Random Multiple Misfire? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Rich84 · 01-15-2016, 05:08 PM

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 · 01-15-2016, 06:13 PM

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 · 01-15-2016, 06:48 PM

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 · 01-15-2016, 08:47 PM

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 · 01-16-2016, 10:29 AM

Thanks guys..I will give that a try.

hugger6933 · 01-16-2016, 09:26 PM

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 · 01-17-2016, 01:20 PM

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 · 01-19-2016, 06:06 PM

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 · 01-20-2016, 02:29 AM

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 · 01-20-2016, 09:03 AM

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 · 01-20-2016, 11:53 AM

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 · 01-20-2016, 12:15 PM

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

LeesTruk · 01-20-2016, 04:09 PM

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 · 01-20-2016, 05:03 PM

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

I do feel stupid.

01-15-2016, 05:08 PM	#1
Rich84 Registered User Join Date: Mar 2012 Location: Woodbury, Ct. Posts: 1,692	Random Multiple Misfire? 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

01-15-2016, 06:13 PM	#2
compsystems Registered User Join Date: Aug 2014 Location: Upland Ca Posts: 18	Re: Random Multiple Misfire? 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.

01-15-2016, 06:48 PM	#3
Rich84 Registered User Join Date: Mar 2012 Location: Woodbury, Ct. Posts: 1,692	Re: Random Multiple Misfire? 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?

01-15-2016, 08:47 PM	#4
BR3W CITY meowMEOWmeowMEOW Join Date: Sep 2009 Location: MKE WI Posts: 7,128	Re: Random Multiple Misfire? 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. __________________ *'66 Short Step / SD Tuned / Big Cam LQ4 / Backhalfed /Built 4l80e / #REBUILDEVERYTHING* MY BUILD THE H8RDCPTR //\\ MY YOUTUBE CHANNEL REV J HD

01-16-2016, 10:29 AM	#5
Rich84 Registered User Join Date: Mar 2012 Location: Woodbury, Ct. Posts: 1,692	Re: Random Multiple Misfire? Thanks guys..I will give that a try.

01-16-2016, 09:26 PM	#6
hugger6933 Registered User Join Date: Oct 2008 Location: Marianna Arkansas Posts: 7,280	Re: Random Multiple Misfire? 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

01-17-2016, 01:20 PM	#7
Rich84 Registered User Join Date: Mar 2012 Location: Woodbury, Ct. Posts: 1,692	Re: Random Multiple Misfire? 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.

01-19-2016, 06:06 PM	#8
Rich84 Registered User Join Date: Mar 2012 Location: Woodbury, Ct. Posts: 1,692	Re: Random Multiple Misfire? 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.

01-20-2016, 02:29 AM	#9
BR3W CITY meowMEOWmeowMEOW Join Date: Sep 2009 Location: MKE WI Posts: 7,128	Re: Random Multiple Misfire? 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. __________________ *'66 Short Step / SD Tuned / Big Cam LQ4 / Backhalfed /Built 4l80e / #REBUILDEVERYTHING* MY BUILD THE H8RDCPTR //\\ MY YOUTUBE CHANNEL REV J HD

01-20-2016, 09:03 AM	#10
Rich84 Registered User Join Date: Mar 2012 Location: Woodbury, Ct. Posts: 1,692	Re: Random Multiple Misfire? 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?

01-20-2016, 11:53 AM	#11
LeesTruk Registered User Join Date: Mar 2015 Location: Manchester, CT Posts: 433	Re: Random Multiple Misfire? 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

01-20-2016, 12:15 PM	#12
Rich84 Registered User Join Date: Mar 2012 Location: Woodbury, Ct. Posts: 1,692	Re: Random Multiple Misfire? It's an orange oil can..Looks like a genie bottle.lol

01-20-2016, 04:09 PM	#13
LeesTruk Registered User Join Date: Mar 2015 Location: Manchester, CT Posts: 433	Re: Random Multiple Misfire? 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

01-20-2016, 05:03 PM	#14
Rich84 Registered User Join Date: Mar 2012 Location: Woodbury, Ct. Posts: 1,692	Re: Random Multiple Misfire? I just googled it..I think your right. It is a light to remind you to change the oil. I do feel stupid.



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