Random Multiple Misfire?

[Rich84]

I just swapped my old 2004 370,000 mile LQ4 with a 2005 with about 70,000 miles. It is running beautiful..But I am getting a Random Multiple Misfire code. Engine runs smooth as silk. We put about 1100 miles on her this week. Sometimes it's in the pending code sometimes it's not. Engine light occasionally flashes.

Really don't know where to start looking.

Thanks

[compsystems]

Check all your harness grounds. If your harness is original, the bolt in the back of the head is a ground point that is known to come loose or get corroded.
Also check to make sure the pink wire to the coils is getting 12+ consistently.

Is the PCM and harness from the old engine or the new one?
Do you think the misfires are actually occurring? Can you feel it stumble?

If you are using the old computer with the new engine, its possible that you need to do a CASE learn.

[Rich84]

I am using the 2004 computer and harness..I cannot feel a stumble at all. It runs really well. Engine light flashes on the highway while the truck is running great. Abs light came on and went off today.. Never saw that before.

What's a Case learn?

[BR3W CITY]

Its process that sync's the Crank Angle Sensor. Usually problems with the crank sensor will trigger false misfire or false knock, and sometimes causes a no-start. Search CASE Relearn and you can see the process to reset/sync it. Not real hard.

[Rich84]

Thanks guys..I will give that a try.

[hugger6933]

Other things to cause a PO300, is a vacuum leak the intakes are a little leaky or at least the gaskets were I think they had an update for them to stop it. Is thew misfire code the only one or does it have a MAF code as well? Other causes for a PO300 could be dirty fuel filter or loss of fuel pressure. And of course a bad coil or coils or spark plug or wires could cause a misfire. Does it misfire under load only or just anytime. Do you have a scanner that can do a graph or misfire counter. Mine does and that might help a bunch to find out the problem. Jim

[Rich84]

So..today it won't start. All I have is a cheapo code reader. I'll bring that and my fuel pressure gauge and see what it says. Unfortunately the truck is 20 miles away. It was running great now it just turns over and over with no start.

Could that be the case relearn problem.

[Rich84]

Update time..So it turns out that the ground wire in the harness was broken. Also the pink hot was not in good shape. It also had a lean code on the driver side for all the cylinders. The wires are fixed and my mechanic did do a "case relearn" and so far it is running great again.

Thanks to everybody for the advice. I can't wait to start my swap into my '84. Which will have a brand new harness so I won't have to worry about 12 year old wires.

[BR3W CITY]

Good to hear. Just keep an eye on it and take her easy for a bit. If you had a few broken wires, tuck it in the back of your mind and try to look there first if you run into another problem.

[Rich84]

Last year it was one of the injector wires..I think I am replacing the harness one wire at a time.
Unfortunately this van is my primary delivery vehicle right now and will probably do about 200 miles today. Fingers are crossed.

One thing that I had with the old motor and is still there with the new one is the oil light. It comes one when you first start it and then goes off after a couple of minutes. That light is connected to the oil level sensor in the pan ..Correct?

[LeesTruk]

Is the "oil light" red or orange? Next question, did you transfer any parts from the original engine to this one? If it's an orange warning, it's most likely the level sensor warning. Check your connector for "green death" or wires for oil saturation. A closed circuit causes this light to illuminate. If it's a red warning light, then check your pressure switch/wiring

[Rich84]

It's an orange oil can..Looks like a genie bottle.lol

[LeesTruk]

This is gonna sound kinda dumb, but does your van have its' owners manual still? Check and see if that's the symbol for oil change time, and it just needs to be reset

[Rich84]

I just googled it..I think your right. It is a light to remind you to change the oil.

I do feel stupid.