B1e9a8u7

New to me rig. It had a miss when acquired, trouble shot for days, addressed a few issues and performed some maintenance i was unsure about. Initially it had a miss that came in as engine warmed up and was very consecutive not like a single cylinder but almost like every cylinder would misfire in order. I adjusted the tps and got the majority of it to go away, now mis was intermitten and not consistant about normmal for a 30yr old vehicle i assume. Now heres the new problem, after adjusting the tps the miss is there, just like it was except only cold. Once engine starts to warm up it will begin to go away. If you drive it it lacks power then surges into power as it cleans itself up, usually less than 5mins of drive time. Ive read the fsm and done most of the checks wthout actually going all the way back to the ecu. What am i missing, think the tps is bad since thats the only common denominator?

Thommo Thompson

well im not a 3 l guru, but i am an EFI tuner.
relly u shouldnt have touched the tps unfortunately. if somethings wrong, mucking with sensors will only make it more difficult to diagnose. put it back to where it was if u still can before its too late.
a hot missfire is usually caused by a vacuum leak or fuel supply problem or a weak spark.
if a weak spark is to blame, u would probably have more missing under load, but it can also be a problem at idle when the compression and suction in the cylinder is slow and mixture is rich. (larger droplets less atomisation more, spark required)
a vacuum leak is most common and is usually more evident when the ecu leans off the fuel supply when the engine gets hot enough to take readibgs from the O2 sensor. extra air when cold isnt as much a problem coz it runs rich predetermined fuel maps.

wrenchmonster

OP, hello and welcome. Please tell us exactly what you've changed out on the truck. Telling us that "some maintenance" was done doesn't paint a clear picture. Be as specific as possible. For example the truck has new NGK spark plugs and factory wires. Anyway, Thommo is correct. Don't mess with sensors. Personally, I don't mess with them at all. Nor do I bump up the timing, as seems to be very popular here. IMO, the best performance upgrades for a 3.0 would be cold air intake, electric fan, header exhaust with an upgrade to at least 2.5" after cat, and then porting (if the engine is dismantled), beyond these things it's difficult for the DIYer to get additional performance. Most of the big performance requires a machine shop. I personally think it's foolish to dismantle EGR systems and change the MAF sensor, etc, etc. These are just &$cking with non-problems. It might feel good to do these things, and guys who've done these "mods" swear by them, but it really doesn't add any performance. As far as I've seen, no one has dyno'd their engines before and after.

In any case, stepping off of my soap box. Sorry guys...

It sounds to me like there is a vacuum problem. 3.0s are sensitive to having all of the vacuum hoses in good shape and have the proper routing. Change out all of the vacuum hoses (do them one by one if you're not super comfortable taking them all off) and also take a good look at the PCV hose and grommet, which are often ignored because they are kinda hard to get to. Basically, anything in the intake tract that has vacuum needs to be checked and/or replaced. While the truck many have hard mechanical problems causing the misfire, it would be easy to cross bad vacuum hoses off of the list.

-Kevin

B1e9a8u7

I adjusted tge TPS cause it checked outta range and had a hunting symptom about 1500rpms. So far ive changed cap, rotor, and plugs. Ohm'd wires they were fine. Also replaced pcv valve cause old one wouldnt fully close. Ive sprayed carb cleaner around all vacuum lines and ports and didnt notice a vacuum leak.

Thommo Thompson

ok can u tell us a bit more about the miss.
when does it happen. under load, at idle, at gentle acceleration?
If the miss is at idle only then its almost certain to be vacuum leak or spark.
The further up the power range it happens the more likely it is fuel regulator or pump or filter.
if its at high rpm but low power (revving) then chexk spark quality or vacuum leaks.

B1e9a8u7

Ok when i 1st acquired the rig. It missed warmed up. Example. (fire, fire, miss, fire fire fire) this would point to a single cylinder if it repeated. The miss i experienced was (miss,miss,miss,miss,miss,miss). So i looked for things in common with all cylinders. 1st i thougt coil was breaking down, checked out good, i replaced cap, rotor, and plugs. No noticable change. Next i checked pcv, it rattled, and i could feel vacuum but if i blew back it wouldnt completly shut off so i replaced it with a new one. No change. Next i checked fuel pressure, seemed to be good, removing vacuum from regulator changed fuel pressure, no fuel in vac lines so assumed it was good. I aslo had a up and down rpm fluctuation of about 500 rpms around 1500. Acted like when idl and e2 contact opened in tps. Checked it and it was out of adjustment. Adjusted it best i could. Mine will not stay anywhere near kohms so its literally set open or closed at specified measurments. This fixed the 1500rpm problem and smoothed my idle up no miss warm except occasional and random fluctuation. Drives good, good power and response. Problem is now when its cold. Its the same constant miss, miss, miss, etc until it begins to warm up, driving about 5mins, it will noticealy surge into power as the miss goes away. Im curious how long does it stay in open loop before switching? Maybe a/f is off in open loop? Too rich cause this condition right so maybe lean the afm?

wrenchmonster

If it were me I'd check the ECT, Cold start injector, fuel injectors, MAF (AFM), O2 sensor 1... in that order.

My suspicion is that you've got a sticky injector or an injector that is bleeding down overnight. The new school way to find this would be using a scope to see which cylinder was at fault. A scope would also be useful for finding and isolating an ignition problem. For a long long time scopes fell out of favor, but have in recent years become popular again.

The old school way of finding a bleeding injector would be to pull the rails, leave the injectors attached. Then place some paper towels or a piece of cardboard underneath all of the injectors. Then prime the fuel system. Don't crank, just prime to build pressure. Then simply walk away and leave it overnight. If there's a leaking injector it will dribble out and leave a stain on the cardboard. Now the failed injector(s) are known.

You could try doing seafoam or other fuel system treatments on the injectors for 3-4 tanks of gas to see if the system could be cleaned up. Best way to do this is on a full tank and a long road trip where the engine sees sustained and higher rpms. In my experience injectors almost always need proper servicing. Now here again folks are going to say to buy injectors with 4 ports/nozzles and how awesome they are, yadda yadda. I personally stick with stock injectors and have them professionally cleaned. There are many services out there that will rebuild and clean injectors for you. My personal favorite is Mr. Injector in Idaho. He offers super fast turn around and does an excellent job. I've also used WitchHunter in the past and they are okay too but I feel Mr. Injector is more meticulous with his cleaning. I've had good luck pulling sets of injectors from junkyards and then will send two sets (or a set with a couple of extras) to Mr. Injector and instruct him to rebuild the best ones. He'll check them all out and choose the best ones for you. If he finds any dead ones he'll also let you know. This avoids any downtime while waiting to get your injectors back. At the mileage that our trucks are at it's a good idea to have the injectors serviced anyway. Even if they are all technically working okay, the cleaning and rebuilding will balance them all out and the engine will run smoother.

-Kevin

Thommo Thompson

ok a miss miss miss miss miss miss is a stalled engine. what do u mean every cylinder is missing.
You havent described if it happens at idle or under power like i asked.

B1e9a8u7

Yes theoretically a miss miss miss... is a stalled engine. But its like whatever cylinder thats coming to fire doesnt, just enough to spin the crank if that makes sense. As far as when, its present from idle all thru the rpm range, load or no load. Once it goes away its a little sporadic at idle but persist all thru rpms up until about 2500 then its not noticable. One thing i did notice is if you run it up in higher rpms it seems to go away a little quicker

Thommo Thompson

ok its fuel and the fact its happening all the time while cold id say the injectors are dirty on the outlets and are restricting spray.
iether that or the solenoids in the injectors are just getting old, or (unlikely) the ecu has failed.