compression test numbers all over the place!

[fireball 440]

compression all over!!!! CYLINDER HEAD REPLACEMENT

I recently bought this 92 explorer 4.0 for dirt cheap. It has a miss and for whatever reason the previous owner removed the t-stat. For $300 I drove it home. Finally got around to opening it up. Plugs looked old, #1 LH side had a tint of green on the electrode. compression test looked like this, using a snap-on compression tester.

All over the place! Wow! I know these first gen are known for cracked heads but WTF is going on here? Also it makes some valvetrain noise that hurts the ears. For $500 I can have a set of rebuilt heads new valves, springs, guides, all gaskets, coolant, and etc to do the job.

Should I go for it and order the heads now? or should I wait until I open it up more?

 

[fireball 440]

OR..... this truck has 121K miles on it, no dents, very little rust, clean interior... if I'm going to dump 500 more into it (I'd have 800 total invested), then why not start toying the idea of a 5.0 conversion? Could a 5.0 swap be done for under $1000?

 

[Maniak]

Did you do the test again after squirting oil into the cylinders? If the pressure came up a bunch then you have ring problems. If the pressures don't come up then its head/valve issue.

Also, I am assuming you either had the throttle open of closed for all the cylinders. Your "supposed" to have it open when you do the test, but more importantly, you need to test them all the same way (all with throttle open or closed)..

As for those numbers, Those are all over the place. I'd expect more than just a cracked head. I'd expect multiple cracks and possibly valve seat damage. Also, if your getting valve train noise I wonder if the lifters/pushrods and/or rockers are really worn on some and just aren't opening the valve all the way.

Other than doing a compression test with oil in the cylinders, I really can't think of anything else you can do to figure out how bad those heads/valves are.

Also, keep in mind that even though heads may be cracked, you can't always see the cracks. Once the heads are magnafulxed, its much easier to see cracks.

~Mark

 

[fireball 440]

Time is not on my side either. The truck is sitting outside in my driveway it wont fit in my tiny garage. So this will be an outside project that will be go status until complete, hopefully one weekend.

I'm not a believer in squirting oil into cylinders to bring compression numbers up. I parked the truck where it sits a week ago running on 5 cylinders.

 

[Maniak]

Time is not on my side either. The truck is sitting outside in my driveway it wont fit in my tiny garage. So this will be an outside project that will be go status until complete, hopefully one weekend.

I'm not a believer in squirting oil into cylinders to bring compression numbers up. I parked the truck where it sits a week ago running on 5 cylinders.

The oil in the cylinder is just to see if you have a ring issue. If you do that and it increases the compression on those low cylinders then fixing the heads won't fix the issue as the issue is Rings/etc.

~Mark

 

[Roadrunner777]

If the thermostat was missing, you have to consider that this may have overheated badly sometime in history.

 

[Mudboy]

a vaccuum test will provide more direct information.
unplug a vaccumm port hook rubber hose to port and to gauge. Make sure your idle is at about factory spec (800ish) and make sure the motor is at operating temp.
figure 18-22" is normal at sea level.
crack the throttle it should drop to 2" then shoot up to about 25" for a second or two after cracking teh throttle
if it flucuates at idle below 18 you have a vaccumm leak or head gasket issue
an intermittent drop would be a sticky valve or similar (normally exhaust
a rapid intermitent drop from normal your also looking at sticking lifters or valves
if the vaccumm flucates with rpm you are looking at beat valve spriongs
fast vibrations within 18 to 22" your looking at ignition. Slow movements would be a abd sensor or something else controlling the air to fuel.

 

[Roadrunner777]

You know, what is happening here is a little unfortunate. I think you are getting the miss because of the outlaying compression values... but 125 PSI or higher, they ought to be firing, maybe rough, but they all should be firing.

Except... the '92 engine uses batch fuel injection. So, the computer cannot compensate by cylinder. Did you ever work out which cylinder was missing?

If this engine sat for a while, and you are just starting to work on it, I would hold judgement on those comp values. A few hours of run-time may even it out, especially if you can get that one missing to fire.

All that said, I cannot say with expertise about the cost of the 5.0 swap. I would definitely look into it. You might look at the modified section and see what's involved. If you start having to make custom mounts, this could get a little rough on a driveway operation.

 

[fireball 440]

I'm not serious about the 5.0 swap that is just a dream.

I think I'll pick up a new set of plugs and see if I can get that dead cyl to fire. I was just assuming it was #5 because of only 125psi, but yes in theory I believe that should fire. Heck I've seen small engines run off of 90psi compression, but then again when my Grand Am died it had a dead miss with 120psi in one cyl & 170 in all the others?

 

[fireball 440]

Oh this vehicle has been run 2 weeks ago. It idled for about 20 minutes and then I drove it 10 miles home.

 

[Roadrunner777]

That's pretty good, you know, I was thinking more if the seller had it under a tree for a couple of years.

 

[fireball 440]

Update! I tore it apart yesterday and found a pretty dry valvetrain. I ordered 4 lifters and 12 pushrods. Pretty cheasy rocker design IMO, and roller lifters on this 4L? Flat lifters would have worked just fine in this engine. Pics coming!

 

[fireball 440]

<<<<<<<<<<<<LOL it says I'm a wannabe under my name! If you guys only knew!

 

[fireball 440]

It's pretty obvious now which cylinder had the miss. That was the cyl. with 135 psi compression.

Doing some cleanup what a mess!

 

[fireball 440]

Oh! This morning I ordered 4 lifters and 12 pushrods. This thing was ran dry, and hot more than once. So I'm waiting on those hopefully Thrus the sooner the better.

If you can see in the pics the rockers and old springs are dry, crusted with baked on oil. The oils been baked on there, overheated more than once.

^^^ I absolutely do not like this rocker design!

 

[fireball 440]

had just enough room to slide the Harley in for the night

 

[fireball 440]

Is there a how to thread on this? I could donate my photos if there is. Here is your lower intake manifold. I've never much cared for these 60 degree or whatever they are V6's. I always prefer a 90 degree motor, but thats imo.

 

[Maniak]

Did you take the heads somewhere to get them magnafluxed? Those heads do NOT like getting hot. They crack somewhat easily.

I have 3 cracked heads in the shed. My cracked ones are cracked between water jackets, between the valves and I've even had a set that cracked on the hump on the top of the head.

The cracks are normally hard to see until the have been fluxed which takes < 5 minutes to do.

I paid my machine shop a 6 pack of beer for fluxing my old heads.. they didn't want to charge me, so I dropped off some beer later.

~Mark

 

[fireball 440]

My old heads I'm sending in as cores I dont want nothing to do with those timebombs. I have a brand new set of heads, RH side is on and torqued down waiting for lifters for the LH side.

 

[fireball 440]

Put her back together as far as I'm gonna go tonight before the clock and beers took over my ambition level. First time I've used RockAuto online parts, ordered lifters and pushrods on Tuesday morning and they showed up Friday 3pm.
I replaced 4 lifters and thats all I was going to spend roller lifters aint cheap, still have 4 bad ones so it'll be noisy but I'll live with it. Depending what time I get up tomorrow she should be a runner.