hey ya'll, i've been having a continuous problem with my truck since i bought it but i cant seem to figure out. when i start the truck specifically in the morning or after its been sitting for more than 6-8 hours it stalls almost immediately. now i know this would seem like a fuel problem but i checked both fuel pumps and replaced the front because it was only at about 25 psi. once the truck dies i can start it back up with no problems. when i get to driving at any point in the day, whether or not it was sitting or just running, the rpm gauge will drop about 500 rpms while cruising and accelerating. i have to mash on the gas pedal to get it back up and once i do it hesitates like its stalling/bogging down and then comes up again. both pumps are putting out proper psi, spark plugs are gaped properly, compression on all cyl. is mint around 140 psi all very even. there's a new coil, complete tune up, fuel filter last week, i removed the vacuum line on the fpr and cant tell if i smell fuel in there or not, if there is there is not very much. all vacuum lines are sealed, recently replaced all gaskets in motor due to loss of cyl #3 a month or two ago, has since been refreshed and new parts have been installed. oh and when the drop of rpm happens the truck has some serious spark knock. had the truck about 10 months now and done tons of work to it and would hate for this to be a deal breaker for the truck, any help is much appreciated thanks.

(PS. sorry for the long post but i feel have to explain it in deep detail because everyone else i've explained it to hasn't understood it)

 

year? engine size? transmission?

you should put a code reader on it it. I bet your ECM is going.

 

This. You never mentioned checking for codes ( Key On Engine Off year ) and what you got. The light doesn’t have to be on for there to be codes.

 

Sounds like a fuel problem.
I am betting on a bad rear fuel module if it is a OBS truck.
This will give the low pressure while on the front tank.
You need to put a fuel pressure gauge taped to the windshield and see what it says when each tank is selected if it is a OBS truck.

 

sorry thought i had in my profile but it must be a different site. its a 1995 f150 with a 302 and a 4r70w 2wd. yes i did forget to mention the only code that comes up is dtc 172. the o2 sensor is also new cause i broke the last one taking it off to do the exhaust.

 

Sounds to me also like a fuel delivery issue.

 

so what kinds of things would make this happen? i changed the pump, filter,m and ive swapped the injectors with ones with less kms from a good running motor(motor didnt work in my truck it was from a 90). and whats this fuel delivery module subford is talking about?

 

The fuel delivery module:
Attachment 281295
/

 

so its the fuel pump? i changed the fuel pump already and have the proper psi

 

You said you changed the front one. We are talking about the rear tanks fuel module.

 

the rear is also fine i get proper psi from both. the problem happens on either tanks

 

Did you change the back fuel module?

 

no never had any problems with it

 

If your front pumps pressure is low it could be because the back pumps module is bad.
That is why I said above check the pressure with a gauge on the road going up a hill on one tank and then do it again on the other tank.
Your symptoms say low fuel pressure and you said the front pump had low pressure.

 

im not understanding why the rear pump would affect the front pump? is it because they both work off the same circuit before the dual tank switch on the dash?