BoostedAce Posted October 3, 2015 Report Share Posted October 3, 2015 I recently just bought a 2001 jeep grand cherokee 4.0L inline 6 as a daily beater. It has 128,000 miles, it has a extended startup/hard start. Vehicle also misfires on 4 & 5 at idle or in gear stopped but drives fine. I ran engine cleaner threw the intake and put plugs in it and seemed to change nothing. Any help would be appreciated. Thanks Quote Link to comment Share on other sites More sharing options...
zeitgeist57 Posted October 3, 2015 Report Share Posted October 3, 2015 Ignition coil could be rusted and arcing? A cheap and easy replacement part that should make a big difference. Quote Link to comment Share on other sites More sharing options...
BoostedAce Posted October 3, 2015 Author Report Share Posted October 3, 2015 Ignition coil could be rusted and arcing? A cheap and easy replacement part that should make a big difference. That was my next purchase, I'll be borrowing someone's Monday since it's all 1 bar. Thanks man Quote Link to comment Share on other sites More sharing options...
STEVE-O Posted October 3, 2015 Report Share Posted October 3, 2015 Do you know how to diag the misfire? This could also be causing the long start but they could be 2 separate issues as well. Quote Link to comment Share on other sites More sharing options...
BigOxley Posted October 4, 2015 Report Share Posted October 4, 2015 fuel pump or relay? Quote Link to comment Share on other sites More sharing options...
Geeesammy Posted October 4, 2015 Report Share Posted October 4, 2015 I recently just bought a 2001 jeep grand cherokee 4.0L inline 6 as a daily beater. It has 128,000 miles, it has a extended startup/hard start. Vehicle also misfires on 4 & 5 at idle or in gear stopped but drives fine. I ran engine cleaner threw the intake and put plugs in it and seemed to change nothing. Any help would be appreciated. Thanks My bet would be a weak pump. I believe the regulator is located within the pump assembly on those, but I am not positive. The best thing to do would be to verify you have the correct fuel pressure. It's possible the fuel filter is just that clogged (which I'd replace when I replaced the pump anyways) so maybe throw a new filter on first and see what happens. If your fuel pressure doesn't improve then it's a failing pump assembly. Quote Link to comment Share on other sites More sharing options...
Geeto67 Posted October 4, 2015 Report Share Posted October 4, 2015 I have a fuel pressure tester if you want to check it. Come by and I will hook it up. Misfires on old jeeps tend to be one of four things: 1) bad cam sensor inside the distributor 2) bad throttle position sensor 3) bad coil 4) clogged injectors. Quote Link to comment Share on other sites More sharing options...
BoostedAce Posted October 5, 2015 Author Report Share Posted October 5, 2015 I'll send you a pm and see when you are free. Quote Link to comment Share on other sites More sharing options...
Second Gen Posted October 5, 2015 Report Share Posted October 5, 2015 Good article on possible issues: http://www.jeepforum.com/forum/f11/4-0-check-engine-light-cylinder-2-3-6-misfire-894762/ His was a problem that Chrysler had a TSB for on the manifold (overheating or bypassing - unsure). Quote Link to comment Share on other sites More sharing options...
Grudes Posted October 5, 2015 Report Share Posted October 5, 2015 Good article on possible issues: http://www.jeepforum.com/forum/f11/4-0-check-engine-light-cylinder-2-3-6-misfire-894762/ His was a problem that Chrysler had a TSB for on the manifold (overheating or bypassing - unsure). I was going to bring that up to. The intake manifold overheats and boils the fuel in the #4 and 5 injectors causing a misfire. Quote Link to comment Share on other sites More sharing options...
BoostedAce Posted October 5, 2015 Author Report Share Posted October 5, 2015 It has the insulator above intake manifold Quote Link to comment Share on other sites More sharing options...
BoostedAce Posted October 6, 2015 Author Report Share Posted October 6, 2015 I tested the fuel pressure today, shut key off and fuel pressure dropped off 5lbs every 15 seconds so I know I found my hard start but I believe it's not misfire related since the car runs fine on acceleration. Quote Link to comment Share on other sites More sharing options...
Geeto67 Posted October 6, 2015 Report Share Posted October 6, 2015 What was the pressure when you turned the key but didn't start the car? Should be between 35-45psi Quote Link to comment Share on other sites More sharing options...
BoostedAce Posted October 6, 2015 Author Report Share Posted October 6, 2015 Engine running was 60lbs engine off was around 50 Quote Link to comment Share on other sites More sharing options...
Geeto67 Posted October 6, 2015 Report Share Posted October 6, 2015 Engine running was 60lbs engine off was around 50 that sounds fine. I don't think it is a pump issue but you may have a small weep bleeding the line down in static. The problem is that it is now cool enough that if you were having thermal failure on the electrical components you wouldn't know it - thermal failure in the ignition system is usually responsible for long hot starts or no starts. do you have a spark tester? put it on each of the plugs and see if your misfire is limited to one cylinder or if it is all of them. If one trace it back and see if you have an interruption in the wire or something causing arc-ing. You can test the crank position sensor with a continuity tester. I just realized above where I wrote Throttle position sensor I meant crank position sensor. my mistake. There should be no continuity between the b and C pins. Test hot and cold. http://www.cherokeeforum.com/f51/testing-cps-5563/ The cam sensor inside the distributor is a common fail point. I have put two or three in my jeep over the years to the point where I sometimes forget to check it when diagnosing ignition problems. Check your coil for cracks. Jegs had an accel coil replacement that I just bought and it is awesome. my coil was still functional but cracked to hell. Quote Link to comment Share on other sites More sharing options...
BoostedAce Posted October 8, 2015 Author Report Share Posted October 8, 2015 Someone let me borrow their coil rail and it didn't fix the misfire problem Quote Link to comment Share on other sites More sharing options...
Geeesammy Posted October 12, 2015 Report Share Posted October 12, 2015 Well? Quote Link to comment Share on other sites More sharing options...
Skinner Posted October 13, 2015 Report Share Posted October 13, 2015 Does it o ly happen when the engine is cold or is it a issue when it warms up as well? Quote Link to comment Share on other sites More sharing options...
BoostedAce Posted October 13, 2015 Author Report Share Posted October 13, 2015 I swapped the coil and it still didn't fix it, it only misfires at idle in gear or in park hot or cold unless the idle is above 1k rpm basically. Quote Link to comment Share on other sites More sharing options...
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