I bought a 1994 F150 4X4 XLT King cab a few months ago. According to the VIN and what I saw under the hood it was a 5.0. While it is not the best running truck it isn’t bad. Yesterday we went to the parts store and bought oil and a filter when we tried to put the filter on it wouldn’t fit. Crossed referenced the old filter and found it was for a 5.8. I did some checking and sure enough it is a 5.8 not a 5.0. It has the 5.0 upper intake is this a problem? Also we checked the compression it ran from 55 psi to 85 psi mostly in the 50 to 55 psi range. What will cause this they all are close together but very low I think. Any help would be appreciated.

 

It's possible someone swapped the plenums and used the 5.0 on the 5.8 lower intake.
Pictures would help to be sure.
Also, the deck height is shorter on the 302, versus the 351. That is easy to see as well.
The fuel rails for a 302 also run directly in front of the plenum and around the rear of the plenum. The fuel rail doesn't on the 5.8

The 5.8 probably has the added oil cooler built in, hence why you had to get a different size filter.

And double check the compression numbers. If it was 55-85psi, I doubt it would even run, let alone idle.
Be sure the throttle plates are open when checking.

 

+100

Easiest to see at the distributor mounting surface, 5.0 is nearly level with the intake gasket surface, 5.8 is about 1" below.

Depends upon the vintage I believe, my 5.8 fuel rails look identical to the 5.0 version only wider.

A good possibility since both motors natively use the same filter.

 

It does have the oil cooler and the deck height is higher. I checked on a 5.0 and the thermostat housing lower bolt is covered by the timing chain cover but on the motor I have it is above the cover.

I checked the compression numbers multiple times because I thought they were low. I also checked the gauge I was using to see if it was ok and it was. I checked it with the fuel pump relay unplugged so it would not run and WOT.

The fuel rails go make a U around the back of the intake.

 

Sounds like a 5.8L to me.

Those compression numbers are not good though. You say you tested the gauge; was this with a known good engine or?

I would do a wet compression test next; if the readings increase in an oiled cylinder it suggests the ring seal is not good. If the numbers are approximately the same, valve issues. Or, do a leak down test and listen/feel where the air escapes to. Crankcase is rings, intake or exhaust is valves.

 

Did a wet test on one cylinder it went up only 5 psi.




This is the only picture i have tonight.

It runs ok and idles good just not a lot of power.

Also someone removed the EGR tube and plugged the exhaust side but the intake side is open. The valve is still there just the tube has been removed.

 

I see no vacuum line to the fuel pressure regulator and it looks like the IAT sensor wires are cut. Is the check engine light on, and are there any codes?

Something is likely worn out. Those compression readings are not good. Burned valves or something else related to valve train is most suspect in my opinion. The similar readings among all cylinders is a clue though.

Is there a plate between the EGR valve & upper intake? Otherwise you're looking at a massive vacuum leak when the PCM tells the EVR to open the EGR. It looks like EVR is still there, and you said the EGR valve is present; usually this is done to keep the PCM tricked into thinking EGR system is all OK when in fact it has been disabled.

With a 5.0L upper intake on there, I wonder if the lower intake was port matched. If not, its a terrible match. The 5.0L upper has big fat rectangular ports, and 5.8L lower has small oval ports. A few of us on here have ported 5.8L truck lower intakes to match the larger 5.0L upper for a cheap higher flowing intake (compared to a stock 5.8L setup anyway). Either the previous person working on this engine built it in some particular way, or its cobbled together..proceed with caution.

 

Timing chain and gear could be worn causing the low compression across all cylinders, if you're positive your gauge is right. I just can't see an engine running at 55 lbs compression.

 

Well....if it is a 5.8, at least it's not a 5.0! You'll need a rebuild if your compression truly is that low, I don't doubt it runs with that compression, pretty amazing what engines can tolerate....if it runs ok then you can keep running it but you'll need to keep the rebuild relevant in your plans.

Does it burn oil?

 

Look at the base of your distributor.

If it does NOT have this diagonal casting, it is a 5.0

If it DOES have this diagonal casting, it is a 5.8

Simplest way to 100% tell.

 

The fuel regulator vacuum hose is not connected and the IAT sensor is I think on the air filter box. Do I need to connect a vacuum hose to the regulator or is it ok running full pressure all the time?

 

Fpr is there to trim the fuel at idle, so it's good to have.

 

If the regulator has been unhooked for awhile, what's the odds it washed down his cylinders and the rings are shot?

 

I think it's doubtful, but certainly possible....it won't run so rich that it'll stink, but it's definitely best left hooked up.