Sudden Power Loss (opinions)

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archerandethansdad

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I was doing a brake stand in my 68 barracuda 318 4 barrel with 200k plus miles. While smoking an old set of tires the sound of the motor changed and the power loss was instant. I went home and checked the compression and although slightly lower then factory 125-135 across the board I didn't notice any other issues. It has been starting to run warmer then before. Now on a 15-20 mile ride it will go up to 200 when it was staying at 180. I thought head gasket but no water in the oil or exhaust in the coolant i used an coolant tester. Oil pressure cold 65-70 once warmed up and at 200 or so at idle 30 but while driving back up to 60.
 
Point type ignition? If so, check the dwell. Should be 28-32 degrees.
 
If you suspect timming chain, you could pull the fuel pump and get a endoscope camera in there and see if you have nylon teeth. Lost a Ford 289 at the magic number of 160,000 to the lame nylon teeth.

IMHO if not nylon teeth probably did not jump a tooth

Just a thought. Maybe you didn't loose power but you damaged your rear brakes and they are really dragging now?

Not sure why people think that (unless they have a line lock) their rear brakes aren't going to get toasted, overcoming all the friction needed to keep the car in one place.
 
Timing chain usually goes on deceleration, it has every time for me.
Usually goes teeth and not tooth and dont run no more..but it could possibly only went a tooth on a nylon gear, ... if it did jump...just check the timing...cause it also moved...they are connected by the intermediate shaft gear...which is another variable...the gear 'stock' isnt pinned....and can spin loose from the Intermediate shaft itself leaving the oil pump/distributor on their own...or let's jet say...behind..as the valve timing says audios

Check the timing.
 
Timing is good. No nylon teeth all steel. Was not timing. Base timing is set at 14 advanced. It is a converted HEI. No points.
 
archerandethansdad said:
Timing is good. No nylon teeth all steel. Was not timing. Base timing is set at 14 advanced. It is a converted HEI. No points.
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Then the timing chain jumping idea is out.

Maybe you tapped a valve floating it at tire frying rpms and slightly bent it.

Cranking will show almost norm but a leak down test will make it obvious.
 
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Any Noise when This happened?

If it will fire get a Laser temp gun and check each exhaust port!
 
Pop the valve covers and check the rockers and springs.
It's possible a pushrod popped through a rocker or a broken valve spring .
 
Maybe something broke loose in a muffler and is partially blocking the exhaust? Sound and power would both change.
 
momentarily piston(s) seizure

bad piston.jpg
 
Mopar Sam said:
Maybe something broke loose in a muffler and is partially blocking the exhaust? Sound and power would both change.
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I edited that out . I assume he had some sort of welded muffler. One cyl not firing anymore will change the sound and kill off 25hp in a hot sec too.
Maybe carbon broke lose from the cross over and hung and burnt a valve.
Maybe a flapper in the manifolds

It's a cliffhanger
 
I like the brake idea. I didn't think of that. If it was a bent seal wouldn't that show on compression test? I get adequate pressure on all cylinders except two are about 10psi higher then the others. I have a bore scope so I could check the cylinder walls for scarring in the case of the piston seizure. It's straight piped to two magnaflow mufflers. I don't believe there is any blockage i get strong exhaust flow from the tailpipes. I have a laser thermometer but i don't have headers just stock manifolds so i don't think i'll get an accurate read of the exhaust temps would I since they all dump into the manifold.
 
Dana67Dart said:
If you suspect timming chain, you could pull the fuel pump and get a endoscope camera in there and see if you have nylon teeth. Lost a Ford 289 at the magic number of 160,000 to the lame nylon teeth.

IMHO if not nylon teeth probably did not jump a tooth

Just a thought. Maybe you didn't loose power but you damaged your rear brakes and they are really dragging now?

Not sure why people think that (unless they have a line lock) their rear brakes aren't going to get toasted, overcoming all the friction needed to keep the car in one place.
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My Bro nailed a 351 modified ( I think, he's a Ford Man, life-long, but helped wrench on almost all my Mopars, over the years..) ripped off some nylon...trashed that one
 
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Well, SOMETHING happened. Have you actually put a timing light ON IT since this happened? You can also rule out a lot with a compression test. Doesn't take long.
 
