I have an interesting low power issue that's emerged on my 1983 30SD with about 100 K miles on it.


Symptoms -

1. starts from cold and idles either cold or warm happily
2. Goes like a bomb from a standing start to 60mph - can keep rpms around 4,000, lots of power, no issues
3. BUT - when trying to accelerate when rpms around 1800 to 2000 or when driving on a level road at about 45 to 50 mph car feels very low on power and get "surging power" feeling. Exactly same feeling as when trying to accelerate hard with a gunked up secondary fuel filter.

The LAST time I had issues like this the problem got worse and worse as the power demand went up and it was easily solved with a new secondary fuel filter. This time I'm much less certain what the problems are.

Here's the state of the car

- valve lash adjusted about 3K miles ago
- rebuilt injectors installed about 5K miles ago
- new primary and secondary fuel filters installed about 3K miles ago
- throttle linkage never adjusted to my knowledge and probably needs it
- very very slight vacuum in diesel tank when you open cap when the car is cold
- original primer pump, spews diesel when you pump it
- banjo bolt in manifold and vacuum switchover valve on bulkhead cleaned about 10 K miles ago
- air filter is clean
- no apparent transmission slip or issues

What I'm planning to do

1. Take it for a drive with the fuel cap off and see if the issue goes away. If it does clean breather on fuel tank.

2. Follow conventional wisdom and do diesel purge, replace both fuel filters and primer pump at same time.

3. Check engine compartment for any obvious disconnected vacuum lines

4. Put her up on ramps and check fuel line clamps and connections underneath for possible problems

5. Adjust throttle linkage

The fact that I have power from a standing start worries me. I think I'm on the wrong track. Anyone got any throughts?

Thanks guys