Engine/Transmission (1998.5 - 2002) Skip / stumble under load

[JohnBoy5]

ok so i am to the point of lighting a match to my truck!!! When i am driving down the road my truck does the strang mild shake stumble thig, i have no codes a new vp44, cam sensor, apps, drive shaft, injectors, flow tubes. i have spent a small fortune trying to fix this. the more of a load i put on the truck the worst it gets. and ideas?



o as i was typing the skip stumble thing it sort of feels like you are driving on a road with little bumps but only does it when i am in the throttle and at idle it also sounds a little funny when in park/neutral...

 

[NIsaacs]

Have you tried it with the Quadzilla disconected ?

Nick

 

[JohnBoy5]

Have you tried it with the Quadzilla disconected ?

Nick

Yea, that was something I forgot to add. I even bought a edge comp...

o and one other thing i just now figured out, if i place the truck in neutral and take it to about 3k rpm it does it there also with no load, it does it at other rpm ranges as well but i was just frustrated with it and noticed it doing it.

the skip is very intermingling but its starting to show up more often.

could that over flow valve on the vp44 cause this?

 

[BDaugherty]

skip/miss under load with a vp44 is most often related to fuel pressure. i'm not saying it couldn't be anything else, but double or triple check fuel pressure and volume first.

 

[ABennin]

I maybe completely wrong here, but could a bad harmonic damper cause this?

 

[JR]

Has it ran right since you had the vp replaced? Just thinking it could be a tooth off which would throw it out of time and may or may not trip a code

Also, you say you replaced the apps, have you went back and tried to reset it to see if that helps? Was it calibrated correctly when you installed it?

 

[JohnBoy5]

I most defiantly have good fuel pressure and flow, that fass pump will drown you if you dot watch it lol

i also wonder about the harmonic damper, could this cause this strange stumble skip problem? the to tick marks are still lined up doesn't that mean its still good?

I did do the apps reset and calibration. The problem was there prior to the vp44 replacement. i actully replaced the vp44 because of this... I put a bluechips vp44 with a new computer on it so i feel really sure i have a good pump! I dont think the timing is off extreme caution was taken when removing the old pump and putting the new pump on and if it were timing it could be there all the time i would think. the truck will drive good for a bit then under hard acceleration it will act up, it gets worst when the truck get to operating temp.

 

[JohnBoy5]

Something else that i just noticed when driving is this scratching sound or air moving back and forth type of sound. i am starting to wonder if i have a blown head gasket that's leaking between the cylinders...

 

[JR]

Sounds like youve covered all the bases that I know of. . . hoping someone else will chime in and. be of more help than I am. The only other thing i could suggest is gto check ALL of your grounds. Make sure all connections are clean and tight and look for any broken/corroded wires that could be hidden by the wire sheaths. Also if your batteries are weak that will give you fits as well

 

[JohnBoy5]

thanks for all the good ideas, i thought i was a good mechanic till now lol. this one really has me stumped big time.

 

[JMetzger]

I thought I read somewhere here that with a tuner that some times the IAT would cause stumbling/miss & they gave a resistance figure of a resistor to fool the Computer.

 

[AClayton]

My truck does the same thing this time of year... ... cannot figure it out! I un-install the Smarty and everything else under heavy loads and for some reason seems to alleviate most of the issues. When the weather warms up, I can put my Smarty back in things are all good again. Truck has done this as long as I remember owning it. Now for what is really strange... . when the Smarty and my Bully Dog box is off and I tow my RV up grades, the truck develops more peak boost. Not much though... . and it has to be a really long pull and lots of pedal pressure, but on my truck, it seems I have the same amount of torque without the power adding boxes. It just doesn't come on as strong and as quickly. Oh well... . it saves tires in the cooler mos. of the year... . lol

 

[JR]

Metzger, I think maybe you are referring to the MAP sensor. John, have you verified proper voltage to your MAP sensor and proper resistance of the sensor? Even though your not showing any codes, that would be my next step is verifying voltage and resistance at the sensors.

 

[JohnBoy5]

Diesel4life, i have thought about that but i was giong to replace it, do you know what the specs are for the map sensor are?

 

[JR]

You will neet to physically disconnect your tuner to do the test. If I remember, should be an orange wire for the supply and you should see 5 volts or very close to that. Once youve verified that, check the grey wire with red stripe (your signal wire) for voltage between 1. 0 and 2. 2 volts. This is all done with the key on, truck not running. You will need to test the grey wire with the harness plugged into the sensor. The best way Ive found to test sensors without cutting or nicking the wires is to use a hair pin or bobby pin or something similar and stick it right next to the wire in the back of the plug and then touch the multi- meter to the hairpin to do your test. Not sure if youve looked at Blue Chips website, but hes got a very well informed site for testing virtually every sensor on the vp powered trucks. And if all else fails, dont hesitate to pick up the phone and call him. Hes very knowledgeable and glad to help.

 

[BenBrauchler]

Go to Blue Chip Diesel's page and read on the VP44



Excellent troubleshooting

 

[Vaughn MacKenzie]

JohnBoy5, out of curiosity how does it run with the Cruise turned on? Maybe try accelerating using the cruise buttons instead of the throttle and see if that has an effect on it. . . this is an interesting read and may be similar to your issue --> http://www.competitiondiesel.com/forums/showthread.php?t=145015

 

[Houser]

I had a lot of the same kind of problems with my 02 and tried all same fixes and ended up finding I just needed to clean up my battery terminals and grounds. I also jumped the APPS ground wire directly to Frame ground. Doing that first would have saved me buying a new VP44.



Mike

Palmer, Ak

 

[twheat]

I had a similar issue. Had it in the shop because I couldn't figure it out. At first they thought it was the APPS but that was new so they ruled that out. Then it dawned on them the owner of the shop who has the same truck as me had the same issue as me years ago. That was it. It was the ECM. I had them put a new ECM in and the truck runs great now. No stumble or miss. Mine always happened under load mainly in 5th and 6th gear. I hope this helps.

 

[KevinRichards]

I had the same Issue with my 99

it was getting Electrical Noise from the Alternator.

There is a Black 6 gauge wire Black with a yellow tracer routing behind the Alternator and Runs Across the front of the Engine I relocated its routing away from the Alternator. The APPS is Sensitive and Malfunctions with the Electrical Noise.

Also The PCM has a Built in Noise Filter that is typical to not do its job you can make your own Filter By warping 12-16 Gauge Wire around the APPS signal wire.

It's Located in the Center plug at the PCM it is Orange with a Purple Tracer

with your filter wire made ground one end to the Passenger side battery and other end on Driver side battery. Your filter should go From PCM to Just Behind your Fuel Filter Housing along the fire wall make a tight Coil kinda like a Phone Cord.

Hope this Helps Good Luck



Kevin