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Car Forum / Jeep / September 2007CJ7 "missing" at highway speeds or under load - HELP!!
I have an 85 CJ7 that has developed a nasty habit of missing extremely bad at highway speeds or when pulling a utility trailer (when the engine is hot). I have replaced the plugs, coil, dist. cap & rotor, and control module - all of which produced nothing except a much lighter wallet. The fuel filter is only about 1 year old. NOW for the manifold leak. It has had an exhaust manifold leak for some time (I know I need to address that issue also). The issue (missing) started after I drove the jeep 6 hours to the beach, (so I could run it on the sand) all week at the beach, and did not have a problem - until 30 minutes into the return trip. It seemed as soon as I let the engine cool off, I could go about 60 miles until it started acting up. Since then it has gotten much worse. I can drive it around town and it seems OK until I hit the highway. All of this said I started thinking that I might have a burnt valve caused by the manifold leak, but I wanted some other opinions before I pulled the head. Any help would be great, because I would really like to get the "Green Goblin" back on the road. Thanks. The cold air from a cracked exhaust manifold can easy warp an exhaust valve. A compression test with a little oil will find it: http://www.georgiazclub.com/tips/ztech/comptest.htm But you're describing an ignition misfire, and I've cooked a set of plugs in a quarter mile. You didn't say you replaced the ignition wires, which without the special pliers to pull them are easily damaged. God Bless America, Bill O|||||||O mailto:LWHughes3rd@aol.com http://www.billhughes.com/ > I have an 85 CJ7 that has developed a nasty habit of missing extremely > bad at highway speeds or when pulling a utility trailer (when the [quoted text clipped - 18 lines] > Goblin" back on the road. > Thanks.  SignaturePosted via a free Usenet account from http://www.teranews.com On Sep 6, 8:54 pm, "L.W. \(Bill\) Hughes III" <LWBillHug...@hughes.net> wrote: > The cold air from a cracked exhaust manifold can easy warp an exhaust > valve. A compression test with a little oil will find it:http://www.georgiazclub.com/tips/ztech/comptest.htm [quoted text clipped - 31 lines] > > - Show quoted text - Thanks for the advise on compression check - I'll give that a try; and I did replace the wires along with the plugs, I just forgot to mention. -Shadow > I have an 85 CJ7 that has developed a nasty habit of missing extremely > bad at highway speeds or when pulling a utility trailer (when the [quoted text clipped - 18 lines] > Goblin" back on the road. > Thanks. How's your timing chain? tw > > I have an 85 CJ7 that has developed a nasty habit of missing extremely > > bad at highway speeds or when pulling a utility trailer (when the [quoted text clipped - 24 lines] > > - Show quoted text - As far as the timing chain is concerned - I have not a clue. Is this something I should check out? >I have an 85 CJ7 that has developed a nasty habit of missing extremely > bad at highway speeds or when pulling a utility trailer (when the [quoted text clipped - 18 lines] > Goblin" back on the road. > Thanks. Did you replace the plug wires? Spdloader > >I have an 85 CJ7 that has developed a nasty habit of missing extremely > > bad at highway speeds or when pulling a utility trailer (when the [quoted text clipped - 23 lines] > > - Show quoted text - Yes,when I replaced the plugs - forgot to mention ;) > I have an 85 CJ7 that has developed a nasty habit of missing extremely > bad at highway speeds or when pulling a utility trailer (when the [quoted text clipped - 18 lines] > Goblin" back on the road. > Thanks. Possibly you are running very lean. The plug condition can tell you a lot when you take them out. Under ideal circumstances, your plugs should be colored a light tan color. If they are perfectly white, and/or have little silver specks on them, your engine is running extremely lean. This could be caused from low fuel pressure, low float level, or possibly something getting plugged up in the carb. One other thing. If you haven't done it yet, you might want to look in to doing the Nutter Bypass. It will improve things very nicely. Here is the how-to article: http://www.4x4wire.com/jeep/tech/electrical/jn-ignition99/ Chris I would replace the fuel filter, it is due. I go through one or more a year when using my CJ off road. The dust and dirt collects under the cap and some goes in every time I add fuel. I always carry a spare even. