Engine compression test

[kris]

Trying to get a car that will last about a year. found a cheap $400 94 Nissan sentra. Have not bought it yet. It has a rough idle and sometimes stalls. when driving i can feel the engine move/maybe a miss. no check engine light is on. car has 190k. car has 1/2 tank of 6 month old gas used iso heat and added 1 gallon of new gas.

I put in new plugs, rotor, cap, wires. Done a fuel pressure test, it was right on the money with regulator off and hooked up 36/43 psi. Sparks on all 4 cylinders.

Now the engine compression test. Note car has 190k oil is old and is full synthetic. I ran the car for 3 mins. then test all ports with out adding oil. within a second or two this are the results i got:
#1 155 psi
#2 150 psi
#3 160 psi
#4 155 psi

spec is standard 199 psi, minimum 171 psi +- 14 psi

Is the engine sound? will old full synthetic drop psi?
does it seem like good buy if i can fix the idle?

thanks
edit: adjust lose throttle linkage, sometime hard start have to feather the pedal.

Topic

[college man]

I have a different spec on the compression for the 4 cyl. SR motor.
standard 178 psi minimum 149 psi 14 psi between cylinders. your border line
on # 2 but still there.

[Stephen Bowen]

Being within spec is only 1/2 of the issue with a compression test. You really want to see numbers that are fairly close to each other. Your numbers are–by spec– border line as mentioned. But in the larger picture? They show fairly even ‘wear’ within the engine. It’s not an exact science. But if you have everything within about 10% of each other? I’d call it decent.

6 month old gas—that’s going to be an issue until it all gets burned out. It’s not going to ever run decent until it gets some fresh gas at 100%. I would be more concerned about changing out the fuel filter as well. You can have all the pressure in the world–but have a clogged up filter? You’ll have pressure for general testing. But it’s also about volume.

Good luck and keep us posted!

S-

[Austin]

Do a leak down. Then again for $400 who really cares. It has compression, drive it till those rings burn up and don’t expect much more.

[Tom]

Many Nissan’s from that era use a Mass Air Flow sensor, which is prone to failing, and will cause all sorts of issues with idle, and driving, even stalling out. I used to look for them cheap on Ebay, and always keep an extra one on hand so when one crapped out on me, I had another to swap in.

[kris]

its a 1.6L xe i got those specs from alldata. Its been know to be wrong. I will go check the shop man. I know the people and they got a new car. they drove it and had no problem until they parked it aside from cv joint thats going out. I trust them.

I think its just the gas.

had an idea to day at work.:
Can i unhook the fuel filter and put hose in jug then empty the gas by turning the key? disabling the starter and spark for safety. Will this hurt the fuel pump?

thanks
edit: alldata has it listed as psi/rpm and max is 199/1350 min is 171/1350. I dont understand this but when i checked the shop man college man was right, thank you for pointing this out.

[Lorrin Barth]

As for pumping out the gas that won’t work. The pump shuts off after one or two seconds if the engine is not running.

[kris]

quick rant: I just hate Nissan wire diagrams and connector views for there testing info.
Issue fixed:
cleaned MAF, IACV, adjusted TPS. It ran better but still stalled. found the IACV had two connectors, one was not hooked up. Fixed!

thanks guys.

on a side not anyone know how to explain the way alldata worded the compression specs?
psi/rpm and max is 199/1350 min is 171/1350. vs standard 178 psi minimum 149 psi 14 psi between cylinders.

[Author]

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