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Considering that you’ve replaced ignition components, we’ll assume (not the best thing to do) that the misfire is not ignition related.
Before doing anything else, confirm that this cylinder has compression; without compression nothing externally will get that cylinder running.
Next would be fuel control; this engine is likely using Central Sequential Port Injection (CSI)
CSI systems use a single electric fuel metering valve that is opened and closed by the computer and is common to all cylinders. So we know that it is working because we’re only dealing with #5.
Leaving the metering valve are 8 individual tubes with poppet valves/nozzles at the end of each tube; one poppet valve per cylinder. The poppet valves are a form of mechanical injector; fuel pressure is applied to the base of the valve’s nozzle to open it and spray fuel. Once the valve/nozzle is opened the fuel pressure in the tube drops and the valve closes with spring pressure.
These poppet valves are famous for sticking.
If this is the case with your misfire; you can attempt having them professionally cleaned. Don’t waste your money with the pour in the tank cleaners; if this is a stuck/dirty poppet it’s to late for that stuff. They need a very aggressive cleaner if it’s going to work at all.
Again if this is the issue and cleaning didn’t work; there is an up dated retro fit CSI unit that does away with the mechanical poppet valves and uses 8 electric injectors. No modifications are needed to install this unit; it’s plug and play; but it’s not cheap to buy.

Dan.

Sorry HT I wouldn’t have replied to this thread if I saw that you already had. Don’t take offence please.

Dan.

I agree with all that you have said about both types of fuel control systems and yes the poppet nozzles can be replaced individually but in my pass experience with these things; it’s a make work project, just replacing one; let alone one of the same design.
If one has become plugged/stuck, the others are close behind; they’ve all seen the same heat soaks and dirt.
So if after having the CSI unit assembly cleaned and #5 is still not operating; I would suggest the up-dated unit.
Again assuming that this is the cause of the problem and that the vehicle hasn’t already had the up-date done?

Dan.

Ok guys I really appreciate the help! I messed up by not including the size of the motor. Its the 5.7 vortec, and no it dosent have individual injectors, so popet valves are on the board to replace. I am also wondering if a cleaner like "sea foam" might be worth a try? it is a rather aggressive cleaner, or will i be waisting my time? I am not oposed to up dating to the new style so I will look into that. But I guess I am clueless as to what is involved or where to get it. Any suggestions?

I understand about the idividual injectors I was thinking in terms of a fuel rails and each injector. How hard is it to pull it out and clean it? The other question I have is the cylinder numbers,in terms of the cpu numbering the cylinders and the print out for the firing order are they the same? in one book the cylinders are counted down one side and up the other, on the firing order they are alternated accross the block. which is correct?

No, you can't manually clean these injectors. They are not even accessible without removing the upper manifold and then they are a sealed unit. As I stated earlier, the way this is diagnosed is by doing an injector balance test using a professional scan tool and a fuel pressure gauge. Once you identify that it is actually an injector causing the problem, then you make the decision to change that one or all of them. As the discussion with the other tech noted, it is recommended to replace all of them at once although it would be quite expensive.

The only attempt you could possibly make at cleaning them would be using a pressure system with professional cleaner but I can tell you from experience, this rarely works on this type of injector and would set you back about $150.

Never heard of a TrailMaster.

Is this a truck, van, suburban?
Which series?
Which engine?
Which transmission?
2wd or 4wd?

If you want to post a link to your video, you can do that here.

It's a GMC Sierra C1500. I believe it's a 5.0 Liter V8 engine. It's a 1/2 ton truck. Here is a link to the video:

Any help is greatly appreciated!

Your mechanic can get codes with a paper clip on this and count blinks of check engine light - he/she just doesn't know that as it's quite old now.

The pre OBD2 codes you still had to take with a grain of salt as some clue if anything at all.

My real question is if this was running perfectly before this test drive did anyone go along with it to see how it was treated or if potential buyer really abused it in a test run? Stuff can happen anytime for no particular reason of course. It can also be a bit scary selling your own vehicle (privately) to strangers really for many folks,

T

My mom did not go along, so we do not know if the person who drove the truck did anything to it.

The mechanic said the vacuum hoses are all okay. The fuel filter is new. The wires look okay and the check engine light does NOT come on. The engine looks fine but it revs as shown in the link. Also, if you put it in drive, the truck dies.

