All 302 blocks the same?
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Junior User
Joined: Feb 2004
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From: Illinois
All 302 blocks the same?
1991 F150 4X4 302 E4OD XLT.
The previous owner put a Towncar 302 engine in the truck.
It supposedly has 110K miles on it.
It has blowby, just about 0-7 lbs oil pressure at idle after warming up.
Around 40 psi at cold start.
I didn't know the true oil pressure until I put a mechanical guage on it.
It has 150-155 pounds compression
except for #8, which is at 135 pounds.
Unless it's a bad pump or clogged pickup screen ( I don't think that would be the case if it has 40 lbs oil pressure when cold), I figure the bearings are worn out on the crank and rods.
I have a 85 Grand Marquis 302. If I got that block rebuilt at a shop, would everything fit up to it? Transmission, exhaust, intake manifolds, heads,
engine mounts etc.
That would give me the least amount of downtime since I don't have the money right now for a remanufactured complete engine.
The previous owner put a Towncar 302 engine in the truck.
It supposedly has 110K miles on it.
It has blowby, just about 0-7 lbs oil pressure at idle after warming up.
Around 40 psi at cold start.
I didn't know the true oil pressure until I put a mechanical guage on it.
It has 150-155 pounds compression
except for #8, which is at 135 pounds.
Unless it's a bad pump or clogged pickup screen ( I don't think that would be the case if it has 40 lbs oil pressure when cold), I figure the bearings are worn out on the crank and rods.
I have a 85 Grand Marquis 302. If I got that block rebuilt at a shop, would everything fit up to it? Transmission, exhaust, intake manifolds, heads,
engine mounts etc.
That would give me the least amount of downtime since I don't have the money right now for a remanufactured complete engine.
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Joined: May 2004
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Thier would be 1 thing I can think of that might be a no go. Does yer 91 F150 have a knock sensor on the back of the block? My 93 F150 has one of these. It's on the top back of the block, looks like a oil pressure switch or a power sterring switch. If your 91 does'nt have a knock sensor then the other block will work with no problems. But I have read were people have just didn't use the knock sensor when they put another block in that didn't have it. Someone else may have done this and will post about it for you. Also your 91 original block was stock factory roller cam & lifters, what yr is the towncar motor? The roller part will make no diffrence, just wanted you to know. Steve
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Junior User
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From: Illinois
Thanks.
I forgot about the knock sensor. The 91 F150 original truck 302 is supposed to have one according to Haynes and parts stores. I think the 1990 Towncar 302 is also supposed to have one. I believe I looked that up online at parts stores.
Whether it's hooked up, I'll have to crawl over the engine to find out I guess.
I'm pretty sure the 85 Marquis 302 doesn't have a knock sensor.
So maybe this idea isn't such a good one.
I don't know if I can get by without the knock sensor if the
EEC needs to have it to run right.
I forgot about the knock sensor. The 91 F150 original truck 302 is supposed to have one according to Haynes and parts stores. I think the 1990 Towncar 302 is also supposed to have one. I believe I looked that up online at parts stores.
Whether it's hooked up, I'll have to crawl over the engine to find out I guess.
I'm pretty sure the 85 Marquis 302 doesn't have a knock sensor.
So maybe this idea isn't such a good one.
I don't know if I can get by without the knock sensor if the
EEC needs to have it to run right.
Junior User
Joined: Apr 2005
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I had a similar oil pressure problem in a 454 Chevy (sorry for the swear word there.) I had bottomed the oil pan out so many times that it was pushing up against the pickup tube and couldn't get enough oil in there to give good hot pressure. My use of synthetic oil saved the engine's life and a custom welded Moroso pan solved the flow problem.
Hotshot
Joined: Dec 2003
Posts: 18,423
Likes: 9
From: iowa
why not just put new rings, and bearings into the block you have in the truck for now. just rehone the cyls and polish the crank and should last a good long time unless you find other major problems, and rering kits with bearings aren't that expensive.
