Sudden Loss of Power

[martintravels]

While driving my newly purchased 1986 Trooper from California to Washington at highway speed (65 mph), I noticed a sudden "bogging down" of the engine.

Prior to this event, the engine seemed to have a fair amount of zip, and would idle at around 1000 rpm.

Now the idle is much lower, to the point where frequent gas pedal action is required to keep the engine from dying. Also the Trooper has nowhere near the zip or power it had before. It has a stock 4 cylinder engine. It is a California model, so it does have some different emmissions control.

Also during the pilgrimage north, the check engine light would periodically come on, especially under a load or at higher speeds.

The Trooper is currently in the shop, but I wanted to tap the resource base here to see if anybody had any ideas.

Thanks,

--Andy

[geeves]

Check engine light could be overheating or oil presure or ecu fault. Loss of power could be a blocked filter ie fuel or air Lack of idle suggests fuel filter. It could also be bad sparkplugs or just old age. What milage has it done and has it had any engine work. A compression test would be a good idea.

[martintravels]

OK, so the rig is back from the shop. They wanted over $1000 to do all the repairs, so I decided to do them myself. Step one was a compression test. All 4 cylinders had good compression: 161, 161, 180, 180.

The number three cylinder had a badly fouled oily plug. The compression was 180 on this cylinder. Close examination of the plug revealed that the gap was much wider than the other three cylinders. An examination of the engine block revealed that a heli-coil was at one point installed (aluminum block). The result of the heli coil installation makes the spark plug sit farther out of the combustion chamber than normal.

1) Is the oil fouling most likely a result of the gap set too large?
2) Does the heli-coil have any bearing on this whole situation?
3) Why is the compression so much higher in the number 3 and 4 cylinders
4) Please tell me that I don't need new rings and seals and possibly an engine rebuild.

Thanks in advance,

--Andy

[geeves]

Application Specification
Compression Ratio
I-Mark (1.5L) .............................................. 9.6:1
P’UP
1.9L ..................................................... 8.4:1
2.3L ..................................................... 8.3:1
Trooper II (2.3L) .......................................... 8.3:1
Compression Pressure
I-Mark ..................................... 178 psi (12.5 kg/cm  )
P’UP & Trooper II ............................ 171 psi (12 kg/cm  )
Minimum Compression Pressure
I-Mark ...................................... 125 psi (8.8 kg/cm  )
P’UP & Trooper II ........................... 120 psi (8.4 kg/cm  )
Maximum Variation Between Cylinders
I-Mark ........................................ 7 psi (0.6 kg/cm  )
P’UP & Trooper II ............................. 9 psi (0.6 kg/cm  )

Lack of compresion can be 3 things.
The good one is battery going flat but this normaly shows as no 4 being low. I dont think this is your problem
Either bad valves or bad rings. To test you can squirt a little new engine oil down each of the bad cylinders and test again. If its rings the presure will improve.
This comes back to milage and its maintenance history and other symptoms. Is it useing oil and what is the milage and has it ever had rings done in the past

[martintravels]

OK, thanks for the tip. I'll try doing another compression test with oil this time.

My neighbor who is a retired mechanic said that the variation in compresstion (particularly the last two cylinders being high) was due to carbon buildup on the chamber walls.

Does that sound like a possible explination?

Gap too big in spark plug = poor combustion = oil buildup = carbon buildup = smaller chamber = higher compression

Also, I have done a little research on what I thought was a helicoil installed in the number three (fouled plug) chamber. It turns out that this is not a helicoil but is in fact an "anti foul" device.

I am unclear on exactly how this helps; all it does is raise the spark plug farther out of the chamber. It also looks as if the diameter of the spark plug hole in the block has been decreased as well. Here a link about anti foulers (in this instance it is used for the O2 sensor, but the principle is the same for spark plugs)

forums.evolutionm.net/showthread.php?t=114931

But it is installed now, and I dare not try and remove it; there is no evidence of any oil leaks around this spark plug.

