Compression test on 4.6L ,All plugs out?

itsaford · #1 02-07-2010, 02:55 PM

Hi, all I was wondering if I need to pull ALL the plugs out of my engine to do a #1 cylinder compression test on my 4.6l. I'm having all kinds of mishaps with this cylinder and I replaced the wires, plugs, coil packs,and a new injector on number 1 and still getting a P301 code on it... Will the reading be off if I don't pull all the plugs or something? Sorry if this is a newb question but its a pain to pull all these plugs in the snow! Thanks

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shifty_85 · #2 02-07-2010, 02:57 PM

you can just pull one at a time but its harder for your motor to spin over with the other 7 plugs in. i used a compression tester with only pulling one out at a time and they all were within specs. so you should be ok.

jethat · #3 02-07-2010, 03:46 PM

you need to test more then 1. I would do atleast 3 to confirm an average the one cylinder has the same as the others. if the 1 cylinder has 0 compression probably getting an average isnt necessary though..

itsaford · #4 02-07-2010, 04:38 PM

Thanks , I intend on seeing something low on my #1 so hopefully I won't need to pull any other plugs. If its normal or ok . I'm gonna park it under a big heavy pine tree covered with ice and snow out back thats already about ready to come down and pray for more snow to finish it off!

shifty_85 · #5 02-07-2010, 05:44 PM

well you gotta rember you loose compression over time. mine were at the low end of the specs but my motor had 132,000 at he time i tested it and it helps to do all cyl's i think the window is within 10PSI of each other. mine were all over but not more then 10PSI

V8Triton · #6 02-07-2010, 08:20 PM

The "correct" way to test compression is with the plugs out, but you can do it with the plugs in just the same. Just compare it to a couple of different cylinders. (Make sure you have 7 spark plugs installed each time) When you do a compression test remove either the fuel injector or fuel pump fuse to keep fuel readings accurate. Also try to make sure you turn the engine over the same amount of time on each cylinder. When removing all the plugs you're supposed to listen for 4 compression strokes to make sure you turn the engine over the same amount of time for each cylinder. If you keep all plugs in maybe just crank for a 3 count on each cylinder to keep it consistent.

jbrew · #7 02-07-2010, 10:05 PM

Compression Test—Compression Gauge Check

Make sure oil in crankcase is of the correct viscosity and at the proper level and that the battery is properly charged.

Operate the vehicle until the engine is at normal operating temperature.

Turn the ignition switch to the OFF position, then remove all spark plugs.

Set throttle plate in the wide-open position.

Install a compression gauge such as Compression Tester in No. 1 cylinder.

Install an auxiliary starter switch in the starting circuit.

With the ignition switch in the OFF position, and using the auxiliary starter switch, crank the engine a minimum of five compression strokes and record the highest reading. Note the approximate number of compression strokes required to obtain the highest reading.

Repeat the test on each cylinder, cranking the engine approximately the same number of compression strokes.

Compression Test—Test Results

The indicated compression pressures are considered within specification if the lowest reading cylinder is within 75 percent of the highest reading. Refer to the Compression Pressure Limit Chart. ~

If one or more cylinders reads low, squirt approximately one tablespoon of clean engine oil on top of the pistons in the low-reading cylinders. Repeat the compression pressure check on these cylinders.

itsaford · #8 02-08-2010, 01:18 AM

Thanks guys, this is great info!!

Depending on the outcome of this test,I'll be buying another ford f150. My 97 xlt 4.6 4x4 is pushing 200,000 miles! I just found a deal on a Loaded 2003 F150 FX4 screw,5.4L ,Long bed...mint black paint for 8500.00 local, all service records. I'll set the old 97 baby aside for a engine transplant and and use as a fun truck or hauler. I got my heart and sole practicly in my 97 I can't part with it yet! Plus its been paid off for years!!I can't stand the price of newer trucks these days let alone having another payment on one.

itsaford · #9 02-08-2010, 03:35 PM

This truck is a fart in the wind!!! I did the compression test on my #1 cyl after letting it mis itself to death to warm the engine up. I got a 125psi on #1 consistant. Now this is a engine that has 180,000+ miles! that is pretty good I'd say.I was expecting a LOW number, mechanical failure type of reading.Plus having the 301 code...right, nothing else, well obviously something is not working on #1.SO MAD I didn't even pull another plug for a compression check. I checked the #1 plug ,looked good installed everything back on # 1 and fired it up.I'm still confused mind you.... PURRRRS like kitten!! Ran this thing balls out for 5 miles and parked it, let it idle alittle . I could barely hear it running! shut it off and well , I don't know....loose wire ,odds of a plugwire boot not on all the way( had the boot off ,hell 8 times... think I would of got it on atleast once right?) BEFORE the compression test on#1 I pulled the injector wire harness from #1 while it was running and it didn't make much of a change ,it still missed but made it slightly worse while off (on the NEW injector). Soooo I'm stuck on this thing dumb founded. Gonna pick up the other truck anyway but geewiz!! I don't know whats up, guess I made the Ford gods mad or something !?

