho]

With that many miles a few De-carbon procedures wouldn't hurt. The carbon inside the combustion chamber may have raised the CR a little bit.

 

[metallicasho]

francis_sawyer, you don't need any kind of tester to view your codes. You can just use a paper clip, peice of paper, and pencil. Just follow this procedure . It is pretty simple thumb

<small>[ October 20, 2003, 04:46 PM: Message edited by: metallicasho ]</small>

 

[Adi Agaj]

hey man,

the way you described your problem, i really understand it and you know something is not your thermostat or your knocking sensor or temp senders as these guys mentioned up there. rant . But is something else that you do not want to know, but sit your head down and pray to the lord hail for your engine so to not be dumping you soon. the same thing i had on my 92 5 speed mtx . Last april 03 (6 months ago i ended up puting another engine in because was way to excpensive to rebuilt and sand down /replace the rod bearings which caused all the knocking sound. I always could hear the knocking when i reved up my engine between 2000 rp/m - 2800 rp.m. So I droped in another engine with 61k out of a 95 SHO <<<<--- this happend to me because i was dum, racing on interstate of 95 south -128 with a mustang and after then i lost oil presure and you should have heard my engine knocking and knoking like the rod bearings and pistons were going to fly out of it.

<small>[ October 20, 2003, 08:43 PM: Message edited by: Adi Agaj ]</small>

 

[francis_sawyer]

I don't know.

Well I have run the codes, surprisingly simple by the way....

KOEO
111 - System checks OK
219 - SPOUT circuit failure timing defaulted to 10 degrees - follow code 213 diagnosis (213 - Ignition SPOUT or SAW circuit open or shorted) What the crap?
542 - Fuel pump open bad ground or always on

KOER
167 - 167 No Throttle Position sensor change in "goose" test (must get at least 25% rotation)
225 - Knock sensor not tested (ignore if not pinging)

Well that's it. Anything you guys see I should be concerned about? (Like 167, I really romped on the gas, but I'm not worried too much about that error, I figure user error).

Also just for clarification I have NEVER heard the sound when the MTX is disengaged, ha which also prevents me from getting the ol' stethoscope out. And it only seems to happen once the engine has warmed up, or the air is on, or say stop and go traffic where I am in certain RPM ranges more often.

For instance today, I put about 80 miles on the SHO driving to onsites. 25 miles, 15, 20, 20. Trip one interstate all the way. Trip two, back to the office I heard it a couple times taking off from stop lights. But the last two drives were a mix of stop and go traffic, along with about a 10 mile stretch of highway.

Let's just say I drove a little more aggressive than normal on trips three and four. Upshift, downshift, stop light peels (no, not any 5000RPM launches, I just replaced the tranny 20,000 ago, bought w/ exploded diff pin), took it to 6000RPM a several times. This is what I noticed:

1. The rattle almost always seems to be from the right part of the engine bay. Lower. (Cats?)
2. Today I did notice though when I seem to have a slight performance problem compared to normal, A: It's after the engine temp is past "M", B: The sound is not on the right, but the left/center of the engine bay. And it may be a different tone (Sorry I shoot guns at the range quite a bit, so my hearing isn't all that great).
3. When I hear the rattle on the right the engine also "feels" rough. There is still no noticeable decrease in power, and a little after 3000RPM the sound smooths out. At 4200 the secondaries kick in. Feels fine, and drives great otherwise.
4. It seems I only hear either noise when I am not looking for it. If I am driving aggressive, say launching from stop lights it doesn't stay in those RPM ranges long enough to do it.


Any takes? Rod Bearings, Knock Sensor, I'll have to do the tap test on the cats, I have noticed a more throaty sound lately. And that would explain the rattle on the right side I guess.

Scott, you seem to be pretty much an expert on rod bearings, any takes on what the symptoms would be?

What do you think, potential serious problem, or should I go jump in a lake and cool my jets?

 

[HopefulSHO]

I didn't realize you were in my own town. Good to see another Omahan on board.

You should have a PM waiting.

Edit: Technically I live in Bellevue now though, heh. Oh well, only 5 miles away.

<small>[ October 21, 2003, 09:10 PM: Message edited by: HopefulSHO ]</small>

 

[betterman]

This probably has nothing to do with your problem but I know on my car the heat shield on the cat was loose and would make a rattling sound.

 

[francis_sawyer]

Well,

It's about two months later, (and 70 some degrees cooler out, nutty weather here). I wanted to post an update, as I hate leaving a post undone. .

Here's the scoop. I have two rattles. The loud horrible one, causing some loss of power, and which I only seem to hear in stop and go, or high temps if I have been driving for extended periods. This one has not happened once since I posted this. I am convinced this one is true detonation. And suspect the A/C is partly to blame. I suppose one of the sensors could be the cause, or maybe not high enough octane at higher tempuratures (doubt). Don't know either way I will have to sort this one out when it get hots again.

The second rattle is more subtle, but happens more frequently. I have virtually eliminated it by using octane booster, or fuel injection cleaner in every tank full of gas. And I have been watching where I get my gas from. There are a few stations in town I will never fill up at. One place I found out their filters had failed on one of their pumping tanks. The rattle is on the right side down low, I suspect one of my catalytic converters is starting to get noisy. If I tap the one on the right it does seem to be a little loose. I've heard these usually fail due to unburned fuel getting to them and torquing them up? And this is controlled by one ofthe sensors. Worth checking?

I am planning on replacing my exhaust anyway. I was ready to go out and blow a grand on Shoshop's. But after finding three or four posts saying they didn't help, or made the sound "tinny" I backed off. Any opinions on this? $1000 for something that allegedly adds 30-40hp sounds too good to pass up.

If I'm not gonna get decent performance out of an exhaust upgrade I'll probably just take the cats off and knock what's left of the honeycomb out this spring.

Any opinions on a fuel sensor, and upgrade exhaust?