Truck specs: 1994 F-150 XLT 5.0 with 153,000 miles.

I bought this truck as a side project to keep me busy in the garage and have had a lot of fun with it. I did a compression test (dry, ignition coil unplugged and fuel relay removed) today with the below results:

Cyl #1 (front passenger side): 130
Cyl #2: 145
Cyl #3: 140
Cyl #4: 145
Cyl #5 (front driver side): 140
Cyl #6: 145
Cyl #7: 145 (actual 143 but rounded up)
Cyl #8: 155 (actual 157 but rounded down)

Based on what I've read the compression in cylinder #1 is just beyond the tolerable range (155 - 23=132). Should I worry about cylinder #1 and/or is it close enough to the allowable range that it isn't an issue? If it is an issue, what should I start digging into next?

In removing all of the plugs, just about each had oil on the plug threads while cylinder #2 and #4 both had oil on the plug's ceramic cover -- it wasn't coated but enough to give you pause. Given this, I think new valve cover seals are in order?

And some background on why I did a compression test. The truck experiences what I believI put one to be pinging or pre-detonation when I really mash the gas or climb a hill. It is worse in Houston's hot weather. It doesn't happen until the truck has been running for about 5-10 minutes. I've been chasing this issue for a while ... new O2 sensor, new IAC, new TPS, new plugs, distributor and cap, new rotor, new EGR, new ignition coil, cleaned out throttle body and intake plenum, cleaned MAF. I'm starting to think it's more and more likely related to carbon build up, so I'm thinking about taking a peak at piston heads when I put on new valve seals. Curious if anyone has another theory?

The truck currently shows codes 121 (I need to adjust the new TPS), 212 (previous owner put wrong IDM in) and 452 (VSS ... I've been working on this one but doesn't seem it would be related to pinging). Tach needle also bounces a little, could be related to VSS maybe?

Appreciate any thoughts or ideas. Thank you!!!

 

#1 is a little low but I would not yank a good running engine for that.

 

I personally wouldn't worry about the compression numbers. I have seen the 5.0 have compression so low it needed ether to start and blow by so bad that a kid used a milk jug to catch the oil from the pcv.

As for the pinging, where is the timing set and do you know if the balancer is still good? Meaning it hasn't slipped and is showing the correct degrees of the crankshaft

 

That's a relief to hear about the compression. This is my first project vehicle so while I've read a lot to educate myself it's reassuring to hear from real world folks. Thank you both!

I've retarded the timing a few degrees to reduce pinging, which has worked a little bit. I've also run a couple of tanks of 93 octane through with no luck. I haven't looked into the harmonic balancer yet.

I started work to remove the heads for new gaskets this afternoon and can plan to look into the balancer next I'm not hearing much motor noise beyond the pinging. Is there a certain way to go about testing or a method you would recommend?

And since I'm disconnecting the injectors to get to valves I'll plan on getting those cleaned as well so I can eliminate that possibility.

 

Read this article on finding tdc

It has an easy DIY for a method with the heads off if you really plan to pull them

 

You can find approximate TDC by using a rod in the #1 spark plug hole and by turning the harmonic balancer slowly until you get the rod (resting against the top of the piston) to it's highest point.

 

how do you know your on compression stroke, vs exhaust stroke

 

That doesn't matter. As long as you can find the top of the stroke then you can figure out if the balancer has slipped

 

Thanks everyone. Just got the first valve cover off, and I'm not an expert, but this seems like pretty good build up ...

 

That looks pretty good actually, typical? Compression test is something to look at carefully in old school iron, back when rings were cast iron and engines were wore out at 75k miles. Modern era engines run much much longer. One thing that hasn't changed, is gum and carbon buildup can cause sticky piston rings. Some kind of solvent may help to free them up.

 

I think you’re chasing a problem that doesn’t exist. Those compression numbers are pretty solid. If you’re just looking for something to work on, pull the engine and do a complete tear down and rebuild. But with that said, I reckon there’s a lot of other stuff on the truck that needs attention, first.

 

I've been chipping away at some of the easier stuff along the way. Mechanically things seem pretty good, it's the pinging that I cannot figure out.

 

When you put 93 octane in did it help at all? I would think it would if we’re talking about carbon build up on the pistons.

 

Also, have you checked fuel pressure? Need to know what readings are KOEO, KOER, FPR disconnected, part and wide open throttle conditions.

 

Installed a new fuel pressure regulator as one that was in truck was no good. The system checked out fine after that fix, good pressure. I didn't notice any difference using 93 octane. Since I've pulled the fuel injectors I may have those cleaned professionally here in town so I can eliminate that possibility.