So, it appears that the new to me 1996 F-150 4.9 5-speed has a blown head gasket. A compression test shows that I only have 15psi between #3 and #4 cylinders and massive amounts of air blowing back through the intake. All other cylinders are between 140-155psi, so that sort of narrows it down. (The popping noise present in the airbox while the engine is running tells the same tale.) The engine has 194,XXX miles on it, and I wouldn't feel right not having the head remanufactured since I'll have it off.

I might add an aftermarket camshaft, but I'm starting to lean more and more to keeping that stock but replacing the timing gears with a quality steel setup. I'm also replacing the rod bearings and oil pump while I'm at it due to a slight rod knock and low oil pressure when hot.

At some point in time, the air injection rail was removed and the ports were sealed in the head. I'm on the fence if I should return it to stock and reinstall the air injection rail and hook it up like it is supposed to be. The rest of the air system is there and fully operational, as far as I know. So my question is this: Should I return the head and air injection system back to stock or should I just not worry about it? What are the pros and cons of either choice?

 

Are the stock cats still present? If they are they're long past being due for replacment, and unless you put a factory Ford cat back on there is no need for the air injection system.

 

I was just about exactly in your shoes ~6 months ago. I was able to find a complete running engine for $100, so that made my decision easy. But considering that you've also got a worn out bottom end, spending $300 for a known-good engine might still be the right choice. That said, rebuilt heads are available for less than $300, so that's a relatively small dollar amount for what is effectively a new head.

As for the air-injection stuff, I ditched mine and have no regrets. If you leave the electronics hooked up (as I did), you won't even set an error code. I left the EGR in place and functional, but with a waded-up ball of aluminum foil in the line to limit flow.

Out of curiosity, how are the air-injection holes currently blocked off? 9/16-18 bolts?

 

The stock cats are still on it. This might be a good time to think about updating the cat to a high flow aftermarket one.

Regarding what has been used to block the ports, they seem to be some sort of large screws/plugs that have sealant on them. Since I didn't put them in, I can't tell you exactly what they are. I can look and take a picture if you would like.

Regarding rebuilding the engine presently in the truck or finding another rebuildable core, I'm on the fence. At a minimum I'll do the head, bearings, and oil pump. I guess I can always pull the pan before I pull the head and check the condition of the mains. They might be fine and since the compression is good on the cylinders besides the two which share the blown head gasket, I might just get lucky.

 

Replacing bearings on a high milage engine is a roulette game, you may get some more miles out of it or you may make it self destruct sooner. The rods tend to go oval shaped over time and the bearings wear to this pattern, insert new bearings and you create pinch points that may lead to a bearing seizure in short order, so IMO if the motor has oil pressure problems it's time for a rebuild where everything is returned to spec, nothing else will give you a reliable powerplant.

 

Thanks for making me feel better about my choice of just chucking in a whole "new" engine. Certainly there was some risk there on my part as I didn't know the guy I bought it from - I just had to take his word that it "ran good when pulled."

In fact it has run well, although oddly enough, the compression was a little better on the old engine which had two broken head bolts and horribly worn bearings. Who knows how long it had been run with an evil mixture of coolant and oil as a lubricant.

 

All excellent points that have been tumbling around in my head. I think what I'll do is pull the head, have it cleaned and surfaced, lap the valves, replace the seals, and slap it back on. I don't have an engine stand or hoist yet, so at least I'll have a running truck that I can use to get these things and another engine to start rebuilding. I've never been one to do things haphazardly and I really don't feel like starting to do so with this engine.

 

I understand that philosophy, but it's gotten me in trouble sometimes when you feel like because you spent more money you magically got a better solution. Keep in mind, the stock 4.9, when treated right, is a very reliable engine capable of going 300,000 miles or more.

I almost went the same route as you are contemplating and stuck a rebuilt head on a very tired short-block. So glad I didn't go that route. Keep in mind, it's possible that you too might have a broken head bolt or two and that's why the gasket blew, or perhaps you'll break one or more upon removing the head.