RustyRatRod said:
Well, SOMETHING happened. Have you actually put a timing light ON IT since this happened? You can also rule out a lot with a compression test. Doesn't take long.
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I totally agree. I'm just trying to nail down something i may not have looked at or considered already. I do get a little fuel vapor out of the drivers side tail pipe and excess condensation but it isn't coolant has no smell at all just condesation.
 
archerandethansdad said:
. I have a laser thermometer but i don't have headers just stock manifolds so i don't think i'll get an accurate read of the exhaust temps would I since they all dump into the manifold
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I have checked my stock 273 and I get 8 distinct temperature signatures. Oddly the 2 front most cylinders (1 and 2) typically read 50 deg hotter than the rest like 425 vs 375. ( I'm going on memory so don't quote me on the actual numbers)

As for compression I did a test a few years ago (cold and dry) and barely got 110 on most cyl and 125 on 1 cyl. 150,000 on the last rebuild.
 
Dana67Dart said:
I have checked my stock 273 and I get 8 distinct temperature signatures. Oddly the 2 front most cylinders (1 and 2) typically read 50 deg hotter than the rest like 425 vs 375. ( I'm going on memory so don't quote me on the actual numbers)

As for compression I did a test a few years ago (cold and dry) and barely got 110 on most cyl and 125 on 1 cyl. 150,000 on the last rebuild.
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Good to know. I will take a look and see what i get. I will look at picking up a leak down tester and see what i get from there as well.
 
Compression test will hide the issue I had! Punched Exhaust Rocker and missing intake pushrod on #1. Had full compression on all cylinders. Just this year!

If you have ever been to a NASCAR race and a car had a Valve train issue it sounds like something is trying to blow out ,but flat and can only push by the rings! This is what my 383 sounded like afterwards.

Use you laser Temp gun to verify. I have stock Cast iron exhaust! Point the laser near the head at exhaust exit!

#1 for me was 75 Degrees! The rest about 450 to 480!
 
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A couple of new Melling Rockers and a set of new pushrods. 900+ miles later and all good!

I believe the issue was due to an incorrect rocker shaft bolt above the #1. It is clearly longer and was bottomed. The shaft may have been lifting a tad.

You have some great tools to narrow the issue, use them!

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archerandethansdad said:
It has been starting to run warmer then before. Now on a 15-20 mile ride it will go up to 200 when it was staying at 180
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Great clue; kudus to you for noticing this.
Check your mechanical advance springs.
If the ignition timing fails to advance, two or three things will happen;
1) engine will lose power, and
2) water temp will go up. This is for two reasons;
a) because with the loss of power, you now have to press the gas-pedal harder, to achieve the same work, and
b) because the heat of combustion is carried lower in the cylinder, transferring heat to the water longer and also firing it into the exhaust manifolds, meaning it has to go thru the exhaust ports which have very-close proximity.
BUT
if the flyweights freeze in the full advanced position then you have different problems, namely;
1) a higher than normal idle-speed
2) difficult hot cranking
3) probably mid-rpm detonation
4) possibly a touchy gas pedal
5) runs just fine at WOT after ~3600rpm.
6) but probably NOT extra heating.

But broken advance springs, or frozen timing are not the ONLY things that can cause a sudden power loss together with an abnormal heat signature...... How's your transmission behaving? lol.

BTW
the last Line-Loc I bought was about $50............... but to be fair, that was 1971, lol.
 
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AJ/FormS said:
Great clue; kudus to you for noticing this.
Check your mechanical advance springs.
If the ignition timing fails to advance, two or three things will happen;
1) engine will lose power, and
2) water temp will go up. This is for two reasons;
a) because with the loss of power, you now have to press the gas-pedal harder, to achieve the same work, and
b) because the heat of combustion is carried lower in the cylinder, transferring heat to the water longer and also firing it into the exhaust manifolds, meaning it has to go thru the exhaust ports which have very-close proximity.
BUT
if the flyweights freeze in the full advanced position then you have different problems, namely;
1) a higher than normal idle-speed
2) difficult hot cranking
3) probably mid-rpm detonation
4) possibly a touchy gas pedal
5) runs just fine at WOT after ~3600rpm.
6) but probably NOT extra heating.

But broken advance springs, or frozen timing are not the ONLY things that can cause a sudden power loss together with an abnormal heat signature...... How's your transmission behaving? lol.

BTW
the last Line-Loc I bought was about $50............... but to be fair, that was 1971, lol.
Click to expand...


Trans is great was rebuilt with less then 5K on it. Timing is not stuck i just had the light on it the other day and i can watch it advance as i rev.
 
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