Rattling / ticking sound under load

[Techno Duck]

'88 3.2L . Mostly stock, M&K muffler and pre-muffler. 911Chips 91oct chip. About 5k miles on valve adjustment.

The cause of this has eluded me. Ive been all over the car looking for anything loose that may have been rattling but after some further troubleshooting i am thinking this is mechanical.

The noise is only present on a warm engine, much louder and obvious when the engine is hot, like after extended idling in traffic or its really warm out (90+ ambient). Its noticeable when accelerating with any load on the engine; up hills for example. Goes away as soon as you lift a little or coast. Light acceleration i do not hear it, but may just be too faint to hear.

The video below has the mic inside the engine bay. I am accelerating up a mid grade hill, to really make the noise more noticeable i am braking lightly while accelerating in 3rd gear and intentionally lugging the engine (2-3k rpm engine speed). At about the 36 second mark i increased braking and really lugged the engine hard, down to probably 1500rpm. Any ideas what this may be? Valve train? Cam chain / tenssioners? Knock / pinging?

Engine feels fine, no loss of power or anything. Looking for some fresh ideas because i am out! Will be bringing to a trusted shop when i get some free time in a few weeks.

Sort of sounded like pinging to me but see no other signs of it; have checked the chip is indeed for 91oct. Checked fuel quality switch is set right and made sure the jumper for CA cars was disconnected. Plugs look fine. Also have added Torco octane booster which effectively brought my octane up to about 95oct...no change.

About 13k miles on engine rebuild, ive done about 5k of those miles. I believe the #3 cylinder exhaust valve guide may be going as i have some oil running down the heat exchanger flange. Super loose valve maybe..? Oil consumption is about 1qt per 1k miles.

https://www.youtube.com/watch?v=i9boR45KrJg

[pmax]

Video is private.

Checked your head studs ?

[Techno Duck]

Whoops, sorry. Should be able to see it now.

Head studs were fine, i checked when i did the valve adjustment.

[Rawknees'Turbo]

That's either detonation due to improper timing, poor fuel, etc., or more likely, a major compression leak from a broken headstud (should probably check those again).

[Techno Duck]

Timing is indeed a possibility, its possible the shop the PO used made an error. Can the timing be checked with the engine in the car or does it need to be pulled?

I think i have ruled out poor fuel. Injectors are new, fuel pump new, FPR new, filter and tank suction screen new. CA 91oct is the best i can do around here unfortunately but the chip is for 91oct.

[jason2guy]

it doesnt sound like knocking or detonation- it almost sounds like something mechanical. hard to tell from a recording

just to be sure its not a lean running condition, which would cause a knock under load, its not a bad idea to install a wideband o2. that way you know what the AFR is. i just installed one in my 81- different altogether from yours- and wasnt surprised to find out im going too lean under WOT, big surprise from CIS

[scarceller]

Do not push that motor like that any more, I agree with the advice on the WBO2.
I suspect a possible lean running condition, check mixture ASAP.

Detonation is far more likely to occur at the lower RPMs simply because the stroke time is significantly longer and than at a higher RPM. The longer fuel sits in the chamber the more heat it absorbs and detonation is far more likely at low RPMs and a lean condition just makes things worse.

I also advise you pull the spark plugs and post close up pics of all 6 plugs so we can see what they look like.

Originally Posted by jason2guy

it doesnt sound like knocking or detonation- it almost sounds like something mechanical. hard to tell from a recording

just to be sure its not a lean running condition, which would cause a knock under load, its not a bad idea to install a wideband o2. that way you know what the AFR is. i just installed one in my 81- different altogether from yours- and wasnt surprised to find out im going too lean under WOT, big surprise from CIS

[prschmn]

I agree with Sal-be VERY careful-check fuel mixure. Not all chips are created equal
or as well as Sals

[scarceller]

Timing at WOT can easily be sanity checked.
Jumper the WOT switch closed, unplug that 3 pin harness from the WOT switch and jumper the 2 pins within the harness side.
Then while at idle parked rev the motor to 3000RPMs and with a timing light check the timing, then go to 4000 and then 5000 and check the timing at all those points, you should not be above 32 deg ever.

