Hi,

I have an 87 trooper with the 4ZD1 2.3l gas engine in it. About 2 1/2 years ago it broke down with a leaking head gasket and a cracked cylinder head. I believe the head cracked when I had a "freeze plug" pop out on the freeway. I got a "freeze plug" from the dealer and installed it in the trooper. It ran ok for a couple of months and then it died.

I got a used cylinder head and had it pressure tested and it tested good but it needed a valve job. I had the shop that tested the head to do the valve work. They also milled the head (as needed) for me. The head sat for about 6 months all wraped up in plastic on the kitchen floor.

About a year ago I went to install the cylinder head in the trooper. I got a new factory head gasket and and installed the cylinder head in the truck.

When I installed the head in the truck I went to check the compression and I got some poor readings. The first time I got the following readings.

Cyl Reading

1 30 PSI
2 30 psi
3 120 psi
4 50 psi


After I got these readings I took the cylinder head bolts out one at a time. Then I got a tap and chased out the cylinder head bolt threads in the block. I then installed new factory cylinder head bolts. I torqued the head bolts to 72 ft-lbs and went to check the compression again. These are the compression numbers I got the second time.


cyl reading

1 50 psi
2 50 psi
3 150 psi
4 70 psi

I have checked the "mechanical" timing several times to make sure it was correct. Everything lines up and the timing belt is tight. I have checked the valves to make sure that they were set correctly.

I am hearing a popping noise when I turn the engine over to check the compression in the engine. The noise is in rhythm with the turning of the engine. The noise is only present when I have the compression gauge screwed into a cylinder to check the compression. When I am not checking the compression the engine turns over just fine with just the regular engine spinning noise.

I am at a loss as to where to go from here. I changed out the cylinder head on my parents 90 trooper about 3 years ago and when I put it back together the compression was fine. I want to get this trooper back together and running.

I am stuck right now. I can't continue with the repair with compression numbers like the ones I am getting and I don't know what is causing the problem. The trooper ran good for 2 years when I first got it. I even got it pass the state emissions test.

I'm sorry for the long post. I am open for any ideas into what is causing this problem.


Thanks,

Mike

You need to do a leak down test. This test will let you know where the leakage is taking place. You can probably rent a leak down tester from the local auto parts chain, or HFT has one for $40-$50.

Once you find out where your leakage is you can start to fix it.

Hi,

I don't have a leak down tester. I see three possible areas for the truck to leak compresssion from. Cylinder Head, Head Gasket, and Engine Block. I am getting a popping sound when I turn the engine to check compression. Sorta like a "passing gas" sound. I am trying to avoid taking the engine apart if I don't have to. Would a head gasket cause this???

thanks,

Mike

Though a leak down test is in order, you might also want to try this and it's a freebie: Check the compression. Pour about a teaspoon of oil down through the spark plug hole and turn the motor over about three times. Then check the compression again. If the second measure is significantly higher than the first, the rings/bore are likely the problem. If not... might be the head gasket, might be valves.

I see the head is new. My bet is on the timing.

Make sure your piston is at TDC when the valves are closed on the intake stroke. you can put a small dowl in the spark plug hole to verify that the piston is at TDC.

Hi,

The "mechanical" timing is correct. I also adjusted the valves when I put the head in. The "popping" sound that i get when I go to check the compresssion has got me stumped. The "popping" sound has got to be a symptom of the problem. It sounds like "passing gas". I only get it when I am checking the compression. When I just "spin" the engine without the compession test screwed in I hear nothing. The valve work was done when I had the cylinder head pressure checked. I did use a new "factory" head gasket. Could I have gotten a defective head gasket from isuzu????

Is the head gasket the only place where I would get an audible compression loss???? Would a leaking head gasket give me an audible compression leak????

Thanks,

Mike

You really need to do a leak down test. Just go do it. You can get a kit from harbor freight for $39

I recently looked at the trooper again. I took it all apart and changed out the head gasket(from isuzu) and I've got the same problem. here is what I have so far.

"used" head tested good and milled.
valve job done on head.
"mechanical" is timing correct.
new timing belt.
valves adjusted correctly
new head gasket installed (from isuzu) twice
all new oil seals (cam, crank, and oil pump)

When the trooper was pulled off the road for repairs I was running 100% anti-freeze in engine. The trooper sat through one winter before the repair was started.

I am hearing a pronounced pop coming from the engine when I am turning the engine over to check the compression. If I unscrew the compresssion guage and let the engine just "spin" I don't hear any poping noise.

What would be causing this poping sound??? I think it is related to the low compression readings.

What are the synptoms of a cracked block?????

Thanks,

Mike

To start with, 100% antifreeze is bad. It is not supposed to be run without being mixed with water. It does not do very well at absorbing heat and dissipating it via the radiator.

Second, popping the freeze plug is bad. There are a few reasons for that to happen, but I suspect you really really overheated the engine. I would not be surprised if the block is warped (or cracked).

Thirdly, when you say you hear the pop "when turning over the engine", is this via the starter, right? With all the spark plugs pulled and the throttle wide open, right? The popping could be several things and should not be related to the compression, unless you are hearing the rods rattling around on the journals because you ate a bearing.

Finally, it has been said at least 3 times above, you need to do a leak down test. You are chasing something strange and unless you can pressurize each cylinder and see where compression is going, you are just guessing at this moment.

As an aside, I find it very strange that you did all you did above and you have the same compression numbers? Did you clean out the head bolt holes? Oil or junk in them will prevent you from torquing the bolts correctly. Other than that, if you are sure your head is good, the valves are good and the gasket is good, then the compression is going down into the block somewhere.

Good luck,
Michael

Michael,

The reason I was running with 100% antifreeze was because I had been running the trooper in the winter with a failing head gasket. I could tell that the gasket was leaking from the white smoke out of the exhaust. The freeze plug popped out AFTER the gasket had already started to fail. Who ever had the trooper before me had changed out one of the freeze plugs with an "aftermarket" freeze plug. The kind that are rubber and that expand when you tighten the bolt.

That freeze plug is the one that popped out on the freeway. I found it sitting on the motor mount after having the trooper towed home. When I replaced the freeze plug that had popped out I ordered the "factory" (metal) freeze plug from Isuzu and installed it in the engine block. I tapped it in with a socket and a hammer. I suspect that when the freeze plug popped out it killed the head gasket and more than likely cracked the head.

I only hear the "poping" when I am checking the compression. It is at "starter" speed. I only hear the poping when I have the compression gauge screwed into the spark plug hole of each cylinder. If I unscrew the compression gauge and have all the spark plugs out of the engine and then "spin" the engine I hear nothing wrong. Just the normal "spinning noise" of the engine.

The "poping" noise that I am hearing is like a loud "passing gas" sound or like a balloon poping. It is in rhythm with the turning of the engine.

I ran the trooper after I replaced the freeze plug for about 2 months before I had to take it off the road. The "smoke screen" that the trooper was creating was getting too bad to drive the trooper safely.

What are the symptoms of a cracked engine block???? Would loosing the freeze plug on the freeway cause the engine block to crack?????

I chased out the head bolt threads in the block with a tap. I even ordered new factory head bolts from Isuzu.
What could be possible causes for this problem????
Thanks for the help.

Mike