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#4710 of 5143 Engine Races at Start
Mar 14, 2010 (10:50 pm)
I just finished replacing the engine in my 2002 Jeep Grand Cherokee Laredo. When I start the car, the engine backfires once or twice and revs out of control. I mean, it really revs up like a bat out of hell. Think: your foot all the way down on the accelerator while your car is in park. I immediately need to kill the engine.
I suspect a major air leak, but inspection of the intake system looks good. The intake manifold is on tight, and I can confirm there are no vacuum hoses disconnected. I'm at a loss of what to try next. Any ideas?
#4711 of 5143 Re: Engine Races at Start [edub70]
Mar 15, 2010 (4:05 pm)
start looking at basics-like,is the throttle linkage hooked up correctly?..the butterfly valve that lets air into the intake? how about the sensor that tells the computer how far the throttle valve is open?..
-jeeps of that year are a real pain,as dalmer/chrystler won't release the comp codes,so we can fix our own cars !?!-even tho we own them,they still want to get their hands in our pockets for as long as we try to operate them !..my -98 laredo-5,2,awd ain't as easy as it could be,where i was trying to change the transfer case so i could have a 2 w d setting,but if i did that,the computer would go nutz....i dunno,but i wish you luck !
Mar 17, 2010 (12:17 pm)
I have an 06 JGC with about 60,000 miles on it, in the last, I would say 2000 miles or so, on a few occassions, I have been stopped at a stop light and when I went to accelerate from the stopped position, my RPM's would climb (4000) but it was as if the tires were on ice and might be spinning. I noticed on the digital gear indicator on the dash, that each of the the P R N D had the broken square indicator around it example [P] [R] [N] [D], I shifted into nuetral and then back into "D" and it went away, and it did it once at highway speed. Does any one have any experience with this happening? Aside from what I have discribed the transmission shifts and drives good as of the last 600 miles that I just drove, could it be a servicing issue? Speaking of servicing, does any one know how to DIY (do-it-yourself)?
#4714 of 5143 Re: 06 JGC Transmission [tthrasher34]
Mar 18, 2010 (3:12 am)
have you changed the trans oil and filters? jeep recommends every 30000 miles
#4715 of 5143 JGC-97 RUNNING ROUGH IN the OVERDRIVE.
Mar 19, 2010 (7:12 am)
">I have JGC 97 with Strait 6 Cyl, Auto Trans,4x4 (130,000 odom) - After about 5 minutes of driving it stutters and wants to stall between 45 to 60 miles an hour and seems to do it when in the overdrive gear, while on open roads( at cruising speeds). Happens mostly while going up inclines. The problem doesn't seem to exist while in lower gears but at one time it did happen while driving in 1st and 2nd gears - until I added some Sea-Foam. Now it seems to happen only in overdrive...There is also sometimes what appears to be occasional very mild slippage while gear changeing thru 2nd to 3rd and 3rd to 4th but I don't always notice it.There are no code lights flashing indicating any problems..... I am thinking about changing fuel filter which is in the tank and I will also replace the fuel pump - while the tank is dropped...Any suggestions? Jeepster98.
#4716 of 5143 Re: 06 JGC Transmission [tuggajb]
Mar 19, 2010 (8:23 am)
filters-or flushing's a good idea,but it also sounds like your six cyl might be missing..try tuning it up..overdrive at 50 mph puts the tack at 15/18 thousamd r.p.m's that's pretty slow-specially if your going up any kind of hill.. plugs/cap/rotor...then see how it runs..
#4717 of 5143 Re: JGC-97 RUNNING ROUGH IN the OVERDRIVE. [serenityknoll]
Mar 22, 2010 (8:02 am)
I have a 97 4x2 with I6, high miles . Everything I say is time consuming and vehicle will be offline several weeks and success is not guaranteed. A mistake could make it worse. Review Haynes manual for all procedures below.
My approach was fix it or junk it. Difficult problems take time to diagnose and mechanics are $$. The dealer is $$$. My dad replaced a fuel pump on his cadillac and the problem was a loose ground wire. But if you have a crackerjack mechanic, they can save time.
