the 89 G 20 with a 6.2 I just bought is hard starting. It takes a lot of cranking before it catches. How does one check the transfer/lift pump for proper operation? The vaccum pump is junk, 5 inches at best. I am going to change that but am conserned the transfer pump is not working right. The glow plugs seem to stay on the right amount of time. I will check them for opens tomorrow. Thanks. Mike

Open the air bleed on the fuel filter, engine running - fuel should pump out. If not, the pump is bad.


If good, the anti-drain back valve in the pump could be faulty - keeps the fuel from draining when engine is off. Can cause hard starting.


As can several bad glow plugs, or wiring burned\deteriorated at the connectors


Vacuum pump supplys several areas - to check, connect vacuum gage directly to pump, no other lines connected. The plastic lines are notorious for deteriorating and leaking.


Should read 22-26" vacuum - if so, connect lines up individually to determine area of leak.

GMCTD, thanks for the reply. Which pump is the anti-drainback valve in, the IP or transfer pump? And is this something I can change in the pump without pulling it? Mike

It is in the mechanical lift pump, and was made available in all diesel versions manufactured after 1990, as part of emissions upgrades.


Any rebuilt pump should be so equipped, but you should probably inquire, to be sure.


Should also mention, here, a dirty fuel filter will cause hard starting, as will dirty air filter.


Easy things to check for.

JUST A NOTE THE VAC. PUMP CONTROLS THE SHIFTING IN AUTO TRANS. BAD PUMP WILL KILL YOUR TRANY.