Does anyone have any other ideas? My mom is trying to sell the truck so I can go to a specific college program. We really need to try and figure something out. The truck wasn't driven after the potential buyer drove. It was only driven the same day we found the problem, to the mechanic.

Please help.

Can only guess at this. Perhaps a super low mile now old truck was driven hard for the first time in ages and blew some carbon or junk in items like idle air speed control which dictates idle speed and really floored it which it should have taken. Junk could have fouled up plain spark plugs - one or more?

The noise is probably some belt driven something. A tech right there would find that if only taking belt off to see if that goes away and spin pulleys without the belt.

I'm not there or here to blame any mechanic or shop but doesn't seem this got looked at very hard OR is perhaps too old a vehicle for some. Just saying can't read codes and looking at vacuum hoses saying they are good isn't enough for me.

Seems like neither you or your Mom are going to do the work and think another tech or shop is in order. I suggest simply explaining what it's doing to the tech not just a service manager who will look at it and allow his/her discretion on what it might need. Possibly just a good throttle body clean out and maybe new plugs. What none of us know is if the potential buyers did anything messing with things underhood not knowing what they were doing?

Unless this truck is rusted badly beyond reasonable repair it should be worth fixing and an easy sell. I've looked, new stuff is outrageously expensive and plenty of people want a truck for its utility not it's good looks

T

Myself nor my mom are capable of doing the work. If it was something I could fix, I would try that but I don't have any car skills besides installing a battery, and checking fluids.

It was a mechanic, who is also a family friend. We did take it to the shop he works at. It wasn't a service manager but an actual mechanic who we talked to. He just seemed very puzzled as to why it revs like that. My mom is nervous about having to pay to tow it to another shop and possibly being overcharged. She doesn't know of any reliable shops in our area. My father and grandfather have both passed and she doesn't know about cars and is afraid of being taken advantage of. I believe she was already taken on a ride with the potential buyer.

The offer was lower and she decided not to accept it.

Thank you for the replies. I will tell her what you all said and hopefully she can get a second opinion. I'll also tell the mechanic who has been looking at it too check the things mentioned.

You really need to find a reliable shop that you can stick with. Ask around for some "word of mouth" references. Don't look for the cheapest one, look for the one that does the best work and treats it's customers the best. Stay away from the chain store type things. They never work out well.

Thanks everyone for your input. We had another mechanic look at it and he told us the vacuum advanced module needs to be replaced. That's what's causing the truck to rev then die if you try to drive it.

Everyone was very helpful in figuring out what was going on.

I hope he knows what he's doing because there is no such component by that name. Maybe he meant Ignition Control module.

Some things get lost in translation from tech to customer to us. Hope it is good now.

Have you checked for vacuum leaks? Inspect all the vacuum hoses.

First thing that comes to mind ..did you have head checked for warpage by machine shop. Second thing ,,, it makes no difference what clock position the rotor ends up. So long as the cap post it ends up pointing at has the #1 plug wire on it with the remaining wires put on in the firing order in direction of rotation . Also , wires must be able to move enough to set timing and dist turn without interference to set timing as well.

i checked head with feeler guage and it was all within tolerance.
so i can drop the distributor down wherever?
or i need to drop it in so that it sits ON the peg marked (1)? or just before it?
Thank you

Another consideration is the fuel injector on this vehicle. It is prone to having the poppet valves go south. If you are using excessive fuel, sometimes black smoke present, you may want to put a fuel pressure guage on this.
A sure way to know if the injector is bad is turn key on engine off. Fuel pressure guage will be in range of 60 psi. Then if the guage drops way down quickly followed by an extended crank time, the injector is bad. I have replaced many injectors on 4.3 liter engines and there are plenty of TSB's on them.

Steve

>>prone to having the poppet valves go south<<
Probably depends whether you are a yank or a rebel....Here, in WA, the poppet valves go north.

Where, to Canada?

Steve

Yes, Canada....We send them to Dan.

thankyou for the distributor instructions, that is exactly what ive done. as far as the poppet issue. there is a pressure fitting at the back of the plunium or whatever its called. do i hook up there? and would this cause to engine to run good cold but not hot? im thinking the timing is advanced when warming up so it will burn the extra fuel??? not to sure. please educate me.

Thanks to all