1997 Ranger 4x4 4.0L engine. Was told by Salesman that Engine was bad. I just bought the truck and ran a scan on it. It gave 2 codes a P0302 and a P0304 which is Cylinder Nr 2 Misfire detected and Cylinder Nr 4 Misfire detected. The engine has new Plugs and spark plug wires. I checked the firing order and the wires and they are correct and in the proper position. I did notice that when I first started it up at the car lot, that it has white or steam blowing out the exhaust pipe but it quit after a few minutes and has not done it since. I thought maybe a blown head gasket, but not likely as Cylinders 2 and 4 are on different banks. I filled the radiator and the overflow tank and will check water level after running it for awhile. Any suggestions or help appreciated. I do have a audel scan guage code reader . Check engine light is on, but the only codes are those 2 above. Also the IM readyness test checks OK so Emissions should be OK. no other codes were noted.
Mel

 

Welcome to the forum

3 things are needed for a cylinder to fire
1. Spark, at the right time
2. Fuel, in the correct mix with air
3. Compression

First two can be intermittent and hard to track down, compression is either good or bad, no fuzzy grey area when compared to other cylinders.

So I would remove all the spark plugs(MUST DO THIS) and then test each cylinder and write down the results.
1997 4.0l has compression ratio of 9.0:1 so using standard multiplier of 18, 9 x 18 = 162
You should expect approx. 160psi in each cylinder

If 2 and 4 are lower than the others add a teaspoon of oil to each and retest, compression WILL go up, but by how much will tell you if it is rings or valve that is leaking.
To add the oil just dip a straw into a bottle of oil and put finger over the end then transfer oil to spark plug hole

If compression number are all within 10% of each other then you can move on to spark or fuel as the cause of the misfires

Head gasket or cracked head is easy and free to test, i.e. the white smoke
Get latex glove or balloon or even a condom

Cold engine
remove rad cap
remove overflow hose from rad and plug port with vacuum cap, gum, putty.....??
Put Glove over rad cap opening and seal with rubber band
cooling system is now sealed, air tight

Disable Spark by pulling off the 4 wire connector on the coil pack, you want a No Start

Crank engine and watch the glove
If it pulses up and down then you have a cylinder to cooling system leak

If it just lays there then you do not

If it pulses, pull out 1 spark plug at a time and crank engine again
When it stops pulsing last spark plug removed was in the leaking cylinder, reinstall spark plug to confirm

In your case you may have two leaks, but you will notice glove doesn't bounce as much when spark plug in one of the leaking cylinders has been removed, continue until no pulsing is seen.

4.0l OHV heads had a weak spot in the casting between valve seats, if engine was EVER overheated the heads will crack there, metal was expanded too far from the overheating

You may want to do this Glove Test first, before compression test, just to confirm a leak or to take it off the table

 

Thank You Ron D I am printing out your instructions. I was going to do a Compression and air leak test next after ordering a screw in compression gauge and an adapter for air test. Thanks again for your replies. It will be a few days before I post the results. Thanks again.
Mel

 

Hello RonD
I did the Glove test using a trojun. When cranking the engine the trojun pulsed the first couple of times, then it filled with air and and stayed that way. So I assume there is a leak. Blown Gaskets or cracked heads. Most likely cracked heads. will post more After the compression test.
Mel

 

YUP, bummer

When you pull the spark plugs keep track of where each one comes from, "Steam Cleaned" tips are a sure sign of a coolant leak into that cylinder

 

Well I had to use a compression gauge with a rubber tip. Just checked NR 4 had the wife crank the engine. Water mixed with oil and only 90 lbs. 4 was one of the cylinders misfiring. P0304 will check the rest tomorrow. Not sure if I will pull the heads or pull the whole engine and replace it with a used one. With over 200,000 miles on it not sure it would be worth doing just the heads before other problems. I will make a decision after I check the other cylinders. Not much more work to pull the heads before pulling the engine.
Mel

 

Unlucky :(

Just did the glove test the other night and it was all ok. Hope you're able to get this running again.

