What did you do with your GMT400 today...or yesterday....

[dbrannon79]

Played with the 93 some while I was charging batteries. wired up the cold advance on the IP so it would work. had to splice in a diode to the fast idle solenoid that pushes on the throttle since I have it wired into the AC so it bumps the idle with the AC running. tested it out to make sure it wasn't going to back-feed into the relay I had for the AC and electric fan. That all seems to work fine.

I also was reading up on this 93 and found what exactly the PO did with turning up the fuel on the IP that's in it. both the transfer pump adjustment and the fuel rate adjustment have been moved. increasing the transfer pump pressure (adjustment inside the IP fuel inlet) also limits the amount of timing advance the solenoid on the IP gives. this would explain why when I manually energize the cold advance solenoid it hardly changes anything other than me seeing fuel flowing faster in the clear return line.

I wonder if I need to attempt to un-do this so it can work properly. I also need to figure out if a fella like me with limited knowledge can get it done without pulling the pump. Maybe @Will L. and @Rockabillyrat can give me some input. whether I should attempt, and if / how to know it's close the normal again.

Last night I searched up and down on the innerweb for the instructions he used on the transfer pump but could not find anything about adjusting it, even on a test bench.

Here is the link to the thread and a screenshot of the post.

DB2: Increase Case Pressure-Turn Up Fuel: Questions...........

i have done both per these instructions: "Transfer pump: This increases case pressure. Looking at intake of pump inside inlet fitting, there's a 5/32 allen screw, turn clockwise looking at it, increasing case pressure and timing advance across board. Be careful, too much and it will blow seals...

www.thetruckstop.us

 

[dbrannon79]

Been working on searching the forums to compile the full history of this 93 together on a timeline. been searching posts here and in DP. Once I have most of all the major things listed I will post something in the build threads here with all the links.

 

[Rockabillyrat]

Played with the 93 some while I was charging batteries. wired up the cold advance on the IP so it would work. had to splice in a diode to the fast idle solenoid that pushes on the throttle since I have it wired into the AC so it bumps the idle with the AC running. tested it out to make sure it wasn't going to back-feed into the relay I had for the AC and electric fan. That all seems to work fine.

I also was reading up on this 93 and found what exactly the PO did with turning up the fuel on the IP that's in it. both the transfer pump adjustment and the fuel rate adjustment have been moved. increasing the transfer pump pressure (adjustment inside the IP fuel inlet) also limits the amount of timing advance the solenoid on the IP gives. this would explain why when I manually energize the cold advance solenoid it hardly changes anything other than me seeing fuel flowing faster in the clear return line.

I wonder if I need to attempt to un-do this so it can work properly. I also need to figure out if a fella like me with limited knowledge can get it done without pulling the pump. Maybe @Will L. and @Rockabillyrat can give me some input. whether I should attempt, and if / how to know it's close the normal again.

Last night I searched up and down on the innerweb for the instructions he used on the transfer pump but could not find anything about adjusting it, even on a test bench.

Here is the link to the thread and a screenshot of the post.

DB2: Increase Case Pressure-Turn Up Fuel: Questions...........

i have done both per these instructions: "Transfer pump: This increases case pressure. Looking at intake of pump inside inlet fitting, there's a 5/32 allen screw, turn clockwise looking at it, increasing case pressure and timing advance across board. Be careful, too much and it will blow seals...

www.thetruckstop.us

View attachment 90913

When you turn up thr fuel screw you will also advace the base timing since the rollers will hit the cam ring earlier.

Transfer pump pressure you need to be careful with. At 130psi is will lock the rotor. I normally set mine to 65-70 psi at 2k rpms. Which is the normal spec for a 4911.

The HPCA solenoid only advances the cam ring about 2* (4* at the crank) so it's not alot of movment. If you increasing TP pressure it will advance the timing. The opposite end of the advance piston is controlled by housing pressure. So if you increase housing pressure then it retards timing. That's how the HPCA works. The check ball holds pressure in the housing and thus keeps the advance piston slightly pushed back. When you energize the HPCA it pushed the check ball open. That drops housing pressure to zero and advances the timing since the advace piston has no housing pressure pushing on it anymore.

Too much housing pressure can cause issues and indicate a leak in the TP system.

 

[dbrannon79]

@Rockabillyrat Is there a way i can check the transfer pressure with the pump still in the engine? a way to connect a gauge just to see if it's "ok" I was just backtracking reading up on what all has been done to this truck in the past. the engine has been running on this pump since 2016 from what I am reading in the forums. Or is this anything I need to worry about.

 

[Rockabillyrat]

You need the adapter to put a gauge to it. You remove the torx screw holding nose cone retainer in place. Then the adapter screws in for the gauge