89 dodge ram cuts out after 1/4 throttle??

[badchallenger09]

Here is an interesting one, my 89 dode w150 with 5.9 TBI 4 spd starts and idles like a dream. It runs excellent up to 1/4 throttle, then it will cut completely out and backfire. It will do it driving or sitting in neutral. I have tested the tps, map sensor, fuel pressure/volume, done a complete tune-up. Everything tests fine, the only questionable sensor is the throttle body temp sensor, it seemed to have too low of ohms at operating temp, however the truck acts the same when it's cold. No codes are present. Fuel flow from the injectors sprays just fine when this happens. RPM's don't have an effect, they can rev to the moon and it runs just fine until the throttle passes a certain point and then it cuts out. I'm getting frustrated and have finally found a vehicle that has me stumped. I've been turning wrenches for over 15 yrs and this one has me at a near loss. Any ideas of what could be causing it would be great!

[jpb53]

Try disabling the EGR and see how it works.

[badchallenger09]

Tried the EGR, pulled the valve and cleaned it and made sure it was sealing, but it made no improvement. Checked to make sure I had power to the speed sensor, it does. I'm sure it's something so simple and obvious that I just can't find it.

[jpb53]

I said to disable it; meaning make it inoperable. Pull the ported vacuum line to it and plug it. Drive it this way and see what happens.

[badchallenger09]

I guess I should have been more specific, the valve IS disabled, but I also cleaned around the poppet to make sure it was not just stuck open. There was no improvement whatsoever and still is none. I am starting to think I have a vacuum leak on the lower side of the intake, right where I can't tell without just pulling it and redoing it.

[badchallenger09]

discovered I don't have any vacuum leaks. Everything appears to be functioning properly, but the problem persists. New discovery though, when the throttle is applied enough that it cuts out and hold it there, it will bog down until it nearly dies and then will come to life and roar like it should at that throttle position. But then bogs down again and will continue to do this cycle until the throttle is returned to closed or only partly open. Injectors are functioning properly and I am getting spark during the bog down as well. On occasion it will backfire through the throttle body just before it comes back to life.

[Chris Stewart]

How does it act driving half or full throttle?
I'm kinda leaning toward a lean condition.
A scan tool that shows running conditions could show O2 sensor values and lean counts.
I have a friend who had a Monte Carlo that acted funny...the star wheel in the distributor cap was slipping on the shaft.

[badchallenger09]

Got it figured out finally. It turned out to be a split in the pressure line inside the fuel tank. Had the pressure, but couldn't keep the volume up under demand. Pressure guage didn't show it either and looking at the spray pattern of the injectors looked good. Had the computer put out a lean code it would have been A LOT easier to troubleshoot. Instead it acted as though nothing was wrong