[i4abuygto]

Please help.
I have a 79 Trans Am that has a Cylinder with plenty of compression and spark but wont fire.
I recently purchased the car and the dip stick was wrong and I ran to much oil for about 50 miles and I am not sure if that had anything to do with this. Engine seems to have more of a shake to it at idle than when I purchased it. This could have been like this when I bought it - I don't know for sure.
When I pull the plug wire off the second cylinder from the front on the passenger side there is no difference on or off. I switched plugs thinking the plug might be fouled and no difference. And that plug runs fine in another cylinder. The dead Cylinder has plenty of compression with plug removed and engine running (only ran for a few seconds to check compression) with the plug out. If a valve was stuck I don't think I would have compression.
Any Ideas?
I can put a compression guage on it to check tomorrow- what should the compression be?

[JLMounce]

What’s that cylinder pumping? Have you tested the rest of the cylinders to verify the dead cylinder is close to the same compression?

What does the plug look like?

[STEELCITYFIREBIRD]

Ignition wire may arcing.
Wires may be on wrong, another cylinder may be dead also.
Was the plug clean, dirty/dark?
Same as others or different coloring, what color....or some pics?

Unclear How did you test compression, with it running? Run a cranking compression test.

If it is mechanical,I'd bet more toward a valve not opening than one stuck open.
Compression test will tell a lot.

[i4abuygto]

Thanks guys for responding so quickly.
The compression just seemed good with the engine running and plug out I could feel great pressure coming out as the piston came up. I know this isnt an exact measure but it had plenty of force coming out of the plug hole. I will test the cylinders for compression tomorrow as my tester is at my sons house. After further investigation it appears that the third cylinder passenger side also isnt firing. I tried switching the wires to no difference. I will check firing order and put new wires on tomorrow and check the compression. Plugs in the good cylinders are dry and a soft nice light brown color - the plug in the bad cylinder is black in color and wet.
As far as the other cylinders with the plug wire removal test seem to make a difference when the plug wire is removed and replaced. Even with using a good rubber coated plyers and vinyl grips I got good shocks with a few of the wires
The wire on the bad cylinders seem to have good spark and doesn't seem to arc across - I do have a few different plug wire that arcs through the boot and gives a good shock so I will be replacing the wires.

[i4abuygto]

Also, do I check compression with engine not running and crank with the starter a few revolutions. All plugs out when I test?

[Hikin Mike]

Originally Posted by i4abuygto

Also, do I check compression with engine not running and crank with the starter a few revolutions. All plugs out when I test?

Pull the coil wire (so it won't start) and crank it until your gauge quits climbing, usually a few seconds.

[getmygoat]

Yes, all plugs out during test - easier on starter/battery

[Sirrotica]

During the compression test the throttle should be blocked open to allow plenty of air through the carb.

Having worked on quite a few Olds 403s, and 350s (same basic engine) one problem you constantly run into is worn rocker arm stands on the middle cylinders because of oil coking from the heat crossover under the intake manifold. Pull the valve cover and see if the aluminum rocker stand is so worn out it's not allowing the valve to open. Someties they will break if the wear is severe. You can still have compression when the rocker arm is barely moving the valve due to rocker stand wear, but the cylinder won't fire.

["QUICK-SILVER"]

Swap the black wet plug with one of the good ones and see if that cylinder starts hitting. BPH (bad plugs happen)

Seen head gaskets blow between middle cylinders on 403's and create more shake than a single dead cylinder would. Fire from one cylinder blows through the gap lighting that cylinder early enough to try and kick back.

As Brad said, worn rockers and stands are common on these.

Clay

[i4abuygto]

Thanks all for your help - Bad news on compression check and I need additional advice.

Here is the compression specs and bad news
Passenger side front cylinder 132lbs middle two cylinders 0 lbs last cylinder closest to fire wall 69lbs

Driver side first three cylinders all around 125lbs last cylinder closest to fire wall 112lbs

So with no compression in middle two cylinders is it head work only? Can I just pull the head with the engine in or do I need to pull the engine to do the work?

Having worked on quite a few Olds 403s, and 350s (same basic engine) one problem you constantly run into is worn rocker arm stands on the middle cylinders because of oil coking from the heat crossover under the intake manifold. Pull the valve cover and see if the aluminum rocker stand is so worn out it's not allowing the valve to open. Someties they will break if the wear is severe. You can still have compression when the rocker arm is barely moving the valve due to rocker stand wear, but the cylinder won't fire.