shifty_85 · #10 02-08-2010, 05:41 PM

make sure all plug wires are down. i had a mis i couldnt figure out turns out my plug wires started working there way loose got some di-electrice spark plug grease put some in all the ends of my wires and now they dont walk out any more.

jbrew · #11 02-08-2010, 06:43 PM

Quote:

Originally Posted by itsaford

This truck is a fart in the wind!!! I did the compression test on my #1 cyl after letting it mis itself to death to warm the engine up. I got a 125psi on #1 consistant. Now this is a engine that has 180,000+ miles! that is pretty good I'd say.I was expecting a LOW number, mechanical failure type of reading.Plus having the 301 code...right, nothing else, well obviously something is not working on #1.SO MAD I didn't even pull another plug for a compression check. I checked the #1 plug ,looked good installed everything back on # 1 and fired it up.I'm still confused mind you.... PURRRRS like kitten!! Ran this thing balls out for 5 miles and parked it, let it idle alittle . I could barely hear it running! shut it off and well , I don't know....loose wire ,odds of a plugwire boot not on all the way( had the boot off ,hell 8 times... think I would of got it on atleast once right?) BEFORE the compression test on#1 I pulled the injector wire harness from #1 while it was running and it didn't make much of a change ,it still missed but made it slightly worse while off (on the NEW injector). Soooo I'm stuck on this thing dumb founded. Gonna pick up the other truck anyway but geewiz!! I don't know whats up, guess I made the Ford gods mad or something !?

Yea, that won't work checking it like that lol. High mileage motors can have high comp numbers as well, - not uncommon. Carbon can build quite a bit over time.

Yea, you have to have all plugs out to be accurate IMO. - Unless your just checking to make sure your not @ 0. Can't really use the chart as a guide unless you follow direction, - no cheating lol.

You can also tap into the vac harness for an expanded check up. That's probably the easiest way a DIY'er can check their converters.

itsaford · #12 02-08-2010, 08:26 PM

I was checking basically for a complete cylinder failure and didn't get the results on #1 to show. I know I need to pull a few more plugs for even a ball park idea of what the compression avg is. But even if all other cylinders were 145 psi or something higher I still shouldn't be running perfect now with knowing 1 is 125psi...right?It's not like I changed anything. so, technically it should be running terrible and giving me the 301 code again?Before it wouldn't even go down the road without feeling the heavy mis like a sand bag got threw in on my fan every time I gave it gas or stayed on the gas for a fully automatic

sand bag fan catcher

(I know bad analogy,I'll claim it though) .. So that to me made me look at minor things again..if there is such a thing.

shifty_85 · #13 02-09-2010, 03:30 AM

im still sayin plugs or the wires arent staying on. ive had so many miss's i cant even rember. at one point my poor 4.6 was running on 5.5-6 cyls 3 wires were broke completly. and the plugs were crap too. but it still ran. lots of back firing and exhuast poping thoe haha and no power at all.

recently i had the prob of the wires working off got some of that crap and no probs since

jbrew · #14 02-09-2010, 06:20 AM

Quote:

Originally Posted by itsaford

I was checking basically for a complete cylinder failure and didn't get the results on #1 to show. I know I need to pull a few more plugs for even a ball park idea of what the compression avg is. But even if all other cylinders were 145 psi or something higher I still shouldn't be running perfect now with knowing 1 is 125psi...right?It's not like I changed anything. so, technically it should be running terrible and giving me the 301 code again?Before it wouldn't even go down the road without feeling the heavy mis like a sand bag got threw in on my fan every time I gave it gas or stayed on the gas for a fully automatic

sand bag fan catcher

(I know bad analogy,I'll claim it though) .. So that to me made me look at minor things again..if there is such a thing.

Lol -

Those guys are right, you can compare three like that to get a good idea. If you know the probem cylinder, - which you do. But yea, some kind of reading would help get rid of those sand bags hopefully

125 on the low and 145 on the high side would be okay. Iduno, I never checked it this way and I haven't had my coffee yet this morning lol. I guess you can follow the 75 percent rule I posted, - maybe ! Crap ! I can't say, I test with No plugs, better let these other guys point you in the right direction.

Good Luck tho, - think I'm just going to watch this one, see how it pans out

itsaford · #15 02-09-2010, 11:11 AM

OH, my head! Late night, got all the readings on the cylinders last night/ today whatever it is... in a friends garage.
#1 125
#2 132
#3 135
#4 122
#5 130
#6 134
#7 125
#8 130
all with a( ish) on end...I'm not that technical.
Now hopefully it will fire up good again tonight after I screw up the plug wire install and find that extension that my engine took from me as my hood came down and slapped my ass,heehaw... ya know the furry kind.. well... kinda.. ok then.... I'm not awake

I got the order of wires down it's just my luck.... however..

its snowing 8" again!