low compression #2 cylinder

[jgt]

after a p0302 code, my mechanic friend said probable bad valve #2. after low reading in that cylinder only. He only did a compression test (not a leak down) and I've spent way too much money on this old truck and wonder if there's an additive we can try before tearing apart the engine.

new: wires, plugs, radiator,shocks,pcv, (2) vac hoses, intake manifold gaskets, oil change, fuel/air filter, brakes/rotors...$800 invested this month and can't spend any more.

All the spark plugs were dry and looked ok when we changed them. The truck ran perfectly fine until a couple weeks ago. starts up good, runs fair for about 10 minutes then rough and CEL flashing with P0302 code.

I read about ranger's "recessed valve" or possible sticky valve? Not a DIY home mechanic at this level, so I'd have to pay out to have this done. Truck has 146,000 miles and runs great otherwise and had timing belt/water pump, clutch, front end work done at 100,000. Seafoam or ?? thanks

 

[RonD]

No, there is no additive for low compression, it is a mechanical issue involving larger parts.

Did mechanic give you the exact compression reading for each cylinder, you should have that if he charged you for it.

The compression numbers don't matter as much as numbers but as a relationship to each other.
170-160-165-165

150-145-155-150

135-130-140-140

These are all fine and normal readings, #2 is lower but that wouldn't be the reason for a mis-fire.

150-110-145-150
This would be a concern for #2

And low compression is low compression all the time, the cold and warm running differences you describe shouldn't matter

1999 will use sequential fuel injection, this means each injector will effect it's cylinder like a bad spark plug would.
When engine is cold the computer runs the injectors rich, when engine warms up the computer switches to a leaner mix for best MPG.
This is when engine starts to miss
So you could have a partially blocked injector or a dirty pintle(injector tip).
With richer fuel mix the cylinder is getting enough fuel to fire, when fuel is lowered cylinder gets starved.

The pintle sprays the fuel into the air stream being pulled into the cylinder, if it gets dirty the fuel drips so doesn't get fully mixed with the air, this creates an even leaner mix that can mis-fire.

Run some Seafoam in the fuel tank, this can clean out injectors and pintles.

Fuel injectors make a tick, tick, tick sound when opening and closing.
With engine idling put a small hose on an injector and upto your ear, listen for the rhythm of the injector, see if #2 sounds different in rhythm or tone

 

[jgt]

injectors were tested with a tool, all good. I will get numbers and more details from him this weekend, but I think it was around 100 and the others 150, not sure though.

Found a 1998 2.5 ranger donor truck with 125k. If mine is a manual and he's an automatic, what do I need to change/do to replace my motor with his? Wiring harness differences? Anything else to look out for if I go that route? thanks

 

[RonD]

You are keeping your trans so that won't matter.

'98 will swap nicely, wiring will be the same, but even if it isn't you can just use the long block from the '98(block and head) and bolt all your '99 stuff to it .

150psi on three and 100psi on one would be a 33% difference so yes that would be why it is mis-firing on that cylinder.

It is most likely a valve issue, so just rebuilding or getting a new head(exchange) might be less expensive and time consuming.
A Leak-down test can tell if it is rings or valves.
2.3l heads above '95 and 2.5l heads are the same, the 2.5l engine has a longer stroke(piston travel) so .2l larger displacement

 

[NIPs]

On my 2.5 I had 180psi, 176, 177, and 146 abt 3 weeks later my engine took a dump

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[jgt]

compression numbers

he told me the numbers were about: 130-45-130-130
and that he thinks its a valve. What's the best way to get it back on the road cheaply? I can get an engine locally used for a couple hundred, but they want me to tow and discard of it. Or $375 for valve job is the estimate. (for the machine guy doing the spring/valves resurfacing) then probably another couple hundred for my guy for labor.

 

[RonD]

Used engine is a "pig in a poke", a mystery to you and in most cases the seller,.
If you were doing the wrench work yourself then it might be worth the risk, but if you are paying someone to swap engines, then even if the seller guaranties the used engine for 6 months, YOU still have to pay for another swap if it goes bad.