Check fuel pressure first. It is very easy to check on this vehicle. It already has a schraeder valve on fuel rail. My fuel pump was OK.
Next, do a compression test. I had one cyclinder that was a little below acceptable range. My mileage was 165K.
See Autozone about borrowing gauges. See harborfreight.com if you want to buy your own.
I did plugs, wires, and coil. (You have to remove plug for compression test so why not). Helped a little, but not dramatic.
Remove and inspect fuel injectors. Mine looked OK, but I did replace the O rings. Replacing injectors is expensive.
OK engine idle eliminates a lot of potential problems. If not, that's another story.
In the Haynes manual under emission controls, they tell you how to check every component. You need a voltmeter with stiff probes so you can backprobe. Make sure you don't short anything.
The next thing I did helped the most. I read it somewhere so I can't take credit. Replace the manifold gasket. On the I6, intake/exhaust manifold share the same gasket. Heat and vibration deteriate the gasket and loosen manifold turning it into a distributed vacuum leak. Not easy. I have 10 different 3/8 extensions and needed all. You might try re-torquing the bolts first to see if it helps.
Make sure you clean engine intake. Fingers and a rag. No easy way. The dirt should be hard and dry. If oily/moist could be a valve problem. It should not be wet. I had one oily/moist input on the cylinder with low compression.
After this you will really understand your engine so repairs become educated guesses instead of guesses. You might find something I didn't list.
There is one more test I can only describe briefly. With an RMS voltmeter you can measure signal from engine computer that controls fuel injectors. RMS value should increase as you increase rpm. Mine was OK. Need an electronic savvy mechanic for this one.
I worked on my car Summer 2008. Gave it to my kid in Sept for his sr year and he loved it.
#4718 of 5143 Re: disconnecting the connector from the oil pressure send unit [rwengr]
Mar 22, 2010 (8:26 am)
Once I understood that the primary latch was a slider, it was easy. Just slide the orange tab to the left or right (I was sweezing it, not a good idea!), then the second latch was disconnected by puting a scew driver in the housing, releasing the latch and connector. The rest was really easy!
#4719 of 5143 Intermittant Starting issue has escalated into a never starting issue.
Mar 27, 2010 (9:17 am)
Itís probably been a year since I talked to you about the intermittent starting issues I was having with my Jeep. I was convinced that the problem was the result of a fuel pump failure. After purchasing a new pump, my mechanic told me there was no reason to install it because my fuel pressure and pump were fine. When I brought it in last, they claim that no error codes were being produced by the computer. Shortly after I picked it up, the check engine light came on but it continued to run fine. Occasionally, the jeepís symptoms would return (maybe 1 in every 50-75 starts) but after waiting a few minutes, the engine would fire right up so I paid little attention to it. A few months ago I noticed an ever so slight noise coming from the engine that I had not noticed before. The best I can describe it as is a faint chirp sound almost with a hint of the sound of slight vacuum pressure. The most interesting thing about this noise is that it continues for a second after the ignition is turned off. I first noticed the sound when I parked in the garage, turned the engine off and heard it when I jumped out of the truck. After noticing it, I cranked it back up and could hear the faint chirp, ping, suck noise.
Iíve been researching the symptoms and asking around a couple people have mentioned two sensor issues on Jeep Grand Cherokees that have been problematic: crankshaft position sensor and/or camshaft position sensor. Iíve located them on my engine but I canít justify digging around and replacing them when I really donít know for sure if either of them are causing the problem.
Does my rambling bring any ideas to your mind? Any advice you can share would be much appreciated. Btw: the jeep last started 2 weeks ago. Iíve made approximately 10 attempts to crank. It turns over but acts as though there is either no fire or no fuelÖ Iíve read that a bad crank sensor will disable the vehicle???
Anyway, let me know what you think. Iím guessing I should probably just take it to a jeep dealership at this point to see what the computer is saying now that it wonít start at all.
2000 Jeep Grand Cherokee Limited
4.7 L Power Tech
All Wheel Drive