can just barely make it to work and back

[keruzam93]

i have a 1996 2 door 5.7 when i first start it it runs fine until i hit about 2500 rpms in any gear and then it stumbles and backfires and just doesnt go anywhere, or just dies out all together. the longer i drive the lower the working rpms go by time im almost to work (15 minute drive) it cant get over 1000. BUT if it dies out and i restart it, or if i pull over and i shut the truck off and restart it its like resetting the thing and its back up to 2500 and drops the longer i drive again. the fuel pressure tested fine and i can hear the pump run every time i turn the key on. also the cats arent plugged and its not the mass air flow sensor. any ideas?

 

[SunlitComet]

you have an obd2 vehicle. get to some one that can read live sensors data that can pick up the on the failure while driving. if the pressure is tested fine through out the driving range and you can verify the cats are not backing up either then the sensor data should point you in the right direction. active or stored code would help to narrow down causes too.

 

[YUKON1999]

i know this probably doesnt sound like it would matter at all but if you havent checked the codes yet look at the intake and make sure its not plugged cuz i had a car that did kindy the same thing and the air intake wasnt connected right so wasnt get enough air, just a thought sense sounded like a problem i had once

 

[keruzam93]

we have a live data scan tool at work but we've been busy and i havent been able to test drive my own vehicle. i wonder if my boss will let me borrow it i guess it would be a big help

 

[Dalton916]

Does the speedometer continue to function properly through all of this?

 

[SunlitComet]

Does the speedometer continue to function properly through all of this?

i dont think his tranny fuse is burned out. a bum fuse should not cause a tranny to slowly stall the engine to death.

 

[keruzam93]

yes the speedometer works fine. no codes either

 

[Dalton916]

i dont think his tranny fuse is burned out. a bum fuse should not cause a tranny to slowly stall the engine to death.

I don't either. I was thinking along the lines of an intermittent loss of signal from the vehicle speed sensor. Loss of that signal puts the trans in "safe mode" and an intermittent in and out of safe mode will make it act amazingly like he's describing. Well, at least it did on my '96 till I noticed the speedometer being erratic. Basically, it would move while the trans was in safe mode. Once I saw that I changed the VSS and all was well again.

 

[SunlitComet]

I don't either. I was thinking along the lines of an intermittent loss of signal from the vehicle speed sensor. Loss of that signal puts the trans in "safe mode" and an intermittent in and out of safe mode will make it act amazingly like he's describing. Well, at least it did on my '96 till I noticed the speedometer being erratic. Basically, it would move while the trans was in safe mode. Once I saw that I changed the VSS and all was well again.

service manual says no such thing. in fact it specifically says the signal is processed by the pcm and passed on to the dash instrument,radio, cruise control, tccm and bpmv. while it may be used to set a code the safe mode should not stall an engine.

---------- Post added at 11:34 AM ---------- Previous post was at 11:32 AM ----------

while you are at it looking around for causes make sure the grounds on right frame rail to engine, rear of right cylinder head and right fender well next to battery are clean and free of corrosion.

 

[Always Wrenching]

It kinda sounds like my old 99 gmc suburban, i had issues that sound just like this. It was the timing getting off because of a worn dizzy gear. My dizzy gear finally sheared off enough that truck died. If its possible mark position and pull the dist. to check the condition of the gear. This is a VERY common issue with vortech 350's