Misfire???

[Austin9504]

My buddy has an 06 1500 Sierra. The truck is obviously missing. So we hooked a scanner to it, the scanner shows no misfires. No current, no history of them. Nothing. He put a new pcm in it, and "says"' he got it programmed. Would the pcm not being programmed be the reason it's not showing anything?? I can still get a few codes out of it

[Jsdirt]

Wrong or defective computer will do that too. I went through a nightmare trying to get my buddy's '96 Tahoe to run on all 8 - would only run on 6 after installing a junkyard computer. Before that, it wouldn't even pop, let alone run, so I was on the right track.

 

Scan tool showed NOTHING - couldn't read fuel trims, misfires, or any other other needed parameters. I was flying totally blind with no means of troubleshooting, other than 6 codes it was throwing. One of them for the cam position sensor - replaced that, code came right back. Plugs wires cap rotor all new - nice bright blue spark you can HEAR as well as see. Timing right on the money. Fuel pressure right on the money. Replaced spider with new. Replaced a few other sensors he had laying around inthe truck (o2, crank position). Engine has only 50k miles on it. Compression is good. No change at all in how it runs after all that money thrown at it.

 

Problem is, I have no way of proving the junkyard sold me a POS computer - I don't think a dealership can just plug one in and say good or bad either. Nice racket GM created there. Junkyard weaseled their way out of their 90 day warranty because I had no way of proving that was the problem. Total screw job ...

 

The Tahoe still runs on 6. I gave up. My buddy will drive it when he needs 4x4. Will start up and run every time ... just on 6. The rest of the time his 20 year old Volvo 940 gets him to work reliably. F*** computers.

[Jsdirt]

Tried swapping it back - was same as before - stone cold dead.

 

Story with this thing was, my buddy was driving it for about a year, then out of the blue it croaked in his garage (luckily). He threw THOUSANDS of dollars at it - fuel pump, sensors, filters, plugs, wires, cap, rotor .... Wouldn't even fart on ether, yet had what seemed like great spark. He suspected a timing issue (valve), so ripped all the accessories off the front, and half the cover before realizing it was integrated with the pan on these newer ones. It sat some more. Then he got motivated, & tried to get the pan down, and had all kinds of trouble. Snapped a few bolts off the Y pipe ... then in frustration, out came the sawzall. Cut Y in half, snapped & stripped all the bolts on the passenger side. Then he called me. I hauled it here, and it sat another year before I could get to it.

 

I got the pan back on, installed the pile of sensors he had bought, and started cranking away. Not even a puff. Shot some ether in - same deal. Went to the local boneyard for the computer. As soon as I plugged it in, it fired right up and ran on 6. Tried EVERYTHING under the sun to make this POS run right. Plugged old computer back in after exhausting all options and it was as dead as it was before.

 

I'm done with the thing .... until he decides to carb it. With the amount of money he's sank into this thing, I doubt that will ever happen. Oh, and it failed inspection for ball joints, tie-rods, pitman arm, & idler. What a waste of money ...

[Doug_Scott]

Even if you could prove the computer was bad, you could not prove that your truck didn't take it out, like it did to the original one.

Before changing computer, was the truck not doing anything? Have you tried going back to the old computer? It may work now if there was a bad connection that got cleaned up by swapping computers. What does the wrecker charge for a computer?

[kstruckcountry]

I told him we should've ripped all the electronic crap out and install a carb & HEI setup before we even started. He was worried about fuel mileage ... LOL. Even my buddies are brainwashed into that line of thinking. I could've tuned that thing to run 10x better than it ever did off the showroom floor. Oh well ....

I'm the opposite, you can't get me far enough from a carbed motor... Sure they run great, unless it's cold, or hot, or high up.... Need retuned more often than the oil needs changed. I understand why people don't like electronics, but I'm not a big fan of many moving parts either.

 

What it comes down to is the problem needs to be diagnosed ASAP, properly. When you get into fixing someone else's hack job, it gets ugly. Don't know what they've done, where, or when. Carbed or not. Like you said, spending all that money sucks, better to spend it and actually fix the problem with the help of a "T word" sometimes.

[fastal]

you can unplug the coils one at a time to isolate the cylinder that is missing the you dont have to pull all the plugs and test all the cylinders

[Doug_Scott]

Tried swapping it back - was same as before - stone cold dead.