 

My 1994 is close to 400k on bottom end, replaced heads at around 280k, my own fault, tried to "make it home", well did make it home, expensive trip, lol.

If oil in the pan is not a milkshake then head replacement in the vehicle is not a bad bet
The 4.0l OHV bottom end can take the miles

 

well I checked a couple of other cylinders and only had a 120 Lbs compression, but the compression gauge was leaking so not a true reading. I am undecided. I can get a good used engine 151,000 miles for $400 Local, or one with 97,000 miles for $500 in another state with a year guarantee. no water in the oil last I checked. Guess I could drain it to find out. Heads would probably be just as much. I took 20 pictures of the engine compartment so I would be sure where everything goes and I will start labeling all of the wires and Hoses. I might just go ahead and pull the heads if the bottom end is not like a milk shake.
Thanks for you advise and help.
Mel

 

Good prices on the 4.0l OHV engines

But still a roll of the dice with used anything, lol

And on a used 4.0l OHV not even the seller may know a head is cracked, it won't show up on leak down or compression test very well, like a head gasket breach, small cracks cause a problem and get bigger.
Glove test is only sure fire way I know to test for it, or pressure test if you can seal the cooling system.

 

Yes it is a roll of the dice. I checked the engine oil again and there is no water in it. did not drain it though. Just checked the dipstick for chocolate vanilla milk shake. Here is what another outfit says although their engine is $750 So I will have to make a decision. It is a hard choice. I will start checking for heads and see what the price is. maybe pull the heads just to see. Will keep the forum posted on what I decide and what I find if I pull the heads.
Mel

 

Most engine resellers are honest and good for their words, that is usually not the issue, as said they just don't know the condition of engine, best guess on their part.

Warranty doesn't cover removal and reinstall, so heads up on that
And another heads up, make sure warranty covers DIY installation, some sellers only warranty if professional mechanic does the install, so ask up front

 

I have to agree with what you say, But any which way I go will be a gamble. Since I didn't know the previous condition of the motor or how it was maintained. The condition of the truck leads me to believe that it was taken care of. A pair of new heads complete will run me $400 to $600 then a gasket set is another $50, and then new head bolts for $53. I could end up with it costing me close to $800 or More to replace the heads alone. On the other hand a $400 or $500 low mileage engine might be a better deal and I would only be out my labor if the engine did not pan out. I think now that the best thing to do is to take a good compression test and do a leakdown and if it turns out OK then pull the heads. Maybe go ahead and pull the engine and check it out on the bench maybe pull the pan and check the bottom end. I won't make a decision until I am able to do a complete compression check and leak down. I need to get a decent compression gauge that doesn't leak so I can get a true reading. THanks for your advise and help.
Mel

 

Well I bought a good compression gauge and done a check this morning. Strange thing. Here are the results. All compression checks were done dry.

#1 was 125 Lbs Dry

#2 was 130 Lbs may have been a little wet. This was a P0302

# 3 was 125 Lbs dry

#4 was 150 Lbs Wet (water). This was also P0304

#5 was 125 Lbs dry

#6 was 125 Lbs dry

Not sure what to think. probably a teaspoon of oil would bring compression up to maybe 150 or less. no water in oil pan. bottom end is probably OK. I am assuming cracked heads. worried about rings if engine was over heated to cause cracked heads. I Blown head gaskets that would be another story. With all of the smog junk and other stuff on the engine, it may be better to pull it and then do more tests and remove the heads.

What say you RonD?
Mel

 

Seems a little low, could just be slower crank speed
Yes, any fluid will help seal the rings and with slower crank speeds increase is larger with fluid

Metal on metal seals are a function of time, they are not air tight, so the slower the piston speed the more time air has to leak out so the lower the compression numbers

I would just pull the heads and look at the cylinder walls

General rule of thumb for compression test on 6 cylinder engine is to throw out the highest and lowest number, add up the other 4 and divide by 4 to get the average, I get 126.25
So all except #4 are withing 10% of average

If you want more info then I would drain coolant, so no water in #2 and #4 and repeat tests on those