Engine/Transmission (1998.5 - 2002) Stumble is injector spray pattern problem

[kdunham]

Hi guys,I'm a long time reader,first time poster. I probably wouldn't ever had a reason to join the Forum except for one recurring problem that ALOT of people can't fix. The problem is that especially in colder weather and with performance boxes the truck will develop a weird stumble,especially on a long pull in higher gears where the truck is under a good constant or increasing load. It'll usually occur somewhere over half-throttle. It's almost like it's sporatically dropping a cylinder,and a little "bucking" usually accompanies it. Here's the punchline. When you have a boost fooler on you're making more boost and hopefully injecting more fuel. Cold air is more saturated with O2 so now you really need some ATOMIZED FUEL to make up for all that boosted cold air coming in. But,if you have an injector that does a "ho-hum" job in normal conditions on a stock truck where maybe the driver doesn't notice any problem,it's going to show up now. The injector may have too high an opening pressure(not so likely) or too LOW AN OPENING PRESSURE. A low opening pressure(which is a result of failure in the mechanics of the injector itself,doesn't have anything to do with a pump of any kind)will allow the injector to just flop the fuel into the cylinder,and not even at the right time. A clean burning cylinder needs ATOMIZED FUEL DELIVERED AT THE RIGHT TIME,which is provided by a GOOD INJECTOR. Some owners will experience a strange engine noise,almost like a cross between a real heavy lifter noise and a wristpin,and it is in rhythm with the engine,however it lessens with deceleration and is HARDLY PRESENT OR NOT PRESENT AT ALL AT IDLE! This is extremely indicative of a failing fuel injector(s). I've been reading some posts about cold weather and performances modules making these trucks run funny. The cold and boost foolers are just enhancing this problem that was there all along. And no,I don't sell injectors but sure as frogs have waterproof butts my Bosch 300's will be here this weekend. Hope some of you find this to be the solution to this long standing problem.

 

[BHight]

thanks for the insight here. am a newby here and have this "problem" with my '00 that has a e-z with everything else stock. guages of course.....

 

[TORQUE THIS]

That might be 1 issue causing a stumble.



My stumble has been occuring since April of 04, still have not found the problem.



I've been thru the wiring, injectors, VP-44, grounds, APPS, IAT, and the MAP. Nothing has cured the problem!

 

[kdunham]

It is also quite possible that there is a mechanical problem of some kind in your case and others,such as a weak or broken valve spring. Hopefully it's not that but if everything on the outside is good then it's time to go inside if you want to be sure it's right. It's a piece of work to go through one of these heads and make sure the recessions are correct,valves and guides are straight,seats seal and the head gets milled properly,but it's all part of the fun. Also,if you or anyone you know works at a repair facility, a scanner such as a Genisys is nice to monitor the "goings on" while driving,hopefully something "burps" on the road test and you can catch it in the datastream.

 

[Dgrizz]

Has anyone figured out what this problem is? I never had this herky-jerky problem until recently!. Luckily for me it does it on all settings of the box except 5x5(doesn't seem to be cold weather related)! Guess I'll just run around ragged until it gets figured out? Unfortunantly it developed after the M5's, and head+cam were installed at the same time so I don't really have any insight as to what it might be? Comp box has been flashing funny lights at me lately too! My guess = the Comp Box, or the stinky injectors at high alt. (4400ft. ), but I know a guy around here w/ similar mods w/M5. 9's having no problems at all (making 693hp)!! David