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's - Gone to the rust pile... Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590 (More Off Road album links at bottom of the view page) > I have an 85 CJ7 that has developed a nasty habit of missing extremely > bad at highway speeds or when pulling a utility trailer (when the [quoted text clipped - 18 lines] > Goblin" back on the road. > Thanks. It's odd that while you were gone, a lot of the stuff that I knew you had experience with came up. I answered the ones I could but figured you would have some better input on some of them. I wasn't an epic substitute for you however, since I did not recommend that anyone check the ground strap at the back of the engine. Sorry. :-) Chris > I would replace the fuel filter, it is due. > [quoted text clipped - 32 lines] >> Goblin" back on the road. >> Thanks. Had fun out Jeeping, almost didn't come back. And another gem for the OP, the air filter on the gas tank vent... When that plugs up, he will get his symptoms. To test, open the gas cap when it happens and see if it is fixed right away. Mine even jumps rpm when the cap opens with a plugged filter. The filter is $2.00 or so and fits in the bottom of the charcoal canister. Mike > It's odd that while you were gone, a lot of the stuff that I knew you > had experience with came up. I answered the ones I could but figured you [quoted text clipped - 40 lines] >>> Goblin" back on the road. >>> Thanks. > Had fun out Jeeping, almost didn't come back. > [quoted text clipped - 54 lines] > > - Show quoted text - Thanks for all of the suggestions - I took it out this weekend without the gas cap on, but it still missed when going up a hill in 5th after it was warmed up. I read your response to another fellow's problem, and I feel I might have the fuel filter on upside down - could this be causing the problem? I also had my brother ride with me when I took it out, and he seemed to think it was a fuel issue, not a burnt valve as I thought. I have not pulled the plugs, but I can do that next weekend and see if it is showing signs of running lean. Thanks for all the help, and I welcome any more suggestions!! -Tim >> Had fun out Jeeping, almost didn't come back. >> [quoted text clipped - 55 lines] > Thanks for all the help, and I welcome any more suggestions!! > -Tim 'Going up a hill in 5th' OK, that can be a whole different animal. You are trying to pull power in overdrive. Even with stock tires, this can cause issues with pinging. First off, the fuel filter. Besides being upside down, they need to be changed every year or more often if you drive on dusty roads. Second the 'miss'. Are you describing a timing knock or 'ping' that makes a rattling noise and bog under heavy load? Does it go away when you drop to top gear? (4th) Even stock with the knock sensor working, the 82 to 86 CJ7 owners manual warns about this. The manual states when it misses under load, to run higher octane in it. If the higher octane still doesn't stop it, you are supposed to stop and lighten the load or slow down to lighten the load. The owners manual also states 'not' to use any alcohol or ethanol mix at all in it. If it is an emergency, only use enough to get to real gas. I have the computer put to sleep in my 86 CJ7 via the 'Nutter' bypass so I have no knock sensor to change the timing when it pings. Mine will 'not' pull power in any gear over 65 mph or over 3300 rpm if I use regular gas or gas full of ethanol. It will miss and bog and gets really bad gas mileage. When I run 91 or 92 octane, the engine picks up and flies. 2nd pulls fast to 4400 rpm at 52 mph or so, 3rd powers up to 75 mph and 4th buries the speedo 'easily'. I was running in the fast lane last week coming home from camping fully loaded and had the speedo pinned at 140 kph for a while. Still got 11L/100 km or 23 mpg on that trip. Mike "I feel I might have the fuel filter on upside down - could this be causing the problem?" You're trolling aren't you!!!!!!!!!!!!!! http://www.jeep4x4center.com/jeep-cj5/inline-fuel-filter.JPG God Bless America, Bill O|||||||O mailto:LWHughes3rd@aol.com http://www.billhughes.com/ > Thanks for all of the suggestions - I took it out this weekend > without the gas cap on, but it still missed when going up a hill in [quoted text clipped - 6 lines] > Thanks for all the help, and I welcome any more suggestions!! > -Tim SignaturePosted via a free Usenet account from http://www.teranews.com |
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