Please look at this - 2000 missfire issues

I'm going insane! I am fairly mechanically inclined, so I did a lot of the normal tune-up/troubleshooting stuff myself. Nothing helped. Today I finally broke down and took it to a mechanic. They had no idea.

The truck stumbles and missfires at idle and all the way through the rpm range - at least that's what it feels like. However when driving and holding steady at say 55 it surges, it doesn't feel like it stumbles. It feels like it runs right for a second and get's more power, then goes back to running like crap with less power. It does this over and over. When towing my boat it feels like it has the power of a 4cyl.

Here is what has been done:

Plugs
Wires
Fuel Pressure reg
Fuel Filter
PCV valve
Professional Injector clean (ran on chem)
Fuel pressure checked - 55psi and holds steady
Vacuum checked - 17 (no idea if this is in spec, I think over 15 is ok?)

There are no codes and never has been and the truck has been doing this for months. The issue is very random and it even seems like some days it runs better than others.

I'm stuck, the mechanic I use is stuck, I would love to hear some ideas if you guys have any.

put a gauge on it with a long hose and check fuel pressure on the road.
other than that put a realtime scan tool on it, even cheapies do this, my 200 dollar accutron does it, anyway, leave it plugged up and go for a ride, using the misfire monitor, see which cylinders are missing. you can also look at tps voltage, map, etc...
other than all that, sure its engine trouble? Your trannies isn't acting funny is it?

I'm sure it's engine. Tranny wouldn't cause it to idle rough while parked (at least I don't think so).

Also, just to put it out there the truck is a 2000 4.8l with only 88k on it. All recommended service has been done on time by the dealer. It seems odd to me I'm having this kind of issue at 88k.

Thanks for the input, so far.

I'm sure it's engine. Tranny wouldn't cause it to idle rough while parked (at least I don't think so).

Also, just to put it out there the truck is a 2000 4.8l with only 88k on it. All recommended service has been done on time by the dealer. It seems odd to me I'm having this kind of issue at 88k.

Thanks for the input, so far.

They can and do, broken flexplates will often through misfire codes, a thought, it is a puller. I DOUBT it though.

Put a pressure gauge on it and drive it, a 2000 with 88k on it has done alot of sitting. These fuel pumps have alot of plastic parts, they don't like fuel varnish.
It is common to hold pressure sitting still, but drop out when demand goes up.

Put it in drive and stall it up, ie foot on brake and gas and see what it does, may see misfires that way to.
Just don't do it to long, heats the trannie up.

If it was a fuel pressure issue, and it's running rough at idle as well as down the road, wouldn't the pressure test at idle show something as well? If pressure was the culprit how could it sit at 55psi and run like crap? Trying to understand is all. Plus I will have to take it back to the mechanic to do this and that means more $$.

What about EGR valve? I had a Ford Ranger that started running like crap and it turned out to be a stuck EGR valve. That was the vacuum type though. This one has some sort of big electric type deal. Are they known to have issues at all? How would I check?

If it was a fuel pressure issue, and it's running rough at idle as well as down the road, wouldn't the pressure test at idle show something as well? If pressure was the culprit how could it sit at 55psi and run like crap? Trying to understand is all. Plus I will have to take it back to the mechanic to do this and that means more $$.

What about EGR valve? I had a Ford Ranger that started running like crap and it turned out to be a stuck EGR valve. That was the vacuum type though. This one has some sort of big electric type deal. Are they known to have issues at all? How would I check?

yes, theoretically the fuel pressure should be fine at idle, but cover all your bases, as for the mechanic deal, I bought a gauge at azone for like 20 bucks, nice to have around, if your gonna wrench much you should have one, but on to other things.

They aren't "known" for egr troubles, but doesn't means thats not it, but on an obd2 vehicles, egr trouble WILL throw codes. Pretty much anything "should" through a code. If its not throwing codes, realtime scan tool monitoring while its missing may be the only way to "see" it.

BUT, if it is messing up and your mechanic is lost find another mechanic, sorry to be blunt but come on shadetrees, that gives the rest of us a bad name. It is completely acceptable to not be able to replicate a problem, but if it is broke and they can't find it, take it somewhere else.

I guess I will look for another mechanic then. That's always a scary prospect. I took my last chevy to the dealer in town for a hesitation/sluggish issue and after they got me for a fuel pressure reg and fuel pump and didn't fix it, I figured it out myself - water in the fuel.

Thanks for your help, I appreciate it.

I guess I will look for another mechanic then. That's always a scary prospect. I took my last chevy to the dealer in town for a hesitation/sluggish issue and after they got me for a fuel pressure reg and fuel pump and didn't fix it, I figured it out myself - water in the fuel.

Thanks for your help, I appreciate it.

WOW, did you talk back with them? I can see getting stuck with parts, as they were one your truck, but they shoulda ate the labor.
Ya, scary I know, on second though though, not the trouble now is it? I can't believe if its missing its not throwing codes.

I dont see you changing coil or ign module, intermit spark may not code. egr can cause problems but sec gen brain usually will code. Even though you changed wires could have bad one or may not be seated also could have hit exhaust somewere and some are shorting . happened to my son 5.7 camaro he ran to close to exhaust I had to find and fix. run and look at in dark or check by exhaust and recheck plug seating on each plug. Good Luck

where you have no DTC codes and the engine is running badly intermittently, I would clean all ground connections,,,battery connections ....remove PCM/computer connector and check for damage/corrosion..etc....

another componet that can cause wierd engine issues with no DTC'S , would be the Engine Coolant Temp sensor....

then you have possibly the cam/crank sensors with an intermittent output throwing the timing off..

best go where the repairer has electronic testing knowledge...with these engines..

Do you have an automatic? Do you get a big surge, engine bucking? Could be the hydrostatic clutch going out.

Is the problem "intermittent" or "consistant"? This sounds familiar to a bad case of "positive battery cable rubbing through to ground".

Depending on the year and rubber vs. metal gas lines, it could be vapor locking....

Do you have an automatic? Do you get a big surge, engine bucking? Could be the hydrostatic clutch going out.

Is the problem "intermittent" or "consistant"? This sounds familiar to a bad case of "positive battery cable rubbing through to ground".

Depending on the year and rubber vs. metal gas lines, it could be vapor locking....

This thread is 2+ years old. I'm pretty sure they figured it out by now.