fuel delivery problem

[nwcatman]

son has a 93 D250, 200,000 miles on it, no mods, all stock. lent it to a buddy that put a half tank of biodesiel in it. since then it sporatically has the following symptoms:

1. runs good under throttle

2. misses and dies at stop signs

3. runs better when engine hot/warmed up

things tried so far:





1. son has removed tank to clean it out, was very clean, no cleaning needed

2. replaced fuel filter 4 times (old filters look good, he puts the old filter back in or a new one and it makes no diff.

3. after a filter change truck runs like a champ for about 5 minutes then starts to die



need help! thanks

 

[dpuckett]

First and foremost, check the liftpump output pressure after the filter. You can get a 1/8NPT tapped banjo bolt from Geno's for $7 or so, then hook it up to a boost gauge for troubleshooting purposes. Then pay attention to what happens after that. The bio is notorious for cleaning up anything and EVERYTHING in the fuel system, so if it had 200K of junk and grime built up, it could well take a few filters to get it all cleaned up. Lift pump output should be in the 5-7psi range at idle, pulling down to no less than 3psi at any time.



IF the lift pump has low pressure or pulls down easily, move your tapped banjo to PRE filter and check again. If the results are the same, it isnt the filter- you need a new lift pump.



Next step- check the pump timing and injector condition. Injectors have to be pulled to check them.



Good luck,

Daniel