1997 F150 4.2 5spd 2wd

truck ran like hell when I got it, codes said something about the intake runners.. the exact code/term escapes me at the moment, but either way one of the little rods fell off the valve that controls the secondary intake runners, you know what I mean I suppose, fixed that and it still had a dead miss

new coil+plugs solved that problem, fuel pump and regulator test good according to the book, although it does not seem to give a psi rating for the 4.2 in this book, its very near 40psi at idle and key on, doubles if you kink the return line, pulled the upper intake to get at the injectors, they all seem to spray a good strong equal amount, though I am not sure how to test them properly?

replaced the upper intake gasket, throttle body and EGR gasket that was blown out, new PCV valve and we cleaned everything, the intake was nasty with all the oily sludge, cleaned the IAC+TB+MAF and the EGR valve itself to ensure it was not blocked, did notice that the little solenoid on the passenger side below the intake, i assume its for the EGR system.. it makes a strange ticking noise when you turn the truck off like its leaking somehow?

the truck drives fine but it idles pretty rough, seems to fall on its face at speed in 4th/5th gear, have to downshift to pass anyone etc. though strangely enough its getting great gas mileage

the converters were already removed when I got the truck, so its throwing o2 sensor codes and multiple misfire codes even though all the plugs are firing good (used a plug tester)

not sure what else to add, I changed plugs again to autolites recommended by.. nearly everyplace I look, had NGKs in it and here is a picture of them, only in for about 2 weeks

http://i8.photobucket.com/albums/a31...m/100_4345.jpg
from the bottom they are cylinder 1 2 3

http://i8.photobucket.com/albums/a31...m/100_4347.jpg
and 4 5 6

passenger side plugs seem to be white, while the driver side are brown, what does this mean exactly?

any questions that will help solve this problem I will try my best to answer, trying to avoid throwing even more money at the problem, spraying carb cleaner all over reviles no apparent vacuum leaks, no oil or water leaks.. for all intents and purposes the truck runs fine.. just idles so rough the doors rattle, the exhaust system has seen better days.. its rather botched together with at least 2 leaks, whoever removed the cats did a very poor job, I cant imagine this is the problem however, since a friend of mine has a similar truck albeit automatic, with a 4.2 thats straight piped with halfassed o2 sensor placement and it runs fine

 

When you had the upper intake off, did you also replace the isolator bolts?

We do NOT recommend Autolite plugs, we recommend Motorcraft. They are NOT the same.

Please list all the codes by P-number.

 

97 doesn't have isolator bolts. However, that was the year that the lower intake gaskets leaked and hydrolocked either number 1 or 4 cylinder. Check the compression on all cylinders first. Double check any vacuum leaks!!

 

just brought home a compression tester, waiting on the engine to cool some before testing it, I will report the findings

as for the spark plugs, I don't know what to use.. seems there are big camps for autolite and motorcraft, I guess time will tell what works best in this particular engine, if problems persist I will switch plugs

one question about the old plugs, why exactly are the passenger side plugs all "whiter" than the drivers side? im not sure exactly but I thought that meant a lean condition, is this a sign that the EGR system is indeed at fault? since it resides on that side of the engines exhaust system

I have nothing to give a list of codes with, the auto parts store simply checked the codes, showed them to me on the tester then buggered off with another customer I do recall multiple o2 sensor codes, EGR blockage and multiple misfire

I checked the EGR valve and the gasket between it and the intake was installed wrong, they missed a bolt hole and the gasket was blocking the port, new gasket installed properly hasnt made any difference in running condition however, maybe the blockage is elsewhere

I will be going back to a different parts store to have the codes checked once I clear them as per the books instructions, and will ask for a print out

going to replace the lower intake gasket as well soon, the upper gasket had been replaced already so i assume the lower has as well? either that or this engine is lucky and has no coolant leak with 160K on it

 

compression test yielded the following results

cylinders 1-2-3 all have around 155-158 psi and pass the leak down test with flying colors

cylinders 5-6 have only 60-65 psi and leak down slightly more than the rest, though not very much at all still

cylinder 4 has 130psi and passes leak down as well

all done according to the haynes manual with a good gauge, all 6 plugs removed etc.

seems to me if the problem on 5-6 was a head gasket the compression would leak down faster bleeding through to the other cylinder? could a lower intake gasket cause a loss of compression if its blown in the right place? whats the track record for head gaskets on this engine

again, the truck has been going every day for over a month and lost no coolant or oil which was changed when I got it, old oil was clean and the new oil is as well

also, when I pulled the new plugs out, 4 of them are pretty much spotless after only a few trips granted, the other 2 however are already starting to turn brown like the 4-5-6 plugs seen in the pictures, these plugs are the two that came out of the cylinders with low compression

 

I'm afraid it's time for a teardown.

