The other night my truck, all of a sudden, developed a bad engine miss at about 3800 RPMS and up..............truck runs perfect, clear as day, below 3800 RPMS. I changed cap, rotor, plugs. I pulled both valve covers everything seems good there. When I rev it up to the missing of the engine..........none of the spark plugs are dropping spark. So I have ruled out a spark or ignition issue.

My next question was a fuel injector............I tested every fuel injector with a voltometer and everything is good there, but that doesn't mean that a fuel injector isnt clogged, but it runs perfect at lower RPMS.

To test the injectors further. I thought if a fuel injector was bad and I unplugged it then it would quit sputtering at high rpms, but would run alot like **** throughout all RPMS. I tested each injector by unplugging it, reving it up, still missed real bad. Did that with all injectors. Now i'm starting to think it could be the front O2 Sensor. The only problem with that diagnosis is that the front O2 is only a year old.


So what I've boiled it down to is either the Front O2 Sensor, or the Timing Chain. The reason I think it could be timing chain is because the miss in the engine is almost a bad backfire like the timing completely changed at high RPMS.
Or possibly the fuel pump...........meaning it has enough pressure to run at low to mid rpms, but at high rpms it doesn't push out enough pressure anymore.

Let me know what you think. Thanks for reading

 

I think you're on the right track with the fuel injectors/system. Have you checked your fuel pressure yet?

 

okay...........I have not, but I will do that right now, I'll let you know the results.

 

My 95 5.2 did that and I replaced all the injectors and I ran fine after that. got my new injectors and put them in and It ran like a champ. How I found out is pulled each plug wire as the engine was runing. If the engine starts to idle
Rough than you know that injector is getting fuel if it does not its not getting fuel

 

awesome I'll try that out too............went everywhere and jsut wanted a simple fuel pressure test and everyone wanted me to come back tomorrow. They could have made a quick, easy 20 bucks what whatever. I'll go try that now too

 

Also were some leather gloves so u dont get shocked

 

The pressure may be fine below the 3800 rpm's. What you need to do is buy one (pressure tester) , and tape it to the wiper arm so you can see what it does at that 3800 rpm mark . To get a true diagnosis of the pressure. Next things to check would be plenum gasket and cat.

 

Okay...........Could be plenum gasket, but the CAT is punched out. No restriction there. I'll look down in there and see if there is oil in there.

 

Okay scorpion I tried the injector thing and all cylinders are getting fuel at idle. It seems to be a miss throughout all cylinders when I rev it up...........the engine goes silent when I hit the high rpms it goes silent and the rpms drop back real quick, then at those rpms it will spit and sputter. I'm thinkin fuel pump. I'm trying to get someone to do a fuel pressure test. My fuel raid does not have a valve for it so I need to use an expensive fuel pressure test kit to fit between the line and the rail.

 

Just wondering if when you are driving and you get into high gear is that about when your truck starts missing does it shake bad when mine was missing It would run fine at idle but when I would rev it up and hold it there it would miss. and when I would drove it in first and 2 it would run fine but when it shifted into 3 and O/D it would shake bad.
Also is your check engine light on do u have any codes