fuel mods gone south

[bigmackloud]

Working on a '90 m923a2 6cta8.3. Tried to turn up the fuel on the injection pump. Adjusted the fuel screw, the star screw, and the smoke screw on the back. (Honestly we walked into this project backwards and adjusted the fuel screw last).


Our problem now is that if you rev the truck, let off, and then press the gas again, it has no power and stalls out. Any ideas?!


We have even tried putting everything back to stock setting (the best we can tell) and it stills has this problem and now it won't idle.

Thanks in advance!

 

[doghead]

You may need to take your IP to a professional shop.

Do you drive this truck daily or are you stranded on the side of the road? If not, do not use HELP, in your thread title, we reserve that for real emergencies on this site.

Where did you get your fuel adjustment information?

 

[bigmackloud]

I apologize, the truck is not on the side of the road. the trucks at my house in Raleigh and needs to go to Wilmington tonight (2-3hr drive).

Mod information came from here and other sources.

Bosch 0 403 436 109
PES6MW100\120RS1143

at the moment, the truck starts fine if you give it a bit of fuel, seems to rev ok, but stalls when you return to idle.

 

[patracy]

Have you adjusted the idle? If you have, then try backing off the governor a bit and readjust the idle.

 

[Suprman]

I turned up my fuel 3 turns and went one click on the governor without incident. I believe the fuel screw is close to the top of the housing if you go too high it can catch and stick. Did you watch and make sure the fuel cutoff solenoid was staying in the retracted position and the spring on the lever is keeping the fuel feed open.

 

[bigmackloud]

Just wanted to follow up on this. I read tons of threads yesterday while searching, where someone would describe a problem but no one ever posted back about what fixed it.

So we kept at it yesterday and ultimately I learned way more about this pump than I ever really wanted to know. Ultimately it was the smoke screw in the back. The set screw on it had moved and we didn't realize it.

nevrenufhp was kind enough to respond last night with a PM. He actually nailed it on the first guess and explained it better than me, so I'll share what he wrote.

"These pumps are a little quirky in their function. The smoke screw on the back is what I'm leaning towards. With rack travel in the wrong place, it is likely hitting the shutoff section of the rack travel. Take out the fuel screw, and adjust the smoke screw on the back until the condition stops. It will smoke pretty bad while testing, but you arent adjusting for smoke, just the engine dying issue."

In the end, we came out 2.5 turns on the fuel screw. Nice little bump in power. May tackle adjusting the gov springs at some future point.

Speaking of the gov springs, how much of an increase in rpm is safe with the 8.3L?

 

[doghead]

Thank you for the update.

 

[Suprman]

I have heard of revving these engines over 3k i dont know how the drivetrain would feel about that though. I did one click in on each there are 2 you have to do one and then hand turn the motor till the second one comes up. I tried 2 clicks first the idle jumped way up so i went down to one. I can go to around 2300 i think now i believe it was limited to 2100 before its a very slight adjustment you wouldnt think it would make such a difference. Nevrenufhp helped me with my first time too.

 

[nevrenufhp]

Hopefully it's all better now.
You can rev them to 3200rpm, but keep the sustained rpm at 2800 or less.