I have a 1981 Toyota Pickup 2.4L gas engine. I'm guessing it has a little over 200,000 miles on it, but it may be 300k. I'm guessing because the odometer only goes to 99,999. Anyways, the truck is performing a little less than what I think to be optimal. I get pretty good mileage, almost 20mi/gal, but every now and then when driving it will die, especially during hard braking. I have done all the normal tune-up stuff a few times(carb clean, spark plugs, timing adjust, idle and fast idle adjust, air filter, oil change, valve clearances were almost perfect) but it seems to make little difference. The rear main seal was replaced with the transmission recently. I have also replaced the valve cover gasket. Another symptom I have is the smell of gasoline at the exhaust pipe and also spits out a bit of oil for a few minutes after starting up, especially on cold days.

The spark plugs look good at the ground strap/electrode, but down in the hard to see inner parts, it is very black and even smells of unburned fuel, but looks like burned oil. Just overall black, and not clean as if I were getting complete combustion.

So I decided to run a compression test the other day.

All four cylinders reached 175 psi, but this took about 10 revs.

I then added a few squirts of oil through the spark plug hole and retested and got about 185psi on all cylinders, but this took about 12 revs.

When looking at the gauge, it went approxamately 45-70-90-125 psi, then slowly to 165/175psi over the next six revs. This is the part that I'm looking to analyze.

Is this too slow of a compression build?

I'm considering replacing the rings, but don't want to if I don't have to. (If it ain't broke don't fix it)

Thanks for the help!

 

When doing a compression test, above all else you want compression to be within 10% of each other on all cylinders, and it sounds like you've got that. Don't worry about what the actual number is, as there are many factors that can affect readings so you can't directly compare to what someone else got for results and make any meaningful conclusions.

The fact the wet test yeilded minimal increase, again even across all cylinders, tells me your rings are fine.

Does the engine consume oil? From what you've described, I'd look at the carb as the culprit. That being said, I'm more of a fuel injection guy, and my experience with carbs is limited to snowmobiles. I'm basing this on the engine dieing, especially under hard braking explanation of the problem. Carbs are not immune to tilt changes the same way EFI is, and if you have power brakes, they would be vacuum powered from the carb/intake manifold area which could be contributing.

 

I guess my biggest concern with the compression test was that it took so many strokes for the compression to build up. My repair manual says to turn over the engine about 4 times and that the compression should rise quickly and evenly.

I wouldn't say my engine was quick, or even. It got to 125 psi quick and even, but then took a while to get to 175 psi.

I also found this site for 22r carb info. It may be helpful to some others.
http://www.bluebassdesign.com/boonin/carb_faq/

Thanks

 

I usually crank the engine 6-8 times when doing a compression test, the number of cranks isn't so important, just make sure you give each cylinder the same number of turns, and then compare the results. Some other compressino test tips:
-compression test an engine when warm, as the metal will all have expanded
-pull the fuel pump fuse (on an EFI vehicle)
-hold the TB open when cranking

As for how long it took your engine to reach max compression at the gauge, I was under the impression 22R's didn't do anything quickly, lol!

 

haha yeah yeah

Slow and Steady Baby! just how I like it

yep, engine was warm and TB was wide open and I did crank all cylinders the same number of times. Maybe this is just the way my truck has always been and I'm just now realizing it? I know it's no race car, but it used to be "peppier"

 

I noticed you changed the plugs, but not the plug wires/coil/ignitor/distributor/whatever you have for ignition. Do you have strong spark? Maybe the fuel filter is due for replacement?

 

Sorry, didn't mention that. The wires, dist cap, rotor, and ignition coil were replaced a few months ago with a tune up.

And the fuel filter was also replaced, as well as the gas tank cap.

I've rechecked the resistance for the plug wires and they are within spec.

How do I test for "strong spark"?

 

Checking for "strong spark" isn't anything that's really measurable per se, I would just pull the plugs and fit them to the plug wires outside the engine, and crank it over watching for spark across the electrodes to make sure everything is good.