 

Story with this thing was, my buddy was driving it for about a year, then out of the blue it croaked in his garage (luckily). He threw THOUSANDS of dollars at it - fuel pump, sensors, filters, plugs, wires, cap, rotor .... Wouldn't even fart on ether, yet had what seemed like great spark. He suspected a timing issue (valve), so ripped all the accessories off the front, and half the cover before realizing it was integrated with the pan on these newer ones. It sat some more. Then he got motivated, & tried to get the pan down, and had all kinds of trouble. Snapped a few bolts off the Y pipe ... then in frustration, out came the sawzall. Cut Y in half, snapped & stripped all the bolts on the passenger side. Then he called me. I hauled it here, and it sat another year before I could get to it.

 

I got the pan back on, installed the pile of sensors he had bought, and started cranking away. Not even a puff. Shot some ether in - same deal. Went to the local boneyard for the computer. As soon as I plugged it in, it fired right up and ran on 6. Tried EVERYTHING under the sun to make this POS run right. Plugged old computer back in after exhausting all options and it was as dead as it was before.

 

I'm done with the thing .... until he decides to carb it. With the amount of money he's sank into this thing, I doubt that will ever happen. Oh, and it failed inspection for ball joints, tie-rods, pitman arm, & idler. What a waste of money ...

 

I know you are done with it, but, sometimes these sort of issues intrigue me. Could you nail it down to which two cylinders were missing? Or were they floating around randomly? Its too bad they don't offer reman pcm's sometimes. Too bad you did not know of a friend with the same or a compatible vehicle to try their ecm.

 

Years ago I was working in a Firestone store and had a reputation around the other Firestone stores of being a good trouble shooting and tune up mechanic. Every once in a while a vehicle would be brought to my location from another store because they could not fix the issue. One of the strangest ones I ran into was a late 70's full size Pontiac wagon with a small block chev 350 in it (Canada generally got chev engines in Olds, Pontiac, and Buicks when order with 350 engines). This car would idle, but would not drive. Engine would kick and buck if you opened the throttle at all. This car was towed into another Firestone by a regular customer, they had it for about a week before it was sent to me. Put it on the scope, and saw the strangest signals I have ever seen. Engine was an 8 cylinder, but would show 6 to 10 plug signals on the screen. An 8 cylinder engine should show 8. Asked the customer that owned the car for the background, and they said car quit at the cottage, and a neighbour got it running again, but not drivable. They had no idea what he did, and he could not be located. I checked all the normal things that we used to check back then, and ended up pulling the distributor out. After I got it out I could see that it was out recently already. Looked inside it, tested pickup coil, module, coil, and fixed the advance weights (they were seized, no idea how it was not fixed last time it was pulled). As I was putting the shaft back in I noticed something odd. The reluctor had 8 'lobes' as it should, but the pickup only had 6 points on it. The neighbour that fixed it for them put an odd fire v6 pickup coil in it. I would never expect the engine to even start let alone idle. Car ran great after that.

 

What happens on these new computer run engines if the crank sensor comes loose? Or cam sensor? If the same cylinders are the ones that always misfire, I can't see how the computer could cause that. When the ecm is changed, did you do a crank relearn?

[Jsdirt]

We've been running our '89 S-10 Blazer with a '00 GMC Jimmy engine in it, carbed/HEI. -8° it fires right up every single day. Block heater helps. Takes a mile or so to get the hiccups out, but it does just fine. Wife commutes 70 miles a day in it. Gets 17 MPG unless it's in the single digits for a few days. No worse than 16. Sits all day at my wife's work with no place to plug it in - starts up fine and gets her home. Manual choke - works great. 93° summer day, same thing - I use it as a tractor in the summer, and sometimes to run errands when it's raining and I don't feel like washing the Silverado again.

 

I also have a '74 Yamaha RD350 2-stroke motorcycle I ride 6 months out of the year. Dual points, not a single electronic part on it, and I'd take that thing cross country right now ... if it wasn't 5° outside with 4' of snow ... Starts first kick every time - 3 kicks if it sits a few weeks. Love that bike. So simple. Different strokes for different folks, I guess.

 

Yeah that Tahoe turned into a first-class nightmare. I'm just glad I don't have to look at it ... and my buddy's glad he can at least run it if he has to, even if it sounds like a Duramax at idle ....

 

 

[Doug_Scott]

Once you locate the cylinder that is misfiring you will need to remove all plugs to check compression properly. You pretty much need to remove them all to replace them if it needs the one plug as well.

[Doug_Scott]

Was the same 2 all the time. Actually 2.5 - there was one cylinder a couple hundred degrees cooler than the ones that were still firing normally, so technically it was running on 5.5 cylinders. I get mad just thinking about it. No reason ANY vehicle should be this complicated and expensive to fix.

