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New sound from the engine


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So last week my boy is driving the car and hears a small "pop" while driving. Not to major, but definitely a "hearable" event. He wondered what the noise was, but attributed it to something he had done inside the car at the same time he heard the noise.

 

Next day I am in the car with him, and I am hearing a sound that is engine-speed dependent. hard to describe. something between a "tap" or a "rattle" that has a frequency of about one cylinder per engine revolution. One might describe it as similar to a "ping" heard in a pinging engine due to low octane or non-optimal tuning. Hard to hear at idle speeds, more noticeable when the engine is under load and/or accelerating.

 

So i need some ideas about what I might check for. It seems that something is a-mis, but nothing too major because the engine still idles really well when it is warm. It may be missing on a cylinder, I am not sure my ear is sharp enough to tell for sure via sound if a cylinder is missing or not at idle on this V8.

 

I haven't checked anything yet, not much time to work on it yet, but here are some things I am thinking, I am looking for more ideas:

 

- check engine vacuum (have gauge and know how to read it, interpreting what it means can be tougher)

- check individual cylinder compression (have a gauge and know how to use it)

- check spark to cylinders

 

Another clue: the sounds seems to definitely be coming from the drivers-side bank of cylinders. The engine is a 302 V8. Engine running at idle seems ok, no noticeable sounds (other than a subtle "clatter" that could be attributed to power steering, AC compressor or other). Engine revved and in park doesn't exhibit any significant noises wither.

 

Other than that, I am struggling for what I can check. I am wondering if perhaps we have had a valve go bad, or some other valve issue. Burned, sticking, cracked etc.

 

My questions are:

- what else can I check

- what precautions should I take (if any) to protect the engine

- how can I rule out valve issues

- etc.

 

Sorry for the vagueness. I know to listen to these engines, and I've been hearing…. something. Question is what does it mean?

 

Thanks for any help or suggestions.

 

Jay Estes

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You can use a timing light to test for fire at each of the plug wires. An infrared thermomenter aimed at the exhaust adjacent to the head will show a nonfiring or misfiring cylinder as cold. A vacuum gauge will tell you if you have a valve seating issue. If those test don't show the location, then I think pulling the valve covers is the next step.

 

Keep in mind that it could just be a fouled plug too

http://www.7173mustangs.com/gallery/1_01_07_15_8_53_18.png

 

"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!

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I would pull the spark plugs and make sure they look OK, none black or carbon build-ups, and gapped correctly. A weak spark can fire when not under load but not fire when the engine is under load.

 

 

“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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Great ideas guys. I'm putting these in work tonight. I am not sure I can recognize a "valve seating issue" with the vac gauge, but what I can do is put the vac gauge on there and take a 5 sec video of what readings I get.

 

I do have a infrared thermal gauge I can put on the header pipe immediately adjacent to each cylinder. I have done this in the past and all cylinders were in reasonably close agreement (to me anyway) usually somewhere between 650 & 750 F (if I remember right) I'll do that again tonight.

 

Next I will put a timing light on each spark wire to verify I am getting spark applied to each cylinder. Easy. My understanding is that if hooking it on the wire induces the strobe to flash, I am getting good spark.

 

Next I will pull each plug and inspect for gap and being fouled. I have had them all out and inspected them in the past, but that was about a year ago, so we'll see what they look like now.

 

I'll do that tonight and if I find no smoking guns, I'll plan to pull the valve cover and see what I can see.

 

Jay

 

PS. THX Boss351 for the compliment. We picked this car up for my son about a year and a half ago. It was restored in the 80's (I believe engine was overhauled then too) and has been garage kept - you can't believe how good the underbody is relative to rust and wear. We are slowing making improvements as my son enjoys driving it to from school and local places. It is his daily driver. Paint has some issues but "looks good from 500yds on a galloping horse", so it makes a good driver. Fun part is my son will participate in a street survival school (http://streetsurvival.org) this saturday where the kids use their own cars and participate in aggressive driving tasks on a closed police training facility. May be his first time to "break the backend free" while driving (at least as far as I know!). I'm hoping this helps protect him in the event of off nominal driving conditions.

