[Martyjoe]

Hello,
I own a 2007 Grand Cherokee Laredo 3.7L, 160,000 mile. It’s been a good vehicle but when you driven it for a spell and it’s warm up and you stop to run in a store quickly, when you come out and start it has a terrible misfire and the engine shakes terribly. If you immediately turn it off and then restart it 9 out 10 times it starts right up. Occasionally it takes two attempts because it will do it again a second time but mostly just one time. It doesn’t do this ever time but occasionally. It always starts just fine when the vehicle is cool. I have try letting it misfire a little longer hoping it will throw a code, but it has never thrown a code. I have Innova 3040RS scanner and there’s never anything in stored memory and it shows no misfires on none of the six cylinders, but there’s something definitely wrong. I have clean and checked all the grounds under the hood, and keep a hot battery. The engine sounds and runs good and idles good without any misfiring. I’m not looking to get rid of, just like to get it solved. I would appreciate any help available. Thank you in advance.

 

[BobP]

O2 sensors?

 

[Martyjoe]

I used my scanner and shows no problem with any of O2 sensors. I taken it to shop a local shop with professional scanner and still no indication of the problem. It never throws a code. It doesn’t do often but I would like to find the problem and get it fixed. The mechanic seems to think it’s might be my computer. I rebooted the computer by disconnecting the battery, turning on the head light switch and jumper wire between the positive and negative cables for 20 minutes before reconnecting the battery (YouTube hack). It starts right back up just fine but still occasionally get that rough misfiring “warm” start up.

 

[07-3.7-4wd street jeep]

Our 07 3.7 4wd has about 220,000 miles. The O2 sensors definitely needed to be replaced, though it never threw codes.
We also needed a Throttle Body cleaning... this did throw codes on and off with random misfires and may be your problem ( sticky/dirty idle circuit). If you have the original O2 sensors I would definitely replace them. We picked up 1.5 to 2 mpg city and highway with the new O2 sensors and TB cleaning. Also lots more bottom end torque. To give you a comparison on how well your engine is running, we can comfortably climb fairly steep hills at about 35 mph locked up in overdrive and get about 17 mpg city and 24 mpg highway on the stock size wheels and tires. I did install a deeper air dam which gave us about 0.75 mpg gain highway and have a freer flowing 2 1/2 inch exhaust, which really helped midrange and higher end power, though I don't think it gave us more mpg. These little 3.7 v-6's are torquey little buggers when in good tune.

 

[Martyjoe]

Thanks, it’s worth a try. The last time I had the mechanic try to find the source of the problem, he cleaned the throttle body in hopes that it might have been the cause, but to no avail. My scanner and his more expensive scanner shows no O2 sensor problems, but again they may be bad. The mechanic is still lending toward the computer. His believes the computer has a glitch in it, causing it to send wrong commands.