No Power from 3.1L Engine

[tomj76]

I have a '90 Celebrity wagon, 3.1L engine, 200k mi.

It starts and idles fine. It seems to misfire a little bit at idle, just based on a little bit of shaking of the engine.

When I open the throttle with the car in park, you can hear poping on the intake. After intially increasing, the RPMs peak and go down. If you remove the air hose from the throttle body, it's very loud.

On the highway, there is no power on acceleration, it also misfires and shudders under load when maintaining speed.

I replaced, cleaned or checked everything I could think of, short of disassembling the engine itself.

-Plugs (replaced)
-Wires (replaced)
-Fuel filter (replaced)
-fuel pump (checked)
-injectors (cleaned, inspected, checked for leaks, sprayed while off the engine)
-air filter (replaced)
-O2 sensor (replaced)
-Catalytic Converter (checked for obstruction, ran car with exhaust discconeected)
-Compression (all cylinders OK per Chevy service manual information)
-Timing (looked OK)
-EGR (cleaned)
-IAC (cleaned)
-MAP (checked output)

I don't hear valve taping when the engine is running, which leads me to believe the lifters, push rods, rocker arms & valves are OK.

I do hear an intermittent "knock" sound from the engine that started one time the vehicle was driven (10-15 mi) after this problem began to occur.

No oil in the coolant, no coolant in the oil.

Any suggestions?

[jdl]

Did you use a vacuum gage on it. Take a reading at idle and 2500 rpms, if the bottom drops out of the gage at the higher rpms, you might have an exhaust restriction. Just a thought.

[maxwedge]

Popping back thru the intake usually indicates a valve train issue ,pull the valve covers check the rockers and look at possible cam lobe failures on the exhaust in particular.

[tomj76]

Thanks. The Vacuum gauge check was next. I don't have one already, so I'm planning on purchasing one this weekend and doing some diagnosis with that.

Thanks for the suggestion on the valve train. I've had this suspicision that it could be a lifter, push rod, rocker arm, or valve spring. However, why would exhaust valve problems be heard on the intake?

[tomj76]

I tested it with a vacuum gauge, and saw slightly low vacuum (15 - 16 inches), with 2 inches variations.

I decided a valve was either sticking or not opening.

I tried a bottle of 'Gunk Valve Medic', no change.

Removed the valve covers and the intake manifold. I noticed A LOT of carbon 'gunk' around the #5 exhaust valve lifter, and in the tube for the rod. I checked each lifter and turned the crank to measure the lobe lift.

The #5 exhaust lobe is non-existant, and the lifter is severly worn (at the lobe contact point)...

I need to replace the camshaft, or junk the car.

Any suggestions on camshafts? I checked Advanced Auto and Autozone.

Tom

[jdl]

Originally Posted by tomj76

Thanks. The Vacuum gauge check was next. I don't have one already, so I'm planning on purchasing one this weekend and doing some diagnosis with that.

Thanks for the suggestion on the valve train. I've had this suspicision that it could be a lifter, push rod, rocker arm, or valve spring. However, why would exhaust valve problems be heard on the intake?

If the exhaust valve is leaking, with the piston on the intake stroke, you'll probably have a cylinder full of hot exhaust gas and the intake valve is open on the intake stroke.

[tomj76]

Thanks. I see what you're saying. I think in my case the exhaust valve was not opening at all (due to the missing lobe on the camshaft) and, as you mentioned, the pop I heard on the intake was any compressed gas in the cylinder getting evacuated when the intake was opened.

Still, I guess that even though there is no "thru path" for intake air to flow through the engine (in the intake, out the exhaust), there must be enough leakage in the system to draw some O2 and fuel into the piston. What does get combusted caused the pop sound, what was left unburned must have flowed into the other cylinders, causing the fouling of the spark plugs.

Now for the camshaft. I know a full rebuild would be recommended, but I'm considering just doing the camshaft and lifters to get another couple of years from this. I can get a Sealed Power kit for under $200. Any opinions on this approach?