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First check to see if a spark plug is loose. My son's f150 came up with this kind of noise. We checked a bunch of stuff and went to remove the plugs and check them and one of the back plugs was barely in the hole! Seems these back plugs are hard to get to (even on a mustang) and they are not always tightened like they should be. Tightened up the plug and sound went away.

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http://www.autospeed.com/cms/article.html?&A=2393 will give you a good guide to using your vacuum gauge

http://www.7173mustangs.com/gallery/1_01_07_15_8_53_18.png

 

"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!

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I do have a infrared thermal gauge I can put on the header pipe immediately adjacent to each cylinder. I have done this in the past and all cylinders were in reasonably close agreement (to me anyway) usually somewhere between 650 & 750 F (if I remember right) I'll do that again tonight.

 

650 to 750?? If that's your readings at idle, then your engine is too lean or timing is too far advanced. They should be in 300-400 degree range if properly tuned.

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The IR thermometers are good for go/no-go tests and coolant temps. The won't work on anything shiny (read low) and accuracy is affected by angle and distance. Still a good tool but has limitations. Chuck

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Alright, here are some results. I haven't had nearly as much time as I would have liked.

 

I took the car for a 10min warm-up around the neighborhood (driving at speeds below 30mph)

 

With it nice and warm, first thing I checked was exhaust temp using my cheap (harbor freight) IR temp gauge. See pic with my handwritten notes. The exhaust temps using my IR gun on our bare long tri-y headers (not shiny) are between 450 and 640.

 

Next I checked the spark. All wires are sending spark.

 

Then I checked vacuum. I was surprised to see it running at about 14-15 in-of-Hg. That's definitely low. I recall it being ~18 when I had it tuned earlier.

 

I took video of the vac gauge. I jacked into in via a T joint at the vac reservoir on the passenger wall of the engine compartment. left everything else in place. I've uploaded those to vimeo. You can watch and listen here: https://vimeo.com/109204811 and here: https://vimeo.com/109204810

 

Bottom line is vac reading is pretty steady maybe +/- 1 at idle, but no major swinging around of the needle. So maybe I have developed a vac leak, but I really rebuilt the carb and intake gaskets at the base of the carb - hard to believe I could have a leak there. Maybe an old hose somewhere - I guess I need to go hunt for it.

 

On throttle bump up, the vac drops 5, then settles back at 15 quickly and stably, then on decel, it goes up 5, but settles back at 15 quickly.

To me that doesn't seem like a burnt valve yet, or other major issue.

 

What does the hot exhaust mean? a cheap IR gauge? Or maybe I have the vacuum advanced too far to accommodate the vac being low? Will that make it run lean (hot?) The other pic attached shows the vac advnace housing is way over near the thermostat housing, so that would be evidence of too far advanced timing too possibly.

 

I didn't check the timing yet, so I need to go get that reading.

 

Thoughts?

 

Jay

IMG_3746.thumb.jpg.b162585ad1417fc11c5329737784cecf.jpg

IMG_3743.thumb.jpg.0bd02ccb16eb6ff29ad9499bfb25a9c8.jpg

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It sounds like ignition problems to me. While each plug may be getting fire, something is weak. Make sure all wires are well seated on the plugs then check the cap for cracks or carbon tracking. Look at the condition of the rotor button as well. Then check the timing and if you haven't found it after that start pulling plugs to see their condition.

 

Exhaust heat comparison is relative-by which I mean temperature variations are more important than actual temperatures if you shot each cylinder in the same spot. Your numbers suggest some weak ignition.

 

One little known fact is how often spark plugs are bad-if dropped or mishandled, they can look good, but have problems.

http://www.7173mustangs.com/gallery/1_01_07_15_8_53_18.png

 

"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!

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Well I do know that the points are probably old... I at one point replaced the condenser (believe it or not I traced some issues to a bad condenser). But I have not looked inside the cap yet.

