94 GT pinging, help please

Canary94GT · Sep 6, 2011

Checked the ohm reading on my temperature sending unit (not the ECT, the one that informs the gauge) and it is ~395 ohms when cold. My Haynes manual says it should be ~74 ohms when cold and around 9.7 ohms when cold (haven't tested that yet).

Also, I think I may be losing a bit of coolant over time, but I can't figure out where as I don't see any drips on the ground. Sometimes when I open the radiator cap, coolant flows back into the overfill tank to just below the "Full Cold" mark. Also, sometimes when the engine is cold and then I let it warm up, the reservoir tank level doesn't change - shouldn't it rise/fall?

My radiator is full to the top.

I had a leaky water pump replaced late last year, then a few months later the "low coolant" light began coming on intermittently. I haven't filled the coolant level at all since then, and it's about 2-3" below the "cold full" mark on the reservoir (which is just below the coolant level sensor).

I don't notice any white smoke from the tail pipes unless it is a cold morning (<50 degrees or so). I don't notice any oil in the coolant or coolant in the oil. Also, all my spark plugs looked like those two I posted pictures of. My o2 sensors were quite white, not green.

Canary94GT · Sep 8, 2011

Today I took the car to Midas finally and they couldn't figure out the problem - the guy who helped me tried increasing the timing to about 11 degrees. We both noticed it didn't seem to make the ping worse, but possibly lessened it slightly.

He recommended I try bumping it up further and see what happens, so I bumped it up to about 14 and took it for a drive - the low rpm pinging didn't seem to get worse.

I went on the freeway and revved it up to about 3000-3500 rpms (which I really don't usually do) in third gear and heard a loud spark knock, that felt like it shook the car a bit. This sounded much more harsh from what I've been hearing in the lower rpm range and from a stop. Not sure if pinging gets louder the higher the rpm or what - but it was definitely a different level of sound. This sounded more like putting a coin in a metal can and sharply shaking it up then down, while the sound I'm hearing at the lower rpms sounds more like coins jingling in a pocket.

I've also noticed that my harmonic balancer is wobbling slightly, by about 1/10" of an inch at idle. Looks like even though it doesn't appear to be spun nor have rubber protruding out the back, it may be on its way out anyway.

99FiveOh · Sep 9, 2011

I really don't want to sound rude and I am very sincere, but Midas is so full of crap I wouldn't take a moped to them if I were you! Increase timing to combat pinging/detonation? That just goes to show you how ignorant these commercial shops are!

If your balancer is wobbling period it's already begun to slip. You really need to listen to our experience on this one. I can't speak for others here but I myself have owned quite a few of these cars and I've had my share of "mystery" issues that mechanic shops could not fix, but the fine folks on here were able to pinpoint with ease. Now I'm pretty much familiar with the entire car and this site has helped me throughout the years to gain valuable knowledge.

Replace your balancer, retime the car and see where you're at. If the pinging remains, try a new distributor. Even if those parts do not fix the problem, they are both parts that commonly go bad and will leave you stranded!

Canary94GT · Sep 9, 2011

I'd normally agree with you about Midas and similar shops - but the guy there that helped me was very nice and knew a lot about these Mustangs and pinging since he has owned a few in the past. So I showed him a list of what I've done and he spent a fair amount of time looking over the car and checking things and determined I've done most of what he'd believe would cause it - and he didn't charge me a dime for the time he spent (the car was there for over 3 hours), which is very nice.

But regardless if it makes sense or not, him increasing the timing did not affect the low rpm "pinging" I'm hearing, which I find quite weird. It was something I wouldn't have thought to try and is an interesting find.

I will be replacing the balancer and will see where things go from there. I will probably then look into a new distributor and/or fuel pump.

99FiveOh · Sep 9, 2011

The balancer may be off, but retarding your timing a little at a time until the pinging stops would be a free test. On the other hand, low rpm pinging is not a result of the typical "too much timing". The only times I've had low rpm pinging was lack of fuel to the motor or PIP sensor failure.

Canary94GT · Sep 9, 2011

Yeah, it sure seems like it's not calculating things correctly.