Does this mean pulling the head and replacing with new head? I will pull the valve cover sometime this week to check this out.

[Schurkey]

When I had no compression on #3 and #5, the head gasket had failed.

It ran long enough thereafter to blowtorch a gouge between the two cylinders into the block, and between the combustion chambers on the head. Gouge in the head is so deep it's not salvageable, MAYBE I can cut the block for re-use. Maybe.

[Sirrotica]

Originally Posted by i4abuygto

Thanks all for your help - Bad news on compression check and I need additional advice.

Here is the compression specs and bad news
Passenger side front cylinder 132lbs middle two cylinders 0 lbs last cylinder closest to fire wall 69lbs

Driver side first three cylinders all around 125lbs last cylinder closest to fire wall 112lbs

So with no compression in middle two cylinders is it head work only? Can I just pull the head with the engine in or do I need to pull the engine to do the work?

Does this mean pulling the head and replacing with new head? I will pull the valve cover sometime this week to check this out.

Just remove the valve over to inspect the valve train pieces. If you find nothing out of the ordinary your next bit of detective work would be to run the engine with the valve cover removed to watch the valvetrain and verify all the valves are opening and closing properly. Olds engines don't usually wipe cam lobes, but I did have one that flattened one lobe once in my career. You want to verify that each valve is working as it should. Be forewarned that oil will run out with the valve cover removed and your driveway or garage floor will get some oil on it in all likelihood.

If you find no problems under the valve cover then it's probably time to remove the head. You can remove cylinder head in chassis, it's harder to do leaning over the fender than working on the engine on a stand. If you have a head gasket problem you'll want to do both sides in an older engine. That is assuming that the block and head aren't damaged from running it with a blown head gasket for an extended period of time, and you won't know that until you pull the head.

Depending on mileage, you might want a automotive machine shop test the head for cracks, and warpage. Then possibly surface the heads, grind the valves and replace the valve seals while they're off the engine. Most service techs have the cylinder heads reconditioned, as opposed to buying new. If you were going to convert the engine to aftermarket aluminum heads in search of better performance, this would be the time to entirely replace the old cast iron units.

Of course with the heads removed you'll want to inspect the condition of all the cylinders and pistons for signs of gouges or scratches. The #8 cylinder closest to the firewall is a concern at 69 lbs. You need to find out if there is a valve problem, or a ring problem in that cylinder. Usually 80 lbs is the minimum that a cylinder will fire at, and your lower than that.

That would be the order I would proceed in if I were doing the job, so this is my suggestion to insure that it goes back together with all the bases covered and will start and run properly after the work is completed.

Someone else may have other suggestions, but that would be my game plan. Good luck, and have fun...................

[geeteeohguy]

Originally Posted by Sirrotica

Just remove the valve over to inspect the valve train pieces. If you find nothing out of the ordinary your next bit of detective work would be to run the engine with the valve cover removed to watch the valvetrain and verify all the valves are opening and closing properly. Olds engines don't usually wipe cam lobes, but I did have one that flattened one lobe once in my career. You want to verify that each valve is working as it should. Be forewarned that oil will run out with the valve cover removed and your driveway or garage floor will get some oil on it in all likelihood.

If you find no problems under the valve cover then it's probably time to remove the head. You can remove cylinder head in chassis, it's harder to do leaning over the fender than working on the engine on a stand. If you have a head gasket problem you'll want to do both sides in an older engine. That is assuming that the block and head aren't damaged from running it with a blown head gasket for an extended period of time, and you won't know that until you pull the head.

Depending on mileage, you might want a automotive machine shop test the head for cracks, and warpage. Then possibly surface the heads, grind the valves and replace the valve seals while they're off the engine. Most service techs have the cylinder heads reconditioned, as opposed to buying new. If you were going to convert the engine to aftermarket aluminum heads in search of better performance, this would be the time to entirely replace the old cast iron units.

Of course with the heads removed you'll want to inspect the condition of all the cylinders and pistons for signs of gouges or scratches. The #8 cylinder closest to the firewall is a concern at 69 lbs. You need to find out if there is a valve problem, or a ring problem in that cylinder. Usually 80 lbs is the minimum that a cylinder will fire at, and your lower than that.

That would be the order I would proceed in if I were doing the job, so this is my suggestion to insure that it goes back together with all the bases covered and will start and run properly after the work is completed.

