boxyjeep Posted October 8, 2018 Share Posted October 8, 2018 I've been trying to get my '88 MJ running right, but continue to experience a rough idle and what sounds like an intake leak somewhere around the #4 cylinder. So far, I've replaced: Exhaust manifold & gasket (replaced gasket twice) Throttle body cleaned, gasket replaced, MAP connector tapped & replaced Valve cover gasket Ensured all manifold bolts are properly tightened in correct order Checked head surface for approximate flatness using straightedge I'm about to pull my hair out on this one. I didn't see any obvious issues or cracks when I took the manifolds off the last time. I just pulled the heat shield off in order to get a better look, but still don't see any visible cracks or other issues. I ordered a mechanics stethoscope and will be using that to try to figure it out. Any ideas or suggestions would be super appreciated. Really hoping that the head isn't warped or cracked. Link to comment Share on other sites More sharing options...
Dzimm Posted October 8, 2018 Share Posted October 8, 2018 Maybe try a little soap and water to see if you get bubbles at the seal. Would at least narrow it down to an exact spot if that's where it's at. Link to comment Share on other sites More sharing options...
boxyjeep Posted October 8, 2018 Author Share Posted October 8, 2018 1 minute ago, Dzimm said: Maybe try a little soap and water to see if you get bubbles at the seal. Would at least narrow it down to an exact spot if that's where it's at. Forgot to mention, tried that as well but didn't see anything noticeable (will get a video on this). The exhaust/intake gasket was my first thought since I used the cheaper one that was included with the new exhaust manifold, so I replaced it with a good Fel-Pro unit and sprayed both sides with Permatex High-Temp Copper spray (but still had the same issue). Link to comment Share on other sites More sharing options...
Dzimm Posted October 8, 2018 Share Posted October 8, 2018 1 minute ago, Chargum85 said: Forgot to mention, tried that as well but didn't see anything noticeable (will get a video on this). The exhaust/intake gasket was my first thought since I used the cheaper one that was included with the new exhaust manifold, so I replaced it with a good Fel-Pro unit and sprayed both sides with Permatex High-Temp Copper spray (but still had the same issue). It's possible it's on the bottom side of the manifold, did you look from underneath? Link to comment Share on other sites More sharing options...
boxyjeep Posted October 8, 2018 Author Share Posted October 8, 2018 Just now, Dzimm said: It's possible it's on the bottom side of the manifold, did you look from underneath? Will be checking that once I get the stethoscope. I just removed the intake manifold heat shield to make things easier to see, but nothing notable. Also checked from underneath using mirror and from the ground, but couldn't see anything significant. Link to comment Share on other sites More sharing options...
Jeep Driver Posted October 8, 2018 Share Posted October 8, 2018 Injector Orings? Link to comment Share on other sites More sharing options...
Dzimm Posted October 8, 2018 Share Posted October 8, 2018 6 minutes ago, Chargum85 said: Will be checking that once I get the stethoscope. I just removed the intake manifold heat shield to make things easier to see, but nothing notable. Also checked from underneath using mirror and from the ground, but couldn't see anything significant. Hmm. What's the air movement like in that area from the fan? Would you be able to keep a match lit to see if it will draw the smoke in? Link to comment Share on other sites More sharing options...
boxyjeep Posted October 8, 2018 Author Share Posted October 8, 2018 44 minutes ago, Jeep Driver said: Injector Orings? Forgot to mention--I replaced these when I replaced the exhaust manifold. No leaks. They are definitely a bit noisy, but there is no fuel leaking and the vacuum leak doesn't appear to be coming from them. 43 minutes ago, Dzimm said: Hmm. What's the air movement like in that area from the fan? Would you be able to keep a match lit to see if it will draw the smoke in? There is a bit of air movement from the cooling fan. May try with the match (wish me luck--don't want to burn the garage down). Link to comment Share on other sites More sharing options...
HOrnbrod Posted October 8, 2018 Share Posted October 8, 2018 Try a cigar: Link to comment Share on other sites More sharing options...
Dzimm Posted October 8, 2018 Share Posted October 8, 2018 22 minutes ago, Chargum85 said: There is a bit of air movement from the cooling fan. May try with the match (wish me luck--don't want to burn the garage down). Yeah keep a fire extinguisher handy. 7 minutes ago, HOrnbrod said: Try a cigar: This is a better and safer method, might be hard getting the smoke to your leak if it's in a manifold tho. Link to comment Share on other sites More sharing options...
HOrnbrod Posted October 8, 2018 Share Posted October 8, 2018 Make an adapter for the throttle body throat and wedge the butterfly open. Used to do this with carbs back in the day... Link to comment Share on other sites More sharing options...
Motorhead X Posted October 8, 2018 Share Posted October 8, 2018 You might try the cigar method with the other end of the tube near the manifold... Link to comment Share on other sites More sharing options...
boxyjeep Posted October 9, 2018 Author Share Posted October 9, 2018 Re-torqued the bolts and it appears to not be leaking. Will keep an eye on it. Link to comment Share on other sites More sharing options...
Jeep Driver Posted October 10, 2018 Share Posted October 10, 2018 2 hours ago, Chargum85 said: Re-torqued the bolts and it appears to not be leaking. Will keep an eye on it. Do you have an aftermarket header/exhaust manifold? Is the flange on the exhaust thicker than that of the intake????? Take a close look at it. Link to comment Share on other sites More sharing options...
boxyjeep Posted October 15, 2018 Author Share Posted October 15, 2018 On 10/9/2018 at 6:24 PM, Jeep Driver said: Do you have an aftermarket header/exhaust manifold? Is the flange on the exhaust thicker than that of the intake????? Take a close look at it. The exhaust manifold is aftermarket but built to OE specs. I was also concerned about thickness differences between the intake and exhaust, so I measured them and found they were the same. This is still holding steady after re-torquing the manifold bolts to 25 ft/lbs in proper order. Link to comment Share on other sites More sharing options...
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