Have I shown you a picture of my plugs? They look kind of lean to me

The fuel pump is still very suspicious to me, since I have heard a sort of gurgling noise from the back of the car that sounds like it's coming from the pump, and also my fuel pump has gotten louder over time.

I just wish I could test the fuel pressure while I drive since it's fine at idle.

Canary94GT · Sep 9, 2011

ordered new harmonic balancer from Autozone, will be here Tuesday

Canary94GT · Sep 9, 2011

I just put the fuel pressure gauge back on there and put some blocks in front of the wheels so my mom could put it under load and I could see how the gauge reacts.

It was reading about 31-32 psi at idle, and when we put it under a slight load (not too much) to the point I heard that "pinging," the fuel pressure didn't drop but went up to around 33-34 psi. Does this sound right?

But while I was out there listening, I did not hear the pinging noise from the front of the car. Maybe it was because the noise was too quiet.

99FiveOh · Sep 9, 2011

You didn't put the car under load! You just free spun the wheels. The motor had about 100 lbs of weight to spin and that's it. You need to give it all 3400 lbs to push and THEN you'll be putting it under load!

What I did was went to the store and got some brass tubing and various fittings to put the gauge outside the back of the hood. Just to where I could see it while I drove in various gears and driving situations.

Anyway, if you're getting pinging without any kind of load on the car something is definitely wrong OR what you're hearing is not pinging!

And that's odd that Autozone had to order the balancer... they usually stock them.

Canary94GT · Sep 9, 2011

I'm not sure if I misunderstood you or you misunderstood me, but the tires did not spin when I tried this.

I just blocked the wheels and tried to accelerate like I was at a stop. Since the car couldn't move forward and the tires weren't spinning as I gave it gas, wasn't that putting a load on it? When I'm actually driving and I accelerate from a stop, I hear that pinging noise. But I also hear it in different gears going up a hill and such. But almost always only occurs under about 2000-2500 rpms.

It seemed to me like a good simulation of the load put on a car when accelerating from a stop.

The noise I hear literally happens right after I put my gas on the pedal to accelerate from a stop, from 600 up to 2000 rpms or so.

I'm wondering if possibly the harmonic balancer's wobble is causing some sort of noise?

Other than pinging, I'm just not sure what else it could be that only occurs at lower rpms and while under load. Can you think of anything?

I'll have to see if I can get some sort of recording device temporarily mounted under the hood to record the noise and share with you.

Canary94GT · Sep 10, 2011

wow sweet, autozone got in the harmonic balancer already

Gonna go pick it up along with the removal/install tools.

Canary94GT · Sep 11, 2011

Replaced balancer and it idles and drives so much more smoothly now. Not a shake at all.

Also, the balancer was spun a tad - I previously set timing at 14 and after the swap it was 18 degrees.

Set it at 10 degrees and it's still pinging in low rpms

99FiveOh · Sep 11, 2011

Now please change the dizzy! And do NOT buy a reman'd one either.

Canary94GT · Sep 11, 2011

You really think it's the dizzy man?

I'm noticing really no other signs of a bad pip, such as missing, hard starting, rough idle, etc

I just don't have much more money to throw stuff at it without being sure :\

99FiveOh · Sep 11, 2011

That sensor does much more than what people think it does! But do whatever you want... maybe you should take it back to Midas lol.

And BTW, you might want to let someone else hear what you think is pinging, since I saw you admit in the thread somewhere that it may not be. Chasing down a solution to a problem that does not exist is counterproductive!

Canary94GT · Sep 11, 2011

Well I've taken it to two shops and had them drive around to listen to what I told them I thought was "pinging."

Neither of them thought otherwise.

It certainly doesn't sound like spark knock I've heard at 3000+ rpm, but I do not know if spark knock sounds different (quieter and less intensive) at lower rpms.

Could it be an exhaust leak? Maybe. Never had one before, but I thought they sounded more poofy than metallic-y. There's also carbon deposits on the tips of my plugs which is an indicator of detonation.

I tried recording it while I drive so I could show you guys but there was too much background noise.

