1994 6.5 diesel won’t rev over 2500 rpm

[Maedale]

Engine only revs to 2500 on the road. If you hold accelerator to floor will pour black smoke. If you let off it will shift and get up to highway speed
Lift pump wired directly to 12 volt
installed clear fuel line and shows no bubbles
have 6 psi fuel pressure at bleed valve and drops to 4 on acceleration
there was no last ditch screen in front housing
Rebulit injection pump installed in last 10000 km
cleaned grounds at rear of engine
disconnected wire to optical sensor and engine died then changed crank pos sensor
no difference in performance with air cleaner removed
engine was completey rebuilt less than 5000 km ago
have tried different fsd with same results
as fsd is remotely mounted also plugged in directly to inj pump to rule out ext cable
Wiring harness changed to inj pump

any ideas would be appreciated

[DmaxMaverick]

Welcome aboard!

Is the SES or STS lamp on? Will the engine speed increase in P or N? If so, it's likely the wastegate, wastegate solenoid valve, vacuum pump, and/or vacuum lines, in no specific order. This, presuming a good injection pump, or it would be on the short list. Other possibilities include, tankful of gasoline, wrong or failed fuel filler cap, pinched/kinked/blocked fuel supply or return line, plugged soot trap, etc.

[Maedale]

Welcome aboard!

Is the SES or STS lamp on? Will the engine speed increase in P or N? If so, it's likely the wastegate, wastegate solenoid valve, vacuum pump, and/or vacuum lines, in no specific order. This, presuming a good injection pump, or it would be on the short list. Other possibilities include, tankful of gasoline, wrong or failed fuel filler cap, pinched/kinked/blocked fuel supply or return line, plugged soot trap, etc.



thanks for replying. Now I realize I should have given more info. Truck ran like this all last summer. Engine light comes on occasionally with code 17 or 18. Engine is naturally aspirated. Have taken fuel cap off with same results. Engine won’t rev up in n or park either. Also hard starting. As I have good fuel pressure I ruled out fuel supply failure

[DmaxMaverick]

That leaves the injection pump, especially with DTC 17 and/or 18, which are pump internal fails.

[Maedale]

That leaves the injection pump, especially with DTC 17 and/or 18, which are pump internal fails.


is it possible that only optical sensor is faulty

[DmaxMaverick]

It is possible, but unlikely you'd only see the codes and the SES lamp occasionally. It sounds like more than just that, though. The PCM should have a persistent hard code and/or a mechanical failure to allow only 2500 RPMs, black smoke, and hard starting. It isn't adding up to only an optical sensor fail. Otherwise, it should run normal between DTC episodes.

[Maedale]

It is possible, but unlikely you'd only see the codes and the SES lamp occasionally. It sounds like more than just that, though. The PCM should have a persistent hard code and/or a mechanical failure to allow only 2500 RPMs, black smoke, and hard starting. It isn't adding up to only an optical sensor fail. Otherwise, it should run normal between DTC episodes.


ok thanks. I was hoping wasn’t inj pump but looks like I’ll have to bite the bullet or scrap it

[DmaxMaverick]

I always hate bearing that bad news, and avoid it when possible. Before diving into a new pump, I'd go over the list I posted, make sure everything is checked, dump in a can or three of SeaFoam, and cross your fingers. If the pump has only 10K on it, it shouldn't have failed. Stranger things have happened, though.

[Maedale]

I always hate bearing that bad news, and avoid it when possible. Before diving into a new pump, I'd go over the list I posted, make sure everything is checked, dump in a can or three of SeaFoam, and cross your fingers. If the pump has only 10K on it, it shouldn't have failed. Stranger things have happened, though.


okay thanks Sea Foam never hurts