 

It is interesting you say that since when I put the strobe timing light on each wire, I thought some cylinders on the passenger side caused a "dimmer light" than the cylinders on the right, but I chalked it up to maybe just lighting differences or my imagination. But, maybe it's possible if the spark was weaker.. the strobe was dimmer? do you think? If you go back and look at where I was checking the spark in the picture of my notes, I actually wrote "Brite" on the 2 cylinders on the drivers side near the firewall.... I erased it after I went back to the other side and rechecked, and I decided I was "probably imagining that"...

 

If that's the case, I probably have bad points, points gaps, bad condenser, a bad rotor or a bad cap, because I have a brand new flamethrower coil. Very small chance that has failed in the last 2K miles...

 

I have a spare points and condenser in the glove box (in case he gets stranded with burned points or something). I could just change that whole lot out pretty quickly. How do I set the gap on the points? Haven't done that is so very long. Do I need to re-time everything to get it to run when I change the points and condenser?

 

Jay


answering my own post here. Doing a little googling on gapping points. Looks like a gap of .017-.021 is where It needs to be when the dizzy is making the biggest gap in the points. Also said to grease the shaft between the new points and dizzy shaft, and readjust the timing after. I have a dwell tach for measuring dwell, but I've never used it (came with the car) If I get that figured out I need to fine tune the points to about 30 on the dwell meter.

 

Someone please howl if I've got some of that wrong.

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It has been decades since I messed with points, but that sounds about right. I have done points by turning the distributor to fully open, removing the old points, setting the new ones at proper gap in the same position and snugging them down. You may still have to fiddle a little, but not much.

 

If you kept your old coil, you might try it. New coil failures are pretty damn common.

 

I'd upgrade to something like the Pertronix II for an easy elimination of points and a stock look I've got a HEI and I hate how much room it takes up under the hood. Makes air cleaner fitment difficult

http://www.7173mustangs.com/gallery/1_01_07_15_8_53_18.png

 

"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!

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Sounds like an exhaust leak. Check the manifolds and donut gaskets for any black carbon build up. Usually exhaust leaks make ping or taping noises only under load. ( well except for really big leaks )

 

Had a Chebby with your same symptoms and turns out the manifold bolt head broke off at the very back of the head. Simple exhaust leak turned into this:

d635483414501dbc4ce9f2f4cf91c401.jpg

 

It can be overlooked so I thought I'd throw that idea out there.

 

 

Sent from my iPhone using Tapatalk

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I've had a cracked sparkplug cause that problem before but the exhaust leak senario sounds very plausible.

351w - Ford racing GT40X 178 cc aluminum heads - Ford racing(crane) 1.7 roller rockers - Comp Cams 280H magnum cam .544" / .544" lift - ARP hardware - hedman longtubes - magnaflow exhaust with X pipe - Duraspark - MSD digital 6al box - MSD TFI coil - optima red top battery - tuff stuff 140 amp alternator - weiand stealth intake  - edelbrock 1406 600 carb  - march pullies and brackets - Be cool fan controller - derale electric fan - FMX trans - motive 4.11 gears - traction lok - lakewood traction bars.                                            

 

 

 

 

 

 

 

 

 

 

 

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And MatrixX WINS the PRIZE! +1 coming on the rep!

 

I'll be damned. Whole left side of the tri-y headers were loose. about half of the bolts I could spin by hand.

Of course I didn't figure that out until I replaced and gapped the points. I just used .020 and it fired right up and ran well. I can set the dwell later.

 

So now it has a new condenser, points and rotor, but that never hurts. Who knows how old the other crap was.

 

damn these header systems. These guys put in a 1/4in thick flange, then they use 7/16in bolt heads which are em-poss-i-bull to get a wrench on (forget a socket!). It's not ALL about airflow and looks you know.. the crap has to be installable & stay in place!

 

Anyway, sure enough, it was exhaust leak. THANK YOU ALL for helping me thru this. It was quite satisfying to hear the engine hum properly again! That old feeling that keeps ya coming back!

 

Jay

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Glad I could help! More importantly it was a simple fix. My 302 had same issue but a little worse but all the manifold bolt I got a full turn by hand before I put the ratchet to them.

 

 

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