6.5TD no fourth gear

[great white]

So, a barometric sensor seems to indicate you have an l56 (vin s). My l65 (vin f) only has a map sensor and that's how they all came to the best of my knowledge.

If you have an l56, it should have come with an egr valve. By the sounds of it, someone has been unplugging things under your hood. Check to make sure the egt circuit is either working as per or has been properly inhibited. A leaking inhibited egr circuit or a malfunctioning one can cause poor running. A reflash or chip (can't remember your year) can turn all that....."stuff"..... off properly in the program. Essentially, you get the l65 program. Then you just have to make sure it's blocked off in the lower manifold.

The 6.5 TD does have a map sensor, but it's a 2 bar map sensor and it's mounted on the intake. Performs a different function from the baro sensor (which is also just a map sensor but a 1 bar) on the firewall. The baro sensor is open (unplugged) to read the ambient barometric pressure and the pcm compares it to the data from the 2 bar map sensor. The pcm uses this info in the lookup tables in the program. Again, to the best of my knowledge, l56 engines have a baro sensor l65 engines don't.

This isn't also one of those trucks with a maf sensor is it?

Good luck.


Sent from my iPhone using Tapatalk

 

[THEFERMANATOR]

So, a barometric sensor seems to indicate you have an l56 (vin s). My l65 (vin f) only has a map sensor and that's how they all came to the best of my knowledge.

If you have an l56, it should have come with an egr valve. By the sounds of it, someone has been unplugging things under your hood. Check to make sure the egt circuit is either working as per or has been properly inhibited. A leaking inhibited egr circuit or a malfunctioning one can cause poor running. A reflash or chip (can't remember your year) can turn all that....."stuff"..... off properly in the program. Essentially, you get the l65 program. Then you just have to make sure it's blocked off in the lower manifold.

The 6.5 TD does have a map sensor, but it's a 2 bar map sensor and it's mounted on the intake. Performs a different function from the baro sensor (which is also just a map sensor but a 1 bar) on the firewall. The baro sensor is open (unplugged) to read the ambient barometric pressure and the pcm compares it to the data from the 2 bar map sensor. The pcm uses this info in the lookup tables in the program. Again, to the best of my knowledge, l56 engines have a baro sensor l65 engines don't.

This isn't also one of those trucks with a maf sensor is it?

Good luck.


Sent from my iPhone using Tapatalk

ALL 94-95 6.5's had the firewall mounted sensor. The OBD1 ECM required it as it didn't sample the 2 bar map in the intake for elevation like the 96+ OBD2 engines did. Stil lsounds to me like a fuel delivery or PMD issue from his description of bucking at speed. And OBD1 trucks are known to have bad OPS switches that cause teh fuel pump not to work.

 

[THEFERMANATOR]

Since it sunds like you found your trsans problem, I suggest you open a new thread in the 6.5 section about your current engine problems and include a link to this one and put a copy of the 6.5 checklist in with it. It sounds like you have a basket case on your hands that had multiple problems, and these issues may require posts in a couple of sections to get the most exposure to solve each of them.