Someone else may have other suggestions, but that would be my game plan. Good luck, and have fun...................

Excellent advise and my experience with Olds engines as well when I worked on a lot of them 30-40 years ago. First order of business is to check the rocker stands/rocker arms.

[i4abuygto]

Thanks guys for the advice. I am disappointed with myself in trusting the dipstick - I kept adding oil until the dipstick read full and that was 8 quarts - stupid me thought that the previous owner just put on an oversized oil pan. I probably drove it 50 miles and white smoke behind me indicated bad news. Seemed to run okay though.

Would running to much oil have caused all of this or does it help in any premature diagnosis.

I will pull the valve cover and check the rocker stands/ rocker arms and hope for the best.

This is the original 403 to the car and the car has not seen a Minnesota winter and is in great shape with no rust. The previous owner had a performance rebuild on the original 403 and the engine had good power and ran strong - with a performance cam TH400 transmission. The internal specs are unknown - I figured about 360hp.
He told me less than 15,000 miles on the rebuild but the speedo was running fast and I trust nothing at this point except that the engine did run strong when I purchased it.

Question for all - I have a rebuilt 68 Xh 400 Grand prix engine that I had built for my 67 GTO and has never been run. I decided to rebuild the original WS 400 for the GTO so I have this extra engine with a Muncie M21 transmission available.
First do you recommend just swapping motors and shelving this original 403 if it needs a head gasket(s).
Second - do you recommend converting to a 4 speed if I do swap motors. - I would need clutch linkage, shifter and related parts to convert. Or, do I just swap the engine and use the TH400 automatic and will it bolt up to the Pontiac, late 60s 400 block.
Let me know your thoughts.
Thanks all, for your help

[i4abuygto]

Additional information is the 400 Pontiac would need carburetor (could use the existing 750 Holley). 400 has the original cast iron intake with no carb. It would also need distributor and ignition, plugs wires and exhaust manifolds or headers. Would the engine swap with 400 headers bolt up to the existing header flange exhaust system?

[Schurkey]

While I like a Pontiac engine in a Pontiac car...swapping from the Olds is going to be a fair amount of work.

Do you have all the brackets--alternator, AC, PS, and the pulleys to go with them? None of the Olds accessory stuff is going to work on the Pontiac engine.

Engine mounts? Both sides, both halves--four pieces. One pair bolts to the frame, one pair bolts to the engine.

No promises Pontiac headers will bolt to your existing exhaust without some rework. You might get lucky.

Is your steering column interconnected with the shift lever, so that it locks and unlocks, and you can get the key out? You'll need the manual trans back-drive assembly so that it still works with a manual trans.

Yes, the transmission and torque converter should bolt right up to the Pontiac engine/flexplate. I'd keep the automatic rather than swap to a manual.

[i4abuygto]

Schurkey,
Thank you for your advice.
The automatic in the car now has an aftermarket slapstick shifter so the steering neutral safety is disconnected - the column collar has to be rotated to left stop for the key to be removed and operate correctly.
I have several sets of brackets around but I would have to verify or acquire the brackets for AC, Power Steering and Alternator (AC is currently disabled anyway).
Is it easier / less expensive to do the headwork/gasket work or swap engines.

I will pull the valve cover when I get a chance and run the engine to find out what is going on and I will followup with more information.
Thank you.

[i4abuygto]

Also, If I were to swap to the Pontiac 400, I would be using the Holley 750 that is currently the carburation for the 403 olds - would the stock cast iron intake manifold or an aftermarket aluminum intake manifold work better for the shaker scoop.

["QUICK-SILVER"]

The 68 400 will need adapters to go in the 79 bird.
Like this..
https://butlerperformance.com/i-2462...tegory:1393557

This is suppose to work with the clam shell frame mounts the car has now.
Frame mounts and their location was the same for the 403 and 400 in 79.

Need to see whats up with the 403
I've never seen worn out rockers cause complete compression loss. Should be sucking and spitting if valves are staying shut.
Clay

[Schurkey]

Originally Posted by i4abuygto

Is it easier / less expensive to do the headwork/gasket work or swap engines.

WAY easier, almost certainly less expensive, to keep the 403.

Doing the Pontiac engine properly will be either a headache, or a major pain in the ass, depending on what parts you already own; and how tough (and expensive) it might be to locate what you don't have.

Originally Posted by i4abuygto

I will pull the valve cover when I get a chance and run the engine to find out what is going on and I will followup with more information.

Good plan.