Backfiring inside intake? No power, bogs down...out of timing?

@Oddball - I used to own a '72 Cutlass Supreme as well! Loved that car! 350 Rocket, 4bbl, shift-kit, 3" exhaust. Traded my truck for it.
 
I have come to the point of really thinking twice about dumping any more money into this car.

I bought another compression tester and here are the results:

Cylinder pressures: C1=180, C2=180, C3=180, C4=30, C5=95, C6=60, C7=160, C8=130. Anything under 157 is bad. So 4, 5, 6 and 8 are no good, requiring both heads to be removed, remachined, revalved and two head gaskets. We are talking some serious cash required, way more than what it is worth.

So I am thinking about selling it and buying something else.

I really don't have the facilities or tools to repair it so garage would have to take on the job, which means paying out of the arse for labor on top of parts.
 
You didn't run through a big puddle just before all this started did you?
 
Water ingestion, hydro-lock, then bent connecting rods.


---- Sorry, didn't see page 2.
 
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Nope, didn't drive it through water. Whether I drove it through water or through a brick wall, the valves are bad and require more money than what it is worth. I am going to put it up for sale and find a :q:q:q:qbox to get around in for now. Gonna miss her though...
 
I still haven't given up on my baby yet...

I have another compression tester and will be doing another more thorough compression test. I didn't warm her up before running the last test because I didn't want to risk any more unnecessary damage. But I see that it is recommended that you get the engine to normal temperature before performing the test. They also say to remove all the spark plugs, although I just removed them one at a time the last time. I don't know if that makes any difference but I may as well follow the directions to a T.

She runs, she just backfires in the intake with a loss of power. So I guess that means that the timing chains are OK. (They seem OK as they are pretty snug like they should be and the tensioners look fine.)

I am wondering if maybe she dropped an intake valve or two... what is strange is that the previous compression test showed that Cyl 4 was "bad" and on the opposite side of the engine Cyl 5, 6 and 8 were "bad".

I have been reading here and there that these engines do not blow the head gaskets? I find that hard to believe, but I guess it is not impossible. There is no water in the oil and my antifreeze doesn't disappear abnormally.

I need to do another comp test first and foremost...
 
Having the other plugs out lets the starter turn the engine over at a faster rate. Still, that might make all the readings a little higher, but it shouldn't change the fact that some were much lower than others.

If you get more or less the same results again, here's another trick. Squirt a few (not too many, just a little) drops of oil into each low cylinder and repeat. If the problem is bad rings, this should temporarily bring the readings up. If not, its a valve/timing issue, which is what the back firing suggests.
 
Camshaft to Crankshaft position correlation fault,
camshaft sensor is not properly synchronized with the crankshaft sensor.

needs reteach programming, it's firing at the wrong time, thus the backfiring.

look into that perhaps ... I'm no mechanic
... but I had something like this on a 2001 GMC Jimmy.

Only problem is that it tore a few teeth off the gear on the distributor.
had to pull the distributor shaft up and re&re bottom gear that lines up with
the camshaft gear, this in turn meshes up and supports the correct cyclinder firing order.

Might not be same as Lincoln LS ... but I though I'd put it out there for you to look into.

PS: flush the crank oil several times, there is metal shavings in there now.
 
joegr said:
Unfortunately, that doesn't explain the compression readings, unless the new readings are better.
Click to expand...

when the misfiring cyclinders haven't reach top center,
how you expect above normal pressure readings in each count ?

is it blowing smoke out the tail pipes ?

if no, then not a compression problem, nor valve, nor rings.

... then again, I'm no Mechanic, so I could be very well wrong.

:: sorry
 
BigRigLS said:
when the misfiring cyclinders haven't reach top center,
how you expect above normal pressure readings in each count ?

is it blowing smoke out the tail pipes ?

if no, then not a compression problem, nor valve, nor rings.

... then again, I'm no Mechanic, so I could be very well wrong.

:: sorry
Click to expand...

When you do a compression test, there is no firing of the cylinders. You spin the starter with the spark plugs out. Ignition and fuel timing don't matter at all for the test. Valve timing, however, is a factor, but that's all mechanical on this one.
 
He would have to have a really bizarre combination of crankshaft sensor error and camshaft sensor error to not be getting any trouble codes about this.
 
even if the code don't show up, but all those banks are misfring, could
still be a correlation fault where the computer is "confused" as to when it
should be sending a "fire-that-cylinder" signal.

no doubt mine was a GMC but I remember all the problems let to the
misfiring being out of wack due to the correlation error.

it needed a re-teach procedure afterwards.


Sorry Joe, I'm done ... I'm no Mechanic and I am probably wrong.
 
HawleyTronics said:
... She runs, she just backfires in the intake with a loss of power ...
Click to expand...

the 'Puter is telling it to fire the cyclinders at the wrong time !!!

the compressed gasses are not in top center position before it gets a spark,
thus you blowing an explosion backwards into the intake.

not cool !!!

my money rides on the correlation error.
 
BigRigLS said:
the 'Puter is telling it to fire the cyclinders at the wrong time !!!

the compressed gasses are not in top center position before it gets a spark,
thus you blowing an explosion backwards into the intake.

not cool !!!

my money rides on the correlation error.
Click to expand...

Alternately, an intake valve is open at the wrong time. Only this fault would also explain the compression readings. Why do so many want to ignore the traditional diagnosis methods?

In any event, I guess we'll see in a day or three...
 
This is so exciting ... can't wait to hear the resolvement !
 
joegr said:
.... Why do so many want to ignore the traditional diagnosis methods?

In any event, I guess we'll see in a day or three...
Click to expand...

Big wall, brown sticky stuff in hand, good throwing arm.

The ICP sensor on my diesel once was a problem. Maybe he should change that on the LS too.
 
BTW, you are all awesome!

I haven't had the chance to get back into her yet, but plan on it in a day or so. (I have a major website job I need to get done that has priority over this right now.)

Keep your dialog going! A lot of great suggestions here and this is an example of Forums in their finest! People helping people. Love it.

I am going to perform a more thorough compression test (including squirting about a tablespoon of oil into each low-compression cylinder to see what that gives me for a reading.

From what I have gathered from this; whether the engine is all-computer controlled or not, part of it IS mechanical. The crankshaft turns two primary timing chains and in turn, those turn two secondary timing chains, and at the end of all those chains are four camshafts.

If it were a timing issue, whereas a chain jumped a couple of teeth, I would think that ALL of the cylinders on that side of the engine would suffer from low compression since the valves opening and closing would be out of sync from TDC? But, with it being various cylinders on both sides of the engine, I can only assume that I have some bad valves/seats/springs?

I guess the next step is just performing another compression test and take it from there...
 
I am haveing pretty much the same problem with my LS its a '00 with the 3.9, and it sounds like the exact same thing happening to mine. I just havent had the time or funds to break into her yet and take care of it. Let me know what you find out
 
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