I will have to try a different location in the engine compartment though

Jerry Leaming · Sep 11, 2011

Stop wasting your time and do a compression check and a leak down test....I've been down this road before and it was a blown head gasket. Also I bet your coolant is disappearing into the cylinder and being burned. Just a small leak wouldnt show in the exhaust but could cause some "bubbles" in the coolant system. Also look at you coolant bottle for oil residual, there might be a oil ring in the bottle. Either way do yourself a favor and do the checks, if nothing else you will eliminate the head gaskets as a problem.

WhiteCobra95 · Sep 13, 2011

I agree with Jerry. The leakdown and compression tests are a really good diea. You can also do a cooling system pressure check, where you pump up the pressure in the cooling system and see if it bleeds down over time (= bad!).

I've also had a couple development engines which had very small coolant leaks into the chamber which were not measurable by the leakdown test, but we could identify the bad cylinder since it had a steam-cleaned spark plug. (Plugs should be a dry tan color, or dry carbon black if you've been on it a lot. Wet black = buring oil, white = too lean, and steam cleaned or white sometimes with green spots = coolant.)

Knock/detonation sounds like marbles in your engine, or like somone hitting a small block of wood. It gets louder with an increased knock intensity at higher loads. Pre-ignition sounds like mega-knock, and you're engine won't survive too many of those (hole in piston). Sustained heavy knock can trigger a preignition by creating a hot spot in the chamber.

The part that stands out as strange to me is that the ping didn't get worse when you bumped up the timing. If it really is knock, it should become WAY more noticeable with the timing advanced - it should sound like a lot more marbles banging against each other.

Exhaust leaks can make loud ticking noises under load, and go away at light load, especialy if the leak is coming from a crack. These can be hard to find and a positive pressure test of the exahust is almost a requirement unless it's a sizable leak.

... just some more ideas. Good luck =)

Canary94GT · Sep 13, 2011

Thank you for the very detailed post! I will definitely keep working on this and look into your ideas.

I did just find out after looking through some receipts that a year ago, when I took my car in to a shop to diagnose this 'pinging' issue, they ran a cooling pressure test and also tested the cooling system for the presence of hydrocarbons. No hydrocarbons were found but they did find leaks in my radiator, so that was replaced. I would like to think they pressurized the system again to make sure everything was okay, but I didn't see that on the receipt.

I'm still trying to record this sound by placing a recorder throughout the engine bay. I have tried placing it on the strut brace on each side of the engine then driving it, but was unable to hear it either due to heavy background noise or the sound was just coming from a different place. I will try to place it near the exhaust (without melting the thing lol) next time.

I have also found it weird that increasing the timing, seafoaming the engine, replacing all these parts, and making the plugs 1 step colder has not changed the pinging. But it couldn't still be something wrong with the air/fuel ratio in that case, or would it still have changed?

This pinging noise does not shake the vehicle like high rpm pinging I've experienced. But it does get worse under load. At these low rpms (about 650 to 1800), it sounds much different (mainly quieter) than the spark knock I've heard at around 3000-3500 rpms due to timing being too advanced. Could it be that the spark knock is just *slightly* too early rather than *way* too early as in the higher rpms, making it less intensive of a knock? I've researched very hard to find sound clips of low rpm pinging and to figure out if it sounds quieter at lower rpms/intensity, but haven't been able to find much of an answer.

My spark plugs do have those black spots on them that I was told was a sign of detonation.

Ugh, I hate not knowing for sure - but I'm trying to pinpoint it. Thank you guys for your help, I'm sorry I'm pretty much a noob with cars!

99FiveOh · Sep 13, 2011

One thing I'll say is that you're going about recording all wrong. Since YOU can hear it from the driver seat, perhaps that's where you need to record it. Or maybe outside with the hood closed. This will block out all the unwanted noises and allow the recorder to hear the noise that's out of the ordinary, like your pinging noise.

Pinging to me sounds just like a metal bladed fan hitting a shroud. It's definitely a metallic sound. I'd be willing to bet if you let us know what town you live in, if someone lives close by they could come take a look for you. What you need is a Mustang guy to have a look.

94 GT pinging, help please

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