Misfires When Cold

My '99 Montana started running rough and the Check Enging Soon light started blinking. I bought an OBD II code reader and it indicated that cylinder 5 is misfiring. I replaced all the plugs. The back ones took about an hour, I got to it from underneath the van. The plugs looked like they had normal wear. After replacing the plugs I cleared the code with the reader. The engine seems to run okay after the change. My wife drove it the next day and she said that it's happening again. She said after about 5 minutes of driving the problem went again. I test drove it and it did the same thing as it did to my wife. Looks like when it's cold cylinder 5 misfires, when a component(?) warms up the misfiring stops. Anybody have any ideas what defective parts is causing this problem?
Thank You

How many miles are on it? Some things to check would be the spark plug wire, condition of the spark, cylinder compression, and the fuel injector.

How many miles are on it? Some things to check would be the spark plug wire, condition of the spark, cylinder compression, and the fuel injector.

It has 97K miles. What's weird is that about 5 minutes into driving the van, the misfire stops. When we'd get home, I would clear out the P0305 code and start up the engine to check for misfiring, runs fine, no Check Engine light. ???

I havent had probs with the Montana doing that (yet)... but I had a Ford Aerostar with the same problem. Turned out the injectors were at fault. Had to replace one, and have the others cleaned. that did the trick. But I went thru 2 tune ups and a number of other unnecessary work before I found it. Tunex finally found it and fixed it.

Thank you for the advice. I'll check the #5 injector. It'll probably won't be for a couple of days. I bought a set of plug wires, haven't try it out yet, maybe it's the injector than I can return the wires. Thanks again.

If you haven't changed the wires in 97K you might as well change them anyway. You will notice a performance gain and possibly eliminate some coil problems later if one does go bad.

Yesterday I replaced the #5 injector, and it fixed the misfire problem (very excited). Thank You nascarjunkie. I also replaced the plug wires after testing the new injector as recommended by GTP Dad. It took two hours to get to the injector, but if I had to do it again, I'm pretty sure I can do it in an hour. Did not run into any problems. I purchased the new injector from NAPA ($90). Visual inspection at NAPA looks good, but when I got home I noticed that the aftermarket one was 1/8" taller. It'd probably work but I didn't want to spend the time installing/uninstalling and take the chance of it leaking or damaging something else. I returned the NAPA injector and bought the original GM ($120), looks exactly the same. We drove the van several times already still no problem. Thank You everyone for the input.

The misfire is back. It came back yesterday afternoon. Now it's complaining about #2 and #3 cylinder, one or the other. The original misfire cylinder (#5), has been good since new injector was installed. Doing the same, runs bad when cold then after driving 5-10 minutes, it would run fine. When the "Check Engine Soon" light stops flashing and go solid this is when the van starts running good again. The van's tab expired a month ago and to renew it needs an emmision. I went to get emmision today, found out that if the code was cleared, it has to be driven for certain amount of time so computer can gather data. After searching/reading the entire forum for misfire problems, I hink I will try replacing the ignition coil. Will update. Thanks

You might also want to check and clean the connections to the injectors. They do get dirty and with a little spray contact cleaner you will get a better signal to each injector. The possibility also exists that the other injectors are going bad too. If one goes bad then it stands to reason that the others will start to go bad shortly thereafter. Also if the resistance is changing on the injectors the computer will get a code from the computer. Just some ideas to consider.

:smile: It's been about a month now since I decided to have the other 5 injectors cleaned and tested, hasn't misfire since. Cost $13 an injector for the cleaning. They put in the wrong seals (larger, gas was leaking a little, very fuamy inside) so I had to buy the correct set from the dealer. All together I had to access the injectors about 5 times, I can get to the injectors in about half an hour. It's running great now, wife is very happy. Thanks everyone

I had similar missing problem with mine. Turns out the nipple on the coil for #5 was coroded. Cleaned it up, and all is fine.

I had similar missing problem with mine. Turns out the nipple on the coil for #5 was coroded. Cleaned it up, and all is fine.
Thanks for the info. Next time I have similar problem I'll remember to check the coil nipple also. Maybe I wouldn't have had to put the money into fixing it. Oh well, the injectors are clean. Thanks

Thanks for the info. Next time I have similar problem I'll remember to check the coil nipple also. Maybe I wouldn't have had to put the money into fixing it. Oh well, the injectors are clean. Thanks


Have you had this problem again? I seem to be going through a similar thing. The misfire was registered on one pair of cylinders and now another.

It had been fine for 5 months.

Thanks

Havn't had any problems since. It's been trouble free since the injector cleaning. A month ago we took a road trip to San Diego from Spokane, put on 3300 miles, no problem at all.