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Bogging and hesitation under a cold start

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aalb1
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Joined: 17 Jun 2006

PostPosted: Thu Nov 16, 2006 9:10 pm    Post subject: Bogging and hesitation under a cold start Reply with quote

My wife has a 98 4.0 Cherokee tipping the odometer at 100k. For a while now it's been having trouble starting. You'd have to give it a decent amount of cranking time before it starts. Once it starts and you shut it off, it will restart like a champ.

But recently it has had some bogging and hesitation when it is still cold and warming up. The idle makes it seem like it wants to stall and it did stalled once too. Once it reaches full operating temperature it runs and accelerates like normal.

It's not throwing any codes. I replaced the plugs, wires, dizzy cap, air filter last spring. I also replaced the cat converter, and exhaust late August.

Any ideas on how I can trouble shoot this?
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dancerman
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Joined: 08 Jun 2006
Location: Atlanta

PostPosted: Fri Nov 17, 2006 3:16 am    Post subject: Reply with quote

How long does it have to sit before the problem is revealed? It could be that the fuel system is not holding pressure after a rest or the fuel pump could be getting weak. You may want to do a compression check to verify all is good in there.
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aalb1
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Joined: 17 Jun 2006

PostPosted: Sat Nov 18, 2006 5:43 am    Post subject: Reply with quote

dancerman wrote:
How long does it have to sit before the problem is revealed? It could be that the fuel system is not holding pressure after a rest or the fuel pump could be getting weak. You may want to do a compression check to verify all is good in there.



I have to wait it just about hits full operating temperature. Until then it will bog at times but not every time. But once again, once it hits full operating temperature it runs flawlessly.

As for the Compression thumbs

Any reason the fuel pump wouldn't be working good during the warm up cycle?

Any other ideas?
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dancerman
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Joined: 08 Jun 2006
Location: Atlanta

PostPosted: Sun Nov 19, 2006 4:06 am    Post subject: Reply with quote

I had a similar problem with another car (not a Jeep, though). It ran crappy (bucking and hesitation) until hot. But eventually, the problem got worse and it ran poorly all the time (but much worse when cold). It was never hard to start though. I had to get the engine computer rebuilt and now it's working fine. There was a leaking capacitor on the board. This is a fairly common problem for this particular car. I'm not aware of this problem with Jeeps but I guess it's a possibility.

I never did know what the exact cause (fuel or ignition) because there were never any codes stored. I suppose it's possible that the computer is cutting fuel pump for some reason.

If there are no codes then this is difficult to diagnose without a engine scope.
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JeepinNH
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Joined: 13 Sep 2005
Location: New Hampshire

PostPosted: Sun Nov 19, 2006 12:33 pm    Post subject: bucking Reply with quote

My 99 with 98k is now exhibiting similar issues except it starts fine. It will buck and sputter at certain rpm's but eventually goes away. Seems to be worse in wet weather. The only way to keep the vehicle going when this happens is to slowly pump the pedal slightly. This happened a few months ago also but went away after new plugs/wires/cap&rotor. I'm now going with the shotgun effect and replacing the coil, CPS and TPS seeing all of these have been posted as issues. They should be arriving in a day or 2 so we'll see. I dislike shotgunning parts but it is so intermittent that it's tough to troubleshoot. I have no faith in mechanics with this type of issue. Of course, there are no codes coming up.
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Mike

Present: 99 Cherokee
Past: 86, 87 Cherokee; 94 Grand Cherokee
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aalb1
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Joined: 17 Jun 2006

PostPosted: Sun Nov 19, 2006 6:22 pm    Post subject: Reply with quote

JeepinNH... Your speaking my language since I thought that the whole distributor setup might be the culprit.

I also know Honda's really well and they have a quirk with them that when their distributor goes bad all the diagnosis in the world will still tell you that the distributor is still good. The only way to tell if it's bad is to swap it out with a known working one and see if the problem goes away.

Needless to say I hate spending money when I don't need to. I'd rather buy a bum a beer.

Keep me posted.
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JeepinNH
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Joined: 13 Sep 2005
Location: New Hampshire

PostPosted: Thu Nov 23, 2006 1:29 pm    Post subject: parts is parts Reply with quote

Yesterday I replaced all 3 components I listed previously (about $200). No change in power but so far no sputtering. Only time will tell if all is good. Every one of the parts was a pain to replace, the CPS was the worst. 11mm bolts way up high. I had to move the front drive shaft out of the way and lower the tranny so I could get at with with 4 feet of extensions. The bolts brought some of the aluminum from the tranny with them, smart Chryco thinking there. Rolling Eyes

I had to break the old TPS to get it off because one of the torx screws fell apart, at least it comes with new ones unlike the CPS. It should also come with them, they look like dealer only bolts made of soft metal. If there's one thing I hate most about American cars it's the quality of the nuts/bolts. I'll update again in a few days.
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Mike

Present: 99 Cherokee
Past: 86, 87 Cherokee; 94 Grand Cherokee
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JeepinNH
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Joined: 13 Sep 2005
Location: New Hampshire

PostPosted: Wed Nov 29, 2006 8:18 am    Post subject: trial and error Reply with quote

