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87 XJ intake bolt tightening

XJake77

NAXJA Forum User
Location
Kentucky
Hi, Everyone. First time posting on this forum. Just bought my first Jeep from a friend about a month ago and have been slowly getting it back up to daily driving condition. Its an 87 Wagoneer/XJ with the 4.0 Renix I6 and automatic transmission. As of right now the biggest problem I have with it is the high idle. I can't tell exactly how high due to not having a tachometer but I know it will pull me along into second without me touching the throttle while in drive. I've cleaned the throttle body and the IAC and freshened up the engine grounds. I decided the next step would be to torque down the intake manifold bolts, but I'm having trouble figuring out how to reach them! All the posts I read make it sound so easy but I've crawled under and over and haven't found an easy solution other than removing other parts which I would like to avoid. Any help will be greatly appreciated. Thanks for your time!
 
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The way I do it is take out the air box and use two people. One person under to hold the socket and extension on the bolt and one on top to work the torque wrench. It's a pain but really doesn't take to long once you figure it out. You need an assortment of extension lengths.

I also seldom mess with the end studs, they tend to snap off with the recommended torque. And/or snap off when trying to remove the nuts.

You really have to ohm test the TPS ground and make sure the TPS is adjusted properly.

I plug off all the vacuum nipples on the intake except for the fuel regulator and see what happens to my idle. I made a little kit for this using the appropriate sized tubing cut into 2-3" lengths and plugged with screws or bolts. I keep the kit in my toolbox for next time.

Check and see if your fuel regulator isn't dumping fuel past the diaphragm directly into the intake.

I use an unlit propane torch and spray the gas near the injector seals. If you have a significant leak past the injector "O" rings the RPM'S will increase.

You can look down the IAC air passage with a flashlight and work the throttle little by hand and watch the IAC piston move. If it doesn't move you Likely have an IAC issue. Don't try to test the IAC dismounted and out of the TB, it will shoot the IAC piston into the neighbors yard (three guesses how I figured this out :) ).
 
Thanks, 8mud! First chance I get I'll break out my torch and multimeter. Are the end studs your talking about the ones that only go through the exhaust manifold and not the intake? if so I think someone has already snapped one of those off before I bought the Jeep. Is this a significant problem If all the other bolts are tightened to spec?
 
Thanks, 8mud! First chance I get I'll break out my torch and multimeter. Are the end studs your talking about the ones that only go through the exhaust manifold and not the intake? if so I think someone has already snapped one of those off before I bought the Jeep. Is this a significant problem If all the other bolts are tightened to spec?

I think all three of my XJ's had a broken stud at one time or the other. Mostly it didn't cause any issues if the rest of the bolts were torqued down properly. I eventually replaced the studs, usually when it was time to for a new exhaust/intake manifold gasket anyway.

I also got my 96 and 88 (used) with broken studs (both dealer serviced). I did blow an exhaust/intake gasket right next to a rear broken stud once, which may or may not have been the cause of the gasket failure. I had a fairly severe exhaust leak blowing right onto the firewall.

I've found loose intake/exhaust bolts on numerous XJ's. I check mine periodically. Fairly common issue, that if caught early can save some grief.
 
Click on the link below and do Tips 1 through 5, and maybe even 27 before wasting any more time on stuff. the Renix does not "high idle" with vacuum leaks like the HOs do.

http://www.naxja.org/forum/showthread.php?t=1115935

It will high idle if you have a significant vacuum leak and the right set of circumstances. Little leaks and the ECU will try to correct. A small vacuum nipple completely open at the intake manifold can give around a 1200 RPM idle. A disconnected (open) brake booster nipple and it gets around 2000 RPM. I've done it experimenting, though I didn't spend a whole lot of time investigating or studying it in depth. Small vacuum leaks and it may go into what I call hunt mode and the RPM's can cycle from a little high to a little low, while the ECU tries to find the sweet spot.

You are right though, IMO it is more likely to be a sensor and/or ground issue. Most likely the TPS. I've gotten my TPS wet before and had my idle go way high. The TPS doesn't like water.