 

do you think its rings? valves possibly, not much else it can be I suppose?

I am rather perplexed by this, it does not build compression on cylinders 5 and 6, the first pulse on the passenger side for example, each cylinder jumps up to about 115 psi, and keeps building until it reaches 160 by the fourth pulse, then it holds pressure very well

5 and 6 however, barely reach 60 psi by four pulses but it does however maintain that pressure for awhile, why does it not drop more rapidly? im no engine expert sadly so maybe this is normal but it seems odd to me

 

Squirt a little oil in the ones that were reading low. If it goes up to normal/almost normat then you can be looking at rings. If little to no change it could be valves or head gasket.

Also when the low cylinder is pumped up listen to the cylinder next to it, if you hear it leaking in the adjacent cylinder, it's probably a head gasket.

 

Not to say that it won't happen, but I've never come across a 97 up 4.2 with a bad head gasket. To properly do a leakdown, you have to remove both rocker arms from the cylinder being tested. As far as the lower compression in 5 and 6, you could have pumped up the lifters while testing all the other ones. Try the compression test again doing 5 and 6 first.

 

replaced just about all of the EGR components and got the codes to stop for that, o2 senors still throwing codes, not sure if its thanks to the missing cats or they are indeed bad.. both maybe?

the book says to test the engine once its warm, first test was on a cold engine, did it again warm and the result are basically the same with different numbers, 5 and 6 are still low even after adding oil to the cylinders, still low compression, I suppose I could retest 5 and 6 on a cold engine, leak down however is not the problem, I suppose it is a problem.. but the low compression is a bigger concern

can the lower intake gasket cause low compression? seems to me it would have to be the valves leaking before the intake gasket could leak?

 

Low compression in 2 cylinders?

There's no way to sugar coat this.

 

please explain, what exactly you mean by "a tear down" as this is most unhelpful without some sort of context, the first thing that comes to mind where I hear "tear down" is completely rebuilding an engine right down to the rod/main bearings, however.. I think its obvious this is not whats needed in this case

however, if you mean pulling the lower intake and possibly the drivers side head to see whats really going on, you could of just said so

at any rate, this is what I plan to do.. I am however going to see if the problem can be solved along the way before I get to the head pulling bit, which is why I would like to know what to look for

how many different faults can actually cause low compression on 2 cylinders near each other, with this particular engine that is

 

Pretty much 2 cylinders next to each would point towards a head gasket. How ever you could also have a valve in each cylinder that is bad. Did you do the wet and dry compression test, to see if it is a top end issue or rings. Remember if the compression doesn't come up with the wet test then the issue is above the pistons and rings. See post #8 in this thread.

Tear down in this case would be at the least to pull the head, that isn't a two screws and wipe with a rag type job. If it were mine and I had to do one head gasket I'd do them both, if one failed the other may not be far behind. Plus they come in pairs at most places any way.

 

small update I suppose

pulled the heads this week, head gasket was not blown, one of the little white ring things on the lower intake gasket was blown though, replaced all the gaskets (head/lower/upperintake/etc.) and the truck still has low compression and runs rough

a friend of mine did suggest something however, weak valve springs, so in the process of checking this we discovered the possible source of all the problems

with the valve covers off, after turning the engine over checking things we noticed something strange, rocker arms were changing location, IE if they sit for a minute in the down position.. they slowly rise back up, and there has always been a slight ticking sound when we shut the engine down, thought it was just the normal creaks and moans of hot metal

turns out.. its the lifters leaking down, you can put your finger on the valve springs and feel the popping and watch the lifter collapse, I assume bad lifters would cause a loss of compression? since they cant open and close properly, and the rough running etc.

either way its a big problem that needs addressed, any magick tricks to bring them back? or should I just replace them all, dont want to risk others being bad too

 

Seems to me if the lifters leaked down a bunch, it would not lower your compression reading.

FWIW, are you sure your spark plug wires are hooked up in the right order? #5 and #6 do not match the order on the coil (the coil is reversed for these two cylinders - the #5 spot on the coil goest to #6 cylinder, and #6 spot on the coil goes to the #5 cylinder).

If the previous owner hooked it up wrong, you would just be repeating their mistake.

This might not explain the low compression, but it could explain the weak running and darker plugs on those two cylinders.