With that said, a SW chip is generally safe for these cars on WOT timing. The other thing you can try is put back a OEM chip and see if it clears up. But check Fuel Mixture first!

[theiceman]

with me that exact sound was a head stud rattling inside the cover ...

[DonNewton]

Chain ramps?

[Techno Duck]

Only had a chance to pull two plugs for a quick check. The below pictures are from the #5 plug. I pulled #6 also and it looks exactly the same. Currently they have 3k miles on them.



'



I pulled all 6 plugs a few months ago, this was with just 1k miles or so

Plugs by Jon | Photobucket

I'm just about due for an oil change so ill check the head studs again. Won't have much time to do anything with the car the next few weeks so ill most likely just setup a time to drop it off at a local specialist for troubleshooting.

Really appreciate the feedback though. Over the past few months i swear i have gone over every inch of the engine and transmission looking for the cause. I did find some things as a result.. a non G50 sway bar on my G50 car, a/c compressor bracket loose and a few other odds and ends.

[Rawknees'Turbo]

Those two spark plugs would indicate extremely lean operation conditions - the insulators look almost bleached white from heat. It would be interesting to look at the insulators and electrodes with a magnifying glass and see if you can see bits of aluminum embedded in them,

[Techno Duck]

The plug looked ok to me, the insulator had a flat white appearance with no deposits on it. Lean would be indicated by the insulator looking glazed I thought?

[DRACO A5OG]

LEAN, Check your AFR.

Was the care warm-hot when you did the recording?

+1 no more load testing like that until you correct the AFR.

Yes, you can check your timing with the engine in the car. Just remove chain covers and put to Z1 and check the cams position/s

[Rawknees'Turbo]

Originally Posted by Techno Duck

The plug looked ok to me, the insulator had a flat white appearance with no deposits on it. Lean would be indicated by the insulator looking glazed I thought?

Flat white with no deposits means that the insulator is getting so hot that everything is burning off off it (should be more tan/brownish in appearance) = indicates lean operating.

When you get a chance, check for aluminum "dust" embedded in the insulator and electrode.

[Techno Duck]

Appreciate the feedback everyone, car will be parked the next few weeks until I have time to work on it but ill be sure to report back what I find.

So assuming it is detonation; Even at fairly mild acceleration i was getting it (only on very hot days). The fuel system is essentially all new so I don't think its a fuel delivery issue. So does overly advanced timing seem like the most likely possibility? Would it take the timing to be off by much to cause my issues? i don't have much experience with timing and its affect on the engine. Does this mean my car is going to feel slower if the timing was off and it's reset correctly... . Just kidding..

I'll swap the chip back to stock when I get back, if that doesn't help I'll likely defer to a local shop to check timing.. Etc if need be.

[Techno Duck]

Back to trying to figure this out. I dropped the car off with Jae @ Mirage last week. Thankfully during a short test run around the block we were able to replicate the noise (so i am not going nuts!). Jae believes it is detonation and not a head stud. I was do for an oil change anyhow so he pulled the lower covers and checked the head studs anyhow (all were good).

Last i spoke with him he was going to swap another AFM on and see if there was any change. He mentioned another step to take was to check the timing at both idle and with the car under load on a dyno.

While we have not checked fuel pressure yet, we do not believe this is the cause as every fuel injection component is new or has been replaced... fuel pump, filter, injectors, regulator.

Is it possible for the cam timing to be off enough to cause this detonation, but have an otherwise normal running engine? This engine did get a split case rebuild some time ago, so i would say its not out of the realm of possibility that an error were made.

Any other suggestions on what could be the cause?

[scarceller]

Get a WideBandO2 gauge on it and check the mixture. You MUST be below 13.0AFR at WOT to be safe. Detonation is often caused by running lean or to much ignition but I'd check the mixture before you assume it's ignition.

[Techno Duck]

Sal, mixture will be checked also when on the dyno to check the timing. This detonation happens at part throttle conditions, i haven't even really checked to see what happens at WOT.