Probably a good idea to check the intake/exhaust bolts anyway. They do come loose. He may have more than one vacuum leak, a little here and a little there and it adds up and even if it isn't his main issue, it can still be an issue.
 
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I still haven't gotten to the manifold bolts, but I've cleaned the throttle body, replaced the TPS (adjusting it to spec), cleaned and tightened the grounds on the passanger side of the engine (helped a lot!), and fixed a vacuum leak. Replacing the TPS did nothing which greatly disappointed me because I thought that was the main cause. The idle is still a little high considering it will still pull me into second gear without me touching the throttle. I still plan on tightening the manifolds, replacing the O2 sensor and checking the engine temp sensor. Problems that still persist: AWFUL gas mileage ( Around 8 mpg), a slightly high idle and the engine running cold with a new thermostat (one tick above 100 if I'm lucky). something odd happened today after about an hour drive I turned the jeep off for about 30 min and when I went to turn it back on the idle was rougher than ever. Don't know if this could aid in any diagnosis. Thanks for all the help!
 
The manifold bolts can be intimidating the first time you do them. Once you do it a couple of times only the air box comes out. I've found it possible to torque all of them to spec with the engine in the car (at least up until the manifold change in 99) except the rear most. Just make sure you have a good selection of extensions and a wobble (and a universal for the rear most). I go at the rear most with a 36" extension. That way the ratchet is about a foot outside the fender so no possible damage to the exterior. The middle lower bolts I end up with about a 11-14" extension. I coat the bolts with nickel anti-seize to prevent them from rusting in the head. Regular or copper won't take the heat.
 
Alright, quick update. in attempting to tighten the bolts yesterday I discovered 2 of them broken off in the engine block. I now have very little doubt as to what is causing my rough/high idle. Anyone out there have any tips on tapping these broken bolts out? I'm sure it's a process that requires the engine being lifted out if the jeep. If someone has done this particular procedure before or if there's a thread already on it that I could be pointed to I'd really appreciate it. Thanks!
 
Alright, quick update. in attempting to tighten the bolts yesterday I discovered 2 of them broken off in the engine block. I now have very little doubt as to what is causing my rough/high idle. Anyone out there have any tips on tapping these broken bolts out? I'm sure it's a process that requires the engine being lifted out if the jeep. If someone has done this particular procedure before or if there's a thread already on it that I could be pointed to I'd really appreciate it. Thanks!

For what it's worth, the first time I tore apart my manifold (1988) I discovered both my frontmost and rearmost bolts were snapped off. I was in a hurry, so I just shrugged and put it all back together with the rest tightened down. Ran it like that for months, and never had a high idle (mine idles low, hahah ). The next time I tore it all apart, I was doing the head gasket so I removed the head and took it into a shop to do the hot-tank/valves/crackcheck/etc. They pulled out the bolts for me. All that to be said, I wouldn't worry toooo much about the bolts, it's a common issue. Your idle is more likely to be a bad vaacum hose or usual RENIX ground type issue.

If your rearmost bolt is broken and you really are keen on drilling it out, you'd probably save yourself a lot of cussing and broken drillbits (space is tight back there) by just pulling the head out, not the whole engine. I don't know how mechanically inclined you are but pulling off the head was not particularly difficult - hardest part being lifting that heavy SOB out/in. If you have a hoist or chainfall it would be even better. As a bonus, it's a lot easier to torque the manifolds back on with the whole deal outside the jeep, and mine ran noticeably nicer after the valve job. You'll just want a new HG (I used a felpro 530-SD), new head bolts (renix era are wierd to find, I used chbs-1128 from headbolts.com) and a manifold gasket. Might want to replace the lifters while the head is off too. Make sure you look up/ do the three-stage torque process when installing the new headbolts!

That's what you do if you suffer from Project Creep like I do :looney: Seriously though, you can probably run it with the broken bolts forever and not really worry about it.
 
Really appreciate the advice! I'll start backtracking on my other projects and leave this one be for now. anyone know what size the bolt is for the main engine ground strap on the engine side?
 
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