By the way, the 1986 Trooper II has about 150,000 miles on it. I don't know the vehicle's history, but by looking at the condition of the engine, I would assume that it is all original including the rings. I do know that the head was replaced about 15 years ago. I also know that there is a huge oil leak. The shop diagnosis used a UV dye to trace the leak, and concluded it was coming from the valve cover (one quart every 100 miles). As far as I know, that is the only oil leak. The oil only leaks when the engine is running.

Thanks again geeves for all your help in guiding me through this. It is much appreciated.

[geeves]

From what I can make out spark plugs work better if they are at the designed depth inside the cylinder Anything that changes this would lead to reduced performance. This thing is just a screw in spacer so should unscrew fairly easily so the plug returns to its normal location but no promises on this one.
It would be intersting to get a sample of whatever is on the piston tops as this will tell if theres oil in there. Useing a long bladed screwdriver gently take a single scrape of the piston top though the spark plug holes. If it comes out clean or dry gray or black its not too bad If its wet looking and oily to touch then its a good time to suspect oil is getting past your rings.
Before you can work out your oil use your going to have to fix the leak. A valve cover gasket is not going to cost much more than a quart of oil. If its loseing that much oil the whole underside of the car will be covered in oil

[martintravels]

The underside of the car is definately coated in a thick layer of oil. It is some nasty stuff.
Of course I am replacing the valve cover gasket (among other things).

I just don't understand how a cylinder with a 180 psi compression could have an oil fouled plug. With that much compression, could oil really be getting past the rings?

So, you think it would be ok to attempt to pull out that "anti foul" spacer? My gut says "don't mess with that thing." Maybe that is because I stripped out a sparkplug on my very first truck and it turned into a helicoil nightmare.

I'll be turning wrenches most of the day today, so I'll let you know what I find.

Thanks,
--Andy

[geeves]

From what the pic shows it just screws in the same as a spark plug. We have no way of knowing if any sealant etc has been used or if its torqued the same as a plug. Good luck on this one If it feels too tight then caution advised.
On the piston there are 2 compression rings and one oil ring If the compression rings are ok then compression is good. If the oil ring is worn or has lost tension then oil will get past it and the compression rings are not designed to stop oil so oil in the cylinder is very possible. This oil will help seal the compression rings causeing high compression and oil consumption

[martintravels]

I pulled the trigger and removed the "anti-foul" device. It came out just fine (no stripped threads). I gave the engine another compression test and this time I got these readings: 180, 180, 180, 200.

These are probably more accurate than the first because this time I had a helper with me, and I was able to observe the needle on the gauge as the engine was being cranked.

Anyway, I replaced the timing belt and adjusted the valves and gave the engine a tune up. It seems to run much smoother than before, and has a lot more zip also.

The jury is still out as to wether the oil leak has been fixed or not. The shop traced it with UV dye to the valve cover gasket. That has now been replaced. But it was using A LOT of oil (1 quart every 100 miles).

I'll check the plug in a week or two after driving it around to see if it is still fouled with oil. If it is, do you think that a bad oil ring on the number three piston cold cause that severe of an oil leak? If it could, where would that oil most likely leak from?

Also, I noticed that sometimes (not always) when I stomp on the gas pedal, the engine bogs down. The Trooper now has a new fuel filter. I also noticed that there seems to be a small exhaust leak somewhere (it occasionally backfires when slowing the engine RPM down). Coluld these problems be related?

Thanks again,

--Andy

[geeves]

With all the extra California emmissions stuff it could. My bet but not with very much money would be on either the O2 sensor or the exhaust gas recirculation with EGR being first choise. I had a Toyota that was leaking exhaust where the EGR joins the inlet manifold This caused similar running probs but nowhere near as bad

[martintravels]

I'vr a;ready replaced the O2 sensor to no avail. The next time I have some free time, I'll give the EGR a once over and report back. Thanks for all your help thus far; it is much appreciated!

--Andy