Well, it's been almost a week since I replaced all the parts. The bucking happened on 2 different occasions but no where near what it did previously. These ones were more of a lag going up a hill. Press the gas a bit harder and it went away. I'll keep driving it and see what happens. Maybe it's time for some FI cleaner to rule dirty injectors out. Will post back if I get full on bucking Cherokee again. I really need this car to be more dependable because it looks like my wife's van needs a tranny... ug Crying or Very sad
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Mike

Present: 99 Cherokee
Past: 86, 87 Cherokee; 94 Grand Cherokee
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JeepinNH
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Joined: 13 Sep 2005
Location: New Hampshire

PostPosted: Thu Dec 21, 2006 3:17 pm    Post subject: update Reply with quote

Well, it happened today. I drove it for 20 mins no issues. Let it sit for 30 then 5 minutes after starting it I had the issue. It first started as I was coasting to a stop just touching the gas. I watched the RPM needle hop up and down. I had to hold the gas a bit to keep it running. It then cleared up. I let it sit for 15 mins then headed out again. Five minutes later it happened at a higher rpm. Pressed the gas harder and it cleared up after a minute or so. The weather was sunny, dry and 50 degrees. This thing is just plain bizarre. It seems to be on warm up which clears itself. Here are my thoughts, anyone have any ideas?
Changed: CPS, TPS, Coil, wires, plugs, cap & rotor (it seems better than it was)
Could it be?
Fuel pump- I figure no because it goes if you step on it or let off on the gas. Only seems to be certain RPM's which varies.
Fuel injectors - Also figure no because it should only affect one not all.
Computer - My best guess because it's so intermittent but I hate to change it without being sure.
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Mike

Present: 99 Cherokee
Past: 86, 87 Cherokee; 94 Grand Cherokee
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dancerman
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Joined: 08 Jun 2006
Location: Atlanta

PostPosted: Fri Dec 22, 2006 10:32 am    Post subject: Reply with quote

Sounds like you have replaced just about everything except the ECU. I feel your pain. Intermittent problems are the most expensive and aggravating. You may want to check that the computer connections are clean and secure before buying a new ECU.
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JeepinNH
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Joined: 13 Sep 2005
Location: New Hampshire

PostPosted: Wed Dec 27, 2006 6:50 am    Post subject: bogging Reply with quote

Yeah, I'm going to hold off on the ECU for a bit. Hopefully whatever the issue is, it will fail completely. Listen to me, sounds like I want to be stranded somewhere.
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Mike

Present: 99 Cherokee
Past: 86, 87 Cherokee; 94 Grand Cherokee
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jeepkid2005
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Joined: 01 Jan 2007
Location: Harrison, AR

PostPosted: Wed Jan 03, 2007 6:09 pm    Post subject: Reply with quote

Are you sure you dont have condensation in the bottom of your Distributer; I take a drinking straw and Duct tape into a shop vac sliding it around the Dizzy's inner workings to remove/oil/dirt/water.
I don't know how good it is for the wiring but I spray all of my wiring and conectors with W/D 40 ( water disipation / 40 th try...) twice a year. It has made the old foot switch dimmer switches work with bending that magical little red tube that comes with it.
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jeepkid2005
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Joined: 01 Jan 2007
Location: Harrison, AR

PostPosted: Wed Jan 03, 2007 6:17 pm    Post subject: Reply with quote

W/D 40 DOES HAVE EXPLOSIVE PROPERTIES; LIKE THE GUY THAT RAN THROUGH THE CARWASH AND WASHED HIS MOTOR AND IT POPED AND SPUTTERED SO INSTEAD OF LIGHTING A PAPER BAG ON FIRE AND DRYING OUT THE CAP HE SPRAYED THE WD 40 INTO THE CAP AND PUT IT RIGHT BACK ON... DON'T KNOW HOW TRUE THIS IS BUT I HEARD THE CAP EXPLODED...SO TAKE IT FOR WHAT IT'S WORTH...
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jeepkid2005
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Joined: 01 Jan 2007
Location: Harrison, AR

PostPosted: Thu Jan 04, 2007 1:00 pm    Post subject: Reply with quote

We used to service Contel trucks and they seemed to have a problem with the Distributers siezing, had that prob on a 400 Cleavland and went to O'Rielys and bought a [u]Rebuilt[/u] Distrib for 35.00 and change, they wanted 33.00 for an advance,35.00 for a module seperatly but got the whole thing for one price. Beats R & Repairing a non-spinning unit. Driving out the gearpin, maybe replacing the bearings yourself...Chipping the gear...
Another Avenue / takes 10 Min to pull it and see if it spins freely.

[/u]
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JeepinNH
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Joined: 13 Sep 2005
Location: New Hampshire

PostPosted: Fri Jan 05, 2007 7:33 am    Post subject: hesitation Reply with quote

I suppose it could be condensation. Since the temps cooled off around here it hasn't happened at all to mine. When I changed the cap and rotor it looked dry as a bone inside.
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Mike

Present: 99 Cherokee
Past: 86, 87 Cherokee; 94 Grand Cherokee
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