[rhandwor]

Have you ever had had a leaking intake manifold which allowed anti freeze to get into the oil. This will determine how long you can get by with a new camshaft. Make sure the cam bearings are good when you change the cam.
Get the heads pressure tested when you do a valve job.
If you had anti freeze in the oil get a rebuilt short block which is fairly easy to change with the heads off.

[tomj76]

No, I've never had (to my knowledge) a problem with antifreeze in the oil. Only one lobe of the camshaft was bad. When I removed it, I measured the other lobes, and they looked within spec. The bearing journals also looked good.

I didn't remove the heads, but I compression tested each cylinder before I started. They were within spec, although the entire 1-3-5 bank was lower than the other. The wet numbers were about equally better for both banks, so I think the difference is due to the valves. When I removed the intake manifold, I noticed a large amount of "sludge" around the #5 push rods and in the oil channels formed in the top of the block. The sludge was a dark hardened material, somewhat like tar, but less fluid. It seemed to be blocking the proper flow of oil to the top of the cam lobe. I wonder if this is what caused the lobe failure?

Even if it did cause the failure of the cam, I'm not clear on what would cause the accumulation of the sludge. When I first started looking at this, I found that the #3, & #5 plugs were several turns from being fully seated. I'm guessing that this allowed the head to run a little hotter, promoting the formation of varnish from the oil. I could be grasping at straws with that explaination.

I realize I haven't been as thorough as I should have been, but I wanted to leave anything alone that was functioning OK, which seems to be the case for the heads, valves, and main bearings.

I'm still in the process of completing this repair, I still have the engine on the stand. The new cam & lifters are in, as are the push rods and rockers. I've re-installed the front cover and the harmonic balancer, but I have not yet put the intake manifold or oil pan back on. Any advice would be welcomed.

[rhandwor]

Due your best to make sure all oil passages are clean. Blow through with air and use brake clean and a nozzle to flush out the passages. You might even need some small wire. If it doesn't have a distributor don't install the plugs. Turn the motor over with the starter until you have oil pressure. Then finish up and start it. Change oil every 3000 miles and you should be ok. Bearings that are starved for oil will be black. Be especially careful when checking oil passages for these bearings.
Since it is on a stand I would remove the pan and clean the strainer for the oil pump. I would also pull a few bearing caps and inspect them while the pan is off. Its much easier to change a bearing on the stand than in the car. This is a little more labor but will pay big benefits if the strainer is bad or a bearing is going bad.

[tomj76]

Thanks for the input. I have already removed, disassembled, cleaned, and reinstalled the oil pump, because I was concerned there could have been some material trapped in it. I cleaned the oil passages with Seafoam and kerosene before installing the new camshaft. The cam bearings looked OK to me. I will check one or two of the main bearings as a precaution.

[tomj76]

Thanks to everyone who advised. I've finished the rebuild. I ended up replacing both crankshaft seals for good measure. The main bearings checked OK.

The car runs good, not great. It has a little random stumble at idle and while maintaining speed on a slight grade. My guess is that some of the cylinder heads have excess carbon deposits due to the flow of partially burned fuel from the cylinder with the nonworking exhaust valve. I'm hoping that will clear up with a few tanks of fuel as the carbon is consumed in normal combustion conditions (wishful thinking perhaps?).

[tomj76]

Random stumble was due to the spark plug wires.

In the process of diagnosis I stripped out one (#3) spark plug. I removed the cylinder head to retap and put in the insert. The insert I used was purchased at Autozone. I tried using red RTV, as recommended, but this didn't hold securely, so I used a combination of RTV and JB Weld epoxy. This seems to be working very well.

Although people say you can do this without taking off the head, I don't believe it's possible. There are too many metal chips from retaping the plug and it's too hard to work between the firewall and the engine. Besides, I took this opportunity to clean all the carbon from the combustion chambers and valve stems. I also put new seals on the valve stems to hopefully eliminate all oil consuption not due to worn pistion rings.

No more stumbles, no more misfires... runs like a top.