 

I thought about the crank relearn ... but everything I read indicated that the vehicle would throw a code for that if that was the case. Either way, with the amount of money my buddy threw into this junk, a trip to the dealer was the LAST thing on either of our minds.

 

I'm convinced that with a good computer, the thing will run mint. They were getting between $60-$80 at junkyards for them ... but without seeing the computer actually run a vehicle, we're right back where we started - UNKNOWN territory ...

 

I told him we should've ripped all the electronic crap out and install a carb & HEI setup before we even started. He was worried about fuel mileage ... LOL. Even my buddies are brainwashed into that line of thinking. I could've tuned that thing to run 10x better than it ever did off the showroom floor. Oh well ....

 

My thinking has changed over the last couple of decades. My first thought now is how much is my time worth. If I could spend $60 to attempt to prove my thinking correct, or spend another 5 or 6 hours dicking around, I will spend the $60. I am a fan of the new technology, while under warranty. Living in a climate like we have here, makes carb engines not pleasant for first 10 minutes.

 

I have been riding bikes since late 70's, and the best running bike overall was a 1999 Honda VFR. Bile started every time, no choke even on 32 degree F days. My current bike is a 2002 Yamaha FZ1. It has carbs, and provided I use stabilizer in the fuel, it will start every time and run great. But, forget the stabilizer, and leave the bike for a month, it will be a bitch to get running. Not the carb technology fault, it is ethanol levels fault, but, the VFR never had that issue.

 

My thinking on new technology is never let the truck know you are intimidated. Once you do, the truck will have you at its mercy. Sort of like not showing a dog you are afraid.

[gmtech4]

My buddy has an 06 1500 Sierra. The truck is obviously missing. So we hooked a scanner to it, the scanner shows no misfires. No current, no history of them. Nothing. He put a new pcm in it, and "says"' he got it programmed. Would the pcm not being programmed be the reason it's not showing anything?? I can still get a few codes out of it

I can't get over he jumped and put a PCM in it lol,

 

Someone needs to inform him on how stuff works , holy cow !!

[gmtech4]

you can unplug the coils one at a time to isolate the cylinder that is missing the you dont have to pull all the plugs and test all the cylinders

Or a scanner can disable each injector one at a time and either feel a difference or not

 

Pulling plug wires is very old school and not required ( at a shop anyways ) lol not in driveways unfortunately , again I never said to "take it to a tech "

 

Lol , I kill me lololol

[Jsdirt]

LOL I hear you there. Sometimes I feel like these engine control systems are all plotting against me ....

 

I just get so damn frustrated, mainly because of the way they engineer these things. If any automakers gave a crap about their techs, or their customers, they'd put a little extra effort into making repairs a little less time consuming. Half the time their top regional factory techs can't even figure out problems on a brand new truck! That's just ridiculous. I look at our Blazer and how great it runs, and how easily I can make repairs if needed, and just get infuriated working on anything post '95. It shouldn't be this way.

 

I have zero patience for electronics ... in case you couldn't tell ... That and the chinese wiring they use today ...

[Austin9504]

I think we're all straying away from the question. I know how to isolate misfires etc. what I'm asking is, would the pcm not being programmed be the cause for the scanner not showing any misfires???

[Jsdirt]

Was the same 2 all the time. Actually 2.5 - there was one cylinder a couple hundred degrees cooler than the ones that were still firing normally, so technically it was running on 5.5 cylinders. I get mad just thinking about it. No reason ANY vehicle should be this complicated and expensive to fix.

 

I thought about the crank relearn ... but everything I read indicated that the vehicle would throw a code for that if that was the case. Either way, with the amount of money my buddy threw into this junk, a trip to the dealer was the LAST thing on either of our minds.

 

I'm convinced that with a good computer, the thing will run mint. They were getting between $60-$80 at junkyards for them ... but without seeing the computer actually run a vehicle, we're right back where we started - UNKNOWN territory ...

 

I told him we should've ripped all the electronic crap out and install a carb & HEI setup before we even started. He was worried about fuel mileage ... LOL. Even my buddies are brainwashed into that line of thinking. I could've tuned that thing to run 10x better than it ever did off the showroom floor. Oh well ....

[Austin9504]

I got involved AFTER he did all of this. I have no idea what was wrong before he replaced all of that. He told me he had to replace the pcm because he is running 35's and his tires ripped the harness to shreds. I told him the same thing, he was throwing his money away. He also put a new bcm on it because "someone" told him that's what was killing his battery. He refused to tell me who though haha.