misfiring only for first minute

[Jack Schmidt]

I have a 1998 Ranger 3.0 V6 auto with 191K miles. About 75% of the time that I fire it up, cylinder 1 misfires until about one minute passes. When I drive it around for a while, turn it off for 10 minutes, and turn it back on, it again misfires for about a minute. I know it's cylinder 1 because once in a while the OBD reports it.

I've installed a new injector and a new set of plugs. I replaced the spark plug wires about 15k miles ago.

Since it misfires only on start-up, and with any engine temperature, I suspect something electrical.

Any ideas?

 

[firebomb]

have you looked at the spark intensity at all? could be the coil pack/s are going ? try to find one of these at auto zone , advance auto part, or even oriley's auto parts etc.. any parts stores. like here they usually 5 buck and you don't have to remove the spark plug to test it. your looking for a white blue color any red yellow to it it going bad. had a expedition 5.4 every time the spark pack would go bad it would cause a misfire and there was 8 of them...


http://www.tooltopia.com/lisle-50850.aspx

 

[RonD]

Yes, check the coil pack with an ohm meter
goggle: ford coil pack testing

Is there a slow coolant leak?
A cold seal issue with #1 could allow coolant to enter after engine cools down.
After start up coolant fouls the mix until burned off and cylinder expanding from heat seals the breach, this would get worse over time, cracked head or blown head gasket would be what this is.
Short 10 minutes stop would allow the 16psi coolant pressure to push enough coolant in to foul the mixture.

Another issue could be a bad intake valve guide seal on #1, this allows oil to run down the valve stem and into the intake.
When you first start the engine the oil on the back of the valve is pulled in and fouls the mixture until it is burned off.

Either of the above could be 75% of the time issues, it would depend on where the valves were on #1 when engine was shut down.

Either of the above should show a bit of smoke at the tail pipe, but only on cold start.
What did the plug look like in #1?
I would also do a cold start run 10 seconds only, then pull the #1 plug and see what it tells you.

My money is on the coil........but other issues should be considered

 

[Jack Schmidt]

Thanks for the responses, guys.

I bought and installed a $45 used coil pack. No change. Spark plug looks clean, just as clean as the #2 spark plug. They're all pretty fresh. I swapped the #1 and #2 plugs and wires so that if the OBD detects the misfire again I'll have a little more info. (I didn't swap the injectors -- that's more work.)

Earlier I did try one of those spark intensity testers, the kind you put inline between the plug and the wire. It looked OK but that could be because I just didn't get from the key switch to the tester fast enough. I should work on getting a remote starter, I guess. Maybe I'll do that next.

Good idea about checking the plug after 10 seconds of running. Will do that as well.

I haven't noticed any coolant consumption but I'll start paying more attention.

The truck doesn't smoke at all, very clean, even during the initial minute.

Thanks again. You guys are great. I'll reply again after I try some of the above.

 

[Jack Schmidt]

After a two-week delay... The truck is consuming coolant. It might have been for a while without me noticing it. The coolant tank is pretty brown and it wasn't before. So looks like my problem a leaky head gasket, right?

If it is, I have to decide whether to fix it or trade it in for another Ranger. This one has 192k miles, an oil leak at the rear main seal, very worn suspension bushings, so-so tires, and a big windshield chip, but everything else works and it has a straight body. What would you guys do?

 

[Jack Schmidt]

So I traded it in on another Ranger because these trucks are really fantastic and because I found a good deal. My old truck was a 1998 XLT 2WD standard cab and standard bed 3.0L V6 auto with 192K miles. I owned it ten years. Its replacement is a 2003 4WD standard cab long bed 4.0L V6 auto with 84K miles and was owned by San Diego Gas and Electric. I plan on keeping it at least as long as I kept the old one. Cost was $6400 plus the trade-in.

 

[Earl43P]

Congrats!

Sounds like a nice upgrade.