Hey again all. Moving on to the next problem with my pickup. It's a '96 F-150 with 4.9L and M5OD. The truck had been sitting for 12 years before I tore into it a few months ago. It started with a CEL and code for lean mixture on banks 1 & 2 and "secondary air injection incorrect flow". It idles anywhere from 1000 to 1500 rpm at all times. I'm also getting 12-13 mpg on the highway.

I have a confirmed crack in both the last two AIR rail ends right where the rail goes into the head. I get a real loud ticking sound under load that sounds like an exhaust leak, yet both maifolds have already been on and off and checked by my local mechanic while doing a valve job. I'm fairly confident it isn't an exhaust leak, because I tried to JB Weld the cracks in the AIR tube and the noise did go away until the JB Weld blew out.

So what I'm trying to ask is: would these cracks in the tube on the head cause a vacuum leak that leads to the symptoms I've described above? Furthermore, is it worth replacing if it turns out to be the problem? I'm a broke college student who's a shadetree mechanic at best, and it seems like there's a hell of a lot of stuff that's gotta come off before I can get to the tube.

I can and will buy the parts and fix the problem over Christmas break if it is recommended to be fixed. Likewise, if the only adverse effect of it being broken is this ticking noise then I might hold off and do it later.

Thanks for all the help. The truck's almost done!

Evan

 

A leak in those air tubes constitutes an exhaust leak since they connect directly to the exhaust ports in the head, and any exhaust leak upstream of the O2 sensor will mess with A/F ratios. And if you're going in there you can just delete the air tube and plug the holes in the head if you don't have emissions tests to pass.

Your high idle problem is not related to this unfortunately, you have a pretty good vacuum leak or the IAC or TPS are messed up.

 

A 96' half ton with AIR system? I'm no 4.9L expert but that sounds off. Is this truck OBDII?

Edit: dumb question.. 4.9L retained secondary air while the 5.8L didn't.

 

Had the same drivetrain in my old 96 and quicksteel works well for about 6 weeks give or take haha. I do have emissions to deal with here so ended up replacing the tube eventually. See if you can get the flared nut ferrule sort of things that actually go in the head. It's been over 10 years since I did that job, in the snow, and I vaguely remember wishing I had new fasteners. And that I wasn't going to stop putting it back together over that.

Like Paul said if you don't have an emissions test, I would block them off but not sure if you need to close the other side somehow. Well, how, anyway because that wasn't the route I took.

Do you have a tach in the truck?

 

Wasn't that bad of a job actually. Start hitting what you can tomorrow with PB Blaster if you decide you will take it on though.

 

Thanks for the technical help conanski. I'll have to test and/or replace TPS. I've already cleaned the IAC and replaced the throttle body gasket, but maybe IAC needs replacing too. As for deleting the upper rail, I would if I was planning to keep the truck more than about 3 years - it's gonna end up as my little brother's first car once he learns to drive, so why not replace the tube that way he has to tear the intake apart again to fix it a few years down the road!! Haha, but also not sure if deleting it would cause the computer to throw a hissy fit - I've got emissions inspection yearly where I live (northern Virginia) and since the truck's OBDII they just plug up to the computer.

Yup its OBDII. And I wish like hell it didn't have secondary air but it does.

Willigaf - I appreciate the advice and suggestions. I'm thinking I'll try and tackle the project when I head home in two weeks. I'll probably replace the tube since this truck is still required to be emissions tested/inspected for the next few years. I'll make sure to get the new ferrule nuts along with the pipe. Out of curiousity, how did you get the quicksteel onto the tube? Mine has a crack that runs all the way around each inlet that goes to cylinders 5 and 6. Did you remove the upper intake to apply it?

And yes, the truck has a tach. At idle, its running usually just over the mark for 1000 rpm - though I'm not sure how accurate it really is

 

Mine were cracked on the front two tubes. Made it much simpler than how big a pain the back two sounds like. It's mold-able though. If you can get jb weld on there I'm sure you can get the quiksteel in there

 

Yes Vac leak! I went to replace mine and found the PVC valve hoes just about in half. Still in the process of getting the New AIR in (waiting on it from UPS) but should be good to go when I get it all back together.

 

Holy thread revival! I replaced the AIR pipe a few months ago, what a disaster! I believe the #2 threads were terribly galled and the ferrule nut was unable to thread in all the way. Unfortunately now I have to do the job all over again to fix the truck properly, which I will do as soon as the truck no longer needs its emissions testing. The upper AIR pipe will come off and bolts will be put into the head, and cranked down TIGHT TIGHT.

For the record, there was one vacuum line which was burned through and replaced, but that honestly didn't help the problem at all. Starting to think it could be mechanical or some other related issue. Idle will still fluctuate between 900-1100 RPM.

 

Yelp even nuggent mine still has a high idel, anywhere from 1600-1800 when warmed up. I have replaced alot of parts and still nothing. Im starting to believe its the computer or throttle body... I am looking today since we dont have a flood here in TN.

 

Any help would be greatly appreciated if anyone has any answers.

 

Have you checked for vacuum leaks?

 

I'd do as minimalist suggested. It seems our trucks have miles of old vac lines and the youngest of the breed are now 23 years old. I've searched for leaks left and right and repaired many lines including one I couldn't have seen without completely removing the upper intake.

 

my green EGR vacuum line had 1" crack long ways with line, it was in the black split wire loom with the rest of the vacuum lines didnt find until I replaced them all

 

So I had to take mine to a shop and was hoping for them to get all 6 of the bolts out for the AIR pipe which I couldn’t because the 6th one was almost rusted in half, they could not so what they did is plugged the holes with bolts and then JB weld the last one really good. Haven’t had any problems out fo them yet, but have only drove about 300 miles since then. I have also deleted my EgR pipe with a piece of metal because I thought I had a leak there, which was causing my high idle but it didn’t help. I have a vac leak somewhere bc it’s still ideling around 1500rmps when warmed up, I did notic that where the PCV valve sits when I sprayed with carb clearance it bogged down on me but dose anyone think that that is letting that much air in to cause a vac leak like that? I did put a piece of wood over the throttle body and closed that off, the truck didn’t die, bogged down quite a bit but still leaking somewhere. Thanks of any help!!!