At 146,000 on the engine I would probably do the valve job.
A leak down test on #2 would you tell you if it is valves or rings for sure.

 

[tomw]

All the spark plugs were dry and looked ok when we changed them. The truck ran perfectly fine until a couple weeks ago. starts up good, runs fair for about 10 minutes then rough and CEL flashing with P0302 code.
****
Valves don't go bad enough in a couple weeks to go to 45psi on test. I would pull the cam cover and see if the follower & hydraulic lifter are 'normal'. The lifter holds up one end of the follower, and should allow the valve at the other end to close when the cam lobe moves. If the lifter were jammed or stuck, it would hold the valve open a bit, allowing or causing low compression. Unless you had a hard run, low on coolant, or some other malady, I would be surprised it could get that bad so quickly. Worth looking at.
You should be able to collapse the lifter and get clearance between the backside of the cam lobe and the follower by pressing on the lifter end firmly for a few minutes (or less). Unless you want to rustproof your underhood, do not start the engine with the cam cover removed..
tom

 

[jgt]

ok

will have my guy look at it, thanks. btw, it was low on coolant, and we replaced the radiator cuz it had a leak. but never really overheated. Husband said he'd just add water/coolant and never saw it overheat.

All the spark plugs were dry and looked ok when we changed them. The truck ran perfectly fine until a couple weeks ago. starts up good, runs fair for about 10 minutes then rough and CEL flashing with P0302 code.
****
Valves don't go bad enough in a couple weeks to go to 45psi on test. I would pull the cam cover and see if the follower & hydraulic lifter are 'normal'. The lifter holds up one end of the follower, and should allow the valve at the other end to close when the cam lobe moves. If the lifter were jammed or stuck, it would hold the valve open a bit, allowing or causing low compression. Unless you had a hard run, low on coolant, or some other malady, I would be surprised it could get that bad so quickly. Worth looking at.
You should be able to collapse the lifter and get clearance between the backside of the cam lobe and the follower by pressing on the lifter end firmly for a few minutes (or less). Unless you want to rustproof your underhood, do not start the engine with the cam cover removed..
tom

 

[NIPs]

When my engine blew the head gasket it never over heated, the highest it got was 210 according to my obd2 scanner and my gauge on the dash never moved and then I pulled off the road to see what the problem was becuz it was misfireing then I drove with misfire and all for another 30miles doing 60mph and that coolant temp after that never went above 180 190, since ur cel was flashing which means catalytic converter failure I would replace the cat to if ur replacing that much, if u want to figure out if its the rings or the valves fill the cap will oil the cap should be off a MT dew bottle or oil container pour the cap of oil in the sparkplug hole hook a compression tester up and turn the key if ur reading is higher then its ur rings if its no change then it couLD be a valve, if the head is not cracked or the head gasket didnt fail

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[tomw]

In most cases, a bad valve will be a bad valve until it is repaired, replaced, or sent to valve heaven. It will not run good, then run bad, then run good. You might even have a chunk of carbon that is on the valve seat area, unlikely, but possible.
It will not start up and run well for 10 minutes then start to run bad.
A head gasket leak could possibly lead to misfire and low compression. It might be forcing coolant into the cylinder or gas into the cooling system depending on temperature and pressure. If you check the coolant for the presence of combustion gases, you might know better. In most cases where a head gasket fails, the spark plug on that cylinder will be 'steam cleaned' by the coolant turning to steam during combustion.
tom

 

[Sunk]

My truck idle OK cold, then got worse as it warmed up until the idle settled out. Through the RPM range it was OK though. It had an intermittent CEL for misfire 1 and/or 2. After checking just about everything at least twice, I pulled the head and found sunk valves on #1 and #2, and #1 was cracked between the valves. I think I paid $350 ish for a rebuilt eBay head.

Oh and I drove it for 40,000 miles like that, and the previous owner probably drove it for at least 20.

 

[NIPs]

So the head was cracked, I'm pretty sure my 2.5 had either cracked head or a blown out headgasket, bcuz when I bought my truck I discovered bars stop leak and lots of it in the radiator and cooling system

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