Senior User
Joined: Feb 2004
Posts: 219
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From: michigan
compression on my 302 75 to 155, I'm jealous of yours
my oil pressure now (think sender broke) is about 1/6 of gauge used to be 1/2 cold or warm running, dropped to 1/6 idling warm. Now its 1/6 all the time
my oil pressure now (think sender broke) is about 1/6 of gauge used to be 1/2 cold or warm running, dropped to 1/6 idling warm. Now its 1/6 all the time
Post Fiend
Joined: Nov 2001
Posts: 14,947
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From: Topsfield, MA
The knock sensor isn't fatal, it can be left plugged in and not attached. Just don't let it ping/knock on ya or you'll ruin it.
Sounds like that motor is ready for scrap, swap it...you've got a good handle on the situation.
Whenever the oil pressure is high when the motor is cold, then gets low...it's the bearings. When the oil is cold, it's thicker. As it warms up, it thins out...when it thins out...you'll loose pressure on an old engine.
Having #8 at 135 and the others at 150+...not good. Are you sure the #7 has good pressure? Sometimes the head gasket will split between cylinders. If not, then #8 has more significant ring/sealing issues.
Sounds like that motor is ready for scrap, swap it...you've got a good handle on the situation.
Whenever the oil pressure is high when the motor is cold, then gets low...it's the bearings. When the oil is cold, it's thicker. As it warms up, it thins out...when it thins out...you'll loose pressure on an old engine.
Having #8 at 135 and the others at 150+...not good. Are you sure the #7 has good pressure? Sometimes the head gasket will split between cylinders. If not, then #8 has more significant ring/sealing issues.
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Junior User
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From: Illinois
I figured maybe the reason for lower compression on #8 was all the years the engine had the PCV valve gases routed into the #8 intake runner.
I tee'd it into the brake booster line when I bought it, but too little too late.
I'll run another compression test and this time put a couple - three squirts of oil
into the cylinder and see if that boosts the compression reading. That should indicate worn rings?
I am hoping to get by with just honing, new rings and lower end bearings.
Probably should have new camshaft bearings put in too I suppose.
For now, I'm going to run a heavier weight oil until I can get everything organized to do the project.
I guess I'll give up on the idea of rebuilding the Marquis 302 block that doesn't have the knock sensor.
Thanks for the suggestions.
I tee'd it into the brake booster line when I bought it, but too little too late.
I'll run another compression test and this time put a couple - three squirts of oil
into the cylinder and see if that boosts the compression reading. That should indicate worn rings?
I am hoping to get by with just honing, new rings and lower end bearings.
Probably should have new camshaft bearings put in too I suppose.
For now, I'm going to run a heavier weight oil until I can get everything organized to do the project.
I guess I'll give up on the idea of rebuilding the Marquis 302 block that doesn't have the knock sensor.
Thanks for the suggestions.
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Post Fiend
Joined: Nov 2001
Posts: 14,947
Likes: 6
From: Topsfield, MA
That will indicate a valve issue if the compression goes up after the oil is put in. It's called a Wet compression test, vs dry. I've heard of that PCV thing too, it came to mind but I didn't mention anything. My 393 has an edelbrock intake which supplies a hole for the PCV hose underneath the middle of the upper intake, vs the back.
You can still use the marquis motor...you don't have to give up on it because of the knock sensor. I don't have mine hooked up on my 393. You can take the sensor out of the old block, leave it plugged in, but tied behind the motor uninstalled. It'll just not be functional, it'll just keep telling the computer nothing is wrong, even if it is knocking...so that is why I mentioned being careful if it knocks. Not all of these had knock sensors...so it's not critical that it be missing from action.
I also wouldn't tee off the brake booster...
You can still use the marquis motor...you don't have to give up on it because of the knock sensor. I don't have mine hooked up on my 393. You can take the sensor out of the old block, leave it plugged in, but tied behind the motor uninstalled. It'll just not be functional, it'll just keep telling the computer nothing is wrong, even if it is knocking...so that is why I mentioned being careful if it knocks. Not all of these had knock sensors...so it's not critical that it be missing from action.
I also wouldn't tee off the brake booster...
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