 

And that is where I usually stand on things: While I'm doing this, I might as well do that. LOL! When you mention mileage potential from any of the big six engine designs, this is exactly why I am on the fence. To be completely honest, I'm not sure of how much of an oil problem it has. My stepfather only owned this truck for about 5 months and then one day, no power and crappy fuel mileage - hence, the blown head gasket. I'm not entirely sure if it does indeed have oil pressure issues, as he is not a mechanic and you can't rely solely on factory gauges. So, I'll have to verify the oil situation on my own. I do know the compression test went as follows: 155, 140, 15, 15, 150, and 155, in order of cylinders 1 to 6 and with a cold engine. Before the head gasket went out, the truck ran great and got decent gas mileage, even though it did have some vacuum leaks due to broken plastic lines to the EGR valve and to the Evap recovery system. The truck did ping when it was hot but that can be due to any number of problems to include carbon build-up and low engine coolant (as it did have at least once due to a missing plug on the radiator allowing coolant to simply escape as opposed to being captured in the reservoir). As of yet, I haven't honestly heard any positive noises that sound beyond a reasonable doubt to be related to rod noise. I've heard some noise in it during the summer, but it sounded more like heavy pinging as opposed to little hammers going at it.

I recently replaced the steering column and had the battery unhooked for quite some time to avoid an airbag deploying on accident while performing the repair. I also removed the instrument cluster to check the CEL to see why it wasn't coming on during a start-up test and discovered the bulb socket wasn't even there. So, I'll have to run the engine a bit to see if codes present themselves such as the knock sensor area and the like. I haven't had time to verify timing yet, so I need to do that as well but I have to address a couple vacuum lines before I can do that (I'll throw a vacuum gauge on it while I'm at it).

So, as you can see, I don't have the full picture of the engine's health other than what was reported to me by my stepfather. I have verified the source of reduced power and crappy fuel mileage, but I have yet to verify how the oiling system truly behaves. It is quite possible it is operating fine as we all know that oil pressure reduces when engines are hot and have come off running down the highway. As far as I know, no pressure warning lights have ever gone off and this engine just might be acting exactly as should be expected. I am tempted to drive the truck around a bit to let it warm up to see exactly what the oil pressure does.

Hopefully, I won't run into any broken bolts when I take the head off; we'll see what happens. I do know that if I run into any obvious condition issues when the head is off my plan of attack will change as a new engine will be the obvious solution.

 

On your '96 model year truck the computer will not like not having the AIR system there. There are sensors in the TAB and TAD valves (not just vacuum actuators), and the computer can tell what's going on. I just ran into this on my '96 with the 4.9. I wasn't paying close enough attention to the vacuum line routing when I replaced the line from the intake to the TAD side..... Lets just say I wound up setting an 'inefficient catalyst burn' code. Fixed the rubber boots on the old plastic lines and got the system working properly and haven't had an issue since. So beware, the newer computer's program is a LOT more sensitive than one might think. That being said, if you use the proper aftermarket converter you should be able to make it all work. My smog pump is going bad (makes a LOT of noise) and I'm going to have to either bite the bullet and get a new one (don't trust a used one) or remove it and replace the cats.

 

Does the '96 have the same "fake" oil pressure gauge as my '91, where it's basically a glorified idiot light? With my old engine, the needle would hang out around center when cold, but as soon as the temps warmed up it would go to the bottom of the scale, basically the equivalent of the oil pressure light going on. I think that meant that oil pressure was something less than 7 lbs.

 

To be honest with you, I'm not completely sure if the gauge is still a glorified idiot light. I've heard it both ways and I haven't asked around if the newer gauges are set up the same way as the 80-86 gauges were. I think I need to install a mechanical oil pressure gauge and go for a drive, even with the blown head gasket. I'm not losing coolant, it isn't pressurizing the coolant system, and fuel isn't making it past the rings.

 

You can tell by looking at the sender, which is located in the side of the block on driver side towards the rear. If it's a small thing about the diameter of a roll of quarters, it's just an on/off switch. A true pressure sender will be larger, maybe 1.5 - 2" diameter.

Also, a gauge will show higher pressure when cold and/or higher RPM's. The phony gauge will sit dead center through all of that.

 

I understand that part; I was referring to how they operate internally and how accurate they are. The gauges in 80-86 models aren't exactly known for their accuracy.

 

It looks like my luck for finding a replacement engine might be looking up. After waiting for over a month to find a suitable engine on craigslist, one popped up last night. (I've been looking for a replacement engine for this truck before I took possession of it just in case it needed one.) It's from a 1992 E-150, with just over 125k miles on it. It came out of a fleet van with regular maintenance so it should be in good shape. It's been pulled out of the van it was in (along with the trans that was attached to it which was then installed in another van) and has everything still bolted to it. I get to go look it over on my lunch break. He explained the only reason he is selling it is because he is moving to a smaller place and can't move all that he has and if he wasn't moving, he would be keeping it for a backup to his current work van. At least this engine has a story, something I couldn't say about an engine I could obtain from a salvage yard or Pull-A-Part. So, hopefully all will be good because the gentleman selling it only wants $250 for it.